Flow-control Arrangements In Axial-cylinder Pumps

Abstract

A fluid-tight seal between each cylinder bore in the barrel of a swash-plate pump and the corresponding port bore in a port plate rotating with the barrel is established by a sleeve, which is accommodated in aligned counterbores of the two bores, provided at the mutually adjacent end faces of the barrel and port plate, and which is sealed in each of these counter bores by a separate compressed O-ring seal, common rotation of the port plate with the barrel being ensured by means independent of the sleeves. The sleeve has sufficient play in the counter bores to allow for slight angular displacement between the respective end faces of the cylinder barrel and the stationary valve face of, for example, a valve plate. Preferably the O-rings are accommodated in annular recesses at each of the two ends of the sleeve and are compressed axially between washers resting respectively against the bottom shoulders of the two counter bores so that the resilience of the O-rings provides an axial thrust force urging the port plate into contact with the valve plate.

Description

This invention relates to axial-cylinder pumps of the kind, thereinafter called the kind specified, in which a number of cylinders are arranged in a so-called cylinder barrel which is mounted for rotation about its axis in a pump housing with the cylinder bores extending substantially parallel to the axis of rotation and being spaced at equal radii round the latter and generally uniformly distributed round the axis, and in which the rotation of the barrel relative to the housing is utilised for producing periodic reciprocation of a piston in each cylinder for each revolution of the barrel, and in which furthermore control of the flow between each cylinder and a high-pressure and a low-pressure port respectively in accordance with the direction of movement of the piston is achieved by co-operation of a port, communicating with each cylinder and arranged in an end face of the barrel, with high-pressure and low-pressure ports in the stationary housing which, by means of mutually sliding sealing surfaces, respectively associated with the barrel and housing, are placed, by the rotation of the barrel, in alternate communication with each cylinder port. In axial-cylinder swash-plate pumps of the kind specified, the actuation of the pistons is achieved by co-operation of an extension of each piston with the surface of a track which is stationary in the housing, and which is inclined to a plane perpendicular to the axis of rotation in accordance with the desired stroke of the pistons. The term "pump," when used in the present specification, is intended, unless the context otherwise requires, to be broad enough to include a machine whether it is to be operated to displace fluid when mechanically driven (pumps in the narrower sense) or for use to produce mechanical power when actuated by fluid pressure (operation as a fluid-pressure motor).

In order to maintain reliable seal of the sliding surfaces utilised to establish, in an axial-cylinder pump of the kind specified, the alternate connections of each cylinder port with the stationary ports irrespective of minor errors of angular alignment, -- and such minor errors, even if not present due to manufacturing inaccuracies, may be produced in operation due to distribution of hydraulic pressure forces acting in the gap, however small, between the co-operating sliding surfaces, -- it has already been proposed to arrange the ports associated with each cylinder in a so-called port plate which is connected with the cylinder barrel for common rotation with it, but is free to carry out a small amount of axial and tilting movement relative to the barrel, and according to that proposal, sealing connection between each cylinder bore and the associated port passage in the port plate is maintained by the provision of sleeve members which project with one of their ends into an extension of the cylinder bore and are sealed therein by a compressible ring accommodated in a circumferential groove in the outer surface of the sleeve to resiliently maintain sealing connection while permitting slight tilting movement of the sleeve in the bore, while the other end of the sleeve is arranged to form an end-surface seal against the adjacent surface of the port plate with a view to maintaining an effective seal at that surface irrespective of slight displacements of the end surface on the adjacent surface of the port plate.

The present invention has for an object to avoid the necessity of providing, in order to minimise leakage losses across the end face of the sleeve, such a sliding end-surface seal and thus the necessity of maintaining high axial contact pressure which results in the transmission of an undesirable force to the port plate. Another object is to provide an axial-cylinder pump having a port plate, rotatable with the cylinder barrel, which is capable of reliable operation under conditions of relatively large angular displacement of the axis of the cylinder barrel relative to the axis of the port plate.

According to the present invention fluid-tight connection between each cylinder and its port in the port plate is established by a sleeve which extends into substantially aligned bores coaxial with the cylinder in the cylinder barrel and with its port in the port plate respectively, in each of which bores the sleeve is capable of a small amount of axial and swivel movement; the port plate is coupled for common rotation with the cylinder barrel independently of the presence of these sleeves, and the sleeve is sealed in each of these bores by a sealing ring of resiliently compressible material, which is compressed in a circumferential groove or shoulder portion of one of the co-operating circumferential wall surfaces of the sleeve and bore so that it maintains, due to its resiliently compressed state, sealing contact with the other of the said co-operating surfaces. Preferably each sealing ring is accommodated in an annular chamber formed within the bore by an outwardly projecting circumferential shoulder determining a reduced-diameter portion of the sleeve near the adjacent end thereof, and is compressed between the face of this annular shoulder and an opposing face formed or suported by the cylinder barrel and port plate respectively, so that the resilient compression of each sealing ring is utilised, in addition to its use for maintaining circumferential seal in the appropriate bore, for also maintaining some axial sealing force between the sealing face of the port plate and the co-operating stationary face which contains the high-pressure and low-pressure ports of the pump housing.

In order that the invention may be more readily understood one, form of swash-plate pump incorporating the present invention will now be described in more detail with reference to the accompanying drawing, in which

FIG. 1 is an elevation of the pump in section through the axis of the cylinder barrel, taken in the direction of maximum inclination of the swash-plate surface to the face of the port plate,

FIG. 2 is a scrap section drawn to a larger scale and shows details of the arrangement of one of the sealing sleeves, and

FIG. 3 is a plan view of part of the port plate with a thrust washer.

Referring now to the drawing, a so-called cylinder barrel 2 is mounted for rotation about its axis in a housing 1. The barrel 2 is connected for common rotation with a shaft 3, which is supported in the housing 1 by bearings 4 and 5. The latter of these is a ball bearing of a kind capable of transmitting axial thrust as well as radial forces, and the shaft 3 is provided with a flange 6 which co-operates with an end face of the cylinder barrel 2 to transmit axial thrust from the latter to the pump housing 1 through a further flange 6a resting against the ball bearing 5. The cylinder barrel 2 is provided with a number of cylinder bores 7 uniformly distributed round the axis of the shaft 3 at equal distances therefrom and extending substantially parallel to the shaft. Each cylinder bore contains a piston 8 having a ball-ended extension 8a which, in a well-known way, co-operates with a track surface on a so-called swash plate 9 through the medium of a so-called slipper 10, a separate slipper 10 being provided on the extension of each piston member 8 for sliding co-operation with the track surface 11 of the swash-plate 9. This surface is inclined to a plane at right angles to the axis of the shaft 3 so that, during each revolution of the cylinder barrel 2, each piston, if its slipper 10 is maintained in contact with the surface 11, will perform one reciprocation in its cylinder. To maintain such contact, the swash plate 9 is equipped with a retainer ring 12 which co-operates with a shoulder 13 of each slipper 10.

To provide alternate connection of each cylinder with the high-pressure and low-pressure ports of the pump, port passages 14 and 15 of the pump housing 1 are continued in a so-called valve plate 16 to form the ports proper in the valve plate 16 of which the surface that faces the end of the cylinder barrel is highly finished, and a so-called port plate 17, having a similarly finished surface for co-operation with this surface of the valve plate 16, is provided with an individual cylinder port 18 for each cylinder bore 7 of the cylinder barrel 2. This port plate 17 is coupled to the shaft 3 so as to rotate jointly with the barrel 2 but is slightly spaced axially from this barrel to leave a narrow gap 19, and a small amount of plate is also provided between the central bore 17a of the port plate and the shaft 3, to allow the lower end face 2a of the barrel 2 to assume a slight angle of inclination to the adjacent end face of the port plate 17 without interfering with the surface contact between the port plate 17 and valve plate 16.

A substantially leak-free connection between each cylinder bore 7 and its associated port 18 in the port plate 17 is however assured by the interposition, between the cylinder barrel 2 and the port plate 17, of a connector sleeve 20 for each cylinder as will be described further below. A force, produced by hydraulic pressure and tending to hold the port plate 17 in contact with the valve plate 16, is provided by making the ports 18 in the port-plate kidney-shaped so as to be substantially narrower in the radial direction of the barrel than the diameter of the cylinder bores 7 and counterbore 21, and by confining the area of which the distributed pressure of leakage fluid acts between the contacting sealing surfaces of the valve plate 16 and port plate 17, to a relatively narrow land 27 surrounding each of the ports 8. This is achieved by the provision in the end face of the port plate 17 of drained recesses 25, 26 which encircle this land.

Each connector sleeve 20 is accommodated for part of its length in a cylindrical counterbore 21 which is provided in the port plate 17 to continue the port 18 axially through the surface facing the cylinder barrel 2, and whose diameter is substantially larger than the width of the port 18 transversely of its direction of revolving movement about the barrel axis. The other end of the sleeve 20 is accommodated in a counterbore 7a at the adjacent end of the associated cylinder bore 7 of the cylinder barrel, this counter-bore being separated from the cylinder bore 7 proper by an annular shoulder 22, and a thrust washer 29 is preferably interposed between the shoulder 22 and the sleeve 20 as described further below. The dimensions of the sleeve 20 are such as to leave some axial clearance between the ends of the sleeve 20 and the bottom of the counter-bore 21 and/or shoulder 22 or thrust washer at the top of the counter-bore 7a, and to leave also some radial clearance at the circumference of the sleeve 20, thus allowing the sleeve 20 to accommodate angular displacement of the barrel 2 relative to the port plate 17 in the manner above indicated. In order to maintain nevertheless the desired fluid-tight seal of the connection between the cylinder bore 7 and the port 18 in the port plate 17, two seals are formed in the counter-bores 21 and 7a respectively by O-rings 23 and 24 of rubber or other resiliently compressible material. These O-rings are accommodated in suitable annular recesses of the sleeve 20, which respectively face the wall of the counter-bore 21 in the port plate 17. and the wall of the sleeve-accommodation counterbore 7a of the cylinder bore 7. The O-rings are arranged to be compressed in their cross-section during the assembly of the device, so as to be applied to the wall of the said bores with sufficient force to ensure a liquid-tight seal. Preferably the recesses accommodating the O-rings 23 and 24 are open at the end faces of the sleeve 20 as illustrated, and the O-rings 23 and 24 being so dimensioned in their cross-section as to be not only compressed in the radial direction of the sleeve 20 but to be also compressed in the longitudinal direction of the latter, between the shoulder forming the end face of the recess accommodating each O-ring and the shoulder 22 or thrust-washer 29 which restrains the axial movement of this O-ring towards the cylinder bore 7. With this arrangement the O-rings 23 and 24, in addition to their sealing function, also act as thrust springs to provide a resilient force applying the end face of the port plate 17 to the co-operating surface of the valve plate 16 independently of any hydraulic pressure.

In order to minimise flow restriction, particularly during the charming of the cylinders through the low-pressure inlet port 15 of the pump housing, the length 18a of each port 18 of the port plate 17 in the direction of its movement round the barrel axis is approximately equal to the diameter of the cylinder bore 7, as will be seen more clearly in FIG. 2. In order to provide nevertheless adequate shoulder surface areas at the end 18b of each port 18 to retain the O-rings 23 and 24 compressed in the axial direction of the cylinders as well as in a radial direction, the shoulder formed by the counter-bore 21 is used to support a substantially rigid thrust washer 28 of a radial width just sifficient to provide such adequate shoulder surface for the O-ring 24 while the diameter of its central aperture is at least approximately equal to the diameter of the axial passage 20a of the sleeve 20 so as to be clear of the port 18 except for the above-mentioned end areas 18b.

A further thrust washer 29, whose central aperture is likewise equal to or somewhat larger in diameter than that of the said axial passage 20a, is similarly supported against a narrow shoulder formed between the cylinder bore 7 and its counterbore 7a so as to provide, notwithstanding the small difference between the diameters of the bore 7 and counterbore 7a, an adequate support surface for the O-ring 23 at the other end of the sleeve 20. This arrangement makes it possible to keep the excess in diameter of the counterbores 7a in the cylinder barrel 2 over the diameter of the cylinder bore 7 at a minimum, thus minimising the hydrostatic thrust force which acts on the shoulder 22 between the bore 7 and counterbore 7a of the cylinder barrel 2 to urge the barrel away from the valve plate 16, and which must be taken-up by the bearing 5.

Various features of the illustrated embodiment may be varied without exceeding the scope of the invention. Thus, when the resilience of one, or both of the O-rings is not required for the provision of an axial thrust force urging the port plate into contact with the valve plate, the thrust ring adjacent to that O-ring, or both thrust rings, may be formed integral with the sleeve 20, so that the sleeve will butt against the shoulder 22 and/or the bottom of the bore 21, the O-ring in question being accommodated in a groove of the thus modified sleeve.

Furthermore, the port plate 17, instead of being driven by a shaft connection as described, could be driven from the cylinder barrel 2, for example, by means of suitably arranged dowels.

Claims

1. An axial-cylinder pump comprising a pump housing, a cylinder barrel mounted in said housing for rotation about an axis of the barrel and having a plurality of cylinder bores extending parallel to said axis at equal radial distances therefrom, a piston in each cylinder, piston-actuating means operable during rotation of the barrel to produce periodic reciprocation of each piston in its associated cylinder, a port plate arranged coaxially with the barrel for common rotation therewith and having one end face adjacent to but slightly spaced axially from, one end face of the barrel and a second, oppositely directed face, said port plate having port bores, one for each cylinder and each communicating at said one face of the port plate with its associated cylinder and terminating at said second face of the port plate in a port for periodic alternate communication, as the barrel rotates, with ports in a valve face provided in the housing, said barrel having communication bores respectively communicating with each cylinder, and each port of the port plate having a communication bore aligned with one of said communication bores of the barrel, a sealing sleeve coaxially accommodated in each communication bore of the barrel and the aligned communication bore of the port plate so as to extend simultaneously in both said communication bores, with radial play in each of said communication bores to permit slight angular movement of the axis of each sleeve relative to the axis of each of said aligned communication bores, each sleeve having in its outer circumferential surface two circumferential recesses respectively facing the walls of the communication bores of the barrel and of the port plate, two resiliently compressed sealing rings for each sleeve respectively accommodated in said two recesses to ensure a fluid-tight seal of the sleeve in the communication bore in question notwithstanding the said radial play, and coupling means, independent of said sleeves, ensuring common rotation of

2. An axial-cylinder pump as claimed in claim 1, wherein said communication bores are formed as counterbores terminating in a shoulder, each of the said recesses of each sleeve being open at the side adjacent to the nearest end of the sleeve, the sealing member in each recess being resiliently compressed between the other side of the recess and said shoulder of the counterbore accommodating said sealing member as well as between the bottom of the recess and the circumference of the counterbore so as to exert, through the intermediary of the sleeve, an axial force tending to move the port plate away from the cylinder barrel and into

3. An axial-piston pump as claimed in claim 2, including an annular abutment plate supported on, and extending in a radial direction, the shoulder formed by the counterbore in the barrel.