Patent GB-1432346-A (GB)
Title: Fluid pressure operating braking systems for vehicles
IPC: B60T8/66
Filed: 1972-04-25
Abstract: 1432346 Anti-skid braking systems AUTOMOTIVE PRODUCTS Ltd 25 April 1973 [25 April 1972] 19129/72 Heading F2F An anti-skid braking system has at least one electrical system associated with a wheel or group of wheels to regulate braking force to the wheel(s) in response to wheel deceleration, whereby a vehicle speed related reference signal is compared with a signal indicative of the angular velocity of the or each wheel such that if the reference signal exceeds the wheel signal for more than a predetermined time period the electrical system operation is modified (overridden) so that the associated brake(s) is/are held released and are not reapplied. The reference signal may be produced by decelerometers or from the angular velocities of one or more wheels by taking a mean value or proportional values of all but the slowest wheel. In Fig. 5 indicating circuitry for the production of an override signal for a wheel, angular velocities from the other three vehicle wheels at inputs 40, 41, 42 are computed to give the reference signal, by capacitors 44, 144, 244 producing peak values, corresponding to vehicle speed, and controlled discharges by transistor circuits 45, 46, 47, 145, 146, 147, 245, 246, 247, variable resistors 46, 146, 246, controlled by a unit 52 for fixed or decelerometer varied values, produce corresponding discharge rates. Further variation of the reference signal is by means of switches 50, 150, 250, 157, 257 and parallel resistors. This signal is inverted and amplified at 59 with a feedback circuit 63 providing further signal variation, and then compared at 70 with a signal at 142 from the associated wheel and a predetermined value signal obtained from a potentiometer 73 to allow for cornering velocity values for wheels on one axle. A Zener diode 77 limits the comparator output to an AND gate 81. Here, a capacitor 84, a resistor 82 and a diode 85 forming a delay signal production in parallel with a resistor 79 cause an output from the AND gate 81 to be delayed, this leading to a solenoid valve controlling brake pressure. Thus on production of an output from the comparator 70, if the wheel signal is less than the reference signal by an amount greater than the predetermined value, the solenoid valve operation is delayed, in case the wheel signal increases in a short period (thus requiring no override) but upon cessation of the comparator signal, the AND gate signal immediately ceases. A similar delay circuit may be in parallel with that including the AND gate 81 for production of a warning signal if the anti-skid system fails and the override circuit produces a continuous signal. Each of the wheels may have this circuitry, or the discharge controlled capacitor circuits may be common for connection to separate comparators in suitable combinations. The predetermined valve circuitry may be common for all wheels or there may be corresponding circuits for each wheel. Furthermore, there may be a common switch for all wheel solenoid valves, the switch being actuated on receipt of any of the comparator outputs. The velocity sensors 31 may be on the wheels or on the axles. The braking system is supplied by a pump charged hydraulic accumulator 12 and controlled by a pedal operated valve 14 for individual wheel circuits.