Patent ID: 6062654
Filing Date: 2000-05-16
Classification: B60T

Abstract:
A brake control valve having a piston assembly which is movable against a spring in response to an actuating force F in a stepped cylindrical bore of a valve housing, the housing and the piston assembly defining a fill pressure chamber and a brake pressure chamber for connecting to vehicle brakes, the piston assembly having port control edges which control communication between a pressure source, a reservoir and the brake pressure chamber, so that both the pressure source and the piston assembly contribute to the pressure in the brake pressure chamber, the piston assembly including a smaller diameter piston and a larger diameter annular piston, the larger diameter piston being slidable in a larger diameter portion of the stepped bore and being slidably coupled to the smaller diameter piston so that movement of the smaller diameter piston causes the larger diameter piston to move only after the smaller diameter piston has moved through a pre-set distance H, the improvement wherein:the larger piston remains sealingly coupled to the smaller piston, the housing and the larger and smaller pistons enclosing the fill pressure chamber, the fill pressure chamber being spaced apart from the brake pressure chamber; anda pressure reducing valve connects the fill pressure chamber with the brake pressure chamber the pressure reducing valve opening to permit fluid flow from the fill pressure chamber to the brake pressure chamber, and when a pre-set brake pressure in the brake pressure chamber is exceeded, the pressure in the fill pressure chamber is released by the pressure reducing valve, and the pressure reducing valve is closed.