Hydrostatic Axial Piston Machine

Abstract

A hydrostatic axial piston machine defines an adjustable displacement volume and includes a housing, a cylinder drum, a plurality of working pistons, a pivot cradle, and a plain bearing. The working pistons are received in the cylinder drum so as to be axially displaceable, and are supported on a sliding surface of the pivot cradle. The pivot cradle is configured to adjust the displacement volume, and is pivotably mounted on the plain bearing. The plain bearing is fixed with respect to the housing. The hydrostatic axial piston machine is configured to form at least one first hydrostatic relief pressure field between the plain bearing and the pivot cradle.

Claims

1. A hydrostatic axial piston machine, defining an adjustable displacement volume, and comprising: a housing; a cylinder drum; a plain bearing fixed to the housing; and a pivot cradle that is pivotably mounted on the plain bearing to enable formation of at least one first hydrostatic relief pressure field between the plain bearing and the pivot cradle, the pivot cradle defining a sliding surface and being configured to adjust the displacement volume; a plurality of working pistons received in the cylinder drum so as to be axially displaceable, and supported on the sliding surface of the pivot cradle; and a first pressure medium source; the hydrostatic axial piston machine further defining a first pressure medium flow path from the first pressure medium source to the first hydrostatic relief pressure field, the first pressure medium flow path including an adjustable throughflow cross section.

2. The hydrostatic axial piston machine of claim 1, further comprising: a second pressure medium source, wherein: the mounting of the pivot cradle on the plain bearing further enables formation of a second hydrostatic pressure relief field between the plain bearing and the pivot cradle; and the hydrostatic axial piston machine further defines a second pressure medium flow path from the second pressure medium source to the second hydrostatic relief pressure field, the second pressure medium flow path including a second adjustable throughflow cross section.

3. The hydrostatic axial piston machine of claim 1, further comprising: an adjustment device that includes a hydraulic actuating cylinder configured to adjust the displacement volume; wherein the hydraulic actuating cylinder defines an actuating pressure chamber that enables formation of the first pressure medium source.

4. The hydrostatic axial piston machine of claim 3, wherein: the adjustment device further includes a hydraulic restoring cylinder configured to restore the displacement volume; and the hydraulic restoring cylinder defines a restoring pressure chamber that enables formation of the second pressure medium source.

5. The hydrostatic axial piston machine of claim 1, wherein: the working pistons delimit a plurality of working chambers in the cylinder drum; and the first pressure medium source includes a pressure medium connection to a subset of the plurality of working chambers in the cylinder drum.

6. The hydrostatic axial piston machine of claim 2, wherein the hydrostatic axial piston machine is configured such that an adjustment of at least one of the first adjustable throughflow cross section and the second adjustable throughflow cross section is coupled to a change in the displacement volume.

7. The hydrostatic axial piston machine of claim 3, wherein: the working pistons delimit at least one working chamber in the cylinder drum; and the first pressure medium flow path extends through the pivot cradle from at least one of the at least one working chamber and the actuating pressure chamber to the first hydrostatic relief pressure field.

8. The hydrostatic axial piston machine of claim 1, wherein: the sliding surface of the pivot cradle and at least one of the working pistons together delimit the first adjustable throughflow cross section; at least one working piston includes a sliding pad, and the sliding surface of the pivot cradle and the sliding pad together delimit the first adjustable throughflow cross section; or at least one working piston includes a sliding pad, and the at least one working piston and the sliding pad together delimit the first adjustable throughflow cross section.

9. The hydrostatic axial piston machine of claim 1, further comprising at least one of: a first throttle device that forms the first adjustable throughflow cross section; and a second throttle device that forms the second adjustable throughflow cross section.

10. The hydrostatic axial piston machine of claim 9, wherein at least one of the first throttle device and that second throttle device respectively includes a controllable valve or a controllable aperture.

11. The hydrostatic axial piston machine of claim 1, wherein at least one of: the plain bearing defines a first bearing surface that includes at least one first relief pressure pocket, the at least one first relief pressure pocket delimiting the first hydrostatic relief pressure field; and the pivot cradle defines a second bearing surface that faces toward the plain bearing and that includes at least one second relief pressure pocket, the at least one second relief pressure pocket delimiting the first hydrostatic relief pressure field.

12. The hydrostatic axial piston machine of claim 11, wherein in a neutral position of the pivot cradle: the displacement volume is zero; and the first relief pressure pocket overlaps the second relief pressure pocket, at least in sections.

13. The hydrostatic axial piston machine of claim 11, wherein: the pivot cradle is configured to pivot about a pivot axis that lies on a neutral plane of the pivot cradle; the second bearing surface of the pivot cradle extends substantially symmetrically relative to the neutral plane; and the second relief pressure pocket extends asymmetrically relative to the neutral plane.

14. The hydrostatic axial piston machine of claim 1, wherein at least one of the plain bearing and the pivot cradle defines a plurality of relief pressure pockets spaced apart from each other along a pivoting direction.

15. The hydrostatic axial piston machine of claim 14, wherein the first adjustable throughflow cross section is configured to supply at least one of the plurality of relief pressure pockets with pressure medium.

16. The hydrostatic axial piston machine of claim 6, wherein the hydrostatic axial piston machine is configured such that an adjustment of at least one of the first adjustable throughflow cross section and the second adjustable throughflow cross section is coupled to a change in a pivot angle of the pivot cradle.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In the drawings:

[0039] FIG. 1 shows, in a longitudinal section, a hydrostatic axial piston machine according to a first exemplary embodiment,

[0040] FIG. 2 shows a hydraulic circuit diagram of the hydrostatic axial piston machine as per FIG. 1,

[0041] FIG. 2a shows, in a schematic illustration, a pressure medium supply of the hydraulic circuit diagram from FIG. 2,

[0042] FIG. 3 shows, in a schematic illustration, a pressure medium source, an adjustable throughflow cross section and a relief pressure field of the axial piston machine as per FIGS. 1 and 2,

[0043] FIG. 4 shows, in a schematic illustration, a pivot cradle of a hydrostatic axial piston machine as per a second exemplary embodiment,

[0044] FIG. 5 shows, in a schematic illustration, a pivot cradle of a hydrostatic axial piston machine as per a third exemplary embodiment,

[0045] FIG. 6 shows a working piston with sliding pad of a hydrostatic axial piston machine as per a fourth exemplary embodiment,

[0046] FIG. 7 shows a working piston with sliding pad of a hydrostatic axial piston machine as per a fifth exemplary embodiment,

[0047] FIG. 8 shows, in a schematic illustration, a plain bearing, a pivot cradle and a working piston with sliding pad of a hydrostatic axial piston machine as per a sixth exemplary embodiment,

[0048] FIG. 9 shows, in a schematic illustration, a pivot cradle of a hydrostatic axial piston machine as per a seventh exemplary embodiment,

[0049] FIG. 10 shows, in a schematic illustration, the pivot cradle of the hydrostatic axial piston machine as per FIGS. 1 and 2,

[0050] FIG. 11 shows, in a schematic illustration, a pivot cradle of a hydrostatic axial piston machine as per an eighth exemplary embodiment, and

[0051] FIGS. 12 and 13 show, in a schematic illustration, two exemplary embodiments of relief pressure pockets on the pivot cradle in a developed-view illustration.

DETAILED DESCRIPTION

[0052] FIG. 1 shows, in a longitudinal section, a hydrostatic axial piston machine 1. In the exemplary embodiment shown, said hydrostatic axial piston machine is designed as a hydraulic pump and therefore has a dedicated high-pressure port HP and a dedicated low-pressure port LP, which are both formed on a housing cover 2 and are not illustrated in FIG. 1. A drive shaft 4 is driven in rotation about an axis of rotation 3 and drives with it a cylinder drum 6 in which there are provided multiple cylinder bores 8 which are arranged so as to be distributed over the circumference, in which cylinder bores a respective working piston 10 is guided in an axial direction. The working pistons 10 are in each case supported in sliding fashion by way of a sliding pad 11 on a sliding surface 12 of a pivot cradle 13. The latter does not rotate but is adjustable in terms of its inclination by way of an actuating cylinder 14 of an adjustment device. In this way, a pivot angle , and thus a displacement volume of the axial piston machine 1, can be adjusted between a minimum pivot angle .sub.min and a maximum pivot angle .sub.max. At the minimum pivot angle .sub.min, the swashplate 12 stands perpendicular to the axis of rotation 3, such that, as the cylinder drum 6 and the working pistons 10 revolve, no stroke movement is generated, and therefore the displacement or delivery volume Vg of the axial piston machine 1 is zero. At the maximum pivot angle .sub.max, the sliding surface 12 is turned toward the axis of rotation 3 to a maximum extent such that, as the cylinder drum 6 and the working pistons 10 revolve, the maximum delivery volume Vg.sub.max is realized as a result.

[0053] The pivot cradle 13 is preloaded in the direction of the maximum pivot angle .sub.max counter to the actuating force of the actuating cylinder 14 by way of a spring 18 of a restoring cylinder 23, which spring is supported on a bushing 16 inserted into the housing cover 2. The actuating cylinder 14 is, in relation to the axis of rotation 3, arranged opposite the restoring cylinder 23. When an actuating pressure chamber 15 of the actuating cylinder 14 is charged with actuating pressure medium, the pivot cradle 13 pivots back to the minimum pivot angle .sub.min. Said movement is limited to the pivot angle .sub.min=0 by a stop 20 which is arranged in the interior of the bushing 16. The actuating pressure chamber 15 is delimited firstly by a bushing 17 which is screwed into the housing cover 2 and secondly by an actuating piston 26 which is mounted over the bushing 17. The actuating piston 26 is, by way of a base thereof, supported via a sliding pad on an articulation point (with ball head) which is inserted into the pivot cradle 13 at an edge side spaced apart from the pivot axis. The bushing 16, the stop 20 and a restoring piston 22 that protrudes into the bushing 16 delimit a restoring pressure chamber 24. The restoring piston 22 is coupled to the pivot cradle 13 by way of a sliding pad and an articulation point (with ball head) spaced apart from the pivot axis.

[0054] The pivot cradle 13 has, parallel to the pivot axis and symmetrically with respect to the section plane illustrated in FIG. 1, two partially cylindrical bearing segments 28 which are in each case pivotably received in a plain bearing 30 which is embedded in a bearing block. In FIG. 1, the bearing segment 28 arranged behind the section plane and the associated plain bearing 30 are illustrated by dashed lines because they are concealed by the pivot cradle 13. Multiple relief pressure pockets 232 are formed into the plain bearing 30 so as to be distributed circumferentially in the pivoting direction, which relief pressure pockets can be supplied with pressure medium by way of a pressure medium source of the axial piston machine 1. In this way, a relief pressure field can be built up between the plain bearing 30 and the pivot cradle 13, more specifically the bearing segment 28 thereof.

[0055] Before the embodiment of the pressure medium charging of said relief pressure field is discussed with reference to FIGS. 2 and 2a, it is the intention to illustrate which basic possibilities for the pressure medium supply to relief pressure pockets, and for the configuration thereof, are proposed.

[0056] The illustrations in the following FIGS. 3 to 13 are highly schematic.

[0057] FIG. 3 shows the principle by which one or the multiple relief pressure pockets 32 are supplied with pressure medium in order to build up the relief pressure field between the bearing segment 28 of the pivot cradle 13 and the plain bearing 30. For this purpose, a pressure medium source 36 is provided which has a pressure medium connection to the relief pressure pockets 32 via a pressure medium flow path 34. Here, the pressure medium connection is controlled by way of an adjustable throughflow cross section, in particular that of a throttle device, arranged in the pressure medium flow path 34. Here, the throughflow cross section may be formed for example by parts which are moved relative to one another in any case during the pivoting of the pivot cradle, for example the pivot cradle and the plain bearing. Alternatively, the throughflow cross section may be formed by a separately controllable throttle device, for example a valve.

[0058] In FIG. 4, the supply of pressure medium to a relief pressure pocket 32 on the pivot cradle, which relief pressure pocket is formed into the sliding surface of the bearing element 28, is realized via those working chambers 9 of the axial piston machine 1 which are charged with high pressure. The figure shows the working piston 10 which is supported on the sliding surface 12 in the pivot cradle. Here, the working piston is supported directly on the sliding surface 12 and is suitably sealed to said sliding surface such that the leakage in the contact region between working piston 10 and pivot cradle 13 is minimal. The relief pressure pocket 32 is connected to the working chamber 9 via the pressure medium flow path 34 which extends through the pivot cradle 13. Here, the pressure medium flow path 34 also extends through the working piston 10. Here, in the pressure medium flow path 34, the adjustable throughflow cross section is in the form of a separately actuable throttle device 38. The relief pressure pocket 32 is of asymmetrical design in relation to a neutral plane 40 of the pivot cradle. Here, a relatively large section of the relief pressure pocket 32 extends counter to the pivoting direction for an enlargement of the displacement volume. The relatively small section extends in said direction.

[0059] FIG. 5 shows a further exemplary embodiment in which the separately actuable throttle device in the working piston 10 is dispensed with and, instead, the adjustable throughflow cross section is provided at the support point of the working piston 10 on the sliding surface 12. The relative movement of the pivot cradle 13 relative to the working piston 10 supported thereon gives rise to an adjustment of the throughflow cross section which is defined by way of the opening-out points of the pressure medium flow path on the working piston and on the pivot cradle. Here, to be able to cover the pivot angle range of the pivot cradle, the opening-out point of the pressure medium flow path 34 in the sliding surface 12 is designed to be slightly larger, such that the displacement of the opening-out point of the working piston 10 which occurs during the pivoting movement relative to the opening-out point in the sliding surface 12 can be covered.

[0060] FIG. 6 shows a further exemplary embodiment, in which the adjustable throughflow cross section 38 is formed by geometries of the sliding pad 11 and of the working piston 10. Here, the pressure medium flow path 34 extends through the working piston 10 and the sliding pad 11. Here, a first section 34a opens out at an end side in a ball head of the working piston 10. A second section 34b extends through the sliding pad 11 from its side in contact with the sliding surface to a spherical recess in which the ball head is received.

[0061] FIG. 7 diagrammatically shows the control principle as has already been discussed in FIG. 4, in the case of which the adjustable throughflow cross section is arranged as an adjustable throttle device 38 in the working piston 10. The sliding pad 11 is also illustrated in this case.

[0062] FIG. 8 shows an exemplary embodiment in which the feed flow of pressure medium into the pivot cradle 13 is realized via a working piston 10 with sliding pad 11. The adjustable throughflow cross section is in this case situated between the sliding pad 11 and the pivot cradle 13.

[0063] FIG. 9 shows an exemplary embodiment in which, in addition to the relief pressure pocket 32 on the pivot cradle, a relief pressure pocket 232 on the plain bearing is provided. In the neutral position, the two relief pressure pockets 32, 232 overlap. If the pivot cradle is then pivoted in the direction of an enlargement of the displacement volume, that is to say in the direction .sup.+, the relief pressure field formed by the two relief pressure pockets 32, 232 is enlarged. Accordingly, the pivot cradle is hydrostatically relieved to an increasing extent with increasing pivot angle .

[0064] FIG. 10 shows a further exemplary embodiment with multiple relief pressure pockets 232 on the plain bearing which are arranged so as to be spaced apart from one another in the pivoting direction .sup.+ and which are fluidically connected via the pressure medium flow path 34 to the pressure medium source 36. Here, each relief pressure pocket 232 is connected via a parallel branch of the pressure medium flow path 34. The relief pressure pockets 232, which are thus supplied with pressure medium in parallel, can be supplied with pressure medium via a common throttle device 38 which is designed as a separately actuable valve.

[0065] As an alternative to this, the supply of pressure medium to the relief pressure pockets 232 may be configured as per FIG. 11. Here, each parallel branch of the pressure medium flow path 34 has a dedicated throttle device 38, which throttle devices are in each case separately actuable. It would also be conceivable for fewer throttle devices 38 than relief pressure pockets 232 to be provided, that is to say for one throttle device to be assigned to multiple relief pressure pockets. In this way, it is possible, in a manner dependent on the pivot angle, for the individual relief pressure pockets 232 to be supplied with pressure medium or to be shut off from the pressure medium supply of the pressure medium source 36. Alternatively or in addition, each individual one of the relief pressure pockets 232 may be supplied with pressure medium with a different throttling cross section of the respective throttle device 38. In this way, the resulting relief pressure field can be adapted in a highly effective manner to the pivot angle and to the forces locally occurring here in the plain bearing 30.

[0066] FIGS. 12 and 13 show relief pressure pockets 32 on the pivot cradle in a schematic illustration. The figures each show the relief pressure pocket 32 and an associated opening-out point of the pressure medium flow path 34 that provides a supply to said relief pressure pocket. The relief pressure pockets 32 are arranged symmetrically with respect to the neutral plane 40. In FIG. 12, on each bearing segment 28 of the pivot cradle 13, two relief pressure pockets 32 are arranged on each side of the neutral plane 40. Opening-out points of the pressure medium flow path 34 into the respective relief pressure pocket 32 are arranged diagonally with respect to one another, in each case in a corner of the relief pressure pockets 32 which, in principle, are rectangular. The relief pressure pockets 32 as per FIG. 12 are supplied with pressure medium via the actuating pressure chamber 15 and via the restoring pressure chamber 24 of the hydraulic pump as per FIG. 1. Here, the relief pressure pockets 32 indicated by A are charged with pressure medium via the restoring pressure chamber 24, and the relief pressure pockets 32 indicated by B are charged with pressure medium via the actuating pressure chamber 15.

[0067] By contrast to the exemplary embodiment as per FIG. 12, FIG. 13 shows relief pressure pockets 32 which extend across the neutral plane 40 and symmetrically with respect thereto. In this case, too, the relief pressure pockets 32 indicated by A are supplied with pressure medium from the restoring pressure chamber 24, and the relief pressure pockets indicated by B are supplied with pressure medium from the actuating pressure chamber 15. Compared with the relief pressure pockets as per FIG. 12, the relief pressure pockets as per FIG. 13 are of narrower form but have the same area.

[0068] FIG. 2 shows a hydraulic circuit diagram of the axial piston machine 1 for the purposes of illustrating the pressure medium supply of the relief pressure pockets 232 as per FIG. 10, which pressure medium supply is, for improved clarity in FIG. 2, shown on a smaller scale in FIG. 2 than in FIG. 2a. The axial piston machine 1 has a high-pressure line 42 and a low-pressure line 44. Here, in the pump operating mode, said axial piston machine delivers pressure medium from the low-pressure line 44 to the high-pressure line 42. The illustration in FIG. 2 illustrates the actuating cylinder 14, which acts on the pivot cradle 13, and the restoring cylinder 23, which likewise acts on the pivot cradle 13. The axial piston machine 1 has an electromagnetically actuable 3/3 proportional directional valve 46, by way of the first end position 46a of which, when the associated electromagnet a is energized, a pressure medium connection is established between the high-pressure line 42 and the actuating pressure chamber 15. By way of an end position 46b which is assumed when the electromagnet B of the valve 46 is energized, the actuating pressure chamber 15 is connected to the tank T. In the first end position 46a, the actuating piston 26 is deployed, and thus the pivot angle is decreased, whereas in the second end position 46b, the actuating piston 26 is retracted, and the pivot angle is increased.

[0069] The restoring pressure chamber 24 of the restoring cylinder 23 can be placed in pressure medium connection with the high-pressure line 42 by way of a 2/2 directional switching valve 52. Said valve is preloaded into a closed position by way of a spring and can, when electromagnetically actuated, be adjusted into a throughflow position such that the stated pressure medium connection is opened up.

[0070] By way of an adjustable throttle device 38 which is designed as a 2/2 directional switching valve and which is electromagnetically actuable, it is possible, as per FIGS. 2 and 2a, for the actuating pressure chamber 15 to be placed in pressure medium connection with the relief pressure pockets 232 arranged on the plain bearing. In FIG. 2, an optional adjustable throttle device (38, dashed lines) is illustrated by way of which the restoring pressure chamber 24 can be placed in pressure medium connection with optional relief pressure pockets (32, dashed lines) on the pivot cradle.

[0071] The axial piston machine 1 also has, for the control of its displacement volume and of the relief pressure field, a control device ECU. For explanation of the pressure medium supply of the relief pressure pockets 232, it shall firstly be assumed that the axial piston machine 1 is being operated in a steady state with a static pivot angle . Accordingly, it is presently the case that no adjustment of the pivot angle is taking place. At this time, the 2/2 directional switching valve 52 is electromagnetically actuated, such that the restoring pressure chamber 24 is supplied with high pressure from the high-pressure line 42. The 3/3 proportional directional valve 46 is adjusted in the direction of the end position 46a by way of the control device ECU and the energization of the electromagnet a, such that the high-pressure line 42 has a throttled pressure medium connection to the actuating pressure chamber 15. The forces of the spring 18 acting on the pivot cradle 13, of the high pressure acting on the restoring piston 22 and of the pressure in the actuating pressure chamber 15, which acts on the actuating piston 26, hold the pivot cradle 13 in equilibrium, that is to say with a constant pivot angle . Since the pivot cradle 13 is presently not being adjusted, the adjustable throttle device 38 is not electromagnetically actuated, such that the spring forces the throttle device 38 into its blocking position. Correspondingly, the relief pressure pocket 232 is not charged with pressure medium, and the relief pressure field does not exist, whereby it is also the case that leakage is prevented.

[0072] It is now sought to realize a decrease of the pivot angle , which means that pressure medium is to be supplied to the actuating pressure chamber 15. Before this takes place, the electromagnet of the throttle device 38 is energized by way of the control device ECU such that the throughflow position of said throttle device connects the actuating pressure chamber 15 to the relief pressure pocket 232. Correspondingly, the relief pressure field builds up between the pivot cradle 13 and the plain bearing 30. Subsequently to this, the magnet a of the 3/3 proportional directional valve is actuated, such that the valve body thereof is displaced to a greater extent in the direction of the first end position 46a, and the throughflow cross section is increased in size. In order to provide the stated time gap between the build-up of the relief pressure field and the adjustment, the throttle device 38 may for example be designed as a fast-switching valve with a significantly shorter switching time than the 3/3 proportional directional valve. With the supply of pressure medium into the actuating pressure chamber 15, the actuating piston 26 is displaced counter to the hydrostatic force and the spring force of the restoring cylinder 23 until a new force equilibrium on the pivot cradle 13 has been established and the adjustment has thus come to an end. At this time, it is also the case that the energization of the electromagnet of the throttle device 38 is deactivated again, such that the relief pressure pocket 232 is separated from its pressure medium supply and the relief pressure field breaks down, such that further leakage via said relief pressure field is prevented.

[0073] During the increase of the pivot angle , the pressure medium supply is controlled as follows: firstly, before the adjustment, the electromagnet of the throttle device 38 is energized again, such that the pressure medium connection of the actuating pressure chamber 15 to the relief pressure pocket 232 is established and the relief pressure field can be built up. Then, by way of a deactivation of the energization of both electromagnets a and b of the 3/3 proportional directional valve 46 by way of the control device ECU, said valve 46 is adjusted into a spring-centered central blocking position 46c in which the actuating pressure chamber 15 is separated from the high-pressure line 42 and is simultaneously placed in throttled pressure medium connection with the tank T via a bypass line 48 and an aperture 50 arranged therein. Accordingly, with the actuating piston 26 retracted, pressure medium can be discharged from the actuating pressure chamber 15 to the tank T, and at the same time, an adequately high pressure for forming the relief pressure field can be maintained in the actuating pressure chamber 15. The pivot cradle 13 performs an adjustment in the direction of the greater pivot angle until force equilibrium on the pivot cradle 13 has been established again. Then, the energization of the electromagnet of the throttle device 38 is deactivated, whereby the pressure medium connection of the actuating pressure chamber 15 to the relief pressure pocket 232 is shut off, and the relief pressure field breaks down.

[0074] The disclosure discloses a hydrostatic axial piston machine of swashplate type of construction, for which a hydrostatic relief pressure field can be built up between a pivot cradle and a plain bearing. Here, for the supply of pressure medium to the relief pressure field in accordance with demand, an adjustable throughflow cross section is provided. Said adjustable throughflow cross section can be varied in terms of its cross section in particular in a manner dependent on an adjustment or restoration of the displacement volume.

LIST OF REFERENCE DESIGNATIONS

[0075] 1 Hydrostatic axial piston machine

[0076] 2 Housing cover

[0077] 3 Axis of rotation

[0078] 4 Drive shaft

[0079] 6 Cylinder drum

[0080] 8 Cylinder bore

[0081] 9 Working pressure chamber

[0082] 10 Working piston

[0083] 11 Sliding pad

[0084] 12 Sliding surface

[0085] 13 Pivot cradle

[0086] 14 Actuating cylinder

[0087] 15 Actuating pressure chamber

[0088] 16, 17 Bushing

[0089] 18 Spring

[0090] 20 Stop

[0091] 22 Restoring piston

[0092] 23 Restoring cylinder

[0093] 24 Restoring pressure chamber

[0094] 26 Actuating piston

[0095] 28 Bearing segment

[0096] 30 Plain bearing

[0097] 32; 232 Relief pressure pocket

[0098] 34 Pressure medium flow path

[0099] 36 Pressure medium source

[0100] 38 Throttle device

[0101] 39 Bearing surface

[0102] 40 Neutral plane

[0103] 42 High-pressure line

[0104] 44 Low-pressure line

[0105] 46 3/3 proportional directional valve

[0106] 46a, 46b End position

[0107] 46c Blocking position

[0108] 48 Bypass line

[0109] 50 Aperture

[0110] ECU Control device

[0111] Pivot angle

[0112] .sub.min Minimum pivot angle

[0113] .sub.max Maximum pivot angle

[0114] Vg Displacement volume

[0115] Vg.sub.max Maximum delivery volume