| 摘要 |
A hydraulic motor vehicle servo brake comprises a pedal-actuated master cylinder (11) with at least one master piston (24). In addition, a brake valve (17) is provided for boosting of the brake force, which brake valve upon actuation by the brake pedal (16) feeds pressure medium supplied by a hydraulic pump (18) connected to a supply reservoir (27) in a controlled way to the master piston (24). Furthermore, a pressure accumulator (45) is provided which is maintained in loaded condition by the pump (18) and is of such capacity as to ensure that it supplies sufficient pressure during the running-up phase of the pump (18) after the motor (147) is started. A control valve (46) connected to the pressure side of the pump (18) comprises a closing member 47 which normally closes a passage to a return conduit (48) leading to the supply reservoir and is pressurized by the pressure of the pump (18) against the force of a closing member spring (49). Thus the pressure of the pump can be reduced when the controlled pressure is low and the pump is in operation. Furthermore, a control valve (50) pressurized by the controlled pressure is provided. The closing member spring (49) influences the closing member (47) by way of a relief piston (53) disposed in a cylinder (52). The relief piston (53) is pressurized against the action of the closing member spring (49) by the controlled pressure. Between the relief piston (53) and the closing member (47) a week auxiliary spring (54) is disposed whose force is just sufficient to keep the closing member (47) in closing position when the relief piston (53) is in lifted position. |
