| 摘要 |
In the case of a brake pressure control valve (10) for a motor vehicle hydraulic or pneumatic brake system a pressure relief valve (74, 90), connected into the pressure medium line between brake master cylinder and the wheel brake cylinders of the rear axle, comprises a differential piston (70) and a first flexible element in the form of a control spring (56), which on the one hand acts on the differential piston in the opening direction of the valve and on the other hand is supported on a clamping piston (50), the cross-sectional area (A1) of which is greater than the sealed-off area (A2) of the smaller piston stage (72) of the differential piston (70). The clamping piston (50) can be acted upon by the master cylinder pressure against the spring force of the first flexible element, and the master cylinder pressure acting on the clamping piston is limited by a valve (40, 44) closing as a function of the vehicle deceleration. According to the invention a second flexible element (94) is provided which acts on the differential piston (70) in the closing direction of the pressure relief valve, its spring force being less than the spring force of the first flexible element. As a result the switching pressure of the pressure relief valve does not always exceed the closing pressure of the deceleration-dependent valve by the same amount, but in the event of an increase in the closing pressure the switching pressure of the pressure relief valve is increased by a greater amount. Consequently a very close approximation to the ideal brake pressure distribution for the particular load condition of a vehicle is achieved by simple means without the need for a mechanical actuation between the rear axle and the vehicle chassis. <IMAGE>
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