Patent GB-1357289-A (GB)
Title: Hydraulic brake pressure control valve for a vehicle braking system
IPC: B60T8/26
Filed: 1972-03-10
Abstract: 1357289 Brake pressure control valves TOYOTA JIDOSHA KOGYO KK 10 March 1972 [11 Oct 1971] 11423/72 Heading F2F An hydraulic brake pressure control valve 10 for a vehicle braking system, comprises: a body 11 defining a cylinder having therein an inlet port 11a for connection to a master cylinder and an outlet port 11b for connection to rearwheel brake cylinders, a differential piston 30 which is slidably disposed within said cylinder to provide first and second pressure chambers A, B being in constant communication respectively with the inlet and outlet ports and which is provided with first and second piston surfaces S 1 , S 2  whereby opposing displacement forces may be provided on the piston respectively in the directions towards the outlet port and away from the outlet port, the effective area of the first piston surfaces being smaller than that of the second surfaces, first valve parts 30c of said piston co-operable with second 15 valve part of the cylinder wall for controlling intercommunication between the chambers in dependence upon the position of the piston in the cylinder of said body, first biasing means 35 for biasing the piston in the direction towards the outlet port and into a normal position of the piston in which the first and second valve parts provide full communication between the chambers, the arrangement of the biasing means and the piston surfaces being such that the piston normally provides full communication between the chambers but, when the pressure in the chamber A exceeds a first predetermined amount, is displaced in the direction away from the outlet port into a displaced position to control intercommunication between the chambers and thereby reduce the pressure rise rate in the chamber B, an assistant plunger 40 slidably disposed within a bore 32 of the piston 30 to subdivide the bore interior into third and fourth pressure chambers C, D of which the chamber C is in open communication with the chamber A and the chamber D is in open communication with the chamber B, and second biasing means 43 for biasing the plunger in the direction away from the outlet port and into a normal position in which the plunger is united axially with the piston, the biasing means 43 having a biasing force smaller than that of the biasing means 35 and the arrangement of the plunger in the bore 32 and the magnitude of the biasing force of the biasing means 43 being such that when the pressure in the chamber A exceeds a second predetermined amount greater than said first amount, the plunger is displaced against the bias of the biasing means 43 and into a displaced position and the effective piston area in the fourth chamber D is reduced in order to reduce further the pressure rise rate in the chamber B. Hydraulic pressure produced in a master cylinder is delivered directly to front-wheel brake cylinders and to the port 11a of the valve 10, the pressure being led from the chamber A to the chamber B via the space between the valve seat 15 and valve face 30c, to the port 11b, and then to rear-wheel brake cylinders. An increase of pressure due to depression of the brake pedal of the master cylinder results in movement to the left, as seen in the figure, of the piston 30 together with the plunger 40 the valve face 30c closing on the seat 15 to block communication between the chambers A and B and causing movement of the piston to the right to open the valve seat; in this manner reciprocatory operation of the piston is effected, the plunger 40 maintaining engagement with the shoulder 42 of the piston by way of the force of the spring 43 and to move unitedly with the piston; at further higher values of pressure, the difference in pressure in the chamber C and D exceeds the force of the spring 43 whereby the plunger is displaced so that the end face of the portion 40a thereof abuts the end wall of the valve body 11, the piston 30 being freed from the force of the spring and conducting opening and closing operation of the valve seat 15 in accordance with the increase of master cylinder pressure.