Electrical machine for a traction drive of an at least partially electrically driven motor vehicle

Abstract

The present invention relates to an electrical machine (10) for a traction drive of an at least partially electrically driven motor vehicle, having: a housing (12); a rotor (14) that is mounted in the housing (12) via a bearing device (16) so as to be able to rotate about an axis of rotation and has a hollow rotor shaft (18) with a laminated core (20) arranged thereon, wherein the hollow rotor shaft (18) comprises a coolant outlet opening (28); and a shaft sealing ring (30) that is arranged between the housing (12) and the hollow rotor shaft (18) and is arranged, with respect to a longitudinal direction of the hollow rotor shaft (18), between the laminated core (20) and the coolant outlet opening (28); wherein the electrical machine (10) furthermore has a coolant pump (34) by way of which it is possible to generate, for a coolant located on the shaft sealing ring (30) and at the coolant outlet opening (28), a flow that leads away from the shaft sealing ring (30).

Description

[0001] Description

[0002] Electric machine for a traction drive of an at least partially electrically powered motor vehicle

[0003] The present invention relates to an electric machine for a traction drive of an at least partially electrically powered motor vehicle. In particular, the present invention relates to an electric machine having improved cooling.

[0004] Electric motors are increasingly becoming a focus of mobility. Electric motors, also known as electric machines, are often constructed from a rotor and stator arrangement. The rotor may, for example, have a hollow shaft and thus be equipped with a cooling structure inside the rotor. Such liquid-cooled rotors of electric machines are inherently prone to leakage due to the shaft seal between the rotor and the housing. Current technology does not offer any way to significantly reduce leakage before it reaches the engine compartment. This can result in disadvantages regarding the operation and long-term stability of the electric motor.

[0005] It is therefore the object of the present invention to provide a solution by which at least one disadvantage of the prior art can be at least partially overcome. In particular, it is an object of the present invention to provide a solution by which problems caused by coolant leakage into the engine compartment can be reduced. In particular, the operating behavior and / or long-term stability of an electric machine should be improved.

[0006] The solution to the problem is achieved according to the invention by an electrical machine having the features of claim 1. Preferred embodiments of the invention are described in the subclaims, in the description or the figures, wherein further features described or shown in the subclaims or in the description or the figures can individually or in any combination constitute an object of the invention, unless the context clearly indicates the opposite.The invention relates to an electric machine for a traction drive of an at least partially electrically powered motor vehicle, comprising a housing, a rotor which is mounted in the housing so as to be rotatable about an axis of rotation via a bearing device, the rotor having a hollow rotor shaft with a laminated core arranged thereon, and wherein the hollow rotor shaft comprises a coolant outlet opening, and comprising a shaft sealing ring arranged between the housing and the hollow rotor shaft, which, with respect to a longitudinal direction of the hollow rotor shaft, is arranged between the laminated core and the coolant outlet opening, wherein the electric machine further comprises a coolant pump, by means of which a flow leading away from the shaft sealing ring can be generated for a coolant located on the shaft sealing ring and on the side of the coolant outlet opening.

[0007] Such an electric machine can provide significant advantages with regard to liquid cooling leakage.

[0008] The subject of the present invention is therefore an electric machine. This can also be referred to as an electric motor and can, in principle, comprise any form of electric motor. In particular, such an electric machine finds application in a traction drive of an at least partially electrically powered motor vehicle, such as a purely electrically powered vehicle or a hybrid-powered vehicle.

[0009] The electrical machine comprises a housing in which active components can be provided and which can thus provide enclosure for sensitive components.

[0010] At least partially arranged in the housing, the electric machine comprises a rotor and a stator. These can interact in a conventional manner through magnetic excitation, so that the rotor is set in rotation and the electric motor is thus driven. The rotor is rotatably mounted about a rotation axis in the housing via a bearing device and comprises a hollow rotor shaft with a laminated core arranged thereon. The provision of a hollow shaft can have the particular advantage that the interior of the hollow shaft can be used to form a cooling structure to cool the magnetic excitation structure of the rotor, namely the laminated core. The laminated core can, for example, be magnetically excitable and thus interact with the stator to set the stator in rotation. It is known that a magnetic excitation structure should be cooled, which can be achieved particularly efficiently by providing a hollow shaft with a cooling structure.In particular, the cooling structure can have one or more coolant channels through which the coolant can be conveyed. For example, the coolant can be an oil, water, glycol, or a mixture comprising, for example, at least one of the aforementioned structures.

[0011] In addition to a coolant inlet, the hollow rotor shaft thus includes a coolant outlet opening for introducing and discharging the coolant into and out of the hollow rotor shaft. Accordingly, the cooling structure can be axially supplied with coolant, for example, via a coolant supply, and the coolant can be axially discharged from the cooling structure via a coolant discharge. The coolant supply and discharge expediently run adjacent to each other, i.e., axially from the excitation structure in the same axial direction.

[0012] A shaft seal is arranged between the housing and the hollow rotor shaft. It is located between the laminated core and the coolant outlet opening, relative to the longitudinal direction of the hollow rotor shaft. This seal serves to prevent, or significantly reduce the risk of, coolant entering the area of ​​the laminated core and negatively affecting it or other components located in the housing.

[0013] According to the invention, the electric machine further comprises a coolant pump, by means of which a flow leading away from the shaft sealing ring can be generated for a coolant located on the shaft sealing ring and on the side of the coolant outlet opening.

[0014] In particular, this design can prevent or at least significantly reduce leakage and the disadvantages associated with leakage.

[0015] By providing a coolant pump as described above, the risk of coolant pressing against the shaft seal, particularly with high pressure, can be prevented or reduced. This would entail the risk of coolant flowing along the shaft seal or penetrating the sealing area and thus reaching the area of ​​the laminated core. Because the coolant pump is suitable and designed to pump coolant away from the shaft seal, the risk of coolant flowing against the seal and penetrating the sealing area can be prevented or at least significantly reduced.

[0016] Accordingly, coolant leakage into the area of ​​the laminated core can be effectively prevented or at least significantly reduced. This prevents leakage fluid from entering the engine compartment or the excitation structure and damaging the respective structure there. In particular, it can be prevented from spreading to the area of ​​the excitation structures of the rotor and stator. Regardless of whether cooling is performed with oil, water, or a water / glycol mixture, the amount of leakage that can often penetrate into the engine compartment or between the rotor and stator according to the state of the art can be potentially critical. In particular, the coolant poses the risk of a certain degree of electrical conductivity, which can negatively impact the insulation system.Even with oil cooling that uses oil from the gearbox, negative effects can occur, as the oil may contain metal particles, which can have negative effects on the insulation system or lead to insulation problems over its lifetime. In extreme cases, this can lead to electrical machine failure due to fault currents.

[0017] Furthermore, coolant penetrating the rotor or stator chamber can decompose due to undetected fault currents, which can lead to a hydrogen / oxygen mixture through electrolysis. Accordingly, the risk of explosion cannot be ruled out, at least theoretically.

[0018] These disadvantages can be reduced or completely prevented according to the invention.

[0019] Furthermore, the coolant pressure no longer depends exclusively on external pumps, but can be further increased by the coolant pump provided by the invention. This can make cooling particularly effective even under high demands.

[0020] Preferably, the flow generated by the coolant pump can act on coolant located adjacent to a sealing lip of the shaft seal. This embodiment thus takes into account the fact that the shaft seal is either rotationally fixed to the housing and rests against the hollow shaft with a sealing lip, or vice versa. Accordingly, the sealing lip, in particular, is an area that can be susceptible to coolant flowing along it. Thus, a flow that conveys the coolant away from the sealing lip can be particularly effective in preventing coolant leakage.

[0021] It may further be preferred for the coolant pump to comprise a pumping element arranged on the hollow rotor shaft, which, when the hollow rotor shaft rotates about its axis of rotation, generates a pumping effect or the described flow on a side of the shaft seal facing away from the laminated core. This configuration can be particularly easy to implement, as additional control units or complex peripherals can be dispensed with. The coolant pump is therefore active when the hollow rotor shaft or rotor is rotating at a high speed and a cooling effect accompanied by a coolant flow is necessary or advantageous. However, depending on the design of the coolant pump, it is possible to prevent air from being sucked in from the engine cavity even at maximum speed.

[0022] In this design, the coolant pressure no longer depends exclusively on external pumps, but can be further increased by a pump integrated into the rotor. Another advantage of this design is that high coolant pressure, and thus particularly effective cooling, is available when needed—namely, at high rotor speeds. This occurs automatically purely through the varying rotor speed, allowing the cooling capacity to be adjusted without complex control systems.

[0023] In addition, the coolant pump in this design can be particularly low-maintenance, since hardly any additional components need to be used, but rather a coolant pump that is activated purely by the rotor speed.

[0024] It may further be preferred that the coolant pump can generate a vacuum at least locally on the shaft seal. In particular, the vacuum can be generated in an area adjacent to the sealing lip. In this embodiment, the coolant can be particularly effectively prevented from penetrating the sealing area, so that leakage can also be particularly reliably prevented. This embodiment is generally easily implemented by a person skilled in the art by positioning and designing the coolant pump accordingly.

[0025] With regard to the coolant pump, it may be preferred that it comprises a ring element which is arranged to encompass the hollow rotor shaft so that it rotates with it, in particular driven by it, wherein the ring element comprises conveying elements which extend at least partially radially with respect to the rotor shaft.

[0026] Alternatively or additionally, it may be preferred that the coolant pump comprises a ring element which is arranged to encompass the hollow rotor shaft so that it rotates with it, in particular driven by it, wherein the ring element comprises conveying elements which extend at least partly axially with respect to the rotor shaft.

[0027] The radial pump concept, which uses radial impeller elements, is particularly suitable for high pressure drops at lower speeds, whereas the axial concept, which uses radial impeller elements, only develops a pressure drop at comparatively high speeds. Accordingly, the selection and design of the impeller elements allows the pumping capacity to be tailored to the desired application or requirements.

[0028] It may further be preferred for the coolant pump to have a disk element that delimits a coolant channel running along the shaft sealing ring. This makes it possible, in a structurally simple manner, for the coolant pump to act on a coolant channel running along the shaft sealing ring. This makes it possible to achieve a very defined conveying force. Furthermore, the amount of coolant present in the channel and at the shaft sealing ring is usually limited, so that even a low pumping power can be sufficient to achieve the desired effect. Accordingly, the coolant pump can be comparatively small, or a sufficient pumping effect can be generated even at a low rotational speed of the rotor.

[0029] With regard to the disc element, it can also be advantageous for it to be sealed to the hollow shaft or the housing, i.e., sealed against liquids. This allows the flow generated by the coolant pump to be generated in a particularly defined manner, which simplifies adaptation to the desired application.

[0030] Particularly in this embodiment, it is preferred that the disc element has passages for the coolant. The coolant can thus flow through the passages in a defined manner. The calibrated holes in the sealing disc can then additionally adjust the flow and prevent the rotor from cavitating.

[0031] Further preferably, the hollow rotor shaft can comprise a second coolant outlet opening which, with respect to a longitudinal direction of the hollow rotor shaft, is arranged between the shaft sealing ring and the coolant pump. In particular, it can be preferred for the second coolant outlet opening to open into the fluid channel running adjacent to the shaft sealing ring. In this embodiment, it can be made possible for the coolant pump to be used particularly effectively not only to generate a corresponding flow in which the coolant is conveyed away from the shaft sealing ring, but also for the coolant pump to be used to fundamentally convey the coolant through the cooling structure of the hollow shaft. Accordingly, the cooling can be particularly effective and also withstand particularly high requirements.

[0032] In the design according to which the coolant outlet opening is arranged on the side of the coolant pump facing away from the laminated core, relative to the longitudinal direction of the hollow rotor shaft, a large portion of the coolant can be drained away without contact with the shaft seal. This minimizes the risk of coolant penetrating the sealing area of ​​the shaft seal.

[0033] The invention is further explained below with reference to the figures, where individual or multiple features of the figures may constitute a feature of the invention, either individually or in combination. Furthermore, the figures are to be viewed only as examples and in no way limiting.

[0034] Fig. 1 shows a schematic view of an electrical machine;

[0035] Fig. 2 shows a detailed view of the electrical machine from Figure 1; and

[0036] Fig. 3 shows a detailed view of a coolant pump of the embodiment shown in Fig. 1; Fig. 4 shows the coolant pump of Fig. 3 in an exploded view; Fig. 5 shows a detailed view of another embodiment of a coolant pump for an electrical machine;

[0037] Fig. 6 shows the coolant pump from Figure 5 in an exploded view;

[0038] Fig. 7 shows a view of an electrical machine with a coolant pump according to Figure 5;

[0039] Fig. 8 shows a hollow rotor shaft for a further embodiment of an electrical machine;

[0040] Fig. 9 shows an electrical machine with the hollow rotor shaft of Fig. 9; and Fig. 10 shows a detailed view of another hollow rotor shaft for an electrical machine.

[0041] Figure 1 shows an electric machine 10. Such an electric machine 10 can be used, for example, in a traction drive of an at least partially electrically powered motor vehicle, such as a hybrid vehicle or a purely electrically powered vehicle.

[0042] The electric machine 10 comprises a housing 12, which can serve as a housing for sensitive components of the electric machine 10. For example, a stator (not shown here) and at least a part of a rotor 14 can be arranged in the housing 12. More specifically, it is provided that

[0043] The rotor 14 is mounted in the housing 12 via a bearing device 16 for rotation about a rotational axis. The rotor 14 has a hollow rotor shaft 18 with a laminated core 20 arranged thereon to interact with the stator or a magnetic excitation structure thereof, thus causing the rotor 14 to rotate.

[0044] Furthermore, a cooling structure 22 is provided within the hollow rotor shaft 18, through which liquid coolant can flow. For this purpose, in the embodiment according to Figure 1, the hollow rotor shaft 18 is mounted so as to be rotatable about a stationary coolant guide 24. The cooling structure 22 can basically be designed as a channel for guiding cooling fluid, which can also be designed as a free volume between the coolant guide 24 and the hollow rotor shaft 18. The flow of the coolant is intended to be represented by the arrows. For guiding coolant through the cooling structure 22, a coolant supply 26 for supplying coolant into the hollow rotor shaft 18 and a coolant outlet opening 28 for discharging coolant from the hollow rotor shaft 18 are provided.Furthermore, a shaft seal 30 is provided between the housing 12 and the hollow rotor shaft 18, which, relative to a longitudinal direction of the hollow rotor shaft 18, is arranged between the laminated core 20 and the coolant outlet opening 28. In the embodiment according to Figure 1, the shaft seal 30 is fixed to the housing 12 and has two sealing lips 32 that slide along the hollow rotor shaft 18 during rotation.

[0045] In principle, however, the shaft sealing ring 30 can also be attached to the hollow rotor shaft 18 and the sealing lips 32 can slide along the housing 12.

[0046] Due to infiltration of the sealing lips 32, for example, caused by the capillary effect or a constant radius on the sealing lips 32 in the presence of a correspondingly high radial velocity of the coolant, there is a risk of pressure buildup, particularly at this point, which can lead to the lifting of the sealing lip 32 during operation. In particular, the area of ​​the sealing lips 32 can thus be susceptible to the penetration of coolant adhering to the sealing lips 32.

[0047] To counteract this, the electric machine 10 further comprises a coolant pump 34, by means of which a flow leading away from the shaft sealing ring 30 can be generated for a coolant located on the shaft sealing ring 30 and on the side of the coolant outlet opening 28.

[0048] The coolant pump 34 is shown in greater detail in one embodiment in Figures 2 to 4. The design of the coolant pump 34 according to Figures 2 to 4 is configured such that it comprises a pump element 42 arranged radially outside the hollow rotor shaft 18, which, when the hollow rotor shaft 18 rotates about its axis of rotation, generates a pumping effect and thus the described flow on a side of the shaft seal 30 facing away from the laminated core 20. More precisely, the coolant pump 34 or the pump element 42 according to Figures 2 to 4 comprises an annular element 36, which is arranged to encompass the hollow rotor shaft 18 and has conveying elements 38 that extend at least partially radially with respect to the hollow rotor shaft 18.

[0049] For example, the ring element 36 can be fixed on the hollow rotor shaft 18 and thus be brought into rotation or driven by the hollow rotor shaft 18.

[0050] It is further shown that the coolant pump 34 has a disk element 40, which delimits a fluid channel 44 running along the shaft seal 30. The disk element 40 is further fixed to the housing 12 in a sealing and thus fluid-tight manner, and it is further provided that the disk element 40 has passage openings 46 for coolant. More specifically, it is provided that the ring element 36 is provided within the disk element 40, with a cover ring 50 being arranged radially between the disk element 40 and the ring element 36.

[0051] The above-described configuration enables the generation of a flow that carries coolant located on the shaft sealing ring 30 and on the side of the coolant outlet opening 28 away from the shaft sealing ring 30. In other words, the coolant pump 34 introduces a flow into the coolant that conveys the coolant away from the shaft sealing ring 30 or its sealing lips 32. The coolant is conveyed in particular through the fluid channel 44 and the through-openings 46, which enables a particularly effective and adaptable pumping performance. In particular, a negative pressure can be generated at the sealing lips 32, which conveys the coolant away from the sealing lips 32. Provision is made here for the coolant outlet opening 28 to be arranged on the side of the coolant pump 34 facing away from the laminated core 20, relative to a longitudinal direction of the hollow rotor shaft 18.

[0052] In particular, the design according to the invention allows the known delivery characteristics of the hydraulic flow machines to be adapted with regard to the pressure in the vacuum zone,

[0053] Figures 5 to 7 show a further embodiment of the coolant pump 34, with Figure 7 showing the coolant pump 34 in an installed situation. This largely corresponds to the previously described embodiment, so that corresponding components are provided with the same reference numerals. According to the embodiment shown in Figures 5 to 7, the coolant pump 34 comprises an annular element 36, which is also arranged so as to encompass the hollow rotor shaft 18, but has conveying elements 38 that extend at least partially axially with respect to the hollow rotor shaft. The disk element 40 is in turn fixed to the housing 12 in a sealing and thus liquid-tight manner, and it is further provided that the disk element 40 has passage openings 46 for coolant. The annular element 36 is arranged within the disk element 40, with a cover ring 50 being arranged radially between the disk element 40 and the annular element 36.The effect is similar to that described above, although a pressure gradient builds up, particularly at higher speeds.

[0054] Figures 8 to 10 show further embodiments of the present invention. According to these embodiments, a particularly effective pumping action for the coolant and thus particularly effective cooling can be enabled. Furthermore, a blocking effect can be created by the coolant upstream of the shaft sealing ring 30, which further reduces the risk of coolant leakage. In particular, Figures 8 to 10 show that the coolant outlet opening 28, or the plurality of coolant outlet openings 28, is arranged between the shaft sealing ring 30 and the coolant pump 34, relative to a longitudinal direction of the hollow rotor shaft 18. Figure 8 shows a correspondingly designed hollow rotor shaft 18, which is illustrated in an installed situation in Figure 9. This allows the coolant pump 34 to act directly on the coolant discharged from the cooling structure 22 and thus increase the pumping capacity.The coolant is passed through the liquid channel 44.

[0055] Figures 8 and 9 show an embodiment in which a seal 52 is arranged between the coolant supply 26 and the hollow rotor shaft 18 to guide the coolant through the coolant outlet opening 28. Furthermore, in Figure 9, the coolant pump 34 is configured according to Figures 3 and 4.

[0056] In the embodiment according to Figure 10, the hollow rotor shaft 18 comprises a shoulder 54 which can replace the sealing ring 52.

[0057] List of reference symbols

[0058] 10 electric machine

[0059] 12 housings

[0060] 14 Rotor

[0061] 16 Storage facility

[0062] 18 Rotor hollow shaft

[0063] 20 sheet packages

[0064] 22 Cooling structure

[0065] 24 Coolant supply

[0066] 26 Coolant supply

[0067] 28 Coolant outlet opening

[0068] 30 shaft seal

[0069] 32 Sealing lip

[0070] 34 Coolant pump

[0071] 36 ring element

[0072] 38 Conveyor element

[0073] 40 disc element

[0074] 42 Pump element

[0075] 44 Fluid channel

[0076] 46 Passage opening

[0077] 50 cover ring

[0078] 52 Sealing ring

[0079] 54 paragraph

Claims

Patent claims 1 . An electric machine (10) for a traction drive of an at least partially electrically powered motor vehicle, comprising a housing (12), a rotor (14) which is mounted in the housing (12) via a bearing device (16) for rotation about an axis of rotation, said rotor having a hollow rotor shaft (18) with a laminated core (20) arranged thereon, wherein the hollow rotor shaft (18) comprises a coolant outlet opening (28), and comprising a shaft sealing ring (30) arranged between the housing (12) and the hollow rotor shaft (18), which, with respect to a longitudinal direction of the hollow rotor shaft (18), is arranged between the laminated core (20) and the coolant outlet opening (28), characterized in that the electric machine (10) further comprises a coolant pump (34), by means of which a flow leading away from the shaft sealing ring (30) can be generated for a coolant located on the shaft sealing ring (30) and on the side of the coolant outlet opening (28).

2. Electrical machine (10) according to claim 1, characterized in that the flow generated by the coolant pump (34) acts on coolant which is located adjacent to a sealing lip (32) of the shaft sealing ring (30).

3. Electrical machine (10) according to claim 1 or 2, characterized in that the coolant pump (34) comprises a pump element (42) arranged on the hollow rotor shaft (18), which generates the flow on a side of the shaft seal (30) facing away from the laminated core (20) when the hollow rotor shaft (18) rotates about its axis of rotation.

4. Electrical machine (10) according to one of claims 1 to 3, characterized in that a negative pressure can be generated at least locally on the shaft sealing ring (30) by the coolant pump (34).

5. Electrical machine (10) according to one of claims 1 to 4, characterized in that the coolant pump (34) comprises a ring element which is arranged to encompass the hollow rotor shaft (18) and has conveying elements (38) which extend at least partly radially with respect to the rotor shaft (18).

6. Electrical machine (10) according to one of claims 1 to 5, characterized in that the coolant pump (34) comprises a ring element (36), which is arranged to encompass the hollow rotor shaft (18) and has conveying elements (38) which extend at least partly axially with respect to the rotor shaft (18).

7. Electrical machine (10) according to one of claims 1 to 6, characterized in that the coolant pump (34) has a disc element (40) which delimits a liquid channel (44) leading along the shaft sealing ring (30).

8. Electrical machine (10) according to claim 7, characterized in that the disc element (40) is sealingly fixed to the hollow shaft (18) or to the housing (12).

9. Electrical machine (10) according to one of claims 1 to 8, characterized in that the disc element (40) has passage openings (46) for cooling liquid.

10. Electrical machine (10) according to one of claims 1 to 9, characterized in that the coolant outlet opening (28), with respect to a longitudinal direction of the hollow rotor shaft (18), is arranged on the side of the coolant pump (34) facing away from the laminated core (20) or between the shaft sealing ring (30) and the coolant pump (34).

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