Parallel hydromechanical underdrive transmission

Abstract

A parallel hydromechanical continuously variable transmission has a housing ( ) that holds a make-up pump ( ), and has internal cavities for holding operating assemblies of the transmission, including an axial piston pump ( ) and an axial piston motor ( ). The pump ( ) and motor ( ) each has a rotating element ( ) and a non-rotating element ( ). Each non-rotating pump element is mounted for tilting movement on trunnions ( P) in its own respective pair of mounting journals in the housing ( ). The tilting axes of the non-rotating elements ( ) lie transverse to the axes of rotation of the rotating elements ( ). The pump ( ) and the motor ( ) are disposed side-by-side in the housing ( ) with the axes of rotation approximately parallel to each other. A stationary manifold ( ), fixed to the housing ( ), has one surface in contact with the rotating pump element ( P) and a second surface in contact with the rotating motor element ( M). Fluid passages ( ) open in the two surfaces in fluid communication with the pump and motor cylinders ( ) through a pump/manifold interface. Internal fluid passages ( ) in the stationary manifold ( ) convey fluid pressurized in the pump ( ) directly to the motor ( ), and convey spent fluid displaced from the motor back to the pump. The transmission ratio is controlled by the tilt angle of the non-rotating pump and motor elements ( ). A tilt angle control apparatus ( ) attached to the housing ( ) and to the non-rotating pump and motor elements ( ) governs that tilt angle.