Anti-lock vehicle brake systems

Claim 1

A wheel slip detector for an anti-lock vehicle brake system, said detector comprising means for producing a d.c. signal the amplitude of which is a function of wheel speed, means for establishing a reference rate of change signal which is representative of a selected value of wheel deceleration, and means for determining over a range of wheel speeds a selected percentage of the instantaneous amplitude of said d.c. signal, said selected percentage of the instantaneous amplitude being proportional to the actual wheel speed and means to produce an output for anti-lock braking control in response to change in the instantaneous amplitude of said d.c. signal greater than said selected percentage and at a rate of change in excess of said reference rate of change parameter, said means for establishing a reference rate of change signal comprises a Miller capacitor which is connected to be discharged by the action of a transistor, and said means for determining a selected percentage of the instantaneous amplitude of said d.c. signal comprises a resistance divider chain which is connected effectively at one end to receive said d.c. signal and at the other end to the collector of said transistor, said capacitor being connected between the base of said transistor and a point on said divider chain at which said selected percentage of the d.c. signal is present.