GB2037879A - A Dual-pump Assembly Comprising Two Axial Piston Pumps - Google Patents

Abstract

The assembly has two tilting head pumps with a common tilt glider 23 on whose centre a control unit 31 acts directly. The tilt glider has roughly semi-circularly arranged ducts 25, separated by webs, which communicate with the pressure sides of the cylinder blocks 11 and which leave the respective suction sides of said blocks exposed. <IMAGE>

Description

SPECIFICATON A Dual-pump Assembly Comprising Two Axialpiston Pumps The invention concerns a dual-pump assembly comprising two axial-piston pumps of drive-flange construction with two cylinder blocks which are pivotal about a common pivot axis and which pivot together with a common component.

A dual-pump assembly comprising two axialpiston pumps of drive-flange construction is already known in which the two cylinder blocks are disposed in a tiltable housing with a control unit common to both acting on said housing (German Gebrauchsmuster No. 66 09 616). Such dual-pump assemblies are already extremely compact and have proved to be excellent but fairly recent studies show that even smaller and more economical models can be expected with pumps of tilting head construction.

Moreover, a dual-pump assembly comprising two swash-plate pumps is already known in which the swash plate surfaces, on which the pistons run, are formed on a common rocker (German Offenlegungsschrift No. 19 49 612).

Such an arrangement does not offer any significant advantages over two separate normal swashplate pumps.

Through public prior use, a dualpump assembly is also known in which two tilting head pumps are arranged parallel with one another in a common housing. In this known assembly, each of the two pumps if fitted in the usual way with its own tilt glider which is guided in its own concave cylindrical wall of the housing, these two concave cylindrical walls being curved about a common axis, namely, about the pivot axis of the two cylinder blocks. However these two tilt gliders controlling the respective blocks have a common control unit which has a two-armed extension lever which engages the two tilt gliders. Both suction sides lie on the neighbouring sides of the two cylinder blocks, the suction ducts passing through the tilt gliders into a common chamber in which the control unit is housed. This necessitates an arrangement which is unfavourable from the flow angle.The two highpressure ducts run to the exterior in a manner similar to that in the known dual-pump assemblies disposed in a tiltable housing. With these pumps, because of the shape of the faces between the cylinder blocks and the tilt glider, the tilt gliders require lateral guides in the part of the casing in which the tilt gliders run, and it is not least because of this that the machining of the two concave cylindrical walls for the convex tilt glider surfaces in the accommodating part of the bottom of the housing is very costly. In addition, articulation elements associated with the control unit must be made with great precision due to kinematic redundancy.Even with precision production, resistance can arise; thus, when the two pumps are placed under different loads, different forces occur at the two separate tilt gliders which place the control unit linkage under load and result in control unit characteristic hysteresis of differing magnitude.

The principal object of the invention is to eliminate these disadvantages and to create a dual-pump assembly which is simpler, and thus cheaper, to produce and which exhibits less susceptibility to trouble, in particular resistances, and whose .characteristic is less influenced by resistances.

This object is achieved, according to the present invention, by a dual-pump assembly which comprises two axial-piston pumps of driveflange construction with two cylinder blocks which are pivotal about a common pivot axis and which pivot together with a common component, wherein said pumps are of tilting head construction, the common component being a tilt glider which supports the corresponding surfaces of the two cylinder blocks.

In other words, starting with the last-described state of the art, namely, with a dual-pump assembly comprising two axial-piston pumps of drive-flange construction form with two tilt gliders which are disposed in a common housing and which are adjusted by a common regulating device by means of transmitting elements, the stated object of the invention is achieved in that the two cylinder blocks, i.e. the two pumps, have a common tilt glider on whose centre the control unit acts directly. With this, one can use the same control unit, at least the same in principle, but of a different rating if necessary, as for a single tilting head pump with just one cylinder block.By articulating the control unit at the centre and eliminating the lateral guide tracks for two swivel carriers, there is no redundacny in the articulation or pivoting kinematics and there is no need for production to be to such high precision requirements.

One particularly expedient embodiment is described in Claim 2. However, it should be pointed out in this connection that, for individual tilting head pumps drawing out of the housing, it is already known for the tilt glider to extend only over that part of the end face of the cylinder block associated with the pressure duct and the surrounding areas, and for that part of the end face of the cylinder block associated with the cylinders which are sucking at any time to be left exposed (German Offenlegungsschrift No. 26 42 900). By applying this known principle to the arrangement in accordance with the invention, however, special advantages are acquired; thus with the two pressure ducts disposed "inside", i.e.

next to one another in the central area of the dualpump assembly, the concave cylindrical face which requires precision machining to match with the convex surface of the tilt glider and which also has to provide the metal-to-metal high pressure seal becomes relatively narrow and thus relatively easy to machine so that the precision requirements are satisfied. The suction from the casing takes place "outside" in each case. The supply of fluid to the casing is effected through a suction inlet in the casing which is expediently located on the outside of the casing on the side opposite to that of maximum angular deviation or tilt of the cylinder blocks. Thus, the driving mechanism is cooled.Whereas with the known dual-pump assemblies described in defining the known state of the art it is necessary to provide a special arrangement for the purpose of flushing the casing with cool oil and to supply special connections for this, this influx of fresh oil into the casing produces adequate cooling. The oil in the casing is set in turbulent motion at the periphery of the cylinder blocks and through the driving parts. In this connection, it may be expedient to arrange deflector plates in the casing in such a way that the oil is guided in favourable fashion from the suction inlet to the exposed parts of the end faces of the cylinder blocks. Depending on specific requirements, these deflector plates may be disposed rigidly on the housing, or fixed to the tilt glider swivel carrier so as to pivot with the tilt glider and the cylinder blocks.The form of the deflector plates depends on the specific flow conditions.

The part of the housing facing the exposed parts of the end faces of the cylinder blocks can expediently be so formed that it provides favourable flow guidance. Here again the flow generated by the rotating parts can and should be taken into account.

Overall, the following advantages are obtained: Reduced production costs due to fewer and simpler components.

Cpmpactness.

Lightness.

Better control unit characteristic through reduction of transverse forces.

Forced cooling of the drive system through the suction of oil and resultant saving of a special flushing line.

Use of the tilt glider adjusting system, already mass-produced for single pumps, in dualpump assemblies as well.

No kinematic redundancy.

Even when the delivery pressure of both pumps differs considerably, no forces are transmitted to the common tilt glider to force this out of its set position.

The face requiring precise machining for guidance of the tilt glider and for the high pressure seal is relatively narrow.

The present invention will now be more particularly described with reference to the accompanying drawings which illustrate one exempiary embodiment and in which: Figure 1 shows a section taken on a section plane which contains the axes of rotation of the drive shafts and the cylinder blocks of a dualpump assembly according to the invention and which thus contains the pivot axis common to both cylinder blocks as well; and Figure 2 shows a section taken on a section plane containing a drive shaft axis and a cylinder block axis, said plane also containing the directions of pivoting of said cylinder block.

Referring to the drawings, a bottom 2 of a housing 1 is bolted thereto by tie bolts 3. Two drive shafts 4 are mounted in the housing 1 by means of a pair of roller bearings 5 in each case.

Each drive shaft 4 is made in one piece with a drive flange 6 and each drive flange 6 has teeth 7 around its periphery, two sets of teeth 7 meshing with one another.

In a modified version not shown in the drawing, it is also possible, in principle, to position a gear wheel on each of the drive shafts 4 between the respective two roller bearings 5 instead of providing theteeth 7 on the peripheries of the drive flanges 6, and to have these two gear wheels meshing with one another. These two gear wheels can then form an auxiliary pump at the same time. However, with the arrangement which has been illustrated in the drawings, an auxiiiary pump can also be disposed on each drive shaft 4.

At the centre of each drive flange, a ball cup houses a ball end 8 which constitutes the extremity of a centre journal 9 which has a platelike thick annular section 1 0. Each centre journal 9 has an associated cylinder block 11. Each cylinder block 11 has a central bore 1 5 and is provided with a groove in which sits an expanding ring 12 against which a support annulus 13 bears.

Said central bore 1 5 accommodates a spring 14 which is braced against the support annulus 1 3 at one end and against the flange 10 at the other, said flange 10 being seated against another expanding ring 16; this arrangement makes it possible to pre-assemble the cylinder block 11, the centre journal 9 and the spring 14.

Cylinders 1 7 are provided in each cylinder block with a piston 1 8 movable in each cylinder 17, each piston being articulated with a piston rod 19. Each piston rod 19 is mounted in the associated drive flange 6 by means of a ball end 20 which is seated in a ball cup therefor. The ball ends 8 and 20 of each drive flange are secured by a retaining plate 42. Each cylinder 17 communicates with a respective duct 21 which, at its other end, opens into or interrupts an end face 22 of the cylinder block. A common tilt glider 23, which bears with convex cylindrical surfaces 26 on a concave cylindrical surface 24 formed on the bottom 2 of the housing, is disposed in front of the end faces 22 of the two cylinder blocks 11.

Two ducts 25 are formed in the tilt glider 23, each duct following a roughly semi-circular path at the flat face of the tilt glider 23 and being a straight outlet at the convex cylindrical surface of the tilt glider, each straight outlet lying opposite an end 27 of a duct 36 in the bottom 2 of the housing.

Each of these two ducts 36 forms a pressure duct which leads to the outside of the bottom 2 at a corresponding pipe connection point.

Centrally of the tilt glider 23 is an aperture 28 in which there is engaged an end 29 of a positioning peg 30 which is fixed in a bore 28a in an adjusting piston 31. The adjusting piston 31 is moved in the usual way by control pressure against a second volume, or preferably against a return spring which is not shown in the drawings.

The housing 1 is fitted, on a flat side thereof, with a suction inlet flange 32 (Figure 2) to which a suction line can be connected and the arrows indicate the fluid flow into the cylinders. Said flange 32 is disposed in the vicinity of the cylinder blocks 11 when they are in their respective positions of minimum angular deviation or tilt. A rear wall 35 of the bottom 2 of the housing is set back relative to the concave cylindrical surface 24 to permit improved flow to the exposed parts of the end faces 22 of the cylinder blocks 11 (see Figure 1). Moreover, a flow deflector plate may be positioned between the suction inlet 32 and the cylinder blocks but said plate is not illustrated.

The adjusting piston 31 is disposed for movements along a cylinder 33 which is sealed off with a plug 34 at both ends, and each plug 34 can have connectors for a control pressure line, or just one of the two plugs 34 may have a connector for a control pressure line and one end of the previously mentioned (but not illustrated) return spring may bear against the other plug 34, the other end of said return spring bearing on the adjusting piston 31.

With further reference to the positioning peg 30, the end 29 thereof engages the tilt glider 23 with very little free motion and thereby always guides the tilt glider 23 correctly; this is so because said peg is also constrained to run in a slot 48 in the bottom 2 of the housing with very little free motion.

With further reference to the ducts 25 which, if one were to look at the flat face of the tilt glider 23, are roughly semi-circular, said ducts are separated from one another at their corresponding ends by webs which are located at the points where the pistons are at their dead centres. In this connection, it must be explained that these separating webs have to be provided because the mouths of the ducts 21 have a certain extent in the peripheral direction, i.e.

measured in the direction of rotation of the respective cylinder block; if these separating webs were not provided, the leading part of the mouth of the respective duct 21 would be in communication with the duct 25 whereas the trailing part thereof would still be in communication with the housing, and this is, of course, unacceptable.

Claims (6)

Claims

1. A dual-pump assembly comprising two axial-piston pumps of drive-flange construction with two cylinder blocks which are pivotal about a common axis and which pivot together with a common component, wherein said pumps are of tilting head construction and wherein the common component is a tilt glider which supports the corresponding surfaces of the two cylinder blocks.

2. A dual-pump assembly as claimed in Claim 1, wherein the dimensions of the tilt glider on the one hand and the side-by-side cylinder blocks on the other hand are such that said tilt glider comprises the bridge between the two cylinder blocks and wherein the tilt glider has two ducts which, at the flat face of the tilt glider are approximately semi-circular and are separated from one another at corresponding ends by webs, whereby said tilt glider covers only the pressure sides thereof at any time whilst at the same time leaving the suction sides of the cylinder blocks at any time exposed, pressure ducts in the tilt glider being disposed next to one another and the respective suction sides of the cylinder blocks being disposed on the sides thereof which are remote from one another, said pumps delivering in one direction and drawing from the housing.

3. A dual-pump assembly as claimed in Claim 1 or Claim 2, wherein a suction inlet is located on a flat side of the housing in whose vicinity the cylinder blocks lie when they are in their positions of minimum angular deviation or tilt.

4. A dual-pump assembly as claimed in any one of the preceding Claims, wherein a flow deflector plate is disposed between the suction inlet and the cylinder blocks.

5. A dual-pump assembly constructed, arranged and operable substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

6. Any features of novelty, taken singly or in combination, of the embodiments of the invention hereinbefore described with reference to the accompanying drawings.