Patent ID: 8291702
Filing Date: 2012-10-23
Classification: F16H

Abstract:
1. A hydrostatic transmission comprising: a pair of main fluid passages; a fluid charging passage for supplying fluid to one of the main fluid passages; a hydraulic motor; and a hydraulic pump fluidly connected to the hydraulic motor via the pair of main fluid passages, wherein during driving of the hydraulic pump, one of the main fluid passages is hydraulically higher-pressurized, and the other of the main fluid passages is hydraulically lower-pressurized, the hydraulic pump including: a pump shaft; a cylinder block fixed on the pump shaft so as to be rotatable integrally with the pump shaft so that an axis of the pump shaft serves as a rotary axis of the cylinder block, wherein the cylinder block includes first and second end surfaces opposite to each other in the axial direction of the pump shaft, the first end surface being nearer to the pair of main fluid passages than the second end surface, wherein the cylinder block includes a plurality of cylinders disposed around the pump shaft, and wherein the cylinder block includes a plurality of cylinder ports extended from the respective cylinders and opened at the first end surface of the cylinder block; a plurality of plungers fitted in the respective cylinders of the cylinder block and projecting at tips thereof outward from the second end surface of the cylinder block; a movable swash plate having a slanted surface against which the tips of the plungers abut; and a port member interposed between the cylinder block and the pair of main fluid passages, wherein the port member includes a surface against which the first end surface of the cylinder block slidably rotatably abuts, wherein the port member includes a pair of kidney ports fluidly connected to the respective main fluid passages and opened at the surface of the port member, wherein the port member includes a charge port fluidly connected to the fluid charging passage and opened at the surface of the port member, wherein during rotation of the cylinder block of the hydraulic pump, the cylinder ports are opened one after another to the pair of kidney ports and the charge port, so that one of the kidney ports is defined as a delivery port via which fluid is delivered from the cylinders to the main fluid passage to be hydraulically higher-pressurized, the other of kidney ports is defined as a suction port via which fluid is sucked from the main fluid passage to be hydraulically lower-pressurized to the cylinders, and fluid is delivered from the cylinders to the fluid charging fluid passage via the charge port, and wherein, when viewed in the axial direction of the pump shaft, the cylinder ports are aligned on the first end surface of the cylinder block on a circle centered on the axis of the pump shaft, and the pair of kidney ports and the charge port are aligned on the surface of the port member on a circle corresponding to the circle on which the cylinder ports are aligned.