Compact coaxial piston transmission

Abstract

A hydrostatic axial piston transmission having a continuously variable transmission ratio includes an axial piston pump driven by an input shaft, the pump having an annular pump cylinder block with a ring of cylinders in which pump pistons reciprocate to pressurize and displace fluid from the pump cylinders. The pump is also coupled to an output shaft for conveying reaction torque from the input shaft directly to the output shaft as a first output torque component. An axial piston hydraulic motor has an annular motor cylinder block with a ring of motor cylinders in which motor pistons reciprocate in a power stroke to apply output torque to the output shaft, and a displacement stroke in which spent fluid is displaced from the motor cylinders for return to the pump cylinders. The pump cylinder block is concentrically disposed within the annulus of the motor cylinder block, and the input shaft and the output shaft lie on a longitudinal axis through the annulus. The pump cylinder block lies against a flat surface which is tilted at an angle with respect to the longitudinal axis of the machine, so that rotation of the pump cylinder block relative to the flat surface causes the pump pistons to reciprocate and displace fluid under pressure through commutating passages to the motor. Rotation of the input shaft drives the pump to displace pressurized fluid through pressure passages while also transmitting reaction torque to the output shaft. The fluid pressurized by the pump energizes the motor to produce a second component of output torque in the output shaft.