Concentric hydraulic brake boost mechanism with system by-pass on piston o.d.

Claim 1

In a hydraulic boost mechanism for a vehicle hydraulic system including a fluid pressure source: a housing defining a bore therewithin having an inlet adapted to be connected to said source and an outlet; a piston slidably mounted in said bore and cooperating with one end of the latter to define a boost chamber therebetween; fluid pressure control means carried by said piston and by the wall of the bore for regulating the fluid pressure level at said inlet between a lower value when said piston is disposed in a first position and a higher value when the piston is shifted toward a second position, said fluid pressure control means including means for maintaining a continuous flow to the outlet independently of the position of the pistons said fluid pressure control means being defined by radially spaced annular surface means on said piston and said bore, respectively; means defining a vent for said boost chamber; control valve means slidably and coaxially arranged in said piston and shiftable from a first condition communicating said boost chamber to the means defining said vent and to a second condition closing communication through the means defining the vent and initiating communication between the inlet and the boost chamber as the control valve means is shifted from the first condition; and first resilient means acting on the control valvE means to urge the latter to said first condition and second resilient means acting on said piston urging the latter to said first position.