Hydrostatic stepless transmission

Patent metadata

Field	Value
Publication number	US-9416859-B2
Application number	US-201313863843-A
Country	US
Kind code	B2
Filing date	Apr 16, 2013
Priority date	Apr 17, 2012
Publication date	Aug 16, 2016
Grant date	Aug 16, 2016

Abstract

A hydrostatic stepless transmission (“HST”) includes a center casing into which a plunger block of a hydraulic pump and a plunger block of a hydraulic motor are inserted. Plunger ports are open and aligned peripherally on an outer peripheral surface of each plunger block. A pair of main fluid passages of a closed fluid circuit fluidly connecting the hydraulic pump to the hydraulic motor are formed in opposite side portions of the center casing. Each of the main fluid passage includes peripheral grooves formed on an inner peripheral surface of the center casing so as to face the plunger ports of the respective plunger blocks, and includes an axial fluid duct formed to be interposed between the peripheral grooves. A bearing gap is provided between the inner peripheral surface of the center casing and the outer peripheral surface of the plunger block so as to cause a dynamic pressure action of fluid.

First claim

What is claimed is:

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.

2. The hydrostatic stepless transmission according to claim 1 , further comprising:
a bearing gap causing an action of dynamic pressure of fluid,
wherein the bearing gap is provided between the inner peripheral surface of the center casing and the outer peripheral surface of each of the first and second plunger blocks so that the center casing fluidly supports the first and second plunger blocks.

3. The hydrostatic stepless transmission according to claim 2 , further comprising;
a dynamic pressure groove provided on at least one of the outer peripheral surfaces of the first and second plunger blocks and the inner peripheral surface of the center casing so as to provide the bearing gap.

4. The hydrostatic stepless transmission according to claim 1 , further comprising:
a partition provided in the center casing between the first and second plunger blocks,
wherein end portions of the respective first and second plunger blocks toward the partition are provided with respective openings at end surfaces thereof facing the partition so as to supply pressurized fluid from the plunger chambers onto the partition.

5. The hydrostatic stepless transmission according to claim 1 , further comprising:
a bearing interposed between the center casing and at least one of the first and second plunger blocks so as to correspond to radial and thrust forces generated in the at least one of the first and second blocks.

6. The hydrostatic stepless transmission according to claim 1 ,
wherein during a normal rotation of the motor shaft, the first main fluid passage is higher-pressurized and the second main fluid passage is lower-pressurized, and
wherein a pressure balancing groove is branched from at least one of the peripheral grooves of the first main fluid passage so as to extend adjacent to at least one of the peripheral grooves of the second main fluid passage.

7. The hydrostatic stepless transmission according to claim 1 , further comprising:
shoes provided on tips of the respective plungers projecting from the first and second plunger blocks and contacting a swash plate of the hydraulic pump and a swash plate of the hydraulic motor, respectively; and
a spring disposed coaxially to each of the pump shaft and the motor shaft so that the shoes are pressed against each of the swash plates by a biasing force of the spring.

8. The hydrostatic stepless transmission according to claim 1 , further comprising:
a valve unit including a fluid duct block, a pair of charge check valves for supplying fluid to the respective first and second main fluid passages, and a pair of relief valves for draining excessively pressurized fluid from the higher-pressurized first or second main fluid passage,
wherein the fluid duct block incorporates the pair of charge check valves and the pair of relief valves.

9. The hydrostatic stepless transmission according to claim 8 ,
wherein in the center casing, a pair of charge fluid ducts are bored to be connected to the respective encased fluid ducts of the respective first and second main fluid passages,
wherein in the fluid duct block, a pair of charge ports are provided to be connected to delivery ports of the respective charge check valves, and
wherein the charge ports are connected to the respective charge fluid ducts by attaching the fluid duct block to the center casing.

10. The hydrostatic stepless transmission according to claim 9 ,
wherein in the fluid duct block, each of the relief valves is connected to each of the charge ports so that the relief valve corresponding to the higher-pressurized first or second main fluid passage absorbs fluid from the higher-pressurized first or second main fluid passage via the corresponding charge port and is opened by operating the fluid as a pilot pressure to drain excessively pressurized fluid from the higher-pressurized first or second main fluid passage.

11. The hydrostatic stepless transmission according to claim 1 ,
wherein the center casing is cylindrical so that the first and second plunger blocks are inserted into the center casing so as to continue to each other so that the pump shaft and the motor shaft are disposed coaxially to each other.

12. The hydrostatic stepless transmission according to claim 1 ,
wherein at least one of the encased fluid ducts of the respective first and second main fluid passages is extended in an axial direction of at least one of the pump shall and the motor shaft.

Assignees

• Kanzaki Kokyukoki Mfg Co Ltd

Inventors

• Iwaki Koji
• Matsuura Jun
• Murashima Daisuke
• Ebihara Tomoyuki
• Kamada Minoru

Classifications

• F16H39/14 Primary

  with cylinders carried in rotary cylinder blocks or cylinder-bearing members · CPC title

• F16H39/00 Primary

  Rotary fluid gearing using pumps and motors of the volumetric type, i.e. passing a predetermined volume of fluid per revolution (control of exclusively fluid gearing F16H61/38) · CPC title