CN117280128A - System comprising a motor and a hydraulic unit, and motor and hydraulic unit - Google Patents

Abstract

The invention relates to a system comprising an electric motor (10) and a hydraulic unit (20), wherein the electric motor (10) has a first shaft (11), the hydraulic unit (20) has 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), and the shaft-hub connection is fluidly connected to the inside of the hydraulic unit (20) for lubrication.

Description

System comprising a motor and a hydraulic unit, and motor and hydraulic unit

Technical Field

The present application relates to a system comprising an electric motor having a first shaft and a hydraulic unit having a second shaft. The present application additionally relates to a hydraulic unit and an electric motor for such a system.

Background

The electric machine is usually configured as an electric motor and is connected to a hydraulic unit configured as a pump. The motor comprises a stator and a rotor, which is connected to or forms a shaft. However, it is also possible to provide that the hydraulic unit drives the motor as a generator.

In order to transmit torque between the shaft of the motor (first shaft) and the shaft of the hydraulic unit (second shaft), it is known to provide a so-called bell box (bell box), said Zhong Xiang separating the motor and the hydraulic unit from each other in a connected manner, and within said Zhong Xiang a transmission shaft connecting the first shaft and the second shaft to each other. Zhong Xiang and the drive shaft have the advantage that the motor and the hydraulic unit can be aligned with each other to a certain extent during assembly, whereby manufacturing errors of the bearings of the first shaft of the motor and of the second shaft of the hydraulic unit in particular can be compensated for. However, there is a disadvantage in that the length of the entire system (direction along the extending direction of the shaft) is increased substantially by Zhong Xiang and the drive shaft. In addition, a large number of components, with corresponding assembly effort and costs, are necessary to construct a complete system.

In order to construct a more compact system requiring fewer components, it is known to insert the first shaft of the electric motor and the second shaft of the hydraulic unit directly into each other thus forming an active and direct shaft-hub connection. Such a more compact system is known, for example, from patent publication DE102016225196 A1. It is proposed there that the shaft-hub connection is lubricated by means of hydraulic fluid transmitted by the hydraulic unit. For this purpose, a leakage oil channel is proposed which extends along the axial direction of the pump shaft and which extends over the entire length of the pump shaft. The hydraulic fluid which is fed from the pressurized transmission chamber of the pump along the bearing of the pump head into the leakage oil channel in the hydraulic unit can thus enter into the end of the leakage oil channel, which is arranged in the hydraulic unit at the front end of the pump shaft. The leakage oil flowing through the central leakage oil passage flows along the shaft-hub connection portion and lubricates the shaft-hub connection portion after being discharged from the leakage oil passage at the shaft-hub connection portion. In order to facilitate such leakage oil flow, a drain (drain) is proposed, by means of which the leakage oil is emptied after lubricating the shaft-hub connection. Thus, a separate drain is required, which has to be formed between the motor and the hydraulic unit or in the motor. Thus, the device adaptation of the electric motor or of an adapter arranged between the electric motor and the hydraulic unit is necessary.

Disclosure of Invention

It is therefore an object of the present application to provide a system comprising a motor and a hydraulic unit, as well as a motor and a hydraulic unit, whereby a leakage oil drain can be further integrated in the hydraulic unit.

This object is achieved by a system, a motor, and an intermediate shaft having the features of the respective independent claims. Advantageous further modifications of the system, the hydraulic unit, the motor and the intermediate shaft are indicated in the dependent claims and in the description, wherein the individual features of the advantageous further modifications can be combined with one another in a technically meaningful manner. In particular, the features described with reference to the system may be applied to a hydraulic unit or a motor and vice versa.

This object is achieved, inter alia, by a system comprising an electric motor and a hydraulic unit, wherein the electric motor comprises a first shaft, wherein the hydraulic unit comprises a second shaft, wherein the first shaft and the second shaft are connected to each other to form a preferably actively locked shaft-hub connection, the shaft-hub connection comprising a central recess, and the shaft-hub connection being fluidly connected (capable of transmitting fluid) to the interior of the hydraulic unit for lubrication, wherein the central recess adjoins at least one lateral channel extending from the central recess to the outer periphery of the shaft-hub connection.

The object is also achieved by a hydraulic unit, wherein the shaft of the hydraulic unit has a central recess and at least one transverse channel, and wherein the at least one transverse channel extends from the central recess to the outer periphery of the shaft.

The object is also achieved by an electric motor, wherein the shaft of the electric motor has a central recess and at least one transverse channel, wherein the at least one transverse channel extends from the central recess to the outer periphery of the shaft.

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

The present application will be discussed hereinafter with reference to a system. However, the described embodiments also explicitly relate to a separate hydraulic unit, a separate motor and a separate intermediate shaft.

In an embodiment of the system, the first shaft and the second shaft are directly inserted into each other to form a shaft-hub connection, in which case the first shaft or the second shaft comprises a central recess, wherein the 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 a second shaft of the hydraulic unit.

The first and second shafts may be directly inserted into each other to form a shaft-hub connection, so that no other components (e.g. a bell housing and a transmission/intermediate shaft) need be provided to connect the shaft of the motor to the shaft of the hydraulic unit.

In alternative embodiments, the first shaft and the second shaft may be indirectly connected by an intermediate shaft. In this case, the shaft-hub connection comprises an intermediate shaft for connecting the first shaft and the second shaft, wherein the central recess and the at least one transverse channel may be formed in the intermediate shaft.

Preferably, a plurality of (at least two, preferably at least four, particularly preferably not more than eight) transverse channels adjoin the central recess, which transverse channels each extend particularly rectilinearly from the central recess to the outer periphery of the shaft. The at least one transverse channel may extend outwardly strictly in a radial direction and thus at right angles to the longitudinal axis of the shaft. However, it is also possible that at least one transverse channel is deployed at a different angle with respect to the longitudinal axis of the shaft. For example, the transverse channel may be formed by a hole.

The present application is based on the finding that a fluid located in at least one transverse channel, in particular leakage oil from a leakage oil chamber of a hydraulic unit, is subjected to centrifugal forces during operation of the system, whereas the fluid can be transported from the central recess into the chamber around the outer circumference of the shaft, wherein the fluid can be sucked in due to the negative pressure thus formed in the recess, as a result of which a specific transport direction of the fluid is predetermined.

In other words: the present application provides, as a basic idea, that the first shaft of the electric motor, the second shaft of the hydraulic unit, or the intermediate shaft has a transverse channel extending in particular radially outwards for conveying leakage oil along the shaft-hub connection. Thus, the leakage oil may be exclusively transported in order to lubricate the contact points between the shafts, and may in particular be circulated back into the leakage oil chamber of the hydraulic unit. Therefore, no additional drain is required for leakage of oil.

In one embodiment, it may be provided, for example, that the hydraulic unit comprises a leakage oil chamber. The leakage oil chamber is in particular a chamber within the hydraulic unit into which hydraulic oil enters from a pressurized transmission chamber of the hydraulic unit during operation. For example, hydraulic fluid enters along bearings of the components that carry the pressurized hydraulic fluid. In this case, the central recess may be provided in the (second) shaft or the intermediate shaft of the hydraulic unit, wherein at least one transverse channel extends 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 and extends from the at least one transverse channel through the second shaft to the direct shaft-hub connection. Alternatively, the central recess may be formed as an axial passage in the intermediate shaft and extend from at least one transverse passage 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 towards the motor, through which inlet leakage oil (after lubricating the shaft-hub connection) can enter the axial channel. Thus, the axial passage does not extend completely through the second shaft or through the intermediate shaft. Thus, an axial passage will be considered a blind hole extending through the shaft from the front end to at least one transverse passage.

In an alternative embodiment, it may be provided that the (first) shaft of the motor has a recess and that it adjoins at least one transverse channel. In this case, the recess is arranged in particular directly adjoining the receptacle for the (second) shaft of the hydraulic unit or for the intermediate shaft. In this embodiment, the leakage oil that has flowed along the contact point of the shaft-hub connection is transported through the (first) shaft of the motor into the chamber around the shaft.

Preferably, in this embodiment, it is possible to provide a separate drain for the leakage oil transported through the at least one transverse channel of the first shaft of the motor.

It is also preferred that at least one transverse channel ends at a point on the outer circumference of the shaft that does not overlap with the other shaft in the connected state. The at least one transverse channel is thus arranged axially offset in one of the shafts with respect to the shaft-hub connection. It is thus ensured that leakage oil can be transported from the leakage oil chamber within the hydraulic unit along a shaft-hub connection arranged outside the housing of the hydraulic unit.

In one embodiment it is preferably provided that the shaft-hub connection is fluidly connected to a leakage oil chamber in the hydraulic unit via at least one passage outside the second shaft. The first passage or a first group of such passages is arranged to drain oil from a leakage oil chamber in the hydraulic unit to the shaft-hub connection.

Such a first passage may be implemented, for example, by mounting the (second) shaft of the hydraulic unit in a direction towards the shaft-hub connection in such a way that there is no shaft seal in the housing of the hydraulic unit. In this case, therefore, the leakage oil flows from the leakage oil chamber through the housing of the hydraulic unit in the direction of the shaft-hub connection along the surface of the (second) shaft. In the case of the first embodiment described above (according to which the central recess and at least one transverse channel are formed in the (second) shaft of the hydraulic unit or in the intermediate shaft), fluid that has come from the leakage oil chamber (after it has flowed along the contact point of the shaft-hub connection) enters into the axial channel in the second shaft (or intermediate shaft). In the second embodiment described above, according to which the central recess and the at least one transverse channel are formed in the (first) shaft of the electric machine, fluid from the leakage oil chamber has been transferred along the second shaft into the chamber around the first shaft.

The passage for the fluid connection of the leakage oil chamber and the shaft-hub connection within the hydraulic unit may additionally or alternatively be formed by at least one, preferably a plurality of openings, which are formed in particular as recesses and preferably as bores, which openings are provided adjacent to the second shaft in the housing or housing part (e.g. in a cap or bearing) of the hydraulic unit. In the case of the first embodiment as described above, the leakage oil may flow out from the leakage oil chamber through at least one opening in the housing to the shaft-hub connection and then into the axial passage in the second shaft or in the intermediate shaft. In the case of the second embodiment described above, the leakage oil that is conveyed through the at least one lateral passage can flow back into the leakage oil chamber through the opening. In this way of connection, it is preferred that the front end face of the first shaft is sealed against the hydraulic unit, so that leakage oil can flow from the leakage oil chamber within the hydraulic unit along the outside of the shaft and along the shaft-hub connection to the recess in the (first) shaft of the electric machine, and from there can be conveyed back through the at least one transverse channel to the opening in the housing, which opening is offset radially outwards relative to the sealed end face of the shaft, into the leakage oil chamber.

Preferably, at least one opening may be closed and preferably has an internal thread for this purpose. Thus, in the delivered state, the opening can be closed, for example by a screw. In this case, the opening may be closed until just before the hydraulic unit is attached to the motor/shortly before the hydraulic unit is attached to the electrode.

In a preferred embodiment, the shaft-hub connection has a splined connection, wherein the splined connection comprises at least one pin having an external tooth structure and at least one receptacle having an internal tooth structure.

The pin with the external tooth structure may preferably be formed on the first shaft of the motor, in which case the receptacle with the internal tooth structure is preferably provided on the front-side end of the second shaft of the hydraulic unit.

Alternatively, the pin, which preferably has an external tooth structure, may be formed on the (second) shaft of the hydraulic unit, in which case the receptacle, which preferably has an internal tooth structure, is provided on the front-side end of the (first) shaft of the motor.

In an even further embodiment, the first shaft of the electric motor and the second shaft of the hydraulic unit may each have a receptacle (which preferably has an internal tooth structure) on their front-side ends, wherein the intermediate shaft forms two pins, each having an external tooth structure for insertion into the respective receptacle, if the first shaft is connected to the second shaft via the intermediate shaft.

In order to fix the motor to the hydraulic unit, the housing of the motor and the housing of the hydraulic unit can be connected to each other in a suitable manner (e.g. by means of a corresponding threaded connection), for example by forming at least one flange or cap.

The first shaft is mounted in the motor, in particular by means of two bearings. The second shaft is mounted in the hydraulic unit, in particular by means of two bearings. In particular, if a pin with an external tooth structure is formed on the second shaft of the hydraulic unit, the pin protrudes beyond one of the bearings and beyond the housing of the hydraulic unit in the direction of the motor.

When the system is implemented in particular, it has been found that the internal and external tooth structures of the spline connection wear severely. The background of this severe wear is the forces acting on the shaft in the hydraulic unit during operation, so it may happen that the pin protruding beyond the bearing is deflected from its neutral position and thus does not maintain its position/alignment in a stationary state in the receptacle of the motor. Another cause of severe wear may be due to errors in the motor or the hydraulic unit, when the motor is connected to the hydraulic unit, the pins in the receptacle do not occupy the desired position/alignment.

It has been shown that a specific ratio range of the pitch circle diameter on the pin to the outer tooth structure length of the outer tooth structure is advantageous in order to reduce wear of the spline connection etc.

Thus, the external tooth structure of the pin (which may be formed on the first shaft of the motor, on the second shaft of the hydraulic unit or on the intermediate shaft) has an external tooth structure length and a pitch circle diameter. The length of the outer ruler structure is the length of the teeth in the extending direction of the shaft. It is now preferred that the ratio of the pitch circle diameter to the length of the outer tooth structure is less than 1.2, particularly preferably less than 1.1, and very particularly preferably less than 1.05. On the other hand, the ratio of the pitch circle diameter to the external tooth structure 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 circle diameter to the external tooth structure length is between 0.95 and 1.05, and particularly preferably equal to 1. The individual invention is seen in this ratio between pitch circle diameter and external tooth structure length, which can be claimed independently of the above-described solution for a system comprising an electric motor and a hydraulic unit.

Thus, the independent invention is seen in a hydraulic unit whose shaft has a pin with an external tooth structure, wherein the external tooth structure has an external tooth structure length and a pitch circle diameter, the ratio between which (i.e. the ratio of the pitch circle diameter to the external tooth structure length) lies within the aforementioned range.

It has been shown that in order to reduce wear of the spline connection, it may alternatively or additionally be provided that the external tooth structure has an error of the order of 07. This error level is defined here in the 1996 standard ZNSI B92.1.

Therefore, also proposed as a separate invention is a hydraulic unit having a shaft with a pin having an external tooth structure, wherein the external tooth structure has an error of the order of 07.

The ratio of the pitch circle diameter to the length of the external tooth structure (in particular, the level of error in connection with the internal tooth structure) as described above has the effect that the wear of the spline connection is minimized.

The hydraulic unit is preferably embodied as a wobble plate unit, which can be operated as a pump or a motor. In the wobble plate unit, the deflection of the pin protruding beyond the shaft of the housing during operation is particularly large due to the forces acting on the shaft in the wobble plate pump. The pin of the wobble plate pump shaft, which protrudes beyond the housing of the wobble plate pump, is thus inserted immediately and directly into the corresponding receptacle of the motor. Alternatively, the hydraulic unit, which may be operated as a pump or a motor, may be implemented as a bevel piston unit, a gear unit, a rotary vane unit, or a screw shaft unit.

The spline connection is preferably a spline in which the narrowed teeth of the external tooth structure engage in the internal tooth structure. Such splines are defined, for example, in ANSI B92.1 in 1996.

Drawings

This and the background art are explained hereinafter by way of example with reference to the accompanying drawings. In the drawings schematically

Fig. 1 shows a perspective view of a hydraulic unit;

fig. 2 shows the connection region of an electrical unit;

fig. 3 shows a second shaft of the hydraulic unit;

FIG. 4 shows a cross-sectional view through an area of an exemplary embodiment of a system;

FIG. 5 shows a cross-sectional view through an area of another exemplary embodiment of a system; and is also provided with

Fig. 6 shows a cross-section through an area of an even further exemplary embodiment of the system.

Detailed Description

The hydraulic unit 20 shown in fig. 1 and configured as a wobble plate pump comprises a housing 26 with a cap 27. Mounted in the housing 26 is a shaft 21 which projects with a pin 22 beyond a cap 27. The pin 22 has an outer tooth structure 23 with an outer tooth structure length 24 and a pitch circle diameter 25. The shaft 21 with the pin 22 is also shown as a single part in fig. 3.

Fig. 2 shows an electric motor 10, the connection area of which is connected to a hydraulic unit 20. The shaft 11 of the motor 10 has a receptacle 12 with an internal tooth structure 13.

A pin 22 of a shaft 21 of the hydraulic unit 20 is inserted in the receptacle 12 of the motor 10 to form a system. The shaft 11 of the electric motor 10 is thus directly connected to the shaft 21 of the electro-hydraulic unit 20, forming an actively locked shaft-hub connection. Thus, no additional components are required to connect the shafts 21, 22 of the motor 10 and the hydraulic unit 20 to each other.

In order that the error deviations of the bearings of the shafts 11, 21 can be compensated, the ratio of the pitch circle diameter 25 to the outer tooth structure length 24 can be between 0.8 and 1.2, and preferably between 0.95 and 1.05. For the same reason, the internal tooth structure 13 has an error of the order of 07.

Fig. 4 and 5 show the areas of the system comprising the electrode 10 and the hydraulic unit 20, respectively. Thus, the end of the hydraulic unit 20 facing the motor 10 and the end of the hydraulic unit 20 facing the motor 10 are shown. In all the exemplary embodiments, it can be seen that the hydraulic unit 20 has a housing 26, which may include a cap 27 as a component. A leakage oil chamber 28 is formed in the housing 26, into which leakage oil chamber hydraulic fluid can flow from the delivery chamber of the hydraulic unit along a corresponding bearing (not shown) of the pump head. In addition, a leakage oil outlet 32 may be provided from which leakage oil may emerge from the leakage oil chamber 28.

In addition, the receptacle 12, which has been described above, can be seen to be in which the pin 22 of the second shaft 21 of the hydraulic unit 20 is inserted at one end of the first shaft 11.

In the embodiment shown in fig. 4, a central recess 29 configured as an axial channel is formed in the second shaft 21 of the hydraulic unit 20. The recess 29 configured as an axial channel is adjoined by two transverse channels 30 which extend in the radial direction to an outer periphery 31. The transverse channel 30 thus extends from the end 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 motor 10.

In the exemplary embodiment shown in fig. 5, a recess 29 is formed in the first shaft 11 of the motor 10, which adjoins the receptacle 12 for the pin 22. From the recess 29, two transverse channels 30 extend to the outer periphery 31 of the first shaft 11.

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

During operation, the first shaft 11 and the second shaft 21 rotate about their longitudinal axes. The result of this is that the leakage oil located in the transverse channel 30 is transported outwards due to centrifugal forces and that a negative pressure is formed in the recess 29.

In the exemplary embodiment shown in fig. 4, such a result is also that a negative pressure is formed in the region of the receptacle 12, so that leakage oil flows from the leakage oil chamber 28 through the passage 33 and along the coupling point between the pin 22 and the receptacle 12. Thus, the coupling between the pin 22 and the receptacle 12 is permanently lubricated. The leakage oil then enters into the recess 29 formed as an axial passage and passes from the transverse passage 31 back into the leakage oil chamber 28.

In the exemplary embodiment shown in fig. 5, the rotation of the shafts 11, 21 also has the result that, due to the centrifugal force acting in the leakage oil chamber 30, a negative pressure is created in the recess 29 so that the leakage oil (hydraulic fluid) flows along the outside of the second shaft 21 through the first passage 33 and along the coupling point between the receptacle 12 and the pin 22, whereby the coupling point is lubricated. Fluid conveyed through the transverse passage 30 flows to a separate leakage oil outlet 32 of the motor 10.

Fig. 6 shows the region of a further embodiment of a system comprising an electric motor 10 and a hydraulic unit 20, which hydraulic unit 20 may be embodied, for example, as a gear pump. In the following, differences with respect to the above-described embodiments will be mainly described.

In this embodiment, the first shaft 11 of the motor 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 thereof (which end has an external tooth structure) into a receptacle 12 of the first shaft 11 and with the other end thereof (which end also has an external tooth structure) into a receptacle formed in the second shaft 21. Thus, the intermediate shaft 40 connects the first shaft 11 and the second shaft 21 in a torque-proof manner (or in a manner that cannot rotate relative to each other), so that the rotational movement of the first shaft 11 is transmitted into the rotational movement of the second shaft 21. Thus, a shaft-hub connection is formed between the first shaft 11 and the second shaft 21.

The intermediate shaft 40 has a central recess 29 extending from the end face of the intermediate shaft 40 facing the first shaft 11 to a transverse channel 30, said transverse channel 30 extending radially outwards towards the outer periphery of the intermediate shaft 40. Within the housing 26 of the hydraulic unit 20, a leakage oil chamber 28 is formed, which surrounds the outer circumference of the intermediate shaft 40 in the region of the discharge of the transverse channel 30.

During operation, the centrifugal force acting on the leakage oil in the transverse channel 30 creates a negative pressure in the central recess 29, so that the leakage oil from the leakage oil chamber 28 flows along the outer circumference 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 discharged back into the leakage oil chamber 28 through the lateral passage 30. Thus, the positive locking connection before the first shaft 11 and the intermediate shaft 40 is lubricated by leakage oil.

In order to improve the flow of leakage oil along the outer circumference of the shaft, the teeth in the external or internal tooth structure, which may be in the shaft-hub connection, may be omitted.

Thus, a compact system is provided comprising a motor and a hydraulic unit, which can be operated with low maintenance.

List of reference numerals

10. Motor with a motor housing

11. First shaft

12. Receptacle base

13. Internal tooth structure

20. Hydraulic unit

21. Second shaft

22. Pin

23. External tooth structure

24. Length of external tooth structure

25. Diameter of pitch circle

26. Shell body

27. Cap cap

28. Leakage oil chamber

29. Concave part

30. Transverse channel

31. The outer periphery

32. Leakage oil outlet

33. Passage way

40. Intermediate shaft

Claims (22)

1. A system, comprising:

an electric motor (10), wherein the electric motor (10) comprises a first shaft (11), and

-a hydraulic unit (20), wherein the hydraulic unit (20) comprises a second shaft (21), wherein

The first shaft (11) and the second shaft (21) are connected to each other to form a shaft-hub connection,

the shaft-hub connection comprises a central recess (29) and

the shaft-hub connection is fluidly connected to an interior (28) of the hydraulic unit (20) for lubrication,

it is characterized in that the method comprises the steps of,

the central recess (29) adjoins at least one transverse channel (30), wherein the at least one transverse channel (30) extends from the central recess (29) to the outer periphery (31) of the shaft-hub connection.

2. The system according to claim 1, characterized in that the first shaft (11) and the second shaft (21) are inserted into each other to form the shaft-hub connection.

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

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

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

6. The system according to one of the preceding claims, wherein the hydraulic unit (20) comprises a leakage oil chamber (28), and wherein the at least one transverse channel (30) extends from the central recess (29) to the leakage oil chamber (28).

7. The system according to claim 6, characterized in that 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. The system according to one of the preceding claims, characterized in that 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 a front end of the second shaft (30) or of the intermediate shaft (40) facing the first shaft (11).

9. The system according to claim 1, wherein the first shaft (11) has a receptacle (12) for the second shaft (21) or for the intermediate shaft (40), and wherein a central recess (29) formed in the first shaft (11) adjoins the receptacle (12), and wherein the at least one transverse channel (30) is formed in the first shaft (11).

10. The system according to claim 9, characterized in that the front end face of the first shaft (11) is sealed with respect to the hydraulic unit (20).

11. The system according to one of the preceding claims, characterized in that the at least one transverse channel (30) ends at a point on the outer circumference (31) of the shaft that does not overlap with the other shaft in the connected state.

12. The system according to one of the preceding claims, characterized in that the shaft-hub connection is fluidly connected to a leakage oil chamber (28) of the hydraulic unit (20) outside the second shaft (21) via at least one passage (33).

13. The system according to claim 12, characterized in that the second shaft (21) is mounted shaft-tightly free within a housing (26) of the hydraulic unit (20) to form a passage (33) in a direction towards the shaft-hub connection.

14. The system according to one of the preceding claims 12 or 13, characterized in that the hydraulic unit (20) has a housing (26) surrounding the second shaft (21), in which housing at least one opening is formed to form a passage.

15. The system according to claim 14, characterized in that the at least one opening can be closed and preferably has an internal thread for this purpose.

16. The system according to one of the preceding claims, characterized in that the hydraulic unit (20) is a wobble plate unit, a bevel piston unit, a gear pump unit, a rotary vane unit or a screw shaft unit.

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

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

19. The hydraulic unit (20) according to claim 17 or 18, characterized in that the recess (29) extends as an axial channel from the at least one transverse channel (30) through the shaft to a front side of the shaft (21) accessible outside the housing.

20. An electric motor (10) for a system according to one of claims 1 to 16, wherein a shaft (11) of the electric motor (10) has a central recess (29) and at least one transverse channel (30), wherein the at least one transverse channel (30) extends from the central recess (29) to an outer periphery (31) of the shaft (11), wherein the shaft (11) has a receptacle (12) for the shaft and the recess (29) adjoins the receptacle (12).

21. Intermediate shaft (40) for a system according to one of claims 1 to 16, wherein the intermediate shaft (40) has a central recess (29) and at least one transverse channel (30), wherein the at least one transverse channel (30) extends from the central recess (29) to the outer periphery (31) of the intermediate shaft (40).

22. Intermediate shaft (40) according to claim 21, characterized in that the intermediate shaft (40) has an external tooth structure at its two ends to form 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).