| 摘要 |
A hydraulic control system for an automatic transmission, having a torque converter or a hydraulic coupler and a servo-operated speed change gear, for use in vehicles, includes a pressure regulator regulating a control hydraulic pressure supplied to the servo-operated speed change gear, and further includes a pressure modulator valve connected to the pressure regulator to assure smooth torque transmission for a large torque demand during low speed operation of the vehicle. A compensating pressure provided by the pressure modulator valve is applied to the pressure regulator valve to assure a control pressure, proportional to the throttle pressure opening or the torque demand, being applied to the servo-operated speed change gear. The pressure modulator valve restricts the control pressure to a value below the maximum constant pressure for a throttle valve opening exceeding a certain value, preventing excessive increase in the control pressure and assuring a constant low control pressure when the vehicle speed increases to a predetermined speed or when the transmission is set for the usual driving range.
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