AXIAL PISTON PUMP SHOE RETAINER

Abstract: A positive displacement axial piston pump or motor with shank of each piston (14) having a reduced diameter to ball-shaped end (24) pivotally connected to a piston bearing shoe (18). A retainer (19) holds the bearing shoes in engagement with a thrust member. The piston shoes have (29) cylindrical socket portions loosely fitted in axial holes in the retainer and the retainer is coaxially supported on the shaft for the pump or motor. The working portion of each piston has a larger diameter than the diameter of the axial hole in the retainer. The retainer has radial slots (30) extending from each hole to the outer periphery of the retainer for the radial insertion of preassembled piston and piston shoe at the reduced diameter shank portion of a piston into a piston shoe hole in the retainer.

Description: AXIAL PISTON PUMP SHOE RETAINER BACKGROUND OF THE INVENTION A retainer for a positive displacement axial pump or motor as heretofore employed is shown in U.S. Patent 5 4,167,895 which shows the type of pump or motor in which the improved retainer of the present invention may be uti¬ lized. SUMMARY OF THE INVENTION In a certain frame size of a pump or motor, like that 10 shown in the above patent, the pistons are as large as can be provided when the preassembled pistons and piston bear¬ ing shoes are assembled with the retainer as heretofore. To employ larger diameter pistons, it is found that a lim¬ iting factor is the available bearing area of the retainer. 15 The retainer of the present invention, however, permits the use of larger diameter pistons without increasing the di¬ ameter of the holes in the retainer that receive the piston bearing shoes, while this retainer still provides sufficient bearing areas for the bearing shoes. This retainer has 20 radial slots extending from each bearing shoe hole to the outer periphery of the retainer. These radial slots each have a width less than the diameter of a bearing shoe hole. The pistons are formed in the usual manner and each has a reduced diameter or necked-down portion in its shank and 25 adjacent a ball-shaped end. The ball end of each piston is secured in the socket of a bearing shoe before being assem¬ bled with the retainer. *- The radial slots in the retainer are shaped to permit > the radial or lateral inertion of the preassembled pistons 30 and piston bearing shoes at the reduced diameter or necked- down portion of each piston into the radial slot and into the piston bearing shoe hole in the retainer. The invention is particularly applicable where the re¬ tainer size, space or bearing area is a limitation to en- 35 larging the piston shoe holes in the retainer, as for example in a given frame size pump or motor that permits the use of larger diameter pistons but does not permit making the piston shoe holes larger. Thus, the invention is a retainer for an axial pump or motor whose pistons have diameters greater than the diame- ters of the piston shoe holes in the retainer, and the re¬ tainer permits the radial insertion of the pistons, with their piston shoes attached, into the radial slots and into the piston bearing shoe holes in the retainer for assembly therewith, prior to assembly with the cylinder barrel. It is an object of the invention to provide a retainer for an axial piston pump or motor that permits the radial or lateral insertion of a piston and piston shoe assembly into a piston bearing shoe hole in the retainer. A further object is to employ larger diameter pistons in a certain frame size pump or motor without being limited by the smaller diameter of the holes in the retainer. THE DRAWINGS FIG. 1 is a longitudinal view of an axial piston pump or motor with a part shown in cross-section and showing parts including the cylinder barrel, pistons, piston bear¬ ing shoes and the retainer for the piston bearing shoes; FIG. 2 is an enlarged view of the face of the retainer of FIG. 1 showing the piston bearing shoe holes with radial slots to each hole; FIG. 3 is a top view of a portion of FIG. 2 showing one radial slot to a piston bearing shoe hole; FIG. 4 is a cross-sectional view along the line IV-IV of FIG. 2; FIG. 5 is a view in perspective showing an assembly of pistons, piston shoes and retainer about to be assembled with a cylinder barrel; and FIG. 6 is an enlarged view in perspective of a portion of the retainer showing one radial slot to a piston-shoe hole. The following description refers by reference numerals to parts shown in the drawings. DESCRIPTION OF AN EMBODIMENT A positive displacement axial piston pump 1 or motor, FIG. 1, is a variable displacement device. It has a hous¬ ing 2 closed at its right end by an end portion 3 integral with housing 2, and closed at its left end by an end head 4 having inlet and outlet ports, not shown. A shaft 5, for operatively connecting to a drive or a driven device not shown, extends through a» bore in the end portion 3 and is rotatably supported by a suitable bearing 6 protected by a shaft seal 7. The other end of shaft 5 is supported in a sleeve bearing 8 in end head 4. The pump 1 has a stationary and a rotating group of members. The stationary group includes a saddle 9 secured to the end portion 3 that provides a pivot support for a cradle 10, and the saddle and cradle each have a large bore through which the shaft 5 extends. The saddle and cradle have mating arcuate bearing surfaces 11,12. The cradle has a front or left face 13 that is flat and provides a thrust face for the pistons 14. An upper arm 15 of the cradle overlies the saddle and serves as a lever arm with a vertical bore 16 for a control pin, not shown, that extends through the housing for lat¬ eral displacement by a servo control device, not shown. Displacement of the control pin accomodates arcuate move- ment of the cradle for tilting the cradle thrust face whose angle of inclination determines the stroke of the pistons 14. The retainer 19 is supported on spherically shaped fulcrum ball 27 that is fitted coaxially of the shaft 5. A spring 28 is confined between the fulcrum ball and the cyl¬ inder barrel to urge the fulcrum ball and the retainer to¬ ward the cradle so that the piston bearing shoes are held against the thrust face of the cradle. The retainer 19 has axial holes 29 for receiving the socket portions of the piston bearing shoes. The diameter of each hole 29 is smaller than the diameter of the working portion of a piston 14. The flange of a bearing shoe has a shoulder surface bearing against the surface of the retainer about the hole 29 and has an outer bearing surface that abuts the thrust face of the cradle. Each hole 29 in the retainer is radially open to a radial stepped slot 30,31 that extends to the radially outer surface of the retainer 19. The shape of each radial slot 30,31, FIGS. 2, 3 and 6, shows it has stepped widths with the smaller width 30 corresponding to the minimum di¬ ameter 26 of the piston, and the larger width 31 accomoda- ting the tapered shank of the piston adjacent to its minimum di.ameter. The widths 30,31 of the radial slot are smaller than the diameter of the hole 29. The narrower width 30 preserves the bearing surface area of the retainer for the flange of the bearing shoe. The rotating group of members of pump 1 or motor in- eludes a cylinder barrel 17, pistons 14, piston bearing shoes 18, and a retainer 19 or harness for holding the pis¬ ton bearing shoes 18. The cylinder barrel 17 is suitably splined to the shaft 5 for rotation therewith. The cylin¬ der barrel has circumferentially spaced axial bores 20 each having a cylinder port 21. Each bore contains a piston fit¬ ted therein which reciprocates with rotation of the cylinder barrel according to the angular position of the thrust face 13 of the cradle 10. The- cylinder barrel has a sleeve, bearing 22 serving as a hydrodynamic bearing supported in the housing 2 and centered on a normal plane through the pivot centers of the piston bearing shoes 18. Piston 14 has a working portion within the cylinder bore and a shank portion terminating in a ball or ball- shaped end 24 which is secured in a socket of a piston bearing shoe 18 for universal connection therewith. The shank portion of the piston has a tapered diameter 25 de¬ creasing toward the ball end. Adjacent to the ball end, the shank portion of the piston has its minimum diameter 26 of, for example, one-eighth inch in axial length. The free end of the piston 14 thus may be said to be necked-down to provide its minimum diameter adjacent to its ball end 24. Each piston 14 is secured to a bearing shoe 18 before assembly with the retainer 19. To assemble with the retainer, the piston 14, with its bearing shoe attached, is radially or laterally inserted, about it necked-down and minimum diameter 26 of its shank portion, through the ra¬ dial slot of the retainer and into the bearing shoe hole in the retainer 19. The piston is then moved axially to bring the socket portion of the bearing shoe into the hole 29. After the assembly of the pistons, bearing shoes and re¬ tainer, the assembly of the pistons into the cylinder bar¬ rel, as illustrated in FIG. 5, is performed in the usual manner.

Claims: We Claim: 1. In a positive displacement pump or motor having pistons, piston bearing shoes, and a retainer, said retainer having circumferentially spaced holes for- receiving and holding the piston bearing shoes, said retainer having ra¬ dial slots through said retainer to each said hole which slots extend to the outer periphery of the retainer for the radial insertion through each said slot and into its asso¬ ciated said retainer hole of a piston with a bearing shoe attached. 2. In a pump or motor as defined in Claim 1 in which said pistons each have a diameter greater than a diameter of said hole in said retainer and a shank portion of said piston has a diameter smaller than said diameter of said hole. 3. In a pump or motor as defined in Claim 1 in which said pistons each have a shank that is necked-down to pro¬ vide a minimum diameter that is less than the width of each of said radial slots and less than the diameter of each of said holes. 4. In a pump or motor as defined in Claim 1 in which said radial slots each has a stepped or tapered width to accomodate the shape of the shank portion of the piston. 5. In a pump or motor as defined in Claim 4 wherein a narrower width of said stepped or tapered width of the radial slot accomodates the piston at a minimum diameter shank por¬ tion and the larger width of said radial slot accomodates the piston at a tapered diameter shank portion for the la¬ teral or radial insertion of the piston through said radial slot. 6. In a pump or motor as defined in Claim 5 wherein said retainer is coaxially supported on a fulcrum ball on a shaft for said pump or motor.

Inventors: BAHNER GERHARD W, HURLEY JOHN A, BAHNER, GERHARD, W., HURLEY, JOHN, A.
Applicants: OILGEAR CO, THE OILGEAR COMPANY
Application year: 1985
Main classification: F01B13
IPC codes: F01B3, F04B1