Concentric radial piston transmission with flexible cam ring

Abstract

An infinitely variable hydrostatic transmission includes a radial piston pump having outwardly opening pump cylinders containing radial pump pistons, and a radial piston motor, arranged concentrically around the pump, having inwardly opening motor cylinders containing radial motor pistons. Fluid passages in the transmission intermittently connect the pump cylinders and the motor cylinders in a closed fluid flow circuit. A flexible cam ring is radially interposed between the pump and the motor in load bearing relation to the pump pistons on an inside surface of the cam ring, and in load bearing relation to the motor pistons on an outside surface of the cam ring. An input shaft is coupled in torque driving relation to the pump, and an output shaft is coupled in torque driven relation through a commutator plate to the cam ring. An adjustment mechanism is provided for adjusting the cam ring to a desired radial profile to set the transmission to a desired transmission ratio. A fluid distribution system has passages, including kidney shaped slots through the comutator plate, for fluid flow of fluid pressurized in the pump cylinders to the motor cylinders during a power stroke of the pump and motor pistons, and for fluid flow of spent fluid from the motor cylinders to the pump cylinders during a suction phase of the stroke of the pump and motor pistons. A control system adjusts the profile of the cam ring to control the transmission ratio, and a pressure compensator automatically reduces the transmission ratio when the resistance torque on the output shaft exceeds a predetermined value, as when the vehicle is ascending a steep hill.