Hydromechanical automotive transmission with brake circuit - has pressure to brake piston steplessly adjustable by electromagnet controlling relief valve

A first epicyclic gear train divides the input power between a first path, containing a hydrodynamic converter and a second, purely mechanical one coupled to the output shaft. A second epicyclic gear train between the converter and output shaft has a hydraulic brake holding one of its members stationary, whose actuating piston is subjected to the fluid pressure at the converter outlet. An auxiliary pump supplies the system with working and control fluid, while a brake holds the converter impeller so as to transmit power solely via the mechanical path. The piston is stepped, with two pressure faces acting in the same direction and hydraulically fully insulated from each other. Both can be subjected to the converter outlet pressure. A relief valve in a passage from the converter chamber periphery to the piston determines the outlet prrssure, while an inlet admits air to the chamber. The operating pressure of the relief valve is steplessly adjusted by an electromagnet (52).