| 摘要 |
A hydrostatic transmission has an engine-driven, bidirectional, variable-displacement drive pump connected in circuit with a bidirectional, variable-displacement propelling motor. A charging pump is also connected to the circuit of the drive pump and the propelling motor. A brake assembly normally locks the output shaft of the propelling motor against rotation and releases same only while being supplied with a hydraulic brake release signal. The control system for the hydrostatic transmission comprises a speed control valve actuated manually to deliver fluid pressure signals to servo controls for adjusting the outputs from the drive pump and the propelling motor, and a brake control valve pilot-operated to deliver the brake release signal to the brake assembly. Also included are a charge sensor valve and a speed control sensor valve. The two sensor valves cooperate to cause the output from the charging pump to pilot-actuate the brake control valve, for the delivery of the brake release signal, only when the charging pump output pressure rises to a predetermined level and, simultaneously, when the speed control valve is being manipulated. Whenever the charging pump output pressure falls below the predetermined level, the sensor valves cause the brake control valve to terminate the production of the brake release signal and to drain the signal output ports of the speed control valve, thereby causing the transmission to stop the vehicle and so avoiding cavitation in the drive pump and the propelling motor. |
