Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
1336199
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VEHICLE HEADLAMP SYSTEM WITH SERIES
HIGH BEAM DAYTIME RUNNING LAMP OPERATION
Background of the Invention
This invention relates to daytime running
lights for motor vehicles and more particularly to a
vehicle headlamp system effective to provide a daytime
running lamp (DRL) function with already existing
headlamps when the vehicle ignition switch is
activated, if permitted by a DRL enabling means. It
further provides for automatic change from DRL to
normal headlamp operation with activation of the
standard headlamp switch and, in one embodiment,
automatic DRL latch-off with a signal to the operator
if a DRL lamp burns out.
Summary of the Invention
The headlamp system of the invention modifies
a vehicle with an engine and an ignition switch
effective to enable engine operation with the
inclusion of a source of electric power at a
predetermined supply voltage, a pair of headlamps on
the front of the vehicle, one on each side thereof, a
headlamp switch having off and on conditions, a DRL
enabling means, first circuit means connecting one of
the headlamps in series with the headlamp switch and
electric power source, a DRL activating switch
effective in a first condition to connect the other of
the headlamps in parallel with the one of the headlamps
and in a second condition to connect the other of the
headlamps in series with the one of the headlamps and
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the electric power source, and second circuit means
responsive to the ignition switch, headlamp switch and
DRL enabling means to put the DRL activating switch in
its second condition when the ignition switch is
activated, the DRL enabling means is enabled and the
headlamp switch is in its off condition, whereby the
headlamps are both energized at approximately half the
predetermined supply voltage for improved visibility of
the vehicle to other vehicle operators during vehicle
operation when full headlamp operation is not chosen,
and otherwise to put the DRL activating switch in its
first condition, whereby the headlamps may both be
energized with the predetermined supply voltage for
illumination of the road for vehicle operation when
full headlamp operation is chosen. Further details and
advantages of the invention will be apparent from the
accompanying drawings and following description of a
preferred embodiment.
Summary of the Drawings
Figure 1 shows a circuit diagram of a
preferred embodiment of the invention.
Figures 2a and 2b show the time variation of
voltage at selected points in the circuit of Figure 1
with a burned out high beam filament to help illustrate
the detection thereof.
Figure 3 shows a variation of the embodiment
of Figure 1.
Description of the Preferred Embodiment
An electric power source such as vehicle
battery 10 has a grounded terminal and a hot terminal
connected through a standard vehicle ignition switch
11, a park brake on indicator lamp 12 and a DRL
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enabling means such as park brake switch 13 in series
to ground. Park brake switch 13 is a switch activated
when the vehicle is in a parked position, even if the
engine is operating. It may be associated with a hand
operated park or emergency brake or alternatively may
be activated in the park position of an automatic
transmission. An alternative DRL enabling means might
be an operator controlled DRL enabling switch as an
option which can be used or not at the operator's
discretion, or a combination of such a discretionary
switch and a park brake switch. Other possible
embodiments will occur to those skilled in the art.
Battery 10 represents any standard vehicle
electrical power system optionally including an engine
driven alternator, voltage regulator, etc. Such a
system generally has an operating voltage of 12-16
volts. Ignition switch 11 represents a standard
ignition switch having at least an off or open
condition as shown and a closed or on condition in
which the circuit is connected therethrough. Park
brake switch 13 has an open condition as shown when the
mechanism creating the parked condition is not
activated and a closed condition connecting the circuit
therethrough when the mechanism is activated.
Battery 10 is also connected to a standard
headlamp switch 15, a portion of which is shown.
Headlamp switch 15 has an OFF condition as shown and a
PARK condition in which battery 10 is connected to
energize park lamps, not shown, as well as, optionally,
the energizing coil of a fog lamp relay 16. Headlamp
switch 15 further has an ON condition in which battery
10 is connected to a standard beam selector switch 17.
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Beam selector switch 17 has a LO condition as shown in
which headlamp switch 15 is connected through a pair of
low beam filaments 18 and 20, one on each side of the
front of the vehicle, in parallel to ground. Headlamp
switch 15 can be considered to be a combination of a
headlamp switch having closed (ON) and open (PARR or
OFF) conditions for controlling headlamps and a fog
lamp switch having closed (PARK) or open (OFF or ON)
conditions for controlling fog lamps, yet to be
described.
Beam selector switch 17 further has a HI
condition in which headlamp switch 15 is connected to
the junction of a pair of high beam filaments 23 and
25. High beam filaments 23 and 25 are also located one
on each side of the front of the vehicle. The other
end of high beam filament 23 is grounded, whereas the
other end of high beam filament 25 is connected to
ground through a DRL ON indicator lamp 21 and to the
armature of a DRL activating switch comprising DRL
relay 22 having a normally closed contact connected to
ground and a normally open contact.
Battery 10 is connected through a fuse 26 to
the armature of fog lamp relay 16 so as to be connected
therethrough to energize fog lamps 27 and 28 in
parallel when fog lamp relay 16 is in an activated
condition but not when fog lamp relay 16 is in an
inactivated condition as shown. The activating coil of
fog lamp relay 16 connects headlamp switch 15 in its
park condition to the collector of an NPN Darlington
transistor 30 having a grounded emitter, which
transistor 30 controls fog lamp activation when
headlamp switch 15 is in its park position. The
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control of fog lamps with or without daytime running
lamps will be described in more detail at a later point
in this description.
DRL relay 22 controls the headlamp
configuration. In the inactivated condition shown, the
high beam filaments are connected across battery 10 in
parallel when headlamp switch 15 is in its ON condition
and beam selector switch 17 is in its HI condition.
This provides normal high beam operation at full
operating voltage and therefore full lamp intensity.
However, battery 10 is further connected through a fuse
31 to the normally open contact of DRL relay 22 so
that, with DRL relay 22 activated, high beam filaments
23 and 25 are connected in series across battery 10.
This is the daytime running light condition which is to
be activated when the ignition switch is in its on
condition, the park brake switch is in its open
condition (DRL enabling switch activated) and headlamp
switch 15 is in its PARK or OFF condition. The high
beam filaments are thus activated at approximately half
normal voltage for less intensity to be seen by other
drivers rather than illuminate surroundings for the
driver of this vehicle. An indication of DRL operation
is provided to the vehicle operator by the energization
of DRL on indicator lamp 21 when DRL relay 21 is
activated.
It should be noted that this operation is for
a four lamp system as shown in Figure 1, wherein each
lamp has only one filament. Another possibility is the
use of dual filament lamps, wherein the high and low
beam filaments are tied together in each lamp on the
ground side. In this case, shown in the modification
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of Figure 3 with similarly numbered primed components,
high and low beam filaments 25' and 20' are both
connected to the armature of DRL relay 22', so that
both high and low beam filaments will be energized in
series with DRL operation.
The activating coil of DRL relay 22 is
connected from junction 32 of ignition switch 11 and
park brake on indicator lamp 12 to the collector of an
NPN Darlington transistor 33 having a grounded emitter
so that transistor 33 controls the activation of DRL
relay 22. Junction 32 is also connected through a
resistor 38 and diodes 40 and 41 in series to the base
of transistor 33, which base is connected to its
emitter through a biasing resistor 42. Thus, when
ignition switch 11 is closed, battery voltage, less two
diode drops, is provided to the base of transistor 33,
which is thereby biased on to conduct and activate DRL
relay 22.
However, the activation of DRL relay 22 by
transistor 33 is defeated, by circuitry to be
described, when park brake switch 13 is closed, when
headlamp switch 15 is in its ON condition, or when
either of high beam filaments 23 or 25 is burned out.
This circuitry obtains a regulated operating voltage
from a terminal VDD connected to terminal 32 through a
resistor 35 (100 ohm for a maximum six volt reverse
voltage, 470 ohm for 12 volts reverse voltage) and to
ground through parallel zener diode 36 (27v) and
capacitor 37 (0.1uF). This terminal VDD is connected
to all other similarly labeled terminals in the circuit
and provides a regulated operating voltage for any
integrated circuit chips such as the comparators to be
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described. The connections are actually direct but are
shown as terminals to remove the connecting lines and
thus simplify Figure 1.
The circuitry for controlling the operation of
transistor 33 includes a comparator 45 with an output
connected to the junction of diodes 40 and 41. A diode
43 connects the junction of diode 40 and resistor 38 to
the junction 46 of park brake switch 13 and park brake
on indicator lamp 12. Comparator 45 is of the type
having an output comprising the collector of a grounded
emitter transistor: its state is either ground, due to
an inverting input at a higher voltage than a
non-inverting input, or open collector, with the
non-inverting input higher. Thus, transistor 33 may be
turned off, even with ignition switch 11 closed, either
by the closure of park brake switch 13 or by a ground
output of comparator 45. The former occurs when the
park brake is activated to close switch 13 (DRL
enabling means deactivated); and it causes the junction
of diodes 40 and 43 to go to one diode drop above
ground, plus, perhaps, a small additional fraction of a
volt due to resistance in the park brake switch 13 and
its wiring. Diodes 40 and 41 ensure that, in this
case, the voltage on the base of transistor 33 is
insufficient to turn it on.
The activation of DRL relay 22 will also be
defeated if the inverting input of comparator 45 is
higher than its non-inverting input and the output is
thus grounded. This occurs when normal headlamp
operation is selected by means of headlamp switch 15,
as described hereinafter. When headlamp switch 15 is
in its ON condition, battery 10 is connected through
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headlamp switch 15 and a diode 47 to a junction 48 of a
resistor 50 (150K) connected to terminal VDD and a
resistor 51 (400K) connected to the inverting input of
comparator 45. This junction 48 iS further connected
through a diode 53 in series with resistors 52 (20K)
and 55 (200K) to ground and, through a resistor 57
(36K) to the non-inverting input of a comparator 56
having an output connected to the junction of resistors
55 and 52 and an inverting input connected through a
diode 58 to junction 46 of park brake on lamp 12 and
park brake switch 13. The non-inverting input of
comparator 45 is connected to the output of comparator
56 and, through a resistor 60 (22K), to terminal VDD.
Junction 48 is further connected through a resistor 62
(120R) to the junction of high beam filaments 23 and
25.
Assuming comparator 56 has an open collector
output, resistors 60 and 55 will establish a voltage of
0.90VDD on the non-inverting input of comparator 45
when ignition switch 11 closes. With headlamp switch
15 in the ON condition, battery voltage will be
connected through diode 47 to junction 48 to produce a
voltage at the inverting input of comparator 45 of
approximately 0. 95VDD; and the output of comparator 45
Will thus be ground, whereby the activation of DRL
relay 22 is defeated. If headlamp switch 15 is in one
of the OFF or PARK conditions, however, the voltage on
the inverting input of comparator 45, as determined by
resistors 50 and 62 in series with high beam filaments
23 and 25, will be approximately 0.44VDD and the output
of comparator 45 will thus be open collector to allow
activation of DRL relay 22, as already stated, assuming
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park brake switch 13 is open. Once DRL relay 22 is
activated, the voltage on the inverting input of
comparator 45 goes up to approximately 0.72VDD due to
the presence of half battery voltage at the junction of
high beam filaments 23 and 25; but this is still
insufficient to ground the output of comparator 45.
In the circuit as described to this point, if
high beam filament 23 were to burn out with DRL
activated and high beam filaments 23 and 25 thus
connected in series, their junction would be at
approximately battery voltage rather than half battery
voltage; and a voltage higher than that on the
non-inverting input of comparator 45 would be applied
through resistor 62 to junction 48 and therefore to the
inverting input of comparator 45. The output of
comparator 45 would thus be grounded, just as if the
headlamps had been turned on by headlamp switch 15.
But the grounding of the output of comparator 45 would
turn off transistor 33 to deactivate DRL relay 22; and
when DRL relay 22 was deactivated, the full battery
voltage would disappear from the junction of filaments
23 and 25, so that comparator 45 would again switch
open collector to allow transistor 33 to once again
activate DRL relay 22. The cycle would then repeat in
an oscillating manner. It is desirable that a burned
out filament 23 not cause such oscillation but that a
signal be given to the vehicle operator, since, in the
daylight, the loss of a lower intensity headlamp may
not be easily noticed from within the vehicle. The
detection of the difference between normal headlamp on
by switch 15 and a burned out filament 23 is
accomplished by the circuit around and including
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comparator 56 and additional circuitry as described
below.
A PNP transistor 63 has an emitter connected
to terminal VDD, a base connected through a resistor 65
(20K) to the collector of transistor 33 and a collector
connected through a diode 66 and capacitor 70 (0.33uF)
to ground. A bias resistor 68 (5K) may optionally
connect the emitter and base of transistor 63.
Transistor 63 is thus connected to charge capacitor 70
through diode 66 when DRL relay 22 is activated. The
junction of diode 66 and capacitor 70 is connected
through a resistor 67 (110K) to the inverting input of
comparator 56. The inverting input of comparator 56 is
further connected through a resistor 71 (300K) to
terminal VDD and through a resistor 72 (110K) and
capacitor 73 (0.33uF) in parallel to ground. A
capacitor 57 (0.01uF) connects the inverting and
non-inverting inputs of comparator 56.
The operation of the circuit when high beam
filament 23 burns out is illustrated by the curves of
Figures 2a and 2b, which show the time variation of the
voltage at the non-inverting and inverting inputs,
respectively, of comparator 56. When transistor 33
turns on to activate DRL relay 22, transistor 63 is
turned on to charge capacitor 70 through diode 66 to
approximately 0.95VDD. This voltage and VDD applied to
the network of resistors 67, 71 and 72 establish a
voltage of approximately 0.57VDD at the inverting input
of comparator 56, as seen in Figure 2b. The
non-inverting input of comparator 56, as seen in Figure
2a, will be at essentially the same voltage as the
inverting input of comparator 45: approximately 0.72VDD
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with DRL activated and both high beam filaments 23 and
25 operating. The output of comparator 56 is thus
normally open collector and does not affect the rest of
the circuit.
If high beam filament 23 burns out, however,
the voltage at the junction of filaments 23 and 25 goes
up to battery voltage, as shown in Figure 2a; and
comparator 45 turns off transistor 33 to deactivate DRL
relay 22. However, it then immediately falls to
approximately 0.44VDD as DRL relay 22 is deactivated.
The voltage at the inverting input of comparator 56, as
seen in Figure 2b, falls slowly as capacitor 70
discharges through resistors 67 and 72 in series.
Although it eventually falls to a voltage of
approximately 0.27VDD, which is below the 0.44VDD of
the non-inverting input, there is a period of time T,
as shown in Figures 2a and 2b, wherein the inverting
input is at the higher voltage and the output of
comparator 56 thus goes to ground. Comparator 56
latches in this state due to the feedback through diode
53 and resistor 52, which pulls down the non-inverting
input. The ground output of comparator 56 further
holds comparator 45 in its ground output state to latch
off DRL relay 22. The resulting lack of illumination
of DRL on indicator light 21 indicates the problem to
the vehicle operator. If an additional error light
were desired to energize in this condition, it could be
added with an energizing circuit responsive to the
ground output state of comparator 56.
If it is filament 25 rather than filament 23
which burns out, the system works in a more direct
manner to produce the same result. The junction of
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12
filaments 23 and 25 is thus grounded, which causes the
voltage at the non-inverting input of comparator 56 to
immediately drop below the 0.57VDD on the inverting
input to latch comparator 56 in its ground output state
and hold DRL relay 22 in its deactivated state as
already described.
In contrast to the condition of a burned out
filament 23 or 25, a normal deactivation of DRL relay
22 due to the switching on of the headlamps by headlamp
switch 15 does not latch on comparator 56, since the
voltage on the non-inverting input of comparator 56
goes high and stays high if headlamp switch 15 is put
in its ON condition. In addition, deactivation of DRL
relay 22 by activation of park brake switch 13 causes
the inverting input of comparator 56 to be immediately
pulled down to just above ground by diode 58 to prevent
latching of comparator 56 in the ground output state as
DRL relay 22 is deactivated and the voltage on the
non-inverting input of comparator 56 drops to 0.44VDD.
The system may be reset from the latched
ground output of comparator 56 in any of three ways.
If park brake switch 13 is closed, the inverting input
of comparator 56 is lowered to one diode drop above
ground to unlatch the comparator from its ground output
state. If headlamp switch 15 is placed in the on
condition, a high voltage will be applied to the
non-inverting input of comparator 56 to unlatch it from
its ground output state. Finally, if ignition switch
11 is turned off and then on again, the system will be
reset with comparator 56 unlatched in the open
collector state.
It is possible that a vehicle owner could
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place different types of headlamps on the two sides of
the vehicle. For example, filament 23 could be an
incandescent bulb and filament 25 a halogen bulb.
These bulbs may not split the full battery voltage
evenly between themselves when connected in series. No
such combinations of bulbs have shown such a wide
disparity of operating voltages when warmed up and
fully on; however, if an incandescent bulb and halogen
bulb are placed in series, the halogen bulb will take
almost the full battery voltage, after power is first
applied, for a short time which may be as long as 100
milliseconds. Thus, the system could potentially be
fooled into thinking the incandescent bulb was burned
out for this short time period. If this is considered
a potential problem, a capacitor 75 (0.33uF) is
connected from the inverting input of comparator 45 to
ground. The charging of capacitor 75 causes a delay
with a time constant of about 130 milliseconds from the
moment when DRL relay 22 is activated and the voltage
at junction 48 first goes higher than 0.44VDD before
the non-inverting input of comparator 45 can go high
enough to ground the output and turn off DRL relay 22.
In the meantime, the halogen and incandescent bulbs
will have come within an acceptable voltage ratio for
normal operation as previously described. It should be
noted that the situation of halogen and incandescent
bulbs on the same vehicle could only occur, at least at
the time this is being written, in dual filament bulbs,
which are connected as shown in Figure 3.
It has already been mentioned that the
activating coil of fog lamp relay 26 is connected to
the collector of transistor 30. Transistor 30 has a
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14
base connected through series resistors 77 (1OK) and 78
(1OK) to ground. The junction of resistors 77 and 78
is connected to the collector of transistor 63. Thus,
transistor 30 is turned on and off, through transistor
63, by transistor 33. In addition, a diode 80 is
connected from the collector of transistor 30 to the
junction of high beam filaments 23 and 25. In
operation, the activating coil of fog lamp relay 16
will be enabled in the normal manner by connection to
ground through diode 80 and the high beam filaments 23
and 25 when the high beam filaments are not energized.
In this case, movement of headlamp switch 15 into the
park condition will complete the circuit through the
activating coil of fog lamp relay 16 to energize fog
lamps 27 and 28. However, full energization of the
high beam filaments 23 and 25 will reverse bias diode
80 to prevent such enabling of the activating coil of
fog lamp relay 16 .
When headlamp switch 15 is in its park
condition and high beam filaments 23 and 25 are
energized at half battery voltage by DRL relay 22, the
half battery voltage drop from battery 10 to the
junction of filaments 23 and 25 may not be sufficiently
high to activate fog lamp relay 16. However, fog lamp
energization is desired in this case, where high beam
filaments 23 and 25 are not fully energized.
Therefore, transistor 30 provides an alternate
activating current path to ground for the activating
coil of relay 16 when turned on by transistor 33.
Thus, fog lamp operation is permitted with DRL high
beam operation at reduced intensity but prevented with
normal full intensity high beam operation.
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A high beam indicator lamp 81 is connected to
ground from the collector of a PNP Darlington
transistor 82 having an emitter connected to junction
48 and a base connected to the emitter through a
biasing resistor 83 (4K), to ground through a resistor
85 (5K) and, through a resistor 86 (3K) to junction 32.
Transistor 82 conducts to energize high beam indicator
lamp 81 only when the voltage at junction 48 is two
diode drops above that (about 0.6VDD) set by the
voltage divider of resistors 85 and 86 across the
ignition voltage. This occurs only when ignition
switch 11 is closed, headlamp switch 15 is ON and beam
selector switch 17 is HI to provide full high beam
filament energization. High beam indicator lamp 81
cannot be energized by transistor 82 turned on directly
from headlamp switch 15 through diode 47, since the 85K
resistance of resistor 62 is much greater than the 20
ohm resistance of lamp 81. In addition, activation of
DRL relay 22 causes only half battery voltage to appear
at the emitter of transistor 82, which keeps transistor
82 turned off.
A resistor 87 (5K) is connected in parallel
with park brake on indicator lamp 12 to enable the rest
of the circuit to work normally if lamp 12 burns out.
The 5K value is sufficiently low to enable circuit
operation but sufficiently high to reduce power
consumption in normal circuit operation and allow the
use of a low wattage resistor for reduced cost. For
further stability and protection in the circuit, a
capacitor 88 may be connected across the inputs of
comparator 56; and a diode 90 may be connected from the
collector of transistor 33 to VDD.
