US3635126A

US3635126A - Hydrostatic button bearings for pumps and motors

Info

Publication number: US3635126A
Application number: US791955*A
Authority: US
Inventors: William K Engel; William B Norick; James L St Germain; Peter Hakkenberg Van Gaasbeek
Original assignee: Caterpillar Tractor Co
Current assignee: Caterpillar Inc
Priority date: 1969-01-17
Filing date: 1969-01-17
Publication date: 1972-01-18
Anticipated expiration: 1989-01-18
Also published as: DE2001484A1; ES403954A1; FR2028516A1; ES375523A1; GB1301108A; BE744564A; GB1301109A

Abstract

In axial-piston, hydraulic pumps and motors, the thrust loadings of the pistons on their bearing supports vary proportionally to pressures in the unit and also circumferentially around the bearing supports. By employing hydrostatic button bearings pressurized in ''''sets'''' around the bearing support with at least one set pressurized with the unit''s inlet pressure and another ''''set'''' pressurized by the unit''s outlet pressure, improved bearing performance is achieved. Also, certain surface configuration forming the sills and recesses of the individual buttons can enhance bearing performance.

Description

United mates Patent Engel 1 11 mm 1451 Jan. 18, 1972 [541 HYDROSTATHC MJTTUN 1m .1-1: 1h GS 2,577,242 12/1951 FOR PUMPS AND MUHURS 7, 8/1958 3,046,906 7/1962 [72] Inventors: William 1K. Engel, Peona; William ]B. 2 804 828 9/1957 Nori glgjoliet; jarnesL. St. Germain, Plain- 327495o 9/1966 field; Peter Halrltenlherg V1111 Gansheelt, Peoria, all of FOREIGN PATENTS OR APPLICATIONS 1 Assisnw Caterpillar Tractor Peoria, 883,348 7/1943 France ..l03/l62 22 Filed: Jan. 17, 1969 Primary Examiner-William L. Fresh PP 1 Attorney-Fryer,Tjensvold,Feix,Phi1li ps& Lempio 52] us. e1. ..92/57, 91/486, 91/505 [571 ABSTRACT [51] int. Cl ..F01h 13/041, F0411 1/26 In axiabpiston hydraulic pumps and motors, the films [58] Field 01 Search .....l03/l62; 230/ 128; 91/ 108, 484-489; loadings of the pistons on their hearing supports vary propob 92/57 tionally to pressures in the unit and also circumferentially around the bearing supports By employing hydrostatic button [56] Rem'emes UM bearings pressurized in sets around the bearing support with UNITED STATES PATENTS at least one set pressurized with the units inlet pressure and another set" pressurized by the un1t"s outlet pressure, 1m- 2,298,350 10/1942 Vickers 103/162 proved bearing performance is achieved, A150, certain surface 3,257,960 6/1966 Keel ...9l/486 fi ti f i the Sills and recesses f the individual Thoma Q..-

buttons can enhance bearing pe fo rnance I 2,449,297 9/1948 Hoffer .....l03/162 2,463,299 1/1949 Nixon ..103/l62 6 Claims, 9 Drawing Figures PATENTEDJAN181972 3,635,126

man 1 0r 3 INVENTORS WILLIAM K. ENGEL PETER H. VAN GAASBEEK WILLIAM B. NORICK BY JAMES L. ST. GERMAlN ATTORNEYS PATENTED JANI8I972 363.512

SHEEI 2 W3 IZ E I INVENTORS WILLIAM K, ENGEL PETER H. VAN GAASBEEK WILLIAM B. NORICK BY JAMES L, ST. GERMAIN W ?W/ 7) I VLATTORNIEYS PATENTEDmmmz 3.635126 SHEET 3 OF 3 E .15 .Q D E ROTATION or THRUST PLATE E E 58 56 7 32 i 34 5o --'-g H 35 5? 59".; l lllllllllll v h M M 57 FORCE DIAGRAM (PRESSURE) INVENTORS WILLIAM K. ENGEL PETER H. VAN GAASBEEK WILLIAM B. NORICK BY JAMES L. ST. GERMAIN K 2 z W M m w fi- ATTORNEYS IIYDROSTATIC BUTTON BEARINGS Wilt FUD/IFS ANN MOTORS BACKGROUND OF THE INVENTION Currently, axial-piston hydraulic pumps and motors are often required to operate at pressures in the range of 5,000 p.s.i. which can develop high-oblique thrust forces on the bearings that vary as the components rotate. When the units are of the variable displacement type, the angle of the oblique thrust forces can vary appreciably.

Prior art units of the above type have employed hydrostatic buttons at the socket end of the piston or connecting rods and a passage through each rod and its associated piston whereby the associated button is pressurized at the cylinder pressure of its rod. Examples of such prior art arrangements are illustrated in US. Pat. No. 2,241,701 issued to Dow and US. Pat. No. 3,121,816 issued to Firth. One of the difficulties with the prior art arrangements is that the pressures in the bearing pad vary sharply, sometimes exceeding the maximum pressure in the unit and at other times going below the minimum pressures required for proper bearing support, particularly on the intake stroke of the associated piston. This situation along with the stabilizing problems of the individual buttons experienced at high-rotational speeds have left room for measurable improvement.

Further, the manufacture of the hydrostatic button bearings and the required fluid supply system for axial pistontype hydraulic units shown in the prior art arrangements are expensive and complex. In addition, individual replacement of the button bearing is often impractical, if not impossible. Thus, considerable difficulty is experienced with correcting clogging problems in the prior art arrangements and should one of the buttons fail to operate properly (clog), the thrust bearing for that piston rod .is lost completely. This situation can quickly cause scoring of the associate runner surface on which the button bearings track and subsequently the failure of the complete thrust bearing system.

In addition, many of the prior art button bearing systems can not efficiently cooperate with mechanical bearings to jointly absorb the thrust forces, which vary with displacement angle, around the thrust plate or ring assembly since it is difficult to simultaneously maintain the proper clearances for the two-bearing arrangements in such systems.

SUMMARY OF THE INVENTION Most of the above difficulties can be eliminated and improved performance achieved by the hydrostatic thrust support system of this invention which is more economical than the prior art systems. Basically, it is employed in axial pistontype hydraulic units having a plurality of connecting rods journaled in a common rotating thrust plate assembly and includes a plurality of pockets circumferentially disposed in the units structure adjacent to the thrust plate assembly, passage means connecting each pocket to a source of pressurized fluid, and a plurality of button bearing means received in each pocket, each button bearing means including a pad area cooperating with a surface on the thrust plate assembly, said pads including a recess having communication with its associated pocket and a circular sill surrounding said recess whereby pressure acting on each button bearing means will urge it toward said surface so the latter will be supported on a hydrostatic film. It is preferred that the buttons be pressurized in semicircular sets, one set pressurized by passages connecting them to the unit's inlet, the other set pressurized by passages connecting them to the units outlet. This provides superior thrust compensation for the circumferentially varying thrust forces about the thrust plate assembly. Further, special pad area configuration will provide a tendency for the individual buttons to tip or tilt slightly due to the hydrodynamic film buildup so that the maximum clearance exists at the leading edge of the but ton which is caused by the rotation of the cooperating surface on the thrust plate assembly. The above arrangement provides for simple and expedient button replacement not possible in prior art designs.

2 BRIEF DESCRIPTION OF THE DRAWINGS The invention will be better understood by reference to the accompanying drawings wherein:

FIG. 1 is a section of a trunnion structure for an axial pistontype hydraulic unit showing the novel hydrostatic button thrust bearing system incorporated therein.

FIG. 2 is an elevation of the trunnion structure with the button bearings removed from their associated pockets in the trunnion and broken lines illustrating the fluid communication passageways connecting the several pockets.

FIG. 3 schematically illustrates the oblique thrust forces acting on the hydrostatic button bearings and an associated mechanical bearing.

FIG. 4 is a section of a broken away portion of the trunnion structure illustrating one of the button bearings in section, and

FIG. 5 illustrates the theoretical pressure profile across a button-bearing face or pad;

FIGS. 6 through 9 illustrate, in plan and section respectively, two-button bearing face or pad configurations.

DESCRIPTION OF A PREFERRED EMBODIMENT The axial piston-type hydraulic unit on which the invention is illustrated is fully described in 11.8. Pat. No. 3,381,472 issued to Brown, ct al., and reference is made to the Brown patent for full construction and operating details of such a unit. In FIG. 1, only the trunnion structure of the unit, along with some of the associated components, are illustrated since these components are principally related to the thrust problems involved. Of course, the current invention is not restricted to the illustrated axial piston-type hydraulic unit and the invention can be employed on other similar-type hydraulic units with many accompanying advantages. Further, it should be appreciated that these hydraulic units can function either as hydraulic pumps or as motors. Basically, the trunnion 10 forms the supporting structure for the thrust plate assembly 11 which is supported for rotation in the center of the trunnion on an inner roller bearing 12 and an outer roller bearing 13, the latter being retained by a bearing block 14 bolted to the trunnion with tapbolts 15. As shown in FIG. 1, tapered roller bearings can be employed and arranged to secure the thrust plate assembly. The hollow thrust assembly includes a female spline 16 for receiving a power shaft and a universal for driving the cylinder barrel (not shown). Also, a circular ring 17 abutting on roller bearing 13 and connected to the thrust plate assembly limits axial movement between the two roller bearings.

The inner portion of the thrust plate assembly 11 includes a radial flange 18, on the periphery of which, roller bearing 12 supports the assembly. In a plurality of sockets 19, circumferentially disposed around the inner face of the radial flan go, the ball ends 20 of piston or connecting rods 21 are received and retained by snaprings 22. The connecting rods are attached to pistons (not shown) in the cylinder barrel 23 which has its ported face 24 supported on a valve plate (not shown). When the cylinder barrel has its port fiace angularly disposed to the radial flange 18, the connecting rods will reciprocate in the barrel with fluid pressures acting on their associated pistons. This situation will cause forces to be applied to the thrust plate assembly through the connecting rods and a passage 25 through each rod can supply lubrication to its socket 19 from the pressure side of its associated piston in a conventional manner.

The angular position of the connecting rods 21 relative to the thrust plate assembly 1 1 during a positive displacement in the hydraulic unit is illustrated in FIG. 3, wherein vectors A, B and C indicate the thrust forces caused by pressures A, B and C acting through the associated connecting rods. As can be seen, the thrust forces vary circumferentially around the thrust plate assembly and each can be converted to an axial component 30 and a radial component 31. It isv the variable axial components of these thrust forces that the instant invention is designed to provide better thrust compensation for than is available in prior art arrangements. The configuration has the following functions and advantages: The hydrostatic buttons support part of the piston thrust load, thus providing lower loads on the antifriction bearing. This allows a smaller antifriction bearing to be used and provides longer bearing life.

The amount of support provided by the hydrostatic buttons is constant for a given pressure, but the axial component of the piston thrust force varies with displacement angle. The antifriction bearing supports the difference in the axial loads as well as the radial component of the piston thrust force.

To accomplish this objective the thrust ring 32 is mounted on a face of the radial flange 18 with dowels 33 so its thrust face 34 can form the runner part of a separate hydrostatic bearing formed with each of the buttons. The individual buttons 35 are circumferentially disposed in

pockets

36 and 37 in the trunnion 10, as can be best seen in FIG. 2. Pockets 36, through

passages

38 and 39, are in fluid communication with one side of the unit while pockets 37, through

passages

40 and 41, are in fluid communication with the other side. Thus, pockets 36 form one semicircular set of buttons while pockets 37 form another semicircular set whereby one set will always be pressurized at the units inlet pressure and the other set always will be pressurized at the units outlet pressure.

Utilizing two semicircular sets," pressurized at the inlet and outlet pressures respectively, avoids the individual pressure peaks occurring on the individual pistons and allows the rigidity of the thrust plate assembly to distribute the thrust loading more evenly on several of the individual button bearings composing the set. Use of the buttons in highand low-pressure sets allows the centroid of the hydrostatic button forces to be located close to the centroid of the axial piston thrust forces, thus minimizing moment unbalance on the thrust plate. With the buttons in sets and located as indicated, pressure in each set is continuous and does not fluctuate between inlet and discharge pressure as it would if the button rotated with the piston and rod and were lubricated by a passage through each piston rod. The passages are arranged so the higher pressure will be on the set with the highest loading, whether the high pressure is the unit's inlet or outlet. It is through such an arrangement that substantial advantages can be gained and button replacement greatly simplified.

The general configuration of each button 35 is best shown is FIGS. 4 to 9 wherein it can be seen that each button includes a head portion 50 and a cylindrical skirt 51 having a groove 52 for a seal 53 which prevents leakage of pressurized fluid around the skirt from pocket 36 (or 37) and

passage

38 or 40. It can be seen that the individual button has considerable freedom of movement within its associated pocket.

The skirt 51 of each button is preferably hollow and may include a strainer or screen 54 over its mouth or opening 55 communicating with pressurized fluid in its associated pocket, which is best seen in FIGS. 3 and 9. The skirt fits loosely in its pocket so the button can tip or tilt about the centerline of the pocket. This arrangement allows the individual button to track smoothly on the associated surface 34 and the bearing formed by the button to be less effected by distortion occurring in the thrust plate assembly due to high-thrust loadings. The buttons having a degree of freedom to tilt and move axially can adjust for such things as nonparallelism between the thrust plate and trunnion, variation in assembled distance between thrust plate and trunnion, difference in running clearance required with changes in pressure, and/or temperature.

Basically each button 35 forms a separate hydrostatic bearing with the pad or face 56 of the button having a recess 57 in communication with the pressurized fluid in its pocket through an orifice or restrictor and a raised circular sill 58 which mates with the flat face or surface 34 of the thrust ring 32 which forms the runner of the bearing.

Since the thrust ring is rotating, there is some hydrodynamic bearing effect along with the hydrostatic bearing formed by the flow of pressurized fluid over the sill 58 of the pad or face 56 and acting in the recess. Movement of the thrust ring in the direction of arrow D tends to increase the flow of the fluid passing over the trailing edge of the sill and results in the slight tip of the button illustrated in FIG. 4. The efiects of these actions are reflected in the force diagram illustrated in FIG. 5, wherein the pressure buildup and dropofi across the pad area is illustrated.

Because of there effects it is desirable to design the pad or face so this undesirable tipping or tilting of the pad or face area can be corrected.

More particularly FIGS. 8 and 9 illustrate the simplest button construction. Basically the construction includes the face or pad area 56 having a recess 57 and a raised circular sill 58, which are more clearly depicted in FIG. 9 which is a section along line IX-IX of FIG. 8. The head portion 50 of the button is larger than the skirt portion 51 which is received in pocket 36. Pressurized fluid is supplied through passage 38 (or screen 54 to the mouth 55 of the button unit 35. From inside the skirt the fluid passes through orifice 59 into recess 57. Thus, as pressure increases in passage 38, the pressure acting against the runner provided by surface 34 will increase, supporting the increased thrust loads acting on thrust ring 32 through the thrust plate assembly, etc.

Since the button is free to wobble and move axially in its pocket, the fluid pressure from passage 38 (or 40) acting on the bottom of the button will tend to urge the button toward the thrust face or surface 34 for optimum clearance between the sill and the thrust face or surface for the pressures involved and best hydrostatic film support. By utilizing this arrangement, the effects of both thermal and mechanical distortion are greatly reduced. Also, the hydrostatic button bearings can be matched with cooperating mechanical bearings for sharing the thrust loading so that problems of over and under compensation can be minimized. Having the sill raised centrally on the pad area also tends to increase the hydrodynamic buildup of pressure on the leading edge of the button pad area, resulting in a favorable tilt of the button. Use of an overbalanced button (face force higher than hub force with recess at full pressure) with a restriction or flow control to reduce recess pressure provides a stable arrangement capable of compensating for changes in pressure profile over the face of the button 7 with changes in speed and oil viscosity. If the button separates too far from the thrust plate, recess pressure drops and the button reseats. If the button tries to contact the thrust plate, recess pressure increases and separates the two surfaces.

FIGS. 6 and 7 illustrate another pad configuration for the button 35 with FIG. 7 being a section along lines VlI-VII of FIG. 6. In this design multiple sills are employed to lessen the hydrodynamic effects referred to above. As can be seen in FIGS. 6 and 7, the face or pad includes an outer minor circular sill 60 which includes a plurality of notches 61 communicating with an inboard groove 62. This minor sill does not provide support but next is a concentric outer major sill 63 followed by a groove recess 64 and then a concentric inner sill 65 with an annular recess 57 located centrally in the pad face. Only the groove recess 64 is supplied with pressurized fluid through interior passages 66 and oil entering the central recess 57 can egress via

passages

67 and 68 to drain. This arrangement tends to change the force diagram, distributing it away from the center area of the button and toward its outer diameter in a ringlike pattern. Since the narrower force ring" will tend to have equal hydrodynamic pressure buildup at diametric opposite sides, it will tend to stabilize the button and lessen its tilt or tipping.

Obviously in the above arrangements the bearings 12 and 13 assist the buttons in stabilizing the thrust plate assembly and provide additional support if the buttons fail to fully compensate or over compensate for the axial thrust loadings, especially at high-swivel angles in the unit. Of course, these bearings absorb the radial component 31 of the oblique thrust forces without assistance from the button bearings.

What is claimed is:

1. In combination with an axial piston-type hydraulic unit having two ports for fluid inlet and outlet, a thrust plate assembly rotatably mounted within the unit and having a plurality of connecting rods journaled in said thrust plate assembly, a hydrostatic thrust bearing system between the unit and said thrust assembly for thrust forces transmitted by the connecting rods to said thrust plate assembly comprising: a plurality of stationary pocket means in said unit adjacent to said thrust plate assembly and circumferentially disposed within the circular periphery of said assembly; a first common passage means in fluid communication with one port of said hydraulic unit commonly connecting a group of pocket means and a second common passage means in fluid communication with the other port of said hydraulic unit commonly connecting the remaining pocket means whereby one group of said pocket means will be connected to the inlet and the other group will be connected to the outlet of said hydraulic unit; a plurality of unitary individual button bearing means and each including a bearing pad and a stem portion, each of said stern portions being received in respective pocket means and being of a size smaller than the size of said pocket means to permit relative axial and tilting movement of said individual button means with respect to said unit, said bearing pad having a central recess in communication with the source of pressurized fluid in its associated pocket means and a raised circular sill area; and a cooperating flat ringlike runner surface mounted with said thrust plate assembly to rotate therewith, said surface disposed parallel to the bearing pads of the several button bearing means whereby pressurized fluid in said pocket means will urge its associated button bearing means toward said rotating runner surface for supporting thrust loads on said thrust plate assembly on a plurality of individual hydrostatic 6 bearings.

2. The combination as defined in claim 1 wherein the thrust plate assembly is supported for rotation on roller bearings and the hydrostatic thrust bearing system cooperates with said roller bearings to compensate for thrust loadings.

3. The combination as defined in claim 1 wherein the pocket means are circular blind bores circumferentially disposed in the body of the hydraulic unit near the circular periphery of the thrust plate assembly whereby axial thrust loadings can be independently compensating by each button bearing means received in said pocket means.

4. The combination as defined in claim 3 wherein both groups of pocket means connected respectively to the inlet and the outlet are in a semicircular arrangement.

5. The combination as defined in claim 1 wherein the pad of each individual button bearing means includes an outer nonload bearing minor circular sill with bleed notches therein, an outer and inner circular sill having a pressurized circular recess therebetween and a center recess having a passage communicating to bleed fluid from said center recess.

6. The combination as defined in claim 1 wherein the group of pocket means commonly connected to the port acting as the inlet of the hydraulic unit are circumferentially disposed behind the pistons of the cylinders communicating with the inlet and the group of pocket means commonly connected to the port acting as the outlet of said hydraulic unit are circumferentially disposed behind the pistons of the cylinders communicating with the outlet.

Claims

1. In combination with an axial piston-type hydraulic unit having two ports for fluid inlet and outlet, a thrust plate assembly rotatably mounted within the unit and having a plurality of connecting rods journaled in said thrust plate assembly, a hydrostatic thrust bearing system between the unit and said thrust assembly for thrust forces transmitted by the connecting rods to said thrust plate assembly comprising: a plurality of stationary pocket means in said unit adjacent to said thrust plate assembly and circumferentially disposed within the circular periphery of said assembly; a first common passage means in fluid communication with one port of said hydraulic unit commonly connecting a group of pocket means and a second common passage means in fluid communication with the other port of said hydraulic unit commonly connecting the remaining pocket means whereby one group of said pocket means will be connected to the inlet and the other group will be connected to the outlet of said hydraulic unit; a plurality of unitary individual button bearing means and each including a bearing pad and a stem portion, each of said stem portions being received in respective pocket means and being of a size smaller than the size of said pocket means to permit relative axial and tilting movement of said individual button means with respect to said unit, said bearing pad having a central recess in communication with the source of pressurized fluid in its associated pocket means and a raised ciRcular sill area; and a cooperating flat ringlike runner surface mounted with said thrust plate assembly to rotate therewith, said surface disposed parallel to the bearing pads of the several button bearing means whereby pressurized fluid in said pocket means will urge its associated button bearing means toward said rotating runner surface for supporting thrust loads on said thrust plate assembly on a plurality of individual hydrostatic bearings.