| 摘要 |
A hydraulic control system contains a hydraulic pressure source for producing hydraulic pressure supplied into the hydraulic servo mechanisms of a hydraulic automatic transmission, the hydraulic pressure is conveyed through a conduit system to a manual distributing valve which distributes the hydraulic pressure in accordance with its position in the various ranges "P", "R", "N", "D" and "L", a pressure regulator valve is located in the conduit system for establishing a line pressure by regulating the hydraulic pressure from the hydraulic pressure source, a governor valve in communication with a change-over valve and with a shift valve provides a governor pressure conforming to the vehicle speed, and a throttle valve is located in the conduit system for obtaining a throttle pressure conforming to the engine throttle opening. The shift valve supplies the line pressure to the required servo mechanism by comparing the governor pressure and the throttle pressure, and the change-over valve supplies the throttle pressure to the pressure regulator valve in accordance with the governor pressure. When the manual distributing valve is in the "R" range and the engine throttle opening is extremely small, the line pressure from the manual distributing valve is discharged and controlled in the throttle valve to take out a relatively low throttle pressure. When the throttle opening exceeds a predetermined value, the throttle valve takes out the line pressure from the pressure regulator valve as it is, thus obtaining a constant high throttle pressure. When the manual distributing valve is in the "D" range, the throttle pressure is applied to the pressure regulator valve through the change-over valve. When the throttle pressure is low, the line pressure of the pressure regulator valve is reduced, and when the throttle pressure is high, the line pressure thereof is increased. Furthermore, as the governor pressure is supplied to the change-over valve, the throttle pressure applied to the pressure regulator valve at a vehicle speed below a predetermined value, is shut off by means of the changeover valve, thus obtaining a constant low line pressure. Moreover, when the manual distributing valve is shifted from the "D" to the "L" range, this valve communicates the line pressure with the pressure regulator valve and, therefore, a high line pressure is produced by the pressure regulator valve, having no relationship with the vehicle speed and the engine throttle opening.
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