GB1410992A - Wheel slip detector for use in anti-lock vehicle brake systems - Google Patents

Abstract

1410992 Anti-skid control MULLARD Ltd 19 June 1973 [19 June 1972] 28587/72 Heading F2F A wheel slip detector circuit for an anti-skid braking system comprises means producing a D.C. signal the amplitude of which is a function of wheel speed, means for establishing a reference rate of change parameter representative of a predetermined wheel deceleration value, and means for determining over a range of wheel speeds, in dependence on the instantaneous amplitude of the D.C. signal, a selected percentage of the instantaneous amplitude (and thus of the actual wheel speed), so as to produce an output for anti-skid control in response to a change in the instantaneous amplitude of the D.C. signal greater than the selected percentage and at a rate of change in excess of the reference rate of change parameter. In Fig. 3, the circuitry comprising resistors R1 to R6, capacitors C1 to C5 diodes D1 to D4, and transistors T1, T2 produces from a wheel speed input, at a coil L of an electromagnetic wheel sensor, comprising a train of pulses, an output fed to a capacitor C6 having an amplitude varying as a logarithmic function of the wheel speed. The combination of the capacitor C6 and resistors R9, R10 provide the reference rate of change parameter since they form a differentiating circuit so that when the voltage at the input side of the capacitor C6 drops below this reference value, transistors T3, T4, normally conductive, are rendered non-conductive, and a non- conductive transistor T5 is rendered conductive providing an output to a solenoid valve for brake release. Spurious high frequency oscillations are prevented by a capacitor C7 and the circuit is made less sensitive to ripple in the signal voltage by a capacitor C8. In Fig. 4, the circuitry comprising resistors R1 to R24, capacitors C1 to C9, diodes D1 to D9, and transistors T1 to T7 produces a signal from the emitter of transistor T7 having a voltage proportional to the wheel speed. This signal is applied to a base of a transistor T8 which, if positive, holds this transistor conductive to hold a transistor T10 conductive. If this signal changes by a negative step, corresponding to a predetermined fraction of a wheel speed change at a rate in excess of the wheel speed change reference rate, a current passing through a transistor 79, coupled to a capacitor C12 and resistors R26, R27, becomes zero. The reference rate is determined by linear decay of voltage across the capacitor C12 discharged by the transistor T9. When this occurs, transistors T8, T10 become non- conductive, producing a signal after phase inversion and amplification to a solenoid valve for brake release. Fig. 5 (not shown), provides a similar circuit to that of Fig. 4.