| 摘要 |
A vehicle brake control valve includes a piston assembly which is movable a stepped cylindrical bore of a valve housing in response to an actuating force against the force of a spring. The piston assembly includes port control edges which control communication between a brake pressure chamber which can be connected to the vehicle brakes, a reservoir, and a pump. Both the pump and the actuating force contribute to the brake pressure which builds up in the brake pressure chamber. The piston assembly includes an actuator piston and an annular piston that sealingly slides within a larger portion of the stepped bore. After the actuator piston moves a pre-set distance (H) it carries with it the annular piston. The annular piston, the actuator piston and a wall of the larger diameter portion of the stepped bore enclose a fill pressure chamber which is separated from the brake pressure chamber to achieve two-stage pressure build-up during manual braking (emergency braking) when the pump is inoperative. The fill pressure chamber and the brake pressure chamber are connected to each other via a pressure reducing valve which opens towards the brake pressure chamber.
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