Abstract: In a hydraulic braking pressure control system comprising a brake device (B.sub.FL, B.sub.FR, B.sub.RL, B.sub.

Abstract: A pressure supply system for a vehicle according to the invention incorporates a pump and an accumulator in which an output pressure of the pump is maintained within a prescribed range by controlling the on-off operation of the pump according to the inner pressure of the accumulator. By changing the prescribed range of pressure according to the actual pressure requirement, for instance according to the change in the travelling speed of the vehicle, the burden on the system is reduced. The prescribed range can be changed either by simply changing the upper and/or lower pressure limits at which the pump is deactivated and activated, respectively, or by operating the pump for a prescribed time period which is dependent on the pressure requirement after a certain reference pressure value is reached. Thus, the structure of the fluid pressure system is simplified, and the generation of unnecessary high pressure can be avoided.

Abstract: A hydraulic pressure control system has a hydraulic pressure control valve which includes a spool slidably received in a housing for axial sliding movement between a rear position in which it permits the communication between an output port and a release port and a front position in which it permits communication between an input port and the output port. The hydraulic pressure control system also has a reaction chamber connected to the output port for providing a hydraulic pressure for biasing the spool rearwardly, and an input pressure working chamber for providing a hydraulic pressure for biasing the spool forwardly, a differential pressure regulating valve is interposed between the output port and the reaction chamber and adapted to be opened in response to the hydraulic pressure from the output port becoming higher than the hydraulic pressure in the reaction chamber by a predetermined value therefor.