Noise reducing control valve for a hydraulic brake booster

Abstract

A hydraulic brake booster operatively connects with a pressurized fluid source and a master brake cylinder to convert the pressure within the pressurized fluid source to a power assist to the master brake cylinder during a brake application. The booster includes a cylindrical housing defining a bore and a piston is slidably mounted in the bore to define a pressure chamber and to operatively connect with the master brake cylinder. A valve member is slidably disposed within a bore within the piston and is movable upon a brake application to communicate the pressurized fluid source to the pressure chamber which urges the piston into engagement with the master brake cylinder. In a rest position inlet and outlet openings on the piston communicate fluid through the piston without any transfer of the force within the pressurized fluid to the piston. Upon movement of the valve member, a land on the valve member cooperates with the piston bore to restrict communication between the inlet and outlet openings which concurrently increases the communication to the pressure chamber and increases the pressure therein. Consequently, the piston is pressure responsive to move relative to the housing to engage the master brake cylinder to assist in a brake application. The valve member land includes a first diameter portion and second diameter portion and a recess between the portions to cooperate with the piston bore to quietly restrict the communication between the inlet and outlet openings.