JPH0527780B

PURPOSE:To prevent a fastening means from slipping and seizing due to start and rapid acceleration in a uniform high speed range, by providing a control means for disengaging the fastening means in accordance with a signals from a vehicle speed sensor and a range switch when the vehicle speed is lower than a set vehicle speed in the uniform high speed range. CONSTITUTION:There is provided a control means 8 which receives a signal from a range switch 7 accodiated with a vehicle speed sensor 6 and a shift lever, and which selectively drive any one of frictionally fastening means 3 in a speed reduction gear mechanism 2 through a hydraulic control circuit 4 in accordance with a previously set term. With this arrangement, when a start or rapid acceleration is carried out during the speed reduction gear being shifted to a uniform high speed range, the frictionally fastening means 3 of the present gear stage is released, and warning is given to the driver while a start and a rapid acceleration become impossible. Accordingly, it is possible to prevent the frictionally fastening means 3 having a small torque capacity in a high speed stage from slipping and seizing in association with the former, thereby it is possible to prevent incomplete operation and lowered durability of the speed reduction gear, etc.