GB1490278A - Skid control system - Google Patents

Abstract

1490278 Skid control systems KELSEYHAYES CO 19 May 1975 [24 June 1974] 21227/75 Heading F2F A skid control system 10 receives wheel speed signals at 12 from a left wheel sensor and at 14 from a right wheel sensor (both may be either front or rear) which are fed to a low and high speed wheel select circuit 20 which outputs the lower wheel speed signal to a wheel speed differentiator and comparator circuit 26 which differentiates the low wheel speed signal and compares the resulting deceleration value with a reference 28, emitting a logical signal at 40 if the wheel deceleration computed by integration exceeds the reference. Circuit 20 also outputs both lower and higher wheel speed signals to a wheel speed differential override circuit 50 which emits a logical signal if the difference between high and low wheel speeds exceeds a reference level. Through OR-gate 48 logical outputs from circuits 26 and 50 control brake release by valve solenoid driver 46 and a modulating valve. Deceleration reference value 28 from reference current generating circuit 30 comprises a combination of currents from first, second and third current sources 32, 34 and 36 respectively. The first 32 generates a current representative of a very low wheel deceleration, the second 34 together with the first a current representative of a wheel deceleration which would occur during an incipient skid condition, and the third 36 generating a current representative of a very high wheel deceleration much greater than maximum non-skidding wheel deceleration. The second current source 34 is controlled by the output 40 from circuit 26 via inverter 38 and the third current source 36 by the output 40 triggering a one-shot multivibrator 42 or alternatively by a reset timer 58 which operates if the duration of the signal from valve solenoid driver 46 exceeds 1À5 seconds to avoid a continuous brake release situation. Sequence of operation.-When the deceleration of the low speed wheel exceeds reference current 28, initially a combination of first and second sources 32 and 34, the output from circuit 26 causes the second source 34 to be switched off and the third source 36 to be switched on for the period of multivibrator 42 (60 to 90 milliseconds) such that the reference 28 will now be greater than the deceleration of the low speed wheel and the output 40 from circuit 26 consequently switched off. Due to the inertia of the modulating valve the duration of the output from circuit 26 will be insufficient to cause brake release unless the wheel deceleration continues to increase exceeding the high reference or the speed differential of high and low speed wheels exceeds the speed reference 52.