| 摘要 |
A changeover valve can be switched to a state in which a second solenoid valve of normally-open type to normally control a second speed-change control valve for a high speed transmission train controls a first speed-change control valve for a low speed transmission train. An oil passage to switch the changeover valve to the state in which the first speed-change control valve is controlled by the second solenoid valve is connected to an oil passage on an output side of the second solenoid valve at a P or R position of a manual valve. When a system failure has occurred while a vehicle is running forward in that D, M position of the manual valve which is a forward running range, the high-speed transmission train is established by a high signal pressure of the second solenoid valve. At the time of the system failure, if the manual valve is switched to the R position which is a reverse running position or to the P position which is a parking position, the manual valve is switched to the above-described state by the high signal pressure of the second solenoid valve. By then switching the manual valve to the D, M position, a low-speed transmission train is established.
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