Patent ID: 9416859
Filing Date: 2016-08-16
CPC Classification: F16H

Claim Text:
1. A hydrostatic stepless transmission comprising: a hydraulic pump including an axial pump shaft, a first plunger block and plungers, wherein the first plunger block is fixed on the pump shaft so as to have an outer peripheral surface extending circumferentially and parallel to the pump shaft, and wherein the plungers of the hydraulic pump are axially reciprocally slidably fitted into respective plunger chambers formed in the first plunger block; a hydraulic motor including an axial motor shaft, a second plunger block and plungers, wherein the second plunger block is fixed on the motor shaft so as to have an outer peripheral surface extending circumferentially and parallel to the motor shaft, and wherein the plungers of the hydraulic motor are axially reciprocally slidably fitted into respective plunger chambers formed in the second plunger block; a closed fluid circuit fluidly connecting the hydraulic pump to the hydraulic motor, wherein the closed fluid circuit includes first and second main fluid passages interposed between the hydraulic pump and the hydraulic motor; and a center casing into which the first and second plunger blocks are inserted so that the center casing includes an inner peripheral surface facing the outer peripheral surfaces of the respective first and second plunger blocks, wherein plunger ports are formed in each of the first and second plunger blocks so as to be connected to the respective plunger chambers and so as to be open at the outer peripheral surface of each of the first and second plunger blocks, and wherein each of the first and second main fluid passages includes a pair of peripheral grooves and an encased fluid duct connecting the peripheral grooves to each other, whereby the peripheral grooves are formed on the inner peripheral surface of the center casing so as to face the respective outer peripheral surfaces of the respective first and second plunger blocks, and whereby the encased fluid duct is formed in the center casing so as to be fluidly connected to the respective plunger ports of the respective first and second plunger blocks via the respective peripheral grooves.