US3896707A

US3896707A - Filled piston retaining means with erosion protection

Info

Publication number: US3896707A
Application number: US391337A
Authority: US
Inventors: William L Holmstrom
Original assignee: Caterpillar Tractor Co
Current assignee: Caterpillar Inc
Priority date: 1973-08-24
Filing date: 1973-08-24
Publication date: 1975-07-29
Anticipated expiration: 1992-07-29
Also published as: GB1457460A; JPS5050701A; JPS5848750B2

Abstract

A piston such as used in axial piston hydraulic translating units, comprising a hollowed-out skirt portion defining a cavity filled with a core of lightweight filler material, the material being retained in place against axial displacement by convex disc core-retaining means forceably insertable within said cavity. In position, the core-retaining means further protects the core filler material from erosion due to high ambient fluid pressure.

Description

United States Patent [191 Holmstrom [451 July 29, 1975 1 FILLED PISTON RETAINING MEANS WITH EROSION PROTECTION [52] U.S. Cl. 92/172; 91/488; 92/248; 92/249; 92/255; 220/305 [51] Int. Cl Fl6j 1/00 [58] Field of Search 92/172, 248, 249, 255; 220/305; 91/488 [56] References Cited UNITED STATES PATENTS 1,167,975 l/1916 Burlingham 92/172 X 1,881,945 10/1932 Raisch 220/24 A 2,541,250 2/1951 Hogg 220/24 A 3,000,304 9/1961 Donaldsonm. 220/24 A 3,325,891 6/1967 Hook et a1. 220/24 A 3,633,467 1/1972 Watanabe et a1 92/248 X 3,741,077 6/1973 Hulsebus et a1. 92/248 X FOREIGN PATENTS OR APPLICATIONS 922,038 l/195 5 Germany 92/249 Primary Examiner-Irwin C. Cohen Attorney, Agent, or Firm-Phillips, Moore, Weissenberger Lempio & Strabala [57] ABSTRACT A piston such as used in axial piston hydraulic translating units, comprising a hollowed-out skirt portion defining a cavity filled with a core of lightweight filler material, the material being retained in place against axial displacement by convex disc core-retaining means forceably insertable within said cavity. In position, the core-retaining means further protects the core filler material from erosion due to high ambient fluid pressure.

3 Claims, 3 Drawing Figures FILLED PISTON RETAINING MEANS WITH EROSION PROTECTION BACKGROUND OF THE INVENTION This invention relates to a reciprocating piston-type fluid translating device such as used for pumps or motors. More specifically, the invention relates to a lightweight core piston of the type used in these units having an improved means for retaining the core against axial displacement during operation of the piston, and for protecting the core material from erosion due to fluid pressure.

Conventionally, the weight of the pistons contained within these translating units is reduced by hollowing out the skirt portion of the pistons. This, however, increases the dead volume of fluid that must be moved within the translating unit, and can have the effect of decreasing the efficiency of these units. Consequently. it is usual to refill the hollowedout portion with a material of lighter weight than that of the piston, and which possesses a sufficiently high bulk modulus to resist compression under the high pressures encountered during operation. Such filler material must be positively retained within the piston in some manner, so that it will not be displaced during operation of the translating units, thereby potentially causing severe damage to such units.

Prior attempts have been made to provide lightweight pistons for use in these hydraulic translating units. Such pistons are commonly made from solid bar stock material and expensive machining operations are required to shape the piston to the desired configuration. Further, the means employed to retain the filler in position within the pistons are frequently inadequate, leading to loosening or dislodging of the filler core during operation of the piston. Also, these retaining means frequently require additional machining operations, further adding to the cost of the piston. Additionally, although prior core designs have usually resulted in a lightweight piston. the retaining means employed have frequently provided no positive protection for the filler material which is directly exposed to the fluid being compressed, resulting in erosion of the filler material, especially at the lips of the passage used for flow of lubricant through the piston.

SUMMARY AND OBJECTS OF THE INVENTION The core retaining means of this invention provides a relatively simple and economical method of retaining a lightweight core of filler material within the bore of a piston, while at the same time protecting this filler material from erosion resulting from exposure to fluid pressure.

Accordingly, it is an object of this invention to provide an efficient and economical means of retaining a core of filler material within the hollowed-out skirt portion ofa piston used in piston-type hydraulic translating units.

It is a further object of this invention to provide coreretaining means which with protect the core filler material from erosion due to fluid pressure.

BRIEF DESCRIPTION OF THE DRAWINGS Other objects of this invention will become apparent from the following description of the drawings wherein:

FIG. 1 is a partially cut-away longitudinal crosssectional elevation of an axial piston hydraulic translating unit including a piston embodying the core-retaining means of this invention;

FIG. 2 is a cross-sectional elevation of the piston of FIG. 1 illustrating the core filler material in conjunction with the core-retaining means of this invention; and

FIG. 3 is a fragmented cross-sectional elevation of a piston illustrating an alternate embodiment of the coreretaining means of this invention.

DETAILED DESCRIPTION OF THE INVENTION FIGS. 1, 2 and 3 illustrate pistons useful in pistontype hydraulic translating units. With particular reference to FIG. 1, axial piston hydraulic pump or motor 10, hereinafter referred to as pump 10, is shown having rotatable drive shaft 11 extending through end wall 12 of cylindrical housing 13. Circular head 14 closes end of housing 13 opposite from end wall 12, and a pair of bearings 16 support drive shaft 11 in end wall 12., and head 14, respectively. Within chamber 17 formed by housing 13 and head 14, annular barrel I8 is disposed in coaxial relationship to drive shaft 11, and has sleeve portion 19 extending towards end wall 12 and carrying first splines 20 which engage second splines 21 on drive shaft 11, so that barrel 18 and drive shaft 11 are con strained to rotate together.

Barrel 18 is provided with a plurality of cylindrical bores 22 (one shown) which extend in a direction parallel to drive shaft 11, and are in equally angularly spaced relationship thereto. A cylindrical hollow-filled core piston 23 is disposed in each bore 22. Each piston 23 is provided with a ball element forming a spherical base portion 24 thereof. Piston 23 is further provided with core-retaining means 25 in the trailing end portion thereof.

To constrain piston 23 to undergo a reciprocating motion as barrel 18 turns, a cam plate 30 is disposed within chamber 17 against end wall 12, having a flat surface 26 angled relative to the rotary axis of drive shaft 11 and barrel 18. Spherical base portion 24 of piston 23 is received in conforming depression 27 of slipper pad 28 which rides against flat surface 26 of cam plate 30. A circular port plate 29 is disposed between barrel 18 and head 14; a first passage 31 extends from bore 22 through port plate 29.

Port plate 29 is provided with a pair of arcuate slots 32 (one shown) having a radius equal to the spacing of first passage 31 from the rotary axis.

Head 14 has conventionally arranged inlet and outlet ports (not shown) formed therein which open to slots 32.

In operation, rotation of drive shaft 11 rotates barrel 18, and piston 23 is reciprocated in bore 22 by cam plate 30. As barrel 18 rotates, piston 23 delivers high pressure fluid through first passage 31 as it passes over the outlet port and port plate 29, and receives inlet fluid through the inlet port as it passes over the inlet port, in a conventional manner.

With particular reference to FIG. 2, piston 23 comprising generally spherical base portion 24 and hollow skirt portion 33 is shown filled with lightweight core filler material 34. This core filler material may be any suitable lightweight material such as that described in the co-pending application of Bristow, et al., Ser. No. 371,666, Filed June 20, 1973, having the same assignee as the present invention.

Preferably, inner wall 3 of hollow skirt portion 33 defines a stepped cavity 37 (shown filled with filler material 34 of a cured epoxy resin, or the like. To provide maximum strength, the cross-section of the cavity is substantially smaller at the end proximate to spherical base portion 24, and substantially larger proximate trailing end 38. The wall connecting the two portions of the cavity may be angled to relieve stresses and suitably accommodate the lightweight filler.

Filler material 34 is held against axial displacement and protected from erosion due to fluid pressure by coreretaining means 25, generally comprising a concavo-convex circular dial having an inwardly converging outer periphery 39. A protrusion 41 is provided in core filler material 34, for example by machining, and coreretaining means 25 is forceably inserted into trailing end 38 of piston 23 and abuts the protrusion 41.

The inwardly converging periphery 39 of core retaining means 25 provides point contact circumferentially around inner wall 36 of hollow skirt portion 33. The forces exerted by core-retaining means 25 against inner wall 36 and filler material 34 retains both coreretaining means 25 and filler material 34 in position.

During operation of piston 23, the forces exerted by fluid pressure upon core-retaining means 25 during compression improve its retaining capabilities and shield the filler material 34 from direct contact with erosive fluid forces.

Core-retaining means 25 may be of any suitable material having sufficient durability to protect filler material 34 from erosion, and sufficient flexibility to permit insertion. A resilient steel is excellent for this purpose.

Axial second passage 42 through core filler material 34 communicating with third passage 43 in spherical base portion 24 is provided as a channel for the flow of lubricant through piston 23. A hole 44 in core-retaining means 25 is provided to permit lubricant to enter second and

third passages

42 and 43. Preferably, second passage 42 is formed by placing a long rod extending the length of the piston 23 into third passage 43 prior to filling cavity 37, as described in the copending application of Hein, et al., Ser. No. 115,639, filed Feb. 16, 1971, now US. Pat. No. 3,707,l 13 having the same assignee as the present invention.

The core filler material 34 is then molded around the rod in the cavity 37, leaving a passage when the rod is removed. Alternatively, the passage may be drilled through the filler material after it has hardened.

With particular reference to FIG. 3, an alternate embodiment of core-retaining means 25 having an outwardlyconverging outer periphery 45 is shown in position against filler material 34 in piston 23.

What is claimed is:

1. in a piston of the type used in hydraulic translating units, wherein said piston has a base portion for engaging said piston to said unit, and an attached skirt portion with a trailing end, said piston defining a hollowed out cavity extending axially from a plane rearward of said base to an opening in the trailing end, and a core of filler material within said cavity and essentially filling the same; means for retaining the core of filler material within said cavity including concavo-convex disc coreretaining means press-fitted within said cavity, said disc core-retaining means having a press-fit outer edge surface defining an acute angle with respect to said cavity, and said disc core-retaining means having its concave face in contact with an annular protrusion on an end portion of said core filler material positioned within said cavity.

2. The invention of claim 1, wherein said concavoconvex disc core-retaining means defines an inwardly converging outer edge surface.

3. The invention of claim 1, wherein said concavoconvex disc core-retaining means defines an outwardly converging outer edge surface.

Claims

1. In a piston of the type used in hydraulic translating units, wherein said piston has a base portion for engaging said piston to said unit, and an attached skirt portion with a trailing end, said piston defining a hollowed out cavity extending axially from a plane rearward of said base to an opening in the trailing end, and a core of filler material within said cavity and essentially filling the same; means for retaining the core of filler material within said cavity including concavo-convex disc core-retaining means press-fitted within said cavity, said disc core-retaining means having a press-fit outer edge surface defining an acute angle with respect to said cavity, and said disc core-retaining means having its concave face in contact with an annular protrusion on an end portion of said core filler material positioned within said cavity.

2. The invention of claim 1, wherein said concavo-convex disc core-retaining means defines an inwardly converging outer edge surface.

3. The invention of claim 1, wherein said concavo-convex disc core-retaining means defines an outwardly converging outer edge surface.