Servo motors for vehicle brake systems

Claim 1

A servo motor for a vehicle braking system of the kind including a pair of fluid pressure sources of different fluid pressures, comprising an internally hollow housing, a movable wall within said housing and dividing the hollow interior thereof into contiguous first and second fluid chambers, a motor output member displaceable by said wall and extending externally of said housing, and fluid flow control valve means for selectively connecting the first chamber to said fluid pressure sources with the second chamber permanently connected to one of said sources only, thereby enabling a fluid pressure differential to be established between said chambers for moving said wall within said housing, said control valve means comprising a valve seat member formed with a pair of spaced passage means, a pair of relatively stationary concentric valve seats on said member and each circumscribing one of said passage means, and a common valve closure member engageable with and selectively tiltable about each seat to thereby open the passage means circumscribed by the other said seat, the end of one of said passage means remote from said valve seats being permanently connected to one of said fluid sources and the corresponding end of the other said passage means being permanently connected to said first chamber, and said movable wall comprising an annular elastic diaphragm whose outer periphery is rigidly fixed relative to the housing and a deflecting plate for operating the common valve closure member, the deflecting plate comprising a plurality of first, radially extending, rigid fingers held in circularly spaced relationship which are selectively pivotable about each said valve seat to thereby achieve said tilting of the common valve closure member and a plurality of second, radially extending, rigid fingers which are shorter than said first fingers and whose radially inner ends are located outwardly of the reaidlly outer of said concentric valve seats.