Parallel hydromechanical underdrive transmission

A hydromechanical transmission for providing a continuously variable speed/torque driving connection between a prime mover and ground engaging members of a vehicle, comprising:

• a housing having a make-up pump and internal cavities for holding operating assemblies of said transmission;
• an axial piston pump having a rotating element and a non-rotating element, said rotating element having a center of mass and an axis of pump rotation that passes through said center of mass;
• a first journal in said housing in which said non-rotating pump element is mounted for tilting about a first journal tilting axis, said first tilting axis lying transverse to said axis of pump rotation;
• an axial piston motor having a rotating motor element and a non-rotating motor element, said rotating motor element having a center of mass and an axis of rotation that passes through said rotating motor element center of mass;
• a second journal in said housing in which said non-rotating motor element is mounted for tilting about a second journal tilting axis, said second tilting axis lying transverse to said axis of rotation;
• said pump and said motor disposed side-by-side in said housing with said axes of rotation approximately parallel to each other;
• a stationary manifold fixed to said housing, having one surface in contact with said rotating pump element and having fluid passages opening in said one surface in fluid communication with said pump cylinders through a pump/manifold interface;
• said stationary manifold having a second surface in contact with said rotating motor element and having fluid passages opening in said second surface in fluid communication with said motor cylinders through a motor/manifold interface;
• said stationary manifold having internal fluid passages for conveying fluid pressurized in said pump directly to said motor, and for conveying spent fluid displaced from said motor back to said pump;
• a tilt control coupled to apparatus attached to said non-rotating pump element and to said non-rotating motor element is mounted in said housing for tilting said non-rotating elements about said first and second tilting axes;
• an epicyclic gear set having a sun gear coupled to an input shaft of said transmission, a ring gear coupled to said rotating element of said pump, and a planet carrier carrying a plurality of planet gears engaged with and between said sun gear and said ring gear, said planet carrier having a connected spur gear that is coupled to said rotating element of said motor and to an output shaft for driving said ground engaging members of said vehicle;
• whereby reaction torque from said pump is summed with torque from said motor in said output spur gear for output through said output shaft.