GB2435910A

GB2435910A - Adjustable hydrostatic axial piston driving mechanism with phase-displaceable displacement movements.

Info

Publication number: GB2435910A
Application number: GB0612581A
Authority: GB
Inventors: Franz Forster
Original assignee: Linde GmbH; Linde Material Handling GmbH
Current assignee: Linde Material Handling GmbH
Priority date: 2005-07-15
Filing date: 2006-06-26
Publication date: 2007-09-12
Anticipated expiration: 2026-06-26
Also published as: GB2435910B; DE102005033104A1; FR2889262A1; DE102005033104B4; GB0612581D0

Abstract

An adjustable hydrostatic axial piston driving mechanism comprising two groups of piston-shaped displacement bodies 13 and two cam discs 9a, 9b which are arranged on opposing driving mechanism ends, against which cam discs, one of the groups of displacement bodies 13, in each case, is supported. The displacement bodies are each longitudinally displaceable, in a displacement space 12. The displacement spaces 12 of the two groups are hydraulically connected in parallel pair-wise. By means of a relative rotation of the two cam discs 9a, 9b with respect to one another, a phase displacement of the displacement movements of the two groups can be generated. In order to reduce a performance drop, due to wear and consequential leakage, the mechanism has at least one axial control plate 18a and axial adjustment means in operative connection therewith to adjust the position of the axial control plate, see channels R1 and R2 and thus control the pressure means supply.

Description

1 2435910 * Adjustable hydrostatic axial piston driving mechanism with

displacement movements, which are phase-displaceable with respect to one another, of the displacement bodies The invention relates to an adjustable hydrostatic axial piston driving mechanism comprising two groups of piston-shaped displacement bodies and two cam discs which are arranged on opposing driving mechanism ends and against which one of the groups of displacement bodies is supported in each case, wherein the displacement bodies associated with each group are arranged on a pitch circle, which is concentric to an axis of rotation of the axial piston driving mechanism and are longitudinally displaceable in each case in a displacement space and wherein the displacement spaces of the two groups are hydraulically connected in parallel pair-wise and a phase displacement of the displacement movements of the two groups can be produced by means of a relative rotation of the two cam discs with respect to one another.

A generic axial piston driving mechanism is disclosed in DI 22 09 996. In this axial piston driving mechanism, which is adjustable regarding the conveying or absorption volume despite the multi-stroke facility of the displacement bodies, the control of the pressure means supply and removal to and from the displacement spaces takes place by means of a control sleeve, which surrounds a cylinder block which is common to the two groups of displacement bodies. The control plate is provided on the inside of the control sleeve and connects radial connecting channels in the cylinder block, which lead to the displacement spaces, to a high pressure and a low pressure connection of the axial piston driving mechanism. This is therefore an adjustable multi-stroke axial piston driving mechanism with a radial control plate. As a result of the wear which inevitably occurs after a relatively long service life of the axial piston driving mechanism, increased leakage and therefore a drop in performances disadvantageously occurs.

* The present invention is based on the object of providing an adjustable axial piston driving mechanism of the type mentioned at the outset, in which the drop in performance, caused by the service life, of the axial piston driving mechanism is reduced.

This object is achieved according to the invention in that at least one axial control plate and axial adjustments means, which are in operative connection therewith, are provided to control the pressure means supply.

Owing to the configuration of the adjustment driving mechanism, according to the invention, with an axial control plate and axial adjustment means, wear in the region of the control plate can be compensated by an axial relative movement between the control plate and the opposing active surface of the component containing the displacement spaces. Thus, despite wear on the control plate and/or the opposing active surface, a uniform spacing can constantly be achieved between these components.

The leakage losses (which are acceptable and functionally necessary to form a hydrostatic relief) therefore remain unchanged over the service life of the axial piston driving mechanism.

According to an advantageous configuration of the invention, the displacement spaces are arranged in a one-or multi-part rotor (as in the known axial piston machines with an oblique disc design: the displacement spaces rotate, the cam disc is stationary). However, it is basically also possible to reverse this principle, in other words to arrange the displacement spaces in a stator and to allow the cam discs to rotate.

In order to achieve a design in which the driving mechanism according to the invention can be composed of the parts of a modular system, it is proposed that the first group of displacement bodies is to be arranged in a first cylinder block and the second group of displacement bodies in a second cylinder block, the cylinder blocks being axially moveably arranged with a spacing, with respect to one another, on a common drive shaft or on Iwo drive shafts which are torsionally rigidly connected to one another, and a control plate, which is fixed to the housing, being arranged axially between the cylinder blocks, the control plate being provided on either side in each case with a control plate against which one of the cylinder blocks rests.

The axial mobility of the cylinder blocks is in this case the essential element of the axial adjustment means which are present in the axial piston driving mechanism according to the invention and in operative connection with the axial control plate.

From the point of view of dimensions which are as compact as possible, a design is favourable in which a common cylinder block is provided for the Iwo groups of displacement bodies, in which cylinder block continuous axial bores are arranged on a common pitch circle, in which bores Iwo displacement bodies are located in each case, which delimit a displacement space axially arranged therebetween, wherein an axial active surface is moulded onto one of the end faces of the cylinder block, in which active face connecting channels guided to the displacement spaces open and which rest against a control plate, which is provided on an axially moveable control body. The axial adjustment required in the event of wear is therefore provided by the axial mobility of the control body.

The longitudinal dimensions of the axial piston driving mechanisms according to the invention are minimised when the control body is arranged in an axial recess of the end face of the cylinder block.

In order to achieve as large a displacement or absorption volume as possible, it is proposed that at least one of the cam discs is configured as a multi-stroke-generating cam disc, which has a plurality of stroke-generating axial cams and on which the displacement bodies of the associated group are supported via roll bodies.

In a development of the invention, the roll bodies are configured in each case as a roll, in particular as a cylindrical or barrel roll, which is * arranged in an end face recess of the displacement body limiting radial and axial relative movements of the roll with respect to the displacement body.

Instead of a ball which rolls in a groove-shaped ball track, a substantially more highly loadable roll is used as a roll body, which rolls on a track which is level in the axial direction of the roll. Thus the displacement body is used as a roll cage, which -with respect to the axis of rotation of the roll -guides the roll both radially and axially and thus in particular prevents the roll moving radially outwardly -with respect to the axis of rotation of the machine.

In contrast to the ball, which merely allows a punctiform or circular contact region to the track, the roll has a higher loadability due to the linear to elliptical contact region of the track, so a "roll piston machine" of this type can be operated at substantially higher pressures in comparison to the ball piston machine. The axial piston machine according to the invention therefore has increased performance which clearly expands the area of use.

In the embodiment of the roll body as a cylindrical or barrel roll a sliding part of the roll on the track is deliberately accepted and this comes from the different peripheral speeds along the roll when the angular speed remains the same. Nevertheless, it is basically also possible to configure the roll as a conical roll, in which this effect does not occur.

A so-called smooth piston, in other words a cylindrical body (solid or hollow piston) can be used as the displacement body, in the end face of which facing the track the roll is embedded. However, the (rectangular) face provided for axial force transmission from the displacement body onto the roll is smaller than the (circular) face, which is provided to transmit the axial force which is hydraulically generated and acts on the inner end face of the piston. In an embodiment of this type of the axial piston machine according to the invention, the area of use will therefore be primarily in the so-called mid pressure region, in other words in the region of about 200 to about 300 bar.

* However, if the displacement body has a first piston section holding the roll and a second hydraulically loadable piston section. which is smaller in diameter, it is possible to match the force-transmitting faces and to therefore reduce the loading of the roll. It is thus aimed to configure the "inner" end face of the displacement body loaded with hydraulic pressure and the "outer" end face of the displacement body, which faces the track and is used as a bearing face of the roll, to be equal in area.

The two piston sections of the displacement body are expediently arranged directly one behind the other. This is therefore an easily producible step piston.

It is particularly advantageous if the first piston section is arranged in a first bore section of the associated displacement space provided to receive transverse forces and the second piston section dips into a second bore section of the displacement space containing pressure means.

The first piston section therefore primarily absorbs the transverse forces, but does not have to have any sealing function. On the other hand, the second piston section, which is longitudinally moveable in a sealing manner in the associated second bore section, is primarily loaded with longitudinal forces and smaller transverse forces. Owing to the larger diameter of the first piston section or the associated first bore section the surface pressures caused in this region by the transverse forces are reduced or conversely -with constant surface pressure -the cam angle (steepness of the axial cams in the peripheral direction) and therefore the lifling volume can be increased and this increases the performance of the axial piston machine.

A favourable configuration of the invention provides that the axis of rotation of the roll at least on brushing over the cam ridge of the axiOl cams, is located inside the first bore section of the displacement space. The displacement body is then substantially free of bending forces, as the transverse forces are substantially still introduced inside the first bore section of the displacement space. This can also be exploited for an increase in performance of the axial piston machine.

If the piston together with the roll body should lift from the track, it may occur that the piston rotates in the displacement space. When the roll body meets the track again damage would be produced to the axial piston driving mechanism. In order to prevent this, a pressing device and/or a securing device against rotation of the piston is required. A securing device to limit the rotation of the displacement body relative to the displacement space can be achieved in that the second piston section has an offset with respect to the first piston section ("eccentric step piston") and therefore a rotation of the displacement body in the displacement space, which is complimentary thereto, is not possible.

It thus favourable if the second piston section and the second bore section, with respect to the first piston section and the first bore section, are radially inwardly offset to the axis of rotation of the cylinder block. This produces a greater outer wall thickness of the second bore section of the displacement space, which is under operating pressure.

Further advantages and details of the invention will be shown in more detail with the aid of the embodiments shown schematically in the figures, in which Figure 1 shows a longitudinal section through an axial piston driving mechanism according to the invention; Figure 2 shows a longitudinal section through a first variant of the axial piston driving mechanism; and Figure 3 shows a longitudinal section through a second variant of the axial piston driving mechanism.

The hydrostatic axial piston driving mechanism which can be adjusted with regard to the conveying or absorption volume and is shown in Figure 1 has a drive shaft 1, on which a first cylinder block 2a and, axially spaced apart therefrom, a second cylinder block 2b are supported. The drive shaft 1 0 and the cylinder blocks 2a and 2b are part of a rotor assembly of the axial piston driving mechanism.

The cylinder blocks 2a and 2b rotate inside two housing halves 3a and 3b of a machine housing, so as to rotate synchronously with the drive shaft 1 and in each case rest against an axial control plate 4a or 4b. The two control plates 4a and 4b are provided on the two sides of a control plate 5, which is arranged axially between the two housing halves 3a, 3b and connects them with one another. Located in the control plate 5 are connection bores 6 and 7 for the supply and removal of pressure oil and these are common in each case to the two cylinder blocks 2a and 2b. The control plate 5is also one of two bearing shields of the bearing of the drive shaft 1. A second bearing shield is formed by a housing cover 8, through which the drive shaft us guided.

Fastened to the housing cover 8, on the inside, is a cam disc 9a, which is provided with a plurality of axial cams lOa distributed on the periphery. The axial cams lOa are part of a sinusoidal function or a function derived from the sinusoidal shape, which is impressed on the cam disc 9a and incorporated in a track 1 la (lifting cam). Similarly to this, a cam disc 9b, which is provided with a plurality of axial cams 1 Ob distributed over the periphery, is fastened to the base of the pot-shaped housing half 3b on the inside of a cam disc 9b.

The axial cams lOb are part of a sinusoidal function or a function derived from the sinusoidal shape impressed on the cam disc 9b, which is impressed on the track 11 b of the cam disc 9b. The lifting cams of the two cam discs 9a, 9b -as in the present embodiments -are preferably the same.

The housing halves 3a and 3b, the control plate 5, the housing cover 8 and the cam discs 9a and 9b are part of a stat or assembly of the axial piston driving mechanism.

Each cylinder block 2a or 2b is provided, on a pitch circle arranged concentrically to the axis of rotation D of the drive shaft 1 (the two pitch circles have the same diameter in the present) embodiment, with * displacement spaces 12, in which a piston-shaped displacement body 13 can respectively be longitudinally displaced. Each displacement body 13 is supported via a roll 14, which is configured here as a cylinder roll, on the track 0111 b of the cam disc 9a or 9b. The roll 14 is located in an end face recess A of the displacement body 13. The recess A of the displacement body 13 thus adopts the function of a cage for the roll 14 and limits the movements thereof within the limits of manufacturing tolerances in the radial and axial direction.

There are therefore two groups of displacement bodies 13, namely one group, which is associated with the cylinder block 2a and the cam disc 9a, and a group which is associated with the cylinder block 2b and the cam disc 9b.

The displacement bodies 13 are configured, in the present embodiment as step pistons, which are provided in each case with a first piston section 1 3a and a second piston section 1 3b with a smaller diameter adjoining it. Similarly to this, the displacement space 12 is configured as a step bore and has a first bore section 1 2a, in which the first piston section 13a of the displacement body 13 is located, and a second bore section 1 2b with a smaller diameter adjoining it, in which the second piston section 1 3b of the displacement body 13 is located.

The configuration of the displacement body 13 as a step piston firstly has the effect that the area ratio between the end face loaded with pressure oil inside the displacement space 12 (circular or ring face) of the displacement body 13 and the face (rectangular face) provided as a bearing face for the roll 14 on the opposing end face of the displacement body within the available space conditions, can be relatively freely selected.

It is therefore possible to achieve equality of area or to relieve the roll 14 by the selection of a larger bearing face.

In combination with a step bore as a displacement space 12 it is achieved that the transverse forces introduced by the roll 14 into the first * piston section 1 3a of the displacement body 13 are received substantially in the region of the first bore section 1 2a of the displacement space 12 and therefore the second piston section 1 3b and the second bore section 1 2b are loaded with lower transverse forces and primarily assume a sealing function.

To improve the sealing function, the second piston section 1 3b can be provided with a piston ring, not shown in the figures.

An annular space RR is formed between the first bore section 1 2a and the second piston section 1 3b by the graduation of the displacement body 13 and the displacement space 12. A venting channel 15 in the first bore section 1 2a ensures that the pressure in the annular space RR substantially corresponds to the pressure in the interior of the machine housing. Neither a reduced pressure nor an excess pressure is produced in the annular space RR on a lifting movement of the displacement body 13 with respect to the pressure in the housing interior, therefore. Only an oil flow is generated, which flows into the annual space RR or out of the annual space RR.

As in the axial piston machine shown according to the invention, the axis of rotation of the roll 14, when the displacement body 13 is dipped in, is located inside the first bore section 1 2a, only a small bending load of the first piston section 130 of the displacement body 13 fakes place in this operating state. Accordingly, the first piston section 13a of the displacement body 13 (like the first bore section 1 2a of the displacement space) is primarily subjected to surface pressure stress.

In the present embodiment, the second piston section 1 3b of the displacement body 13 has an offset e with respect to the first piston section 13a. Owing to this measure it is achieved that the displacement body 13 is secured against rotation relative to the displacement space 12. It is thus prevented that the roll side-turns in the event of (undesired) lifting from the track 11 and on returning to the track 11 a or 11 b destroys the latter and itself.

In this context it is advantageous for the offset e to take place with respect to the axis of rotation D of the drive shaft 1 so the outer wall thickness of the cylinder block 2a or 2b is not reduced but increased.

The roll 14 is hydrostatically relieved by a longitudinal channel L, which opens in the end face of the displacement body 13 loaded with pressure oil in order to achieve a rolling movement which is as low in friction as possible, inside the receiver A. With low loading of the roll, it is also possible, however, to dispense with hydrostatic relief of this type.

The adjustment of the conveying or absorption volume of the axial piston driving mechanism according to the invention takes place by means of a relative rotation of the two cam discs 9a and 9b with respect to one another. A phase displacement of the displacement movements of the two groups of displacement bodies 13 is thus achieved. Depending on the phase displacement, the volumes displaced by the displacement bodies 13 during pump operation or conversely -during motor operation -the movement fractions of the displacement bodies 13 generated by the injected pressure means are added or subtracted, as is known per Se. In order to generate the relative rotation, in the present embodiment, the cam disc 9b is mounted, in a hydrostatically relieved manner, in the housing half 3b and can be rotated by means of a drive 16 relative to the cam disc 9a. Alternatively to this, it would also be possible to rotate the cam disc 9a, instead of the cam disc 9b or to rotate the two cam discs 9a and 9b in each case by half the angular amount, with respect to one another.

The design shown in the embodiment according to Figure 1 is suitable for a variant production from the modular system, with which both conventional driving mechanisms with only one cylinder block (constant and adjustable) and also the present adjustment driving mechanism, which has two cylinder blocks, can be produced.

In the variant shown in Figure 2 of the axial piston driving mechanism according to the invention, a cylinder block 2, which is common to the two groups of displacement bodies 13, is provided. One group of displacement bodies 13 in each case dips from one of the end faces Si or S2 of the cylinder block 2 in stepped axial bores, which extend axially through the cylinder block 2. Between two displacement bodies 13, in each case, which are located in a common axial bore, one displacement space 12 is formed in each case.

An axial recess N is incorporated into the end face S2 of the cylinder block 2, the end of which forms an active face W, in which connecting channels, 17 leading to the displacement spaces 12 open. The active surface rests against a control plate 1 8a of a control body 18 located in the recess N. The control body 18 is held in a rotationally engaged manner in the base of the housing half 3b and is stepped in this region in order to form two annular channels Ri, R2, to which, on the one hand, through-channels 19 opening in the control plate 1 8a and, on the other hand, supply channels 20a, 20b are connected, the latter being provided with the end connection bores 6 or 7. The control body 18 is axially moveable and is pressed in the direction of the active surface W by a spring force. Located in each displacement space 12 is a compression spring 21, which presses the two displacement bodies 13, in each case, against an associated track 11 a or 11 b and ensures that the displacement bodies 13 do not lift up. A special securing device against rotation is therefore not necessary.

A stepped annular body 23 is placed against the inner ring of the rolling bearing 22 of the drive shaft 1 on the right in the figure and can be loaded by pressure from the supply channels 20a, 20b in the direction of the inner ring. Axial forces, which are applied by the drive shaft 1 on the rolling bearing 22 are therefore at least partially compensated.

The embodiment according to Figure 3 differs from that in Figure 2 in that the drive shaft 1 extends completely through the housing halves 3a, 3b of the machine housing, so gripping is possible on both sides. This axial piston driving mechanism is therefore suitable for installation in the cardan train of ) * an all-wheel vehicle with a cardan shaft adjoining each shaft end El or E2 of the drive shaft 1 (central drive).

Claims

* Claims L An adjustable hydrostatic axial piston driving mechanism

comprising two groups of piston-shaped displacement bodies and two cam discs which are arranged on opposing driving mechanism ends and against which one of the groups of displacement bodies is supported in each case, wherein the displacement bodies associated with each group are arranged on a pitch circle which is concentric to an axis of rotation of the axial piston driving mechanism and are longitudinally displaceable in each case in a displacement space and wherein the displacement spaces of the two groups are hydraulically connected in parallel pair-wise and a phase displacement of the rotation movements of the two groups can be produced by means of a relative rotation of the two cam discs with respect to one another. charactensed in that at least one axial control plate and axial adjustment means in operative connection therewith are provided to control the pressure means supply.

2. An adjustable axial piston driving mechanism according to claim 1, characterised in that the displacement spaces are arranged in a single-or multi-part rotor.

3. An adjustable axial piston driving mechanism according to claim 2, characterised in that the first group of displacement bodies is arranged in a first cylinder block and the second group of displacement bodies is arranged in a second cylinder block, wherein the cylinder blocks are axially moveably arranged on a common drive shaft or on two drive shafts connected to one another in a torsionally rigid manner, with a spacing from one another and wherein a control plate, which is fixed to the housing, is arranged axially between the cylinder blocks and is provided on either side, in each case, with a control plate, against which one of the cylinder blocks rests.

4. An adjustable hydrostatic axial piston driving mechanism according to claim 2, characterised in that a common cylinder block is provided for the Iwo groups of displacement bodies, in which cylinder block continuous axial bores are arranged on a common pitch circle, in which bores Iwo displacement bodies are located in each case, which delimit a displacement space arranged axially therebetween, an axial active surface being moulded onto one of the end faces of the cylinder block, in which active surface connecting channels guided to the displacement spaces open and which rests against a control plate, which is provided on an axially moveable control body.

5. An adjustable hydrostatic axial piston driving mechanism according to claim 4, characterised in that the control body is arranged in an axial recess of the end face of the cylinder block.

6. An adjustable axial piston driving mechanism according to any one of claims 2 to 5. characterised in that at least one of the cam discs is configured as a multi stroke-generating cam disc, which has a plurality of stroke-generating axial cams and on which the displacement bodies of the associated group are supported via roll bodies.

7. An adjustable axial piston driving mechanism according to claim 6, characterised in that the roll body in each case is configured as a roll, in particular a cylinder roll, which is arranged in an end face recess of the displacement body limiting radial and axial relative movements of the roll with respect to the displacement body.

8. An adjustable axial piston driving mechanism according to claim 7, characterised in that the displacement body has a first piston section holding * the roll and a second hydraulically loadable piston section. which is smaller in diameter.

9. An adjustable axial piston driving mechanism according to claim 8.

characterised in that the two piston sections of the displacement body are arranged directly one behind the other.

10. An adjustable axial piston driving mechanism according to claim 8 or 9, characterised in that the first piston section is arranged in a first bore section, provided to receive transverse forces, of the associated displacement space and the second piston section dips in to a second bore section of the displacement space containing pressure means.

1 L An adjustable axial piston driving mechanism according to claim 10.

characterised in that the axis of rotation of the roll, at least during contact on the cam ridge of the axial cam is located inside the first bore section of the displacement space.

12. An adjustable hydrostatic motor unit according to any one of claims 8 to 11, characterised in that the second piston section has an offset to the first piston section.

 3. A multi-stroke hydrostatic axial piston machine according to claim 12.

characterised in that the second piston section and the second bore section are radially inwardly offset with respect to the first piston section and the first bore section, to the axis of rotation of the cylinder block.