US3633467A

US3633467A - Hydraulic pump or motor device plungers

Info

Publication number: US3633467A
Application number: US886648A
Authority: US
Inventors: Makoto Watanabe; Naoyuki Kitayama
Original assignee: Komatsu Ltd
Current assignee: Komatsu Ltd
Priority date: 1968-12-28
Filing date: 1969-12-19
Publication date: 1972-01-11
Anticipated expiration: 1989-01-11

Abstract

A plunger for a pump or a motor comprising a plunger body having a hollow interior having a generally cylindrical inner surface and a filler body molded in the interior and prevented from axial, spiral and circumferential displacement relative to the plunger body by two portions of the inner surface differently shaped from each other and also from the generally cylindrical portions. The two portions may be two spiral grooves having different pitches from each other, or a groove having circumferentially varying depth. These grooves are radially deeper than the inner surface at the open end of the hollow interior.

Description

United States Patent Dec. 28, 1968, Japan, No. 43/114438 HYDRAULIC PUMP OR MOTOR DEVICE PLUNGERS 8 Claims, 4 Drawing Figs.

US. Cl 92/172,

92/248 Int. Cl F16j l/00 Field of Search 92/248,

Primary Examiner-Martin P. Schwadron Assistant Examinerlrwin C. Cohen Attorney-Steinberg and Blake ABSTRACT: A plunger for a pump or a motor comprising a plunger body having a hollow interior having a generally cylindrical inner surface and a filler body molded in the interior and prevented from axial, spiral and circumferential displacement relative to the plunger body by two portions of the inner surface differently shaped from each other and also from the generally cylindrical portions. The two portions may be two spiral grooves having different pitches from each other, or a groove having circumferentially varying depth. These grooves are radially deeper than the inner surface at the open end of the hollow interior.

HYDRAULIC PUMP R MOTOR DEVICE PLUNGERS This invention relates in general to fluid pressure translating device of the reciprocating type, and more particularly to a new and improved plunger construction particularly adapted for use in hydraulic pumps or motors.

Generally speaking, the plunger-type hydraulic pump is characterized by a higher pressure generated thereby than pressures generated by the gear pump or the vane pump. In such a plunger-type hydraulic pump where the operating liquid medium is highly pressured, it is desirable that the volume of the pressured liquid medium is as small as possible on the ground that it is impossible to neglect an influence of compressibility of the liquid medium on the volumetric efficiency of the pump. In a pump of the class described having a small suction stroke volume, if a large output per unit time is required, it is necessary to rotate the pump at a correspondingly high speed. As the plunger of the pump reciprocates once per one rotation of the driving shaft of the pump, the higher the rotating speed the larger the inertia force, so that it is necessary to correspondingly strengthen the plunger reciprocating mechanism. However, it is undesirable to weight the plunger, and therefore, it is required to reduce the inertia force of the plunger. It is well known that an inertia force of a body proportionates to a mass thereof and the square of the velocity thereof. Under these circumstances, many attempts have been proposed to reduce the mass of the plunger in such a manner that the major internal portion of the plunger is removed for lightening the plunger as light as possible. However, if the plunger is provided with a hollow interior opened to the liquid medium, the volumetric efficiency becomes inferior due to the compressibility of the liquid medium filled in the hollow interior as set forth hereinbefore. In view of this, it is undesirable to provide a hollow interior in the plunger but it is desirable to form a solid plunger. In order to solve the contradictory requirements, such a plunger as having a hollow interior filled with a filler body of a light weight and a high bulk modulus has been proposed in order to make a pump possible to rotate at a high speed under a high pressure, for example, as disclosed in our U.S. Pat. application, Ser. No. 754,184, and now abandoned.

However, a plunger having a hollow interior simply filled with a filler body is disadvantageous because it is probable that the filler body is removed from the hollow interior due to vibration caused by the high speed operation and incomplete connection of the filler body with the plunger body. If the filler body is removed from the hollow interior, it is natural that the filler body will displace relative to the hollow interior as far as the latter is simply cylindrical. In accordance with the invention of the U.S. Pat. application, Ser. No. 754,184, the axial displacement of the filler body relative to the hollow interior is prevented by means of a snap ring. However, the circumferential displacement or rotation of the filler body relative to the hollow interior also probably occurs and is to be prevented. When the filler body rotates in the hollow interior relative thereto, it is apparent that these members are worn, and therefore, various disadvantages troubles such as shakiness, jolt, noise, etc., are caused before long.

The primary object of this invention is to provide a plunger having a small inertial mass without lowering the volumetric efficiency and the durability in operation at a high speed for use in the plunger pump or motor, overcoming the abovestated drawbacks.

Briefly stated in accordance with one aspect of this invention, there is provided a plunger for a pump or motor compris ing a plunger body having a hollow interior having a generally cylindrical inner surface, at least two portions of the inner surface departing from an open-end thereof, differing from each other and from the other portion of the inner surface in shape, and the hollow interior having a cross-sectional area at at least one of the two portions larger than that of the hollow interior at the open end, and a filler body in the plunger body interior and having portions received in the two portions of the inner surface to prevent axial, spiral and circumferential displacements of the filler body relative to the plunger body.

The invention will be better understood and other objects and additional advantages of the invention will become-apparent upon perusal of the following description taken in connection with the drawings, in which:

FIG. 1 is a longitudinal section of a hydraulic fluid pressure translating device incorporating one embodiment of the present invention;

FIG. 2 is a central sectional view on-an enlarged scale of the improved plunger construction used in connection with the device illustrated in FIG. 1;

FIG. 3 is a cross-sectional view thereof taken alongthe line 33 ofFIG. 2; and

FIG. 4 is a central sectional view on an enlarged scale of another embodiment of this invention.

Similar numerals refer to similar parts throughout the several views.

While this invention is susceptible to embodiment in many different forms, there are shown in the drawings and will herein be described in detail two embodiments of the invention, with the understanding that the present disclosure is to be considered as an exempliflcation of the principles of the invention and is not intended to limit the invention to the particular embodiments illustrated. The scope of the invention will be pointed out in the appended claims.

Referring now to the drawings, and particularly to FIG. 1, an axial plunger type of hydraulic fluid pressure translating device is shown. The axial pump or motor includes a housing indicated generally at 10 having an end plate 11 removably secured thereto. A drive shaft 12 is rotatably supported at opposed ends of housing 10 by

suitable bearings

15 and 16, which also secure drive shaft12 against axial movement. The shaft 12 is drivingly connected, as by splines 13, to a cylinder block 14 for rotation of cylinder block 14 and drive shaft 12 together.

The cylinder block 14 includes plungers, two of which are shown at 20, reciprocally mounted within bores or cylinders 23 in the cylinder block 14. Although only two plungers are shown in FIG. 1, it is to be understood that the cylinder block 14 includes a circumferentially arranged plurality of axially disposed cylinders within the cylinder block, each cylinder having an inner end of a plunger reciprocating therein.

The outer ends 21 of the plungers 20 are spherical ends, which are in engagement with slippers 34 so as to be rotatably and swingably held by the latter. The slipper 34 is rotatably mounted on a swash plate 31 which is swingable within the housing 10 about an axis 33 transverse to and intersecting the axis of the drive shaft 12.

When the drive shaft 12 is externally driven by a suitable means, the cylinder block 14 is rotated, and therefore, the plungers 20 are also revolved on the axis of the'drive shaft 12. Because the swash plate 31 in inclined to the axis of the drive shaft 12, the plungers 20 are reciprocated relative to the cylinders 23 for pumping. The liquid medium sucked into a cylinder from an inlet 17 through a port plate 19 is exhausted to an outlet 18 through the port plate 19 after a half turn of the drive shaft 12 under a pressure.

As is best seen in FIG. 2 and FIG. 3, the plunger 20 includes an axially elongated body 200 which is generally cylindrically shaped, and which includes a portion of reduced'diameter'201 adjacent the forward end thereof which merges into the spherical end 21. The plunger 20 is preferably formed of a wear resistant material that is capable of withstanding high stresses, such as a heat treated steel or steel alloy. In order to reduce the weight of the plunger 20, an'axially elongated generally cylindrical cavity 202 is formed generally centrally therein, and extends substantially the entire length of the body 202. An axially extending centrally disposed opening 203 is formed in the forward end of the plunger 20, the purpose of which will hereinafter become apparent.

In order to prevent adverse compressibility effects due to the presence of liquid medium in the cavity 202, a filler body 204 is provided in the cavity 202. The filler body 204 is preferably an inert, light-weight material of sufficient high bulk modulus as to avoid significant compression by the liquid medium. Lightgweight metallic materials such as aluminum or magnesium, and alloys thereof, are suitable for this purpose. Thermo-setting artificial resins are also suitable for this purpose. Such a material may be conventionally transfer molded or compression molded into the cavity 202. Other materials may be poured or injection molded, if desired. The cavity 202 in the plunger may be formed by drilling, or if desired, the plunger 20 may be forged with the cavity 202 being formed in the forging operation. A central axially extending hole 205 is formed in filler body 204, and is positioned in alignment with the hole 203 in the forward end of the plunger 20, to allow liquid medium to flow through the plunger from the cylinder 23 to provide lubrication to the forward end of the plunger 20, and to hydrostatically balance the slipper 34.

Novel means are provided for retaining the filler body 204 against axial, spiral and circumferential displacements within the plunger chamber 202, including at least two portions of the generally cylindrical inner surface areas of the plunger chamber 202. In accordance with this embodiment, the two

portions

206 and 207 are formed in a single generally circumferential groove in the inner surface. That is to say, the single circumferential groove is radially formed and has varying depth. A portion 207 of the groove is deeper than another portion 206 from the general inner surface of the plunger chamber 202. The groove may be an ellipse in the diametrical direction of the plunger chamber 202 in view of machining operation. The elliptic groove has the two deepest portions 207 and four intermediately deep portions 206. By virtue of e the above-mentioned manner for forming the filler body 204,

it completely fills the groove having the

portions

206 and 207,

and therefore, the filler body 204 is restricted not only from axial displacement but also, at the same time, from any spiral and/or circumferential displacement relative to the plunger body 200. In order to prevent the axial displacement of the filler body 204 relative to the plunger body 200, it is also noted that, in accordance with this invention, the filler body 204 has a portion where the cross-sectional area is larger than that of the end 208 thereof.

Reference is now made to FIG. 4 illustrating another embodiment of a plunger 20 in accordance with this invention. The plunger 20' is made similarly to the plunger 20 of the first embodiment, but is formed with a different cavity 212. The plunger cavity 212 is also generally cylindrical, but has an intermediate part 213. A portion 215 situated deeper in cavity 212 than the intermediate part 213 of the generally cylindrical inner surface of the plunger cavity 212 is formed with a screw thread groove. Another portion 216 before the intermediate part 213 towards the open-end of the plunger cavity 212 of the inner surface thereof is formed with another screw thread groove. The two

screw thread grooves

215 and 216 are different in pitch, and particularly, in a preferred embodiment, one of the two pitches is positive forming a right-hand thread while the other is negative forming a left-hand thread, so that these two

screw thread grooves

215 and 216 are to be turned in opposite directions for axial displacement in the same direction. For facilitating the machining, the plunger cavity 212 has a smaller diameter in the portion 215 than the portion 216. It is preferred that the screw thread groove 216 is not axially extended up to the open-end of the plunger cavity 212, so that a part 217 of the plunger cavity 212 remains without being formed with the groove 216. A filler body 214 is formed similarly to the preceding embodiment, so that the two screw threads are formed in the generally cylindrical outer surface thereof and completely complement and fill the recessive inner screw thread groove 215 and the outer screw thread groove 216 which is nearer to the open-end of the plunger body 210. By virtue of these screw threads, of which the pitches are different from each other, the filler body 214 is restricted not only from axial displacement but also, at the same time, from any spiral and/or circumferential displacement relative to the plunger body 210.

Thus, it will be seen that with both embodiments of the invention the plunger has a plunger body formed with a bore extending axially along the interior of the plunger body from one end thereof and defined by the inner generally cylindrical surface of the plunger body. This bore is filled by the filler body which has an outer surface directly engaging and completely complementary to the inner surface. One of these surfaces is formed with surface cavities and the other of the surfaces is formed with surface projections complementary to and filling the cavities, and all of these surface cavities and projections are situated inwardly of the end of the plunger body up to which the filler body extends so that these complementary surface cavities and projections prevent axial displacement of the filler body out of the plunger body. In the case of FIGS. 2 and 3, the complementary surface cavities and projections form the substantially elliptical enlargement of the filler body which is illustrated in FIG. 3, and it will be noted that this enlargement is formed by a pair of projections of the filler body having the

portions

206 and 207 which are of a gradually diminishing radial depth with respect to the generally cylindrical inner surface of the plunger body, with each projection extending circumferentially about the axis of the plunger body through approximately to provide the cross section of the filler body which is illustrated in FIG. 3. As a result the pair of complementary surface cavities and projections shown in FIG. 3 will prevent circumferential as well as axial movement of the filler body with respect to the plunger body.

In the case of FIG. 4, the complementary surface cavities and projections are in the form of the illustrated

screw threads

215 and 216 with the screw thread 216 having a larger diameter than the screw thread 215 and forming a thread of characteristics different from the thread 215 so that in this case also the complementary surface cavities and projections serve to prevent both circumferential and axial movement of the filler body with respect to the plunger body.

While particular embodiments of this invention have been illustrated and described, modifications thereof will readily occur to those skilled in the art. It should be understood therefore that the invention is not limited to the particular constructions disclosed but that the appended claims are intended to cover all modifications which do not depart from the true spirit and scope of the invention.

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

l. A plunger for a pump or motor, comprising an elongated plunger body formed with a bore extending axially along the interior of said plunger body from one open end thereof and defined by an inner surface of said plunger body which is of a generally cylindrical configuration, a filler body situated within and filling said bore of said plunger body, said filler body having an outer surface which is complementary to and engages the entire area of the inner surface of said plunger body, said surfaces being formed respectively with complementary surface cavities and surface projections which respectively completely fill said cavities, an axial space defined between said one open end of said plunger body and said surface cavities and projections, said axial space having a radial dimension less than the radial dimension of the nearest complementary surface cavity and projection, whereby all said surface cavities and projections are situated inwardly of said one end of said plunger body up to which said filler body extends, so that all of said complementary surface cavities and projections are axially displaced away from said one end of said plunger body for preventing axial movement of said filler body out of said plunger body through said one end of the latter, each of said complementary surface cavities and projections extending at least through approximately 180 about the axis of said plunger body, and said plurality of complementary surface cavities and projections having a configuration which prevents axial, spiral, and circumferential movement of said filler body with respect to said plunger body.

2. The combination of claim 1 and wherein there are only two surface cavities and complementary surface projections respectively filling said surface cavities.

3. The combination of claim 2 and wherein said two complementary surface cavities and surface projections respectively filling said cavities are circumferentially displaced with respect to each other through 180 about the axis of said plunger body but are in axial alignment with respect to each other, with each of the surface cavities and the surface projections filling the latter having a configuration which provide each surface projection with a radial dimension with respect to the plunger body axis which gradually increases through approximately 90 and decreases through the remaining 90, so that the pair of complementary surface cavities and projections form in cross section an area of substantially elliptical configuration.

4. The combination of claim 1 and wherein said complementary surface projections and cavities are in the form of screw threads which respectively differ from each other so that turning at one of the screw threads will result in binding at another of the screw threads.

5. The combination of claim 4 and wherein said screw threads which form the complementary surface cavities and projections are axially displaced with respect to each other along the axis of said plunger body.

6. The combination of claim 5 and wherein there are only two screw threads forming a pair of surface cavities and complementary surface projections filling the surface cavities.

7. The combination of claim 6 and wherein said two screw threads are located one nearer to said one end of said plunger body than the other, and that one of said screw threads which is nearer to said one end of said plunger body having a diameter greater than the other of the screw threads.

8. The combination of claim 6 and wherein said two screw threads are respectively a left-hand thread and a right-hand thread.

Claims

1. A plunger for a pump or motor, comprising an elongated plunger body formed with a bore extending axially along the interior of said plunger body from one open end thereof and defined by an inner surface of said plunger body which is of a generally cylindrical configuration, a filler body situated within and filling said bore of said plunger body, said filler body having an outer surface which is complementary to and engages the entire area of the inner surface of said plunger body, said surfaces being formed respectively with complementary surface cavities and surface projections which respectively completely fill said cavities, an axial space defined between said one open end of said plunger body and said surface cavities and projections, said axial space having a radial dimension less than the radial dimension of the nearest complementary surface cavity and projection, whereby all said surface cavities and projections are situated inwardly of said one end of said plunger body up to which said filler body extends, so that all of said complementary surface cavities and projections are axially displaced away from said one end of said plunger body for preventing axial movement of said filler body out of said plunger body through said one end of the latter, each of said complementary surface cavities and projections extending at least through approximately 180* about the axis of said plunger body, and said plurality of complementary surface cavities and projections having a configuration which prevents axial, spiral, and circumferential movement of said filler body with respect to said plunger body.

3. The combination of claim 2 and wherein said two complementary surface cavities and surface projections respectively filling said cavities are circumferentially displaced with respect to each other through 180* about the axis of said plunger body but are in axial alignment with respect to each other, with each of the surface cavities and the surface projections filling the latter having a configuration which provide each surface projection with a radial dimension with respect to the plunger body axis which gradually increases through approximately 90* and decreases through the remaining 90*, so that the pair of complementary surface cavities and projections form in cross section an area of substantially elliptical configuration.