Control System

Abstract

An antilocking system for vehicle brakes includes a wheel sensor having plural contacts for controlling the system. The contacts are connected in parallel and have different resistance values associated with them so that different signals are produced when the contacts are closed individually and together. A minimum number of common conductors is used to conduct these signals from the rotating wheel sensor to the vehicle-mounted control circuit. The control circuit includes switches responsive to the various signals and logic circuitry associated with the switches to control the fluid valves of the braking system.

Description

BACKGROUND OF THE INVENTION

It has been proposed in antilocking systems for vehicle brakes to provide a number of contacts in the wheel sensor so as to produce, for example, a signal indicating a first threshold value of wheel rotational deceleration, a signal indicating a second threshold value of wheel rotational deceleration, and a signal indicating the occurrence of wheel rotational acceleration. These systems and the sensors associated with them have required n30 1 conductors to transmit the signals from the rotating wheel assembly to the control circuitry carried by the vehicle frame, where n equals the number of contacts involved.

SUMMARY OF THE INVENTION

Accordingly, it is of primary concern in connection with the present invention to provide an antilocking system for vehicle brakes wherein a minimum number of conductors are required to transmit the signals from the wheel sensor to the control circuitry.

More specifically, the present invention is directed to an arrangement wherein a pair of conductors is sufficient for the purposes intended regardless of the number of contacts associated with the wheel sensor.

The present invention utilizes a plurality of contacts associated with the wheel sensor, which contacts are connected in electrical parallel and having in series individually therewith resistance values which are different so that, over a pair of common conductors, voltages may be established at the control circuitry which are uniquely identifiable with the individual contacts of the sensor.

It is a further object of the invention to provide an improved form of control circuitry in association with the wheel sensor assembly described hereinabove.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic view showing the system according to the present invention as associated with a single vehicle wheel.

FIG. 2 is a diagram illustrating various signals associated with the system and corresponding positions of the control valves.

FIG. 3 is a circuit diagram illustrating one embodiment of the invention.

FIG. 4 is a diagram representing voltages and indicating in tabular form the disposition of the wheel sensor contacts and certain states of circuitry during operation.

FIG. 5 is a circuit diagram showing a modified form of the invention.

FIG. 6 is a diagram similar to FIG. 4 but showing the data associated with FIG. 5.

FIG. 7 is a circuit diagram showing a further modification of the invention; and

FIG. 8 is a diagram similar to FIGS. 4 and 6 but showing data associated with the modification of FIG. 7.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In FIG. 1, a vehicle wheel is indicated generally by the reference character 1 and will be seen to include a hub la provided with a brake disc 1b and a conventional rim portion 1c upon which the vehicle tire 2 is mounted. The wheel is mounted through the medium of its hub upon an axle 5 by means of ball bearings 3 and 4, it being appreciated that the axle 5 may be of any type inclusive of steerable axles.

The brake disc 1b has the usual caliper 6 associated therewith which carries a brake pad 7 adapted to be forced into engagement with the brake disc 1b through the medium of the piston 8. The hydraulic system for the brakes includes the usual master cylinder 10 operated by a pedal 11 and adapted to pressurize the main conduit 9 thereby to actuate the piston and force the brake pad 7 against the brake disc 1b. The main conduit 9 contains a normally open inlet valve I and a branch conduit 12 contains a normally closed outlet valve O adapted to return the pressure medium from the main pressure line into a collecting device or to the main line upstream of the inlet valve I in a fashion disclosed, for example in copending application Ser. No. 743,400 filed July 9, 1968, now Pat. Pat. No. 3,542,437 issued Nov. 24, 1970.

Mounted on the vehicle wheel is a sensor 13 which may be provided with a mounting flange portion 15 for the purpose of securing it to the vehicle wheel and as described in the aforesaid copending application, the sensor includes an elastically suspended inertial mass adapted to rotate about an axis which is parallel or coaxial with the wheel axis and which inertial mass is operative to actuate switches V.sub.1, V.sub.2 and B, for example, and the signals produced thereby, as will be hereinafter described, are transmitted to the control circuitry 14 by means of a pair of conductors 22 and 23. The conductor 22 may extend through a suitable passage 5a in the axle 5 for connection with a contact pin 19 spring urged by the member 21 against the contact button 17 which is in turn connected to the switch circuitry. The contact button 17 is insulated from the housing of the sensor 13 by means of an insulating washer 18 and, as shown, it will be appreciated that the switch circuitry is grounded as at 16 to the sensor housing so that the circuitry is completed through the ground conductor 23 previously mentioned.

The control circuitry 14 includes a discriminator 24 and logic circuitry 25 which together control the inlet and outlet valves I and O, thereby to control the pressure medium acting at the piston 8 to control the braking action of the vehicle wheel 1.

The wheel sensor switches V.sub.1 and V.sub.2 are connected respectively in series with resistors R.sub.1 and R.sub.2 whereas the switch B is connected in the parallel switch circuit so as to effect short circuit thereof. The switch V.sub.1 is adapted to close in response to a first threshold of wheel rotational deceleration; the switch V.sub.2 is adapted to close upon attainment of a second threshold of vehicle wheel rotational deceleration; and the switch B is adapted to close in response to some value of wheel rotational acceleration. In general, the effect of these switching actions is to control the inlet and outlet valves I and O through the control circuitry 14 in such fashion that when the master cylinder 10 is operated initially to cause application of the brakes through the normally open inlet valve I by transmitting pressure within the medium in the main line 9, the consequent wheel rotation deceleration occurring, upon reaching the first threshold value, closes the switch V.sub.1 which operates to close the normally open inlet valve I, thereby to maintain a constant fluid pressure within the main line 9. Thereafter, the constant pressure causes further deceleration of the wheel so that the switch V.sub.2 then closes which operates to open the outlet valve O and reduce the pressure in the main line 9. The sensor switch mechanism may be such that once the switch V.sub.1 closes, it will not reopen until the switch B is closed. When the brake pressure is reduced, the wheel will accelerate ultimately to close the switch B and open the switch V.sub.1 which will retain the inlet valve in the closed position and which will, through the control circuitry 14 as hereinafter described, close the outlet valve O thereby establishing a constant pressure after the initial reduction. The wheel may then start to decelerate which will immediately open the switch B and cause the inlet valve I to open thus increasing the pressure in the main line 9 which immediately starts to decelerate the wheel again and close the switch B which then closes the inlet valve I and this cycle of opening and closing the switch B and consequent opening and closing of the inlet valve I will be cyclically repeated at relatively high frequency during the control cycle. The net effect is to cause the speed of the vehicle to oscillate about some ideal value which will effect most efficient braking without allowing locking of the wheel and consequent skidding thereof.

Because of the different resistance values associated with the switches V.sub.1 and V.sub.2 and B, the impedance in the control circuitry as established by the various switches will be such as is illustrated in the upper portion of FIG. 2. In FIG. 2, the ordinate Z represents the impedance values wherein the value Z' represents the normal value when all of the switches are open; the value Z" indicates the impedance value when the switch V.sub.1 is closed; the value Z'" represents that value of impedance occurring when both switches V.sub.1 and V.sub.2 are closed and the substantially zero value Z"" occurs when the short circuiting switch B is closed. FIG. 2 also shows the relative state of the inlet and outlet valves I and O.

With reference to FIG. 3, an embodiment of the control circuitry 14 is shown. As illustrated, the parallel switches V.sub.1, B and V.sub.2 are connected in series across the battery voltage with the resistor 28 so as to establish various voltages as shown in FIG. 4 at the junction 26 or across the junction 26 and 27 dependent upon the condition of the switches V.sub.1, B, and V.sub.2. As shown in FIG. 4, the voltage V is at the value V' which corresponds to the voltage of the positive terminal P when all of the switches are open; it is at a value V" when the switch V.sub.1 is closed; it is a value V'" when the switch B is closed; it is a value V"" when the switches V.sub.1 and B are simultaneously closed as described above; and is at substantially zero potential as indicated by the value V""' when the switch V.sub.2 is closed.

The discriminator includes three transistors T.sub.a, T.sub.b, and T.sub.c having their respective bases connected through the medium of resistors 29, 30 and 31 to the junction 26. The PNP transistor T.sub.a has its emitter connected directly to the conductor P and its collector is connected to ground through the voltage divider resistor chain 32, 33 between which one output a to the logic circuitry is taken. The PNP transistor T.sub.b has its emitter connected between the positive voltage and ground by means of the voltage divider resistor chain 34, 35 and its collector is connected to ground through the voltage divider resistor chain 36, 37 between which the second output b to the logic circuitry is taken. The NPN resistor T.sub.c has its collector connected to the positive conductor P through the resistor 38 and its emitter is directly connected to ground. Thus, when the voltage V' is applied at the junction 26, the two transistors T.sub.a and T.sub.b are nonconducting whereas the transistor T.sub.c is conducting so that the three outputs a, b and c to the logic circuitry are all at ground potential initially. In FIG. 4, the switching potential for the transistor T.sub.a is indicated by the voltage line S.sub.a ; that of the transistor T.sub.b is indicated by the voltage S.sub.b and the switching level for the transistor T.sub.c is indicated by the voltage level S.sub.c.

Consequently, when the switch V.sub.1 is closed and the voltage V" established at the junction 26, the transistor T.sub.a will conduct causing a positive voltage to appear at the terminal a.

The positive voltage at the terminal a is applied through an OR gate 81 to the amplifier 44 which operates to close the normally open inlet I. As will be described hereinafter, the OR gate 81 may be used to allow a simple form of sensor switch mechanism to be employed as, for example, is disclosed in aforementioned copending application, i.e., sensor switches in which V.sub.1 and B are not operated in such fashion that V.sub.1 remains closed until B is closed but, to the contrary, wherein the transition between rotational deceleration and wheel rotational acceleration always establishes a condition wherein all the switches are open.

When, after switch V.sub.1 is closed, the switch V.sub.2 subsequently closes because of the attainment of the second threshold of wheel rotational deceleration, substantially zero potential is established at the junction 26 so that both transistors T.sub.a and T.sub.b are driven conductive whereas the transistor T.sub.c 1 is driven nonconductive. The conductive conditions of the two transistors Ta and Tb will cause positive voltages at both the terminals a and b whereas the nonconductive condition of the transistor T.sub.c will cause the voltage at c to rise to some positive value. In addition to the aforesaid OR gate 81, the logic circuitry includes the inverters 39 and 40, the AND inverter 41 and the bistable device 42. The bistable device 42 may be a J-K flip-flop in which the J output from the inverter 40 is effective when it goes negative to set the bistable device to a "1" output so as to energize the amplifier 43 and cause the normally closed outlet valve O to open. This condition of the outlet valve will be retained until the condition occurs at which there is no potential appearing at the terminal c whereas a positive potential appears at the terminal b, which condition will cause a negative potential output at the AND inverter 41 to set the output of the bistable device 42 to "0." It will be appreciated of course, that a negative output appears from the AND inverter 41 only when both inputs thereto are positive.

In the lower portion of FIG. 4, the "0" and "1" values in the tables corresponding to the switches V.sub.1, V.sub.2 and B indicate respectively open and closed conditions thereof whereas these same values as applied to the terminals a, b and c indicate respectively negative and positive potentials. If, as discussed above, the OR gate 81 and conductor 80 connecting its second input to the output of the bistable device 42 is used, it is not necessary to utilize a sensor switch arrangement wherein V.sub.1 remains closed until B is closed and consequently, the next to last column in FIG. 4 and the corresponding voltage V'" can't happen.

The purpose of providing either a sensor switch arrangement wherein V.sub.1 remains closed until B is closed or alternatively to provide the OR gate 81 and conductor 80 as shown in FIG. 3 is to assure that the inlet valve cannot obtain an open condition while the outlet valve 0 is also open. In the arrangement of FIG. 3, it will be appreciated that once the contact V.sub.2 is closed, the bistable device 42 will be set to a condition in which the outlet valve 0 is open. If, during subsequent acceleration of the vehicle wheel all of the valves V.sub.1, B and V.sub.2 are opened, the conductor 80 and OR gate 81 will retain the inlet valve I in closed condition due to positive potential appearing at the conductor 80, thus doing away for the necessity of providing an arrangement wherein the switches V.sub.1 and B are arranged so that V.sub.1 remains closed until B is closed. During subsequent cycling, it is of course important that the switches do open so as to permit the inlet valve to open to again retard the vehicle rotational speed and cause the switch B to open again which then again reopens the inlet valve whereafter the wheel may accelerate again and close the switch B to again close the inlet valve I due to establishment of the voltage potential V'" and consequent switching of the two transistors T.sub.a and T.sub.b.

a further modification of the invention is shown is FIG. 5 wherein the three transistors T.sub.d, T.sub.e and T.sub.f are utilized with their respective bases connected to the terminal 26 through resistors 47, 48, and 49, and, in the case of the latter two transistors T.sub.e and T.sub.f, by zener diodes 45 and 46 having different zener voltages. All of these transistors are normally nonconducting when the voltage at junction 26 is at the positive potential of the battery and the switching potentials for the several resistors are S.sub.d, S.sub.e and S.sub.f as indicated in FIG. 6. The resistors R.sub.1 and R.sub.2 are different and when the switch V.sub.1 is closed, the transistor T.sub.d will conduct to produce a positive output at the terminal d which completes the circuit through the winding 51 of the magnetically operated device whose armature 52 is connected to the normally open switch 50 so that when the circuit through the switch 50 is completed, the normally open inlet valve I is actuated to closed condition. When the switch V.sub.2 is closed, and transistors T.sub.d and T.sub.e thereby both placed in conductive condition, a circuit will be completed through the winding 56 of the solenoid device connected to the switch 53 so as to move the armature 58 in the direction to close the switch and thereby complete the circuit to open the normally closed outlet valve O. Once the switch 53 is closed, the diode 54 constitutes a holding circuit for the winding 56 so that the outlet valve will remain in open condition until the transistor T.sub.f is driven conductive due to closing of the switch B whereby the winding 57 is energized to oppose the effect of winding 56, in conjunction with the normal spring tension as indicated by the arrow 55, to open the switch 53 and allow the outlet valve to be returned to its normally closed condition. In FIG. 6, the switching threshold for the respective transistors T.sub.d, T.sub.e and T.sub.f are indicated by the voltage levels S.sub.d, S.sub.e and S.sub.f whereas the voltage levels V.sub.1, V.sub.2 and V.sub.B respectively are established when the respective switches V.sub.1, V.sub.z and B are closed. It will be appreciated, of course, that the voltage level V.sub.z may be established due either to closing of the switch V.sub.2 or closing of both switches V.sub.1 and V.sub.2 but will, in any event, be below the switching threshold level S.sub.e but above the switching threshold level S.sub.f.

The diode 83 is provided for the purpose of retaining the inlet valve I in closed condition so long as the outlet valve O is in open condition and thus, according to FIG. 6 and the illustration of FIG. 5 the requirement for the switch V.sub.1 remaining closed until the switch B is closed is not contemplated unless so desired, in which case the diode 83 may be omitted.

A further modification of the invention is shown in FIG. 7 which, as contrasted to the systems of FIGS. 3 and 5, utilizes but two transistors T.sub.g and T.sub.h as active switching elements of the discriminator circuit whereas the systems of FIG. 3 and FIG. 5 both use three transistors as the active switching elements. The third active switching element in the embodiment of FIG. 7 is effected by the diode D. The transistor T.sub.g has its base connected to the junction 26 through the resistor 60 whereas its collector is connected to ground through the voltage divider resistor chain 61, 62 the output to the power stage Darlington pair 63, 64 being taken between the resistor 61 and 62 to actuate the normally open intake valve I to closed condition when the transistor T.sub.g becomes conductive. The transistor T.sub.h has its base connected to the junction 26 through the resistor 65 and its emitter is connected across the positive conductor P and ground through the voltage divider resistor chain 68, 69 and its collector is connected to the terminal h which is the single input to the bistable device hereinafter described. The diode D is connected between the junction input h and the junction 26 in forward direction. As shown in FIG. 8.

When the switch V.sub.1 is closed, the transistor T.sub.g is driven conductive thereby to close the normally open inlet valve I, the switching threshold for the transistor T.sub.g being indicated by the voltage level S.sub.g in FIG. 8 which corresponds substantially to the voltage level established by closing of the switch V.sub.1. The voltage level established by closing of the contact V.sub.2 is below the switching threshold S.sub.d for the diode D and causes the input at h to go substantially to ground potential or, more precisely to that value corresponding to the forward voltage of the silicon diode D. This voltage level at the input h causes the bistable device to be set to that condition in which the Darlington pair 78 and 79 conducts to open the normally closed outlet valve O. The pair 78, 79 form part of the bistable circuit.

When the circuitry is initially switched on, the transistor 71 will immediately conduct since its emitter-collector path is directly connected across the positive potential P to ground through the resistor 70 whereas the voltage at the base of the transistor 78 will build up more slowly due to the integrating effect of the capacitor 76 operating through the resistor 72. Thus, at the moment of switching, the bistable circuit has a preferred condition in which the transistor 71 conducts and the Darlington pair 78, 79 is nonconductive. An intermediate voltage appears at the input h due to the voltage drop at the transistor 71 and across the diodes 74 and 75, the resistors 73 and 77 being of substantially the same value. When, however, the input h goes substantially to zero due to closing of the switch V.sub.2, the transistor 71 becomes nonconductive so that the voltage at the base of the transistor 78 rises to switch on the Darlington pair 78, 79. Although the diode D allows the potential at input h to go negative or substantially to ground as the potential at junction 26 correspondingly falls, the potential at input h can not correspondingly rise due to the blocking action of the diode D. The bistable input at h is restored to high potential to thus reset the bistable to its condition in which the transistor 71 conducts and the Darlington pair 78, 79 is nonconductive only when the transistor T.sub.h becomes conductive due to closing of the contact switch B.

Again, as in FIG. 5, the inlet and outlet valves I and O may be coupled by a diode to obviate the necessity for the condition illustrated in the next to last column in FIG. 8.

It will be understood that the above description of the present invention is susceptible to various modifications, changes and adaptations.

Claims

We claim:

1. In an antilocking control system for vehicle brakes of the type having a brake pressure source, a wheel and associated braking member, and pressure control means for controlling the brake pressure applied to said braking member, the improvement comprising, in combination:

sensor means for actuating said pressure control means in accord with changes in rotational speed of the wheel, said sensor means including a plurality of switches responsive to different states of change in rotational speed of the wheel;

a pair of conductors connected to said switches; and

a control circuit connected to said conductors and responsive to different signals to actuate said pressure control means correspondingly, said control circuit including a discriminator circuit having a plurality of switch elements responsive to said different signals;

said switches being connected in parallel and including impedance means in series with individual switches to produce said different signals.

2. In the system as defined in claim 1 wherein said switch elements comprise switching amplifiers having different switching thresholds corresponding to said different signals.

3. In the system as defined in claim 2 wherein said switching amplifiers are transistors.

4. In the system as defined in claim 3 wherein at least some of said transistors have zener diodes at their inputs, said zener diodes having different zener voltages.

5. In the system according to claim 1 wherein one of said switch elements of said discriminator circuit constitutes a diode and another of said switch elements is a transistor having its output connected to said diode.

6. In an antilocking control system for vehicle brakes of the type having a brake pressure source, a wheel and associated braking member, a normally open inlet valve connecting the braking member to said brake pressure source, pressure reducing means for selectively reducing the brake pressure at said braking member, and a sensor for detecting changes in rotational speed of the wheel, the improvement comprising, in combination;

a control circuit for actuating said inlet valve and said pressure reducing means, said control circuit including a first switching means for closing said inlet valve in response to a first threshold of wheel deceleration, a second switching means responsive to a second threshold of wheel deceleration, a third switching means responsive to wheel acceleration, and a bistable device controlling said pressure reducing means, said bistable device having said second and third switching means as inputs thereto;

said sensor having first, second and third switches for respectively actuating said first, second and third switching means, said switches being connected in parallel;

a pair of conductors connecting said switches to said control circuit; and

resistor means in series with individual ones of said switches, said resistor means having different values for each switch.

7. In the system as defined in claim 6 wherein said switching means are transistors actuated between conductive and nonconductive states.

8. In the system as defined in claim 6 wherein said first switch actuates said first switching means, said second switch actuates said first and second switching means, and said third switch actuates said first, second and third switching means.

9. In the system as defined in claim 8 wherein said first and second switching means are transistors, said third switching means comprising a diode connected between the input to said bistable device and said third switch.

10. In an antilocking control system for vehicle brakes of the type having a brake pressure source, a wheel and associated braking member, and pressure control means for controlling the brake pressure applied to said braking member, the improvement comprising, in combination:

sensor means for actuating said pressure control means in accord with changes in the rotational speed of the wheel, said sensor means including a plurality of switches responsive to different states of change in rotational speed of the wheel;

a pair of conductors connected to said switches; and

a control circuit connected to said conductors and responsive to different signals to actuate said pressure control means correspondingly, said control circuit including a power stage for said pressure control means and a flip-flop for actuating said power stage and having a single input connected thereto;

said switches being connected in parallel and including impedance means in series with individual switches to produce said different signals.