Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02225644 1998-02-06
WO 97/07003 PCT/US96/I350 i'
MICROPROCESSOR-BASED CONTROL FOR TRAILER BRAKES
BACKGROUND OF THE INVENTION
This invention relates to controllers for electrically actuated braking
systems such
as those used to apply the brakes of towed vehicles, i. e. , trailers, in
response to
t 5 commands from the towing vehicle. More particularly, the invention relates
to electronic
controllers for braking systems which operate in response to inertial sensors
and/or
manually actuated switches, or the like, to actuate a towed vehicle's brakes
in a particular
controlled manner.
Substantial effort and progress has been made towards the goal of providing
more
stable and more responsive electronic brake system controllers which actuate
the
electromagnetic brake shoe actuators of a towed vehicle. For example, it is
known that
continuous braking excitation is likely to promote trailer brake lockup which
causes a
substantial decrease in braking efficiency and loss of operator control. Prior
art brake
controllers have eliminated these undesirable effects by applying pulsating
excitation to
the brakes by means of a constant pulse width applied at varying frequencies
or a varying
pulse width applied at a constant frequency. It is also known that trailer
brake lockup
may occur if the towed vehicle's brakes are applied too rapidly. However, the
brakes
may feel sluggish and may not be f,-ully actuated in a timely manner if the
brake current is
applied too slowly. Prior art controllers have been designed to apply current
to the
brakes in a controlled manner which avoids these problems and which releases
the brakes
rapidly when the brake actuation signal is removed to prevent continued
actuation of the
towed vehicle's brakes. Another example of progress in prior art brake
controllers is the
accommodation of different towed vehicle weights and brake system
characteristics which
are variables having a substantial impact upon the proper braking of the towed
vehicle..
Although substantial progress has been made in brake system controllers, most
of
these prior art devices have relied on the extensive use of analog
technologies to
implement the controller circuitry. There are several drawbacks to these
analog desigr.~s.
First, analog circuits often exhibit operational variations (drift) over
temperature extremes
and component variability. Second, because the operation of the controller is
hardwired
into the design of the circuitry, these prior art devices have only limited
flexibility which
necessitate complete redesigns of the circuitry when changes are desired in
the brake
controller operational parameters or when the addition of new operational
features are
desired. Finally, since analog designs rely on small variations in voltage
during normal
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WO 97/07003 PCT/CTS96/13507
operation, they are often sensitive to voltage fluctuations and radio
frequency noise
sources which may cause operational problems.
SUMMARY OF THE INVENTION
The present invention provides a new and more effective electronic brake
system
controller that eliminates many of the above-mentioned problems of the prior
art devices
I
caused by the reliance on analog circuit technologies.
The electronic brake controller of the present invention implements a
microcontroller-based design that works in conjunction with analog circuit
technology to
provide improved operation and reliability over an extended temperature range
and an
improved response to braking conditions. The programming of the
microcontroller can
be quickly modified and adapted to implement a variety of analog circuits,
resulting in a
brake controller that has the flexibility to provide varied features and
capabilities.
In the preferred embodiment, the brake controller of the present invention
applies
pulsating excitation to the brakes of the towed vehicle in a controlled manner
such that
brake lockup is avoided, and provides a gain adjustment control that
accommodates
different towed vehicle weights and brake system characteristics. Furthermore,
the brake
controller displays the magnitude of the braking current, and terminates the
braking
current if the magnitude exceeds a threshold value.
One aspect of the present invention is to provide a brake controller which
implements a microcontroller. Another aspect of the present invention is to
provide a
brake controller having a microcontroller which is programmed to generate a
pulse width
modulated (PWM) signal. A further aspect is the use of one programming
interrupt to
switch the PWM drive signal high and another programming interrupt to switch
the PWM
drive signal low, and to enable one interrupt to switch the signal both high
and low if the
demand for braking current exceeds a particular threshold. Still another
aspect of the
present invention is to provide a brake controller having a microcontroller
which
generates a PWM drive signal that has a duty cycle which is inversely
proportional to the
demand for brake current. Yet another aspect is to provide a brake controller
which
implements both software and hardware to sense the magnitude of brake current.
Still another aspect of the present invention is to provide a brake controller
which '
discontinues brake current supply when its magnitude exceeds a particular
threshold, and
thereafter periodically determines if the threshold continues to be exceeded.
Another
aspect of the brake controller of the present invention is that it enables an
operator to
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CA 02225644 1998-02-06
WO 9717003 PCTlUS96/13501
ascertain and adjust the threshold position of a decelerometer, and to do so
by use of
electronic means and optical readout. Yet another aspect of the present
invention is to
use a bicolored LED to determine the threshold position.
r
Another aspect of the present invention is to provide a brake controller which
enables an operator to selectively input the number of axles of a towed
vehicle, and to do
so by use of electronic means. An additional aspect of the brake controller is
that it uses
multiple LEDs to indicate the magnitude of brake current. Yet another aspect
is to
perform a method of brake current magnitude indication which is dependent on
the
number of axles of a towed vehicle, and the flashing of the LEDs when overload
current
conditions exist.
A further aspect of the present invention is a brake controller having a
decelerometer which is disabled when a manual control is employed. Another
aspect of
the present invention is to provide a brake controller having a self test mode
of operation.
Yet another aspect is the provision of a brake controller having a power
control circuit
which provides a separate means of controlling the application of brake
current. A
further aspect is a power control circuit which enables brake current to be
applied only if
a manual control is operated or if the brake lights of a towing vehicle are
lit.
Still another aspect of the brake controller of the present invention is the
provision
of a verification to an operator that the brakes of a towed vehicle are
electrically
connected to the brake controller. An additional aspect of the invention is
the provision
of a brake controller which discontinues brake current and notifies an
operator when an
open ground exists. Another aspect is a brake controller having a control
circuit which
monitors the functioning of a microcontroller and resets it if a malfunction
is detected.
Another aspect of the invention is the provision of a brake controller having
a lain
adjustment circuit which initiates the activation and deactivation of a towed
vehicle's
brakes using different time constants. Further aspects include the use of
means including
a Zener diode to maintain a constant operating voltage to the sensor input
circuit, and 'the
use of means including a potentiometer in the sensor input circuit so that the
current level
therein can be adjusted to compensate for component tolerances. Still another
aspect is a
brake controller which uses means including a capacitor or other means to
increase a
driving voltage that is supplied to a power switching circuit.
Yet another aspect of the present invention is to provide a brake controller
where
the output current sampling is not performed across a resistor, but instead is
done using
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WO 97/07003 PCT/US96/13507
the drain to source resistance of the output MOSFETS during any "on" state
(Rds/on) to
save cost and space on the circuit board, to eliminate the heat that is
generated by such a
resistor, and to prevent the brake controller from overheating and entering a
thermal
runaway situation. Another aspect is a brake controller that does not utilize
a power
control circuit and thereby is lower in cost.
A further aspect of the present invention is a brake controller that uses a
baseline
level which is correlated to the temperature dependency and/or tolerances of
its
components and which is established when detecting whether the brakes are
connected.
Another aspect is a brake controller that provides a display of the level of
braking current
via LEDs that is done by analyzing the duty cycle of the PWM drive signal
instead of
using the current values actually calculated by the current sense circuit.
Still another aspect is a brake controller that provides a reduced level of
braking
current in response to a braking demand by the operator of the vehicle when
marginal
overload current conditions were originally present. An additional aspect is a
brake
controller that can detect when a lamp load is mistakenly connected to a brake
magnet
terminal. Still another aspect is a brake controller that, after a self test
is completed, the
microcontroller automatically enters normal brake controller operation even if
a voltage is
maintained at the microcontroller's self test pin.
To achieve these and other aspects and advantages. the brake controller of the
present invention comprises an input circuit for generating a brake level
signal
representing the desired braking, a power switching circuit, and adapted for
coupling to
the brakes of the towed vehicle and to the power supply of the towing vehicle
for
selectively supplying power from the towing vehicle power supply to the brakes
of the
towed vehicle in response to a switching control signal supplied to a control
input
terminal, and a microcontroller coupled to the input circuit and to the power
switching
circuit, the microcontroller generates and supplies a switching control signal
to the control
input terminal of the power switching circuit thereby causing the power
switching circuit
to deliver a braking current to the brakes of the towed vehicle that is
proportional to the
brake level signal supplied to the microcontroller by the input circuit.
Additionally, the brake -controller may include a brake light circuit adapted
for
coupling to a brake light of a towing vehicle for generating an output signal
when the
brake lightswitch is activated as a basis for determining that the brakes of
the towing
vehicle are actuated. The input circuit may include a sensor input circuit
coupled to the
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CA 02225644 2001-06-27
brake light circuit for sensing the deceleration of the towing vehicle in
response to the
output signal from said brake light circuit, and a manual input circuit for
receiving input
from an operator of the towing vehicle of a desired braking force of the towed
vehicle's
brakes.
The brake controller may also include a gain adjustment circuit coupled to the
manual input circuit and to the sensor input circuit for receiving brake level
signals output
therefrom that are indicative of a desired level of braking and for generating
a gain-
adjusted brake level signal in response to a brake level signal received from
either the
manual input circuit or the sensor input circuit. Additionally, the brake
controller may
include a power control circuit adapted for coupling to a power supply of the
towing
vehicle for supplying power to the brakes of the towed vehicle through the
power
switching circuit.
The brake controller may further include a current sensing circuit for sensing
a
level of braking current supplied from the power control circuit to the brakes
of the towed
vehicle through the power switching circuit, and for generating a current
level signal
representing the sensed level of braking current and a display circuit for
displaying
information to the operator of the towing vehicle.
These and other features and advantages of the present invention will be
further understood and appreciated by those skilled in the art by reference to
the
following specification, claims and appended drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings:
Fig. 1 is a block circuit diagram showing the brake controller of the present
invention;
Figs. 2A-2B are schematic circuit diagrams showing the brake controller of the
present
invention;
Fig. 3 is the flow diagram of the main program for the microcontroller of the
present invention;
Fig. 4 is the flow diagram of the "SELF TEST" subroutine for the
microcontroller
of the present invention;
Fig. 5 is the flow diagram of the "SET AXLES" subroutine for the
microcontroller of the present invention;
Fig. 6 is the flow diagram of the "REVERSE LED" subroutine for the
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CA 02225644 2001-06-27
microcontroller of the present invention;
Fig. 7 is the flow diagram of the "INT1" interrupt for the microcontroller of
the
present invention;
Figs. 8A-8B are the flow diagrams of the "INTTC1" interrupt for the
microcontroller of
S the present invention;
Fig. 9 is the flow diagram of the "INTTC2" interrupt for the microcontroller
of
the present invention;
Fig. 10 is the flow diagram of the "CHECK CURRENT" subroutine for the
microcontroller of the present invention;
Fig. 11 is the flow diagram of the "DISPLAY CURRENT" subroutine for the
microcon~roller of the present invention;
Figs. 12A-12B are schematic circuit diagrams showing a second embodiment of
the brake
controller of the present invention;
Figs. 13A-13E are the flow diagrams of the "INTTC1" interrupt for the
microcontroller of the second embodiment of the present invention;
Fig. 14 is the flow diagram of the "CHECK LEVEL" subroutine for the
microcontroller of the second embodiment of the present invention;
Fig. 15 is the flow diagram of the "FLASHRATE" subroutine for the
microcontroller of the second embodiment of the present invention;
Figs. 16A and 16B are the flow diagrams of the "SAMPLE GAIN" subroutine for
the microcontroller of the second embodiment of the present invention;
Figs. 17A-17B are schematic circuit diagrams showing a third embodiment of the
brake
controller of the present invention;
Fig. 18 is the flow diagram of the "INT1" interrupt for the microcontroller of
the
of the third embodiment of the present invention;
Figs. 19A-19F are the flow diagrams of the "INTTC1" interrupt for the
microcontroller of the third embodiment of the present invention;
Figs. 20A and 20B are the flow diagram of the "INTTC2" interrupt for the
microcontroller of the third embodiment of the present invention;
Figs. 21A and 21B are the flow diagrams of the "SAMPLE GAIN" subroutine for
the microcontroller of the third embodiment of the present invention;
Fig. 22 is the flow diagram of the "CHECK CURRENT" subroutine for the
microcontroller of the third embodiment of the present invention;
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CA 02225644 2001-06-27
Fig. 23 is the flow diagram of the "COMPARE CURRENT" subroutine for the
microcontroller of the third embodiment of the present invention; and
Figs. 24A and 24B are the flow diagrams of the "DISPLAY CURRENT"
subroutine for the microcontroller of the third embodiment of the present
invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Referring now to Fig. 1, shown is a block circuit diagram of the brake
controller
of the present invention having a microcontroller 10 as its central component.
Connected
to microcontroller 10 are a variety of circuits which, starting from the upper
left and
proceeding counterclockwise, include a voltage supply circuit 12, a brake
light circuit 14,
a sensor input circuit 16, a manual input circuit 18, a gain adjustment
circuit 20, a
display circuit 22, a power switching circuit 24, a current sense circuit 26,
and a power
control circuit 28.
The general operation of the brake controller during normal operating
conditions
begins with signals supplied to gain adjustment circuit 20 from either sensor
input circuit
16 or manual input circuit 18 when braking of the towed vehicle is demanded.
The gain
adjustment circuit generates a signal output that represents the magnitude of
the desired
braking, and is received by microcontroller 10 which generates a PWM drive
signal in
response thereto. This signal is supplied to power switching circuit 24 which,
in
conjunction with power control circuit 28, applies current to the towed
vehicle's brakes
according to the duty cycle of the PWM drive signal. Current sense circuit 26
senses the
current draw of the towed vehicle's brakes and in cooperation with
microcontroller 10
monitors for a short circuit condition in the brakes. Preferably, current
sense circuit 26
is disabled until a predetermined delay period lapses following each time the
PWM drive
signal is turned off and is disabled prior to each time the PWM drive signal
is turned on
in order to prevent misreading of the braking current. Although sensor input
circuit 16 is
preferably constructed using the inertial sensor described below, it could
also be
implemented using a ramp~circuit that gradually increases (i.e., ramps) the
braking level
signal during the time that the brake light is illuminated. A more detailed
discussion of
the operation of the brake controller and its individual components is
provided below.
Figs. 2A-2B are schematic diagrams showing the details of the brake controller
circuits
and their interconnection with one another and the microcontroller, with each
of the brake
controller components generally indicated by the reference numerals assigned
above.
Microcontroller 10 is the central component of the brake controller of the
present
CA 02225644 2001-06-27
invention and, in the preferred embodiment, is a Toshiba TMP47C241
microcontroller.
The microcontroller 10 has four channels of analog input, with pin 2 receiving
input from
the current sense circuit 26, pin 3 receiving input from the sensor input
circuit 16, pin 4
receiving input from the manual input circuit 18, pin 5 receiving input from
the gain
adjustment circuit 20. The microcontroller 10 has two input channels with pin
9
receiving input from the current sense circuit 20, and pin 24 receiving input
from the
brake light circuit 14. Microcontroller 10 has ten output channels, with pin 7
connected
to the power control circuit 28, pin 8 connected to the sensor input circuit
16, pins 10-13
and 16-18 connected to the display circuit 22, and pin 15 connected to the
power
switching circuit 24. Connected to pins 20 and 21 is ceramic resonator X1
which
provides a 4MHz clock frequency for proper functioning of the microcontroller.
Also
connected to the microcontroller via pins 6, 22, and 23 is a watchdog control
circuit
consisting of resistor R35, diode D3, and capacitor C11. This circuit monitors
pin 6
which, during normal operating conditions of the microcontroller, is kept in a
high state.
However, pin 6 is pulled low if the microcontroller malfunctions, causing the
watchdog
circuit to reset the microcontroller through reset pin 22. The watchdog
control circuit
also provides a "power on" reset which, during power up, keeps the
microcontroller in a
reset state until it has received its full operating voltage and ceramic
resonator X1 is
providing the proper frequency, thus preventing the microcontroller from
operating until
it is in proper sequence and is internally set. In the preferred embodiment,
R35 is a 10
KOhm resistor and C11 is a 0.22 uF capacitor. Furthermore, Figs. 2A-2B show
pins 14, 25,
and 26 of microcontroller 10 connected to ground, pins 27 and 28 connected to
each other
by means of resistor R40 which is a 10 KOhm resistor in the preferred
embodiment, and
pin 1 connected to ground through capacitor C9 which is a 0.01 uF capacitor in
the
preferred embodiment. The programming for microcontroller 10 is described
below in
connection with Figs. 3-11.
Figs. 2A-2B show the voltage supply circuit, generally indicated by the
numeral 12,
which supplies operating voltages to the brake controller components. This
circuit is
connected to the towing vehicle's battery wherefrom it receives a 12-volt
supply of
operating voltage. The 12-volt battery supply voltage is directly supplied to
power
control circuit 28 and, in some circumstances (detailed below), to brake light
circuit 14
by means of switch SW1. Voltage regulator U1 receives the 12-volt battery
supply
voltage through resistor Rl and converts it to 5 volts which is supplied to
the remaining
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CA 02225644 2001-06-27
brake controller components as indicated in Fig. 2A. Varistor Z1 provides
voltage
protection for U1 and has a clamping voltage of 22 volts. In the preferred
embodiment,
R1 is a 51 Ohm resistor, C1 is a 0.27 uF capacitor, and C2 is a 220 uF
capacitor.
The brake light circuit, generally indicated by the numeral 14 in Fig. 2A, is
S connected to the' brake lights of the towing vehicle (not shown) and
supplies a signal to
the microcontroller 10 indicating whether the brake pedal of the towing
vehicle is
pressed. This signal is necessary for adjusting the sensitivity of the
decelerometer of
sensor input circuit 16 and for setting the number of axles of the towed
vehicle (described
in detail below). If the brake pedal has been pressed, the voltage generated
at the brake
lights drives the base of transistor Q2 through resistors R3 and R4, causing
Q2 to conduct
such that its collector voltage is lowered. The collector voltage of Q2, and
thus the signal
indicating whether the brake pedal has been pressed or not, is supplied to pin
24 of
microcontroller 10. In addition to receiving voltages from the brake lights of
the towing
vehicle, the brake light circuit may also receive the 12-volt battery supply
voltage through
switch SW 1, as mentioned above. Switch SW 1 may be closed when the manual
control
of manual input circuit 18 is operated, causing the towing vehicle's brake
lights to light
even though the brake pedal of the towing vehicle may not be pressed. The use
of SW 1
in this manner, as a means of lighting the towing vehicle's brake lights to
indicate manual
braking, is required by law in some foreign countries, although unnecessary in
the United
States. Brake light circuit 14 is also connected to sensor input circuit 16,
for reasons
which will be discussed below. In the preferred embodiment, R2 is a 10 KOhm
resistor,
R3 is a 150 Ohm resistor, R4 is a 10 KOhm resistor, C3 is a 0.1 uF capacitor,
and Z2 is
a 7.5-volt Zener diode.
Fig. 2B shows the sensor input circuit, generally indicated by the numeral 16,
which
signals the microcontroller to apply current to the towed vehicle's brakes if
braking of the
towing vehicle is of sufficient magnitude. The main component of this circuit
is a
decelerometer consisting of infrared LED 1, phototransistor Q 1, and a
mechanical "flag"
therebetween (not shown) that modulates the light incident on Q1 from LED1.
When
microcontroller 10 maintains a voltage at pin 8 such that transistor Q3 is
active, current
will be able to flow through LED1 such that light is emitted. LED1 is
connected to brake
light circuit 14 through potentiometer V 1 and resistor RS such that LED1
receives its
operating current, and thus the decelerometer is active, only when the brake
lights are lit.
This voltage supplied by the brake Light circuit is maintained at 7.5 volts by
means of
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CA 02225644 2001-06-27
Zener diode Z2 and filtered by capacitor C3 in order to prevent voltage
fluctuation that
would undesirably cause the current through LED1 to fluctuate. Thus, a
constant current
flows through LED 1 when the brake lights are lit and Q3 is active.
Potentiometer V 1 is
in series with LED1 and is adjusted such that the constant current flowing
through LED1
is set, during rrtanufacture, to compensate for component tolerances. This is
sometimes
necessary in order to compensate for mechanical misalignment and tolerance
differences
of different brake controllers. In the preferred embodiment, V 1 is a 1 KOhm
potentiometer and RS is a 270 Ohm resistor. The constant current through LED 1
causes
it to emit a constant amount of light which is received by phototransistor Q1
to the extent
permitted by the flag in between. This flag is mechanical in nature and its
positioning
between LED1 and Q1 is dependent on the magnitude of deceleration forces it
experiences. If no deceleration forces are present, the flag allows very
little light emitted
by LED1 to reach Q1, and the decelerometer is said to be in a level state. As
deceleration forces are increased, the flag permits increasing amounts of
light to reach
Q1, and the decelerometer is said to become increasingly unbalanced. The
sensitivity of
this decelerometer can be adjusted with an external control that changes the
positioning of
the flag such that more or less light is allowed through for a particular
deceleration force.
If the flag permits sufficient light to reach the base of phototransistor Q1,
Q1 conducts
and pin 3 of microconuoller 10 receives a voltage signal indicating that the
decelerometer
has been actuated. The voltage supplied to pin 3 of the microcontroller,
although limited
by the 5-volt collector voltage, is proportional to the amount of light
received by Q1 and,
thus, the amount of deceleration force created by the towing vehicle's brakes.
The pin 3
voltage signal enables the level of sensitivity of the decelerometer to be
precisely
monitored by means of bicolored LED6, described in greater detail below in
connection
with display circuit 22. The voltage applied to pin 3 of the microcontroller
is also
supplied to gain adjustment circuit 20 through R7, for reasons described
below. In the
preferred embodiment, C4 is a 0.001 uF capacitor, and R6, R7, and R8 are 3.3
KOhm,
43 KOhm, and 22 KOhm resistors, respectively.
In the preferred embodiment of the present invention, sensor input circuit 16
is
dominated by manual input circuit 18 (described below) such that the
decelerometer is
immediately disabled and does not contribute to the towed vehicle's braking
current when
the manual control of circuit 18 is actuated by the operator of the towing
vehicle. Based
on an input signal from manual input circuit 18, microcontroller 10 disables
the
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CA 02225644 2001-06-27
deceierometer by grounding pin 8 which deactivates Q3 and prevents current
from
flowing through LED1.
Fig. 2B shows the manual input circuit, generally indicated by the numeral 18,
having a manual control which may be actuated by the operator of the towing
vehicle to
cause braking of the towed vehicle at any particular time, and which is
especially useful
for reducing sway of the towed vehicle during normal driving conditions. The
manual
control of manual input circuit 18 consists of a continuous roll-on
potentiometer V2 which
provides up to a 5-volt signal to pin 4 of microcontroller 10 representing the
magnitude of
desired manual braking. This signal is also supplied through resistor R9 to
gain
adjustment circuit 20, described in detail below. Upon operation of the manual
control of
manual input circuit 18, and reaching a minimum threshold, the microcontroller
disables
the decelerometer of sensor input circuit 16, as described above, and may
close switch
SW 1 such that the 12-volt battery supply voltage is supplied to brake light
circuit 14, as
described above. In the preferred embodiment, V2 is a 5 KOhm potentiometer and
R9 is
a 47 KOhm resistor.
The gain adjustment circuit, generally indicated by the numeral 20 in Fig. 2B,
generates a signal which controls the extent of towed vehicle braking and
which is
dependent on the magnitude of the signal received from either sensor input
circuit 16 or
manual input circuit 18. As mentioned above, when signals from both the manual
input
circuit and sensor,input circuit are received, the manual input circuit
dominates and the
decelerometer of the sensor input circuit is disabled. In response to the
application of an
input signal from either the manual input circuit or the sensor input circuit,
the voltage at
pin 12 of amplifier U3d rises with a time constant defined by resistors R7,
R9, and R10
and capacitor C7. As will be seen below, this gradual increase in voltage
results in a
gradual braking of the towed vehicle such that undesirable abrupt changes in
braking
current can be avoided which have a negative effect on the performance of a
brake
controller. In the preferred embodiment, R10 is a 150 KOhm resistor, C7 is a
1.0 uF
capacitor, and the charging time is approximately 1.5 seconds. The output of
amplifier
U3d is controlled by potentiometer V3 which is a gain adjustment control set
by the
operator of the towing vehicle. V3 provides gain limiting to limit the amount
of current
applied to the towed vehicle's brakes such that brake lockup can be avoided.
This gain
limiting is preferably adjusted when trailer load and driving conditions are
changed, and
is in addition to the 5-volt limits provided in the manual and sensor input
circuits. The
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CA 02225644 2001-06-27
resulting signal, rising with a time constant defined by R7, R9, and R10 and
C7, is then
supplied to pin 5 of microcontroller 10 which, through programming discussed
in detail
below, generates a PWM drive signal in response thereto that controls the
braking of the
towed vehicle. In the preferred embodiment, V3 is a 5 KOhm potentiometer, R11
and
R12 are 45.3 KOhm and 47 KOhm resistors, respectively, and CS and C6 are both
0.001
uF capacitors. Upon discontinuation of the input signal to the gain adjustment
circuit, the
signal applied to amplifier U3d decreases as C7 discharges through diode D1
and resistor
R7 and R9. The time constant of this discharge is preferably very short such
that the
towed vehicle's brakes can be deactivated quickly, and is approximately 100
milliseconds
in the preferred embodiment.
The power control circuit of Fig. 2A is generally indicated by the numeral 28
and
provides the necessary voltage to drive MOSFETS Q8 and Q9 of power switching
circuit
24, described in greater detail below. The 12-volt battery supply voltage can
be supplied
to the power switching circuit through transistor Q6 which is controlled by
pin 7 of
microcontroller 10 through transistor Q5. When the pin 7 signal is high, QS
conducts
and pulls the base of Q6 low such that the 12-volt battery voltage is supplied
to the power
switching circuit. However, when the pin 7 signal is low, Q6 is deactivated
and the 12-
volt battery voltage is not supplied to the power switching circuit through
diode D4.
Microcontroller 10 controls the power control circuit 28 such that the driving
voltage to
power switching circuit 24 is supplied only when necessary, thus preventing
constant
electrical excitation that would increase the quiescent current requirement
from the
battery. In the preferred embodiment, the driving voltage is supplied only if
the manual
control of manual input circuit 18 is operated or if the brake pedal of the
towing vehicle
is pressed such that the brake lights of brake light circuit 14 are lit. In
the preferred
embodiment R21, R22, and R23 are 22 KOhm, 1 KOhm, and 4.7 KOhm resistors,
respectively.
The power switching circuit of Fig. 2B is generally indicated by the numeral
24 and
is the means by which braking current is applied to the towed vehicle's
brakes. Braking
current from current sense circuit 26 (described below) and supplied to the
source of
MOSFETS Q8 and Q9 is applied to the towed vehicle's brakes (not shov~in) when
MOSFETS Q8 and Q9 conduct. Two MOSFETS are employed in the preferred
embodiment, although only one MOSFET may be used for proper functioning of the
circuit. The driving voltage to the gates of MOSFETS Q8 and Q9, when available
from
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CA 02225644 2001-06-27
power control circuit 28, is controlled by means of transistor Q7 and a PWM
drive signal
received from pin 15 of microcontroller 10. The PWM drive signal is generated
by the
microcontroller's programming and has a duty cycle which is inversely
proportional to the
magnitude of the input signal received from gain adjustment circuit 20. When
the PWM
S drive signal is high, it drives Q7 such that the voltage generated by power
control circuit
28 is shorted to ground and is not applied to the gates of Q8 and Q9, thus
causing no
current to be applied to the towed vehicle's brakes. However, when the PWM
drive
signal is low, Q7 is inactive and the voltage switched by power control
circuit 28 is
applied to the gates of Q8 and Q9 through resistors R31, R37, R38, and R39,
causing Q8
and Q9 to conduct such that the towed vehicle's brakes receive current. The
amount of
current supplied to the towed vehicle's brakes is dependent on the duty cycle
of the PWM
drive signal, with a lower duty cycle corresponding to more braking current.
The voltage
that is provided by power control circuit 28 is held on capacitor C 12 which
acts as a
charge pump and enables the voltage supplied to the gates of Q8 and Q9 to be
in excess
of 12 volts. This is preferable to drive the MOSFETS because the source of QS
and Q9
is at approximately 12 volts by means of connection to the battery supply
voltage through
current sense circuit 26. Zener diode Z4 is preferably a 16-volt Zener diode
that protects
the gates of the MOSFETS by limiting the voltage supplied thereto to 16 volts
with
respect to source. In the preferred embodiment, C 12 is a 100 uF capacitor,
and R31,
R36, R37, R38, and R39 are 1.8 KOhm, 5.6 KOhm, 270 Ohm, 270 Ohm, and 270 Ohm
resistors, respectively.
The current sense circuit of Fig. 2A is generally indicated by the numeral 26
and
senses the magnitude of the current supplied to the towed vehicle's brakes
through
MOSFETS Q8 and Q9 of power switching circuit 24. The current sense circuit is
connected to the 12-volt battery supply voltage and supplies current to the
drain of
MOSFETS Q8 and Q9, the magnitude of which is sensed across resistor R30. The
resulting signal is amplified by amplifiers U3b and U3c and their
corresponding resistive
networks, with potentiometer V4 providing calibration for the current sensing.
In the
preferred embodiment, V4 is a 5 KOhm potentiometer, and R30, R28, R29, R34,
and
R33 are 0.005 Ohm, 3.3 MOhm, 45.3 KOhm, 45.3 KOhm, and 301 KOhm resistors,
respectively. In the preferred embodiment. R27, R32, R26, and R24 are 301
KOhm, 470
Ohm, 150 KOhm, and 300 KOhm resistors, respectively. The amplified signal is
then
supplied, through resistor R25, to pin 2 of microcontroller 10 which
calculates the current
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CA 02225644 2001-06-27
magnitude and displays this value by means of display circuit 22, described in
detail
below. Microcontroller 10 compares the current magnitude to a current
threshold value
stored in memory which, in the preferred embodiment, is 30 amps.. If the
current
magnitude exceeds this value, the programming of the microcontroller
(described below)
shuts the current off to the towed vehicle's brakes to protect the brake
controller circuitry
from excessive current, and samples it again approximately every ~/e second.
Zener diode
Z3 is preferably a 4.7-volt Zener diode which prevents the voltage supplied to
pin 2 of
microcontroller 10 from exceeding 5 volts, thus preventing damage to the
microcontroller. In the preferred embodiment, C 10 is a 0.001 uF capacitor and
R25 is a
4.7 KOhm resistor.
Current sense circuit 26 also supplies the amplified signal from amplifiers
U3b and
U3c to the noninverting pin of amplifier U3a. When the current across R30
exceeds 30
amps, the gain distribution of U3a causes transistor Q4 to be driven which
lowers the
voltage supplied to pin 9 of microcontroller 10, indicating that "overload"
current
conditions exist. Thus, amplifier U3a and transistor Q4 provide the analog
equivalent of
the threshold current sensing accomplished by means of pin 2 and programming
of
microcontroller 10, as described above. In the preferred embodiment, C8 is a
0.1 uF
capacitor, R20 is a 47 KOhm resistor, and R19 is a 1 KOhm resistor.
The display circuit of Fig. 2A is generally indicated by the numeral 22 and
consists
of LEDs 2-5, a bicolored red/green LED6, and associated current limiting
resistors. In
the preferred embodiment, R13, R14, R15, and R16 are each 270 Ohm resistors,
and R17
and R18 are each 470 Ohm resistors. LEDs 2-5 are connected to pins 10 through
13 of
microcontroller 10 and are primarily used to display the magnitude of current
supplied to
the towed vehicle's brakes, although other applications are described below in
connection
with the programming of the microcontroller. Bicolored LED6 is connected to
pins 16
through 18 of microcontroller 10 and has a red component and a green
component. The
red component of bicolored LED6 is activated whenever current is applied to
the towed
vehicle's brakes, with a brighter intensity corresponding to higher braking
current. The
green component of LED6 is activated when the decelerometer of sensor input
circuit 16
is level such that pin 3 of microcontroller 10 is within a specific range.
$oth components
of LED6 can be used in conjunction with the external control of sensor input
circuit 16 to
adjust the sensitivity of the decelerometer. By analysis of the point at which
the output of
LED6 changes from green to red upon application of the brake pedal of the
towing
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CA 02225644 2001-06-27
vehicle, the towing vehicle's operator can bring the decelerometer to a
threshold position
whereby even a slight braking of the towing vehicle changes the state of the
decelerometer from level to unbalanced and causes an immediate contribution to
the
towed vehicle's braking current.
Now that the circuits comprising the brake controller of the present invention
have
been detailed, the programming for the microcontroller, which controls and
coordinates
the operation of the brake controller components and the braking of the towed
vehicle, is
discussed below. The flow diagrams for this programming are shown in Figs. 3-
11.
The main program for the microcontroller is shown in Fig. 3. The program
begins with block 100 that signifies the beginning of the main program. Next,
block 102
initializes the stack pointer for proper sequencing of the interrupts and
subroutines, and
initializes the microcontroller's timer, ports, and variablesand disables the
bicolor LED.
Block 102 also enables the interrupts INT1, INTTC1, and INTTC2, described in
greater
detail below in connection with Figs. 7, 8A, 8B and 9, respectively. Next,
block 104
determines whether a "self-test" request has been made by means of the
grounding of pin
27 of the microcontroller. The self test is preferably only performed by the
manufacturer
and tests whether the controller circuitry is functioning properly. If a self
test request has
been made, the program proceeds to block 106 which calls the SELF-TEST
subroutine,
described in greater detail below in connection with Fig. 4. Upon return, or
if a self-test
request has not been made, the program proceeds to block 108 which determines
whether
it is the first time that the power has been turned on to the microcontroller.
Block 108
makes this determination by analyzing variable firstpowerup which is reset at
the time of
first powerup and subsequently set during the SET AXLES subroutine, described
in
greater detail below in connection with Fig. 5. If variable firstpowerup is
reset, the
program proceeds to block 110 which calls the SET AXLES subroutine. Upon
return, or
if it is not the first time that the power has been turned on to the
microcontroller, the
program proceeds to block 112 to wait for interrupts INT1, INTC1, and INTTC2,
described in greater detail below in connection with Figs. 7, 8A, 8B and 9,
respectively.
Fig. 4 shows the SELF-TEST subroutine for the microcontroller. This subroutine
sets up the parameters to perform the self test operation during interrupts
INTTC 1 and
INTTC2. The self test operation is preferably only performed by the
manufacturer, and
causes the PWM drive signals generated in the interrupts to continuously sweep
from
maximum to minimum values so that the functioning of the brake controller can
be
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CA 02225644 2001-06-27
examined. The SELF-TEST subroutine begins with block 120 that signifies the
beginning
of the subroutine. Next, block 122 sets a loop variable Y equal to 16. Block
124 then
decrements loop variable Y by one each time through the loop, and turns on and
off all
five LEDs of the display circuit one at a time. The timing of the interrupts,
enabled in
the main program, determines the timing of the delay between the flashing on
and off of
the LEDs. The subroutine then proceeds to block 126 that determines if loop
variable Y
is equal to 0. If not, the subroutine loops back to block 124. If loop
variable Y is equal
to 0, which would indicate that block 124 had flashed all five of the LEDs
sixteen times,
the subroutine proceeds to block 128 which sets variable m equal to 6. As long
as this
variable is not set equal to 6, interrupts INTTC 1 and INTTC2 (Figs. 8A-8B and
9) perform a
self test of the brake controller. Next, block 130 causes the subroutine to
return.
Fig. 5 shows the SET AXLES subroutine for the microcontroller. This subroutine
enables the operator of the towing vehicle to set the number of axles of the
towed vehicle
which is preferably used in the DISPLAY CURRENT subroutine (Fig. 11 ) to
properly
display the magnitude of current provided to the towed vehicle's brakes. This
routine
uses the display to prompt the operator to manipulate the vehicle's brake
pedal and the
manual control to input the number of axles of the towed vehicle. As explained
below, it
is possible for the microcontroller to automatically determine the number of
axles of the
towed vehicle based upon a sensed current level detected during
initialization. This
subroutine begins with block 140 which signifies the beginning of the
subroutine. Next,
block 142 sets variable axles, indicating the number of axles of the towed
vehicle, to the
default value of 2. This is done for safety purposes in case variable axles is
not set later
in the subroutine, and two is chosen as the default value because the majority
of towed
vehicles will have two axles. The subroutine then proceeds to block 146 that
determines
if the brake pedal of the towing vehicle has been pressed. If not, block 144
causes all
five of the LEDs of the display circuit to flash once a second, and loops back
to block
146 to prompt an operator to press the vehicle's brake pedal. When block 146
determines that the brake pedal has been pressed, the subroutine proceeds to
block 148
which turns off all of ~c LEDs of the display circuit, waits until the brake
pedal has been
released and stable, atzd resets variable x to 0 for use later in the
subroutine. Next, block
150 disables interrupts INT1, INTTC 1, and INTTC2 because of the possibility
of
interference with the rest of the SET AXLES subroutine. Block 152 then
determines
whether the brake pedal of the towing vehicle has been pressed again. If not,
the
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WO 97/07003 PCT/CTS96/13507
subroutine proceeds to block 154 which samples the manual input circuit
channel (pin 4).
Next, block 156 determines if the most significant bit of the manual input
circuit channel
is greater than 1, indicating that th.e manual control has been operated such
that a first
threshold has been surpassed. If so, block 158 sets variable x, and the
subroutine
S proceeds to block 164. If the most significant bit of the manual input
circuit channel is
not greater than 1, block 160 uses loop timing to create a delay. Next, block
162 calls
the REVERSE LED subroutine (Fig. 6) which causes a different one of the LEDs
of the
display circuit to be turned on each time block 162 is executed. The purpose
of this
sequencing of LEDs is to prompt the user to operate the manual control of the
manual
input circuit. The delay created in block 160 keeps a particular LED on for a
certain
period of time such that the sequencing of LEDs can be recognized. After block
162, the
subroutine proceeds to block 164.
Block 164 of the SET AXLES subroutine determines if variable x was set by
operation of the manual control. If not, the subroutine loops back to block
152. If
variable x is set, block 166 first turns all of the LEDs of the display
circuit off, then aims
LED2 on and sets variable axles equal to 1. Next, block 168 determines if the
most
significant bit of the manual input circuit channel is greater than 6,
indicating that the
manual control has been operated such that a second threshold has been
surpassed. If
not, the subroutine loops back to block 152. If the second threshold has been
surpassed,
block 170 turns LED3 on and sets variable axles equal to 2. Next, block 172
determines
whether the most significant bit of the manual input circuit chaptlel is
greater than 9,
indicating that the manual control has been operated such that a third
threshold has been
surpassed. If not, the subroutine loops back to block 152. If the third
threshold has been
surpassed, block 174 turns LED4 on and sets variable axles equal to 3. Next,
block 1'76
determines if the most significant bit of the manual input circuit channel is
greater than
12, indicating that the manual control has been operated such that a fourth
threshold has
been surpassed. If not, the subroutine loops back to block 152. If the fourth
threshoki
has been surpassed, block 178 turns LEDS on and sets variable axles equal to
4. Next,
the subroutine loops back to block 152. If block 152 determines that the brake
pedal of
the towing vehicle has been pressed a second time during this subroutine
indicating that
the variable axles has been set to a particular value, the subroutine proceeds
to block 180
which enables the interrupts and sets variable x equal to 4 to be used as a
loop variable.
Next, block 182 turns all LEDs of the display circuit off and waits for '/z
second using
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WO 97/07003 PCT/US96/13507
the timing of the interrupts to calculate the delay. Next, block 184 turns on
the particular
number of LEDs of LED2, LED3 , LED4, and LEDS that is equal to the number of
axles
of the towed vehicle which is stored in variable axles. Block 186 then waits
for '/2
second using the timing of the interrupt to calculate the delay, and
decrements loop
variable x by 1. The delays provided by blocks 186 and 182 are positioned such
that the
LEDs are kept on and off long enough such that flashing of the LEDs can be
recognized.
Next, block 188 determines if the loop variable x is greater than 0 and, if
so, loops back
to block 182. If the loop variable is not greater than 1, indicating that the
number of
LEDs equal to the number of axles have been flashed four times, the subroutine
proceeds
to block 190 which delays for I/z second (needed for timing purposes) using
the timing of
the interrupts to calculate the delay. Next, block 192 sets variable
fzrstpowerup to
indicate that the first powerup of the brake controller has been completed.
Block 194
then causes the subroutine to return.
Fig. 6 is the REVERSE LED subroutine for the microcontroller. This subroutine
is called in block 162 of the SET AXLES subroutine to provide a sequencing of
the
LEDs. The subroutine begins with block 200 which signifies the beginning of
the
subroutine. Next, the subroutine proceeds to block 202 which determines if the
variable
led status is equal to 1. This variable is initialized to 1 in block 102 of
the main program
and is changed by means of execution of this subroutine. If variable led
status is 1, the
subroutine proceeds to block 204 which turns all LEDs of the display circuit
off, then
turns LED2 on and sets variable led status to 2 so that LED3 will be turned on
the next
time the subroutine is called. If variable led status is not equal to 1 in
block 202, then
block 206 determines if it is equal to 2. If so; block 208 turns all LEDs of
the display
circuit off, then turns LED3 on and sets variable led status equal to 4 so
that LED4 will
be turned on the next time the subroutine is called. If variable led status is
not equal to 2
in block 206, then block 210 determines if it is equal to 4. If so, block 212
turns all
LEDs of the display circuit off, then turns LED4 on and sets variable led
status equal to
8 so that LEDS will be turned on the next time the subroutine is called. If
variable led
status is not equal to 4 in block 210, then block 214 determines if it is
equal to 8. If so,
block 216 turns all LEDs of the display circuit off, then turns LEDS on and
sets variable
led status equal to 1 so that LED2 will be turned on the next time the
subroutine is
called. Then block 219 determines whether the variable m is equal to 8. If it
is, block
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CA 02225644 2001-06-27
220 sets the variable led status equal to 9. If variable led status is not
equal to 8 in block
214 indicating that the variable had somehow been set to an invalid number,
then block
218 sets variable led status equal to 1 as a default value. After execution of
blocks 204,
208, 212, 220, ~or 218, block 221 causes the subroutine to return.
There are three interrupts which control the operation of the microcontroller
during normal operating conditions. Interrupt INT1 is an asynchronous
interrupt having
the highest priority of the three interrupts. INT1 is performed when pin 9 of
the
microcontroller is pulled low due to activation of transistor Q4 of the
current sense circuit
indicating that the sensed current exceeds 30 amps or that an open ground
exists.
Interrupt INTTC1 is second in priority and is performed every 4 milliseconds.
Interrupt
INTTC2 is last in priority and is performed at some point after each execution
of the
INTTC 1 interrupt, the exact timing determined by the input of the gain
adjustment circuit
channel. Amongst other things, INTTC1 normally switches the PWM drive signal
high
and INTTC2 switches the signal low, the timing of INTTC2 being very important
because
it establishes the duty cycle of the PWM drive signal. However, there are
exceptions
when the INTTC1 interrupt switches the PWM drive signal low in addition to
switching it
high. These exceptions exist when the demand for braking current from the gain
adjustment circuit exceeds a threshold limit such that the PWM drive signal's
duty cycle
must be extremely low. When this occurs, the PWM drive signal must be switched
low
soon after the INTTC1 interrupt switches it high, and the time of execution of
INTTC1 is
too long such that INTTC2 cannot switch it low at the appropriate time. It is
during
these circumstances that the INTTC1 interrupt switches the PWM drive signal
both high
and low. As detailed below, the extent to which the demand for braking current
exceeds
the threshold limit determines the PWM drive signal's duty cycle and, thus,
when
INTTC1 switches the signal low.
Shown in Fig. 7 is the INT1 interrupt for the microcontroller. The interrupt
begins with block 230 which signifies the beginning of the interrupt. Next,
block 232
saves the data in the microcontroller's registers in random access memory
(RAM). Block
234 then sets variable overloadon to indicate that overload current conditions
exist such
that the braking current should be cut off, and sets variable timel equal to
~67. Variable
timel is decremented in the INTTC 1 interrupt (Figs. 8A-8B) and establishes
the time at which
the current is to be sampled again. Next, block 236 restores the data in the
microcontroller's registers from RAM, blocks 232 and 236 thus ensuring that
the
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CA 02225644 2001-06-27
microcontroller returns to exactly the same point it was at before the INT1
interrupt was
performed. Block 238 then causes the interrupt to return.
Shown in Figs. SA-8B are the INTTC1 interrupt for the microcontroller. INTTC1
begins
with block 240 which signifies the beginning of the interrupt. Next, block 242
saves the
data in the registers of the microcontroller in RAM. Block 246 then determines
if the
first powentp of the brake controller has been completed by checking whether
the variable
firstpowerup was set in the SET AXLES subroutine (Fig. 5). If variable
firstpowerup is
not set, this indicates that the microcontroller is currently in either the
SELF-TEST
subroutine or the SET AXLES subroutine during which time the interrupts, if
not
disabled, are used for the timing of delays. In these circumstances, it is
undesirable to
have the interrupts perform any braking functions, so block 248 of the
subroutine is
bypassed and the subroutine proceeds to block 250. If variable firstpowerup is
set, then
block 248 calls the CHECK CURRENT subroutine which is described in detail
below in
connection with Fig. 10. Block 248 also switches the PWM drive signal high
such that
no current is applied to the towed vehicle's brakes. Next, block 250
determines if a self
test request is present by checking whether pin 27 of the microcontroller is
grounded, and
whether variable z is equal to 0. Variable z is set equal to 0 in block 276 of
INTTC1
when the driving voltage of the power control circuit has been turned on. If
both
conditions are not met in block 250, then block 252 turns off the intensity of
the red
component of bicolored LED6 of the display circuit. After block 252, or if
both
conditions are met in block 250, the interrupt proceeds to block 254 which
loads the
Timerl and Timer2 registers. The Timerl register determines when the INTTC1
interrupt is performed, and is loaded with a value causing INTTC1 to be
performed every
4 milliseconds. The Timer2 register determines the exact time when the INTTC2
interrupt (Fig. 9) is performed after INTTC1 to switch the PWM drive signal
low, and is
loaded with variable setwidth. Variable setwidth corresponds to the value of
the gain
adjustment circuit channel (pin 5) sampled below in block 264. The Timer2
register
causes INTTC2 to be performed sooner when variable serwidth, and thus the
demand for
braking current is increased. As such, the duty cycle of the PWM drive signal
is lowered
as the demand for braking current increases. Next, block 256 determines' if
variable
integersetwidth is greater than hexadecimal FA, and whether variable
firsrpowerup is set
indicating that the first powerup of the brake controller has been completed.
Variable
integersetwidth is an 8-bit variable which corresponds to the value of the
input channel of
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WO 97/07003 PCT/US96/I350T
the gain adjustment circuit (pin 5) sampled below in block 264. Variable
setwidth is the
most significant byte of variable integersetwidth. If variable integersetwidth
is greater
than hexadecimal FA, this indicates that there is an extremely high demand for
braking
current such that INTTCl must switch the PWM drive signal low. Therefore, if
the two
. 5 conditions of block 256 are met, block 258 switches the PWM drive signal
low (off) and
turns bicolored LED6 intensity (red component) on. After block 258, or if the
two
conditions of block 256 are not met, the interrupt proceeds to block 260 which
detertrtines
whether variable firstpowerup is set indicating that the first powerup of the
brake
controller has been completed, and whether variable setwidth is less than or
equal to 2.. If
variable setwidth is greater than 2, then the DISPLAY CURRENT subroutine
called in
block 268 and the sampling of the gain adjustment channel in block 264 should
be
performed in INTTC2. The purpose of this is to equalize the functional loads
of INT'TC1
and INTTC2. If both conditions of block 260 are not met, then the interrupt
proceeds to
block 270. If both conditions of block 260 are met, then block 262 determines
if variable
timel is equal to 0. Variable timel is equal to 0 only when overload current
conditions
do not exist, or when it is time to sample the current which had previously
been cut off
due to overload current conditions. If variable timel is not equal to 0,
indicating that
overload current conditions exist and that it is not time to sample the
current, then the
interrupt proceeds to block 266 which sets the variable setwidth equal to 1.
By ignoring
the input from the gain adjustment circuit channel and setting variable
setwidth equal to 1,
variable setwidth is kept beneath a threshold value such that IhjTTC2 (block
340) does not
switch the PWM drive signal low and the current to the towed vehicle's brakes
remains
cut off. If variable timel is equal to 0 in block 262, then block 264 samples
the gain
adjustment circuit channel and uses information therefrom to update variable
integersetwidth, and variable setwidth. However, if variable m is equal to 6
indicating that
a self test is requested, then the gain adjustment circuit channel is ignored
and variable:
setwidth is set equal to variable g which is incremented in block 316 and
causes sweeping
of the PWM drive signal. Block 264 also sets variable overloadon to 0
indicating thal.
overload current conditions may no longer exist. After blocks 264 and 266, the
interrupt
proceeds to block 268 which calls the DISPLAY CURRENT subroutine, described in
more detail below in connection with Fig. 11.
Next, block 270 of INTTC 1 determines if variable firstpowerup is set
indicating
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WO 97/07003 PCT/US96/13507
that the first powerup of the brake controller has been completed. If not, the
interrupt
proceeds to block 290. If variable fzrstpowerup is set, then block 272 samples
the manual
input circuit channel (pin 4) to determine if the manual control has been
operated. If so, W
block 272 also grounds pin 8 of the microcontroller such that the
decelerometer of the
sensor input circuit is disabled. Next, block 274 checks pin 24 of the
microcontroller to
determine if the brake pedal of the towing vehicle has been pressed. If either
the brake
pedal has been pressed or the manual control has been operated, the interrupt
proceeds to
block 276 which turns on the driving voltage of the power control circuit by
means of pin
7 of the microcontroller. Block 276 also enables bicolored LED6, and sets
variable z
equal to 0 to indicate that the driving voltage of the power control circuit
is on. If neither
the brake pedal nor the manual control has been operated in block 274, then
block 278
turns the driving voltage of the power control circuit off by means of pin 7
of the
microcontroller, disables bicolored LED6, and sets variable z equal to 1 to
indicate that
the driving voltage of the power control circuit is off. After blocks 276 and
278, the
interrupt proceeds to block 280 which determines if variable setwidth is
greater than
hexadecimal E which would indicate that there is an extremely high demand for
braking
current such that INTTC1 must switch the PWM drive signal low. If variable
setwidth is
not greater than hexadecimal E, then the interrupt proceeds to block 284. If
variable
setwidth is greater than hexadecimal E, then block 282 switches the PWM drive
signal
low and turns bicolored LED6 intensity (red component) on. Next, block 284
determines
if variable z is equal to 0 which would indicate that the driving voltage of
the power
control circuit is on. If so, block 286 samples the sensor input circuit
channel (pin 3) and
turns the green component of bicolored LED6 on IF pin 3 of the microcontroller
10 is
within a specific range, indicating that the decelerometer is level. If
variable z is not
equal to 0 in block 284, then block 288 automatically turns on the green
component of
bicolored LED6 indicating that the decelerometer is level. After blocks 286
and 288, the
interrupt proceeds to block 290 which determines if variable setwidth is
greater than
hexadecimal D which would indicate that there is an extremely high demand for
braking
current such that INTTC1 must switch the PWM drive signal low. Block 290 also
determines if variable firstpowerup is set indicating that the first powerup
of brake
controller has been completed. If both conditions of block 290 are met, then
block 292
switches the PWM drive signal low and turns bicolored LED6 intensity (red
component)
on. After block 292, or if both conditions of block 290 are not met, the
interrupt
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CA 02225644 1998-02-06
WO 97107003 PCT/CTS96/I3507
proceeds to block 294.
Block 294 of INTTC1 determines if variable overloadon is set indicating that
overload current conditions exist. If not, then the interrupt proceeds to
block 300. If
variable overloadon is set, block 296 determines if variable timel is equal to
0 which
" 5 indicates that the previously cut-off current is to be sampled again. If
variable timel is
equal to 0, the interrupt proceeds to block 300. If variable timel is not
equal to 0, them
block 298 decrements variable timel by 1. Because variable timel is set to 67
in
interrupt INT1 (Fig. 7) and the CI-IECK CURRENT subroutine (Fig. 10) if
overload
current conditions are detected, and because INTTC1 decrements this value by 1
every 4
milliseconds (each time the interrupt is performed), the time period during
which the
brake controller waits to sample the current after overload current conditions
are detected
is approximately 268 milliseconds. Next, block 300 determines if flag variable
tc2 is set
which is always set during INTTC2 and indicates here that INTTC2 was
interrupted by
INTTC 1. If flag variable tc2 is set, then block 302 sets flag variable tcl to
later indicate
to INTTC2 that it had been interrupted by INTTC 1. If flag variable tc2 is not
set, them
block 304 resets flag variable tcl. After blocks 302 and 304, the interrupt
proceeds to~
block 306 which determines if a self test request is present by checking
whether pin 2 7 of
the microcontroller is grounded. If a self test request is not present, then
block 308 seas
variable m equal. to 0. After block 308, or if a self test request is present,
block 310
determines if variable m is equal to 6, caused by execution of the SELF-TEST
subroutine.
If variable m is not equal to 6, then the interrupt proceeds to block 314. If
variable m is
equal to 6, then block 312 decrements variable tpwm which is set to 25 in
block 316.
Next, block 314 determines if variable tpwm is equal to 0, and, if not, the
interrupt
proceeds to block 318. If variable tpwm is equal to 0, then block 316
increments variable
g and variable tpwm is set to 25. variable g is a 4-bit variable which cycles
between i.ts
minimum and maximum values through incrementation in block 316, and causes a
sweeping effect of the PWM drive signal if variable setwidth is set equal to
variable g, in
block 264 of INTTC1 or block 358 of INTTC2, because the self test operation is
being;
performed (when variable m is equal to 6). Next, block 318 enables the
interrupts, this
being a precautionary measure because the interrupts should already be
enabled. Blocl~:
318 also restores the microcontroller's registers from RAM. Block 320 then
causes the
interrupt to return.
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WO 97/07003 PCT/US96/13507
Shown in Fig. 9 is the INTTC2 interrupt for the microcontroller. Under normal
operation conditions, this interrupt determines the pulse width of the PWM
drive signal,
switching the signal low and causing the driving voltage from the power
control circuit 28
to be applied to the gates of MOSFETS Q8 and Q9. INTTC2 is performed at some
point
after each execution of the INTTC 1 interrupt, the exact timing determined by
the value of
variable setwidth loaded into the Timer2 register during block 254 of INTTC 1.
As
variable setwidth increases in magnitude corresponding to an increase in the
demand for
braking current, the sooner INTTC2 is performed such that the PWMdrive
signal's duty
cycle is decreased. This interrupt begins with block 330 which signifies the
beginning of
the interrupt. Next, block 332 saves the microcontrolIer's registers in RAM,
sets flag
variable tc2 to indicate that INTTC2 is in progress if later interrupted by
INTTC1, and
enables the interrupts in order to allow INTTC 1 to interrupt if needed (INTTC
1 has
higher priority). Next, block 334 determines if variable integersetwidth is
greater that
hexadecimal 2C, and, if so, the interrupt proceeds to block 336 which calls
the PWM
delay routine. This routine provides a variable delay which depends on the
value of the
least significant four bits of the first byte of information received from the
gain
adjustment circuit channel (pin 5). This delay provides a fine adjustment to
the time
period during which the PWM drive signal remains high before being switched
low in
block 344, and thus affects the PWM drive signal's duty cycle. This delay is
in addition
to that provided by operation of the Timer2 register, which determines when
INTTC2 is
performed after INTTC1, and is desirable only when the demand for braking
current
exceeds the threshold value in block 334. After block 336, or if variable
integersetwidth
is less than hexadecimal 2C in block 334, the interrupt proceeds to block 338
which
determines if variable fzrstpowerup is set indicating that the first powerup
of the brake
controller has been completed. If not, such that braking functions should not
be
performed in the interrupt, the interrupt proceeds to block 350. If the first
powerup has
been completed, then block 340 determines if variable integersetwidth is
greater than
hexadecimal 4, a threshold value below which no current is to be applied to
the towed
vehicle's brakes. If not, the interrupt proceeds to block 350. If variable
integersetwidth
is greater than hexadecimal 4, then block 342 determines if flag variable tcl
is reset and
if variable timel is equal to 0. Flag variable tcl is set in INTTC 1 to
indicate when the
present execution of INTTC2 is a continuation after having been previously
interrupted by
INTTC1. If flag variable tcl is set, it is undesirable to apply the current to
the towed
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CA 02225644 2001-06-27
vehicle's brakes in INTTC2. If variable timel is not equal to 0, then the
brake controller
is waiting to sample current that had been previously cut off due to. overload
current
conditions. . If both conditions of block 342 are not satisfied, then the
interrupt proceeds
to block 350. If both conditions of block 342 are satisfied, then block 344
switches the
PWM drive signal low such that current is applied to the towed vehicle's
brakes. Next,
block 346 determines if variable setwidth is greater than 1, a threshold value
above which
the intensity (red component) of bicolored LED6 should be enabled. If not,
then the
interrupt proceeds to block 350. If variable setwidth is greater than 1, then
block 348
enables the intensity (red component) of bicolored LED6, indicating that a
threshold
amount of current is being applied to the towed vehicle's brakes.
Next, block 350 of INTTC2 determines if variable firstpowerup is set,
indicating
that the first powerup of the brake controller has been completed, and if
variable setwidth
is greater than 2. If it is the first powerup of the brake controller, then no
braking
functions should be performed in INTTC2. If variable setwidth is less than 2,
then the
DISPLAY CURRENT subroutine called in block 352 and the sampling of the gain
adjustment circuit channel of block 358 should be performed in INTTC1. The
purpose of
this is to equalize the functional loads of INTTC1 and INTTC2. If both
conditions of
block 350 are not satisfied, then the interrupt proceeds to block 360. If both
conditions
of block 350 are satisfied, then block 352 calls the DISPLAY CURRENT
subroutine,
described in detail below in connection with Fig. 11. After block 352, the
interrupt
proceeds to block 354 that determines if variable timel is equal to 0.
Variable timel is
equal to 0 only when overload current conditions do not exist, or when it is
time to
sample the current which had previously been cut off due to overload current
conditions.
If variable timel is not equal to 0, indicating that overload current
conditions exist and
that it is not time to sample the current, then the interrupt proceeds to
block 356 which
sets the variable setwidth equal to 1. By ignoring the input from the gain
adjustment
circuit channel and setting variable serwidth equal to 1, variable setwidth is
kept beneath a
threshold value such that INTTC2 does not switch the PWM drive signal low and
the
current to the towed vehicle's brakes remains cut off. If variable timel is
equal to 0 in
block 354, then block 358 samples the gain adjustment circuit channel azid
uses
information therefrom to update variable integersetwidth and variable
setwidth. However,
if variable m is equal to 6 indicating that a self test is requested, then the
gain adjustment
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CA 02225644 2001-06-27
circuit channel is ignored and variable setwidth is set equal to variable g
which is
incremented in block 316 of INTTCl and causes sweeping of the PWM drive
signal.
Block 358 also sets variable overloadon to 0 indicating that overload current
conditions
may no longer exist. After blocks 356 and 358, the interrupt proceeds to block
360
which resets flag variables tcl and tc2, indicating that INTTC2 is no longer
in progress.
Next, block 362 restores the microcontroller's registers from RAM, and block
364
ensures that the interrupts are enabled. Block 366 then causes the interrupt
to return.
Shown in Fig. 10 is the CHECK CURRENT subroutine for the microcontroller.
This subroutine is called during the INTTC1 interrupt (Figs. 8A-8B) to sample
the braking
current sensed by the current sense circuit and to store its magnitude in
memory for
display by the display circuit. This subroutine also determines, by means of
microcontroller programming, whether overload current conditions exist. The
subroutine
begins with block 370 which signifies the beginning of the subroutine. Next,
block 372
samples the current channel which is pin 2 of the microcontroller. The
subroutine then
proceeds to block 374 which stores the results of the sampled current channel
in RAM.
Next, block 376 determines if the stored current value is greater than 30
amps, a
threshold limit stored in memory. If not, the subroutine proceeds to block 380
that
causes the subroutine to return. If the stored current value is greater than
30 amps, then
block 378 sets the variable overloadon to indicate that overload current
conditions exist
such that the braking current should be cut off, and sets the variable timel
equal to 67.
Variable timel is decremented in the INTTC1 interrupt (Figs. 8A-8B) and
establishes the time
at which the current is to be sampled again. Block 380 then causes the
subroutine to
return.
Shown in Fig. 11 is the DISPLAY CURRENT subroutine for the microcontroller
This subroutine displays, by means of the LEDs of the display circuit, the
magnitude of
the sensed braking current stored in memory during the CHECK CURRENT
subroutine
(Fig. 10), The subroutine begins with block 390 which signifies the beginning
of the
subroutine. Next, block 392 determines if variable axles, set in the SET AXLES
subroutine (Fig. 5), is equal to 1. If so, the subroutine proceeds to block
394 which
determines if the voltage corresponding to the braking current stored in
memory during
the CHECK CURRENT subroutine is greater than constant c13. If not, then the
subroutine proceeds to block 410 which causes the subroutine to return. If the
voltage
corresponding to the braking current is greater than constant c13, then block
396 turns
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CA 02225644 2001-06-27
LED2 on, and proceeds to block 398 that determines if the voltage
corresponding to the
braking current is greater than constant c14. If not, then the subroutine
proceeds to block
410 that causes the subroutine to return. If the voltage corresponding to the
braking
current is greater than constant c14, then block 400 turns on LED3, and
proceeds to
block 402 which determines if the braking current is greater than constant
c15. If not,
then the subroutine proceeds to block 410 which causes the subroutine to
return. If the
voltage corresponding to the braking current is great than constant c15, then
block 404
turns on LED4, and proceeds to block 406 which determines if the voltage
corresponding
to the braking current is greater than constant c16. If not, then the
subroutine proceeds
to block 410 which causes the subroutine to return. If the voltage
corresponding to the
braking current is greater than constant c16, then block 408 turns on LEDS,
and proceeds
to block 410 which causes the subroutine to return. In the preferred
embodiment of the
present invention, constants c13, c14, c15, and cl6 correspond to 0.3, 2.5,
3.75, and 5
(amps), respectively. The remaining blocks of the DISPLAY CURRENT subroutine
are
similar to those described above. If block 412 determines that variable axles
is equal to
2, then the subroutine progressively turns on LEDs 2-5 by comparing the
voltage
corresponding to stored braking current to constants c9, cl D, cll , and c12
which, in the
preferred embodiment, correspond to 0.3, 3.3, 6.6, and 10 (amps),
respectively. If block
432 determines that variable axles is equal to 3, then the subroutine
progressively turns
on LEDs 2-5 by comparing the voltage corresponding to stored braking current
to
constants c5, c6, c7, and c8 which, in the preferred embodiment, corresponding
to 0.1,
S, 10, and 15 (amps), respectively. If block 452 determines that variable
axles is equal to
4, then the subroutine progressively turns on LEDs 2-5 by comparing the
voltage
corresponding to stored braking current to constants cl , c2, c3, and c4
which, in the
preferred embodiment, corresponding to 0.1, 6.6, 13.3, and 20 (amps),
respectively. If
variable axles is not equal to 1, 2, 3, or 4, then block 472 causes the
subroutine to return.
To summarize the operation of the brake controller of the present invention
during
normal operating conditions, the signal causing braking of the towed vehicle
originates
from either the sensor input circuit or the manual input circuit. If the brake
pedal of the
towing vehicle is pressed, then the brake light circuit provides the voltage'
necessary to
-27-
CA 02225644 2001-06-27
drive LED1 which drives Q1 if a sufficient deceleration force is experienced
by the
decelerometer of the sensor input circuit. The resulting signal is then sent
to the gain
adjustment circuit. If the manual control of the manual input circuit is
operated, then this
signal is supplied to the gain adjusunent circuit and pin 4 of the
microcontroller, and the
microcontroller grounds pin 8 such that LED1 and the sensor input circuit are
disabled.
Whether the input signal supplied to the gain adjustment circuit is from the
sensor input
circuit or the manual input circuit, the gain adjustment circuit gradually
causes a signal to
be supplied to pin 5 of the microcontroller. This signal is limited by the
setting of the
gain adjustment potentiometer. The microcontroller generates a PWM drive
signal based
on the magnitude of the input received from the gain adjustment circuit, and
this signal is
supplied to transistor Q7 of the power switching circuit. Transistor Q7 is
driven when
the PWM drive signal is high, causing the driving voltage provided by the
power control
circuit to not be applied to the gates of MOSFETS Q8 and Q9. When the PWM
drive
signal is low, transistor Q7 is not driven and the driving voltage provided by
the power
control circuit is applied to the gates of Q8 and Q9. This voltage drives the
MOSFETS
and allows current from the 'current sense circuit to be applied to the brakes
of the towed
vehicle. The magnitude of braking current is dependent on the duty cycle of
the PWM
drive signal, with more current applied when the duty cycle is low. The
current sense
circuit senses the magnitude of braking current across resistor R30 and
supplies this
signal to pin 2 of the microcontroller. Using either software threshold
sensing via pin 2
or hardware threshold sensing via pin 9, the microcontroller shuts the braking
current off
if its magnitude exceeds a threshold limit, and samples it again approximately
every '/
second. The microcontroller displays the magnitude of braking current by means
of
LEDs 2-5 of the display circuit. The red component of LED6 of the display
circuit is
activated whenever current is supplied to the towed vehicle's brakes, and the
green
component is activated whenever the decelerometer of the sensor input circuit
is level.
In an alternate embodiment of the brake controller of the present invention,
an
additional feature is provided to enable the operator of the towing vehicle to
verify that
the brakes of the towed vehicle are electrically connected to the brake
controller without
requiring the operator to attempt to activate the brakes. This verificatioti
is desirable
because it provides assurance to the operator that he or she is in control,
thus promoting
increased driving confidence. To implement this additional feature, a green-
colored LED
is preferably used for LED2 instead of the conventional red, as shown in Fig.
12B.
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CA 02225644 1998-02-06
WO 97f67003 PCT/CTS96/13507
Furthermore, additional programming is provided for microcontroller 10, as
described in
greater detail below.
To verify that the brakes of the towed vehicle are electrically connected to
the
h
brake controller, microcontroller 10 of the alternate embodiment is programmed
to
periodically determine if current is able to flow through MOSFETS Q8 and Q9.
Current
will be able to flow only if the brat{es are connected because, otherwise, an
open circuit
will be present at the source of Q8 and Q9. To determine if current is able to
flow, the
programming of microcontroller 10 periodically provides driving voltage to the
gates of
Q8 and Q9. This is achieved by periodically supplying a low signal, via pin 7,
to
transistor QS such that power control circuit 28 supplies driving voltage to
power
switching circuit 24, and by supplying pulses to transistor Q7, via pin 15, at
the same
time. In the preferred embodiment, driving voltage is provided to the gates of
Q8 and. Q9
every four seconds, with pin 15 supplying two pulses, 4 milliseconds apart,
for each four-
second interval of time. When the driving voltage is thus being provided, a
small amount
of current will flow through Q8 and Q9 for a very short duration of time if
the brakes are
connected. This current, although incapable of noticeably activating the
brakes, is sensed
across resistor R30 of current sense circuit 26. As described above in
connection with
circuit 26, this signal is amplified by amplifiers U3b and U3c and their
corresponding
resistive networks, and is supplied to pin 2 of microcontroller 10 through
resistor R25..
Microcontroller 10 then compares the current magnitude to a verification
threshold value
stored in memory and, if the threshold is exceeded, sets a variable brakesyes
to indicate
that the towed vehicle's brakes are connected.
Verification that the brakes are connected is indicated to the operator of the
vehicle by activation of LED2 if variable brakesyes is set. Such activation
only occurs
when the towed vehicle is idle so that LED2 can perform its other functions
which are
described above. Preferably, microcontroller 10 has two modes of operating
LED2 to
indicate that the brakes are connected. The first mode maintains LED2 in a dim
state,
when variable brakesyes is set, by sending repetitive signal pulses thereto
with a low duty
cycle. The second mode of operation flashes LED2 every 8 seconds when variable
' 30 brakesyes is set. The operator of the vehicle can select the preferred
mode of operation
at the time of installation of the brake controller when the power is first
turned on. The
second mode, or flashing mode, is selected if the manual control of manual
input circuit
18 is operated at the time of installation of the brake controller. Otherwise,
the first
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WO 97/07003 PCT/US96/13507
mode, or dim mode, is implemented by default. The mode of operation of LED2
then
remains the same for the life of the brake controller unless the controller or
battery is
disconnected, in which case the mode may again be selected when power is
returned.
In another alternate embodiment, the verification feature described above also
S provides a means of detecting whether "overload" current conditions exist
without
requiring the operator to attempt to activate the brakes. As before, the brake
current
generated by the periodic supply of driving voltage to the gates of Q8 and Q9
is sensed
by current sense circuit 26, and the resulting signal is supplied to
microcontroller 10. In
this embodiment, however, microcontroller 10 compares the current magnitude to
two
threshold values. In addition to the verification threshold value which
establishes the
minimum current required to verify that the brakes of the towed vehicle are
connected,
the current magnitude is also compared to a second maximum current threshold
value
which determines whether "overload" current conditions exist. This second
maximum
current threshold value is preferably 10 amps which, due to the very short
duration of
applied current, provides an indication of overload current conditions similar
to the 28- or
30-amp threshold of the preferred embodiment. If the current exceeds this
second
maximum current threshold value, then microcontroller 10 shuts the current off
to the
towed vehicle's brakes and samples it again approximately once every four
seconds. To
indicate to the operator that overload current conditions have been detected
by the
verification feature, microcontroller 10 causes LED2 to flash approximately
once every '/a
second. This is in contrast to the previously-discussed situation where
overload current
conditions are detected when activation of the towed vehicle's brakes is
attempted. In this
previously-discussed situation, microcontroller 10 of the alternate embodiment
notifies the
operator by flashing LEDs 2-5, similar to the preferred embodiment. However,
unlike
the preferred embodiment, the flashing occurs once every I/4 second and is not
dependent
on the shape of the current waveform or the time it takes to reach overload
current
conditions.
In another alternate embodiment of the present invention, an additional
feature is
provided to prevent current from being sent to the towed vehicle's brakes if
the "circuit
ground" somehow becomes disconnected from actual battery ground. Notification
is also
provided to the operator of the vehicle of such an event. This feature is
desirable because
such a disconnection, referred to as an open ground, may prevent proper
operation of the
brake controller and may be indicative of a serious problem with the towing or
towed
-30-
CA 02225644 2001-06-27
vehicle. To implement this additional feature, a resistor RSO and a Zener
diode ZSO, in
series, are connected between the positive battery terminal and the base of
transistor Q4
of current sense circuit 26, as shown in Fig. 12A. Preferably, R50 is a 47
KOhm resistor
and ZSO is a 20-volt Zener diode. Additional programming is not required for
S microconuoller 10, as is evident by the following description of the
operation of the
alternate embodiment.
Normally, when current is discontinued to the brakes after a period of
activation,
the energy remaining in the brakes attempts to discharge through diode DS to
circuit
ground. However, if an open ground exists because the circuit ground terminal
is
disconnected from battery ground, these pulses of voltage attempt to discharge
through
capacitor C 13. Because of its connection to capacitor C 13, the battery
positive tet7ninal
then receives these pulses of voltage which cause the battery supply voltage
to rise.
Because voltage pulses generated by an open ground are relatively large, this
increase in
the battery voltage is typically substantial. If the battery supply voltage
exceeds a voltage
1S supply threshold, then resister RSO and Zener diode ZSO supply driving
voltage to the
base of transistor Q4 which causes pin 9 of microcontroller 10 to go low. As
described
above, when overload current conditions exist, this causes microcontroller 10
to perform
interrupt INT1 and to shut the current off to the towed vehicle's brakes. In
addition,
LEDs 2-S will flash, due to the sampling of current approximately every 2S0
milliseconds, such that the operator of the towing vehicle will know that
either overload
current conditions or an open ground exists. The voltage supply threshold
associated with
resister RSO and Zener diode ZSO is preferably established at a certain
tolerance above
the maximum normal battery supply voltage so that small voltage pulses
generated from
sources other than an open ground, such as from the ignition of the towing
vehicle, do
2S not cause the brake current to be cut off.
The above-noted changes in the operation of the brake controller of the most
preferred alternate embodiment can be seen in connection with the additional
flowcharts
provided in Figs. 13-16 and described in detail below. It should be noted that
the
flowcharts of Figs. 3-7, 9, and 11 of the original embodiment have been
retained in this
alternate embodiment, with detailed descriptions thereof provided above.
Figs. 13A-13E show the INTTC1 interrupt for the microcontroller. Block S00
signifies the beginning of the interrupt. Next, block S02 then executes the
CHECK
CURRENT subroutine, and switches the PWM drive signal high such that no
current is
-31-
CA 02225644 2001-06-27
applied to the towed vehicle's brakes. Next, block 504 determines if variable
n is greater
than 0 which would indicate that close to the maximum level of braking is
being
demanded. If not, then the program proceeds to block 514. If block 504
determines that
variable n is greater than 0, then block 506 determines if variable count is
equal to 9
which would be the case if overload conditions do not exist. If the condition
of block
506 is not satisfied, then the program proceeds to block 510. If the condition
of block
506 is satisfied, then block 508 switches the PWM drive signal low such that
current is
applied to the towed vehicle's brakes. After block 508, block 510 determines
if variable
std is set equal to TRUE which would indicate that the self test has been
performed. If
not, then the program proceeds to block 514. If the self-test has been
performed, then
block 512 turns the bicolored LED's red component on.
Next, block S 14 determines if variable m is equal to 0 (indicating that the
self-test
is not being perfbrmed) and if variable z is equal to 0 (indicating that the
brake controller
is to provide brake current). If both conditions of block 514 are not met,
then the
program proceeds to block 518. If both conditions of block 514 are met, then
block 516
turns the bicolored LED's red component off. Next, block 518 loads the timerl
and
timer2 registers which determine when the interrupts are executed. Then block
520
determines if variable insetwidth is less than 4, if the brake lights of the
towing vehicle
are not lit, and if the self test is completed.
Basically, the first two conditions just noted are to determine whether there
is an
appreciable brake demand. If the conditions of block 520 are not satisfied,
then the
program proceeds to block 524. If the conditions of block 520 are satisfied,
then block
522 turns the bicolored LED's red component on. After block 522, then the
program
proceeds to block 524 which determines if variable setwidth is less than or
equal to 3. If
not, then the program proceeds to block 534. If block 524 determines that
variable
setwidth is less than or equal to 3. then block 526 determines if variable
count is equal to
. 9 which would indicate normal (not overload) conditions. If not, then block
532 sets
variable setwidth equal to 1 and variable integersetwidth equal to hexadecimal
13, and the
program proceeds to block 530. If block 526 determines that variable, count is
equal to 9,
then block 528 samples the gain channel. Next, block 530 executes the DISPLAY
CURRENT subroutine. The program then proceeds to block 534.
Block 534 of the INTTC 1 interrupt determines if variable integersetwidth is
greater than hexadecimal FO which would indicate a very high demand for
braking
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CA 02225644 1998-02-06
WO 97107003 PCT/U896/I3507
current. If not, then the program proee~ds to block 542. If a very high demand
for
braking current is determined to be present in block 534, then block 536
determines if
. variable count is equal to 9, which would indicate normal (not overload)
conditions. If
not, then the program proceeds to block 540. If block 536 determines that
variable count
is equal to 9, then block 538 turns the PWM drive signal low. Next, block 540
turns the
bicolored LED's red component on and sets the timer3 and timer4 registers to
zero.
Next, block 542 determines if the self test is completed and, if not, then the
program
proceeds to block 566. If the self test is completed, then block 544 samples
the manual
gain channel. Next, block 546 determines if variable intmanual is greater than
8 or if the
brake lights of the towing vehicle are lit. If neither condition is met, then
the program
proceeds to block 550. If at least one of the conditions in block 546 is met,
then the
program proceeds to block 548. Block 550 turns the PWM power off, disables the
bicolored LED, and sets variable z equal to TRUE to indicate that the brake
controller is
not active. Block 548 turns on the PWM power, enables the bicolored LED, and
sets
variable z equal to FALSE (or 0) to indicate that the brake controller is to
be active. The
program then proceeds to block 552.
Block 552 of the INTTC 1 interrupt determines if variable setwidth is greater
than
hexadecimal E, and, if not, the program proceeds to block 560. If variable
setwidth is
greater than hexadecimal E, then block 554 determines if variable count is set
equal to 9
indicating normal (not overload) conditions. If not, then the program proceeds
to block
558. If it is, then block 556 turns the PWM drive signal low. , Block 558 then
turns the
bicolored LED red component on. Next, block 560 determines if variable z is
equal to 0
which would indicate the brake controller is to be active. If not, then block
564 turns the
bicolor green off to reduce current, and the program proceeds to block 566. If
block _'>60
determines that variable z is equal to 0, then block 562 checks the sensor
level, and the
program proceeds to block 566.
Block 566 of the INTTC1 interrupt determines if variable setwidth is greater
than
hexadecimal D, and, if not, the program proceeds to block 574. If it is, then
block 56~8
determines if variable count is equal to 9. If count is equal to 9, then block
570 turns the
PWM drive signal low. After block 570, or if count is not equal to 9, the
program
proceeds to block 572 which turns the bicolored LED's red component on. Block
574
decrements the variable time. Next, block 576 determines if variable timel is
greater
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CA 02225644 1998-02-06
WO 97/07003 PCT/US96/13507
than 0. Variable timel keeps track of the 250 millisecond timing for overload
conditions.
If variable timel is not greater than 0, then the program proceeds to block
580. If it is,
then block 578 decrements variable timel and sets variable count equal to 0.
Next, block
580 determines if variable timel is equal to 0. If not, then the program
proceeds to block
586. Block 586 turns all of the LEDs off. If the condition of block 580 is
met, then
block 582 sets variable count equal to 9 which indicates normal (not overload)
conditions.
Next, block 584 determines if variable timel is greater than 30, which is
equivalent to
120 milliseconds. If not, then the program proceeds to block 594. If block 584
determines that variable timel is greater than 30, then block 588 determines
if variable
temp is TRUE. If block 588 determines that variable temp is TRUE, then the
program
proceeds to block 590 which turns on LED2 (green). If block 588 determines
that
variable temp is not TRUE, then block 592 turns all LEDs on for flashing
purposes.
Next, block 594 determines if variable time is equal to 0 and if variable
time3 is greater
than 0. If both conditions are not met, the program proceeds to block 598. If
either
condition is met, block 596 decrements variable time3 prior to proceeding to
block 598.
Next, block 598 determines if variable tc2flag is TRUE which would indicate
that
interrupt INTTC2 was in execution and had been interrupted by the current
execution of
interrupt INTTC1. If the condition of block 598 is not satisfied, then block
602 sets
variable tclflag equal to FALSE, and the program proceeds to block 604. If the
condition of block 598 is satisfied, then block 600 sets variable tclflag
equal to TRUE.
Block 604 then determines if the self test mode has not been selected. If it
has, then the
program proceeds to block 608. If the self test mode has not been selected,
then block
606 sets variable m equal to 0 to indicate that a self test has not been
requested. The
program then proceeds to block 608.
Block 608 determines if variable m is TRUE, caused by execution of the SELF-
TEST subroutine. If variable m is not TRUE, then the interrupt proceeds to
block 612.
If variable m is TRUE, then block 610 decrements variable tpwm which is set to
25 in
block 614. Next, block 612 determines if variable tpwm is equal to 0, and, if
not, the
interrupt proceeds to block 616. If variable tpwm is equal to 0, then block
614
increments variable g and variable tpwm is set to 25. Block 616 of the
interrupt
decrements variable time4 which is used to determine when to sample current to
ensure
that the brakes are connected.
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In block 618, the interrupt determines whether the variable intsetwidth is
less tloan
hexadecimal F and whether variable m is equal to 0. If both of these
conditions are not
met, the interrupt routine proceeds to block 674 where the intemtpt routine is
ended. If
a
both of the conditions tested in block 618 are met, the interrupt routine then
determines
whether the variable count is equal to 9 and whether the variable tclflag is
equal to 0 i.n
block 620. If both of these conditions are not met, interrupt routine is ended
by
proceeding to block 674. If both of the conditions in block 620 are met, block
622
determines whether the variable time4 is equal to 1 and whether the variable
std is TRUE.
If both of these conditions are not met, the interrupt proceeds to block 626,
otherwise
block 624 first turns the PWM power on, turns the PWM drive off for a
predetermined
delay and then turns the PWM drive on. In block 626; the interrupt determines
whether
variable time4 is equal to 0 and whether the variable std is TRUE. If both of
these
conditions are not met, the interrupt routine is ended by advancing to block
674. If both
of these conditions in block 626 are;- met; block 628 sets the variable brakes
equal to NO
and checks the brake current. Next, block 630 determines whether current is
less than 6.
If so, block 632 sets the variable threshold equal to 1 prior to proceeding to
block 646,
If the variable current is not less than 6, routine proceeds to block 634
where it
determines whether the variable current is less than 10. If the variable
current is less
than 10, block 636 sets the variable threshold equal to 3 before proceeding to
block 646.
If the variable current is not less than 10, the routine proceeds to block 638
where it is
determined whether the variable current is less than 14. If the,variable
current is less
than 14, block 640 sets the variable threshold equal to 5 and proceeds to
block 646. If
the variable current is not less than 14, the routine proceeds to block 642
where it is
determined whether the variable current is less than 19. If the variable
current is less
than 19, block 644 sets the variable threshold equal to 7 and the routine
advances to block
646. If the variable current is not less than 19, the routine proceeds
directly to block 646
without affecting the variable threshold.
In block 646, the routine turns the PWM power on, turns the PWM drive off for
a
predetermined delay, checks the current, turns the PWM drive on, and turns the
PWM
power off. Then, block 648 determines whether the variable threshold equals 1
and the
current is less than 4. If both of these conditions are met, the routine sets
the variable
brakes to TRUE in block 650 before proceeding to block 664. If, both of the
conditions
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in block 648 are not met, the routine advances to block 652 where it
determines whether
the variable threshold is equal to 3 and the current is greater than 14. If
both of these
conditions are met, the routine advances to block 654 where its sets the
variable brakes to -
TRUE before advancing to block 664. If both of the conditions in block 652 are
not met,
the interrupt proceeds to block 656, where it determines whether the variable
threshold is
equal to 5 and the current is greater than 16. If both of these conditions are
met, the
interrupt proceeds to block 658 where it sets the variable brakes to TRUE
before
advancing to block 664. If neither of the conditions set forth in block 656
are met, the
interrupt proceeds to block 660 where it determines whether the variable
threshold is
equal to 7 or the current is greater than 22. If both of the conditions in
block 660 are
met, the routine sets the variable brakes to TRUE in block 662 before
proceeding to
block 664, otherwise, the routine proceeds directly to block 664 without
changing the
variable brakes.
Block 664 determines whether the current is greater than 80. If the current is
not
greater than 80, the routine advances to block 668. If the current is greater
than 80, the
variable brakes is set equal to 9, which indicates overload condition when
brake current is
not being demanded. Then, in block 668, the interrupt determines whether the
variable
brakes is set at NO. If it is not, the routine advances to block 672. If
brakes is NO, the
routine advances to block 670 where it turns all the LEDs off before
proceeding to block
672 where the interrupt sets the variable time4 equal to 250. Next, in block
674, the
interrupts are enabled and the registers are restored prior to executing a
return from the
INTTC1 interrupt routine.
Fig. 14 illustrates a flow diagram for the CHECK LEVEL routine 676 according
to the second embodiment of the invention. CHECK LEVEL routine 676 begins in
block
678 where the variable s is set to FALSE. Then, in block 680, the routine
checks
whether the variable intsetwidth is greater than 16. If this variable is not
greater than 16,
the routine advances to block 684. If, on the other hand, the variable
intsetwidth is
greater than 16, the routine advances to block 682 where it turns the bicolor
green off
prior to ending the routine by advancing to return block 704.
In block 684, the routine determines whether the variable intsetwidth is less
than
8. If this variable is not less than 8, the routine advances to block 692,
otherwise, the
routine advances to block 686 where it turns the bicolor green off. After
block 686, the
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routine determines whether the variable intmanual is less than 6. If this
variable is less
than 6, the routine advances to 690 where it sets the variable s to TRUE prior
to ending
the routine by proceeding to block 704, otherwise, the routine directly
advances from
block 688 to block 704. In block 692, the routine sets the variable x to FALSE
and then
.. 5 proceeds to block 694 where it determines whether the va:iable intmanual
is less than 1.2.
If it is not, the routine advances directly to block 698, otherwise, it first
advances to
block 696 where it sets the variable x to TRUE. In block 698, the routine
determines
whether x is TRUE and whether the brakes have been pushed. If both of these
conditions
are TRUE, block 700 of the routine: turns the bicolor green on, to indicate
level condition
prior to ending the routine by advancing to block 704. If either of the
conditions in block
698 are not met, the routine turns the bicolor green off in block 702 before
ending the
routine by advancing the block 704.
Fig. 15 shows the FLASHRATE routine 706 according to the second embodiment
of the present invention. This routine begins in block 708, where all LEDs are
turned
off, and the interrupts are disabled. Next, in block 710, the routine sets the
variable
flashfast equal to TRUE before advancing to block 714 where it samples the
manual
control. Then, in block 716, the rautine determines whether the variable
manualmsb is
greater than 4. If it is not, the routine advances to block 720, otherwise,
the routine first
executes block 718 where the variable flashfast is set to FALSE and LED2
(green) is
turned on. Then, in block 720, the variable std is set equal to TRUE. Then,
the routine
advances to block 724.
Then, in block 724, the routine checks whether the variable flashfast is equal
to 0.
If not the routine proceeds to block 728, otherwise the routine advances to
block 726. In
block 726, the routine sets the variable led status equal to 1, sets the
variable time equal
to 200, and sets the variable time3 equal to 1 before proceeding to block 730.
Block 728
sets the variable time3 equal to 0 before proceeding to block 730. In block
730, the
routine enables the interrupts. Then, in block 732, the routine turns all the
LEDs off
prior to returning to the point in the program where this routine was called
as shown in
block 734.
Figs. 16A and 16B show the SAMPLE GAIN routine 736 that is implemented in
the second embodiment of the present invention. SAMPLE GAIN routine 736 begins
in
block 738 where the routine selects a gain channel, performs analog to digital
conversion
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and sets the variable setwidth equal to the variable gainmsb. Next, in block
740, the
routine checks to determine where the variable m is greater than 0. If so, the
routine sets
the variable setwidth equal to the variable g in block 742 prior to advancing
to block 744, -
otherwise, the routine advances directly from block 740 to block 744. In block
744, the
routine stores the levels for the variables gainlsb, and gainmsb in the
variable intsetwidth.
Next, in block 746, the routine determines whether the variable intsetwidth is
less than 18
and whether the variable m is equal to 0, and whether the variable brakes is
set to TRUE.
If anyone of these conditions is not met, the routine advances directly to
block 770. If all
of these conditions in 746 are met, the routine advances to block 748 where
the routine
determines whether the variable time is equal to 0. If not, the routine
advances directly
to block 770, otherwise the routine advances to block 750 where the routine
determines
whether the variable led status is equal to 1. If not, the routine advances to
block 762
otherwise, the routine advances to block 752. In block 752, the routine then
determines
whether the variable time3 is equal
to 0. If it is, the routine advances to block 754 where it turns LED2 on, sets
the variable
time equal to 20, and sets the variable led status equal to 2 prior to
advancing to block
758. In block 756, the routine sets the variable time equal to 200 prior to
advancing to
block 758. In block 758, the routine determines whether the variable flashfast
is equal to
TRUE. If so, the routine sets the variable time equal to 1 in block 760 prior
to
advancing to block 770, otherwise the routine advances directly to block 770
from block
758.
In block 762, the routine checks to determine whether the variable led status
is
equal to 2. Ifso, the routine advances to block 764 where it turns off all the
LEDs, such
the variable time equal to 200, sets the variable time3 equal to 8, and sets
the variable led
status equal to 1 before proceeding to block 766. If, in block 762, that the
variable led
status is not equal to 2, the routine advances directly from block 762 to
block 766. In
block 766, the routine determines whether the variable flashfast is set equal
to TRUE. If
so, the routine advances to block 768 where it sets the variable time3 equal
to 0 and sets
the variable time equal to 3 prior to advancing to block 770. If the variable
flashfast is
not equal to TRUE in block 766, the routine advances directly to block 770.
In block 770, the routine sets the variable n equal to FALSE prior to
advancing to
block 772 where it determines whether the variable intsetwidth is greater than
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hexadecimal FA. If so, the routine sets the variable n equal to TRUE in block
774 prior
to advancing to block 776, otherwise, the routine proceeds directly from block
772 to
block 776. In block 776, the routine determines where the variable setwidth is
equal to 0.
If so, the routine advances to block 778 where it sets the variable setwidth
equal to 1
before ending the routine by proceeding to block 780. Alternatively; if the
variable
setwidth is determined to be a value other than 0 in block 776, the routine
advances
directly to block 780 where the routine is ended.
As presently contemplated, a most preferred alternate embodiment of the
present
invention is shown in the schematic diagrams of Figs. 17A-17B, with the
operation thereof being
the same as the original embodiment discussed above unless indicated
otherwise.
Analysis of Figs. 17A-17B show that the output current sampling is no longer
performed across
resistor R30 of Figs. 2A-2B and 12A-12B. Instead, current sampling is done
using the Rds/on "on"
resistance of the output MOSFETS (Rds/on). The benefits of this arrangement
are many.
First, the use of the MOSFET's Rdslon saves cost and space on the circuit
board.
Second, the heat that was generated by resistor R30 is eliminated. Finally,
using the
internal MOSFET Rds/on helps prevent the brake controller from overheating and
entering a thermal runaway situation. This is because the temperature of the
MOSFET
increases with increasing current flow, resulting in an increase in its
Rds/on. With such
an increased internal resistance, a smaller current is required to develop the
voltage
across the MOSFET which indicates overload current conditions, resulting in
increased
protection to the brake controller at elevated operating temperatures. A
typical combined
internal MOSFETS resistance of Q8 and Q9 is of the order of 15 milliohms which
corresponds to a 0.45-volt drop when an output current of 30 amps is present.
Figs. 17A-17B also show that the power control circuit has been removed in an
effort to
save cost. However, transistor QS is still implemented as follows. As before,
an
operational amplifier circuit is used to sense the sampled current by
amplifying the
differential mode signal that is developed across its terminals. But with the
circuit
arrangement of Figs. 17A-17B, in which the drain of the MOSFET is connected to
the battery
supply voltage, a very large differential mode signal is present when there is
no flow of
current to the brakes. This signal would incorrectly indicate a very large
current, which
would cause the current sense circuit to register overload current conditions.
In order to
prevent this situation from occurring, transistor QS is used by the
microcontroller to
disable the current sensing when there is no flow of current to the brakes.
Pin 7 of the
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microcontroller drives the base of Q5. When on, QS pulls the output of
amplifier U3b
low, which disables the current sensing. The microcontroller turns QS on every
time the
pin 15 PWM drive signal is switched high (when there is no brake current),
with QS
remaining high for a precautionary period of time after the PWM drive signal
is switched
low in order to accommodate the rise time of the turn-on transient.
Another change to the circuit is the inclusion of a resistor R43 (preferably,
1
KOhm) coupled in series to the base of transistor Q7, and a diode D7 having
its anode
coupled between resistors R36 and R43 and its cathode connected to the
collector of
transistor Q4. Whenever there is an open ground condition, a high voltage is
generated
on the 12 volt battery line. This in turn generates an overload condition
through R41 and
Z5, which provides a drive to the base of Q4 and the collector of Q4 goes low
thereby
generating an intetntpt. This causes the cathode of diode D7 to also go low at
that time.
When the cathode goes low, it cuts the drive of the base of Q7 causing its
collector to go
high. When the collector of Q7 is high MOSFETS Q8 and Q9 are turned on to
allow the
voltage transients to dissipate in the brake magnets without damaging MOSFETS
Q8 and
Q9 as a result of high voltage.
As before, one of the purposes of the current sampling is to detect whether
any
magnets are connected. This is done by providing a low PWM (pin 15) pulse
every 4
seconds, at times when braking is not being demanded, to verify that a current
above a
particular threshold level is established. This applied pulse is very short so
as to make
any braking action very minimal and unnoticeable to the operator of the
vehicle. If the
braking connection is so detected, then the green LED, LED2, will be in a dim
state or
will flash once every 8 seconds, depending on which mode of indication was
initially
selected by the vehicle's operator. If the brake connection is determined to
not be
present, then the green LED, LED2, will be off. If the current that is
established by the
short pulse exceeds a predetermined higher threshold value which corresponds
to overload
current conditions being present, then this condition can also be indicated to
the operator
of the vehicle.
With the requirement to detect small currents, the design of the U3b amplifier
circuit must be well-balanced in order to keep the common mode rejection high.
This
demands that the resistors be at one percent tolerance at minimum, and have
the same
temperature coefficients so that they are balanced over the entire operating
temperature
range. However, the output of operational amplifier U3b is temperature
dependent.
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Because of this, fixed threshold~means cannot be used to sense braking
currents. Instead,
a baseline level must be used which is correlated to this temperature
dependency and
which is established when detectin g whether the brakes are connected (done
when there is
no braking demand). Two consecutive pulses of current are supplied, with the
first pulse
being very short and generating a voltage at test point 5 (TPS) which is the
baseline value
and which is typically about D.4 volts in the most preferred alternate
embodiment. Tb.e
second pulse is wider, with any dii:ference in TPS voltages (generated when
the second
pulse voltage is higher) indicating that the brakes are connected. The
baseline value is
stored and is also used to display the current magnitude. This is accomplished
by
subtracting off the baseline value from the sampled current magnitude (voltage
resulting
therefrom) to establish the true level of current flowing to the brakes. Also,
by
establishing a baseline current in this fashion, the microcontroller may
automatically
determine the number of axles on the towed vehicle without requiring an
operator to
manually input the number of axles in the event that the brake controller
utilizes the
number of axles in any manner.
Another change in the most preferred alternate embodiment is that the display
of
the level of braking current via LBDs is now done by analyzing the duty cycle
of the
PWM drive signal instead of using the current values actually calculated by
the current
sense circuit, as provided above.
Another change in the most preferred alternate embodiment is that, after the
first
250 millisecond period is over following the detection of overload current
conditions, the
PWM drive signal will be adjusted so that only seventy percent (in the
preferred
embodiment) of the maximum voltage demand will then be applied. If this
lowered level
of excitation does not cause overload current conditions again, then the
brakes will
function accordingly. As such, this method is useful for providing a reduced
level of
braking current in the response to a braking demand by the operator of the
vehicle when
marginal overload current conditions were originally present.
The most preferred alternate embodiment also enables the brake controller to
detect when a lamp load is mistakenly connected to a brake magnet terminal. In
such a
' 30 situation, the filament load will cause the baseline current value to be
higher than norrnal,
which may cause operational problems. To solve this problem, the
microcontroller
compares the baseline value to a threshold level that would be surpassed if a
lamp load is
present. If this new threshold level is exceeded, then overload current
conditions are
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indicated to the vehicle's operator.
Another change in the most preferred alternate embodiment is that software
watchdogs are implemented in both the INTTC 1 and INTTC2 interrupts which
reset the
microcontroller if one of the interrupts is not executed in the appropriate
period of time4
milliseconds in the preferred embodiment. This prevents the microcontroller's
programming from getting hung up due to a malfunction.
Still another change in the most preferred alternate embodiment is that, after
the
self test is completed, the microcontroller automatically enters normal brake
controller
operation even if a voltage is maintained at the microcontroller's self test
pin.
The above-noted changes in the operation of the brake controller of the most
preferred alternate embodiment can be seen in connection with the additional
flowcharts
provided in Figs. 18-24 and described in detail below. It should be noted that
the
flowcharts of Figs. 3-6 and 15 of the original embodiment have been retained
in this
alternate embodiment, with detailed descriptions thereof provided above.
Shown in Fig. 18 is the INT1 interrupt for the microcontroller of the most
preferred alternate embodiment. This interrupt begins with block 1500 which
signifies
the beginning of the interrupt. Next, block 1502 saves the microcontroller's
registers in
RAM. Block 1504 then determines if variable integersetrvidth is less than
hexadecimal 24
which would indicate that effectively no brake demand is present. If this
condition is
satisfied, then block 1506 sets variable brakes equal to 9 and the program
returns from
the interrupt. If block 1504 determines that some brake demand is present,
then block
1508 sets variable overloadon equal to TRUE and variable timel equal to 67.
Next,
block 1510 sets variable count equal to 0, turns the PWM drive off, and
restores the
microcontroller's registers from RAM. Block 1512 then causes the interrupt to
return.
Figs. 19A-19F show the INTTCl interrupt for the microcontroller. Block 1514
(Fig. 19A) signifies the beginning of the interrupt. Next, block 1516 sets the
watchdog
control registers to certain values which, if exceeded, cause the
microcontroller to be
reset. Block 1518 then executes the CHECK CURRENT subroutine, and switches the
PWM drive signal high such that no current is applied to the towed vehicle's
brakes.
Next, block 1520 determines if variable n is greater than 0 which would
indicate that
close to the maximum level of braking is being demanded. If not, then the
program
proceeds to block 1532. If block 1520 determines that variable n is greater
than 0, then
block 1522 determines if variable count is equal to 9 which would be the case
if overload
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conditions do not exist. If the condition of block 1522 is not satisfied, then
the progr~un
proceeds to block 1528. If the condition of block 1522 is satisfied, then
block 1524
determines if variable overloadon is not set such that overload current
conditions are not
present. If overload conditions are present, then the program proceeds to
block 1528. If
block 1524 determines that variable overloadon is not set, then block 1526
switches the
PWM drive signal (drive) low such that current is applied to the towed
vehicle's brakea.
After block 1526, block 1528 determines if variable std is set equal to YES
which would
indicate that the self test has been performed. If not, then the program
proceeds to block
1532. If the self test has been performed, then block 1530 turns the bicolored
LED's red
component on.
Next, block 1532 determines if variable m is not equal to 8 (indicating that
the
self test is not being performed) and if variable z is equal to 0 (indicating
that the brake
controller is to provide brake current). If both conditions of block 1532 are
not met, then
the program proceeds to block 1536. If both conditions of block 1532 are met,
then
block 1534 turns the bicolored LED's red component off. Next, block 1536
determinca if
variable overloadon is set and if variable setwidth is greater than
hexadecimal D. If not,
then the program proceeds to block 1540. If both conditions of block 1536 are
met, then
block 1538 sets variable setwidth equal to hexadecimal D in order to limit the
braking
current level to seventy percent (in the preferred embodiment) of its maximum
value.
Next, block 1540 loads the timerl and timer2 registers which determine when
the
interrupts are executed. Block 1542 then decrements variable time by 1 which
is used in
the timing of the turning on and off of the LEDs. Next, block 1544 determines
if
variable m is not equal to 8 which would indicate that the microcontroller is
not in its
self test mode. If the microcontroller is in the self test mode, then the
program proceeds
to block 1718 (Fig. 19F). If not, then block 1546 determines if variable
intmanual is less
than 4, if the brake lights of the towing vehicle are not lit, and if the self
test is
completed.
Basically, the first two conditions just noted are to determine whether there
is an
appreciable brake demand. If the conditions of block 1546 are not satisfied,
then the
program proceeds to block 1550. l:f the conditions of block 1546 are
satisfied, then block
1548 turns the bicolored LED's red component on. The section of the INTTCI
intermpt
a
generally labelled 1549 in Fig. 19P'~ takes care of the fine steps when the
PWM duty cycle
is low. Block 1549-1 checks to determine if the variable intsetwidth is less
than 31. If it
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is not, then the program proceeds to block 1550. Otherwise, the block 1549-2
determines
if the variable dummy4 is FALSE or 0. If it is not, then the program proceeds
to block
1550. Otherwise, the block 1549-3 checks to see if the variable count is equal
to 9. If
not, the program proceeds to block 1550. Otherwise, operation in block 1549-4
is carried
out. Block 1549-4. turns the PWM drive OFF, the bicolor LED red component ON
and
provides a fixed delay. Then block 1549-5 provides a fixed delay if variable
gainmsb is
greater than ~. This delay is implemented in block 1549-6. Block 1549-7 checks
if the
variable gainmsb is greater than 10. If it is, then a fixed delay implemented
by block
1549-8 is provided. If the variable gainmsb is not greater than 10, then the
block 1549-8
is skipped and consequently the delay is bypassed. The program then flows to
block
1549-9, wherein a decision is made whether the variable gainmsb is greater
than 14. If
the decision is positive, meaning that gainmsb is greater than 14, then a
fixed delay
implemented by block 1549-10 is executed. Otherwise this delay is bypassed. It
will be
apparent from this discussion that a means is thus provided for providing a
variable delay
based on the value of the variable gainmsb, which is the least significant
nibble of the
sampled value of the gain channel. Following the delay as discussed above, the
PWM
drive is turned ON to remove the current from the brake actuator magnets, and
the drive
to the red part of the bicolored LED turned OFF (block 1549-11). The program
then
proceeds to block 1550.
Next, block 1550 determines if variable time is set equal to 0 and variable
time3 is
greater than 0. Both of these variables are used for timing functions. If the
conditions of
block 1550 are satisfied, then block 1552 decrements variable time3. After
block 1552,
or if block 1550 determines that its two conditions are not satisfied, then
the program
proceeds to block 1554 which determines if variable setwidth is less than or
equal to 4. If
not, then block 1564 sets variable check equal to FALSE, and the program
proceeds to
block 1566 (Fig. 19C). If block 1554 determines that variable setwidth is less
than or
equal to 4, then block 1556 determines if variable count is equal to 9 which
would
indicate normal (not overload) conditions. If not, then block 1558 sets
variable setwidth
equal to 3 and variable integersetwidth equal to hexadecimal 13, and the
program
proceeds to block 1562. If block 1556 determines that variable count is equal
to 9, then
block 1560 samples the gain channel. Next, block 1562 executes the DISPLAY
CURRENT subroutine and sets variable check equal to TRUE. The program then
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proceeds to block 1566.
Block 1566 of the INTTC 1 interrupt determines if variable integersetwidth is
6 greater than hexadecimal FO which would indicate a very high demand for
braking
current. If not, then the program proceeds to block 1578. If a very high
demand for
braking current is determined to be present in block 1566, then block 1568
determines if
variable count is equal to 9, which would indicate normal (not overload)
conditions. If
not, then the program proceeds to 'block 1574. If block 1568 determines that
variable
count is equal to 9, then block 1570 determines if the overloadon flag is not
set indicating
overload conditions are not present. If the condition of block 1570 is not
met, then the
program proceeds to block 1574. If the condition of block 1570 is met, then
block 1572
turns the PWM drive signal low. Next, block 1574 turns the bicolored LED's red
component on. Next, block 1578 determines if the self test is completed and,
if not, then
the program proceeds to block 1610 (Fig. 19D). If the self test is completed,
then block
1580 samples the manual gain channel, and block 1582 sets variable x equal to
FALSE.
Next, block 1584 determines if variable intmanual is greater than 8 or if the
brake pedal
of the towing vehicle is pushed. If neither condition is met, then the program
proceeds to
block 1588. If at least one of the conditions in block 1584 is met, then block
1586 sets
variable x equal to TRUE. Block 1588 then determines if variable x is equal to
TRUE
and, if not, the program proceeds to block 1590 which disables the bicolored
LED and.
sets variable z equal to YES to indicate that the brake controller is not
active. If block:
1588 determines that variable x is equal to TRUE, then block 1592 enables the
bicolored
LED and sets variable z equal to FALSE (or 0) to indicate that the brake
controller is to
be active. The program then proceeds to block 1594.
Block 1594 of the INTTC 1 interrupt determines if variable setwidth is greater
than
hexadecimal E, and, if not, the program proceeds to block 1604. If variable
setwidth is
greater than hexadecimal E, then block 1596 determines if variable count is
set equal to 9
indicating normal (not overload) conditions. If not, then the program proceeds
to block
1602. If it is, then block 1598 determines if variable overloadon is equal to
0 which
would indicate non-overload conditions. If the condition of block 1598 is not
met, then
the program proceeds to block 1602. If the condition of block 1598 is met,
then blocl;
1600 turns the PWM drive signal low. Block 1602 then turns the bicolored LED
red
component on. Next, block 1604 determines if variable z is equal to 0 which
would
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indicate the brake controller is to be active. If not, then block 1606 turns
the bicolor
green on to reduce power, and the program proceeds to block 1610. If block
1604
determines that variable z is equal to 0, then block 1608 checks the sensor
level, and the
program proceeds to block 1610.
Block 1610 of the INTTC 1 interrupt determines if variable setwidth is greater
than t
hexadecimal D, and, if not, the program proceeds to block 1618. If it is, then
block
1612 determines if variable count is equal to 9 and if variable overloadon is
equal to 0.
If both conditions are satisfied, then block 1614 turns the PWM drive signal
low. After
block 1614, or if both conditions of block 1612 are not met, the program
proceeds to
block 1616 which turns the bicolored LED's red component on. Next, block 1618
determines if variable timel is greater than 0. Variable timel keeps track of
the 250
millisecond timing for overload conditions. If variable timel is not greater
than 0, then
the program proceeds to block 1622. If it is, then block 1620 decrements
variable timel
and sets variable count equal to 0. Next, block 1622 determines if variable
timel is equal
to 0. If not, then the program proceeds to block 1626. If the condition of
block 1622 is
met, then block 1624 sets variable count equal to 9 which indicates normal
(not overload)
conditions. Next, block 1626 determines if variable timel is greater than 0.
If not, the
program proceeds to block 1630. If it is, then block 1628 turns all of the
LEDs off
except for the bicolor LED, and the program proceeds to block 1630. Block 1630
determines if variable timel is greater than 30, which is equivalent to 120
milliseconds.
If not, then the program proceeds to block 1636. If block 163p determines that
variable
timel is greater than 30, then block 1632 determines if variable dummy4 is
equal to 0
which means the brake controller is required to provide braking current. If
block 1632
determines that variable dummy4 is equal to 0, then the program proceeds to
block 1636.
If block 1632 determines that variable dummy4 is not equal to 0, then block
1634 turns all
LEDs on for flashing purposes except for the bicolor LED. Next, block 1636
determines
if variable tc2flag is greater than 0 which would indicate that interrupt
INTTC2 was in
execution and had been interrupted by the current execution of interrupt INTTC
1. If the
condition of block 1636 is not satisfied, then block 1638 sets variable
tclflag equal to
FALSE, and the program proceeds to block 1642. If the condition of block 1636
is
satisfied, then block 1640 sets variable tclflag equal to TRUE. Block 1642
then
determines if the self test mode has not been selected. If it has, then the
program
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proceeds to block 1646 (Fig. 19E). If the self-test mode has not been
selected, then
block 1644 sets variable m equal to 0 to indicate that a self test has not
been requested.
. The program then proceeds to block 1646.
Block 1646 of the INTTC 1 interrupt decrements variable time4 which is used to
determine when to sample current to ensure that the brakes are connected.
Next, block
1648 determines if variable time4 is equal to 0 and if variable times is
greater than 0. If
both conditions are not met, then the program proceeds to block 1652. If both
conditions
of block 1648 are met, then block 1650 decrements variable times and sets
variable tirrae4
equal to 70. Next, block 1652 determines if variable times is equal to 0. If
not, then the
program proceeds to block 1656. If it is, then block 1654 sets variable times
to 15.
Block 1656 then determines if variable brakesyes is equal to 9 (indicating
overload
conditions when brake current is not being demanded) and if variable dummy4 is
equal to
1 (indicating no brake current demand). If both conditions are not satisfied,
then the
program proceeds to block 1664. If both conditions of block 1656 are
satisfied, then
block 1658 determines if variable time4 is greater than 30. If not, then block
1660 turns
the first LED on, and the program proceeds to block 1664. If block 1658
determines that
variable time4 is greater than 30, then block 1662 turns all LEDs off except
the bicolor.
Next, block 1664 determines if variable times is equal to 1 indicating that it
is time to
detect whether the brakes are connected. If not, then the program proceeds to
block 1718
(Fig. 19F). If it is, then block 1666 determines if variable integersetwidth
is less than 20
which would indicate no brake current demand. If the condition of block 1666
is not
met, then the program proceeds to block 1718 (Fig. 19F). If it is, then block
1668
determines if variable count is equal to 9 and if variable tclflag is equal to
0 (indicating
that interrupt INTTC2 had not been interrupted by the current execution of
interrupt
INTTC 1 ). If both conditions are not satisfied, then the program proceeds to
block 1718.
If both conditions are satisfied, then block 1670 determines if variable time4
is equal to 1
and if variable std is equal to YES (indicating that the self-test was
completed). If both
conditions are not satisfied, then the program proceeds to block 1718. If both
conditions
are satisfied, then block 1672 sets variable brakesyes equal to FALSE, turns
the PWM
drive signal low, executes subroutine CHECK CURRENT, delays a predetermined
period
of time, and then switches the PWrvI drive signal high. Next, block 1674 sets
variable
current msbmod equal to variable current msb + 1 in order to establish the
threshold level
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of current used to sense that the brakes are connected. Block 1676 then
determines if
variable current msbmod is greater than 0. If not, then block 1680 sets
variable current
lsbmod equal to variable current lsb + 1, and the program proceeds to block
1682 (Fig. .
19F). If the condition of block 1676 is satisfied, then block 1678 sets
variable current
lsbmod equal to variable current Isb, arid the program proceeds to block 1682.
Block 1682 of the INTTC 1 interrupt determines if variable current lsbmod is
greater than 6 which would indicate that the baseline value of voltage
corresponding to
current is too high. If not, then the program proceeds to block 1686. If it
is, then block
1684 sets variable current lsbmod equal to 2. Next, block 1686 switches the
PWM drive
signal low, and block 1688 delays for a predetermined period of time that is
eight times
that of before. Block 1690 then executes the CHECK CURRENT subroutine, and
block
1692 switches the PWM drive signal high. Block 1694 executes the COMPARE
CURRENT subroutine. Next, block 1696 determines if variable i is equal to TRUE
which would be the case if the threshold is exceeded such that the connection
of the
brakes is confirmed. If not, then the program proceeds to block 1700. If the
condition
of block 1696 is satisfied, then block 1698 sets variable brakesyes equal to
TRUE. Block
1700 then sets variable templsb equal to variable current lsbmod, sets
variable tempmsb
equal to variable current msbmod, and adds 12 to variable current msbmod to
establish the
lamp load threshold for current. Next, block 1702 determines if variable
current msbmod
is less than 12. If not, then the program proceeds to block 1706. If it is,
then block
1704 increments variable current lsbmod. Block 1706 then adds 4 to variable
current
lsbmod, and block 1708 executes the COMPARE CURRENT subroutine. Block 1710
then determines if variable i is equal to TRUE or if variable current lsb is
greater than 3.
If neither condition is true, then the program proceeds to block 1713. If at
least one of
the conditions of block 1710 is true, then block 1712 sets variable brakesyes
equal to 9
(indicating overload current conditions when no brake current is being
demanded). Block
1713 sets variable current lsbmod equal to variable templsb (to restore it),
and sets
variable current msbmod equal to variable tempmsb (to restore it). Block 1714
then
determines if variable brakesyes is equal to 0 indicating that no brakes are
present. If the
a
condition of block 1714 is not satisfied, then the program proceeds to block
1718.
Otherwise, block 1716 turns all of the LEDs off. Block 1718 then enables the
interrupts, ,
and the program returns from the interrupt via block 1720.
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Shown in Figs. 20A and 20B is the INTTC2 interrupt for the microcontroller.
This interrupt begins with block 1722 which signifies the beginning of the
interrupt.
Next, block 1724 determines whether variable m is not equal to 8. If it is
not, the
r
INTTC2 routine is completed in block 1726. If m is equal to 8, block 1728 of
the
routine sets the watchdog control registers to certain values which, if
exceeded, causes the
microcontroller to be reset. Block 1728 also sets variable tc2flag equal to
TRUE to
indicate that interrupt INTTC2 is active if ultimately interrupted by INTTC1.
Additionally, block 1728 enables the interrupts, and block 1730 determines if
variable
check is equal to TRUE which would indicate that the gain was sampled in
interrupt
INTTC 1 and that variable setwidth is less than or equal to 4. If the variable
check is not
TRUE as determined in block 1730. then the variable var is set to equal the
variable
gainmsb, which is the least significant nibble of the sampled value of the
gain channel. If
the variable check is TRUE, then the block 1734 sets the variable var to equal
the
variable prevgainmsb which is the same as the gainmsb during last sample.
Block 1736
IS checks to see if the variable intsenvidth is greater than hexadecimal 1F.
If the condition
of the block 1736 is not satisfied. the routine advances to block 1760 (Fig.
20B)
otherwise it advances to block 1737. Block 1737 checks to see if the variable
count is
equal to 9. If the condition of the block 1737 is not satisfied, then the
program proceeds
to block 1750. If the condition of block 1737 is satisfied, then the blocks
1738 throul;h
1748 add a variable delay based on the value of variable var. This provides an
additional
resolution to the PWM drive signal. If the variable var is less than or equal
to
hexadecimal 12 as determined by the block 1738, then a delay of approximately
60
microseconds is provided in block 1740. If the variable var is greater than
hexadecimal
12, then this delay is bypassed.
Similarly, block 1742 determines if variable var is less than or equal to 8.
If it is,
then another delay of 60 microseconds is added in the program as implemented
by block
1744. If the variable var is not equal to or less than 8, then the delay of
block 1744 is
bypassed. Similarly, block 1746 determines if variable var is less than or
equal to 4. If
so, then another delay of 60 microseconds is added via block 1748. If variable
var is
greater than 4, then this delay provided by block 1748 is bypassed. Block 1750
determines if variable setwidth is ~~reater than hexadecimal 1F. If so, the
routine
h
proceeds to block 1752 (Fig. 20B), otherwise it proceeds to block 1760. If, in
block
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WO 97/07003 PCT/US96/13507
1752, the variable tclflag is equal to 0, then the program proceeds to block
1754,
otherwise it goes to block 1760. Then three events happen in sequence, as
shown in
block 1754. First, PWM drive signal is turned OFF so that the current to the
brakes is
turned on. Second, a delay is implemented. Third, the current sense is
enabled. This
sequence is necessary because of the exponential rise of the current in the
brakes.
After executing the block 1754, the program flows to block 1756. This block
checks if variable s is equal to 0 and variable std is equal to constant YES.
If both
conditions are true, then the block 1758 turns the red bicolored LED on, so
that it shows
the intensity proportional to the braking action. The program then proceeds to
check the
condition in block 1760. This condition checks if variable setwidth is greater
than 4. If
not, the program proceeds to block 1770. If condition in block 1760 is TRUE,
then the
program proceeds to block 1762. The routine DISPLAY CURRENT is implemented in
this block. One or more or none of the four LEDs are lighted, depending on the
duty
cycle of the PWM. Block 1764 determines if the variable count equals 9. If it
does, then
the gain channel is sampled. If the variable count does not equal 9 in block
1764, then
the variable setwidth is set equal to 3. In block 1770, the variables tclflag
and tc2flag
are reset to FALSE. In block 1772, the registers are restored to the same
values that they
had before entering the interrupt subroutine INTTC2. Arrival of the program to
block
1774 indicates proper operation, hence the watchdog count is cleared. The
interrupts are
enabled in block 1776 and the program returns from interrupt in block 1778,
which is the
end of the interrupt subroutine INTTC2.
Fig. 21 shows the SAMPLE GAIN subroutine for the microcontroller that begins
with block 1780. Block 1782 sets previous variable gainmsb (which keeps track
of where
the gain is sampled) equal to variable gainmsb in order to initialize it to
the last value of
the sampled gain, and samples the gain channel for a new value. Next, block
1784 sets
variable setwidth equal to variable gainlsb. Block 1786 then stores the newly
sampled
gain into variable integersetwidth. Block 1788 sets variable dummy4 equal to
FALSE to
initialize it for the subsequent programming blocks. Next, block 1790
determines if
variable integerset<vidth is less than 25 which would indicate that there is
no demand for
braking current. If the condition of block 1790 is not satisfied, then the
program
proceeds to block 1791, which sets variable time4 equal to 4, sets variable
times equal to
1 and then advances the program to block 1794 (noted below) bypassing block
1792. If
block 1790 is satisfied and thus determines that there is no demand for
braking current,
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the program proceeds to block 1792 which sets variable dummy4 equal to TRUE to
indicate that condition and sets variable overloadon equal to FALSE to
reinitialize the
overload status variable. After block 1792, block 1794 determines if variable
dummy4 is
set equal to TRUE and if variable 8~rakesyes is set equal to TRUE. Variable
brakesyes is
TRUE if the brakes are connected. If both conditions of block 1794 are not
satisfied,
then the program proceeds to block 1818 (Fig. 21B). If both conditions of
block 1794
are satisfied, then block 1796 determines if variable time is equal to 0. If
not, then the
program proceeds to block 1818. If block 1796 determines that variable time is
equal t.o
0, then block 1798 determines if variable led status is equal to 1. If not,
then blocks
1810-1816 cause the LED2 to flash every 8 seconds, and the program proceeds to
block
1818. If block 1798 determines that variable led status is equal to 1, then
blocks 1800-
1808 cause a dimming of the LED2. Block 1818 then sets variable n equal to
FALSE as
a means of initialization for the subsequent blocks. Next, block 1820
determines if
variable integersetwidth is greater than hexadecimal F7 which would indicate
that the
demand for braking is close to its maximum level. If not, then the program
proceeds to
block 1824. If the condition of block 1820 is satisfied, then block 1822 sets
variable n
equal to TRUE to indicate that close to the maximum level of braking is being
demanded.
Next, block 1824 determines if variable setwidth is equal to 0 indicating that
there is no
demand for braking. If condition of block 1824 is not satisfied, then the
subroutine
returns via block 1828. If the condition of block 1824 is satisfied, then
block 1826 sets
variable setwidth equal to 1. The subroutine then returns via block 1828.
Shown in Fig. 22 is the CH13CK CURRENT subroutine for the microcontroller.
Block 1830 signifies the beginning of the subroutine. Next, block 1832 samples
the
current sensed by pin 2 of the microcontroller. Block 1834 stores the least
significant and
most significant bytes of the sampled current into variable integercurrent.
Next, block
1836 stores the baseline current value into temporary variables by setting
variable templsb
equal to variable current Isbmod and variable tempmsb equal to variable
current msbmo,d.
Block 1838 then adds 2 to the baseline current value in variable current
msbmod. After
block 1838, block 1840 determines if variable current msbmod is less than
hexadecimal 2
which would indicate overflow caused by the addition in block 1838. If so,
then block
1842 increments the value of variable current lsbmod to reflect the overflow
caused by
x
the addition. After block 1842, or if block 1840 determines that variable
current msbrraod
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WO 97/07003 PCT/US96/13507
is not less than 2, the program proceeds to block 1844, which adds 12 to the
value in
variable current lsbmod. Block 1836-1845 establishes the overload current
condition
threshold of approximately 30 amps. Next, block 1845 determines whether
variable
current lsbmod is less than 12. If it is, then current lsbmod is set to 12 in
block 1845A
otherwise block 1845A is bypassed and the program advances to block 1846,
which
executes the COMPARE CURRENT subroutine to compare the sampled current
magnitude to the overload current condition threshold, with variable i being
set to TRUE
if the overload threshold is surpassed. Upon return from the COMPARE CURRENT
subroutine, block 1848 restores the original baseline values by setting
variable current
lsbmod equal to variable templsb and variable current msbmod equal to variable
tempmsb.
Block 1850 then determines if variable i is set equal to TRUE indicating
overload current
conditions. If not, then the subroutine returns via block 1854. If overload
current
conditions are indicated in block 1850, then block 1852 sets variable
overloadon equal to
TRUE, variable time equal to 67, variable count equal to 0, and turns the PWM
drive
off. Block 1854 then causes the subroutine to return.
Shown in Fig. 23 is the COMPARE CURRENT subroutine for the
microcontroller. Block 1856 signifies the beginning of the subroutine. Next,
block 1858
sets variable i equal to FALSE. This value of this variable at the end of this
subroutine
will indicate whether the sampled current magnitude is greater or lesser than
a
predetermined current value. After block 1858, block 1860 determines if
variable current
lsb (representing the least significant byte of the sample current,magnitude)
is greater than
variable current Isbmod. If so, then block 1862 sets variable i = TRUE, and
the
program proceeds to block 1864. If the condition of block 1860 is not
satisfied, then the
program proceeds directly to block 1864. Block 1864 determines if variable
current lsb
is equal to variable current lsbmod and if variable current msb (representing
the least
significant byte of the sampled current magnitude) is greater than variable
current
msbmod. If both conditions are not satisfied in block 1864, then the program
proceeds to
block 1868. If both conditions are satisfied in block 1864, then block 1866
sets variable i
equal to TRUE. Block 1868 then causes the subroutine to return.
Figs. 24A and B show the DISPLAY CURRENT subroutine for the
microcontroller. Block 1870 signifies the beginning of the subroutine. Next,
block 1872
determines if variable count is equal to 0 which would indicate overload
current
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conditions. If it is, then there is no need to display the current magnitude,
and the
subroutine returns via block 1874. If block 1872 determines that variable
count is not
equal to 0, then block 1876 determines if variable dummy4 is TRUE, which would
indicate that essentially no braking demand is present. If so, block 1878
determines i:f
variable led status is equal to 7. Variable led status is set equal to 7
elsewhere in the
program when the first display LED is turned on in order to indicate that the
brake
controller has been activated. Variable led status will be equal to 7 in block
1878 if it is
the first time without a demand for brake current since the brake controller
had been
activated. If the condition of block 1878 is not satisfied, then the program
proceeds to
block 1888. If block 1878 determines that variable led status is equal to 7,
then blocl~;
1880 turns all LEDs off and turns the green LED on. Next, block 1882
determines if
variable flashfast is equal to 0. This variable is optionally set by the
vehicles operator,
and is 0 if indication of brakes being present is to be made by flashing the
LED2 once;
every 8 seconds. Variable flashfast is not equal to 0 if a dimming of the LED2
is used to
indicate that the brakes are present. If block 1882 determines that variable
flashfast is
equal to 0, then block 1886 turns all LEDs off, sets variable time3 equal to
1, sets
variable time equal to 200, and sets variable led status equal to 1. The
program then
proceeds to block 1888. If block 1882 determines that variable flashfast is
not equal to 0,
then block 1884 sets variable time equal to 4, variable time3 equal to 0, and
variable led
status equal to 1. Block 1888 then causes the subroutine to return.
Returning analysis of the DISPLAY CURRENT subroutine to block 1876, if
variable dummy4 equals FALSE (indicating that a demand for braking current is
present),
then block 1890 determines if the brakes of the towing vehicle have not been
pressed and
if variable integermanual is less than hexadecimal 10 such that very little
manual braking
has been demanded. If both conditions of block 1890 are satisfied, then the
subroutine
returns via block 1892. If both conditions of block 1890 are not satisfied,
then block
1894 (Fig. 24B) determines if variable count is equal to 9. If it is not, then
the program
proceeds to block 1898. If the condition of block 1894 is satisfied, then
block 1896 turns
all LEDs off in order to reinitiate the display. Block 1898 then determines if
variable
brakesyes is FALSE, indicating that there is no electrical connections between
the
controller and the brakes. If this connection is present, the program proceeds
to block:
1904. If block 1898 determines that the brakes are not connected, then block
1900
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determines if the sampled current is higher than a minimum threshold level
indicating that
brake current is definitely flowing and that the brakes must therefore be
connected. This
is a safety check which ensures that the setting of variable brakesyes is
correct. If the
sampled current does not cross the minimum threshold level, then block 1902
causes the
subroutine to return. If block 1900 determines that sufficient current is
flowing to
indicate the presence of brakes, the program advances to block 1901, which
sets the
variable brakesyes equal to TRUE and block 1904 then determines if variable
integersetwidth is greater than hexadecimal 24, which should always be the
case at this
point in the program. If for some reason it is not, then the program proceeds
to block
1910. If block 1904 determines that variable integersetwidth is greater than
hexadecimal
24, then block 1906 determines if variable brakesyes is TRUE, indicating that
the brakes
are connected. If not, then the program proceeds to block 1910. If block 1906
determines that the brakes are connected, then block 1908 turns the green LED
on, and
sets variable led status equal to 7 so that block 1878 (described above) knows
that the
brake controller has been made active. Block 1910 then determines if variable
setwidth is
greater than hexadecimal 4, which would indicate a particular threshold level
of duty
cycle of the PWM drive signal. If not, then the program proceeds to block
1914. If
block 1910 determines that variable setwidth is greater than hexadecimal 4,
then block
1912 turns the first two LEDs on. Next, block 1914 determines if variable
intsetwidth is
greater than hexadecimal 7 which would indicate another threshold level of
duty cycle of
the PWM drive signal. If not, then the program proceeds to block 1918. If
block 1914
determines that variable intsetwidth is greater than hexadecimal 7, then block
1916 turns
the third LED on. Block 1918 then determines if variable setwidth is greater
than
hexadecimal 9 which would indicate another threshold level of duty cycle of
the PWM
drive signal. If not, then the subroutine returns via block 1922. If the
condition of block
1918 is satisfied, then block 1920 turns the fourth LED on, and the subroutine
returns via
block 1922.
The above description is considered that of the preferred embodiments only.
Modifications of the invention will occur to those skilled in the art and to
those who make
or use the invention. Therefore, it is understood that the embodiments shown
in the
drawings and described above are merely for illustrative purposes and are not
intended to
limit the scope of the invention.
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