Power train with infinitely variable ratio transmission

A power train, particularly for use in motor vehicles, comprising an infinitely variable ratio transmission including an input portion having a first adjustable pulley, an output portion having a second adjustable pulley, an endless flexible torque transmitting element trained over said pulleys, and first and second primary adjusting units arranged to determine the extent of torque transmitting engagement between said flexible element and the respective pulleys, said primary adjusting units being actuatable by a fluid at a pressure which is variable at least as a function of torque to be transmitted by the transmission;

• means for generating said pressure including a hydromechanical torque sensor arranged to transmit at least a portion of torque to one of said input and output portions and including a plenum chamber arranged to receive pressurized fluid from a source and having an outlet, and a regulating valve for controlled evacuation of fluid from said plenum chamber by way of said outlet, said regulating valve having at least two components movable relative to each other in dependency upon the magnitude of torque being applied between said input and output portions to maintain the fluid in said plenum chamber at a pressure which is a function at least of the applied torque and which is transmittable to said adjusting units;
• transmission ratio changing means including an additional adjusting unit for at least one of said pulleys, said additional adjusting unit being arranged to operate in parallel with the respective primary adjusting unit and to receive fluid from said source;
• a ratio selecting valve connected between said source and said additional adjusting unit;
• and a pressure regulating valve connected between said source and said plenum chamber in parallel with said ratio selecting valve to influence the pressure of fluid at least at an inlet of said ratio selecting valve.