Hydraulic power brake unit

TLDR: In this paper, a hydraulic power brake unit including a power piston operatively engaging a conventional master cylinder and an annular valve spool having differential end areas communicating with the power chamber formed by the power piston and being normally positioned in the housing is described.

Abstract: A hydraulic power brake unit including a power piston operatively engaging a conventional master cylinder and an annular valve spool having differential end areas communicating with the power chamber formed by the power piston and being normally positioned in the housing to communicate hydraulic fluid from a pressure source to the power steering unit and communicate the power chamber to the power source reservoir. When the brake pedal is actuated, an actuating spring acting between the valve spool and a reaction piston attached to the pedal pushrod is compressed and the valve spool is moved to restrict fluid communication from the pressure source to the power steering unit and divert the flow to the power chamber while simultaneously blocking communication of the power chamber to the reservoir so that the power chamber is pressurized and the power piston fluidly displaced to actuate the master cylinder. The power chamber pressure acts on the differential area of the valve spool to resist its movement by the actuating spring and causes it to function as a regulating valve which continuously provides a power chamber pressure proportional to the force of the actuating spring. Upon a malfunction caused loss of hydraulic pressure the reaction piston moves into abutting engagement with the power piston to provide a rigid force transmitting link between the pushrod and the master cylinder whereby the brakes are actuated independently of the hydraulic boost.