| 摘要 |
PURPOSE:To reduce fuel consumption by disposing a main servo valve and an auxiliary servo valve in parallel, providing the auxiliary servo valve with a throttle valve opened/closed according to the vehicle speed, forming a hydraulic power source of a first and a second pumps, and stopping the second pumps at high speed. CONSTITUTION:A main servo valve 4 is switched by the relative rotation between an input shaft and an output shaft so as to feed/discharge operating oil, discharged from a pump, to/from a power cylinder 6, and an auxiliary servo valve 10 is provided between the above-mentioned input-output shafts and interlocked with the main servo valve 4. These main and auxiliary servo valves 4, 10 are disposed in parallel. A vehicle speed sensing valve 16 opened/closed according to the vehicle speed is provided upstream of the auxiliary servo valve 10, and a pump is formed of a first pump 2 and a second pump 12. At the low speed time, the vehicle speed sensing valve 16 is closed, and discharge oil from the pumps 2, 12 joins each other so as to be led to the main servo valve 4, thus obtaining large assist force. With the increase of the vehicle speed, the vehicle speed sensing valve 16 is gradually opened, and at the time of high speed of a specified value or higher, the second pump 12 is stopped. Fuel consumption can be thus reduced at high speed in need of engine horse power. |
