Hydraulic mechanical transmission

A hydraulic mechanical transmission comprising:

• a first hydraulic unit having a first shaft;
• a second hydraulic unit connected in hydraulic fluid communication with the first hydraulic unit, the second hydraulic unit including a second shaft and a rotating group that is coupled to the second shaft so as to rotate in unison with the second shaft about an axis defined by the second shaft, the rotating group including a cylinder block that defines a plurality of axial cylinders, the rotating group also including pistons mounted to slide within the axial cylinders, the second hydraulic unit further including a rotatable component that is rotatable relative to the second shaft about the axis of the second shaft, the rotatable component including a swashplate that opposes ends of the pistons;
• at least one of the first and second hydraulic units having variable displacement;
• and
• a mechanical torque transfer arrangement for transferring torque between the first shaft and the rotatable component of the second hydraulic unit;
• wherein, in use, one of the first and second hydraulic units operates as a hydraulic pump and the other of the first and second hydraulic units operates as a hydraulic motor;
• wherein the ends of the pistons include shoes that travel along an arcuate path around the swashplate as relative rotation occurs between the rotatable component and the rotating group about the axis of the second shaft;
• and
• wherein the second hydraulic unit is connected in hydraulic fluid communication with the first hydraulic unit by high and low pressure lines, wherein the rotatable component also includes a commutation structure for providing fluid communication between the high and low pressure lines and the axial cylinders of the rotating group while maintaining separation between the high and low pressure lines, wherein the commutation structure maintains fluid communication between the high pressure line and the rotating group regardless of a rotational position of the rotatable component about the axis defined by the second shaft, the commutation structure also maintaining fluid communication between the low pressure line and the rotating group regardless of a rotational position of the rotatable component about the axis defined by the second shaft, and wherein the commutation structure is adapted to rotate in unison with the swashplate relative to the second shaft such that in operation, a rotational position of the commutation structure about the axis of the second shaft does not change relative to the swashplate.

A hydraulic mechanical transmission comprising:

• a first hydraulic unit having a first shaft coupled to a first rotating group and having a variable displacement;
• a second hydraulic unit having a second shaft coupled to a second rotating group and having a fixed displacement, wherein the second hydraulic unit is connected in hydraulic fluid communication with the first hydraulic unit;
• and
• a mechanical torque transfer arrangement for transferring torque between the first shaft and the second hydraulic unit;
• wherein, in use, one of the first and second hydraulic units operates as a hydraulic pump and the other of the first and second hydraulic units operates as a hydraulic motor;
• wherein the first and second rotating groups each include a swashplate opposing a plurality of axial pistons slidable within a plurality of axial cylinders, wherein the angle of the swashplate of the first rotating group is movable relative to an axis of the first shaft such that the first hydraulic unit has variable displacement, and wherein the angle of the swashplate of the second rotating group is fixed relative to an axis of the second shaft such that the second hydraulic unit has fixed displacement.