Electric drive

Abstract

The present invention relates to an electric drive (10) comprising a rotor (12) and a stator (14), wherein the rotor (12) is rotatably mounted radially within the stator (14) by means of a hollow shaft (16), wherein a cooling structure (22) for liquid cooling of the rotor (12) is provided within the hollow shaft (16), wherein the hollow shaft (16) is rotatably mounted about a stationary coolant guide (20), wherein the stationary coolant guide (20) has a coolant supply (24) for supplying coolant to the cooling structure (22) and a coolant return (26) for removing coolant from the cooling structure (22), wherein the coolant guide (20) has an inlet (30) for radially outwardly introducing coolant from the coolant supply (24) to an inner wall (32) of the hollow shaft (16).and wherein the coolant guide (20) has an outlet (34) at a position axially spaced from the inlet (30) for guiding coolant into the coolant return (26).

Description

[0001] The present invention relates to an electric drive. In particular, the present invention relates to an electric drive that features improved cooling.

[0002] Electric motors are increasingly becoming the focus of mobility. Electric motors, also known as electric machines, often consist of a rotor and stator assembly. The rotor can, for example, have a hollow shaft and thus be equipped with an internal cooling structure. Such liquid-cooled rotors of electric machines, whether using oil as a coolant or a water / glycol mixture, generally require sufficient coolant pressure to operate under suitable parameters. Particularly when the coolant is supplied via a gearbox, pressure drops can occur, which must be compensated for to ensure effective cooling.

[0003] There is a constant need to improve the cooling performance of a cooling system.

[0004] It is therefore an object of the present invention to provide a solution by which at least one disadvantage of the prior art can be overcome, at least partially. In particular, it is an object of the present invention to provide a solution by which a pressure loss of the coolant can be reduced, thereby creating a measure to improve the cooling performance of a cooling system.

[0005] The problem is solved according to the invention by an electric drive having the features of claim 1. Preferred embodiments of the invention are described in the dependent claims, in the description or the figures, wherein further features described or shown in the dependent claims or in the description or the figures may individually or in any combination constitute an object of the invention unless the context clearly indicates otherwise.

[0006] An electric drive is described, comprising a rotor and a stator, wherein the rotor is rotatably mounted radially within the stator by means of a hollow shaft, wherein a cooling structure for liquid cooling of the rotor is provided within the hollow shaft, wherein the hollow shaft is rotatably mounted about a stationary coolant guide, wherein the stationary coolant guide has a coolant supply for supplying coolant to the cooling structure and a coolant return for removing coolant from the cooling structure, wherein the coolant guide has an inlet for radially outwardly introducing coolant from the coolant supply to an inner wall of the hollow shaft, and wherein the coolant guide has an outlet at a position axially spaced from the inlet for directing coolant into the coolant return.

[0007] Such a drive can reduce pressure loss of coolant in a cooling structure of a rotor and thereby provide improved cooling performance.

[0008] The subject of the present invention is therefore an electric drive. This can be used, for example, in electrically powered vehicles, such as electric motor vehicles.

[0009] The electric drive, also known as an electric machine, comprises a rotor and a stator in a manner known per se. The rotor and stator interact through magnetic excitation, causing the rotor to rotate and thus enabling the electric motor to generate driving force. This interaction can be achieved using appropriate magnetic excitation structures, such as coils, which are energized to generate the excitation. In particular, the rotor is radially mounted within the stator. The electric drive can, for example, be a radial flux machine. In this case, the rotor includes a hollow shaft, which is rotatably mounted. The use of a hollow shaft offers the advantage that its interior can be used to form a cooling structure for the rotor's magnetic excitation structure.For example, a laminated core is arranged around the hollow shaft, which is magnetically excitable and can thus interact with the stator to set the rotor in rotation. It is known that heat is generated in a magnetic excitation structure during operation and that the excitation structure should therefore be cooled. According to the invention, this is achieved particularly efficiently by providing the hollow shaft with a cooling structure located within it. 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 oil, water, glycol, or a mixture comprising, for example, at least one of the aforementioned components.

[0010] It is further provided that the hollow shaft is rotatably mounted on a stationary coolant guide, in particular that it is coaxial with the coolant guide. Accordingly, the hollow shaft rotates around the stationary coolant guide when the rotor is in operation. This is achieved in a manner known per se by providing appropriate bearings. The stationary coolant guide has a coolant inlet for supplying coolant to the cooling structure and a coolant return for removing coolant from the cooling structure. Thus, the coolant can be directed from the coolant guide into the cooling structure and back again. The coolant guide expediently runs in the axial direction to supply and remove the coolant on the gearbox side.This allows coolant to be directed into the interior of the hollow shaft in a space-saving manner, thus enabling effective cooling of the rotor from the inside.

[0011] To achieve cooling, the coolant supply is further provided with an inlet for the radial outward application of coolant to an inner wall of the hollow shaft, and the cooling structure has an outlet at a position axially spaced from the outlet for directing coolant into the coolant return system. Accordingly, the coolant is guided radially from the stationary coolant guide to the inner wall of the hollow shaft and from there back into the coolant guide, or more precisely, into the coolant return system. Radial guidance of the coolant to the inner wall can be any guidance that has a radial component.Preferably, the radial guide can be an exactly radial guide or one which has an angle to an exactly radial guide of approximately 60° at most, for example a maximum of 48°, preferably in the direction of the outlet.

[0012] With the invention, it is thus possible to integrate a coolant pump into the rotor above a certain rotor speed. Then, because the coolant flows against the inner wall of the hollow shaft, it is carried along by the rotation of the hollow shaft and set into a swirl, so that it moves axially towards the outlet and from there can flow into the coolant return system.

[0013] The coolant pressure no longer depends solely on external pumps, but can be further increased by a pump integrated into the rotor. Such a pump can operate in a particularly simple manner and without complex peripherals, as it works purely through the rotation of the rotor. The coolant is drawn along by the rotation of the rotor or the inner wall of the hollow shaft, thus being set into rotation and accelerated.

[0014] The pumping capacity depends critically on the rotor speed and the inner diameter of the rotor shaft or hollow shaft. Large inner diameters of the hollow shaft are preferred, as this increases the pressure level available above a certain speed or reduces the speed required to reach a certain pressure level. Accordingly, the solution according to the invention is highly adaptable and can be easily adjusted to the desired application and cooling capacity.

[0015] A further advantage of this design is that high coolant pressure, and thus particularly effective cooling, is present when needed, namely at high rotor speeds. This occurs automatically solely through the varying rotor speed, allowing for adjustment of the cooling capacity without complex controls.

[0016] The design described above thus makes it possible to compensate for the pressure loss caused by the supply of the cooling medium from the gearbox side and instead to easily integrate a pump into the rotor, which may even increase the coolant pressure.

[0017] It may be preferred that the coolant return system has a first section for guiding the coolant axially towards the inlet and a second section for guiding the coolant in the opposite direction to the first section. In this configuration, the coolant can thus flow over a comparatively long axial path, thereby allowing for a very large active cooling surface on the rotor, since the inlet and outlet can be located at a relatively large axial distance. This, in turn, can also permit particularly effective cooling.

[0018] Furthermore, in the first section, the coolant can thus be gradually converted from a swirling flow to an axial flow. A long axial path allows the coolant to be diverted from the swirling flow in the hollow shaft to an axial flow with minimal pressure loss, which in turn has a positive effect on the coolant pressure and consequently on the cooling efficiency. In particular, if the coolant is supplied from the gearbox side, this design allows the coolant to be guided into the hollow shaft on the side opposite the gearbox, carried towards the gearbox, then through the outlet, and flowing back towards the inlet in the first section. In the second section, it flows through the coolant return system towards the gearbox.

[0019] It is particularly advantageous for the first section to have a curved deflection structure for redirecting the coolant in an axial direction. It has been shown that a curved structure can capture the swirling flow and gradually convert it into an axial flow. In this configuration, any potential pressure drop can be reduced particularly effectively. Accordingly, this structure can also serve to counteract pressure loss, if necessary increasing the coolant pressure and thus ensuring effective cooling.

[0020] Preferably, the coolant guide, and in particular the coolant return, can have an outlet in the form of a scooping element. In this configuration, the coolant, which is in swirling flow, can be drawn in particularly effectively and without pressure loss and directed into the coolant return. A scooping element can be understood to be, in particular, an element that has a spoon-like or ladle-like section which draws in the coolant and directs it into the coolant return over a large radius. In particular, the stationary coolant guide can thus serve as a stationary scoop wheel, which in turn can effectively counteract any pressure loss.

[0021] It may be further preferred that the coolant guide comprises a stationary guide tube in which the coolant supply and part of the coolant return are formed, and that a housing element with an outer wall is fixedly mounted on the guide tube, with a coolant channel forming part of the coolant return within the outer wall. For example, the coolant return portion can be located between the outer wall and the guide tube, or between the outer wall and an inner wall. This embodiment allows for a particularly simple design for guiding the coolant. Furthermore, a coolant return system of the desired configuration can be easily formed within the outer housing without negatively affecting the swirl flow outside the outer wall.Accordingly, this design can also effectively counteract a loss of coolant pressure.

[0022] For example, in a design in which the coolant return has a first area for guiding the coolant axially towards the inlet and a second area for guiding the coolant in the opposite direction to the first area, the first part may be located below the outer wall and the second part may be located in the guide tube.

[0023] It may be further preferred that the stationary coolant guide comprises an outer wall that is conically shaped and has a cross-section that thickens from the inlet to the outlet. This design allows the coolant to be further accelerated on its way from the inlet to the outlet, which in turn can also have a further positive effect on the coolant pressure.

[0024] In a further preferred embodiment, the inlet may have an axial opening with a radially extending baffle surface positioned adjacent to the axial opening to deflect the coolant in a radial direction. This embodiment allows for a simple design with good adaptability. In detail, the stationary coolant guide can be designed as a simple guide tube, which is axially open on its side facing away from the gearbox. The baffle surface can then be designed to deflect the coolant exiting the axial opening in the desired manner, so that it is guided in the desired shape to the inner wall of the hollow shaft. The shape of the baffle surface and its axial distance from the axial opening allow the coolant flow to be influenced as desired, which permits advantageous adaptation to the desired application.

[0025] It may be advantageous for the hollow shaft to have at least one drive element on its inner surface for accelerating the rotation of the coolant. Providing one or more drive elements can significantly increase the pumping capacity, which further improves the coolant flow and thus the cooling efficiency. A drive element can be easily formed by elements arranged on the inner wall of the hollow shaft that increase the rotation of the coolant. In principle, any conveying element known to those skilled in the art can be used here.

[0026] It is further preferably possible for a transmission input shaft to run outside or inside the stationary coolant guide. In this configuration, a particularly space-saving and structurally simple coolant supply and discharge to the transmission side can be achieved by allowing the coolant to flow through the transmission input shaft into the coolant guide and vice versa. In this configuration, it is also preferably possible for the rotor to be rotationally fixed to the transmission input shaft.

[0027] The invention is further explained below with reference to the figures, whereby one or more features of the figures, individually or in combination, can constitute a feature of the invention. Furthermore, the figures are to be considered merely exemplary and in no way limiting. Fig. Figure 1 shows a schematic detail view of an electric drive according to an embodiment of the present invention; Fig. 2 shows a detailed view of the electric drive from Fig. 1; and Fig. Figure 3 shows another detailed view of the electric drive. Fig. 1.

[0028] In the Fig. Figure 1 shows an electric drive 10. Such an electric drive 10, which can also be called an electric machine, can be used, for example, in an electrically powered vehicle, such as a motor vehicle.

[0029] The electric drive 10 comprises a rotor 12 and a stator 14, wherein the rotor 12 is rotatably mounted radially within the stator 14 by means of a hollow shaft 16. A laminated core 18 is arranged outside the hollow shaft 16 to interact with the stator 14 or a magnetic excitation structure thereof and thus set the rotor 12 into rotation. Accordingly, in the Fig. Figure 1 shows an embodiment in which the electric drive 10 comprises a radial flux machine.

[0030] In the design according to Fig. In Figure 1, the hollow shaft 16 is rotatably mounted about a stationary coolant guide 20. A cooling structure 22 for liquid cooling of the rotor 12 is provided within the hollow shaft 16. This cooling structure can be configured as a channel for guiding the coolant, or alternatively as a free volume between the coolant guide 20 and the hollow shaft 16. The flow of the coolant is indicated by the arrows. The coolant guide 20 serves to introduce coolant into and discharge coolant from the cooling structure 22. For this purpose, the stationary coolant guide 20 includes a coolant inlet 24 for supplying coolant to the cooling structure 22 and a coolant return 26 for removing coolant from the cooling structure 22. The coolant inlet 24 and the coolant return 26 run parallel within the coolant guide 20.

[0031] More precisely, the liquid cooling on the transmission side is achieved by a transmission input shaft 28 running outside the stationary coolant guide 20. The transmission input shaft 28 can be mounted on the coolant guide 20 by means of a plain bearing. Thus, coolant can flow through the transmission input shaft 28 into the coolant guide 20 and, after passing through the cooling structure 22 and the coolant guide 20, flow back into the transmission input shaft 28.

[0032] The coolant guide 20 further comprises an inlet 30 for radially outwardly introducing coolant from the coolant supply 24 to an inner wall 32 of the hollow shaft 16 and, at a position axially spaced from the inlet 30, an outlet 34 for guiding coolant into the coolant return 26.

[0033] With regard to the inlet 30, it is provided that it has an axial opening 36 with a radially extending baffle surface 38 positioned adjacent to the axial opening 36 for deflecting the coolant flowing out of the axial opening 36 in a radial direction. This allows the coolant to be guided radially to the inside of the hollow shaft 16 and carried along with it during rotation of the hollow shaft 16. The baffle surface 38 can thus serve as a deflecting surface for redirecting the coolant flow. The coolant is thereby guided in the cooling structure 22 to an end of the cooling structure 22 radially opposite the inlet 30 and thus reaches the outlet 34. This can be improved by having the stationary coolant guide 20 include an outer wall 40 that is conically shaped and has a cross-section that thickens from the inlet 30 to the outlet 34. The outer wall 40 can, in principle, have a smooth surface.

[0034] The coolant guide 20 has an outlet 34 in the form of a scooping element, so that the outer wall 40, or the coolant guide 20 itself, can function as a scoop wheel. The scoop wheel is designed to tap into the high-pressure zone in the fluid-filled hollow shaft 16 at a point at the rearmost end under the lamination stack 18, thus not impeding the heat absorption capacity of the coolant. It scoops the fluid from the high-pressure zone as close as technically possible to the inner diameter of the hollow shaft 16.

[0035] In the variant shown here, the hollow shaft 16, with an outer diameter of Ø 76 mm and an inner diameter of Ø 69 mm, is capable of carrying an external thread that allows clamping of the lamination stack 18 and also carries the splined shaft-type positive locking element 42 for the positive and non-positive transmission of all forces and moments. The hollow shaft 16 can be manufactured cost-effectively by cold forming from suitable steel alloys with minimal machining effort and, due to its large inner diameter, offers ideal conditions for combination with the scoop wheel of the coolant guide 20.

[0036] For a coolant return 26, in the Fig. Figure 1 shows that the coolant guide 20 comprises a stationary guide tube 44 in which the coolant supply 24 and part of the coolant return 26 are formed, and that a housing element 46 with an outer wall 40 is fixedly seated on the guide tube 44, wherein a coolant channel 50 is formed within the outer wall 40, which is part of the coolant return 26. More precisely, the coolant channel 50 is formed between the outer wall 40 and an inner wall 52 and has corresponding guide elements 56 for forming a curved deflection structure 54.

[0037] In principle, the coolant return system 26 is designed to have a first section 58 for guiding the coolant axially towards the inlet 30 and a second section 60 for guiding the coolant in the opposite direction to the first section 58. The first section 58 features the curved deflection structure 54 for deflecting the coolant in an axial direction. Additionally, to support the guide tube 44, which is rigidly connected to the outer wall 40 and inner wall 52, forming the so-called scoop wheel, a sliding bearing can be implemented on the transmission input shaft 28, which can be designed as a support bearing.

[0038] In the Fig. Figure 2 shows the coolant guide 20, and in particular its external structure comprising the outer wall 40 and the inner wall 52, in greater detail. It is particularly evident that the deflection structure 54 is arranged between the outer wall 40 and the inner wall 52, through which the coolant can be converted from a swirling flow to an axial flow.

[0039] In the Fig. Figure 3 shows this structure in greater detail without the outer wall 40. In particular, the following are shown in the Fig. 2 further passages 62 are shown, in which the coolant can be deflected from the first area 58 to the second area 60.

Claims

[1] Electric drive (10), comprising a rotor (12) and a stator (14), wherein the rotor (12) is rotatably mounted radially within the stator (14) by means of a hollow shaft (16), wherein a cooling structure (22) for liquid cooling of the rotor (12) is provided within the hollow shaft (16), characterized byin that the hollow shaft (16) is mounted so as to be rotatable about a stationary coolant guide (20), wherein the stationary coolant guide (20) has a coolant supply (24) for supplying coolant into the cooling structure (22) and a coolant return (26) for discharging coolant from the cooling structure (22), wherein the coolant guide (20) has an inlet (30) for the radially outwardly directed introduction of coolant from the coolant supply (24) to an inner wall (32) of the hollow shaft (16), and wherein the coolant guide (20) has an outlet (34) for conducting coolant into the coolant return (26) at a position axially spaced from the inlet (30). [2] Electric drive (10) according to claim 1, characterized bythat the coolant return (26) has a first region (58) for guiding the cooling liquid axially in the direction of the inlet (30) and a second region (60) for guiding the cooling liquid in the direction opposite to the first region (58). [3] Electric drive (10) according to claim 2, characterized by that the first region (58) has a curved deflection structure (54) for deflecting the cooling liquid in an axial direction. [4] Electric drive (10) according to one of claims 1 to 3, characterized by that the coolant guide (20) has an outlet (34) in the form of a scoop element. [5] Electric drive (10) according to one of claims 1 to 4, characterized bythat the coolant guide (20) comprises a fixed guide tube (44) in which the coolant supply (24) and a part of the coolant return (26) are formed, and that a housing element (46) with an outer wall (40) is seated on the guide tube (44) in a positionally fixed manner thereon, wherein a coolant channel (50) is formed within the outer wall (40), which is part of the coolant return (26). [6] Electric drive (10) according to one of claims 1 to 5, characterized by in that the fixed coolant guide (20) comprises an outer wall (40) which is conically shaped and has a cross-section which thickens from the inlet (30) to the outlet (34). [7] Electric drive (10) according to one of claims 1 to 6, characterized bythat the inlet (30) has an axial opening (36) with a radially extending baffle surface (38) positioned adjacent to the axial opening (36) for deflecting the cooling liquid in the radial direction. [8] Electric drive (10) according to one of claims 1 to 7, characterized by that the hollow shaft (16) has at least one driver element on its inner wall (32) for rotatingly accelerating the cooling liquid. [9] Electric drive (10) according to one of claims 1 to 8, characterized by that a transmission input shaft (28) runs outside or inside the fixed coolant guide (20). [10] Electric drive (10) according to one of claims 1 to 9, characterized by that the electric drive (10) comprises a radial flux machine.

Images