A power transmission assembly for a vehicle with prime mover, prime mover output shaft, and right and left traveling devices, comprises a power distribution unit that receives rotary power from the prime mover output shaft and distributes it between right and left transmission units, which each include: a center section with a closed fluid circuit, a lateral first portion, and a second portion perpendicular thereto; a hydraulic pump mounted on the first portion such that a pump shaft is parallel to the prime mover output shaft; a hydraulic motor on the second portion fluidly connected to the hydraulic pump via the closed fluid circuit, having a lateral motor shaft; and a speed reduction device on a distal side of the hydraulic motor that transmits power from the hydraulic motor to the right or left traveling device.

A hydrostatic assembly employing a 1.sup.st hydraulic piston drive unit is described in which the output is increased without using additional servo assemblies by incorporating a 2.sup.nd hydraulic piston drive unit, coupling the drive shafts of both drive units together, and employing a common means to simultaneously adjust displacement of both the 1.sup.st and 2.sup.nd hydraulic piston drive units. In such embodiments, coupling the drive shafts together such that the 1.sup.st hydraulic piston drive unit is rotationally offset with respect to the 2.sup.nd hydraulic piston drive allows for a reduction in the amplitude of pressure pulsations associated with the hydrostatic assembly output, thereby smoothing out operation and improving durability.

A hydrostatic assembly employing a 1.sup.st hydraulic piston drive unit is described in which the output is increased without using additional servo assemblies by incorporating a 2.sup.nd hydraulic piston drive unit, coupling the drive shafts of both drive units together, and employing a common means to simultaneously adjust displacement of both the 1.sup.st and 2.sup.nd hydraulic piston drive units. In such embodiments, coupling the drive shafts together such that the 1.sup.st hydraulic piston drive unit is rotationally offset with respect to the 2.sup.nd hydraulic piston drive allows for a reduction in the amplitude of pressure pulsations associated with the hydrostatic assembly output, thereby smoothing out operation and improving durability.

A transaxle for a vehicle is provided, the transaxle including a pump assembly having an input shaft extending from a housing and a pump disposed on a first hydraulic mounting member attached to the pump housing. The pump may be driven by an electric motor mounted on the vehicle. A motor assembly in a separate housing is also provided, and the transaxle may use a pair of dual planetary gear reduction mechanisms driven by a motor output shaft, each reduction mechanism driving an axle driving one of a pair of driven wheels of the vehicle. The axes of rotation of the pump shaft, motor shaft, electric motor output and the axles may all be located on a common plane to provide a compact unit.

A transaxle for a vehicle is provided, the transaxle including a pump assembly having an input shaft extending from a housing and a pump disposed on a first hydraulic mounting member attached to the pump housing. The pump may be driven by an electric motor mounted on the vehicle. A motor assembly in a separate housing is also provided, and the transaxle may use a pair of dual planetary gear reduction mechanisms driven by a motor output shaft, each reduction mechanism driving an axle driving one of a pair of driven wheels of the vehicle. The axes of rotation of the pump shaft, motor shaft, electric motor output and the axles may all be located on a common plane to provide a compact unit.

A hydraulic mechanical transmission includes a first hydraulic unit having a first shaft and a second hydraulic unit having a second shaft. The second hydraulic unit is connected in hydraulic fluid communication with the first hydraulic unit by high and low pressure lines. At least one of the first and second hydraulic units has variable displacement. A mechanical torque transfer arrangement transfers torque between the first shaft and the rotatable component of the second hydraulic unit. 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.

A hydraulic mechanical transmission includes a first hydraulic unit having a first shaft and a second hydraulic unit having a second shaft. The second hydraulic unit is connected in hydraulic fluid communication with the first hydraulic unit by high and low pressure lines. At least one of the first and second hydraulic units has variable displacement. A mechanical torque transfer arrangement transfers torque between the first shaft and the rotatable component of the second hydraulic unit. 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.

A hydraulic mechanical transmission includes a first hydraulic unit having a first shaft and a second hydraulic unit having a second shaft. The second hydraulic unit is connected in hydraulic fluid communication with the first hydraulic unit by high and low pressure lines. A valve having a variable orifice is positioned along the high and low pressure lines, and at least one of the first and second hydraulic units has a variable displacement. A mechanical torque transfer arrangement transfers torque between the first shaft of the first hydraulic unit and a rotatable component of the second hydraulic unit. 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.

A hydraulic mechanical transmission includes a first hydraulic unit having a first shaft and a second hydraulic unit having a second shaft. The second hydraulic unit is connected in hydraulic fluid communication with the first hydraulic unit by high and low pressure lines. A valve having a variable orifice is positioned along the high and low pressure lines, and at least one of the first and second hydraulic units has a variable displacement. A mechanical torque transfer arrangement transfers torque between the first shaft of the first hydraulic unit and a rotatable component of the second hydraulic unit. 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.

A hydraulic mechanical transmission includes a first hydraulic unit having a first shaft and a second hydraulic unit having a second shaft. The second hydraulic unit is connected in hydraulic fluid communication with the first hydraulic unit by high and low pressure lines. A mechanical torque transfer arrangement transfers torque between the first shaft of the first hydraulic unit and a rotatable housing of the second hydraulic unit. One of the first and second hydraulic units operates as a hydraulic pump and the other operates as a hydraulic motor, and both of the first and second hydraulic units have variable displacement.