Hydraulic Pump

Abstract

An axial piston pump having flapper valves on the inlet ports and a continuous flexible ring member providing valving for the outlet ports. The ring member has an elastic sealing surface adjacent to the outlet ports to prevent reverse flow from the pump outlet to the cylinder bores. The ring member is deflected away from the outlet ports when the cylinder bores are pressurized. The deflection of the ring member varies with the amount of fluid flow from the cylinder. Since the amount of fluid flow from a single cylinder in this type of pump is sinusoidal, the outer edge deflection of the ring member is in the form of a sine wave. The ring member also seals the outlet ports to prevent back-flow through the pump when the input shaft is not being driven.

Description

This invention relates to axial piston pumps and more particularly to axial piston pumps having movable valving to control fluid flow.

The present invention is primarily used in axial piston pumps in which the cylinder block is held stationary within the housing and the pistons driven reciprocably in the cylinder block by a wobble plate which is driven by the input shaft. In this type of axial piston pump it is necessary to provide fixed valve members between the inlet and outlet ports of each bore in the cylinder block. Prior art devices have used flapper type valves, sliding valves or poppet type valves to control fluid flow at the inlet and outlet ports of the pump. While the operation of these type valves is satisfactory, they do have associated therewith pressure peaks which are undesirable.

The present invention incorporates a flat ring or disc type valve which covers the outlet ports of the pump. This flat valve member is made from a resilient material such as beryllium copper or spring steel and has bonded thereto an elastic material such as Buna-N rubber. The Buna-N rubber is adjacent to the outlet ports of the pump to provide a positive sealing surface for the outlet ports. The flat valve member is positioned adjacent to the outlet ports by a deflection limiter having a cone-shaped portion which prevents excessive stress in the flat ring valve. The flat ring valve is responsive to the fluid flow from the cylinder bores of the pump and will open according to the amount of flow which is being delivered. In a wobble plate type axial piston pump the fluid flow from a single cylinder bore is sinusoidal. That is, fluid flow develops from a minute amount at the beginning of a pumping stroke to a maximum amount at approximately one-half way through the pumping stroke and then recedes to a minute amount at the end of a pumping stroke. If the fluid flow were plotted for one full revolution a sine wave would be generated. The flat valve member compensates for this flow variation by deflecting in the form of a sinusoidal-shaped curve at the discharge ports of the pump. Due to the ability of the plate valve to assume the sinusoidal shape, pressure peaks which accompany typical flapper type valves are not present in a pump employing this invention.

It is, therefore, an object of this invention to provide in an axial piston pump an improved valving member which substantially lessens the pressure peaks at the discharge port.

It is another object of this invention to provide in an improved axial piston pump an outlet valve controlling fluid flow from the pump comprised of a flexible disc member and an elastic material.

It is another object of this invention to provide in an improved axial piston pump a flexible type valve controlling inlet flow to the pump and a continuous flexible ring valve having elastic sealing surface adjacent to the outlet ports to control fluid flow from the pump.

Still another

of this invention is to provide in an improved axial piston pump a flexible ring outlet valve having a metal ring portion and an elastic ring portion bonded thereto and a deflection limiter for controlling the maximum opening of said outlet valve.

These and other objects and advantages of the present invention will be more apparent from the following description and drawings in which:

FIG. 1 is a cross-sectional plan view of an axial piston pump;

FIG. 2 is a cross-sectional view taken along line 2--2 of FIG. 1; and,

FIG. 3 is a cross-sectional view taken along line 3--3 of FIG. 1.

Referring to the drawings wherein like characters represent like or corresponding parts, there is seen an axial piston pump 10 having a two piece housing consisting of portions 12 and 14. Housing portion 12 is a cup-shaped member having a mounting flange 16 and a bore 18 for rotatably journaling an input shaft 20. The housing portion 12 also has a flat surface 22 supporting a race 24 of a roller bearing 26 which rotatably supports a wobble plate or wedge shaped portion 28 secured to the input or drive shaft 20. A second roller bearing 30 is rotatably mounted on the wobble plate 28 adjacent a bearing race 32 against which abuts a plurality of pistons 34 reciprocably disposed in a plurality of cylinder bores 36 formed in a stationary cylinder block 38. The pistons are urged toward the bearing race 32 by return springs 35. The cylinder block 38 also has a central bore 40 in which is rotatably journaled one end 42 of the drive shaft 20. The outer diameter 44 of the cylinder block 38 is positioned in an annular recess 46 on the housing portion 12.

The housing portion 14 is also a cup-shaped member having swaged portion 48 which abuts a surface 50 of the housing portion 12 to secure the two portions 12 and 14 together. A seal member 52 is compressed between shoulders 54 and 56 on the housing portions 12 and 14 respectively to prevent fluid leakage from within the housing past the swaged portion 48. An inlet valve member 60a is sandwiched between a valve plate 58 and a gasket plate 60 which together are positioned between the housing portion 14 and the cylinder block 38. The valve plate 58 has a plurality of inlet ports 62 and a plurality of radially inwardly and axially extending outlet ports 64, one inlet and outlet port for each cylinder, formed therein and carries a round 0-ring type seal 66 between the inlet and outlet ports 62 and 64 to prevent the interchange of fluid therebetween. The inlet valve member 60a is comprised of a sheet metal member 68a made of a flexible material such as spring steel or beryllium copper and has an elastic member 70a from an elastic material such as Buna-N or a fluoroelastomeric bonded to that side of the sheet metal member 68a which faces the valve plate 58. The gasket plate member 60 is comprised of a sheet metal member 68 made of suitable types steel and has an elastic member 70 from an elastic material such as Buna-N or a fluoroelastomeric bonded to both sides of the sheet metal member 68. The elastic member 70 abuts the inlet valve 60a at the uncoated side of said inlet valve and the cylinder block 38 near their outer diameters to prevent fluid flow outwardly from the cylinder bores 36. The inlet valve member 60a is flat in its normal position and has a plurality of flapper portions 72a having one flapper portion 72a abutting to each of the inlet ports 62. The flapper portions 72a deflect toward the cylinder bores 36 and away from the valve plate 60 during the suction stroke of the pistons 34. This deflection of the flapper portions 72a is limited by a corresponding number of formed gasket plate portions 72, which prevent excessive stress in the flapper portions 72a of the inlet valve 60a. However, when the pistons 34 are reciprocated in the bores 36 and pressure develops therein the fluid pressure and the spring tension of the deflected flapper portions 72a will cause the flapper portions 72a to move against the inlet ports 62 to prevent the discharge of fluid through the inlet ports 62.

The outlet ports 64 are adjacent an outlet chamber 74 formed in the housing portion 14. The fluid communication between the outlet port 64 and the outlet chamber 74, however, is controlled by an outlet valve 76 comprised of a flexible annular disc or ring member 78 made from a flexible material such as spring steel or beryllium copper and an elastic material 80 such as Buna-N rubber bonded to the disc 78 so as to be adjacent the outlet port 64. The disc valve 76 is positioned adjacent the outlet ports 64 by a deflection limiter 82 which has a threaded portion 84 threaded into the cylinder block 38 and a conically shaped portion 86 adjacent the outlet valve 76. As fluid pressure is developed in the cylinder bores 36 by the pistons 34 the fluid will flow through horseshoe-shaped passages 88 in the inlet valve 60 and through the outlet ports 64 to the outlet chamber 74. The disc valve 76 will be deflected away from the outlet port 64 by the pressure therein against the deflection limiter 82. The amount of deflection of the outlet valve 76 is dependent on the fluid flow from the cylinder at any particular time. The fluid flow from the cylinder bore is sinusoidal in character and therefore the deflection of the outlet valve 76 will be sinusoidal in nature. The peak deflection of the valve will occur at the outlet port when the piston is at approximately 50 percent of the stroke. Thus, the maximum deflection point will travel around the deflection limiter as the wobble plate 28 is rotated. At any instant in time the valve, adjacent the ports under pressure, will form a standing sine wave. When the pistons in the cylinder bores are on the intake stroke, the flapper 72a of the inlet valve 60a opens to admit fluid to the cylinder; while the outlet valve 76 will close due to the fluid pressure in outlet chamber 74 and the spring of the flexible member 78 so that the elastic material 80 will seal against the outlet port 64 to prevent back flow through the pump.

Obviously, many modifications and variations of the present invention are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

Claims

What is claimed is:

1. An axial piston pump comprising, valve plate means having a plurality of axial inlet ports, and a plurality of axial outlet ports; an outlet flow chamber in fluid communication with said outlet ports; cylinder block means having a plurality of axially extending cylinder bores each in fluid communication with each of one of said inlet and outlet ports; piston means slidably disposed in said cylinder bores and being reciprocal therein to establish fluid flow into and out of said cylinder bores; inlet valve means disposed between said cylinder block and said valve plate means having flapper means adjacent each said inlet ports for opening in response to the suction stroke of pistons when fluid is flowing into said cylinder bores and being closed by spring tension of said flapper means and pressure in said cylinder bores when fluid is being expelled therefrom and a plurality of flapper deflection limiting means inclined to the cylinder bores and the flapper means for limiting the opening of said flapper means; outlet valve means comprising a continuous flexible ring having a sealing surface adjacent said outlet ports for preventing flow from said outlet flow chamber to said cylinder bores when said flapper means are open, and said continuous flexible ring being displaced from said outlet ports proportional to the amount of fluid flowing from the cylinder bore when said flapper means is closed to permit fluid flow selectively from said cylinder bores to said outlet flow chamber when said pistons are expelling fluid from said cylinder bores; and deflection limiter means including a threaded portion extending centrally through said valve plate means, said inlet valve means and said outlet valve means and being threadably secured centrally in said cylinder block means for securing together said valve plate means, said inlet valve means, said outlet valve means and said cylinder block means, and a conical section adjacent said flexible ring for limiting the maximum deflection of said flexible ring.