GB2127497A - Pump assembly - Google Patents

Abstract

A pump assembly comprises two axial piston pumps, each formed by a cylindrical drum (8, 9) rotatable about a common axis. Each drum has a plurality of pistons (14, 21) displaceably mounted in bores therein, one end of each piston of a respective pump bearing against a respective tiltable bearing surface (16, 23) one at each end of the drums. In order to reduce the axial length of the pump assembly, the drums are arranged co-axially about a rotatable shaft (5), with one of the drums (8) located over at least a substantial part of its length within the other (9) of said drums, the inner drum (8) being coupled to the rotatable shaft (5) for rotation therewith and the outer drum (9) being coupled to the inner drum (8) for rotation therewith. <IMAGE>

Description

SPECIFICATION Pump assembly The present invention relates to a pump assembly comprising two axial piston pumps producing separate outflows, and more particularly to such assemblies in which each of the two pumps is provided with a respective cylindrical drum which is connected for rotation to a rotatable shaft and in which drum cylinders are arranged, in each of which a piston is displaceable, the pistons which are each displaceable in a particular cylindrical drum each bearing against a tiltable bearing surface which is formed on a bearing support body, one of the bearing support bodies being arranged at each side of the assembly.On rotation of a cylindrical drum, the individual pistons thereof are consecutively displaced in the cylinders to pump the working liquid from a liquid inlet to a liquid outlet, the stroke of the pistons being set by the degree of tilting of the associated bearing surface from the plane normal to the cylinder axis.

Pump assemblies of this kind are known in the so-called "tandem-arrangement", or "back-toback arrangement", in which two axial piston pumps are arranged co-axially in series with one another. This design has, however, the disadvantage that it has a very long structure. For a large number of applications, however, the maximum available structural length is predetermined. In particular, when the assembly is to be directly attached by means of co-operating flanges to a reciprocating internal combustion engine in series arrangement, and is to be installed, together with the latter, in a machine, for example, a construction machine, the installation space required for a double pump assembly of this length is frequently not available. On the other hand, there is adequate space available in the radial direction corresponding to the width of the reciprocating engine.

It is already known to arrange two axial piston pumps using the tiltable bearing surface principle of construction on parallel shafts one beside the other. This structure necessitates the use of a cog wheel connecting gearing to drive the two shafts, and is thus extremely expensive.

The aim of the invention is to provide an assembly comprising two tiltable bearing surface pumps on a single shaft, which has an extremely short structural length and in which design of the cylindrical drums and their bearings is particularly advantageous.

According to the invention, there is provided a pump assembly comprising two axial piston pumps producing separate outflows, each of said pumps having a respective cylindrical drum connected for rotation to a rotatable shaft, each said drum having a plurality of cylinders therein in each of which cylinders a respective piston is displaceably arranged, all the pistons located in the cylinders of a respective drum bearing at one end against a respective tiltable bearing surface formed on a respective bearing support body, the respective bearing support bodies for the two drums being located at opposite ends of the arrangement, wherein the cylindrical drums are co-axially arranged with respect to said shaft, one of said drums being located over at least a substantial part of its length within the other, the inner of said drums being connected in radially set manner to said shaft for rotation therewith, and the outer of said drums being connected with some radial freedom to the inner of said drums for rotation therewith.

Such a co-axial arrangement of the two cylindrical drums on a single shaft, in which one drum is located, at least partially, within the other, leads to only an extremely short structural length for the arrangement. Preferably, the outer cylindrical drum is supported for rotation on a bearing block fixed to a housing for said pump assembly, and in which bearing block are arranged channels for the supply and discharge of the working fluid to said inner cylindrical drum. Such an arrangement provided a particularly advantageous bearing for the two cylindrical drums.

In a preferred embodiment of the invention, both the connection of the inner cylindrical drum to the shaft and the connection of the inner cylindrical drum to the outer cylindrical drum are disposed at least approximately in a plane at right angles to the axis of rotation so that transverse forces act on the inner cylindrical drum only in the plane, simply because this plane is correspondingly located in the vicinity of the plane in which the piston forces, which result from the reaction forces at the bearing surface and from centrifugal force, act on the cylindrical drum.

Expediently, the bearing support body of the outer pump rests against a bearing block which is fixed to the housing and which accommodates the channels which serve to supply and discharge the working liquid for the inner cylindrical drum, and the bearing support body of the inner pump rests against a housing component (a control base member) in which are arranged the channels which serve to supply and discharge the working liquid for the cylindrical drum of the outer pump.

As a result of the arrangement in accordance with the invention, the pistons of the inner pump are arranged on a substantially smaller pitch diameter than those of the outer pump. Whilst the inclination of the pump remains uniform, the pistons of the outer pump thus possess a substantially longer stroke. Moreover, a larger periphery is available so that when the individual cylinders are adequately spaced from one another, more cylinders can be accommodated in the outer pump. For this reason, it is expedient to so design the pumps that the displacement volume of the outer pump is substantially greater than, possibly is a multiple of, the displacement volume of the inner pump. Nevertheless, it may be desirable to ensure that the pistons of the inner pump have a larger diameter than those of the outer pump.

The outer pump can also be designed as a double-flow pump of known construction, the control channels in the rotary slide control valve, for example, being subdivided to accommodate two streams, or preferably at the end of the cylindrical drum which is allotted to the rotary slide control valve, the cylindrical opening channels of each alternate cylinder opening on a smaller pitch diameter than the openings of the interposed cylinders, so that two separate, approximately semi-circular pump pressure channels are arranged radially one about the other. In this case, all the cylinders in the cylindrical drum can be arranged at the same pitch diameter, but it can also be provided that each alternate cylinder is arranged on a larger pitch diameter, although expediently all the pistons move towards the same tiltable bearing surface.

In a particularly advantageous use of a pump in accordance with the invention, the outer pump is allotted to a closed-cycle main drive system, whilst the inner pump, which produces a smaller (usually substantially smaller) output flow, is used to supply the operating hydraulic system, e.g.

cylinders in an open cycle. For example, as applied to a mobile drive system, the outer pump may be allotted to the main drive system which operates in a closed cycle, whilst the inner pump is allotted to the operating hydraulic system, e.g. cylinders which operate in an open cycle. In the case of a dredger drive system, however, the outer pump may be arranged to supply cylinders in an open cycle, or optionally can be switched over via block control devices to supply traction motors, whilst the inner pump is arranged to supply the rotating mechanism motors, which can operate either in an open or a closed cycle, depending upon the design of the overall assembly. This applies in particular when the outer pump represents a double-flow pump so that each flow can be assigned to a drive system.

The invention will now be further described with reference to the drawing, which is a schematic side-sectional view of a double-pump assembly in accordance with the invention.

Referring to the drawing, a housing component 1 abuts against one end of a cylindrical housing component 2 against which, at the other end, there abuts a control base member 3, the components 1 and 2, and 2 and 3, or 1 and 3, being connected together by connecting elements, for example screw connections, which have not been shown in the drawing. A shaft 5 is supported in the housing component 1 at one end by means of a roller bearing 4 and at the other end is supported in the control base member 3 by means of a roller bearing 6.

The shaft 5 is provided with splines 7, and an inner cylindrical drum 8 is provided with cooperating splines, so that the cylindrical drum 8 is connected by these splines to the shaft 5 so as to be resistant to torsion, and at the same time in such a way that the cylindrical drum 8 cannot carry out any radial movements relative to the shaft 5 in the plane of the splines.

An outer cylindrical drum 9 and the inner cylindrical drum 8 are also both provided with co operating splines 10 by means of which the cylindrical drum 8 is connected to the cylindrical drum 9 so as to be resistant to torsion, these splines 10, however, being so dimensioned that the cylindrical drum 9 is provided with radial play relative to the cylindrical drum 8. The outer cylindrical drum 9 is supported by means of a roller bearing 11 on a bearing block 12 which forms part of the housing component 1.

The outer cylindrical drum 9 is provided with cylindrical bores 13, a respective piston 14 being displaceable in each cylindrical bore 13. Each piston 14 rests by way of a shoe 1 5 against a tiltable bearing surface 1 6 which is formed on a tiltable bearing support body 1 7. The tiltable bearing support body 17 can either be supported by a part-spherical surface 18 therof on a correspondingly-shaped counter-surface 1 9 of the bearing body 12, or on the intermediate housing component 2, or, alterntively, can be tiltably supported in known manner in the intermediate housing component 2 by means of bearing pins which cannot be seen in the drawing because they are arranged behind the bearing block 12.

The cylindrical drum 8 is provided with cylindrical bores 20, a respective piston 21 being displaceable in each cylindrical bore 20. Each piston 21 rests by way of a shoe 22 against a tiltable bearing surface 23 which is formed on a bearing support body 24 which is pivotally supported by a part-spherical surface 25 thereof on a corresponding concave part spherical surface 26 of the control base component 3.

Between the bearing block 12 and the inner cylindrical drum 8, there is arranged a control plate 28 in which are arranged two approximately semi-circular control channels 29, one of which is connected to a channel 30 in the bearing block 1 2 and the other of which is connected to a channel 31 also in the bearing block 12, the channel 31 representing the suction channel which opens into an inlet connection 32, whilst the channel 30 represents the outlet pressure channel which opens into an outlet connection 33.

In the cylindrical drum 8, there is mounted an expanding ring 34 against which, through an intermediate ring 35, there bears one end of a spring 36 which at its other end bears against an intermediate plate 37 which in turn bears against a ring 38. The ring 38 in its turn bears through a plurality of pins 39, each of which is arranged in a bore in the cylindrical drum 8, against the flat end face of a ring 40 which has a part-sphericai surface which in turn rests against a part-spherical support surface formed in a retaining plate 41 which prevents the shoes 22 from lifting off the tiltable bearing surface 23. A corresponding support spring serving to exert pressure on the outer cylindrical drum 9 and/or a retaining plate 42 which prevents the shoes 1 5 from lifting away from the tilting surface 1 6 can also be provided, althrough this spring has not been shown in the drawing.

Between the end face of the cylindrical drum 9 and the control base component 3, there is arranged a control plate 44 in which are formed two approximately semi-circular channels 45, one of which is connected to a channel 46 in the control base component 3 and the other of which is connected to a channel 47 also in the control base component 3.

By pivoting the body 24 on which the bearing surface 23 is formed, it is possible to adjust the stroke of the piston 21, and by pivoting the bearing support body 17, it is possible to adjust the stroke of the pistons 14. The cylindrical drum 8 with the pistons 21 and the bearing surface 23 carried by the bearing support body 24 thus together form a pump which conveys a separate liquid flow into the channel 30, 33, whilst the cylindrical drum 9 together with the pistons 14 and the bearing surface 1 6 formed on the support body 1 7 form a second pump which conveys a liquid stream into the channel 46, 47 in dependence upon the degree of tilting of the bearing support body 17.

Claims (12)

1. A pump assembly comprising two axial piston pumps producing separate outflows, each of said pumps having a respective cylindrical drum connected for rotation to a rotatable shaft, each said drum having a plurality of cylinders therein in each of which cylinders a respective Diston is displaceably arranged, all the pistons located in the cylinders of a respective drum bearing at one end against a respective tiltable bearing surface formed on a respective bearing support body, the respective bearing support bodies for the two drums being located at opposite ends of the arrangement, wherein the cylindrical drums are co-axially arranged with respect to said shaft, one of said drums being located over at least a substantial part of its length within the other, the inner of said drums being connected in radially set manner to said shaft for rotation therewith, and the outer of said drums being connected with some radial freedom to the inner of said drums for rotation therewith.

2. A pump assembly as claimed in Claim 1, wherein said outer cylindrical drum is supported for rotation on a bearing block fixed to a housing for said pump assembly, and in which bearing block are arranged channels for the supply and discharge of the working fluid to said inner cylindrical drum.

3. A pump assembly as claimed in Claim 1 or Claim 2, wherein both the connections of the inner cylindrical drum with the shaft and with the outer drum are arranged at least approximately on a plane at right angles to the axis of rotation.

4. A pump assembly as claimed in Claim 2 or Claim 3 as dependent thereon, wherein the bearing support body of the outer pump is supported against the bearing block which is fixed to the housing.

5. A pump assembly as claimed in any one of Claims 1 to 3, wherein the bearing support body of the outer pump is supported against a part of a housing for the pump assembly.

6. A pump assembly as claimed in any one of the preceding Claims, wherein the bearing support body of the inner pump is supported against a part of a housing for the pump assembly in which are arranged channels for supplying and discharging working liquid for the outer pump.

7. A pump assembly as claimed in any one of the preceding Claims, wherein the displacement volume of the outer pump is greater than that of the inner pump.

8. A pump assembly as claimed in any one of the preceding Claims, wherein the outer pump is in the form of a double-flow pump with a common tiltable bearing surface.

9. A pump assembly substantially as hereinbefore described with reference to and as shown in the drawing.

10. A mobile drive system including a pump assemly as claimed in Claim 7, wherein the outer pump is allotted to the main drive system which operates in a closed cycle, and the inner pump is allotted to the operating hydraulic system operating in an open cycle.

11. A mobile drive system as claimed in Claim 10, wherein the inner pump is allotted to a drive system for a rotating mechanism.

12. A dredger drive system including a pump assembly according to Claim 7, wherein the outer pump operates in an open cycle and serves to supply cylinders and optionally propulsion engines, and the inner pump supplies the rotating mechanism.