This invention relates generally to hydrostatic transaxles.
Hydrostatic transaxles (“HSTs”), including integrated hydrostatic transaxles (“IHTs”), are known in the art and are more fully described in, among others, U.S. Pat. No. 5,314,387, which is incorporated herein by reference in its entirety. Generally, an HST includes a center section or the like on which is mounted a hydraulic pump and a hydraulic motor. The hydraulic pump and the hydraulic motor each carry a plurality of reciprocating pistons that are in fluid communication through porting formed in the center section. As the hydraulic pump rotates, the pump pistons move axially as they bear against an adjustable swash plate where the degree of axial movement depends upon the angular orientation of the swash plate. Axial movement of the pump pistons forces a hydraulic fluid through the porting, which forces the motor pistons against a thrust bearing to thereby rotate the hydraulic motor. As the hydraulic motor rotates, hydraulic fluid is returned to the hydraulic pump through the porting. In this manner, the rotation of the hydraulic pump is translated to the hydraulic motor and the rotation of the hydraulic motor may be used to drive one or more axles of a riding lawn mower, small tractor, or the like.
Zero-turn, hydrostatic transaxles (HZTs) are also known in the art. Generally, an HZT is utilized in connection with a vehicle to provide for the independent control of each of the drive wheels of the vehicle. By way of example, HZTs are described in U.S. Pat. Nos. 5,078,222 and 6,283,235 which are incorporated herein by reference in their entirety. Additionally, Eaton has developed and marketed HZTs as their models 771 and 781. The Eaton model 771 is an assembly with one pump and one motor where two Eaton model 771 assemblies, a right and a left, are required for zero turn drive. The Eaton model 781 consists of two units similar to the Eaton model 771 but joined together to make one assembly.