Automatic transmission with overdrive inhibitor

Abstract

An automatic transmission for motorcar of the type including a main transmission and an auxiliary transmission is disclosed. The auxiliary transmission has a plurality of speed changing stages and when it assumes a certain lower speed stage, any speed changing to higher speed stage is inhibited in the main transmission. The main transmission is provided with a solenoid valve which makes it possible to carry out speed changing to higher speed stage when it is turned on, while the auxiliary transmission is provided with a hydraulic control device which is communicated with a hydraulic servo via a hydraulic passage. The hydraulic servo is operatively associated with a speed reduction frictional engagement element which allows the auxiliary transmission to assume a certain lower speed stage. The solenoid valve is electrically connected to a pressure switch which is so constructed that it is turned off when the hydraulic servo is supplied with hydraulic oil and it is turned off when hydraulic pressure is released from the hydraulic servo. When the auxiliary transmission assumes a certain lower speed stage, the hydraulic servo is supplied with hydraulic oil and the solenoid valve is turned off. Thus, any speed changing to higher speed stage is inhibited in the main transmission.

Dependencies are inferred from the claim text.