Patent GB-1436949-A (GB)
Title: Method of reducing the speed of a vehilce and a braking control system for a vehicle
IPC: B60T8/82
Filed: 1973-05-15
Abstract: 1436949 Anti-lock braking systems REGIE NATIONALE DES USINES RENAULT and AUTOMOBILES PEUGEOT 15 May 1973 [19 July 1972] 23173/73 Heading F2F A braking-control system for a vehicle having front wheels and rear wheels acts to interrupt and reapply front wheel braking utilizing a comparison of signals representative of front wheel speed and rear wheel speed. Information significant of rear wheel speed is stored in a store 13, and front wheel braking is interrupted when front wheel speed falls below a certain proportion of this stored speed. In an anti-lock cycle rear wheel braking is interrupted for a sufficient period to ensure that at the end of the period the rear wheels are rolling without slip. Figs. 1, 2, 4 illustrate parts of such a system. Fig. 1 shows a circuit for determining which of the rear wheels has a faster peripheral speed. Respective sensors provide pulse signals at a frequency proportional to the rotational speed of the rear wheels to shaper circuits 1, 2 which generate signals to respective counters 3, 4 and to respective stores 5, G. A fixed clock 7 is connected to the counters 3, 4. The counters 3, 4 count clock pulses between sensor pulses and when a sensor pulse arrives at the input of circuit 1 (say) the latter sends signals to counter 3 and store 5 in such a way that the previous count in counter 3 is transferred to store 5 before the counter 3 is reset to zero-the count is proportional to the reciprocal of the wheel speed. The operation of circuit 2, counter 4 and store 6 with the clock 7 is analogous and a comparator 8 reads the values in stores 5, 6 and has two outputs to provide complementary logical signals to a gate 9 should one stored value be greater than the other; the gate 9 is connected to the sensors and transmits signals from the faster rotating wheel to the circuitry illustrated by Fig. 2. As seen in Fig. 2 the output from gate 9 is shaped in a circuit 10 which generates signals for counters 11, 12 and stores 13, 14. A clock 16 is connected to the input of counter 11 and two other clocks 17, 18 are connectible to the input of counter 12 by way of a gate 19. The counters 11, 12, stores 13, 14 and clocks 16, 17, 18 act in a similar way to the corresponding components of Fig. 1 although the clocks 16, 17, 18 have different frequencies. A comparator 20 provides a " 1" signal if the value in store 13 is less than in store 14 and the output of comparator 20 operates by way of a gate 21 a bi-stable 22, and also a bi-stable 23 to operate gate 19. An output 23a of bi-stable 23 also serves to start calculation of brake release line by acting on an up/down counter 27 by way of a gate 24 and by way of a bi-stable 25 and a gate 26. Clocks 28, 29 are connectible by gates 24, 26 respectively to count-up and count-down of the up/down counter 27. An output signal from counter 27 during counting down when the count reaches zero is inverted by an inverter 30 to provide a reset signal for bistables 25, 22 and a set signal for a bi-stable 31 whose reset input is connected to circuit 10. The signal at the output of bi-stable 31 and a signal E generated, for example, from a switch operated by the brake pedals are fed to a gate 32 which controls a gate 15. When the vehicle is not being braked, the vehicle speed and rear wheel peripheral speed are the same. Since clock 16 has a higher frequency than clock 17 the count at inputs A to comparator 20 from store 13 is greater than the count to inputs B to comparator 20 from store 14, and the output from comparator 20 is hence 0. However, on braking the signal E changes to " 0 " and causes gate 15 to be inhibited and the count represented at inputs A remains set while that from inputs B increases until comparator 20 is caused to generate a "11 " signal to energize bi-stable 22 to provide a signal F which interrupts rear wheel braking; when the output from comparator 20 returns to " 0 " bi-stable 23 acts on gate 19 to connect clock 18 to counter 12, clock 18 having a slightly higher frequency than clock 17 so that after the next sensor pulse the count at inputs A becomes less than the count at inputs B; the bi-stable 23 also opens the gate 24 so that counting up in the up/down counter 27 of the pulses from the clock 28 commences. As the wheel accelerates the output from comparator 20 drops back to 0, which causes bi-stable 23 and gate 19 to change over to their original states, and also causing bistable 25 to change state opening gate 26 and blocking gate 24. The counter 27 thus proceeds to count down, and when the counter reaches zero the resulting signal resets bi-stable 25 and bi-stable 22 to restore braking and also resets bi-stable 31 to open gate 15 so that at the next sensor pulse the sample count in counter 11 corresponds to wheel speed at the time (equal to vehicle speed). A monostable circuit (not shown) is thrown into its unstable state when the bi-stable 23 changes from its original state and returns to its stable state after a time by which the brakes should have been reapplied: when it returns to its stable state the monostable supplies a signal to store 13 so that comparator 20 will provide a zero signal, counting down in counter 27 will commence and braking will shortly be restored. Fig. 4 illustrates the part of the system controlling front wheel braking. The input to shaper circuit 40 corresponds to the speed of a front wheel (or the faster of two front wheels) and utilizing counter 41, store 42 and clock 43 a count corresponding to the reciprocal of wheel speed is stored in store 42 and presented to the inputs A<SP>1</SP> of a comparator 44 where it is compared with an inputs B<SP>1</SP> which receives a count corresponding to the reciprocal of actual vehicle speed, being connected to store 13. The frequency of clock 43 is selected to be a certain proportion of the frequency of clock 16, so that when the count presented at inputs A<SP>1</SP> is less than that at inputs B<SP>1</SP> the front wheel speed must be greater than that certain proportion of the speed for the time being stored in store 13 so that, with the brake pedal operated, front wheel braking is maintained. When the count at inputs A<SP>1</SP> becomes greater than that at inputs B<SP>1</SP> signifying that front wheel speed has fallen below said certain proportion the output of the comparator 44 changes so that front wheel braking will be interrupted.