Safeguard for shift control for auxiliary gearing of automatic transmission.

摘要

In an automatic transmission including an auxiliary gearing drivingly connected to a main gearing, the auxiliary gearing is shiftable between a high gear position wherein a direct clutch is engaged and a reduction brake is disengaged and a low gear position wherein the direct clutch is disengaged and the reduction brake is engaged. An one-way clutch is arranged to complement the action of the reduction brake. A shift valve which controls the auxiliary gearing is subject to a solenoid hydraulic pressure generated by an electro-hydraulic transducer including a solenoid. A reverse-select hydraulic pressure, generated by a manual valve when the manual valve is placed at reverse drive position, is directly applied to the shift valve to hold the shift valve at a low gear position wherein the direct clutch is disengaged and the reduction brake is engaged to condition the auxiliary gearing in the low gear position thereof.