US3866519A

US3866519A - Piston of piston type fluid pump motor

Info

Publication number: US3866519A
Application number: US324128A
Authority: US
Inventors: Takayaki Miyao; Hiroaki Maeda; Masanori Sato
Original assignee: Aisin Seiki Co Ltd
Current assignee: Aisin Corp
Priority date: 1972-01-27
Filing date: 1973-01-16
Publication date: 1975-02-18
Anticipated expiration: 1992-02-18

Abstract

A piston used in a piston type fluid pump motor comprises a plurality of piston heads which are each rotatably mounted on a single rod by ball-and-socket joints. Reduced friction between the piston heads and a cylinder wall avoids seizure of the piston and cylinder wall during operation.

Description

tlnitd States Patent Miyao et al. 1 Feb. 18, 1975 [54] PISTON 0F PISTON TYPE FLUID PUMP 2,956,845 10/1960 Wahlmark 92/256 MOTOR 3,382,813 5/1968 Schauer 91/506 [75] Inventors: Takayaki Miyao; Hiroaki Maeda,

both of Toyota; Masanori Sato, Nagoya, all of Japan [73] Assignee: Aisin Seiki C0,, Ltd., Kariya-shi,

Aichi-ken, Japan [22] Filed: .Ian. 16, 1973 [2]] Appl. No.: 324,128

[30] Foreign Application Priority Data Feb. 18, 1972 Japan 47-17330 Jan. 27, 1972 Japan 47-10106 [52] 11.8. C1. 91/488 [51] Int. Cl. ..F01b 13/04 [58] Field of Search 91/499507; 92/256 [56] References Cited UNITED STATES PATENTS 893,558 7 9 Williams 91/507 FOREIGN PATENTS OR APPLICATIONS 699,027 12/1964 Canada 91/ 199 1,023,811 2/1963 Great Britain 220,417 8/1924 Great Britain 1, 91/505 Primary Examiner-William L. Freeh Attorney, Agent, or FirmOblon, Fisher, Spivak, McClelland & Maier 13 Claims, 17 Drawing Figures PATENTEU F531 8 I975 SHEET 2 OF 7 SHEET 3 or 7 MENTED FEB] 81975 PATENTEU 71.866519 SHEET 8 OF 7 FIG.||

PISTON OF PISTON TYPE FLUID PUMP MOTOR BACKGROUND OF THE INVENTION 1. Field Of The Invention This invention relates generally to a piston used in a piston type fluid pump motor and more particularly to a unique piston having reduced friction between piston heads and a cylinder wall.

2. Disclosure Of the Prior Art In the past, various types of fluid pump motors have been proposed. While somewhat satisfactory, prior fluid pump motors have had the disadvantages that friction associated with a piston head caused seizure of the piston head with a cylinder wall requiring down time and repair or replacement.

SUMMARY OF THE INVENTION Accordingly, one object of the present invention is to provide a new and improved unique piston.

Another object of the present invention is to provide a new and improved unique piston of a piston type fluid pump motor for minimizing friction between the piston and the wall of a cylinder so as to prevent a seizure.

Briefly, in accordance with this invention, the foregoing and other objects are in one aspect attained by utilizing a piston in a piston type fluid pump motor which comprises a plurality of piston heads which are each rotatably mounted on one rod by ball-and-socket joints.

BRIEF DESCRIPTION OF THE DRAWINGS Various other objects, features and advantages of the invention will be more fully appreciated as the same becomes better understood from the following detailed description when considered in connection with the accompanying drawings, wherein like reference characters designate like or corresponding parts throughout the several views, and in which:

FIG. 1 is a front view of one embodiment of a piston according to this invention;

FIG. 2 is a sectional view taken along the line II-II of FIG. 1;

FIG. 3 is a sectional view taken along the line III-III of FIG. 2;

FIG. 4 is a sectional view taken along the line IVIV of FIG. 2;

FIG. 5 is a sectional view of one embodiment of an axial piston type hydraulic pump motor having a piston according to this invention;

FIG. 6 is a partial enlarged sectional view of FIG. 5;

FIG. 7 is a front view of another embodiment of a piston according to this invention;

FIG. 8 is a sectional view taken along the line VIII- -VIII in FIG. 7;

FIG. 9 is a sectional view taken along the line IX-IX in FIG. 8;

FIG. 10 is a sectional view taken along the line X-X in FIG. 8;

FIG. 11 is a front view of yet another embodiment of a piston according to this invention;

FIG. 12 is a sectional view taken along the line XII- -XII in FIG. 11;

FIG. 13 is a sectional view taken along the line XIII- -XIII in FIG. 12;

FIG. 14 is a sectional view taken along the line XIV--XIV in FIG. 12; and,

FIG. 15 is a sectional view of an embodiment of the invention used in an axial piston type fluid pump motor.

FIG. 16 is a front view of the embodiment of a piston according to this invention shown in FIG. 15; and,

FIG. 17 is a sectional view taken along the line XV-XV in FIG. 16.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings, wherein like reference characters designate identical, or corresponding parts throughout the several views, and more particularly to FIG. I a piston 10 comprises two

piston heads

12 and 14 and a rod 16.

The piston head 12, as shown in FIGS. 2 and 3, in sectional views, comprises a housing 18 of a substantially cylindrical shape and a pair of

bushes

24 and 26 of a semicylindrical shape which are respectively fitted in the housing and fixed to the housing by bending both

ends

20 and 22 of the housing in a radial direction. As shown in FIGS. 2 and 4, the piston head 14 comprises a housing 28 of a substantially cylindrical shape and a pair of

bushes

34 and 36 of a semicylindrical shape which are respectively fitted in the housing and fixed thereto by bending one end 30 and the housing in a radial direction and a fitting ring 32 within the housing. The piston head 12 is rotatably mounted or jointed at substantially a middle part of the rod 16 by a ball-andsocket joint which is formed with a convex spherical surface 38 formed at a substantially middle part of the rod 16 and a concave

spherical surface

40 and 42 formed in the

bushes

24 and 26 and positioned facing the convex spherical surface. The piston head 14 is also rotatably jointed at one end of the rod 16 by a ball-andsocket joint which is formed with a convex spherical surface 44 formed at one end of the rod 16 and a concave spherical surface 46 and 48 formed in the

bushes

34 and 36 and positioned facing the convex spherical surface.

As seen in FIG. 2, two grooves 50 and 52 are formed on the outer surface of the piston head 14 for lubricating the outer surface and the cylinder wall. A groove 54 is formed on the outer surface of the piston head 12 for supplying a lubricant between the outer surface and the cylinder wall. The groove 54 is connected, through a hole 58 formed in the piston head 12 and the rod 16, to a hole 56 formed in the rod 16.

In FIGS. 5 and 6, the reference numeral 60 designates an axial piston type hydraulic pump motor which is a piston type fluid pump motor. A plurality of cylinders 68 are formed in an axial direction in a cylinder barrel 66 connected to a rotary shaft 62 with a plurality of pins 64 treated by crowning. Within the cylinders 68, each piston 10 is respectively slidably fitted. The other end of the rod 16 of the piston 10 is jointed through a ball-and-socket joint to a shoe 74 slidably mounted on a sliding surface 72 of a swash plate 70. The ball-andsocket joint is formed with a convex spherical surface 76 formed on the other end of the rod 16 and a concave spherical surface 78 formed in the shoe 74 facing the convex spherical surface.

When the rotary shaft 62 is rotated by suitable means and a lubricant at low pressure is supplied through the oil-passage 80, the cylinder barrel 66 is also rotated by the rotation of the rotary shaft 62, so that the piston 10 is reciprocated in the cylinder 68 by the slant of the sliding surface 72 of the swash plate 70. Accordingly, the lubricant at low pressure supplied through the oilpassage 80 of the slot for low pressure, is exhausted as a lubricant at high pressure from the oil-passage 82 of the slot for high pressure.

It has been well-known that a motor can perform a reversal operation. In that case, the piston is pressed to the slant plate 70 by the hydraulic pressure, whereby a force W is applied to the other end of the rod 16 of the piston 10 by the slant of the sliding surface 72 of the swash plate 70 as shown in FIG. 6.

When a conventional piston formed with a single part is used, a gap for sliding is provided between the outer surface of the piston and the cylinder wall, so that an axis of the piston is inclined to an axis of the cylinder whereby the piston contacts the cylinder wall at both ends of the outer surface facing it.

The contact between the piston and the cylinder wall is substantially linear so that the pressure at the contact part is high enough to cause the lubricant membrane to break in addition to causing friction between the piston and cylinder wall and seizure of the piston and cylinder.

On the other hand, when the piston 10 of this invention is employed, the

piston heads

12 and 14 are respectively jointed to the rod 16 by the ball-and-socket joint so as to be rotatable. The axis of the rod 16 is inclined to the axis of the cylinder 68, however, the axes of the

piston heads

12 and 14 are not respectively inclined to the axis of the cylinder 68 even though the piston head axes are not consistent as seen in FIG. 6 so that the

piston heads

12 and 14 are respectively in surface contact with the cylinder wall, so that there is virtually no friction between the piston heads and the cylinder wall, and accordingly no seizure of the piston heads and the cylinder wall occurs.

Incidentally, in the drawings, each piston head is jointed longitudinally through the ball-and-socket joint at the middle portion of the rod 16. However, it should be understood that it is not always necessary to joint the piston heads at the middle portions of the rod. If the piston heads are jointed to the middle part of the rod, uniform pressure at the contact surface between the outer surface of the piston head and the cylinder wall is advantageously provided. It should be further understood that when the piston of this invention is used, the ball-and-socket joint may be placed in the cylinder at any time.

In another embodiment of the present invention shown in FIGS. 7-10, the piston 84 comprises a pair of

piston heads

86 and 88 and a rod 90. The piston head 86 comprises a housing 92 of a substantially cylindrical shape and a bush 98 of a substantially cylindrical shape which is fitted within the housing and fixed to the housing by bending one end 94 of the housing in a radial direction and providing a caulk 96.

The piston head 88 comprises a housing 100 of a substantially cylindrical shape and a bush 106 of a substantially cylindrical shape which is fitted within the housing and fixed to the housing by bending one end 102 of the housing in a radial direction and providing a caulk 104. The piston head 86 is rotatably jointed to a middle portion of the rod 90 by a ball-and-socket joint formed with a convex spherical surface 108 formed at a middle portion of the rod 90 and a concave spherical surface 110 formed by a bush 98 to face surface 108.

The piston head 88 is also rotatably jointed to one end of the rod 90 by a ball-and-socket joint formed with the convex spherical surface 112 formed at one end of the rod and a concave spherical surface 114 formed in the bush 106 to face surface 112. A part of the concave spherical surface is formed by caulking one end 116 of the bush 98.

A similar operation and result of the piston of a first embodiment is attained by the piston 84 of an alternative embodiment of this invention.

In the alternative embodiment shown in FIGS. 11-14, a piston 120 comprises a pair of piston heads 122 and 124 and a rod 126. The piston head 122 is formed by a single part of a cylindrical shape, and is rotatably jointed to a middle portion of the rod 126 by a ball-and-socket joint having a convex spherical surface 128 formed at a middle portion of the rod 126 and a corresponding concave spherical surface 130 formed in the piston head. The piston head 124 similarly is formed by a single part of a cylindrical shape and is rotatably jointed to one end of the rod 126 by a ball-andsocket joint having a convex spherical surface 132 formed at one end of the rod 126 and a corresponding concave spherical surface 134 formed in the piston head.

A part of the concave spherical surface 130 is formed by caulking a portion 136 of the piston head 122, and a part of the concave spherical surface 134 is formed by caulking a portion 138 of the piston head 124.

A similar operation and result can be attained with this embodiment as with the first embodiment. In the embodiments described above, two piston heads are employed; however, it should be understood that more than two piston heads can be employed.

As stated above, the piston of this invention comprises a plurality of piston heads which are each rotatably jointed to one rod by ball-and-socket joints, so that there is virtually no friction between the piston and the cylinder wall and accordingly no seizure of the piston and the cylinder wall results.

In FIG. 15, the reference numeral 10 designates an axial piston type fluid pump motor wherein a casing 211 is formed by connecting three

divisional parts

212, 214 and 216 with a plurality of bolts 218. In a casing 211, a swash plate 220 placed at left side thereof is pivoted by the casing 211 with a trunnion axis (which is perpendicular to the paper), and a valve plate 222 is fixed to the casing 211 by a plurality of pins 224. A rotary axis 230 connecting the swash plate 220 through

holes

226 and 228 to the valve plate 222, is pivoted by the casing 211 through

bearings

232 and 234.

On the rotary shaft 230, a cylinder barrel 236 is provided between the swash plate 220 and the valve 222. A cylinder barrel 236 is divided into two parts 238 and 240. One part 238 connected to the valve 222 is rotatably and axis-swingably jointed to a rotary shaft 230 by a plurality of keys treated by crowning and is pressed to the valve 222 by a spring 244. The other part is mounted to the rotary shaft 230. The pistons 248 fitted to each of a plurality of cylinders 246 formed in the cylinder barrel 236 are each rotatably jointed to the rod 252 by a universal joint wherein the first piston head 254 sliding in one part 238 and a second piston head 256 sliding in the other part 240 are jointed to one rod 252 connected through a shoe 250 to the swash plate 220.

In FIG. 15, the rotary center of the first piston head 254 to the rod 252 of the piston 248 corresponds to the centroid of the piston head. The rotary center of the second piston head 256 corresponds to the centroid of a piston-shoe system consisting of the piston 248 and the shoe 250. In the piston 248 shown in FIGS. 16 and 17, the second piston head 256 has four lubricant recesses 286 which are each connected to a hole 288 through holes 290 so as to provide static bearing pressure at the movement. The second piston head 256 is rotatably jointed at a substantially middle portion of a rod 252 by a ball-and-socket joint which is formed with a convex spherical surface 278 formed at the substantially middle portion of the rod 252, and a concave spherical surface 280 formed in a bush 272, which is fixed in a housing 266 by a caulking 270. A slot 294 for low pressure and a slot 296 for high pressure are formed on the valve 222. When the rotary shaft 230 is driven by suitable power to supply a low pressure fluid from the slot 294, the cylinder barrel 236 is rotated by the rotation of the rotary shaft 230, so that each piston is reciprocated in the cylinder by the incline of the swash plate 220. The low pressure fluid supplied from the slot 294 is exhausted as a high pressure fluid from the slot 296 to provide a pumping action.

It has been known that a motor action can be provided by a reversal action. In a motor operation, a centrifugal force proportional to weight and square of rotary speed is provided to each of the pistons 248 and shoes 250. However, the other part 240 of the cylinder barrel 236 is mounted to the rotary shaft 230. Each piston 248 is rotatably jointed to the rod 252 by a balland-socket joint through the first piston head 254 sliding in one part of the cylinder barrel 236 and the second piston head 256 sliding in the other part, and the rotary center of the first piston head 254 to the rod 252 corresponds to the centroid of the piston head. Similarly, the rotary center of the second piston head 256 to the rod 252 corresponds to the centroid of the piston-shoe system. Accordingly, a centrifugal force applied to the piston-shoe system is received by the rotary shaft 230 and does not reach one part 238. The friction force between the second piston head 256 and the cylinder wall is increased by the centrifugal force, but the friction force between the first piston head 254 and the cylinder wall is not increased by the centrifugal force. Accordingly, the disadvantages of decrease of volume efficiency, friction and the seizure of the one part 238 and the valve plate 222 can be completely overcome by the centrifugal force in the piston-shoe system. When the rotary shaft 230 is bent, the cylinder 246 formed in the cylinder barrel 236 is curved but no trouble occurs because the piston heads 254 and 256 are rotatably jointed to the rod 252.

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

What is claimed as new and desired to be secured by Letters Patent of the United States is:

1. A piston used in a piston type fluid pump motor which comprises at least two piston heads fitted in a cylinder barrel having coaxially aligned portions, each of said piston heads being rotatably jointed by a balland-socket joint to a rod which is movably connected to a swash plate,

whereby a torque generated on said swash plate is transmitted to said cylinder through said piston heads.

2. A piston according to claim 1, wherein each of said piston heads comprises:

a housing of a substantially cylindrical shape rotatably jointed by said ball-and-socket joint formed with a convex spherical surface on said rod and a concave spherical surface on said piston head.

3. A piston according to claim 1, wherein the other end portion of said rod is connected to a shoe which is slidably fitted onto a swash plate.

4. A piston according to claim 1, wherein a shoe is fitted to one end of said rod and slidably fitted to a swash plate whereby said rod can move reciprocally.

5. A piston according to claim 1, wherein a bush is mounted in said piston head to joint with said rod by said ball-and-socket joint.

6. A piston according to claim 1, wherein said piston is used in an axial piston type fluid pump motor.

7. A piston according to claim 1, which further comprises a lubricant recess on each of said piston heads which is connected to a lubricant passage in a rod.

8. A piston as set forth in claim 1, wherein said rod has a middle portion and two end] portions.

9. A piston according to claim 1, wherein one of said piston heads is jointed at the middle portion of the rod and a second of said piston heads is jointed to one end portion of said rod.

10. A piston as set forth in claim 9, further comprisdrive means for applying a torque to said piston heads; and

means for providing a reaction force to the other end portion of said rod.

11. A piston according to claim 1, wherein one of said piston heads is fitted to one part of a cylinder barrel connected to a valve and rotatably jointed to a rotary shaft, and the other of said piston heads is fitted to a separate part of said cylinder barrel mounted to said rotary shaft.

12. A piston as set forth in claim 10, wherein said means for providing a reaction force to the other end portion of said rod is a swash plate.

13. A piston according to claim 11, wherein a rotary center of said first piston head corresponds to a cen troid of said piston and a rotary center of said second piston head corresponds to a centroid of a piston-shoe system.

Claims

1. A piston used in a piston type fluid pump motor which comprises at least two piston heads fitted in a cylinder barrel having coaxially aligned portions, each of said piston heads being rotatably jointed by a ball-and-socket joint to a rod which is movably connected to a swash plate, whereby a torque generated on said swash plate is transmitted to said cylinder through said piston heads.

2. A piston according to claim 1, wherein each of said piston heads comprises: a housing of a substantially cylindrical shape rotatably jointed by said ball-and-socket joint formed with a convex spherical surface on said rod and a concave spherical surface on said piston head.

8. A piston as set forth in claim 1, wherein said rod has a middle portion and two end portions.

10. A piston as set forth in claim 9, further comprising: drive means for applying a torque to said piston heads; and means for providing a reaction force to the other end portion of said rod.

13. A piston according to claim 11, wherein a rotary center of said first piston head corresponds to a centroid of said piston and a rotary center of said second piston head corresponds to a centroid of a piston-shoe system.