Pump device

Abstract

Pump device with a plurality of individual pistons (10) which are divided into two groups (14, 16) and which are arranged opposite each other and in rows one behind the other and are guided longitudinally in a piston receptacle (20) for a counter-rotating piston movement, and with a driven control means (24) which, with a control surface (26) each, controls the individual pistons (10) of each group (14, 16) in succession from a suction stroke to a pressure stroke and vice versa, characterized in that the control surfaces (26) of the control means (24) are arranged between the two groups (14, 16) of pistons (10).

Description

[0001] The invention relates to a pump device with a plurality of individual pistons, which are divided into two groups and which are arranged opposite each other and in rows one behind the other, and are guided longitudinally in a piston receptacle for counter-rotating piston movement, and with a driven control means which, with a control surface, controls the individual pistons of each group in succession from a suction stroke to a pressure stroke and vice versa.

[0002] DE 10 2013 008 679 A1 discloses an axial piston pump of swashplate design, particularly for hydraulic systems, with a cylinder drum rotatably driven about an axis within a pump housing. Pistons are arranged axially movable in a row within the cylinder drum, their actuating ends, accessible outside the cylinder drum, bearing at least indirectly against a swashplate. This swashplate can be pivoted to desired angles of inclination relative to the axis to adjust the stroke of the pistons and thus the fluid system pressure generated by them. The swashplate is mounted on the pump housing via a swashplate bearing for its pivoting movements. A supply device is provided by means of which the system-pressurized fluid reaches at least the swashplate bearing. Furthermore, a pressure device holding the swashplate in contact with the swashplate bearing may be provided.In this way, even during long-term operation with a large number of adjustment cycles and / or high-frequency swivel movements of the swashplate, flawless bearing and a correspondingly high level of operational reliability can be guaranteed.

[0003] DE 10 2013 008 676 A1 discloses another axial piston pump, particularly for use within hydraulic systems, with a cylinder drum rotatable about an axis in a pump housing, in which piston-cylinder units are arranged offset on a circle, wherein the pistons are supported at least indirectly on a swashplate with their actuating end accessible outside the cylinder drum, and wherein a control device is arranged between the stroke chambers of the piston-cylinder units and a stationary fluid inlet and a stationary fluid outlet of the connection plate, which has fluid channels for the targeted transfer of fluid from the fluid inlet to the stroke chambers and from the stroke chambers to the fluid outlet, wherein at least one pressure equalization channel is provided in the control device between the fluid channels for the targeted build-up or release of fluid pressure in the stroke chambers.This approach makes it possible to minimize pressure surges occurring when the fluid flows over the control edges between the cylinders and the pressure-side and suction-side fluid channels. This is achieved by initiating a pressure build-up via a pressure equalization channel before reaching a pressure-side fluid channel, or a pressure reduction via a compensation channel before reaching a suction-side fluid channel. This ensures a smooth pressure build-up in the area of ​​the changeover from suction side to pressure side.

[0004] DE 10 2004 060 954 A1 discloses a generic hydraulic piston machine or pump device designed in the manner of a so-called double swashplate pump, with a plurality of pistons arranged in series and slidably guided in a cylinder, each defining a working chamber. Pressure medium can be supplied to this chamber via a suction valve located on the piston and discharged from it via a pressure valve. The piston is penetrated by a pressure-equalizing pressure medium flow path, which is at least partially bounded by a capillary tube inserted into the piston. By using such a capillary tube with a constant capillary diameter, the known solution eliminates the need for an additional nozzle bore, thus facilitating unobstructed operation.

[0005] Starting from the prior art of a double swashplate pump, the invention aims to improve upon the aforementioned prior art.

[0006] A pump device with the features of claim 1 in its entirety solves such a problem.

[0007] Because, according to the characterizing part of claim 1, the control surfaces of the control element are arranged between the two groups of pistons, the individual pistons or pump pistons act equally on the control element from both sides, so that the mutually acting piston forces cancel each other out. In this respect, a reduction in stress is also achieved for the bearing of a drive shaft, which drives the control element in a swashplate-like fashion with the respective control surfaces rotating around its circumference.

[0008] The pump device according to the invention, with the aforementioned force compensation, is particularly suitable for pumping fluids at very high pressures, typically in the range of several hundred bar. Specifically, the pump device can be used to pump a fluidic medium into a central tank filled with hydrogen, thereby displacing the hydrogen so that the displaced hydrogen can be extracted from the tank for further use, for example, during vehicle refueling. It is understood that the pump device can also be readily used for other technical applications, particularly in the low-pressure range.

[0009] In a preferred embodiment of the pump device according to the invention, the two control surfaces of the control means are formed as part of a control disk, which is mounted on a drive shaft and can be driven in a rotating direction by means of which, and the control surfaces are inclined towards each other relative to the drive shaft. In this way, force compensation is achieved in a particularly space-saving manner during the operation of the pump device.

[0010] In a further particularly preferred embodiment of the pump device according to the invention, the control disc is mounted on the drive shaft in a rotationally fixed manner by means of a driver and is guided axially displaceably on the drive shaft by means of a centering device using at least one energy storage element, in particular in the form of two compression springs, and is positioned in a central position between the two groups of pistons. Connections between the drive shaft and the control disc, such as a connection by means of a key or a splined shaft, are used as drivers. In this way, a self-centering system is created which can compensate for any unevenness in the material pairing between the control disc and the pump pistons by means of the centering device, thus ensuring low-friction, long-lasting operation of the pump device.Furthermore, the central arrangement in the middle and inside the pump device allows the interior of the pump device housing with its movable components to be better sealed from the environment, for example by using well-sealing housing end covers.

[0011] In a further preferred embodiment of the pump device according to the invention, the centering device has two opposing centering sleeves, preferably of the same design, each of which is supported at one free end on the control disc and at the other free end on the respective compression spring, preferably with the same spring force. This results in particularly low-vibration operation of the pump device.

[0012] In a further preferred embodiment of the pump device according to the invention, it is provided that the respective compression spring of the centering device is supported with one free end on an inner flange extension on the centering sleeve and with its other free end on a fixed bearing point in the form of a locking ring, and that both the centering sleeves and the compression springs as well as the locking rings extend coaxially along the longitudinal axis of the device and thereby encompass the drive shaft.

[0013] Preferably, it is further provided that all pistons are guided with one piston end in an associated sliding guide, which is supported on the adjacent control surface by means of a preloading device with a predefinable preload in every position of the control disk.

[0014] Preferably, it is further provided that a shoe part of the respective sliding guide, consisting of two shoe parts, has an annular, flange-like widening which, in every travel state of a piston, is in contact with a control ring, which is supported on a contact cone of the preloading device, which is preloaded by an energy storage device in the form of a further compression spring, which is supported with one free end on parts of the device housing in a stationary manner and with its other free end is in movable contact with the contact cone.In this way, the respective preload device with its compression spring ensures that one shoe part, with its flange-like widening, can be tilted or pivoted around a piston's ball joint in such a way that the free end face of the other shoe part, which is thus carried along in the movement, remains in contact with the corresponding, adjacent control surface of the control disc. In this respect, the control disc, during its rotating motion, can directly transmit the resulting force to the respective piston for a pumping motion without obstruction.

[0015] Preferably, the pistons of each group are identical in design and are mounted in pairs opposite each other in their respective piston chambers, facing the control disc. Accordingly, the pistons of each group act in pairs on the control surfaces of the control disc, which are provided with the same inclination in this pump operating area, thus achieving complete mutual force compensation, which benefits smooth and wear-free operation.

[0016] Preferably, the control surfaces, at the same inclination, form a control cone along a hypothetical extension, the cone angle of which is less than 30°, preferably less than or equal to 20°. By selecting a constant angle for the control cone, the displacement volume per stroke of the pump device can be predetermined and kept constant during operation. The pump output is then determined by the volume flow rate and pressure.

[0017] In a further particularly preferred embodiment of the pump device according to the invention, the pre-tensioning device at least partially comprises the centering device, which are arranged coaxially to each other. This also contributes to compaction, and the pump device as a whole is exceptionally small despite its high performance.

[0018] In a further preferred embodiment of the pump device according to the invention, the respective mounting cone has a control surface for the assembly with the control ring that is conical or convex on its outer circumference and has a hollow cylindrical central recess by which it is guided along the centering sleeve so as to be movable. In this way, gentle control and centering for the respective sliding guide is achieved.

[0019] In a further advantageous embodiment of the pump device according to the invention, each piston has an additional piston end that defines a fluid chamber with a variable volume. A valve assembly allows fluid to flow from the suction side into the respective piston chamber during a suction stroke of the respective piston, and during a pressure stroke of the respective piston, while closing off the suction side, allows fluid to flow under pressure from the respective piston chamber to the pressure side of the pump device. In this way, continuous pump operation is achieved with the pump device.

[0020] Advantageously, the valve assembly features two check valves assigned to each fluid chamber, which separate the suction side from the pressure side during piston operation in every piston position. This allows for reliable and cost-effective pump operation.

[0021] In a further preferred embodiment of the pump device according to the invention, the control disc is rotatably guided in a control chamber within a pump housing. This control chamber, equipped with connection points in the pump housing, allows for the drainage of leakage oil resulting from pump operation with the pistons. Regardless of whether the pump device is used for high-pressure or low-pressure applications, and optionally for applications in a medium pressure range, leakage oil drainage is achieved at a significantly lower discharge pressure.

[0022] For efficient operation of the pump device, the suction and pressure sides each open into an annular space within the pump housing, to which the fluid chambers of all pistons are connected. Accordingly, both annular spaces are designed with the same volume to ensure a constant pressure profile, which simplifies manufacturing.

[0023] The pump device according to the invention will now be explained in more detail with reference to an exemplary embodiment shown in the drawing. The drawing shows, in a general and not to scale, the following: Fig. 1. Partly in longitudinal section, partly in elevation, the pump device as a whole; and Fig. 2 in enlarged view a single pump piston with sliding shoe guide, as it is used in the pump device according to the Fig. 1 is used.

[0024] The in Fig. Figure 1 shows a pump device comprising a plurality of individual pistons 10 of the same design, which are arranged concentrically around a longitudinal axis 12 of the pump device. The pistons 10 can be divided into two groups 14 and 16, with each group 14 or 16 preferably comprising at least five individual pistons 10, or preferably more, within the multiple arrangement. However, for the solution according to the invention, one piston 10 per group 14 or 16 is sufficient. The number of pistons 10 used ultimately depends on the desired pumping capacity of the device. As can be seen further from the Fig. As follows, for a counter-rotating piston movement, the individual pistons 10 are arranged in pairs opposite each other on a common axis 18, which runs parallel to the longitudinal axis 12. Furthermore, the pistons 10 of each group 14, 16 are arranged in rows one behind the other transversely to the longitudinal axis 12, with one row, for example, comprising the five pistons 10 of a group 14 or 16. The pistons 10 are each guided precisely in a piston receptacle 20 in the device housing 22, and the direction of travel of each piston 10 in the piston receptacle 20 is parallel to the aforementioned longitudinal axis 12.

[0025] Furthermore, in Fig. Figure 1 shows a driven, rotating control means 24 which, with a control surface 26, actuates the individual pistons 10 of each group 14, 16 successively from a suction stroke to a pressure stroke and vice versa. The two control surfaces 26 of the control means 24 are thus arranged between the two groups 14, 16 of pistons 10. Viewed in the direction of the Fig. As seen in Figure 1, the piston pair 10 arranged at the bottom of a plane is in its maximum extended forward position due to the position of the control means 24 for a suction stroke, and the piston pair 10 shown at the top is in its rearmost retracted position due to the control means 24, in which a pressure stroke has already been completed. The pistons 10 in the row between these two positions occupy an intermediate piston position (not shown) for each row of a group 14, 16.

[0026] As can be seen further from the Fig. As 1 results, the two opposing control surfaces 26 of the control means 24 are part of a control disk 28, which is mounted on a drive shaft 30 and can be driven in a rotating direction by means of this shaft, wherein the control surfaces 26 are inclined towards each other relative to the drive shaft 30, which extends coaxially to the longitudinal axis 12. The drive shaft 30 is oriented in the direction of the Fig. 1, seen on its right side, leads out of the device housing 22 and is provided with a spring-and-groove connection 32 for the attachment of a drive device, such as a pump motor. Each piston 10 of each group 14, 16 is received in pairs opposite each other to the control disk 28 in an identically designed piston chamber 34, so that all piston chambers 34 have the same volume.

[0027] The control disc 28 is shown in the longitudinal section view according to the Fig. 1 designed as a wedge, wherein the control surfaces 26, at the same inclination relative to the longitudinal axis 12, define a control cone in a fictitious extension, the cone angle of which is less than 30°, preferably less than or equal to 20°. It is understood that, in the direction of view towards the Fig. Figure 1 shows a rotation of the control disc 28 around the longitudinal axis 12 by means of the drive shaft 30 through 180°, with the narrowest point of the control disc 28, including the fictitious control cone, then located at the top and the widest point at the bottom. Because the control disc 28 is driven in a rotation by means of the drive shaft 30, all pistons 10 of each group 14, 16 are successively switched from a maximum suction stroke to a maximum pressure stroke and from there back to a maximum suction stroke.

[0028] The control disk 28 is mounted on the drive shaft 30 in a rotationally fixed manner by means of a driver 36 in the form of a keyway and is positioned in a central position between the two groups 14, 16 of pistons 10 by means of a centering device 38 on each side. For this purpose, the centering device 38 has two opposing centering sleeves 40, preferably of the same design, each of which is supported at one free end against the control disk 28 and at its other free end against an energy storage device in the form of a compression spring 42 with preferably the same spring force. The respective compression spring 42 is supported at one free end against an inner flange extension of the centering sleeve 40 and at its other end against a fixed bearing point in the form of a locking ring 44.Both the centering sleeves 40 and the compression springs 42, as well as the locking rings 44, extend coaxially along the longitudinal axis 12 and encompass the drive shaft 30. Furthermore, each compression spring 42 is mounted annularly on the outer circumference of the drive shaft 30 and is enclosed externally by the respective centering sleeve 40, which engages a guide recess 46 in the control disk 28 at its free end face adjacent to the other centering sleeve 40. The two compression springs 42 are mounted directly on and encompass the drive shaft 30. Each locking ring 44 is a sliding and rolling bearing and therefore consists of two parts.The part of the respective locking ring 44 that is installed in the direction of the device housing and to which the position line 44 leads is stationary and is fixedly attached to the housing, whereas the second part, which is installed in the direction of the associated centering sleeve 40, rotates with the drive shaft 30 and thus together with the adjacent associated spring 42 including the centering sleeve 40.

[0029] The drive shaft 30 is mounted inside the device housing 22 by means of several sliding bearings 48 and, within the scope of the passage to the outside, is guided in a sealed manner in a receiving bushing 52 inside a housing plate 50 on the free end face of the device housing 22.

[0030] All pistons 10 are guided at their free, front piston end in an associated sliding guide, which is also referred to in technical terms as a sliding shoe 54. The respective sliding guide is supported by means of a preload device 56 with a predefinable preload in every position of the control disk 28 against the associated adjacent control surface 26. The details of such a piston-sliding shoe pair 10, 54 for the in Fig. The axial piston machine shown in 1, in particular in the form of a swashplate machine, is in Fig. 2 is shown in more detail. The pairing 10, 54 mentioned above each comprises a piston 10, which has a spherical ball joint 60 at the end of a piston shaft 58. This ball joint is at least partially received by a ball socket 62 of the sliding shoe 54. The ball joint 60 has a diameter along its largest outer circumference that is larger than the diameter of the piston shaft 58 along its largest outer circumference, with the respective diameter being determined transversely to the displacement movement of the piston 10.

[0031] At the transition point between the rod end 60 and the piston shaft 58, a constriction 64 is present, which is reduced in diameter compared to the adjacent rod end 60 and the piston shaft 58. This constriction 64 results primarily from the manufacturing process of the piston 10. Besides hardening the material, the constriction 64 also serves to limit the free pivoting movement of the sliding shoe 54 on the rod end 60, acting as a stop. The piston 10 also has a longitudinal channel 66, which extends through the entire piston 10 with essentially the same inner diameter. At the end of the piston 10, the longitudinal channel 66 exits into the surrounding environment via funnel-shaped extensions 68.

[0032] The sliding shoe 54 comprises two shoe parts 70, 72, which, in conjunction with the ball joint 60, form the ball socket 62, with each shoe part 70, 72 providing a bearing surface for parts of the ball joint 60 of the piston 10. One shoe part 70, with a diameter reduction 74, surrounds the ball joint 60 of the piston 10 in a press fit such that only rotational movements are permitted for the piston 10 and / or the sliding shoe 54 about all axes. In this respect, one shoe part 70, with its bearing surface, forms a kind of linear circumferential contact point 76 for the outer circumference of the ball joint 60. The other shoe part 72, however, supports the ball joint 60 with its bearing surface as shown in the illustration. Fig. 2 the rod head 60 axially and thus forms a shell-shaped bearing point 78 with it.

[0033] Furthermore, one shell part 70 has a central recess 80 which is at least partially penetrated by the joint head 60 with its free end face and by the other shoe part 72, wherein the central recess 80 forms a longitudinal guide for the cylindrical outer circumference of the other shoe part 72 with an inner cylindrical guide surface 82.

[0034] As already explained, the piston 10 is guided in a longitudinally movable direction within an associated piston receptacle 20 in the device housing 22, and the sliding shoe 54 with its two shoe parts 70, 72 is pivoted via its ball joint 60, whereby one shoe part 70 carries the other shoe part 72 along with it via its internal guide surface 82 and vice versa. Furthermore, the other shoe part 72 has a nozzle channel 84 extending from its free end face, which opens into a fluid chamber 86 between the shoe part 72 and the piston head 60, the fluid chamber 86 being in turn connected to the longitudinal channel 66 of the piston 10 in a fluid-carrying manner.In this way, the fluid to be pumped by the pump device, acting as a lubricant, can be conveyed via the respective piston chamber 34 and the longitudinal channel 66 with the funnel-shaped extensions 68 into the fluid chamber 86, and from there a supply to the front, free end face 88 of the shoe part 72 is ensured via the nozzle channel 84. For improved lubricant application between the free end face 88 of the shoe part 72 and the adjacent control surface 26 of the control disc 28, a circular cylindrical recess 90 is provided in the free end face 88 of the shoe part 72, which is in direct contact with the fluid supply via the nozzle channel 84. Thus, unimpeded, low-wear operation is achieved through the aforementioned internal lubricant supply with the fluid or medium to be pumped.

[0035] As can be further seen from the Fig. As shown in Figure 2, one shoe part 70 of a shoe part 54 has an annular, flange-like widening 92 which, in every travel state of a piston 10, is in contact with a control ring 94, which is supported on a contact cone 96 of the preloading device 56, which is preloaded by an energy storage device in the form of a further compression spring 98, which is supported at one free end on parts of the device housing 22 in a stationary position and at its other free end is in movable contact with the contact cone 96 (control ring 94, contact cone 96 and compression spring 98 are in Fig. (1 designated only once). The preloading device 56 is constructed identically for both groups 14 and 16. In any case, the respective preloading device 56 ensures that the control ring 94, which is carried along by the compression spring 98 acting on the contact cone 96, is positioned such that one shoe part 70 with its extension 92 is tilted or pivoted about the ball joint 60 in such a way that the free end face 88 of the other shoe part 72, which is carried along in the movement, remains in contact with the adjacent control surface 26 of the control disc 28. For this purpose, the opposing surfaces of each control ring 94 are in contact with the flange-like extension 92, and the control ring 94 thus encompasses one shoe part 70 and is guided longitudinally on it. In this way, the control disc 28, during its rotating motion, can directly transmit the resulting force to the piston 10 for a conveying motion.The force transmission via the spring-loaded mounting cone 96 onto the control ring 94 and the widening 92 of one shoe part 70 is in . Fig. 2 indicated by arrows.

[0036] As can be seen further from the Fig. As shown in Figure 1, a transverse base of each piston shaft 58 defines the piston chamber 34 with variable volume. For fluid supply, the respective piston chamber 34 is coaxially enclosed by the compression spring 98 via an adjacent, underlying contact cone 96 and connected by a branch channel 100 to a circumferential, channel-like annular space 102 in the device housing 22. While the respective branch channel 100 runs parallel to the longitudinal axis 12 in the pump or device housing 22, a fluid connection point 104 for the fluid or media supply of the pump device as a whole is provided transversely to the longitudinal axis 12 in the device housing 22. A fluid at a very high pressure, for example in the range above 900 bar, can be supplied to the pump device via the respective fluid connection point 104. In the Fig. Figure 1 shows, in a highly simplified form, two check valves 106 and 108, one on the suction side of the pump device and one on the pressure side. If the pump device is according to the Fig. When 1 is in operation, the rotating control disk 28 moves the uppermost pair of pistons 10 towards each other, causing the two check valves 106 to open and the check valves 108 to remain closed due to suction. In this way, high-pressure fluid flows through the respective fluid connection point 104 into the annular space 102 and from there through the branch channel 100 into the piston chamber 34, the volume of the piston chamber 34 necessarily increasing due to the movement of the piston 10. In a maximum suction position, the pistons 10 assume their lowest position after the Fig. 1 one.

[0037] Subsequently, with further rotation of the control disc 28, the following occurs again: Fig. The position shown in Figure 1 is assumed for the upper piston pair, with the result that the respective piston 10 moves into its rearward position as the piston chamber 34 decreases. During the resulting fluid ejection movement, the check valve 106 closes and the valve 108 opens, so that during the pressure stroke, with the valve 108 open, fluid below the pressure level on the inlet side is ejected towards an outlet side via a further fluid connection point 110 in the device housing 22. For the fluid supply to the further fluid connection points 110 with the check valve 108 open, a spur-shaped transverse channel, which can be blocked by the ball of the check valve 108, opens into an annular channel 112 (in Fig. (1 designated only once), into which the respective further fluid connection point 110 for each group 14, 16 opens. During the corresponding pressure stroke, with the check valves 108 open, the check valve 106 influencing the suction side is closed. After completion of the pressure stroke, the piston 10 passes over the spur-shaped transverse channel with the check valve 108 and takes its position in the Fig. 1. Fully retracted position before another suction stroke takes place with valve 106 open.

[0038] It is understood that only the control disc 28 rotates radially during fluid delivery, and the pistons 10 remain stationary in their piston receptacles 20 in the receiving cylinder, moving only back and forth in directions parallel to the longitudinal axis 12. In any case, the suction side can have a maximum pressure equal to the pressure side (suction <= pressure). As can be seen further from the Fig.As shown in Figure 1, the control disc 28 is rotatably guided in a so-called control chamber within the device housing 22, which is provided with opposing connection points 116, 118 in the device housing 22. The purpose of the two bores 116, 118 is to allow leakage oil to drain and to perform active flushing for cooling. Fluid can flow from connection 116 to 118 or vice versa. The pressure in the housing can be either higher or lower than the ambient pressure. With the pump device according to the invention, flow rates under very high pressure can be achieved, whereby the device as a whole is largely force-balanced, or rather, the forces that occur are compensated, so that long-lasting, wear-free operation is ensured, which has no equivalent in the prior art. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2013 008 679 A1

[0002] DE 10 2013 008 676 A1

[0003] DE 10 2004 060 954 A1

[0004]

Claims

[1] Pump device with a plurality of individual pistons (10) which are divided into two groups (14, 16) and which are arranged opposite each other and in rows one behind the other and are guided longitudinally in a piston receptacle (20) for a counter-rotating piston movement, and with a driven control means (24) which, with a control surface (26), controls the individual pistons (10) of each group (14, 16) in succession from a suction stroke to a pressure stroke and vice versa, characterized by , that the control surfaces (26) of the control means (24) are arranged between the two groups (14, 16) of pistons (10). [2] Pump device according to claim 1, characterized by , that the two control surfaces (26) of the control means (24) are part of a control disk (28) which is mounted on a drive shaft (30) and can be driven in a rotating direction by means of this shaft, and that the control surfaces (26) are inclined towards each other relative to the drive shaft (30). [3] Pump device according to one of the preceding claims, characterized by , that the control disc (28) is mounted on the drive shaft (30) in a rotationally fixed manner by means of a driver (36) and is guided axially displaceably on the drive shaft (30) by means of a centering device (38) using at least one energy storage device, in particular in the form of two compression springs (42), in a central position between the two groups (14, 16) of pistons (10). [4] Pump device according to one of the preceding claims, characterized by , that the centering device (38) has two opposing centering sleeves (40), preferably of the same design, which each support their one free end on the control disc (28) and their other free end on the respective associated compression spring (42), preferably with the same spring force. [5] Pump device according to one of the preceding claims, characterized by, that the respective compression spring (42) of the centering device (38) is supported with one free end on an inner flange extension on the centering sleeve (40) and with its other free end on a fixed bearing point in the form of a locking ring (44) and that both the centering sleeves (40) and the compression springs (42) as well as the locking rings (44) extend coaxially along the longitudinal axis (12) and encompass the drive shaft (30). [6] Pump device according to one of the preceding claims, characterized by , that all pistons (10) are guided with each piston end (60) in an associated sliding guide (54) which is supported by means of a preloading device (56) with a predeterminable preload in each position of the control disk (28) on the adjacent control surface (26). [7] Pump device according to one of the preceding claims, characterized by, that a shoe part (70) of the respective sliding guide (54), consisting of two shoe parts (70, 72), has an annular, flange-like widening (92) which, in every travel state of a piston (10), is in contact with a control ring (94) which is supported on a contact cone (96) of the preloading device (56) which is preloaded by an energy storage device in the form of a further compression spring (98) which is supported with one free end on parts of the device housing (22) in a stationary manner and with its other free end is in movable contact with the contact cone (96). [8] Pump device according to one of the preceding claims, characterized by , that the preloading device (56) at least partially comprises the centering device (38), which are arranged coaxially to each other. [9] Pump device according to one of the preceding claims, characterized by, that the respective mounting cone (96) has a control surface on its outer circumference which is conical or convex for the mounting with the control ring (94) and has a hollow cylindrical center recess by which it is guided movably on the centering sleeve (40). [10] Pump device according to one of the preceding claims, characterized by , that all pistons (10) with each additional piston end define a piston chamber (34) with variable volume, which, by means of a valve arrangement (106, 108), allows fluid to flow from the suction side into the respective piston chamber (34) in a suction stroke of the respective piston (10) and, in a pressure stroke of the respective piston (10), allows fluid to flow under pressure from the respective piston chamber (34) to the pressure side of the pump device while shutting off the suction side. [11] Pump device according to one of the preceding claims, characterized by, that the valve assembly has two check valves (106, 108) assigned to each piston chamber (34), which separate the suction side from the pressure side during piston operation in each travel position of a piston (10). [12] Pump device according to one of the preceding claims, characterized by , that the control disc (28) is rotatably guided in a control chamber within the pump device housing (22), which is provided with connection points (116, 118) in the device housing (22), allows a drainage of leakage oil resulting from the pumping operation with the pistons (10) and enables active flushing of the device housing (22) to achieve an additional cooling effect. [13] Pump device according to one of the preceding claims, characterized by , that the suction side and the pressure side each open into an annular space (102, 112) in the device housing (22), to which the piston spaces (34) of all pistons (10) are connected.

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