| 摘要 |
A back-up device for an electronic control system of an automatic transmission in an automotive vehicle, of the type including at least first and second frictionally engaging elements hydraulically actuable, respectively, for establishing a first speed ratio for lower speed running of the vehicle and a second speed ratio for higher speed running of same, selector valves adapted to selectively assume first and second positions, respectively, for connecting the first and second frictionally engaging elements to an operating fluid source, electromagnetic valves for driving the selector valves to select the first position or the second position, and an electronic control unit for selectively energizing and deenergizing the electromagnetic valves in accordance with a predetermined gear shifting manner responsive to electrical signals indicative of the vehicle speed and the engine output. The back-up device comprises a vehicle speed sensing device for generating an output signal having a value thereof increasing as the vehicle speed increases, and a control mechanism for causing the selector valves to assume the second position, irrespective of the operation of the electromagnetic valves, when the value of the output signal from the vehicle speed sensing device exceeds a predetermined value, thereby prohibiting establishment of the first speed ratio in the event of failure in the electronic control system during high running of the vehicle. |
