Vehicle wheel slide protection systems

Claim 1

A vehicle wheel slide protection system for use with a vehicle wheel provided with brakes, including a wheel speed transducer having first and second output terminals and which produces an oscillatory signal at a frequency dependent on the speed of rotation of the wheel, and a brake control circuit for releasing the brakes of the wheel, in use, when the rate of decrease of said frequency exceeds a predetermined value, said control circuit having an earth terminal and including a comparator input stage for squaring pluses received from the wheel speed transducer and inverting and non-inverting input terminals, comprising first and second input terminals connected to the respective first and second transducer output terminals, a pair of equal value resistors connecting the input terminals of said comparator to the respective inverting and non-inverting input terminals of the comparator, a pair of equal value capacitors connecting the input terminals to said earth terminal of the circuit, a supply with two supply rails, a bias circuit for biasing said comparator input terminals to a d.c. level intermediate the supply voltage, said bias circuit comprising a transistor having a collector, a base and an emitter, said emitter being connected to one supply rail and said collector connected via a load to the other supply rail, a first resistor connecting the base of the transistor to said one supply rail, a second resistor connecting the base of the transistor to one input terminal, and a third resistor connecting the other input terminal to the other supply rail, the transducer normally providing a connection between the input terminals so that the transistor is turned on and current flowing through the base-emitter junction thereof and said second and third resistors biasing the input terminals, the transistor being turned off when the connection between the input terminals by the transducer is severed.