Note: Descriptions are shown in the official language in which they were submitted.
CA 02230469 1998-04-O1
-1
BRAKE CONTROLLER
BACKGROUND OF THE INVENTION
This invention relates generally to towed vehicle brake controllers and,
in particular, to a novel towed vehicle brake controller which can be
retrofitted
to a tow vehicle to effect a gradual application of the towed vehicle brakes
proportional to the movement of the tow vehicle brake pedal.
Towed vehicles, such as recreational and utility trailers adapted to be
towed by automobiles and small trucks, are commonly provided with electronic
braking systems. The electric brakes generally include a pair of brake shoes
located at each wheel which, when actuated, frictionally engage a brake drum.
An electromagnet is mounted on one end of a lever to actuate the brake shoe,
and is drawn against the rotating brake drum when an electric current is
applied,
thereby pivoting a lever to actuate the brake shoes. Typically, the braking
force
provided is proportional to the electric current applied to the electromagnet.
The
I5 electric current may run as high as 12 amperes on a double axle trailer.
The first electric brake controllers for actuating towed vehicle brakes
incorporated a large rheostat switch mounted in a position for the driver of
the
tow vehicle to be able to manually activate the towed vehicle brakes as
needed.
Later designs employed a hydraulic slave cylinder in the controller with a
2o hydraulic line connecting the tow vehicle brake system to the controller.
Thus,
when the vehicle brakes were applied, the controller sent an electrical
current to
the towed vehicle brakes in proportion to the pressure applied to the tow
vehicle
braking system. Alterations to tow vehicle hydraulic braking systems where
generally discouraged by automobile manufacturers, resulting in the
25 introduction of electronic brake controllers which did not connect directly
to the
tow vehicle hydraulic systems. These electronic controllers were simply timers
which applied the towed vehicle brakes at a pre-set time interval after the
application of the tow vehicle brakes. The "timer" type controllers did not
sense
or accommodate the difference between gradual brake application and an
3o emergency stop. That is, when the tow vehicle brake is applied, the towed
CA 02230469 1998-04-O1
-2
vehicle brakes were applied after the pre-set time interval, regardless of the
braking conditions.
An improvement over the timer-type controllers was the addition of a
mercury switch which employed the inertia of small amount of liquid mercury
to close a pair of contacts during rapid deceleration of the tow vehicle,
triggering full application of the towed vehicle brakes during an emergency
stop.
Still further improvements over the timer-type controllers consisted of
the incorporation of a pendulum or similar device to sense deceleration of the
1 o tow vehicle caused by braking. An electronic circuit would generate a
brake
control signal proportional to the pendulum displacement during deceleration.
These designs suffer from several inherent problems. First, because the towing
vehicle and towed vehicle are connected together, the driver must initially
slow
the towed vehicle by application of the tow vehicle brakes. The towing vehicle
must undergo sufficient deceleration for the pendulum or similar device to
activate the towed vehicle brakes. If the controller is fine-tune adjusted,
and a
heavy towing vehicle is pulling a lightweight towed vehicle, the deceleration
sensor system works well. However, very few drivers are capable of adjusting
these controllers with the degree of precision necessary for optimal
performance. In the more common situation, where a light tow vehicle is
pulling a heavy towed vehicle, it is impossible to produce maximum towed
vehicle braking by setting the control so that it activates with emergency-
type
stopping power even in normal, non-emergency stopping situations. Essentially,
the momentum of the heavy towed vehicle will "push" the tow vehicle,
preventing it from decelerating at a sufficient rate to fully activate the
towed
vehicle brakes.
Regardless of the type of deceleration sensor or brake control signal
initiator device, known electronic brake controllers also usually include an
analog pulse width modulator which receives the brake control signal from the
3o sensing unit. The pulse width modulator is responsive to the brake control
signal for generating an output signal comprising a fixed frequency pulse
train.
CA 02230469 1998-04-O1
-3
The pulse width modulator varies the duty cycle of the pulse train in
proportion
to the magnitude of the brake control signal, thus the duty cycle of the pulse
train corresponds to the amount of towed vehicle braking desired. The output
of
the pulse width modulator is typically used to control the switching of power
transistors on and off, supplying power to the towed vehicle brakes, with the
resulting brake application directly proportional to the duty cycle of the
pulse
width modulator output.
SUMMARY OF THE INVENTION
Among the several objects and advantages of the present invention may
l0 be noted the provision of a brake controller capable of activating towed
vehicle
brakes in a gradual manner responsive to the displacement of the tow vehicle
brake pedal;
The provision of such a brake controller which allows for the activation
of towed vehicle brakes in a manner balanced with the tow vehicle brake
application;
The provision of such a brake controller which permits the appropriate
amount of towed vehicle brake application to accommodate varied braking
Sltuat1011S;
The provision of such a brake controller which utilizes a
microcontroller;
The provision of such a brake controller which may be adjusted to
compensate for varied conditions of the tow vehicle braking system;
The provision of such a brake controller which may be adjusted to
compensate for a variety of weight distributions between the tow vehicle and
the
towed vehicle;
The provision of such a brake controller which is capable of activating
towed vehicle brakes without activation of the tow vehicle braking system; and
The provision of such a brake controller which is simple in design, easy
to install and to maintain, and well suited for its intended purpose.
In accordance with the present invention, a brake controller is provided
that can be attached to the brake pedal of a tow vehicle and electronically
CA 02230469 1998-04-O1
-4
connected to the brakes of the towed vehicle to allow for a balanced
application
of the towed vehicle brakes in response to movement of the tow vehicle brake
pedal.
In a first embodiment of the present invention, a brake controller sensing
unit which operates independently of tow vehicle deceleration or tow vehicle
brake force is disclosed. The brake controller includes a casing having an
internal spring-loaded reel or drum with tapered circumferential edge. The
controller is connected between the tow vehicle brake pedal and a stationary
fixture, such as the engine firewall. The reel is positioned between a light
1 o source and an optical detector. An optical connector is in turn
electronically
connected to the towed vehicle brakes so as to cause variable actuation of the
towed vehicle brakes in response to the output of the optical detector.
Depressing the tow vehicle brake pedal causes the spring-loaded reel to turn
under the force of the spring. The further the brake pedal is depressed, the
further the reel rotates. During rotation, the tapered edge of the drum acts
as a
variable-size shutter, proportionally blocking and passing light from the
light
source to the optical detector in a variable amount dependent upon the
position
of the tapered edge of the drum, which is in turn dependent upon the position
of
the tow vehicle brake pedal. The brake control signal output by the optical
2o connector is independent of any tow vehicle deceleration, sensing only the
relative displacement of the tow vehicle brake pedal arm from the rest
position.
As such, the towed vehicle brakes may be actuated by depressing the brake
pedal when the tow vehicle is at a full stop (such as when parked on an
incline)
or when there is a compete failure of the tow vehicle braking system. In such
an
emergency situation, depressing the tow vehicle brake pedal would not result
in
deceleration of the tow vehicle, however, the brake controller of the present
invention would continue to function, and actuate the towed vehicle brakes.
In a second preferred embodiment of the brake controller of the present
invention, an optical coupler is employed to detect angular displacement of
the
3o tow vehicle brake pedal arm from a rest position. The brake controller
includes
a casing mounted on the tow vehicle brake pedal arm and having an internal
CA 02230469 1998-04-O1
_$
spring-loaded winder securing one end of a connecting cable. The opposite end
of the connecting cable is passed out a vertically elongated opening in the
casing
and fastened under tension to a stationary fixture, such as the engine
firewall.
As the cable exits the casing, it passes between the light source and optical
receiver of an optical coupler. At rest position (i.e. no displacement of the
tow
vehicle brake pedal) the cable fully blocks the optical coupler, and no signal
is
generated. As the tow vehicle brake pedal is depressed, the spring-loaded
winder maintains the tension on the connecting cable, and the angle at which
the
cable exits the casing shifts proportional to the displacement of the brake
pedal.
The alteration in the geometry of the connecting cable connection points
results
in the unblocking of a portion of the light source, and the generation of a
proportional brake control signal by the optical coupler. The cable is
adjusted
such that full depression of the brake pedal results in the cable completely
clearing the optical coupler, resulting in a full-strength signal. The optical
connector is in turn electronically connected to the towed vehicle brakes so
as to
cause variable actuation of the towed vehicle brakes in response to the brake
control signal of the optical detector.
In a third preferred embodiment of the brake controller of the present
invention, an optical coupler is used to count index marks on the spring-
loaded
2o reel or on a tensioned element such as the tensioned links of a chain
connected
to a spring-loaded winder. The index marks may be comprised of holes, slots,
or of reflective strips. Similarly, a ball-chain or link-chain or similar
indexed
element may be employed wherein the individual elements of the chain function
in a manner identical to the marks, with each ball or link alternately
blocking
and exposing the optical coupler receiver element to the light source. The
count
of the indexes, e.g. marks or chain elements, is electronically transmitted to
a
microcontroller which has been programmed to actuate, electronically, the
towed vehicle brake system. For example, as the towing vehicle brake pedal is
depressed, the drum or winder rotates and the series of slots, reflective
strips, or
chain links corresponding to the movement is counted by the optical coupler or
reflective sensor. A signal representative of the count is transmitted to the
CA 02230469 1998-04-O1
~- 6
microcontroller which has been appropriately programmed, and which in turn,
increases through a power transistor, the actuation of the towed vehicle
brakes
based upon the number of marks or links counted. As the reel continues to
rotate and the greater number of marks, slots, or chain links pass through the
light, the microcontroller will increase the braking power of the towed
vehicle
brakes.
The foregoing and other objects, features, and advantages of the
invention as well as presently preferred embodiments thereof will become more
apparent from the reading of the following description in connection with the
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
In the accompanying drawings which form part of the specification:
Figure 1 A is an elevational view of the first preferred embodiment of the
brake controller of the present invention attached to a brake pedal arm and to
the
firewall of a tow vehicle;
Figure 1 B is an enlarged sectional view of interior of the housing with
the tapered spring-loaded reel in the rest position;
Figure 1C is an enlarged sectional view similar to Fig. 1B, with the reel
in the full-on position;
Figure 2A is a sectional view similar to Fig. 1 B, employing a wire and
optical angle sensor, shown with the brake pedal in the rest position;
Figure 2s is an enlargement of the wire and optical angle sensor of Fig.
2A, with the wire shown in the depressed brake pedal position;
Figure 3 is an illustration of several different index means which may be
employed on the reel of one embodiment;
Figure 3A is a sectional view of the spring-loaded reel portion of one
embodiment of the brake controller of the present invention employing a chain
and optical counter;
Figure 3s is an enlargement of the chain and optical counter of the brake
controller shown in Fig. 3A;
CA 02230469 1998-04-O1
_7
Figure 4 is a flow chart illustrating the steps in the operation of the brake
controller of the present invention.
Figure 5 is a block diagram of the electronic brake controller of the
present invention; and
Figure 6 is a schematic circuit diagram illustrating a preferred
embodiment of the electronic brake controller shown in Fig. ~.
Corresponding reference numerals indicate corresponding parts
throughout the several figures of the drawings.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The following detailed description illustrates the invention by way of
example and not by way of limitation. The description will clearly enable one
skilled in the art to make and use the invention, describes several
embodiments,
adaptations, variations, alternatives, and uses of the invention, including
what I
presently believe is the best mode of carrying out the invention.
Turning to Figure 1 of the drawings, the first preferred embodiment of
the brake controller of the present invention is indicated generally by
reference
numeral 10. As can be seen in the drawing, the controller 10 includes a
housing
12 appropriately mounted or attached to a brake pedal arm 14 in any suitable
manner. Housing 12 includes an opening 16 on the peripheral edge adjacent the
2o engine firewall 18 of the tow vehicle. A cable or chain 20 extends out of
the
opening 16 and is secured to the engine firewall 18. As will be described
later,
the cable or chain 20 is kept under constant tension.
Controller 10 also includes an optical coupler, indicated generally as
reference numeral 22 in Figs. l s and c. The optical coupler 22 includes a
light
emitter 24 on one side of the housing 12 and a light receiver 26 on the
opposite
side of the housing. The optical coupler is electronically connected to a
towed
vehicle braking system (not shown) by wires 28.
Figures 1 s and c illustrate a spring loaded reel 30 which is included
inside the housing. The reel 30 is appropriately mounted inside the housing
and
operatively connected to a flat spring 32. A first end of the cable or chain
20 is
connected to the reel 30 and the opposite end is secured to the engine
firewall
CA 02230469 1998-04-O1
_. g
18. The cable or chain 20 is maintained at a constant tension by the flat
spring
32, and maintains the reel in a predetermined position when the tow vehicle
brake pedal is not depressed. It will be appreciated, by viewing Figs. 1 s and
c
that the reel includes a light sensor opening 34 that allows the light emitted
by
the optical coupler light emitter 24 to pass unobstructed to the light
receiver 26
when the brake pedal is fully depressed as shown in Fig. 1 s, and as will be
explained below.
In the first preferred embodiment, the opening 34 in reel 30 defines a
tapered radial cutout which allows the reel to serve as a rotating shutter so
as to
variably interrupt the optical coupling light passing through the device. The
cable or chain 20 and the flat spring are preloaded in housing 12 so that the
tapered radial cutout 30 is positioned adjacent to, and not exposing the light
receiver 26 as shown in Fig. 1 B. When the light is interrupted or blocked, no
signal is sent to the electronically connected trailer brakes. As the brake
pedal is
depressed, and the brake pedal arm and controller 14 move towards the firewall
18, the flat spring urges the reel to rotate in the direction of arrow D, and
to take
up the slack in cable or chain 20. This allows rotation of the reel and the
tapered radial cutout to gradually uncover the light beam. Conversely, as the
brake pedal is released, the flat spring will urge the reel to rotate in the
opposite
direction and allow the cable or chain to pull out. As the reel rotated in the
opposite direction of arrow D, the tapered radial cutout begins to cover the
area
of opening 34. The tapered radial cutout thus allows the edge of the reel to
act
as a variable shutter. When the brake pedal is depressed, the light passing
through opening 34 is increased to the receiver 26. The increased light
results in
optical coupler 22 relaying an electronic impulse or brake control signal to
the
towed vehicle brakes, thereby actuating the brakes. When opening 34 is
positioned such that the light is fully unblocked, as is shown in Fig. 1C the
towed vehicle brakes are actuated in the full "on" position. As will be
appreciated by one skilled in the art, due to the tapered radial opening 34,
the
amount of light transmitted through the device can vary from full light, as
shown in Fig. 1 c to no light as shown in Fig. 1 s. The conventional
electronic
CA 02230469 1998-04-O1
~- 9
circuits (not shown) can actuate the towed vehicle brakes in proportion to the
amount of light transmitted, allowing variable or graduated trailer braking
corresponding to the travel of the tow vehicle brake pedal. One skilled in the
art
will recognize that this embodiment of the brake controller of the present
invention may be utilized to replace traditional deceleration sensors and
brake
force sensors in existing prior art brake controllers, as it generates a brake
control signal which is proportional to the displacement of the tow vehicle
brake
pedal.
In a second preferred embodiment of the brake controller of the present
t0 invention shown in Fig. 2A, the controller 100 includes a housing 102
appropriately mounted or attached to the tow vehicle brake pedal arm 14 in any
suitable manner. Housing 102 includes a vertically elongated opening 104 in
the peripheral edge of the housing adjacent the engine firewall 18. A cable
106
under constant tension extends from a spring-loaded winder 108 within the
housing, through the opening, and is secured to the engine firewall. An
optical
coupler 110 mounted within the housing is employed to detect angular
displacement of the tow vehicle brake pedal arm 14 from a rest position by
detecting changes in the geometry of the cable 106, and is electronically
connected to the towed vehicle brake system (not shown). As cable 106 exits
the housing, it passes between the light source and optical receiver 112 of
the
optical coupler 110. At rest position (i.e. no displacement of the tow vehicle
brake pedal) the cable fully blocks the optical coupler, and no brake control
signal is generated. (Fig. 2A) When the tow vehicle brake pedal is depressed,
the spring-loaded winder 108 maintains the tension on the cable, and the angle
at which the cable exits the housing shifts proportional to the displacement
of
the brake pedal. The alteration in the geometry of the cable connection points
results in the unblocking of a portion of the light source, and the generation
of a
proportional brake control signal by the optical coupler. The cable is
adjusted
such that full depression of the brake pedal results in the cable completely
3o clearing the optical coupler, as shown in Fig. 2s, resulting in a full-
strength
brake control signal. The optical connector is electronically connected to the
CA 02230469 1998-04-O1
-10
towed vehicle brakes so as to cause variable actuation of the towed vehicle
brakes in response to the brake control signal of the optical detector.
A third preferred embodiment of the present invention is indicated
generally by reference numeral 200 in Fig. 3. The embodiment of controller 200
includes a spring-loaded reel 202 mounted in housing 203, having a plurality
of
slots, as shown generally at 204, holes 206, or reflective strips 208. The
reel is
contained within a housing secured in a conventional manner to the arm of the
tow vehicle brake pedal. Within the housing, an optical light emitter 210 is
positioned on one side of the reel and, if the embodiment includes slots 204
or
1 o holes 206, an optical receiver 212 is similarly positioned on the other
side of the
reel. A model HOA0901 opto-interrupter available from Honeywell, consisting
of a single infrared light emitting diode and two infrared detectors is
preferred.
If reflective strips 208 are used, the optical emitter 210 can be a
combination
emitter/receiver secured within the housing 203 on one side of the reel
without
departing from the scope of the invention. Independent of the optical coupler,
reel 202 is spring loaded as previously described relative to the first
preferred
embodiment, and a cable is secured to the reel at one end, exits the housing,
and
is correspondingly affixed at its opposite end to the vehicle firewall,
actuating
rotation of the reel upon displacement of the tow vehicle brake pedal.
Alternately, within the scope of this embodiment the reel with the holes
or reflective strips may be replaced by the combination of a spring loaded
winder 216 and a chain 218, as is shown in Fig. 3A. One end of chain 218 is
secured to the winder, and the opposite end is secured to the engine firewall
18,
to be maintained under a constant tension by the spring loaded winder. In the
preferred alternate embodiment, the chain 218 is a linked-ball type chain,
however, various chain types, including flat links are within the scope of the
invention. As the tow vehicle brake pedal is depressed, the spring loaded
winder 216 will rotate to maintain constant tension on the chain 218, and
cause
individual balls or links 220 in the chain to repeatedly interrupt the signal
generated by the optical coupler 221, as they pass between the optical
coupler's
emitter 210 and receiver 212, as shown in Fig. 3B. The chain is positioned
CA 02230469 1998-04-O1
-11
adjacent the optical coupler by a guide, 223 and compressed against the guide
~by a threaded set screw 225. As the t:ow vehicle brake pedal is released, the
winder will rotate in the opposite direction, and the balls or links will
again
move between the components of the optical coupler 221, but in the opposite
direction.
The optical coupler (including the emitter 210 and receiver 212 or
combination emitter/receiver) is electronically connected to a microcontroller
222 (Fig. 4) by wires 28 and counts the marks, consisting of either holes,
reflective strips, or chain links, as the spring loaded reel or winder rotates
in
response to the movement of the tow vehicle brake pedal, as described above.
Microcontroller 222 is electronically connected to the brake system of a towed
vehicle 224. The microcontroller is preprogrammed to increase electrical power
or actuation of the trailer brakes responsive to an increase in the number of
marks counted. As the coupler counts the marks, i.e. as the tow vehicle brake
pedal is continually depressed, the microcontroller sends an increasingly
stronger signal to a power transistor 226 and increases the towed vehicle
brake
application. Correspondingly, as the brake pedal is released, and returns to
the
original position, the reel or winder will rotate in the opposite direction,
and the
count of the marks will be decremented. The microcontroller, tracking the
2o current count value, will decrease the application of the towed vehicle
brakes
proportional to the return movement of the brake pedal. It will be appreciated
by those skilled in the art that the braking power applied to the trailer
brakes
thus is varied in proportion to the brake pedal position of the tow vehicle.
Within the scope of the invention the microcontroller can be
programmed with any type of counting/actuation program. The microcontroller
could count the marks back to a standard position and remember the count.
Then, each successive time the tow vehicle brake pedal is depressed, the
microcontroller could count off the same number of marks and apply the towed
vehicle brakes. In this manner, the braking of the towed vehicle may be
customized. The microcontroller may be further programmed to ignore marks
beyond a full "on" position to accommodate for variable such as the loss of
CA 02230469 1998-04-O1
-12
brake fluid in the towing vehicle brake system which would allow the brake
pedal to be depressed farther than normal.
Additionally, the brake control signal generated by the microcontroller
need not be at a I:I ratio with the brake pedal position, i.e. ranging from 0%
towed vehicle brake application to 100% towed vehicle brake application. A
gain control selection unit 228 is mounted in a position accessible by the tow
vehicle operator, and preferably includes a push-button means for selecting a
desired gain setting. Each gain setting selectable by the operator results in
a
different proportion of towed vehicle braking relative to the same tow vehicle
brake pedal travel distance. The proportional amounts corresponding to each
gain setting and the displacement of the tow vehicle brake pedal are
preprogrammed into the microcontroller, and accessed dynamically during
operation in the form of a table-lookup. For example, as shown in Tables 1-9
below, with an operator selectable gain setting of one, and a mark count of
five
I5 from maximum pedal displacement, the microcontroller will apply a mere 6%
of
maximum possible braking force. With a gain setting of five, and the same
pedal displacement, the microcontroller will apply 30% of maximum possible
braking force.
TABLE 1 TABLE 2
Gain Mark Braking Gain Mark Braking
Settin Count % Settin Count
1 11 0 2 11 0
1 10 I 2 10 2
1 9 2 2 9 4
1 8 3 2 8 6
1 7 4 2 7 8
1 6 5 2 6 10
1 5 6 2 5 12
1 4 7 2 4 14
1 3 8 2 3 16
1 2 9 2 2 18
1 1 10 2 1 20
1 0 11 2 0 22
CA 02230469 1998-04-O1
-13
TABLE 3 TABLE 4
Gain Mark Braking Gain Mark Braking
Settin Count % Settin Count
3 11 0 4 11 0
3 10 3 4 10 4
3 9 6 4 9 8
3 8 9 4 8 12
3 7 12 4 7 16
3 6 15 4 6 20
3 S 18 4 S 24
3 4 21 4 4 28
3 3 24 4 3 32
3 2 27 4 2 36
3 1 30 4 1 40
~3 0 33 4 0 44
TABLE S TABLE 6
Gain Mark Braking Gain Mark Braking
Settin Count % Settin Count
S 11 0 6 11 0
5 10 5 6 10 6
5 9 10 6 9 12
5 8 1S 6 8 18
5 7 20 6 7 24
5 6 25 6 6 30
5 5 30 6 S 36
5 4 35 6 4 42
5 3 40 6 3 48
S 2 45 6 2 54
5 1 50 6 1 60
5 0 55 6 0 66
CA 02230469 1998-04-O1
-14
TABLE 7 TABLE 8
Gain Mark Braking Gain Mark Braking
Settin Count % Settin Count
7 11 0 8 11 0
7 10 7 8 10 8
7 9 14 8 9 16
7 8 21 8 8 24
7 7 28 8 7 32
7 6 35 8 6 40
7 5 42 8 5 48
7 4 49 8 4 56
7 - 3 56 - 8 3 64
7 _ 2 _ ~3 8 2 72
7 i __ 70. 8 1 80
_
7 a 77 _ 8 0 88
TABLE 9
Gain Mark Braking
Settin Count
9 11 0
9 10 9
9 9 18
9 8 27
9 7 36
9 6 45
9 5 54
9 4 63
9 3 72
9 2 81
9 1 90
l 99
In the preferred operation of this embodiment of the brake controller,
there are nine separate linear gain settings, and a tow vehicle brake pedal
displacement range of eleven marks. One skilled in the art will recognize that
the microcontroller may be preprogrammed with any number of gain settings,
to both linear and non-linear, and that the range of brake pedal displacement
may
increased or decreased. Accordingly, variations in the number and type of gain
settings, and the brake pedal displacement range are considered within the
scope
of this invention.
CA 02230469 1998-04-O1
- 1$
After installation of the microcontroller embodiment of the present
invention in a tow vehicle, the brake controller must be initialized to the
maximum displacement of the tow vehicle brake pedal. Initialization is
performed by the operator fully depressing the tow vehicle brake pedal to the
maximum braking position, and then pressing a "Set Brake" switch 230 located
either on the controller housing or on the gain control selection unit. The
microcontroller receives a signal from the switch, and enters an
initialization
mode. As the operator releases the brake pedal, and the reel or winder rotates
within the housing, the microcontroller counts from zero the number of marks
1o which pass the optical coupler. In the preferred embodiment, the eleventh
mark
is considered to be the appropriate brake initiation point, i.e. the
displacement
position of the tow vehicle brake pedal from maximum braking at which the
microcontroller will actuate the towed vehicle brakes. The power delivered to
the towed vehicle brakes at the eleventh mark is proportional to the gain
setting
I S selected as described above. Once the brake pedal returns to the rest
position,
the microcontroller records the total number of marks corresponding to the
pedal displacement, and signals that the initilization procedure has been
completed and the system is ready for normal operation. It will be noted by
one
skilled in the art that the operator need not fully depress the tow vehicle
brake
20 pedal before initializing the system. If the system is initialized to a
less-than
maximum brake pedal depression, the responsiveness of the towed vehicle
brakes to the brake pedal position of the two vehicle will be greatly
increased.
Operation of the microcontroller embodiment of the present invention is
described below in reference to the flow chart of Fig. 4. Upon activation
(Block
25 300), the brake controller loads either the default values into the ports
and
registers of the microcontroller, or the stored settings resulting from a
completed
initialization procedure as described above (Block 302). Upon completion of
the load step, the brake controller beings the normal operation cycle. The
microcontroller continually checks the count of the marks detected by the
30 optical coupler, and the direction of any pedal travel (Block 304). An
increment
in the mark count corresponds to a release of the pedal, and a decrement
CA 02230469 1998-04-O1
-16
corresponds to a depression of the brake pedal during braking. If there is no
change in the brake pedal position (Block 306), the microcontroller repeats
the
check procedure. If a change in the brake pedal position is detected, the
microcontroller compares the current count of the marks with the predetermined
brake initiation range (Block 308). In the preferred embodiment described
above, the brake initiation range is between counts zero and eleven. If the
current count of marks is outside of the brake initiation range, no towed
vehicle
braking is indicated, and the check procedure cycle repeats.
If the current count of marks is within the brake initiation range, the
1o microcontroller must determine the appropriate level of towed vehicle
braking
to apply. First, the current gain setting is checked to determine if there has
been
a change (Block 310). If there is a change, the new value is stored (Block
312).
If there has been no change since the previous cycle, or if a new value has
been
detected and stored, the microcontroller utilizes the current count of marks
and
the gain setting to determine the appropriate towed vehicle braking percentage
from the stored look-up tables (Block 314). Based on the determined towed
vehicle braking percentage, the final step in the cycle is for the
microcontroller
to load the appropriate setting into the timer registers which produce signal
controlling the towed vehicle brakes. (Block 316). Upon completion of the
2o register load step, the microcontroller starts the entire cycle over by
again
reading the tow vehicle brake pedal position and direction. (Block 304).
Turning to Figs. 5 and 6, the various system components comprising the
brake controller 200 of the third preferred embodiment are shown. Electrical
power is supplied to both the brake controller 200 and to the towed vehicle
brake system 224 by the tow vehicle battery 400, typically rated at +12 volts.
The voltage supplied to the brake control system from the vehicle battery is
regulated to +5 volts by a voltage regulator 402.
The microcontroller 222, preferably a model 83C751 manufactured by
Phillips Semiconductor of Sunnyvale, California, receives power from the
3o voltage regulator 402 and input signals from the Set Brake switch 230, the
Set
Gain switch 228, and the optical coupler 213. The microcontroller includes an
CA 02230469 1998-04-O1
-17
internal timer which can be programmed to run for a length of time determined
by a value loaded into one or more internal timing registers. The values
stored
in the timing registers correspond to the particular combination of tow
vehicle
brake pedal position and gain setting as described above.
The optical coupler is preferably a model HOA0901 manufactured by
Honeywell, and is configured to provide an input signal to the microcontroller
responsive to the displacement of the tow vehicle brake pedal as described
above. The operations of the Set Brake and Set Gain switches are similarly
described above in conjunction with the initialization of the brake controller
and
with the selection of the desired towed vehicle braking force.
Output from the microcontroller is directed towards control of the Brake
Intensity display 404 and the Gain display 406. The Brake Intensity display
404
provides the operator with a visual indication of the towed vehicle braking
percentage being appl ied by the brake controller 200 at any given moment.
Similarly, the Gain display 406 provides a continuous visual indication of the
currently selected gain setting.
Additionally output from the microcontroller 22~ is directed towards
control of the output device 226, a TOPFET high side switch, preferably a
model BUK202-SOX manufactured by Phillips Semiconductor of Sunnyvale,
California. An output enable switch 408 interrupts the connection between the
microcontroller and the output device 226 whenever the tow vehicle brake light
switch 410 is not enabled. The connection to the brake light switch 410 is
important to prevent the unlikely event that the set brake switch 230 is
pushed
with the brake pedal just slightly depressed to a point with fewer than eleven
chain counts to pedal-rest-position, resulting in the towed vehicle brakes
being
activated with the tow vehicle brake pedal in the "rest" position.
Accordingly,
the brake light switch 410 acts to eliminate activation of the towed vehicle
brakes absent sufficient movement of the tow vehicle brake pedal from a rest
position. Assuming the output enable switch 408 is closed, as during normal
3o tow vehicle braking, the microcontroller 222 sends a cyclic output signal
of +5
volts to the output device 226 at a rate dependent upon the value stored in
the
CA 02230469 1998-04-O1
-18
internal timing registers of the microcontroller. When the output signal from
the microcontroller drives the input of the output device high (+$ volts), the
output device activates, and allows current at +12 volts to flow through the
towed vehicle brakes 224. When the microcontroller output signal drops to +0
volts, the output device switches off, preventing current flow through the
brakes. By controlling on-off ratio of the output signal, and correspondingly
the
current flow to the towed vehicle brakes, the microcontroller 222 can control
the
towed vehicle brake application.
In addition to controlling the flow of current to the towed vehicle
to braking system, the output device 226 further includes components
configured
to detect and indicate to the operator open circuit and shori circuit
conditions.
An open circuit indicator 412 and a short circuit indicator 414 continually
check
the integrity of the towed vehicle brake circuits.
A manual control circuit 416, consisting of a variable resistor 418 and a
timer 420 is additionally connected to the input of the output device 226.
When
the operator actuates the manual control circuit 416, the timer 420 triggers
the
illumination of the towed vehicle brake lights by closing a switch 422 and
sends
a +$ volt cyclic signal to the output device 226. The on-off ratio of the
cyclic
signal is proportional to the level of braking manually selected by the
operator.
2o In view of the above, it will be seen that the several objects of the
invention are achieved and other advantageous results are obtained. As various
changes could be made in the above constructions without departing from the
scope of the invention, it is intended that all matter contained in the above
description or shown in the accompanying drawings shall be interpreted as
illustrative and not in a limiting sense.
