Axial piston hydraulic device with forced lubrication means

Abstract

A hydraulic pump or motor of the axial displacement piston type has a housing containing a rotatable barrel having angularly spaced cylinder bores extending parallel to the axis of rotation and each having a piston movable longitudinally therein. Protruding ends of the pistons ride against a slanting cam surface causing each piston to reciprocate as the barrel rotates. Suitable porting at the opposite end of the barrel provides inlet, outlet, and distributing ports whereby a pumping effect or a motor action may be realized. Heretofore, lubrication of moving elements which are away from the primary flow path including the cam surface has been provided for by leakage from the primary flow path towards a drain outlet in the outer wall of the housing and is sometimes inadequate due to centrifugal pumping action and other effects. This invention assures adequate lubrication of all parts by situating the drain outlet at or near the rotary axis of the system.

Description

BACKGROUND OF THE INVENTION

This invention relates to transducers for interconverting fluid pressure energy and mechanical motion energy and more particularly to hydraulic pumps and motors of the axial piston form.

Rotary hydraulic pumps and motors of the axial piston type have a housing enclosing a rotating barrel in which pistons are provided for reciprocation in a direction parallel to the rotary axis. The pistons are reciprocated by interaction with a cam surface or equivalent linkage. Such axial piston devices are used extensively for driving a variety of mechanisms such as those employed on earthmoving vehicles, for example. In a typical usage one such device may be driven by the vehicle engine to function as a pump for supplying fluid under pressure to fluid motors which in some cases may be an essentially similar device.

The particular fluid used in such devices is normally oil which in addition to serving as a power transmitting medium also serves to provide lubrication to the device. While certain surfaces of the mechanism which need lubrication are inherently exposed to the fluid flow path between the inlet and outlet ports, other surfaces such as the cam surface for example are isolated from the primary flow path. Heretofore it has been the practice to provide a drain outlet in the outer wall of the housing and to rely on leakage past the barrel, pistons and other elements to lubricate surfaces which are not exposed to the primary flow path.

Adequate lubrication in devices of this kind is highly important from the standpoint of reducing wear and overheating and to forestall the possible seizure of relatively moving parts which can occur in extreme situations. We have now found that the conventional practice described above is not always entirely adequate.

Under certain operating conditions, such as high speed low load operation, leakage from the primary flow path may not be sufficient to forestall undesirable effects and that the situation is aggravated by centrifugal forces which tend to direct leakage flow directly to the drain outlet and away from moving surfaces located near or adjacent to the rotary axis. We have further found that this can have undesirable effects additional to the lack of lubrication at the certain surfaces. For example, the main shaft of the device, which connects with an engine or driven load, must pass through a seal. Under some circumstances the centrifugal pumping action described above is sufficient to create a partial vacuum inside the seal sufficient to draw in air with resultant highly undesirable aeration of the oil.

SUMMARY OF THE INVENTION

This invention is a device of a type discussed above wherein adequate lubrication at necessary points is more completely assured. Basically, this is accomplished by eliminating the conventional drain outlet at the radially outer portion of the device and providing instead a drain outlet at or near the rotary axis appropriately placed to force leakage fluid to travel radially inwardly past radially inward surfaces which require lubrication. In addition to assuring lubrication of parts which might otherwise be starved of lubricant this has a further effect of avoiding the creation of negative pressures which might otherwise cause oil aeration.

Accordingly, it is an object of this invention to provide for more adequate and assured lubrication of hydraulic devices of the axial piston form.

The invention together with further objects and advantages thereof will best be understood by reference to the following description of preferred embodiments taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is an angled axial section view of a hydraulic pump embodying the invention, taken along angled line I--I of FIG. 2;

FIG. 2 is a cross-section view of the apparatus of FIG. 1 taken along line II--II thereof;

FIG. 3 is an additional cross-section view of the apparatus of FIG. 1 taken along line III--III thereof;

FIG. 4 is an angled axial section view of a hydraulic pump of the general type shown in FIG. 1 but having modified lubrication means; and

FIG. 5 is a cross-section view of a portion of the apparatus of FIG. 4 taken along line V--V thereof.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawing and particularly to FIG. 1 thereof a hydraulic device 11 of the axial piston type may be adapted to function either as a pump or a motor as is well understood in the art. To facilitate description the device 11 will be herein referred to as a pump and described with reference to this mode of operation, it being apparent that the invention is equally applicable to motors of the axial piston form.

Pump 11 has a rotary drive shaft 12 which extends through one end wall 13 of a cylindrical housing 14 to support and drive an annular barrel member 16. Drive shaft 12, which may be coupled to a driving engine in any suitable known manner, has a flange 17 abutting a bearing 18 disposed in a step 19 of a bore 21 through end wall 13. To prevent leakage of oil out of housing 14 through bore 21 and prevent the entrance of air into the housing, bore 21 has an additional step 22 in which an annular seal 23 is disposed and retained by a snap ring 24.

Drive shaft 12 is disposed along the axis of housing 14 and extends a short distance into a central well 26 in a circular end plate 27 which closes the end of the housing opposite from end wall 13. Well 26 and the adjacent end portion of drive shaft 12 are stepped to receive an additional bearing 28 which journals the adjacent end of the drive shaft within end plate 27.

Considering now the means by which a pumping action is achieved, barrel 16 is disposed within housing 14 in coaxial relation to shaft 12 and has splines 29 engaging splines 31 on a portion of shaft 12 near flange 17 thereof. Accordingly, rotation of the drive shaft 12 turns barrel 16 relative to housing 14. Referring now to FIG. 2 in combination with FIG. 1, barrel 16 has a plurality, nine in this instance, of cylinder bores 32 which extend parallel to the rotary axis of the barrel and which are equi-angularly spaced therearound, successive ones of the cylinder bores being designated by numerals 32A to 32I respectively in the drawings. Each such cylinder bore 32 receives one of a plurality of cylindrical pistons 33 each having a ball element 34 formed on an end which protrudes from barrel 16 within housing 14. To force reciprocation of the pistons 33 as barrel 16 turns, a fixed cam plate 36 is disposed against the inner surface of housing end wall 13. Cam plate 36 has a flat surface 37 facing barrel 16 that is angled relative to the axis of the barrel. The ball element 34 of each piston 33 is received in a matching cavity 38 of an associated one of a plurality of slipper pad elements 39 which ride against surface 37 of cam plate 36.

To maintain slipper pads 39 in contact with cam surface 37, an annular retainer ring 41 is disposed coaxially around shaft 12 and splined engaged to splines 31 of the shaft and has an outer surface 42 with a curvature corresponding to an annular segment of a spherical surface. An annular retainer plate 43 has a matching inner surface 44 in contact with surface 42 and extends outward to overlap each slipper pad 39 a short distance. A compression spring 46 acts between barrel 16 and ring 42 to urge the ring away from the barrel and thus holds the slipper pads 39 against cam surface 37. It may be noted that spring 46 serves the further purpose of urging barrel 16 towards end cover plate 27 to maintain the barrel in preferred operating position. This action is augmented by an additional spring 47 disposed coaxially around shaft 12 within barrel 16 and which acts between a first snap ring 48 engaged in the shaft and a second snap ring 49 engaged in the barrel, this advantageous spring disposition being the subject matter of copending application Ser. No. 330,413 of Paul A. Becksvoort et al for COMPACT AXIAL PISTON HYDRAULIC DEVICE filed concurrently herewith and assigned to the assignee of the present application.

As shaft 12 completes each full revolution each piston 33 is forced by cam surface 37 to undergo one complete reciprocation within the associated cylinder bore 32. Considering now the means by which such reciprocation of pistons 33 effects a pumping action, with reference to FIGS. 1 and 2, a passage 51 extends from each cylinder bore 32 towards the adjacent end surface of barrel 16. Disposed between barrel 16 and end plate 27 is a relatively thin annular port plate 53 having a pair of arcuate slots 54A and 54B lying along a hypothetical circle centered on the axis of shaft 12 and having a radius equal to the radial distance of passages 51 from such axis. Port plate 53 and the slots 54 thereof are positioned whereby slot 54A communicates with the passages 51 leading to those pistons which are in the process of retracting from the port plate at any given time while slot 54B communicates with the passage 51B leading to those pistons which are in the process of moving towards the port plate at any given time, any passage 51 associated with a piston momentarily at an extreme or dead-center position in the reciprocation thereof being out of communication with either slot 54. Thus the retreating pistons 33 create a suction at slot 54A tending to draw fluid into the piston bores communicated therewith while the opposite moving pistons tend to force fluid out of slot 54B. Referring now to FIG. 3 in conjunction with FIG. 2, end plate 27 has a fluid inlet port 56 communicating with an inlet passage 57 leading to slot 54A of FIG. 2 and further has a fluid outlet port 58 communicating with a passage 59 leading to slot 54B of the port plate. Thus if inlet port 56 is communicated with a suitable fluid supply, rotation of the drive shaft 12 generates a forced flow from the input port 56 to output port 58 to provide the desired pumping action.

Referring now again to FIG. 1 some fluid leakage will occur past the pistons 33, as well as between barrel 16 and port plate 53 and between port plate 53 and shaft 12 to cause fluid to enter the chamber 61 between barrel 16 and end wall 13 of housing 14. This leakage fluid is relied upon to lubricate the several relatively moving adjacent surfaces which are within chamber 61 or in communication therewith, such as the cam surface 37, the surfaces of slipper pads 39 which ride upon the cam surface, the adjacent surfaces of slipper pad cavity 38 and piston ball elements 34 and of retainer ring 42 and retainer plate 44 and bearing 18.

Heretofore it has been the custom to provide a drain outlet in the outer wall of housing 14 to avoid an excess build-up of such leakage fluid within chamber 61. This can fail to provide an optimum amount of lubrication under certain conditions such as high speed, low load operation in which fluid pressures in the primary flow path may be relatively low. Moreover a centrifugal pumping action occurs in chamber 61 causing such leakage to tend to flow directly to the drain outlet thereby starving the above described relatively moving surfaces of adequate lubrication.

To assure adequate lubrication and to avoid an undesirable negative pressure within chamber 61, the present invention provides for drainage of chamber 61 at or near the rotary axis of the mechanism. In this embodiment of the invention, a drain passage 62 extends along the axis of the main shaft 12 itself. Passage 62 communicates with a transverse passage 63 in drive shaft 12 that in turn communicates with region 61 at the outer surface of the shaft near flange 17. Drain passage 62 opens at the opposite end into well 26 of end plate 27. While well 26 may be vented to an external drain, it is advantageous to return the draining fluid directly to the primary working fluid flow path, preferably to a relatively low pressure portion thereof which is normally the inlet side in the case of a pump although it is the outlet side in a motor. Thus, referring to FIGS. 1 and 3 in combination, an angled passage 64 in end plate 27 may connect well 26 with fluid inlet port 56. Accordingly, when any significant degree of centrifugal pumping action is present in chamber 61, leakage fluid cannot escape from chamber 61 except by filling such chamber and thereby assuring lubrication of the several relatively moving surfaces described above. Further no appreciable subatmospheric pressure can be generated within the radially inward region of chamber 61 to cause air flow past seal 23 and consequent undesirable aeration of oil.

Modified constructions are possible which achieve the same effect of forcing leakage fluid drainage at a point near or close to the rotary axis of the mechanism. FIGS. 4 and 5 illustrate a modification of the pump 11' showing two such alternate means of providing a centrally located drainage path that may be used jointly as shown in FIGS. 4 and 5 or either of which may be used separately. In the embodiment of FIGS. 4 and 5 the general construction of pump 11' is similar to that of FIG. 1 and accordingly like parts are designated by like reference numerals with a prime mark attached and the general structure will not be redescribed except for those portions wherein the modifications are present.

In the embodiment of FIG. 4, no drain passage is provided along the axis of drive shaft 12'. To drain fluid from chamber 61' to well 26' of end plate 27', one or more passages 66 are provided in barrel 16' to communicate the radially inward region of chamber 61' with the central bore 67 of barrel 16'. Thus, leakage fluid may, after substantially filling chamber 61', pass between drive shaft 12' and the inner wall of barrel 16' through bearing 28' and into well 26'. This embodiment of the invention also differs from that previously described in that the drain passage 64' within end plate 27' does not communicate with the fluid inlet port but instead extends radially to a drain outlet opening 68 in the circumferential wall of the end plate, it being apparent that the drain outlet passage 64' could be communicated with the inlet port as in the previous instance if desired.

FIGS. 4 and 5 in conjunction illustrate still another means by which drainage of chamber 61' near the central region thereof may be accomplished either supplementary to the previously described means or as an alternate thereto. In particular, one or more of the splines 29 of barrel 16 or the splines 31 of drive shaft 12 may be eliminated to provide for drainage flow between the central region of chamber 61' and barrel bore 67. In this example, one of the splines 31' of shaft 12 is absent for this purpose.

While the invention has been described with respect to certain specific embodiments, it will be apparent that many other modifications are possible and it is not intended to limit the invention except as defined in the following claims.

Claims

What is claimed is:

1. A rotary hydraulic device comprising:

a housing having a chamber therein,

a shaft extending into said housing and being journalled thereto for rotation about an axis extending therein,

an annular barrel member disposed in said housing in coaxial relationship to said shaft and being coupled thereto for rotation about said axis with said shaft, said barrel having a plurality of angularly spaced cylinder bores extending parallel to said axis, wherein said barrel member has internal splines engaging external splines on said shaft to couple said barrel member thereto,

a plurality of pistons each being disposed in an individual one of said cylinder bores for reciprocation therein and having an end protruding from said bore,

means disposed within said housing chamber and engaging said protruding ends of said piston for causing each piston to reciprocate in the associated one of said cylinder bores as said barrel rotates,

port means in said housing for admitting fluid to said cylinder bores when said pistons therein are moving away from said port means and for releasing fluid from said bores when said pistons therein are moving towards said port means, and

means defining a fluid drain passage for said housing chamber, said drain defining means being communicated with said chamber at a point which is radially inward from the circumferential portions thereof and which is at least in proximity to said rotary axis whereby said fluid must move radially inward relative towards said axis in order to escape from said chamber, and wherein at least a portion of said drain passage is defined by at least one omitted one of said splines.