Hydraulic actuator assemblies for vehicle brakes

Abstract

An hydraulic actuator comprising a pair of oppositely acting hydraulic pistons working in a bore incorporates an automatic slack adjuster assembly which is housed in aligned bores in the pistons and acts as a strut to determine the relative retracted positions of the pistons. The adjuster assembly comprises a clamp member movable with the piston, and an adjuster member, the members including interengaging parts which co-operate with each other to form a releasable detent, in combination with a spring ring for biassing the interengaging parts into engagement, and the piston and the clamp member are provided with interengaging inclined faces to provide a wedge action and enhance the engagement of the interengaging parts when the bore is pressurized, and a stop loaded by a spring is provided in the bore with which the adjuster member is adapted to co-operate when movement of that member in a brake-applying direction exceeds a distance sufficient to take up the braking clearances. Additional movement of the clamp member in the same direction is operative to increase the effective length of the strut with the detent released until the force of the engagement of the interengaging parts at a predetermined point exceeds the force of the spring. The detent is re-engaged to prevent further relative axial movement between the two members whereafter, further movement of the strut with the piston is accommodated by movement of the stop against the loading in the spring.