JP2001295753A - Piston assembly for fluid transfer device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piston assembly for use generally with a fluid transfer device and, more precisely, a mechanical interface between the piston and slipper of the piston assembly. SOLUTION: The piston assembly for the fluid transfer device has a mechanical coupling for efficiently transmitting an actuating force between the piston and the slipper, thereby maintaining the height of a predetermined thin film of fluid between the slipper and a surface against which the slipper moves. This is achieved by providing both the piston having a formed spherical end portion thereon and the slipper having a cavity to accommodate the spherical end portion, to thereby maintain a predetermined distance between the center of the spherical end portion and a point making contact with a surface inside the cavity of the slipper.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

FIELD OF THE INVENTION The present invention relates generally to a piston assembly for use in a fluid transfer device, and more particularly to a mechanical interface between a piston and a slipper of the piston assembly.

[0002]

2. Description of the Related Art Piston assemblies used in fluid transfer devices such as hydraulic pumps and / or motors are well known in the art. These piston assemblies typically use slippers that are mechanically coupled to the piston. The mechanical connection usually has a sphere connected to the end of the piston and fits into the cavity of a slipper having a corresponding sphere shape. Once the piston sphere has been inserted into the slipper cavity, a portion of the cavity wall is swaged around the top of the piston sphere, forming a mechanical bond. This type of connection is disclosed in U.S. Pat. No. 5,2,2, issued Jan. 18, 1994 and assigned to the assignee of the present invention.
79, 205. The spherical surface over the sphere is known as mating contact and, as is well known, it is difficult to produce a satisfactory ball and socket joint without protrusions and / or other defects. In conclusion, the point of contact between the sphere on the piston and the spherical cavity in the slipper cannot be repeated with any certainty. FIG. 8 of U.S. Pat. No. 3,354,786, issued Nov. 28, 1967 and assigned to Chamberlain Industries Limited.
Teaches a mechanical coupling for a radial piston motor that generally reduces the problems associated with conventional spherical-spherical couplings. In this device, a pair of arcs are provided in a cavity in the piston, and the sphere is provided on a slipper and located in the cavity of the piston. This device helps to reduce the problems associated with known defects in known spherical-to-spherical couplings. A fundamental problem that persists with known slipper technology is the control of the fluid film thickness between the slipper and the surface on which the slipper is "on" or in contact. If the fluid film is too thin, the slipper will drag or scratch the surface; if the fluid film is too thick, excessive leakage will occur. Thicker fluid films reduce friction and torque losses, while thinner fluid films increase volumetric efficiency by minimizing fluid leakage. Many known devices that attempt to control the fluid flow or volume introduced between the slipper and the surface on which the slipper rides include mounting an orifice between the supply fluid and the space between the slipper and the surface. It is performed by This is shown in FIG. 1 of US Pat. No. 3,354,786.
At 2, the use of an orifice 144 attached to a slipper or shoe 116 is more clearly shown.
Having a mechanical connection between the piston and the slipper that will function to provide and maintain an optimal fluid film thickness between the slipper and the surface on which it is riding, which fluid film thickness is excessively leaky It is necessary to provide adequate lubrication without causing cracking.

[0003]

SUMMARY OF THE INVENTION The present invention is intended to overcome one or more of the problems set forth above.

[0004]

SUMMARY OF THE INVENTION In one aspect of the present invention, a piston assembly for a fluid transfer device is provided. The fluid transfer device includes a housing having fluid inlet and outlet ports, a barrel having a plurality of bores disposed in the housing, and a ramp surface, each piston assembly comprising:
Each of the plurality of bores is slidably disposed in the bore and in contact with the inclined surface. The barrel rotates with respect to the housing and the inclined surface. The piston assembly includes a piston defining a reference axis and has a body portion and a coupling portion extending along the reference axis. The passage extends through both the body portion and its coupling portion. The coupling portion has a spherical end with a predetermined cross-sectional dimension. The piston assembly also includes a slipper having a coupling portion, a sealing and sliding portion, and a passage interconnecting the coupling portion and the sealing and sliding portion. The sealing and sliding portion has a face surface and a recess formed in the face surface and extending inward from the face surface and connecting to a passage in the face surface. The coupling portion has a cavity formed in the coupling portion and communicating with the passage of the coupling portion, a first portion large enough to receive a spherical end of the piston, and a first end of the spherical end. It has a second portion large enough to establish contact with the spherical portion of the piston at a predetermined maximum distance from the center.

According to another aspect of the present invention, there is provided a method of preparing a piston assembly having a piston and a slipper,
In operation, the sealing and sliding surfaces of the slipper are urged to deform to a substantially concave shape. Each step comprises forming a piston having a mating portion with a spherical end at one end, having a sealing and sliding surface at one end and large enough to accommodate the spherical end of the piston at the other end. Forming a slipper having a coupling portion with a cavity formed in the coupling portion, and a contact point between the spherical end of the piston and the cavity at a predetermined maximum distance from the center of the spherical end. Forming a cavity to establish

[0006]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.
Referring to FIG. 1, there is shown a fluid transfer device 10, such as an axial piston pump, including inlet and outlet ports 14 and 16, a sloped surface 18, a barrel 20, a plurality of piston assemblies 22, and a housing 12 having a clamp plate 23. including. Without departing from the essence of the invention, the inclined surface 18
Can be placed on a known adjustable swash plate (not shown). The barrel 20 has a plurality of bores 24 formed in the barrel to accommodate each of the piston assemblies 22. It can be seen that the fluid transfer device 10 may be either a hydraulic pump or a hydraulic motor. Each of the piston assemblies 22 includes a piston 26 and a slipper 28 mechanically coupled thereto. A reference axis 30 is formed in the piston 26 and includes a body portion 32
And extends through the coupling portion 34. Passageway 36 extends continuously through body portion 32 and coupling portion 34 of piston 26. The coupling portion 34 has a spherical end 38 with a predetermined cross-sectional dimension and a predetermined length of radius.

Referring to FIG. 2 in conjunction with FIG. 1, the slipper 28 is shown in greater detail and forms a reference axis 40 extending therethrough and includes a sealing and sliding portion 42 and a coupling portion 4.
4 inclusive. Passageway 46 extends through sealing and sliding portion 42 and coupling portion 44 of slipper 28. The sealing and sliding portion 42 includes a face surface 48 and a recess 50 formed in the face surface and extending inward from the face surface 48 along the reference axis 40. The recess 50 is provided for the passage 4 in the recess.
It leads to 6. The coupling portion 44 forms a cavity 52 having a first portion 54, a second portion 56, and a bottom portion 58. The first part 54 is the spherical end 3 of the piston 26.
8 is large enough to accommodate First part 54
Is formed by a flange 59 such that when the spherical end of the piston is placed in contact with the second portion of the cavity, the flange 59 is swaged around a portion of the spherical end 38 in a known manner. You. The second part 56 includes the piston 2
6 includes a spherical surface 60 having substantially the same cross-sectional dimensions and shape as the spherical end 38 and located adjacent the first portion 54. The bottom portion 58 of the cavity 52 in the slipper 28 is large enough to terminate the sphere 60 at a predetermined maximum distance "d" from a center point defined by the radius of the sphere 60, and along the reference axis 40. Extending second recess 62
To form The predetermined maximum distance “d” is generally equal to or less than 60% of the length of the predetermined radius of the spherical surface 60. The second recess 62 communicates with the passage 46.

Referring to FIG. 3, another embodiment of the slipper 28 is shown. Similar members have similar member numbers. The first portion 54 of the cavity 52 is the same as the first portion 54 of the slipper 28 of FIG. 2, and the bottom portion 58 of the present embodiment has a bottom surface 64. Second portion 56 of cavity 52
Is formed by the conical surface 66. Conical surface 6
6 is sized and shaped to assure that the point of contact is maintained at a predetermined maximum distance "d" from the center of the spherical end 38 when the spherical end 38 of the piston 26 is assembled therein. ing. In the present embodiment, the tip angle of the conical surface is 10
To 30 degrees. The predetermined maximum distance "d" is typically no greater than 60 percent of the length of the predetermined radius of the spherical end 38. In this embodiment, the conical surface 66
Although formed by a single straight line, it will be appreciated that the conical surface may be a stepped surface if needed.

Referring to FIG. 4, slipper 28 is shown generally and how the physical configuration of slipper 28 of the present invention is affected by the forces acting on the slipper from the operating pressure of fluid transfer device 10. Includes a general illustration of what to receive. More specifically, force “F” represents the force from piston 26 acting through spherical end 38. Power "F"
Is the piston 2 opposite the spherical end 38 of the piston 26
6 is established by the operating pressure in the system acting on the end of the body part 32. The plurality of reaction forces "RF"
Established by the operating pressure in the system guided through 6 and 46 to the area between the slipper 28 and the inclined surface 18. System pressure acts on the face surface 48 and the recess 50. The length of each reaction arrow "RF" generally indicates that its strength decreases as the pressurized fluid approaches the outer edge of the face surface 48 which is open to low or atmospheric pressure. The shape of slipper 28 is directly affected by the location at which force “F” is applied to second portion 56 of cavity 52. As shown in FIG.
0 deforms into a substantially concave shape. It can be seen that the shape shown in FIG. 4 has been exaggerated for illustrative purposes. However, it is important to understand that the shape of the face surface 48 is slightly concave to help maintain a targeted fluid film between the inclined surface 18 and the slipper 28.

It will be appreciated that various alternatives may be utilized without departing from the essence of the invention. For example,
The size or width of the face 48 could be varied as needed to compensate for different system pressures and / or control leakage from the face. Further, the second portion 56 of the cavity 52 in the slipper 28
However, other shapes could be used. For example, the shape could be formed by a radius greater than the radius of the spherical end 38 of the piston 26, or by a parabola.

[0011] When operating the availability fluid transfer device 10 on the industry as a pump, fluid is received from the low pressure source such as a reservoir (not shown) in the inlet port 14, the piston 26 rotates the barrel 20 is retracted When filling, each bore 24 in the barrel is filled. Once the piston 26 reaches the fully retracted position (fills with fluid) and moves in the opposite direction, fluid is forced out of the outlet port 16 under pressure. Outflow port 16
At the passage 3 of the associated piston assembly 22
Through 6 and 46, it is constantly fed into the area between the slipper 28 and the inclined surface 18. Similarly, outflow port 1
The fluid pressure of 6 also acts on the associated piston 26 end. As described above in connection with FIG. 4, the force created by the pressure acting on the end of the associated piston 26 is transmitted through the piston 26 and the slipper 28 and the relationship between the face surface 48 and the inclined surface 18 In a very close sliding and sealing relationship separated only by a thin film of fluid.

The fluid film established by the present invention reduces frictional contact while reducing slipper 28 and inclined surface 18.
Leaks from intervening areas are also minimized. Since the reaction force "RF" acts in the opposite direction to the force "F", the interface between the second portion 56 of the cavity 52 in the slipper 28 and the spherical end 38 of the piston 26 is direct. Affected by In each of the embodiments, controlling the predetermined maximum distance "d" forces the slipper to deflect in a targeted manner, such that the face surface 48 and recess 50 maintain a uniform minimum fluid film height. The result is to take a concave shape. If the predetermined maximum distance "d" is exceeded excessively, the face surface 48 may be forced into a convex shape which is detrimental to the ability to control a uniform minimum fluid film height. The convex shape of the face surface 48 may result in unnecessary fluid leakage as well as excessive wear and / or rubbing between the sloped surface 18 and the slipper face 48.

A piston assembly 2 that provides a sealing and sliding face surface 48 which is urged to deform to a generally concave shape during operation.
The method of preparing 2 is shown. One step involves forming a piston having a coupling portion 34 at one end with a spherical end 38. Another step involves slipper 2 having a sealing and sliding face surface 48 at one end and a coupling portion 44 at the other end.
8 is formed. A cavity 52 is formed in the coupling portion 44 and is large enough to accommodate the spherical end 38 of the piston 26. Another step involves shaping the cavity 52 to establish a point of contact between the spherical end 38 of the piston 26 and the cavity 52 at a predetermined maximum distance from the center of the spherical end 38. The shape of the cavity 52 may be spherical, conical, or any other suitable shape. If the cavity 52 is conical, it is generally 10
Will have a predetermined apex angle that falls in the range between.

From the above, it is apparent that the present piston assembly 22 provides an effective device for controlling the fluid film height between the face surface 48 of the slipper 28 and the inclined surface 18 during operation. . By controlling the predetermined maximum distance "d", the face surface 48 is encouraged to deflect into a concave shape, i.e., effectively reducing scuffing and / or wear while minimizing fluid leakage. Prepare an interface with a uniform fluid film height. Other aspects, objects, and advantages of the invention can be obtained from a study of the drawings, the disclosure, and the appended claims.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a fluid transfer device incorporating an embodiment of the present invention.

FIG. 2 shows one of the slippers taken from the fluid transfer device of FIG.
FIG. 4 is an enlarged view of one embodiment.

FIG. 3 is an enlarged view of another embodiment of a slipper taken from the fluid transfer device of FIG.

FIG. 4 is an enlarged view of the slipper, schematically illustrating forces acting on the slipper during use in the fluid transfer device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Fluid transfer apparatus 12 Housing 14 Inflow port 16 Outflow port 18 Inclined surface 20 Barrel 22 Piston assembly 23 Clamping plate 24 Bore 26 Piston 28 Slipper 30 Reference axis 32 Body part 34 Coupling part 36 Passage 38 Spherical end

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Noah Dee Manling Illinois, USA 61523-9110 Chiloco North Wild Spruce Lane 13627 (72) Inventor Terry Dee Altman, Illinois United States 61523-1940 Chiracosi West David Avenue 1608 (72 Inventor Jan Ye United States of America Illinois 60435−8583 Joliet College Street 1700

Claims (10)

[Claims] A housing having fluid inlet and outlet ports, a sloped surface, a barrel rotating with respect to the housing and the sloped surface with a plurality of bores disposed within the housing, and the plurality of bores. A piston assembly for a fluid transfer device having a respective piston assembly slidably disposed in each bore of said bore surface and in contact with said inclined surface, said body defining a reference axis and extending along said reference axis. A piston having a portion and a coupling portion having a spherical end with a predetermined cross-sectional dimension; a piston having the body portion and a passage extending through the coupling portion of the body portion; a coupling portion, a sealing and sliding portion; A slipper having a passage interconnecting the coupling portion and the sealing and sliding portion, wherein the sealing and sliding portion is formed in the face surface and formed in the face surface. A recess extending inward from the face surface and connecting to the passage in the face surface, the coupling portion having a cavity formed in the coupling portion and coupled to the passage in the coupling portion; Establishing contact between a first portion large enough to accommodate the spherical end of the piston and the spherical end of the piston at a predetermined maximum distance from the center of the spherical end. A second portion of a size and shape sufficient for the piston assembly. 2. The slipper defines a reference axis extending through the coupling portion and the sealing and sliding portion, and the second portion of the cavity of the slipper has a conical shape with a predetermined tip angle. The piston assembly according to claim 1, wherein the piston assembly is formed by a surface. 3. The piston assembly according to claim 2, wherein said tip angle is in a range of 10 to 30 degrees. 4. The spherical end of the piston has a predetermined radius, and the predetermined maximum distance from the center of the spherical end is less than 60 percent of the predetermined radius. The piston assembly according to claim 1, wherein 5. The cavity having a bottom portion, wherein the second portion of the cavity of the slipper is formed by a spherical surface having substantially the same cross-sectional dimensions as the spherical end of the piston. The piston of claim 1, wherein a recess is formed in the bottom of the cavity and is large enough to terminate the spherical surface at the predetermined maximum distance from the center of the spherical end. Assembly. 6. A housing having an inlet and an outlet port and a ramp surface, and a barrel defining a plurality of bores disposed in the housing and operable to rotate relative to the housing and the ramp surface. A piston assembly disposed in each bore of the plurality of bores and in contact with the angled surface, the piston assembly having a body portion and a piston having a spherical end, sliding and sealing. And a slipper having a coupling portion, wherein the coupling portion is large enough to establish contact with the spherical end of the piston at a predetermined maximum distance from the center of the spherical end. A fluid transfer device, forming a cavity having a portion. 7. A method of preparing a piston assembly having a piston and a slipper, wherein during operation the sealing and sliding face of the slipper is urged to deform to a generally concave shape, the method comprising providing a spherical end. Forming a piston having at one end a coupling portion comprising: a sealing and sliding face surface at one end; and a large enough to receive the spherical end of the piston at the other end.
Forming a slipper having a coupling portion with a cavity formed therein; and contacting the piston with the spherical end at a predetermined maximum distance from the center of the spherical end. Shaping the cavity to establish a point. 8. The method of claim 7, wherein shaping the cavity includes creating a conical surface having a predetermined tip angle. 9. The method of claim 8, wherein generating the conical surface comprises maintaining the predetermined tip angle within a range of 10 to 30 degrees. 10. The method of claim 7, wherein shaping the cavity includes creating a sphere having substantially the same cross-sectional dimension as the spherical end of the piston.