CONTROL DEVICE FOR AUTOMATIC TRANSMISSION

PURPOSE:To enable a multiple speed change gear mechanism to function as intended by switching a overdrive speed change mechanism to function in the case when valve means for controlling speed change operation of said multiple speed change gear fail. CONSTITUTION:In normal speed changing control, a control means 200 makes a multiple speed change gear mechanism 20 makes speed change operation between 1st speed step and 2nd speed step and between 2nd speed step and 3rd speed step by on-off-controlling of 1st and 2nd solenoid valves 71, 72, and also obtains 4th speed step from the state of 3rd step by switching 3rd solenoid valve 73 off and bring an overdrive speed changing gear mechanism 40 in operation. In the case when, for example, a failure detecting means 205 detects that 5th solenoid valve 106 has failed causing changing over to 3rd speed step to become impossible, an alternate 3rd speed step (3') can be obtained as the result of multiplication of respective reduction ratios, by switching said solenoid valve 73 off while solenoid valve 72 is on and bringing said overdrive speed changing gear mechanism 40 in operation, leaving said multiple speed change gear mechanism 20 fixed on 2nd speed step, thus intended speed changing becomes possible even when the related valve mechanism fails.