A pump operation piston biased by a neutral spring mechanism and a larger volume operation spring biased by a larger volume operation spring in a larger volume direction operatively move pump and motor volume adjusting members, respectively, is provided. A first pressure control valve commonly controls supply-discharge of pressure oil that presses the pump operation piston in a first slide direction and the motor operation piston in a smaller volume direction. A second pressure control valve controls supply-discharge of pressure oil that presses the pump operation piston in a second slide direction. Biasing forces of the neutral spring mechanism and the larger volume operation spring are so set that, after the pump operation piston is moved in the first slide direction by a predetermined distance, the motor operation piston starts moving.

A hydrostatic transaxle includes: a casing that is provided with an openable and closable filter insertion port and is filled with hydraulic oil; a hydraulic continuously variable transmission that is arranged inside the casing; a filter holding member that includes a support base that is a hollow cylindrical portion and oil-tightly partitions an inside of a cylinder and an outside of the cylinder, and a filter connection port that is a hollow cylindrical portion extending from a peripheral side surface of the support base and communicating with the inside of the cylinder, the support base communicating the inside of the cylinder to the port, and arranged between the center section and the casing facing the port; and a filter body that is freely inserted to and removed from the casing via the filter insertion port.

A hydrostatic transaxle includes: a casing that is provided with an openable and closable filter insertion port and is filled with hydraulic oil; a hydraulic continuously variable transmission that is arranged inside the casing; a filter holding member that includes a support base that is a hollow cylindrical portion and oil-tightly partitions an inside of a cylinder and an outside of the cylinder, and a filter connection port that is a hollow cylindrical portion extending from a peripheral side surface of the support base and communicating with the inside of the cylinder, the support base communicating the inside of the cylinder to the port, and arranged between the center section and the casing facing the port; and a filter body that is freely inserted to and removed from the casing via the filter insertion port.

A hydraulic motor-driven fuel boost pump includes redundant safeguards against overspeeding the impellers. A flow limiter limits the amount of hydraulic fluid that can be supplied to the hydraulic motor, thereby limiting the torque that can be applied to the impellers. A control valve also transitions between a non-restrictive operating state and a restrictive operating state. In the restrictive operating state the control valve regulates the displacement of the swash plate when in the non-restrictive operating state. The control valve does not counter the bias of the swash plate control spring when in the restrictive operating state.

A hydromechanical continuously variable speed transmission is provided. The hydromechanical continuously variable speed transmission can include: the HST 10 in which the planetary gear mechanism 11 is housed in the planetary gear support case 71 mounted on a face of the center section 35 to form the HMT unit 100, the face being on the side opposite to the side on which the HST case 23 is mounted, and the HMT unit 100 is further provided with the housing mounting face 35d for fixing the HMT unit 100 to the housing 91 of the traveling power transmission mechanism 89, the housing mounting face 35d being provided on the center section 35 so as to surround the outer circumference of the mounting face 71a on which the planetary gear support case 71 is mounted.

A hydromechanical continuously variable speed transmission is provided. The hydromechanical continuously variable speed transmission can include: the HST 10 in which the planetary gear mechanism 11 is housed in the planetary gear support case 71 mounted on a face of the center section 35 to form the HMT unit 100, the face being on the side opposite to the side on which the HST case 23 is mounted, and the HMT unit 100 is further provided with the housing mounting face 35d for fixing the HMT unit 100 to the housing 91 of the traveling power transmission mechanism 89, the housing mounting face 35d being provided on the center section 35 so as to surround the outer circumference of the mounting face 71a on which the planetary gear support case 71 is mounted.

A port plate assembly of a hydraulic unit includes a port plate and a journal bearing. The port plate includes a fixed-speed interface side having a fixed-speed interface surface, and a variable-speed interface side having a variable-speed interface surface. A plurality of kidney-shaped apertures is defined at a kidney pitch diameter about a central bore of the port plate between the fixed-speed interface surface and the variable-speed interface surface. The port plate also includes control cylinder interface formed at a control cylinder radial offset from a central axis of the central bore, where a ratio of the control cylinder radial offset to the kidney pitch diameter is between 1.629 and 1.639. The journal bearing is installed in the central bore of the port plate, where the journal bearing provides an interface for a fixed-speed shaft and a variable-speed shaft of the hydraulic unit.

A port plate assembly of a hydraulic unit includes a port plate and a journal bearing. The port plate includes a fixed-speed interface side having a fixed-speed interface surface, and a variable-speed interface side having a variable-speed interface surface. A plurality of kidney-shaped apertures is defined at a kidney pitch diameter about a central bore of the port plate between the fixed-speed interface surface and the variable-speed interface surface. The port plate also includes control cylinder interface formed at a control cylinder radial offset from a central axis of the central bore, where a ratio of the control cylinder radial offset to the kidney pitch diameter is between 1.629 and 1.639. The journal bearing is installed in the central bore of the port plate, where the journal bearing provides an interface for a fixed-speed shaft and a variable-speed shaft of the hydraulic unit.

A micro-traction drive unit according to the present invention includes an inner ring, an outer ring, a plurality of rolling elements, a retainer, a micro-traction drive case and a power-transmitting shaft coaxial with the inner ring and incapable of relative rotation around an axis to the retainer. An opposite end of the power-transmitting shaft from the inner ring forms an input end operatively connected to a driving source. An input end of the pump shaft is detachably connected to a central hole of the inner ring in a state incapable of relative rotation around the axis via the access opening of the micro-traction drive case by connecting the micro-traction drive case to the HST case so as to surround the input end of the pump shaft of the HST.

A transaxle for use as a drive apparatus of a vehicle is provided. The transaxle includes a main housing joined to a gear housing to enclose a transmission and a reduction gear set. The transmission includes a pump assembly and a motor assembly arranged in a parallel configuration on one side of a center section. A charge pump is contained within a pocket on an opposing side of the center section. A charge pump cover assembly secures the charge pump in the pocket and has a charge relief assembly that extends into a void volume defined by a ring gear of the gear reduction set. The gear reduction set drives an axle extending from the gear housing.