Direct-coupling control system for fluid gear in automatic vehicular transmission

Claim 1

In a direct-coupling control system for a fluid gear in an automatic vehicular transmission, having a fluid gear provided with input and output members; a direct-coupling mechanism capable of connecting said input and output members of said input and output members of said fluid gear mechanically and directly by a locking force which is determined on the basis of a function of a difference between a working pressure and an internal pressure in said fluid gear; and a control means provided between a pressure supply source and said direct-coupling mechanism and adapted to control the working pressure, the improvement wherein there is provided a means for controlling the internal pressure in said fluid gear so as to reduce the same in proportion to an increase in a variable selected from the group consisting of vehicle speed and engine output, said internal pressure control means comprising a pressure retainer valve in an intermediate portion of an oil passage connecting said fluid gear with an oil tank, said pressure retainer valve having a valve body urged in a valve-opening direction by the internal pressure in said fluid gear and in a valve-closing direction by an urging member, and a tubular passage for introducing a fluid pressure representative of the selected variable from the group consisting of vehicle speed and engine output and connected to a pressure working chamber to move said valve body in the valve-opening direction.