Vehicle hydraulic braking system with anti-skid pressure control means

A shut-off valve in an anti-skid pressure control device of a hydraulic braking system for an automotive vehicle, the anti-skid pressure control device including a solenoid valve disposed in a primary fluid passage of the braking system which connects a master cylinder and a brake cylinder to feed a brake fluid from the master cylinder to the brake cylinder to apply a brake to a drive wheel of the vehicle, said solenoid valve being selectively placed in one of a first position for communication of the brake cylinder with the master cylinder, and a second position for communication of the brake cylinder with a reservoir, the solenoid valve being switched between said first and second positions under the control of a controller to control a level of a braking pressure in the brake cylinder for preventing an excessive amount of slip of the drive wheel, the anti-skid pressure control device further including a pump for pumping the brake fluid from the reservoir and returning the pumped fluid via a pump passage to a portion of the primary fluid passage between the master cylinder and the solenoid valve, wherein

• said shut-off valve is disposed at a connection of said pump passage and said primary fluid passage, said shut-off valve normally maintaining fluid communication between portions of said primary fluid passage on both sides of said connection, said shut-off valve being closed to prevent a flow of the brake fluid therethrough in a direction from said pump toward said master cylinder while the brake fluid is fed via said pump passage to said shut-off valve, said shut-off valve comprising;
• means for defining a shut-off valve chamber formed at a connection of said pump passage and said primary fluid passage;
• a shut-off valve seat which partially defines said shut-off valve chamber, and through which the brake fluid from said master cylinder is fed into said shut-off valve chamber;
• a shut-off valve member accommodated in said shut-off valve chamber such that the shut-off valve member may be seated on and moved away from said shut-off valve seat;
• biasing means for biasing said shut-off valve member in a direction away from said shut-off valve seat;
• means for defining a shut-off piston chamber constituting a part of said pump passage;
• a shut-off valve piston slidably received in said shut-off piston chamber so as to define a first and a second pressure chamber on opposite axial ends thereof, said first pressure chamber being connected to said pump passage while said second pressure chamber being open in said shut-off valve chamber, said shut-off valve piston normally permitting said shut-off valve member to be placed away from said shut-off valve seat, and
• means for defining a restrictor passage communicating with said first and second pressure chambers, said restrictor passage allowing the brake fluid to flow from said first pressure chamber to said second pressure chamber when said pump is actuated to feed the brake fluid to said first pressure chamber, said restrictor passage giving a restriction to a flow of the fluid therethrough toward said second pressure chamber and thereby generating a pressure differential between said first and second pressure chambers, said pressure differential causing said shut-off valve piston to move toward said second pressure chamber and thereby seat said shut-off valve member on said shut-off valve seat.