Patent ID: 6880448

Claim:
A hydrostatic transmission, comprising: a hydraulic pump and a hydraulic motor; a center section having a pump running surface on which the hydraulic pump rotates and a motor running surface on which the hydraulic motor rotates, the center section having porting by which the hydraulic pump and the hydraulic motor are in fluid communication; wherein the porting terminates in a pair of equidistantly spaced, generally arcuate shaped openings on the pump running surface, the pump running surface includes a plurality of generally v-shaped grooves extending from each of the ends of the generally arcuate shape openings, and each of the grooves has an arc-length that is approximately 24.5 percent of the arc-length of the average distance between the ends of the generally arcuate shaped openings; and wherein the hydraulic pump comprises a pump cylinder block having seven pump cylinder bores in which seven pump pistons are carried and wherein each of the grooves has an arc length that is approximately 31 percent of the average diameter of at least one of the pump cylinder bores.