Actuator assemblies for hydraulic braking systems

Claim 1

An actuator assembly for a vehicle hydraulic braking system comprising a housing, means in said housing defining at least two separate chambers, each chamber having a first inlet for connection to a fluid pressure source and an outlet for connection to a slave cylinder of a wheel brake, an expander piston working in a first bore in said housing in communication with each chamber and movable between a first advanced position, in which the effective volume of the chamber with which that bore is in communication is at a minimum and said inlet and outlet connections are open, and a second retracted position, in which the effective volume of that chamber is at a maximum and the inlet connection is closed and the outlet connection is open, a movable wall in said housing and normally acting to urge said expander pistons into said first advanced positions, said movable wall having a first area remote from said expander pistons and a second area opposed to the first area, means for normally applying fluid under pressure to said first area to urge said expander pistons into said first positions, and a second inlet connection in said housing through which fluid under pressure is adapted to be applied to said second area of the movable wall when the deceleration of a braked wheel controlled by fluid from at least one of said outlets exceeds a predetermined value, said fluid under pressure applied to said second area equalizing the pressure over the first and second areas of the movable wall and thus permitting the expander pistons to move towards said second retracted positions.