Auxiliary brake light control system

The present invention relates to an auxiliary brake light control system which has its primary application in motor vehicles equipped with standard transmissions. In such vehicles, the brake lights are normally illuminated by means of a pressure switch associated with the brake pedal whenever pressure is manually-applied to the brake pedal by the driver. However, as the car slows toward a stop, or after it has actually stopped the driver normally releases his foot from the brake pedal and moves his left foot over to the clutch and his right foot over to the gas pedal thereby turning off the brake light to falsely indicate to those following that the car is not stopped. However, since the car is actually cruising at a very low speed or stopped, severe safety hazards may result. The present invention provides an auxiliary brake light control system which senses the motion of the motor vehicle by means of magnets attached to a rotating shaft whose speed of rotation is proportional to the speed of the motor vehicle to generate a first signal when the speed of the motor vehicle is faster than a predetermined speed and a second signal when it is moving slower than the predetermined speed. A relay coil is normally energized in response to the first signal to keep the brake lights off unless the operator applies pressure to the brake pedal, but for switching the relay coil to a de-energized state whenever the speed falls below a predetermined value for turning on the brake lights even if the operator removes his foot from the brake pedal. The detected signal from the rotating shaft is amplified, smoothed to a DC level, and applied to a comparator whose output controls a transistor switch to maintain the relay coil energized or de-energized, as desired. A DPDT switch is responsive to the state of the relay coil for supplying 12 volt battery potential to the brake lights when the relay coil is de-energized.

BACKGROUND OF THE INVENTION 
1. Field Of The Invention 
The present invention relates generally to an auxiliary brake light control 
system for motor vehicles having standard transmissions so that the brake 
lights will be illuminated when the vehicle is stopped even when the 
driver's foot is released from the brake pedal. 
2. Description Of The Prior Art 
Motor vehicles provided with automatic transmissions and those provided 
with manual transmissions are generally equipped so that the brake lights 
are illuminated when the vehicle is stopped, but only when the driver's 
foot is depressed upon the brake pedal. 
Today's manual and automatic transmission motor vehicles have a single 
brake light system wherein the brake light is illuminated in response to 
the manual application of pressure to the brake pedal. However, whenever 
the manually-applied pressure is removed from the brake pedal, the brake 
lights turn off giving followers of the motor vehicle the erroneous 
indication that the motor vehicle is moving, whereas the motor vehicle may 
be traveling at extremely slow speeds or even stopped. 
The brake light control system of the present invention solves 
substantially all brake light problems inherent in such motor vehicles 
providing an auxiliary means of illuminating the brake lights even when 
the driver's foot is removed from the brake pedal. 
BRIEF SUMMARY OF THE INVENTION 
It is an object of the present invention to provide an auxiliary brake 
light control system for a motor vehicle. 
It is another object of this invention to provide an auxiliary brake light 
control system for use in combination with a conventional 
pressure-responsive brake pedal-actuated brake light control system. 
It is still another object of the present invention to provide an improved 
brake light system including both a brake light actuation system 
responsive to the application of manually-applied pressure applied to the 
brake pedal and the vehicle is stopped or moving at a very low speed and 
to an auxiliary system responsive to the motion of the vehicle for 
actuating the brake lights even when the operator's foot is removed from 
the brake pedal. 
It is yet another object of the present invention to provide an auxiliary 
brake light control system responsive to the rotation of a shaft whose 
actual speed of rotation is substantially proportional to the speed of the 
motor vehicle for turning on the brake lights whenever the speed falls 
below a predetermined value even if the driver's foot is removed for the 
brake pedal. 
It is a further object of this invention to provide an improved brake light 
system for a motor vehicle equipped with a manual or an automatic 
transmission. 
It is still a further object of the present invention to provide an 
improved brake light control system for a motor vehicle including means 
responsive to the actual speed of the motor vehicle for actuating the 
brake lights when the motor vehicle is stopped or moving at a very low 
speed, even though the operator's foot is removed from the brake pedal. 
It is yet a further object of the present invention to provide a pair of 
independently-operated brake light control systems for use in a motor 
vehicle, one system being responsive to the application of 
manually-applied pressure to the brake pedal, and the other system being 
responsive to the speed of the motor vehicle even when the operator's foot 
is removed from the brake pedal. 
The present invention contemplates a brake light control system for use in 
a motor vehicle having a transmission, a brake system, a brake pedal for 
manually-operating the brake system, and at least one rotatable shaft 
whose speed of rotation is substantially proportional to the speed of the 
motor vehicle. The brake light control system of the present invention 
includes, in combination, brake lights including a left brake light and a 
right brake light. 
A pressure-detecting switch means responsive to the manual application of 
pressure to the brake pedal is used for turning on the brake lights and is 
responsive to the removal of the manually-applied pressure from the brake 
pedal for normally turning off the brake lights. An auxiliary brake light 
control system, including a brake light control means, is used for turning 
on the brake lights in response to the rotation of said at least one shaft 
even when the manually-applied pressure has been removed from the brake 
pedal to indicate that the vehicle is stopped or moving very slowly, 
thereby avoiding giving erroneous brake light information to those 
following the vehicle. 
The present invention includes magnetic means operatively coupled to the 
shaft for rotation therewith. A sensing inductive coil is used for 
detecting the rotation of a magnetic means and for generating a first 
signal in response to the rotational speed being greater than a 
predetermined value and for generating a second signal in response to the 
rotational speed being less than said predetermined value. An amplifier is 
used to amplify at least the first signal and for generating a high output 
signal in response thereto. The output signal from the amplifier is then 
integrated to provide a relatively smooth DC value signal equivalent 
thereto. A comparator compares the DC signal to a reference signal, and 
includes means for delaying the output of the comparator. The comparator 
output moves in one direction to cause a switching means to complete a 
conductive path through a relay coil and in a second direction to turn a 
transistor switch off to de-energize the relay coil. The relay coil acts 
upon a DPDT switching means and a combination of switches associated 
therewith to insure illumination of the brake lights whenever the relay is 
de-energized to indicate that the speed of the motor vehicle has fallen 
below the predetermined value. 
These and other objects and advantages of the present invention will become 
more fully understood after reviewing the detailed description of the 
preferred embodiment, the claims, and the drawings, which are briefly 
described hereinbelow.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIG. 1 shows an electrical schematic diagram of the auxiliary brake light 
control system of the present invention. In FIG. 1, an inverting input 
node 11 is shown as being directly connected to the inverting input of an 
operational amplifier 13 whose output is taken from the operational 
amplifier output node 15. Input node 11 is connected through a resistor 17 
directly to ground. The output node 15 is also connected to the input node 
11 through a feedback register 19 for providing negative feedback for 
amplification purposes. The positive voltage input node 21 is connected 
directly to the +V input of the operational amplifier 13 and to a source 
of positive potential +V. Node 21 is connected to one plate of a capacitor 
23 whose opposite plate is connected back to a negative or ground input 
node 25 which is connected directly to ground and to the ground input of 
the operational amplifier 13. 
The non-inverting input of the operational amplifier 13 is connected 
through a resistor 27 to one terminal of a sensing inductive coil 29 whose 
opposite terminal is grounded. The coil 29 senses signals produced by the 
magnets 33 mounted on the rotatable shaft 31 which can be, for example, 
any rotatable shaft on the motor vehicle which rotates at a speed 
proportional to the speed of the motor vehicle. As the shaft 31 rotates in 
proportion to the speed of the motor vehicle, the magnets 33 are sensed by 
the coil 29 and a first signal is produced when the speed of rotation of 
the shaft 31 is grater than a predetermined value while a second signal is 
produced or generated when the speed of rotation of the shaft 31 is less 
than a predetermined or given value. 
The operational amplifier output node 15 is connected through a resistor 35 
to the anode of a diode 37 whose cathode is connected through a resistor 
43 to the positive input of a comparator 45. A resistor 39 has one 
terminal connected to ground and its opposite terminal connected to the 
junction of the cathode of diode 37 and one terminal of the resistor 43, 
while a capacitor 41 has one plate grounded and its opposite plate 
connected to the junction of the cathode of the diode 37 and the one end 
of resistor 43 whose opposite end is connected to the positive input of 
the comparator 45. A negative input node 47 is connected directly to the 
negative input of the comparator 45. The output node 57 of the comparator 
45 is connected back to the negative input node 47 through a feedback 
resistor 59, while the negative input node 47 is connected through a 
resistor 49 and a lead 51 to form a variable tap for a potentiometer 53. 
The potentiometer 53 has one terminal connected to ground and its opposite 
terminal connected to a positive source of potential +V through a resistor 
55. 
The comparator output node 57 is connected through a resistor 65 to the 
base of a transistor 67 whose emitter is grounded, and its collector is 
connected to a collector output node 69. The collector output node 69 is 
connected to the anode of a diode 71 whose cathode is connected to a 
positive source of potential +V. Node 69 is also connected to one terminal 
of a relay coil 73 whose opposite terminal is connected to a positive 
source of potential +V. The relay coil 73 operates the switching system 
and the DPDT switch of block 75 as hereinafter described with respect to 
FIGS. 2 and 3. 
The comparator output node 57 is also connected through a resistor 61 to 
the anode of a light-emitting diode (LED) 63 whose cathode is grounded. 
When the output of the comparator 45 is normally high, indicating that the 
sensing coil 29 detects that the speed of rotation of the shaft 31 is 
above the predetermined value, the LED 63, conventionally a greed LED, 
will conduct light to give a visual indication that the brake lights are 
not on. However, when the output of the comparator goes low, the 
transistor 67 turns off thereby breaking the conductive path through the 
relay coil 73 and deenergizing the coil 73. With the relay coil 73 
de-energized, the DPDT switching means and the associated switches change 
position to illuminate the brake lights even if the driver has removed his 
foot from the brake pedal. 
The operational amplifier 13 is a conventional device such as one of a 
LM324, and it significantly amplifies the voltage present at its 
non-inverted input and supplies the amplified signal to the output node 
15. An integrator is disposed between the output 15 of the operational 
amplifier 13 and the positive input node 47 of the comparator 45. The 
integrator includes resistors 35, 39, and 43 together with capacitor 41. 
This network smooths the signal present at the operational amplifier 
output 15 and converts it to a substantially DC level signal equivalent 
thereto. This DC level signal is supplied to the positive input of the 
comparator 45, and it is either at a high level or a low level depending 
upon whether the first or second signal was produced by the sensing coil 
29. A voltage divider network comprising resistor 55 and potentiometer 53 
together with resistor 49 and capacitor 41 can be used to provide a delay 
dependent on the RC time constrant of the circuit so that the output of 
the comparator 45, which is normally high, will not drop low immediately 
upon the sensing of the generation of the second signal, but will remain 
high for a predetermined period of time or predetermined delay period, as 
desired. 
The comparator 45 is a conventional operational amplifier such as a 
conventionally available LM324, identical to that of operational amplifier 
13, and it has been configured in FIG. 1 as a comparator, as known in the 
art. The output of the comparator 45 is normally high as long as the 
sensing coil detects that the shaft is rotating above the predetermined 
speed. This high signal will cause the LED to illuminate a green color 
indicating that the brake lights are not on. Simultaneously, the high at 
the output of the comparator will turn the transistor switch on to insure 
that current flows through the relay coil and keep it in a normally 
energized state. 
As soon as the speed of the motor vehicle has dropped below the 
predetermined given speed, the sensor 29 generates the second output 
signal which appears as a low DC signal at the positive input of the 
comparator 45 and causes the signal at the comparator output to go low. A 
low signal at the output of the comparator 45 causes the LED 63 to turn 
off and the transistor 67 to switch to a nonconducting state, thereby 
breaking the conductive path between the positive source of potential +V 
and ground through the relay coil 73 and the transistor switch 67. The 
relay coil 73 is therefore switched to a de-energized state causing the 
contacts of the DPDT switching means and the switches of the associated 
switching network to change state, as hereinafter described, and enable 
the brake lights to be illuminated even if the operator's foot has been 
removed from the brake pedal. 
FIG. 2 illustrates a twelve VDC DPDT relay used in the circuit of FIG. 1. 
This is a conventional device such as a model number 275-206 and is 
conventionally available. FIG. 2 illustrates the DPDT switch with the 
contacts in the position associated with the de-energization of the relay 
coil 73. 
In FIG. 2, the relay coil 73 is shown as having one terminal connected to 
the contact terminal P13 and its opposite terminal connected directly to 
the contact terminal P14. When the relay coil 73 is de-energized, the 
remaining contacts are as described hereinbelow. The P1 contact 77 
connects to the P9 movable contact 81 to form a conductive path between 
contact terminals P1 and P9 via the normally closed contact 77 and the 
moveable contact 81. However, when the relay coil is energized, the 
moveable contact 81 will move to the left and engage contact 79 so as to 
complete a continuous path between the contact terminal P5 and the contact 
terminal P9 via the normally open contact 79 and the moveable contact arm 
81. 
Similarly, the moveable contact arm 87 will normally connect the contact 
terminal P12 with the normally closed contact 83 and the normally closed 
contact 83 connects directly to the contact terminal P4 so as to provide a 
continuous path between the contact terminal P4 and the contact terminal 
P12 via contact 83 and the moveable contact arm 87. When the switch is 
energized, the moveable contact arm 87 engages the normally open contact 
85 and completes a continuous path between the contact terminal P8 and the 
contact terminal P12. The circuit of FIG. 2 illustrates the DPDT switch of 
block 75 of FIG. 1. 
FIG. 3 illustrates the switching means of block 75 of FIG. 1 and their 
interrelationship to the switch contact terminals of the DPDT switch of 
FIG. 2. In FIG. 3, the contact terminal P1 is shown as being connected 
directly in one terminal of a brake light 89 whose opposite terminal is 
grounded at ground node 91. A second contact terminal P4 is connected 
directly to one terminal of the opposite brake light 93 whose opposite 
terminal is grounded at note 91. The contact terminals P1 and P4 are 
commonly connected together at node 121. Node 121 is connected through a 
switch 123 to the contact terminal P8 which supplies a positive voltage 
potential thereto. The switch 123 is designated S.sub.BP and illustrates 
the conventional pressure-sensitive switch associated with the brake pedal 
of a motor vehicle wherein the pressure sensitive switch S.sub.BP closes 
in response to the manual application of pressure applied thereto 
indicating that the brake pedal has been depressed and for connecting a 
positive source of potential +V from contact terminal P8 directly to the 
brake lights 89 and 93 for illuminating same. This is the primary brake 
light control system already present in most motor vehicles including 
those with manual transmissions. 
Furthermore, in FIG. 3, contact terminal P9 is connected via led 95 to the 
moveable arm of a switch 97, designated S1, whose normally opened terminal 
is connected directly to a common switch output node 111 via lead 108, 
node 107, and lead 99. The switch 97 or S1 is a normally open, 
relay-operated switch which remains open as long as the relay coil 73 is 
energized, but which closes in response to the de-energization of the 
relay coil 73 to complete a conductive path between the contact terminal 
P9 and the common node 111 via lead 95, the closed switch 97, lead 108, 
node 107, and lead 99. Similarly, the contact terminal P12 is connected 
via led 103 to the switch arm of a second normally open relay-operated 
switch 105 or S2 whose normally open contact is connected to an output 
node 107 and via led 99 to the common switch output node 111. Lastly, the 
contact terminal pin P8 is connected directly to the switch arm of a third 
normally opened relay-operated switch 109 or S3 whose normally opened 
contact is connected directly to the common switch output node 111. 
Contact terminal P13 is connected to contact terminal P14 through the relay 
coil 73, while the negative or ground contact terminal P5 is grounded. The 
common switch output node 111 is connected through a normally open 
ignition switch 101 or S.sub.I whose opposite switch terminal is connected 
directly to a +12 volt source of battery potential. The ignition system is 
represented by block 113 and includes an ignition switch S.sub.I. Whenever 
the ignition key is inserted into the ignition and turned, the ignition 
switch 101 closes to complete a current path between the +12 volt battery 
and the common output node 111 through the closed ignition switch 101 node 
125 and lead 127. 
The +12 volt battery is, therefore, normally present at the common node 111 
so long as the ignition switch is turned on. As long as the ignition 
switch is on, the voltage at node 111 is coupled to the normally open 
brake pressure switch 123 so that whenever the brake pedal is depressed, 
the switch 123 closes to supply the voltage to node 121 and hence to the 
brake lights 89 and 93 via contact terminals P1 and P4, as conventionally 
known in motor vehicles today. 
The operation of the auxiliary brake light control system of the present 
invention will now be briefly described. Assuming that, under normal 
conditions, the motor vehicle is moving along at some significant speed so 
that the speed of rotation of the rotatable shaft 31 and the magnetic 
means 33 mounted thereon causes the sensing coil 29 to generate the first 
signal and supply it to the non-inverting input of the operational 
amplifier 13 via resistor 27. The operational amplifier then amplifies the 
first signal significantly and produces an amplified equivalent thereof at 
its output 15. The signal at the output 15 is then integrated or smoothed 
out to produce a substantially DC signal equivalent thereto which is then 
fed to the positive input of the comparator 45. A reference which can be 
varied and which represents the predetermined speed, is supplied to the 
negative input of the comparator so that when the signal at the positive 
input is a relatively high DC signal indicative of the first signal 
generated by the sensing coil, the output of the comparator goes high, but 
when the signal at the positive input is low, indicating that the second 
signal is being produced or generated by sensing coil 29 meaning that the 
speed of the motor vehicle has gone below some predetermined desired 
speed, the output of the comparator goes low. 
When the signal at the comparator output node 57 is high, LED 63 conducts 
to indicate that the brake lights are not on and the signal is fed via 
resistors 65 to the base of a switching transistor 67 which normally 
conducts to form a current path between a positive source of potential and 
ground through the relay coil 73 causing the relay coil to remain 
energized. 
As long as the relay coil 73 remains energized, contact arm 81 will be 
closed on contact 79 to couple contact terminal P5 to P9 while moveable 
contact arm 87 will engage contact 85 to normally connect contact terminal 
P8 to P12. However, since switches S1 and S2 remain normally open, no 
energy is transferred. 
However, when the signal at the output of the comparator 45 goes low, the 
LED 63 turns off and transistor 67 is switched to a nonconductive state 
thereby de-energizing the relay coils 73. When the relay coil 73 is 
de-energized, the contacts are as shown in FIG. 2 on the DPDT switch. The 
switches S1, S2 and S3 immediately close in response to the 
de-energization of the relay coil thereby completing a current path 
between the common node 111 and its associated +12 volt battery potential. 
When the switches S1, S2 and S3 close, switch S1 connects the battery 
potential by a lead 95 to contact terminal P9 whereas closed switch S2 
connects to battery potential via led 103 to the contact terminal P12. 
Since P12 is connected to P4 and P9 is connected to P1 in the DPDT switch 
of FIG. 2, the power is fed from the contact terminals P1 and P4 through 
the brake lights 89 and 93, respectively, to the grounded node 91 thereby 
completing a current path therethrough and illuminating the brake lights 
even if the manually applied pressure has been removed from the brake 
pedal and the switch S.sub. BP is opened. This insures that the persons 
riding behind the motor vehicle equipped with the system of the present 
invention do not receive a false brake light signal indicating that the 
vehicle is moving even when it is actually stopped. 
The auxiliary brake light control system of the present invention insures 
that even if the driver's foot is removed from the brake pedal, as 
conventionally done in motor vehicles provided with manual transmissions 
wherein the driver removes his right foot from the brake and places his 
right foot on the gas pedal while his left foot goes to the clutch, the 
sensing coil 29 will detect that the rotational speed of the shaft 
indicative of the speed of the motor vehicle has dropped below a 
predetermined speed so as to cause the relay coil 73 to be de-energized, 
the switches S1, S2 and S3 to close, the DPDT switch to conduct the 
battery potential through the closed switches to illuminate the brake 
lights to indicate that the motor vehicle is stopped. 
It will be understood by those skilled in the art that various 
modifications, changes, variations, substitutions, and alterations, can be 
made in the structure, components and circuitry of the present invention 
without departing from the spirit and scope thereof which is limited only 
by the appended claims.