Pressure sensitive signal device for vehicle brake pedal

A brake pedal actuation sensor includes an optical coupler. In a preferred embodiment: the optical sensor is carried by a housing; a shutter is provided to interrupt the optical coupling according to the distance between the housing and a bearing; the shutter is carried by the bearing; and the distance between the housing and the bearing is dependent upon the force applied to the brake. Additionally, a circuit responsive to an output of the optical coupler is provided for generating an electrical output signal indicating brake pedal actuation.

BACKGROUND OF THE INVENTION 
The present invention pertains to a force sensitive brake pedal assembly 
and in particular to a signal generating circuit which provides an 
electrical signal output according to the force applied to the brake 
pedal. 
Vehicle braking systems employ switches operative to provide an indication 
of brake pedal depression. These switches are used to activate vehicle 
brake lights, for example. One type of switch is a mechanical switch 
actuated whenever the brake pedal is depressed. Another type of switch is 
actuated by pressure changes in the hydraulic fluid of the vehicle's 
hydraulic brake system. Another type of mechanical switch includes an 
operative connection in the mechanical linkage of the vehicle's brake 
system. 
Such prior systems have several disadvantages. Fluid pressure switches 
occasionally cause leakage in the area where the pressure sensitive switch 
interfaces with the hydraulic system. Mechanical switches connected in the 
mechanical linkage increase the magnitude of force required to actuate the 
brake pedal. Another disadvantage of the mechanical switch systems is they 
require adjustment when installed and during the life of the system 
because of linkage wear. Furthermore, a slight force applied to a vehicle 
brake pedal by the driver through inadvertent resting of the driver's foot 
on the brake pedal, may cause the associated switch to be actuated even 
though the brake system has not been energized. As a result, a false 
indication of braking is provided by the vehicle's brake lights. 
Additionally, the prior art switches are generally slow acting and switch 
failure can occur due to electrical contact erosion 
Other prior systems include a force sensitive resistor having a variable 
resistance dependent upon the force applied to the brake pedal. Circuitry 
responsive t the variable resistance provides an output, or outputs, 
according to the magnitude of the force applied to the brake. Although the 
force sensitive resistor an its associated circuitry solve many of the 
problems of the prior art, the variable resistor does not necessarily 
maintain constant characteristics over the entire temperature range to 
which an automobile is typically exposed. 
SUMMARY OF THE PRESENT INVENTION 
The present invention is embodied in a system having an optical coupler to 
detect brake pedal actuation. Systems embodying the invention include a 
shutter positioned to interfere with the light transmission of the optical 
coupler. Relative positioning of the shutter and optical coupler on 
separate mountings allows the force applied to the brake pedal to be 
translated into an electrical signal dependent thereon. An embodiment of 
the invention includes a bearing which carries the shutter and a housing 
which carries the optical coupler. 
The invention has several advantages. First, the optical coupling requires 
neither a mechanical switch nor a pressure sensitive switch. Additionally, 
the optical coupler and its associated circuitry provide an indication of 
brake actuation substantially independent of temperature. These and other 
objects, advantages, and features of this invention will become apparent 
upon review of the following specification in combination with the 
drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now specifically to drawings, and the illustrative embodiments 
depicted therein, a vehicle brake system 20 is illustrated in FIG. 1 as 
including a brake pedal 21 carried by a brake pedal arm 22. A push-rod pin 
23 connects brake pedal arm 22 to a push-rod 24. Push-rod 24 in turn 
transmits force from brake-pedal arm 22 to the vehicle's braking mechanics 
25 in order to actuate braking. 
A sensor assembly 26 is mounted between push-rod 24 and push-rod pin 23 in 
order to provide an electrical indication of brake pedal actuation. The 
sensor assembly is connected with output module 27 via electrical 
connector 28. The output module is connected to the vehicle's battery 29 
as well as to various output devices designated 30 through 35. Output 
devices 30 through 35 may include, but are not limited to: brake actuation 
indicators (e.g., brake lights); a vehicle speed control; a device 
associated with automatic power transmissions which prevents the torque 
converter from locking up; a device for preventing unintentional vehicle 
acceleration; an interlock mechanism which requires brake actuation prior 
to movement of the transmission selector lever from "park" or "neutral" 
position to any other operating condition; an anti-dive type system 
intended to prevent excessive downward movement of the front of the 
vehicle upon vehicle braking; and anti-lock braking devices. 
Sensor assembly 26 includes a housing 40 (FIG. 2) provided with slotted 
screw holes 41 and 42 in bearing ear slots 43 and 44. The housing further 
includes compression stops 45 and 46. The housing carries an optical 
coupling assembly, including an infrared emitter 47, having a base-line 
internal infrared detector, and an infrared detector 48, on printed 
circuit board 49. Sensor assembly 26 further includes a bearing 52 (FIG. 
3). Bearing 52 including pads 53 and 54, as well as a shutter 55, 
positioned on a common base. In a preferred embodiment, pads 53 and 54 are 
made from a silicone made from commercially available s2097 and t350. 
However, any resilient material may be used which satisfactorily resists 
compression. Additionally, bearing ears 56 and 57 include screw holes 58 
and 59. 
The operation of sensor assembly 26 will be described with reference to the 
FIGS. 4 and 5. Bearing 52 (FIG. 4) is carried by push-rod pin 23. Housing 
40 includes a flat side 62 which is keyed to fit with a flat side 70 of a 
push-rod hole 66. Push-rod hole 66 is made large enough to receive sensor 
assembly 26 between push-rod pin 23 and push-rod hole 66. Upon assembly 
(FIG. 5), bearing 52 fits snugly on push-rod pin 23, bearing ears 56 and 
57 fit tightly within bearing ear slots 43 and 44, and the housing fits 
snugly within push-rod hole 66. Furthermore, the housing and the bearing 
are held together by screws (not shown). Screws are inserted through holes 
41 and 42 in housing 40 and are received by threaded screw holes 58 and 59 
in bearing 52. Slotted screw holes 41 and 42 (FIG. 2) allow the housing to 
slide around the screws which are secured in the bearing. 
When force is applied to brake pedal 21, push-rod pin 23 carries bearing 52 
in the direction indicated in FIG. 4. Movement of bearing 52 in turn 
causes compression of pads 53 and 54 in proportion to the force applied to 
the brake pedal. A compression distance 63 is thereby dependent on the 
magnitude of the force applied to the brake pedal. Movement of bearing 52 
moves shutter 55 in to and out of the light path between infrared emitter 
47 and infrared detector 48. In this manner, the shutter interferes with 
the transmission of light, or optical coupling, between infrared emitter 
47 and infrared detector 48. The amount of interference caused by the 
shutter is directly related to the compression distance. In this 
embodiment, the smallest amount of interference with the transmission of 
light results when no force is applied to the brake pedal. While pad 
compression is taking place, housing 40 pushes push-rod 24 to activate 
automotive braking mechanics 25 (FIG. 1). 
A second embodiment 67 of sensor assembly 26 is illustrated in FIGS. 6 
through 8. In this embodiment, the sensor assembly is reversed with 
respect to the direction of application of force applied to bearing 52. 
Thus, when placed within push-rod hole 74, flat side 62 of housing 40 and 
flat side 75 of push-rod hole 66 are reversed with respect to flat sides 
62 and 70 of the embodiment of FIGS. 2 through 4. Housing 40 includes 
stops 78 and 79 (FIG. 8) which limit the relative movement between housing 
40 and bearing 52. Bearing 52 (FIG. 7) includes a single compression pad 
69 which is used in place of the two compression pads 53 and 54 of the 
embodiment illustrated in FIGS. 2 through 4. Single compression pad 69 is 
on the opposite side of bearing 52 from shutter 55. Compression pad pad 69 
also has a larger pad area as compared with the two pads 53 and 54 of the 
first embodiment. By mounting compression pad 69 opposite shutter 55, as 
shown in FIG. 8, shear forces experienced by the two pads of the first 
embodiment are avoided. 
As seen in FIG. 8, force applied to brake pedal 21 (FIG. 1) causes bearing 
52 to move toward flat end 62 of housing 40 against the force produced 
from the compression of pad 69. Accordingly, as force is applied to the 
brake pedal, shutter 55 (FIG. 8) moves out of the light path between 
infrared emitter 47 and external infrared detector 48. Accordingly, in the 
embodiment of FIGS. 6 through 8, when no force is applied to brake pedal 
21, shutter 55 completely blocks the infrared light path between emitter 
47 and detector 48. As force is increased, the shutter moves out of the 
infrared light path. 
A circuit 100 (FIGS. 9A and 9B) generally includes a sensor 101 (FIG. 9a), 
a controller 102, a power supply 103 (FIG. 9B), a voltage doubler 104, a 
driver 105, and an output circuit 106. Circuit 100 will be described in 
more detail hereinafter. 
Sensor 101 of circuit 100 includes infrared emitter and detector 47 (FIG. 
9A) and infrared detector 48. Infrared emitter and detector 47 includes an 
infrared emitter D1 electrically connected in series with a resistor R1 
between a supply voltage Vc and signal ground, and an infrared detector T1 
connected in series with a resistor R2 between supply voltage Vc and 
signal ground. Infrared detector 48 includes a detector T2 connected in 
series with a resistor R3 between supply voltage Vc and signal ground. 
Infrared detectors T1 and T2 are Darlington transistors. Detector T1 is 
optically coupled to emitter D1 to provide a reference potential dependent 
upon the ambient temperature within sensor assembly 26 (FIG. 4). Detector 
T2 (FIG. 9A) is optically coupled to emitter D1 to provide an output 
signal dependant upon the extent to which shutter 55 (FIG. 4) interferes 
with the light path between emitter D1 (FIG. 9A) and detector T2 (FIG. 4). 
Control circuit 102 includes a differential amplifier 115 and a comparator 
116. An output 110 of infrared detector T1 is provided through a resistor 
R4 to a non-inverting input 112 of amplifier 115. An output 111 of 
infrared detector T2 is provided through a resistor R5 to an inverting 
input 113 of amplifier 115. An output 117 of amplifier 115 is connected 
with non-inverting input 112 via a feedback resistor R6. A resistor R7 is 
connected between inverting input 113 and signal ground. Output 117 of 
amplifier 115 is applied to an inverting input 119 of comparator 116. A 
non-inverting input 120 of comparator 116 is connected via resistor R8 
with a voltage divider defined by resistors R9 and R1O connected in series 
between supply voltage Vc and signal ground. This provides a threshold 
voltage to the non-inverting input of comparator 116. Comparator 116 
further includes feedback resistor R11 connected between its output 121 
and its non-inverting input 120. 
In control circuit 102, output 121 of comparator 116 is connected via a 
diode D2 and resistor R12 to the base of an output transistor T3. A 
pull-up resistor R13 extends between Va and a junction 122 between diode 
D2 and resistor R12. 
Power supply 103 (FIG. 9B) receives direct current power via a battery 
terminal 125 and signal ground 126. Diode D3 and resistor R14 are 
connected in series between battery terminal 125 and a transistor T4. 
Diode D3 protects power supply 103 against a negative voltage polarity at 
terminal 125. A supply voltage Va is provided at a junction 127 between a 
resistor R14 and transistor T4. Supply voltage Va is limited by zener 
diode D4 connected between terminal 127 and signal ground. Zener diode D4 
will limit the voltage at terminal 127 to the reverse breakdown voltage of 
diode D5. A resistor R15 is connected between base 128 of transistor T4 
and junction 127. A supply voltage Vb is provided at a junction 130 
between an output terminal 129 of transistor T4 and a capacitor C1. 
Capacitor C1 connects terminal 129 to signal ground and provides smoothing 
of voltage Vb. A voltage regulator 132 receives supply voltage Vb as its 
input and supplies a regulated 5 Volt output Vc at terminal 133. A 
capacitor C2 is provided between terminal 133 and signal ground to reduce 
voltage ripple on terminal 133. An oscillator 135 and an output driver T5 
are powered from the battery side of transistor T4 whereas the remainder 
of circuit 100 is powered by supply voltages Vb and Vc. 
Supply circuit 103 further includes oscillator 135 defined by resistors 
R16, R17, R18, R19, a capacitor C3, and an operational amplifier 134. An 
output 136 of oscillator 134 is connected through a diode D5 and a 
resistor R20 to base 128 of transistor T4 for causing transistor T4 to be 
pulsed on and off. On/off pulsing of transistor T4 causes supply voltages 
Vb and Vc to be intermittent. This reduces the average power consumption 
of circuit 100. 
Voltage regulator 132 is illustrated in FIG. 8C. The regulator includes 
resistors R21 and R22 connected in series between its output Vc and signal 
ground to provide a reference voltage, which represents the level of 
supply voltage Vc, to a control input 140 of a controlled diode D6. Diode 
D6 is connected between the base of transistor T6 and ground. A resistor 
R23 and a capacitor C4 are connected between supply voltage Vb and signal 
ground. The junction of resistor R23 and capacitor C4 is connected to a 
junction 141 of the cathode of diode D15 and the base 142 of transistor T6 
to supply a drive signal to base 142. When the reference voltage provided 
to terminal 140 indicates Vc is above approximately 2.5 Volts, diode D6 
will decrease the base drive signal. When the reference voltage at 
terminal 140 indicates the reference voltage at terminal 140 is above 2.5 
Volts, diode D6 will increase the base drive signal. 
Circuit 100 further includes a voltage doubler 104 which includes an 
oscillator 142 which generates a pulse signal output 144. Oscillator 142 
is defined by an operational amplifier 143, resistors R24, R25, R26, R27, 
and a capacitor C5. Output 144 is provided to a capacitor/diode network, 
including capacitors C6 and C7 and diodes D7 and D8, which produces a DC 
voltage at 145 which is approximately twice the output voltage 144 of 
oscillator L 142. Such voltage doubler is conventional and its operation 
is known to those of ordinary skill in the art. 
Output 145 of voltage doubler 142 is applied as the drive signal to the 
gate of an N-channel FET T5, via resistors R28 and R30, which is part of 
an output driver 105 capable of providing an output voltage of 
approximately 24 volts Output driver 105 further includes voltage 
protection diodes D9 and D1O. Diode D9 is a 27 Volt zener connected from 
the drain to the gate of FET T5 in order to protect against load dumps and 
transients. Diode D10 is an 18 volt zener connected from the source to the 
gate of FET T3 in order to protect against reverse voltage potentials. 
Drive circuit 105 further includes a reverse voltage protection network 
147 including a diode D6 and resistor a R29. 
Circuit operates as follows. The signals established at outputs 110 (FIG. 
9A) and 111 by internal detector 47 and external detector 48 are compared 
by differential amplifier 115. The signal on output 117 of amplifier 115 
is a function of the difference between the inputs. When brake pedal 21 is 
being pressed, the output from comparator 115 is greater than the 
threshold applied to non-inverting input 119 of comparator 116 and output 
121 of comparator 116 is switched low which pulls base 118 of transistor 
T3 low. With transistor T3 turned off, the gate drive signal at 149 can 
increase to a positive level established by voltage doubler 104. 
Transistor T5 may then provide an output voltage of approximately 24 
Volts. When output 121 is switched low, a diode D12 will be biased on 
which will hold transistor T4 on to override the intermittent pulses 
supplied by oscillator 136. Thus, during detected brake actuation, the 
supply voltages Vb and Vc are constant and not intermittent. When the 
brake pedal is not pressed with sufficient force to drive output 121 low, 
transistor T3 is held on by voltage Va applied via resistors R12 and R13 
to hold driver T5 off. 
In the illustrated embodiment, circuit 100 includes an optional additional 
output 106 (FIG. 9A). Output 17 of amplifier 115 is applied to an 
inverting input 152 of a comparator 155. A non-inverting input 153 of 
comparator 55 is connected via resistor R33 with a voltage divider defined 
by resistors R31 and R32 connected in series between supply voltage Vc and 
signal ground. This provides a threshold voltage to non-inverting input 
153. Comparator 155 further includes feedback resistor R34 connected 
between its output 154 and its non-inverting input 153. 
The threshold applied to the non-inverting input 153 of comparator 155 can 
be greater than or less than the threshold applied to input 120 of 
comparator 116. The threshold applied to comparator 116 is selected 
depending upon the output 30 through 35 to be driven by output circuit 
106. When the force applied to brake pedal 21 causes output 117 to exceed 
the threshold level applied to input 153, output 154 will be driven low. 
This will provide a drive signal to another one of the output devices 30 
through 35 that the brake pedal has been actuated. When output 154 is low, 
a diode D13 will be biased on, which will hold transistor T4 on to 
override the intermittent pulses supplied by oscillator 136. Thus, during 
detected brake actuation, the supply voltages Vb and Vc are constant and 
not intermittent. 
Additional outputs (not shown) similar to 106 may be provided for actuating 
output devices 30 through 35. These additional outputs may be provided by 
additional comparators having a first input coupled to output 117 of 
amplifier 115, a second input coupled to a respective threshold input, and 
an output coupled to transistor T4 via a diode. By applying different 
threshold levels to the each such additional comparator, circuit 100 can 
be made to respond to the amount of brake force applied to brake pedal 21. 
Accordingly, as the force applied to the brake pedal is increased, the 
number of outputs receiving an indication of brake pedal actuation will 
increase. 
Temperature compensation is provided by using two optical detectors T1 and 
T2. Detector T1 provides a reference and detector T2 provides an output 
dependent upon the position of shutter 55. Both sensors operate in the 
same environment so that the transistors are similarly effected by 
temperature. Accordingly, the difference between the outputs of the 
sensing transistors as indicated at output 117 of differential amplifier 
115 will be relatively unaffected by temperature. 
In one example of the circuit, the following values were provided for the 
elements of the oscillator, the voltage doubler, the power supply, and the 
voltage regulator: 
______________________________________ 
C3 0.1 uF 100 V. C5 0.1 uF 100 V. 
R4 1.8M Ohms C6 0.1 uF 100 V. 
R3 100K Ohms R8 100K Ohms 
R5 100K Ohms R9 100K Ohms 
R6 100K Ohms R10 1M Ohms 
R7 100K Ohms C4 0.001 uF 
100 V. 
R34 100K Ohms R35 100K Ohms 
C7 0.01 uF 100 V. R1 100K Ohms 
R2 10K Ohms C1 0.1 uF 
C2 10 uF R33 620 Ohms 
______________________________________ 
Circuit 100 as illustrated in FIGS. 9A, 9B, and 9C and described above is 
responsive to output signals from the embodiment of sensor assembly 26 
illustrated in FIGS. 2 through 4 Those of ordinary skill in the art will 
recognize that circuit 100 requires minor modifications to be responsive 
to output signals from the embodiment of sensor assembly 26 illustrated in 
FIGS. 6 through 8 When used with the embodiment illustrated in FIGS. 2 
through 4, the output signal on output 117 (FIG. 9A) of differential 
amplifier 115 will increase with increasing force applied to the brake 
pedal. When used with the embodiment of FIGS. 6 through 8, the output 
signal 117 will decrease with increasing force applied to the brake pedal. 
Circuit 100 will therefore merely require a logic inversion for the 
outputs of the comparators receiving the output signal from amplifier 117. 
The circuit modifications to circuit 100 are therefor well within the 
level of skill of the ordinary artisan, and will not be described in 
greater detail. 
Changes and modifications in the specifically disclosed embodiments can be 
carried out without departing from the principles of the invention which 
is intended to be limited only by the scope of the appended claims, as 
including the doctrine of equivalents.