Device for controlling hydraulic pressure in hydraulic brake system of

Abstract

A device for controlling the hydraulic pressure in the hydraulic braking system of a vehicle, in such a manner that the hydraulic pressure in the rear wheel cylinder is increased at a rate smaller than that in the front wheel cylinder, after a predetermined level of deceleration of the vehicle is reached. The device has a valve chamber in which a ball valve is disposed movably. A differential piston has two opposing pressure receiving surfaces of different areas exposed in the inlet and outlet chambers. The arrangement is such that, when the predetermined level of deceleration is reached, the ball valve is moved due to its inertia to a position for interrupting the communication between the inlet and the outlet chambers. Once the communication between two chambers is interrupted, the pressure in the master cylinder is transmitted across the differential piston. The transmitted pressure is lowered at a rate corresponding to the ratio of the areas of pressure receiving surfaces of the differential piston. The movement of the ball valve is freed from the dynamic pressure of the braking fluid and from the change in viscosity of the same, thanks to a specific arrangement of a restriction passage through which the valve chamber communicates the inlet chamber.