GB1380744A - Vehicle brake control system and a control unit for such a system - Google Patents

Abstract

1380744 Anti-lock braking systems R R GUNTER and H OUWERKERK 22 May 1973 [24 April 1972] 18949/72 Heading F2F A brake pressure modulator 7 in an anti-lock braking system is controlled by an electronic control unit comprising a first lock prediction comparator 3 which provides an output signal indicative of whether an input signal significant of the angular deceleration of a wheel exceeds a predetermined value, a second lock prediction comparator 4 which provides an output signal indicative of whether the angular deceleration exceeds a threshold value proportional to the angular velocity of the wheel and a gate 5 connected to receive the output signals from the two comparators 3, 4 and providing a control signal indicating a prediction that the wheel will lock and the brake should be released when the output signals from the comparators indicate that both the first and second lock prediction conditions are satisfied: the unit also includes a first reselection comparator 8 which provides an output signal indicative of whether the time which has elapsed since the wheel began to accelerate following release of the brake has exceeded a predetermined value, a second reselection comparator 9 which provides an output signal indicative of whether the angular velocity of the wheel subsequent to the release of the brake exceeds a threshold value proportional to the angular velocity of the wheel at the time of application of the brake, and a gating arrangement which receives the control signal from the comparators 3, 4 and the output signals from comparators 8, 9 and provides a command signal indicating that the brake should be re-applied when the control signal from comparators 3, 4 indicates that locking of the wheel is no longer predicted and the output signals from comparators 8, 9 indicate that at least one of the reselection conditions is satisfied. In the embodiment of Fig. 1, the gate 5 comprises an AND gate which feeds a signal to an electronic switch 6 controlling the brake pressure modulator 7 to cause the brake to be released when both the prediction conditions are satisfied. The signals from comparators 8, 9 are applied to an OR gate 10 connected to a gate 11 which also receives a signal from AND gate 5 via an inverter 12 and the switch 6 is thereby operated to reapply the brake when any one of the prediction conditions is no longer satisfied and at least one of the reselection conditions is satisfied. The predetermined value for the comparator 3 may be adjusted in stepwise manner in dependence upon the deceleration of the vehicle. Further the threshold value for comparator 4 may be adjusted in stepwise manner in dependence upon the angular velocity of the wheel at the commencement of braking in each cycle of a braking operation. Still further, the threshold value for comparator 9 may be adjusted in a stepwise manner in dependence upon the deceleration of the vehicle and the angular velocity of the wheel at the time the brake is applied in each brake cycle. Fig. 2, shows in more detail an exemplory embodiment of the invention with predicton comparators C1, C2 and reselection comparators C3, C4. The outputs of comparators C1, C2 are connected to a three-input NAND gate N1, the third input of which is connected to a voltage source +V1 through a switch S1 closed when the brake pedal is pressed. The predetermined value for comparator C1 is variable by a potentiometer P1 or automatically by the action of a switch F1 in the feedback circuit of an amplifier A6 which switch F1 is controlled by the output signal of a vehicle deceleration comparator C7. The threshold value for comparator C2 is variable by the action of a switch F2 controlled by an angular velocity comparator C6. The threshold value for comparator C4 is variable by the action of switches F4, F5, F6. The unit also includes a track and hold circuit comprising two resistors R, a capacitor CA, an electronic switch F3 and a feedback amplifier A3 which track and hold circuit provides a signal significant of the angular velocity of the wheel at the time the brake is applied in each brake cycle of a braking operation. A NAND gate N2 is connected to a power switching unit 24 for a solenoid 25 of a brake pressure modulator, which NAND gate N2 has its two inputs from NAND gate N1 and from a NAND gate N3 which forms a flip-flop circuit with NAND gate N2.