WO2025093473A1 - Pump device - Google Patents

Abstract

The invention relates to a pump device having: multiple individual pistons (10) which are subdivided in two groups (14, 16) and which are each, being located opposite one another and behind one another in rows for the purpose of piston movements in opposite directions, guided longitudinally movably in a piston receptacle (20); and a drivable control means (24) which, via one control face (26) each, controls the individual pistons (10) of each group (14, 16) in a sequence of a suction stroke and a delivery stroke and vice versa, wherein the control faces (26) of the control means (24) are located between the two groups (14, 16) of pistons (10).

Description

Pump device

The invention relates to a pump device with a plurality of individual pistons which are divided into two groups and which are arranged opposite one another and in rows one behind the other for an opposing piston movement, each of which is guided so as to be longitudinally displaceable in a piston receptacle, and with a drivable control means which, with a control surface in each case, controls the individual pistons of each group in succession from a suction stroke to a pressure stroke and vice versa.

DE 10 2013 008 679 A1 discloses an axial piston pump in a swash plate design, particularly for hydraulic systems, comprising a cylinder drum rotatably driven about an axis in a pump housing, in which pistons are arranged in a row one behind the other for axial movement, which pistons are supported at least indirectly with their actuating end accessible outside the cylinder drum on a swash plate, which is pivotable to the desired angle of inclination relative to the axis in order to adjust the stroke of the pistons and thus the fluid system pressure generated by them, wherein the swash plate is mounted on the pump housing for its pivoting movements via a swash plate bearing, and wherein a supply device is provided, by means of which fluid under system pressure reaches at least the swash plate bearing. Furthermore A pressure device can be provided to hold the swashplate in contact with the swashplate bearing. This ensures proper bearings and correspondingly high operational reliability, even during long-term operation with a large number of adjustment cycles and/or high-frequency pivoting movements of the swashplate.

DE 10 2013 008 676 A1 discloses a further axial piston pump, in particular for use in hydraulic systems, having a cylinder drum which can be driven to rotate about an axis in a pump housing and in which piston-cylinder units are arranged offset on a circle, wherein the pistons are supported at least indirectly on a swash plate with their actuating end accessible outside the cylinder drum, and wherein a control device is arranged between the displacement chambers of the piston-cylinder units and a stationary fluid inflow and a stationary fluid outflow of the connection plate, which control device has fluid channels for the targeted transfer of fluid from the fluid inflow into the displacement chambers and from the displacement chambers to the fluid outflow, 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 displacement chambers. This opens up the possibility of minimizing pressure surges that occur when the control edges between cylinders and the pressure-side and suction-side fluid channels overflow. This is achieved by initiating a corresponding pressure buildup via a pressure compensation channel before reaching a pressure-side fluid channel, or by initiating a pressure reduction via a compensation channel before reaching a suction-side fluid channel. This creates a gentle pressure buildup in the area of the changeover from the suction side to the pressure side.

DE 10 2004 060 954 A1 discloses a generic hydraulic piston machine or pump device which is designed in the manner of a A so-called double swash plate pump is designed with a plurality of pistons arranged one behind the other in a cylinder and displaceably guided, each of which defines a working chamber into which pressure medium can be fed via a suction valve arranged on the piston and from which pressure medium can be discharged via a pressure valve, wherein the piston is penetrated by a pressure-equalizing pressure medium flow path which is delimited at least in sections 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 to form an additional nozzle bore, which facilitates unobstructed operation.

Based on the generic state of the art relating to a double swash plate pump, the invention is based on the object of improving the said state of the art.

A pump device having the features of patent claim 1 in its entirety solves this problem.

Because, according to the characterizing part of patent claim 1, the control surfaces of the control means are arranged between the two groups of pistons, the individual pistons or pump pistons act equally on the control means from both sides, so that the mutually acting piston forces cancel each other out. This also relieves the load on the bearing of a drive shaft, which drives the control means in rotation in the manner of a swash plate with the respective control surfaces.

The pump device according to the invention with the mentioned force compensation can be used in particular for pumping fluids at very high pressures, usually in the range of several 100 bar. In particular, the pump device can be used to To pump a fluid medium into a central tank filled with hydrogen in order to displace the hydrogen so that the displaced hydrogen can be removed from the tank for further use, for example, during a vehicle refueling process. It goes without saying that the pumping device can also be used for other technical applications, particularly in the low-pressure range.

In a preferred embodiment of the pump device according to the invention, the two control surfaces of the control means are part of a control disk mounted on a drive shaft and rotatably driven by the drive shaft, and the control surfaces are inclined toward each other relative to the drive shaft. In this way, force compensation during operation of the pump device is achieved in a particularly advantageous, space-saving manner.

In a further particularly preferred embodiment of the pump device according to the invention, the control disk 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 device, in particular in the form of two compression springs, in a central position between the two groups of pistons. Connections between the drive shaft and the control disk, such as a connection by means of a key or a splined shaft, are used as drivers. In this case, a self-centering system is created which can compensate for any unevenness in the material pairing between the control disk and the pump piston by means of the centering device, thus ensuring low-friction, long-term operation of the pump device. Furthermore, the central arrangement in the middle and inside the pump device means that the interior of the device housing of the pump device with its movable components is can be better sealed from the environment, for example by using well-sealed housing end covers.

In a further preferred embodiment of the pump device according to the invention, the centering device comprises two opposing centering sleeves, preferably of the same design, each of which is supported with one free end on the control disc and with the other free end on the respectively associated compression spring, preferably with the same spring force. This achieves particularly low-vibration operation for the pump device.

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 its one free end on an inner flange widening on the centering sleeve and with its other free end on a fixed bearing point in the form of a fixing ring and that both the centering sleeves and the compression springs as well as the fixing rings extend coaxially along the longitudinal axis of the device and thereby encompass the drive shaft.

Preferably, it is further provided that all pistons are guided with one piston end in an associated sliding guide, which is supported by means of a pretensioning device with a predeterminable pretension in each position of the control disc on the adjacent control surface.

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 each travel state of a piston, due to the movement of the control disc, is in contact with a control ring, which is supported on a contact cone of the pretensioning device, which in this respect is supported by an energy storage in the form of a further compression spring is preloaded, which is supported stationary with one free end on parts of the device housing and with its other free end is in movable contact with the contact cone. In this way, the respective preloading device with its compression spring ensures that one shoe part with its flange-like widening can be tilted or pivoted around a rod end of a piston in such a way that the free end face of the other shoe part of the sliding guide or sliding shoe, which is thus carried along in the movement, remains in contact with the associated, adjacent control surface of the control disc. In this respect, the control disc can directly transmit the resulting force to the respective piston for a pump delivery movement without hindrance during its rotating movement.

Preferably, the pistons of each group are of identical construction and accommodated in pairs opposite each other in their respective piston chambers on the control disc. Accordingly, the pistons of each group act in pairs in a common actuation plane on the control surfaces of the control disc, which are provided with the same inclination in this pump operating range, thus achieving complete, mutual force balance, which benefits smooth and wear-free operation.

Preferably, the control surfaces, with the same inclination, define a control cone in a fictitious extension, whose cone angle 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 for the pump device can be specified accordingly and kept constant during operation. The pump performance is determined by the volume flow and pressure.

In a further particularly preferred embodiment of the pump device according to the invention, it is provided that the pretensioning device at least partially encompasses the centering device, which are arranged coaxially with each other. This also benefits compactness, and the pump device as a whole is extremely compact while maintaining high performance.

In a further preferred embodiment of the pump device according to the invention, the respective contact cone has a conical or spherical control surface on its outer circumference for engagement with the control ring and a hollow cylindrical central recess with which it is guided along the centering sleeve for movement thereon. This achieves gentle control or centering for the respective sliding guide.

In a further advantageous embodiment of the pump device according to the invention, it is provided that all pistons, each with a further piston end, delimit a fluid chamber of variable volume, which, by means of a valve device, enables the inflow of fluid from the suction side into the respective piston chamber during a suction stroke of the respective piston and the outflow of fluid under pressure from the respective piston chamber to the pressure side of the pump device during a pressure stroke of the respective piston while blocking the suction side. In this way, continuous pumping operation is achieved with the pump device.

In this case, the valve device advantageously has two check valves assigned to each fluid chamber, which separate the suction side from the pressure side in each travel position of a piston during piston operation. In this way, pump operation can be realized in a functionally reliable and cost-effective manner. 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, which is provided with connection points in the pump housing, allowing 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 possibly for applications in a medium pressure range, leakage oil removal is achieved at a significantly lower discharge pressure.

For efficient operation of the pumping device, the suction side and the pressure side each open into an annular chamber in the pump housing, to which the fluid chambers of all pistons are connected. The two annular chambers are therefore designed to have the same volume to ensure a constant pressure distribution, which helps simplify manufacturing.

The pump device according to the invention will be explained in more detail below using an exemplary embodiment as shown in the drawing. The drawings are schematic and not to scale.

Figure 1 partly in longitudinal section, partly in elevation, the pump device as a whole; and

Figure 2 shows an enlarged view of a single pump piston with sliding thrust guide, as used in the pump device according to Figure 1.

The pump device shown in Figure 1 has a plurality of individual pistons 10 of the same design, which are arranged concentrically around a longitudinal axis 12 of the pump device in a multiple arrangement. The pistons 10 can be divided into two groups 14, 16, with each group 14 or 16 in the multiple arrangement preferably at least five individual pistons 10 or preferably more are associated with each group. However, for the solution according to the invention, just one piston 10 per group 14 or 16 is sufficient. The number of pistons 10 used ultimately depends on the desired pumping performance with the device. As can be seen from Figure 1, for a counter-rotating piston movement, the individual pistons 10 are arranged in pairs opposite one another on a common axis 18 that 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 aforementioned pistons 10 of a group 14 or 16. The pistons 10 are each precisely guided 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.

Furthermore, Figure 1 shows a drivable, rotating 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. In this way, the two control surfaces 26 of the control means 24 are arranged between the two groups 14, 16 of pistons 10. As viewed in the direction of Figure 1, the piston pair 10 arranged at the bottom in a plane is, due to the position of the control means 24, in the maximum deflected front position for a suction stroke, and the piston pair 10 shown at the top is, due to the control means 24, in its rearmost retracted position, in which a pressure stroke has already been completed. The pistons 10 located in a row between each other assume an intermediate piston position (not shown) for each row of a group 14, 16.

As can be further seen from Figure 1, the two opposing control surfaces 26 of the control means 24 are part of a control disc 28 which is mounted on a drive shaft 30 and can be driven in rotation by means of the latter, the control surfaces 26 being arranged opposite the drive shaft 30, which extends coaxially to the longitudinal axis 12, are inclined towards one another. The drive shaft 30 is led out of the device housing 22 on its right-hand side, as viewed in the direction of Figure 1, and is provided with a tongue and groove connection 32 for the engagement of a drive device, such as a pump motor. Each piston 10 of each group 14, 16 is accommodated in pairs opposite one another in relation to the control disk 28, each in an identically designed piston chamber 34, so that all piston chambers 34 have the same volume.

The control disk 28 is designed as a wedge in the longitudinal sectional view according to Figure 1, wherein the control surfaces 26, with the same inclination relative to the longitudinal axis 12, delimit 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, viewed in the direction of Figure 1, when the control disk 28 rotates around the longitudinal axis 12 by 180° by means of the drive shaft 30, the narrowest point of the control disk 28 with the fictitious control cone is then at the top and the widest point is at the bottom. Because the control disk 28 is driven in rotation by the drive shaft 30, all pistons 10 of each group 14, 16 are switched one after the other from a maximum suction stroke to a maximum pressure stroke and from there back again to a maximum suction stroke.

The control disc 28 is mounted on the drive shaft 30 in a rotationally fixed manner by means of a driver 36 in the form of a key and is positioned on each side in a central position between the two groups 14, 16 of pistons 10 by means of a centering device designated as a whole by 38. For this purpose, the centering device 38 has two opposing centering sleeves 40, preferably of the same design, which are each supported with one free end on the control disc 28 and with their other free end on 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 with one free end on an inner flange extension of the centering sleeve 40 and with its other end on 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 thereby encompass the drive shaft 30. Furthermore, the respective compression spring 42 is mounted in a ring shape on the outer circumference of the drive shaft 30 and is outwardly encompassed by the respective centering sleeve 40, which engages in a guide drive 46 in the control disk 28 adjacent to the other centering sleeve 40 on its free end face. The two compression springs 42 are mounted directly on the drive shaft 30 and encompass it. The respective locking ring 44 represents a sliding and rolling bearing and therefore consists of two parts. That part of the respective locking ring 44 which is installed in the direction of the device housing and to which the position line 44 leads is stationary and is firmly installed with the housing, whereas the second part, which is installed in the direction of the assignable centering sleeve 40, rotates with the drive shaft 30 and thus together with the adjacent associated spring 42 including the centering sleeve 40.

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

All pistons 10 are guided with a free, front piston end in an associated sliding guide, which is also technically referred to as a sliding shoe 54. The respective sliding guide is supported by means of a pretensioning device 56 with a predeterminable preload in every position of the control disk 28 on the associated adjacent control surface 26. The details of such a piston-sliding shoe pairing 10, 54 for the axial piston machine shown in Figure 1, in particular in the form of a Swashplate machine, is shown in more detail in Figure 2. The mentioned pairing 10, 54 each has the piston 10, which has a spherical joint head 60 at the end of a piston shaft 58, which is at least partially received by a ball socket 62 of the sliding block 54. The mentioned joint head 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, wherein the respective diameter is determined transversely to the displacement movement of the piston 10.

At the transition point between the joint head 60 and the piston shaft 58, there is a constriction 64 which is reduced in diameter compared to the adjacent joint head 60 and the piston shaft 58, the constriction 64 resulting in particular from the manufacture of the piston 10. In addition to material hardening, the constriction 64 also has the task of limiting the free pivoting movement of the sliding block 54 on the joint head 60 in the manner of a stop. The piston 10 further has a longitudinal channel 66 which extends continuously through the piston 10 with essentially the same inner diameter, the longitudinal channel 66 exiting into the environment at the end of the piston 10 via funnel-shaped extensions 68.

Overall, the sliding block 54 has two shoe parts 70, 72, which, in cooperation with the joint head 60, form the ball socket 62, whereby each shoe part 70, 72 forms a bearing support for parts of the joint head 60 of the piston 10. One shoe part 70, with a diameter reduction 74, surrounds the joint head 60 of the piston 10 in such a way as to be press-fitted, that only rotational movements are possible for the piston 10 and/or the sliding block 54, namely around all axes. In this respect, the one shoe part 70 with its support forms a kind of linear, circumferential contact point 76 for the outer circumference of the joint head 60. The other shoe part 72, however, supports the joint head 60 axially with its support as shown in Figure 2 and thus forms a shell-shaped bearing point 78 with it.

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

As already explained, the piston 10 is guided, viewed in the longitudinal direction, back and forth in an associated piston receptacle 20 in the device housing 22, and its joint head 60 enables pivoting of the sliding shoe 54 with its two shoe parts 70, 72, with one shoe part 70 driving the other shoe part 72 via its internal guide surface 82, and vice versa. Furthermore, the other shoe part 72 has a type of nozzle channel 84 extending through it from its free end face, which opens into a fluid chamber 86 between the shoe part 72 and the piston head 60, with the fluid chamber 86 in turn being fluid-conductingly connected to the longitudinal channel 66 of the piston 10. In this way, the fluid to be pumped by the pump device can be conveyed as lubricant 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 disk 28, a circular-cylindrical recess 90 is introduced into the free end face 88 of the shoe part 72, which is in direct media-carrying connection with the fluid supply above the nozzle channel 84. In this way, an unobstructed, low-wear operation is achieved by the aforementioned internal lubricant supply with the fluid or medium to be pumped.

As can also be seen from 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, due to the control disk 28, is in contact with a control ring 94 which is supported on a contact cone 96 of the pretensioning device 56, which is pretensioned in this respect by an energy store in the form of a further compression spring 98 which is supported stationary with one free end on parts of the device housing 22 and is in movable contact with the contact cone 96 with its other free end (control ring 94, contact cone 96 and compression spring 98 are only shown once in Figure 1). The corresponding pretensioning device 56 is constructed identically for both groups 14, 16. In any case, the respective pretensioning device 56 ensures that the control ring 94, which is thereby driven, is adjusted via the compression spring 98 acting on the contact cone 96 in such a way that the one shoe part 70 with its widened portion 92 is tilted or pivoted around the joint head 60 in such a way that the free end face 88 of the further shoe part 72, which is thus driven in the movement, remains in contact with the adjacent control surface 26 of the control disk 28. For this purpose, the opposing surfaces of the respective control ring 94 are in contact with the flange-like widened portion 92, and to this extent the control ring 94 encompasses the one shoe part 70 and is guided longitudinally thereon. In this way, the control disk 28, during its rotating movement, can directly transmit the resulting force to the piston 10 for a conveying movement. The resulting force introduction via the spring-loaded contact cone 96 onto the control ring 94 and the widening 92 of one shoe part 70 is indicated by arrows in Figure 2. As can be further seen from Figure 1, a transversely extending bottom 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 is 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 to the pump device as a whole is introduced transversely to the longitudinal axis 12 into 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. Figure 1 shows, in a highly simplified form, two check valves 106, 108, one on the suction side of the pump device and one on the pressure side. When the pump device according to Figure 1 is in operation, the uppermost pair of pistons 10 moves towards each other with the rotating control disk 28, whereby the two check valves 106 open and the check valves 108 remain in their closed position shown due to suction. In this way, high-pressure fluid flows via the respective fluid connection point 104 into the annular space 102 and from there via the branch channel 100 into the piston chamber 34, whereby the volume of the piston chamber 34 inevitably increases due to the movement of the piston 10. In a maximum suction position, the pistons 10 assume their lowest position according to Figure 1.

Subsequently, upon further rotation of the control disc 28, the position shown in Figure 1 is again assumed for the upper piston pair, with the result that the respective piston 10 reaches its rearward position while reducing the piston chamber 34. During the resulting ejection movement of fluid, the check valve 106 closes and the valve 108 Opens so that during the pressure stroke, when the valve 108 is open, fluid is expelled below the pressure level on the inlet side in the direction of an outlet side, via a further fluid connection point 110 in the device housing 22. For the corresponding fluid supply to the further fluid connection points 110 when the check valve 108 is open, a needle-shaped transverse channel, which can be blocked by the ball of the check valve 108, opens into an annular channel 112 (denoted only once in Figure 1), into which the respective further fluid connection point 110 for each group 14, 16 opens. During the corresponding pressure stroke, when the check valves 108 are open, the check valve 106 influencing the suction side is closed. After completion of the pressure stroke, the piston 10 passes over the puncture-shaped transverse channel with the check valve 108 and assumes its fully retracted position in Figure 1, before another suction stroke takes place with the valve 106 open.

It is understood that only the control disk 28 rotates radially during fluid delivery, and the pistons 10, held stationary in their piston receptacles 20 in the receiving cylinder, are only moved back and forth in directions parallel to the longitudinal axis 12. In any case, the suction side can have a maximum of the same pressure as the pressure side (suction < = pressure). As can be seen from Figure 1, the control disk 28 is rotatably guided in a so-called control chamber within the device housing 22, which is provided with opposite connection points 116, 118 in the device housing 22. The purpose of the two bores 116, 118 is to drain leakage oil and to actively flush it through for a cooling effect. Fluid can flow from connection 116 to 118 or vice versa. The pressure in the housing can be either greater or less than the ambient pressure. With the pump device according to the invention, flow rates can be achieved under very high pressure, whereby the device as a whole is largely force-balanced, or the occurring forces are compensated, so that long-lasting, wear-free operation is guaranteed, which has no equivalent in the state of the art.

Claims

Patent claims 1. Pump device with a plurality of individual pistons (10) which are divided into two groups (14, 16) and which are arranged opposite one another and in rows one behind the other for an opposing piston movement, each of which is guided so as to be longitudinally displaceable in a piston receptacle (20), and with a drivable 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 in 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 in that the two control surfaces (26) of the control means (24) are part of a control disc (28) which is mounted on a drive shaft (30) and can be driven in rotation by means of the latter, and in that the control surfaces (26) are inclined towards one another with respect to the drive shaft (30). 3. Pump device according to one of the preceding claims, characterized in 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 store, 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 in that the centering device (38) comprises two opposing centering sleeves (40), preferably of the same type, which are each supported with one free end on the control disc (28) and with their other free end on the respectively assignable compression spring (42), preferably with the same spring force. 5. Pump device according to one of the preceding claims, characterized in that the respective compression spring (42) of the centering device (38) is supported with its one free end on an inner flange widening on the centering sleeve (40) and with its other free end on a fixed bearing point in the form of a fixing ring (44) and that both the centering sleeves (40) and the compression springs (42) as well as the fixing rings (44) extend coaxially along the longitudinal axis (12) and thereby encompass the drive shaft (30). 6. Pump device according to one of the preceding claims, characterized in that all pistons (10) are guided with one piston end (60) in each case in an associated sliding guide (54) which is supported by means of a pretensioning device (56) with a predeterminable pretension in each position of the control disc (28) on the adjacent control surface (26). 7. Pump device according to one of the preceding claims, characterized in 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 each travel state of a piston (10), due to the movement of the control disc (28), is in contact with a control ring (94) which is supported on a contact cone (96) of the pretensioning device (56), which is pretensioned in this respect by an energy store in the form of a further compression spring (98) which is supported with its one free end in a stationary manner on parts of the device housing (22) and with its other free end is in movable engagement with the contact cone (96). 8. Pump device according to one of the preceding claims, characterized in that the pretensioning device (56) at least partially comprises the centering device (38), which are arranged coaxially to one another. 9. Pump device according to one of the preceding claims, characterized in that the respective contact cone (96) has a conical or spherical control surface on the outer circumference for contact with the control ring (94) and has a hollow-cylindrical central recess with which it is guided so as to be movable along the centering sleeve (40). 10. Pump device according to one of the preceding claims, characterized in that all pistons (10) each delimit a piston chamber (34) with a further piston end, which by means of a valve device (106, 108) enables the inflow of fluid from the suction side into the respective piston chamber (34) in a suction stroke of the respective piston (10) and the outflow of fluid under pressure from the respective piston chamber (34) to the pressure side of the pump device in a pressure stroke of the respective piston (10) while blocking off the suction side. 11. Pump device according to one of the preceding claims, characterized in that the valve device has two check valves (106, 108) assigned to each piston chamber (34), which separate the suction side from the pressure side in each travel position of a piston (10) during piston operation. 12. Pump device according to one of the preceding claims, characterized in that the control disc (28) is rotatably guided in a control chamber within the pump device housing (22), which control chamber is provided with connection points (116, 118) in the device housing (22), enables drainage of leakage oil resulting from the conveying operation with the pistons (10) and enables active flushing of the device housing (22) in order to achieve an additional cooling effect. 13. Pump device according to one of the preceding claims, characterized in 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.