| 摘要 |
In a hydraulic control system for the automatic transmission of a vehicle, an arrangement is provided for controlling the supply and release of pressurized oil to a first hydraulic servo for operating the vehicle under high speed conditions and to a second hydraulic servo for operating the vehicle under low speed conditions. The hydraulic control system includes oil passages connected to the first and second hydraulic servos, a speed-change valve, a timing valve and a manual valve. Based on a signal determined by the running speed of the vehicle the speed-change valve controls the flow of pressurized oil to the first hydraulic servo. The timing valve is in communication with both the first and second hydraulic servos and opens and closes flow to the second hydraulic servo. The timing valve includes a valve housing which forms separate oil chambers and a valve body which is displaceable within the housing for controlling the flow of oil therethrough. The manual valve has a number of positions for selecting the desired speed condition of the vehicle and the oil passages provide communication between the manual valve and the timing valve. Ordinarily, when operating under high speed conditions and the pressurized oil supplied to the first servo drops below a predetermined value corresponding to the engine output of the vehicle, the valve body is displaced so that pressurized oil is supplied to the second hydraulic servo through one of the oil chambers in the timing valve. However, if the valve body becomes stuck the usual supply of pressurized oil cannot be directed to the second servo and to assure that proper low speed conditions are provided, pressurized oil is supplied to the timing valve through the manual valve and then is conveyed through the proper oil chamber and oil passage to the second hydraulic servo.
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