System with electric machine and hydraulic unit and electric machine and hydraulic unit - Patents.com

Abstract

The present invention relates to a system comprising an electric machine (10) having a first shaft (11) and a hydraulic unit (20) having a second shaft (21), the first shaft (11) and the second shaft (21) being connected to each other to form a shaft hub connection, the shaft hub connection having a central recess (29), the shaft hub connection being fluidly connected to the interior of the hydraulic unit (20) for lubrication.

Description

[Technical field]

[0001] The present invention relates to a system comprising an electric machine having a first shaft and a hydraulic unit having a second shaft. The present invention further relates to a hydraulic unit and an electric machine for such a system. [Background technology]

[0002] The electric machine is usually configured as an electric motor and is connected to a hydraulic unit configured as a pump. The electric machine comprises a stator and a rotor connected to or forming a shaft. However, it may also be provided that the hydraulic unit drives the electric machine as a generator.

[0003] For the transmission of torque between the (first) shaft of the electric machine and the (second) shaft of the hydraulic unit, it is known to provide a so-called bell housing, which is spaced apart in a manner that connects the electric machine and the hydraulic unit, and inside the bell housing, a transmission shaft connects the first shaft and the second shaft to each other. The bell housing and the transmission shaft have the advantage that the electric machine and the hydraulic unit can be aligned to a certain extent with each other during assembly, in particular so that manufacturing tolerances for the bearings of the first shaft of the electric machine and the second shaft of the hydraulic unit can be compensated. The disadvantage, however, is that the length of the entire system (in the direction of the extension of the shafts) is substantially increased by the bell housing and the transmission shaft. Furthermore, a large number of parts with corresponding assembly expenditures and costs are necessary to build the complete system.

[0004] In order to build a more compact system, which requires fewer components, it is known to insert the first shaft of the electric machine and the second shaft of the hydraulic unit directly into one another, thus forming a positive and direct shaft-hub connection. Such a more compact system is known, for example, from DE 10 2016 225 196 A1. It is proposed that the shaft-hub connection is lubricated by the hydraulic fluid conveyed by the hydraulic unit. For this purpose, a leakage oil channel is proposed running in the axial direction of the pump shaft, which leakage oil channel extends over the entire length of the pump shaft. The hydraulic fluid passing from the pressurized conveying chamber of the pump along the bearing of the pump head to enter the leakage oil chamber inside the hydraulic unit therefore enters the end of the leakage oil channel, which is arranged at the front end of the pump shaft inside the hydraulic unit. The leakage oil flowing through the central leakage oil channel, after leaving the leakage oil channel at the end assigned to the shaft-hub connection, flows along the shaft-hub connection and lubricates the shaft-hub connection. To facilitate this leakage oil flow, a drain is proposed through which the leakage oil flows out after lubrication of the shaft-hub connection. A separate drain is therefore required which must be formed between the electric machine and the hydraulic unit or within the electric machine. Therefore, an equipment adaptation of the electric machine or an adapter piece which is arranged between the electric machine and the hydraulic unit is required. Summary of the Invention [Problem to be solved by the invention]

[0005] It is therefore an object of the present invention to provide a system comprising an electric machine and a hydraulic unit, as well as an electric machine and a hydraulic unit, whereby it is possible to further integrate a leakage oil drain into the hydraulic unit. [Means for solving the problem]

[0006] The object is achieved by a system, a hydraulic unit, an electric machine and an intermediate shaft with the features of the respective independent claims. Advantageous further developments of the system, the hydraulic unit, the electric machine and the intermediate shaft are specified in the dependent claims and in the description, the individual features of the advantageous further developments may be combined with one another in a technically meaningful manner. In particular, features described with respect to the system may also be applied to the hydraulic unit or the electric machine and vice versa.

[0007] The object is in particular achieved by a system comprising an electric machine with a first shaft and a hydraulic unit with a second shaft, the first and second shafts being connected to one another to form a shaft hub connection, preferably for positive locking, the shaft hub connection comprising a central recess, the shaft hub connection being fluidly connected to the interior of the hydraulic unit for lubrication, the central recess being adjacent to at least one transverse channel, the at least one transverse channel extending from the central recess to an outer periphery of the shaft hub connection.

[0008] The object is also achieved by a hydraulic unit, the shaft of which has a central recess and at least one transverse channel, the at least one transverse channel extending from the central recess to the outer periphery of the shaft.

[0009] The object is also achieved by an electric machine, the shaft of which has a central recess and at least one transverse channel, the at least one transverse channel extending from the central recess to an outer periphery of the shaft.

[0010] The object is also achieved by an intermediate shaft for connecting the first shaft and the second shaft of such a system, the intermediate shaft having a central recess and at least one transverse channel, the at least one transverse channel extending from the central recess to the outer periphery of the intermediate shaft.

[0011] The invention is discussed below with reference to a system, however the described embodiments also explicitly relate to an independent hydraulic unit, an independent electric machine and an independent intermediate shaft.

[0012] In one embodiment of the system, the first shaft and the second shaft are directly inserted into each other to form a shaft-hub connection, where the first shaft or the second shaft comprises a central recess and at least one transverse channel extends from the central recess to the outer periphery of the respective shaft. Preferably, the central recess and the at least one transverse channel are formed in the second shaft of the hydraulic unit.

[0013] Since the first shaft and the second shaft can be directly inserted into each other to form a shaft-hub connection, no additional components (such as a bell housing and a transmission / intermediate shaft) need to be provided to connect the shaft of the electric machine to the shaft of the hydraulic unit.

[0014] In an alternative embodiment, the first shaft and the second shaft may be indirectly connected by an intermediate shaft, in which case the shaft hub connection comprises an intermediate shaft for connecting the first shaft and the second shaft, and the central recess and at least one transverse channel may be formed in the intermediate shaft.

[0015] Preferably, a plurality of (at least two, preferably at least four, particularly preferably not more than eight) transverse channels adjoin the central recess and in each case extend in a particularly linear manner from the central recess to the outer circumference of the respective shaft. At least one transverse channel can extend outwardly, strictly radially and therefore perpendicular to the longitudinal axis of the shaft. However, it is also possible that at least one transverse channel is aligned at a different angle to the longitudinal axis of the shaft. The transverse channel(s) can be formed, for example, by a bore.

[0016] The invention is based on the discovery that a fluid located in at least one transverse channel (in particular leakage oil from a leakage oil chamber of the hydraulic unit) is subjected to centrifugal forces during operation of the system, which can transport the fluid from a central recess into a chamber surrounding the outer periphery of the shaft, and that the fluid can be sucked in as a result of the negative pressure thereby created in the recess, with the result that a specific transport direction of the fluid is predefined.

[0017] In other words, the invention, in its basic idea, provides that the first shaft of the electric machine, the second shaft of the hydraulic unit or the intermediate shaft has a transverse channel running outwardly, in particular radially, to transport the leaking oil along the shaft-hub connection, so that the leaking oil can be transported in particular for lubrication of the contact points between the shafts and in particular circulated back into the leaking oil chamber of the hydraulic unit, so that no further drain is required for the leaking oil.

[0018] In one embodiment, for example, it may be provided that the hydraulic unit comprises a leakage oil chamber. The leakage oil chamber is in particular a chamber inside the hydraulic unit into which hydraulic oil enters during operation from a pressurized conveying chamber of the hydraulic unit. For example, the hydraulic fluid enters along a bearing of a component conveying the pressurized hydraulic fluid. In this case, a central recess may be arranged in the (second) shaft of the hydraulic unit or in the intermediate shaft, with at least one transverse channel extending from the central recess to the leakage oil chamber. The recess is preferably formed as an axial channel in the (second) shaft of the hydraulic unit, extending from the at least one transverse channel through the second shaft directly to the shaft hub connection. Alternatively, the central recess is formed as an axial channel in the intermediate shaft, extending from the at least one transverse channel through the intermediate shaft to the front end of the intermediate shaft. The axial channel extending in the axial direction of the shaft thus has an inlet at the front end facing the electric machine, through which leakage oil can enter the axial channel (after lubricating the shaft hub connection). Thus, the axial channel does not extend completely through the second shaft or through the intermediate shaft, and is therefore considered a blind hole that extends from the front end through the shaft to at least one transverse channel.

[0019] In an alternative embodiment, it may be provided that the (first) shaft of the electric machine has a recess and at least one adjacent transverse channel. In this case, the recess is in particular arranged directly adjacent to a receptacle for the (second) shaft or for the intermediate shaft of the hydraulic unit. In this embodiment, the leaking oil that has already flowed along the contact points of the shaft-hub connection is conveyed through the (first) shaft of the electric machine into a chamber surrounding the shaft.

[0020] Preferably in this embodiment, a separate drain can be provided for leaking oil conveyed through the at least one transverse channel of the first shaft of the electric machine.

[0021] It is also preferably provided that the at least one transverse channel terminates at a point on the circumference of the shaft that does not overlap with the other shaft in the connected state. Thus, the at least one transverse channel is arranged axially offset with respect to the shaft hub connection in one of the shafts, thereby ensuring that leakage oil can be transported from a leakage oil chamber inside the hydraulic unit along the shaft hub connection arranged outside the housing of the hydraulic unit.

[0022] In one embodiment it is preferably provided that the shaft hub connection is fluidly connected via at least one passageway on the outside of the second shaft to a leakage oil chamber inside the hydraulic unit, a first passageway or a first group of such passageways being provided for leakage oil to flow from the leakage oil chamber inside the hydraulic unit to the shaft hub connection.

[0023] Such a first passage can be implemented, for example, by mounting the (second) shaft of the hydraulic unit in the housing of the hydraulic unit in the direction towards the shaft-hub connection without a shaft seal. In this case, the leakage oil therefore flows from the leakage oil chamber along the surface of the (second) shaft in the direction towards the shaft-hub connection through the housing of the hydraulic unit. In the case of the first embodiment described above, where by the first embodiment a central recess and at least one transverse channel are formed in the (second) shaft of the hydraulic unit or in the intermediate shaft, the fluid coming from the leakage oil chamber enters the axial channel in the second shaft (or in the intermediate shaft) after flowing along the contact point of the shaft-hub connection. In the second embodiment described above, where by the second embodiment a central recess and at least one transverse channel are formed in the (first) shaft of the electric machine, the fluid coming from the leakage oil chamber along the second shaft is conveyed into a chamber surrounding the first shaft.

[0024] The fluid connection of the leakage oil chamber inside the hydraulic unit and the passage for the shaft hub connection may additionally or alternatively be formed by at least one opening, preferably a plurality of openings (particularly formed as recesses and preferably as holes) arranged adjacent to the second shaft in the housing or housing component of the hydraulic unit (e.g. in a cover cap or a bearing). In the case of the first embodiment described above, the leakage oil can flow from the leakage oil chamber through at least one opening in the housing to the shaft hub connection and then into an axial channel in the second shaft or in the intermediate shaft. In the case of the second embodiment described above, the leakage oil conveyed through the at least one transverse channel can flow back into the leakage oil chamber through the openings. In this connection, it is preferred if the front end face of the first shaft is sealed relative to the hydraulic unit so that leakage oil can flow from a leakage oil chamber inside the hydraulic unit, along the outside of the shaft and along the shaft hub connection to a recess in the (first) shaft of the electric machine, from where it can be transported back into the leakage oil chamber, through at least one transverse channel, to an opening in the housing that is offset radially outward relative to the sealed end face of the shaft.

[0025] Preferably, at least one opening can be closed and preferably has an internal thread for closure, so that in the delivery state the opening can be closed, for example by a screw, in which case the opening can be closed until just before the mounting of the hydraulic unit to the electric machine.

[0026] In a preferred embodiment, the shaft hub connection comprises a splined connection comprising at least one pin having an external tooth formation and at least one receptacle having an internal tooth formation.

[0027] A pin, preferably having an external toothing, may be formed on a first shaft of the electric machine, in which case at least one receptacle, preferably having an internal toothing, is arranged on a front end of a second shaft of the hydraulic unit.

[0028] Alternatively, a pin, preferably having an external toothing, may be formed on a second shaft of the hydraulic unit, in which case at least one receptacle, preferably having an internal toothing, is arranged on the front end of the (first) shaft of the electric machine.

[0029] In yet a further embodiment, the first shaft of the electric machine and the second shaft of the hydraulic unit may each be provided with a receptacle on its front end, preferably having an internal toothing, and the intermediate shaft forms two pins, each having an external toothing for insertion into the receptacle when the first shaft is connected to the second shaft by the intermediate shaft.

[0030] To fasten the electric machine to the hydraulic unit, the housing of the electric machine and the housing of the hydraulic unit may be connected to one another in a suitable manner (e.g. by means of a corresponding screw connection), for example by forming at least one flange or cover cap.

[0031] The first shaft is in particular mounted by two bearings in the electric machine. The second shaft is in particular mounted by two bearings in the hydraulic element. In particular, if a pin with an external toothing is formed on the second shaft of the hydraulic unit, the pin protrudes beyond one of the bearings in the direction of the electric machine and beyond the housing of the hydraulic unit.

[0032] When specifically implementing the system, it was found that the internal and external tooth structures of the spline connection were severely worn. The background to this severe wear could be that as a result of the forces acting on the shaft inside the hydraulic unit during operation, the pin protruding beyond the bearing can deflect from its neutral position and therefore not maintain its position / alignment in the stationary state in the receptacle of the electric machine. Another reason for severe wear could be that when connecting the electric machine to the hydraulic unit, as a result of the tolerances of the electric machine or the hydraulic unit, the pin in the receptacle does not take the desired position / alignment.

[0033] In order, inter alia, to reduce wear of the splined connection, a certain range of ratios between the pitch diameter of the external toothing on the pin and the length of the external toothing has been shown to be advantageous. The external toothing of the pin, which may be formed on the first shaft of the electric machine or on the second shaft of the hydraulic unit or on the intermediate shaft, therefore has an external toothing length and a pitch diameter. The external toothing length is the length of the teeth in the extension direction of the shaft. It is preferred here that the ratio of the pitch diameter to the external toothing length is smaller than 1.2, particularly preferably smaller than 1.1 and also particularly preferably smaller than 1.05. On the other hand, the ratio of the pitch diameter to the external toothing length should be at least 0.8, preferably at least 0.9 and particularly preferably at least 0.95. In a particularly preferred embodiment, the ratio of the pitch diameter to the external toothing length is between 0.95 and 1.05, particularly preferably equal to 1. An independent invention is also found in this ratio of the pitch diameter to the external toothing length, which can be claimed independently of the above-described solution for a system with an electric machine and a hydraulic unit.

[0034] The independent invention is therefore found in a hydraulic unit, the shaft of which has a pin having an external tooth structure, the pin having an external tooth structure length and a pitch diameter, the ratio of which (i.e. the ratio of the pitch diameter to the external tooth structure length) is within the ranges described above.

[0035] In order to reduce wear of the splined connection, it has been shown to be alternatively or additionally specified that the external toothing structure has tolerances of class 07. The tolerance classes are specified here in the standard ANSI B92.1 from 1996.

[0036] Therefore, as an independent invention, a hydraulic unit is also proposed having a shaft with a pin having an external tooth structure, the external tooth structure having a tolerance of class 07. The above-described ratio of pitch diameter to length of the external toothing structure, particularly in combination with the tolerance class of the internal toothing structure, has the effect that wear of the spline connection is minimized.

[0037] The hydraulic unit is preferably embodied as a swashplate unit capable of operating as a pump or a motor. In the swashplate unit, the deflection of the pins of the shaft protruding beyond the housing during operation is particularly large as a result of the forces acting on the shaft inside the swashplate pump. The pins of the shaft of the swashplate pump protruding beyond the housing of the swashplate pump are therefore immediately and directly inserted into corresponding receptacles of the electric machine. Alternatively, the hydraulic unit capable of operating as a pump or a motor can be embodied as a bent-axis piston unit, a gear unit, a rotor type unit or a screw spindle unit.

[0038] The splined connection is preferably a spline in which tapered teeth of an external tooth structure engage with an internal tooth structure. Such splines are defined, for example, in ANSI B92.1 from 1996.

[0039] The invention and technical background are explained below by way of example with reference to the figures. [Brief description of the drawings]

[0040] [Figure 1] FIG. [Diagram 2] FIG. 2 shows the connection area of ​​the electric unit. [Diagram 3] FIG. 4 is a view showing a second shaft of the hydraulic unit. [Figure 4] FIG. 2 is a cross-sectional view through a region of an exemplary embodiment of the system. [Diagram 5] FIG. 13 is a cross-sectional view through a region of a further exemplary embodiment of the system. [Figure 6] FIG. 13 is a cross-sectional view through a region of yet a further exemplary embodiment of the system. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0041] The hydraulic unit 20 shown in Figure 1 and configured as a swashplate pump comprises a housing 26 having a cover cap 27. Mounted in the housing 26 is a shaft 21 with a pin 22 protruding beyond the cover cap 27. The pin 22 has an external tooth formation 23 having an external tooth formation length 24 and a pitch diameter 25. The shaft 21 with the pin 22 is also shown as a single component in Figure 3.

[0042] 2 shows an electric machine 10 with its connection area to a hydraulic element 20. The shaft 11 of the electric machine 10 has a receptacle 12 with an internal toothing arrangement 13. The pin 22 of the shaft 21 of the hydraulic unit 20 is inserted into the receptacle 12 of the electric machine 10 to form the system. Therefore, the shaft 11 of the electric machine 10 is directly connected to the shaft 21 of the electro-hydraulic unit 20, forming a shaft hub connection for positive locking. Therefore, no further components are required to connect the shafts 21, 22 of the electric machine 10 and the hydraulic unit 20 to each other.

[0043] In order that the tolerance deviations of the bearings of the shafts 11 and 21 can be compensated for, the ratio of the pitch diameter 25 to the length 24 of the external toothing structure is between 0.8 and 1.2, preferably between 0.95 and 1.05. For the same reason, the internal toothing structure 13 has a tolerance of class 07.

[0044] 4 and 5 show the areas of the system consisting of the electric machine 10 and the hydraulic unit 20. Thus, the end of the hydraulic unit 20 facing the electric machine 10 and the end of the hydraulic unit 20 facing the electric machine 10 are shown. In all exemplary embodiments, it can be seen that the hydraulic unit 20 has a housing 26, which may be provided with a cover cap 27 as a component. A leakage oil chamber 28 is formed inside the housing 26, so that hydraulic fluid can flow from a conveying chamber of the hydraulic unit into the housing 26 along a corresponding bearing (not shown) of the pump head. Furthermore, a leakage oil outlet 32 ​​may be provided, from which leakage oil can leave the leakage oil chamber 28.

[0045] Furthermore, the receptacle 12 already described above can be seen at one end of the first shaft 11 into which a pin 22 of the second shaft 21 of the hydraulic unit 20 is inserted. In the exemplary embodiment of Fig. 4, a central recess 29 configured as an axial channel is formed in the second shaft 21 of the hydraulic unit 20. This recess 29 configured as an axial channel is bordered by two transverse channels 30 extending radially up to the outer periphery 31. The transverse channels 30 thus run from the ends of the recess 29 into the leakage oil chamber 28. The recess 29 ends on the end face of the second shaft 21, on the side facing the electric machine 10.

[0046] In the exemplary embodiment shown in Fig. 5, a recess 29 is formed in the first shaft 11 of the electric machine 10 adjacent to the receptacle for the pin 22. Starting from the recess 29, two transverse channels 30 extend to the outer periphery 31 of the first shaft 11.

[0047] In both exemplary embodiments, a passage 33 is formed along the outer circumferential surface or through a bearing of the second shaft 21 of the hydraulic unit 20, through which leakage oil can flow from the leakage oil chamber 28 under appropriate pressure conditions. The exemplary embodiment of Figure 5 provides a separate leakage oil outlet 32 ​​in the electric machine 10 that is fluidly connected via a transverse channel 30 to a recess 29 in the first shaft 11.

[0048] In operation, the first shaft 11 and the second shaft 21 rotate about their longitudinal axes, which results in leakage oil located in the transverse channel 30 being carried outwards as a result of centrifugal force and a negative pressure being formed in the recess 29.

[0049] 4, this also results in a negative pressure being formed in the area of ​​the receptacle 12 such that the leakage oil flows from the leakage oil chamber 28 through the passage 33 and along the connection point between the pin 22 and the receptacle 12. The connection point between the pin 22 and the receptacle 12 is thus permanently lubricated. The leakage oil then enters the recess 29 formed as an axial channel and passes back into the leakage oil chamber 28 through the transverse channel 31.

[0050] 5, rotation of the shafts 11, 21, as a result of centrifugal force acting on the leakage oil in the transverse channel 30, causes a negative pressure to form in the recess 29, resulting in the leakage oil (hydraulic fluid) flowing along the outer side of the second shaft 21 through the first passage 33 and along the coupling point between the receptacle 12 and the pin 22, and also causing the coupling point to be lubricated. The fluid conveyed through the transverse channel 30 flows to a separate leakage oil outlet 32 ​​of the electric machine 10.

[0051] 6 shows an area of ​​a further embodiment of a system consisting of an electric machine 10 and a hydraulic unit 20, which may for example be embodied as a gear pump. In the following, mainly the differences with respect to the embodiment described above are explained.

[0052] In this embodiment, the first shaft 11 of the electric machine 10 is indirectly connected to the second shaft 21 of the hydraulic unit 20. The first shaft 11 is connected to the second shaft 21 via an intermediate shaft 40, which is inserted with one end having an external toothing in the receptacle 12 of the first shaft 11 and with its other end also having an external toothing in a receptacle formed in the second shaft 21. The intermediate shaft 40 thus provides a torque-resistant connection between the first shaft 11 and the second shaft 21, such that the rotational movement of the first shaft 11 is transferred to the rotational movement of the second shaft 21. A shaft hub connection is thereby formed between the first shaft 11 and the second shaft 21.

[0053] The intermediate shaft 40 has a central recess 29 extending from the end face of the intermediate shaft 40 facing towards the first shaft 11 to a transverse channel 30 which extends radially outwards towards the outer periphery of the intermediate shaft 40. In the housing 26 of the hydraulic unit 20 a leakage oil chamber 28 is formed which surrounds the outer periphery of the intermediate shaft 40 in the area where the transverse channel 30 exits therefrom.

[0054] During operation, centrifugal force acting on the leakage oil in the transverse channel 30 creates a negative pressure in the central recess 29 such that leakage oil from the leakage oil chamber 28 flows along the outer periphery of the intermediate shaft 40 into the receptacle 12 of the first shaft 11 and from there into the central recess 29. The leakage oil in the central recess 29 is drained back into the leakage oil chamber 28 through the transverse channel 30. Thus, the positive locking connection between the first shaft 11 and the intermediate shaft 40 is lubricated by the leakage oil.

[0055] To increase leakage oil flow along the circumference of the shaft, the teeth of the external or internal toothing in the shaft-hub connection may be omitted. Thereby, a compact system comprising an electric machine and a hydraulic unit is provided, which can be operated with low maintenance. [Explanation of symbols]

[0056] 10 Electrical Machinery 11 First Shaft 12 Receptacle 13 Internal tooth structure 20 Hydraulic Unit 21 Second Shaft 22 pin 23 External tooth structure 24 External tooth structure length 25 Pitch diameter 26 Housing 27 Cover cap 28 Leaking Oil Chamber 29 Recess 30 Transverse Channel 31 Outer circumference 32 Oil leakage outlet 33 Passage 40 Intermediate shaft

Claims

1. 1. A system comprising: An electric machine (10) comprising a first shaft (11); a hydraulic unit (20) having a second shaft (21); the first shaft (11) and the second shaft (21) are connected to each other to form a shaft hub connection; The shaft-hub connection has a central recess (29); The shaft hub connection is fluidly connected to the interior of the hydraulic unit (20) for lubrication; The hydraulic unit (20) includes a leakage oil chamber (28), the central recess (29) is adjacent to at least one transverse channel (30), the at least one transverse channel (30) extending from the central recess (29) to an outer periphery (31) of the shaft-hub connection; A system, characterized in that the fluid located in the at least one transverse channel (30) from the leakage oil chamber (28) of the hydraulic unit (20) is subjected to centrifugal force during operation of the system, the fluid being transported from the central recess (29) into the leakage oil chamber (28) surrounding the outer periphery of the second shaft (21), whereby the fluid is sucked in by the negative pressure created in the central recess (29), a specific transport direction of the fluid is predefined and the fluid circulates.

2. The system of claim 1 , wherein the first shaft (11) and the second shaft (21) are inserted into one another to form the shaft hub connection.

3. 3. The system of claim 2, wherein the first shaft (11) and / or the second shaft (21) comprises the central recess (29), and the at least one transverse channel (30) extends from the central recess (29) to an outer periphery (31) of the shaft.

4. The system according to claim 2 or 3, wherein the central recess (29) and the at least one transverse channel (30) are disposed in the second shaft (21).

5. The shaft hub connection comprises an intermediate shaft (40) for connecting the first shaft (11) and the second shaft (21); The system of claim 1 , wherein the central recess (29) and the at least one transverse channel (30) are formed in the intermediate shaft (40).

6. A system as described in any one of claims 1 to 5, wherein at least one transverse channel (30) extends from the central recess (29) to the leakage oil chamber (28).

7. The system of claim 6, wherein the central recess (29) extends as an axial channel from the at least one transverse channel (30) through the second shaft (21) to the shaft hub connection.

8. 6. The system of claim 5, wherein the central recess (29) extends as an axial channel from the at least one transverse channel (30) through the second shaft (21) or through the intermediate shaft (40) to an end of the second shaft (21) or an end of the intermediate shaft (40), the end of the second shaft (21) or the end of the intermediate shaft (40) facing the first shaft (11).

9. 9. The system according to claim 5 or 8, wherein the first shaft (11) has a receptacle (12) for the second shaft (21) or for the intermediate shaft (40), the central recess (29) formed in the first shaft (11) is adjacent to the receptacle (12), and the at least one transverse channel (30) is formed in the first shaft (11).

10. The end surface of the first shaft (11) is sealed to the hydraulic unit (20). The system of claim 9 .

11. The system of any one of claims 1 to 10, wherein the at least one transverse channel (30) terminates at a point on the circumference (31) of the shaft that does not overlap with other shafts in a connected state.

12. The system according to any one of claims 1 to 11, wherein the shaft hub connection is fluidly connected to a leakage oil chamber (28) of the hydraulic unit (20) via at least one passage (33) on the outside of the second shaft (21).

13. 13. The system according to claim 12, wherein the second shaft (21) is mounted without a shaft seal within a housing (26) of the hydraulic unit (20) to form a passage (33) in a direction towards the shaft hub connection.

14. 14. The system according to claim 12 or 13, wherein the hydraulic unit (20) has a housing (26) surrounding the second shaft (21), and in the housing (26) at least one opening is formed to form a passageway.

15. The system of claim 14, wherein the at least one opening can be closed, preferably having an internal thread for said closure.

16. The system according to any one of claims 1 to 15, wherein the hydraulic unit (20) is a swashplate unit, a bent-axis piston unit, a gear pump unit, a rotary vane unit, or a screw spindle unit.

17. A hydraulic unit (20) for a system according to any one of claims 1 to 16, wherein the second shaft (21) of the hydraulic unit (20) has a central recess (29) and at least one transverse channel (30), the at least one transverse channel (30) extending from the central recess (29) to an outer periphery (31) of the shaft (21).

18. 18. The hydraulic unit (20) of claim 17, wherein the hydraulic unit (20) has a leakage oil chamber (28), and the at least one transverse channel (30) extends from the central recess (29) to the leakage oil chamber (28).

19. 19. A hydraulic unit (20) according to claim 17 or 18, wherein the central recess (29) extends as an axial channel from the at least one transverse channel (30) through the shaft to a side of the second shaft (21), the side of the second shaft (21) being accessible outside the housing.

20. An electric machine (10) for a system according to any one of claims 1 to 16, wherein a shaft (11) of said electric machine (10) has a central recess (29) and at least one transverse channel (30), said at least one transverse channel (30) extending from said central recess (29) to an outer periphery (31) of said shaft (11); An electric machine (10), wherein the shaft (11) has a receptacle (12) for the shaft, the central recess (29) being adjacent to the receptacle (12).

21. An intermediate shaft (40) for a system according to any one of claims 1 to 16, said intermediate shaft (40) having a central recess (29) and at least one transverse channel (30), said at least one transverse channel (30) extending from said central recess (29) to an outer periphery (31) of said intermediate shaft (40).

22. 22. The intermediate shaft (40) of claim 21, wherein the intermediate shaft (40) has an external toothed structure at an end of the intermediate shaft (40) for forming a shaft hub connection with the second shaft (21) of the hydraulic unit (20) and with the first shaft (11) of the electric machine (10).

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