ELECTRIC DRIVE

Description

Technical area

[0001] The present invention relates to an electric drive, in particular an electric drive system with rotor cooling. State of the art

[0002] In an electric drive with a coaxial arrangement, an output shaft that outputs power is arranged coaxially within a hollow rotor shaft of an electric motor. Cooling a rotor typically involves inducing a lubricating fluid / cooling fluid into a gap between the rotor shaft and the output shaft. However, due to the small size of the gap between the rotor shaft and the output shaft, smoothly introducing the lubricating fluid / cooling fluid into the gap between the rotor shaft and the output shaft poses a problem.

[0003] An electric drive with the features recited in the preamble of the independent patent claim is already known from EP 0 587 389 A1. The rotor shaft bearings and output shaft bearings, which are arranged on a support element or bearing plate on the axial side of the drive facing away from the gearbox, are positioned within an axial installation space delimited by the sealing elements assigned to the rotor shaft and the output shaft, respectively. WO 2020 / 069744 A1 discloses another, structurally comparable electric drive in which the bearings and sealing elements assigned to the rotor shaft are arranged in pairs, axially staggered relative to the bearings and sealing elements assigned to the output shaft. An output shaft bearing is provided there between the rotor shaft seal and the output shaft seal. In the solutions cited, the spatial area spanned by the two sealing elements mentioned is comparatively large.The invention aims to further improve the cooling of an electric drive of the aforementioned type. Disclosure of the invention

[0004] The present invention provides an electric drive that achieves the above object, wherein the electric drive comprises an electric motor module and a transmission mechanism module connected to the electric motor module, wherein the electric motor module comprises a hollow rotor shaft attached to a rotor, which transmits power to the transmission mechanism module, wherein the transmission mechanism module comprises an output shaft arranged coaxially within the rotor shaft, wherein the rotor shaft and the output shaft extend along an axial direction of the electric motor module and a flow space is defined between the rotor shaft and the output shaft, wherein at an end of the electric motor module facing away from the transmission mechanism module in the axial direction, the output shaft extends beyond the rotor shaft and a support element is provided that surrounds the rotor shaft and the output shaft,wherein a first sealing element is provided between the support element and the rotor shaft, and a second sealing element is provided between the support element and the part of the output shaft extending beyond the rotor shaft, so that a cavity fluidically communicating with the flow space is formed between the rotor shaft, the output shaft, and the support element, and wherein a through hole connecting the cavity to the environment is formed in the support element.

[0005] Since the invention provides that the first sealing element and the second sealing element are arranged in the axial direction between a bearing for the rotor shaft and a bearing for the output shaft, a cavity with small dimensions can be provided at an inlet / outlet of the flow space between the rotor shaft and the output shaft in order to quickly establish a lubrication / cooling line. Short description of the characters

[0006] Fig. 1shows a sectional view of an electric drive according to the first embodiment of the present invention. Detailed embodiments

[0007] A more detailed description of an embodiment of the present invention is given below with reference to the accompanying drawings.

[0008] Fig. 1shows an electric drive 10 according to an embodiment of the present invention in a sectional view. The electric drive 10 can be an electric drive for a motor vehicle, but the present invention is not limited thereto. The electric drive 10 has an electric motor module 11 and a transmission mechanism module 12. The electric motor module 11 transmits power to the transmission mechanism module 12, and the transmission mechanism module 12 transmits the power to wheels of the motor vehicle to drive the vehicle. Optionally, the electric drive 10 can further have an inverter module (not shown) that serves to supply the electric motor module 11 with three-phase current.

[0009] The electric motor module 11 includes a main housing 20 and a stator 21 and a rotor 22 housed in the main housing 20, the rotor 22 having a hollow rotor shaft 23 fixed to the rotor 22. One end of the rotor shaft 23 in the axial direction is coupled to the gear mechanism module 12. Specifically, an end of the rotor shaft 23 facing the gear mechanism module 12 is supported by a bearing disposed in a bearing seat formed in a support plate / end cover integrally molded with the main housing 20 of the electric motor module 11. The support plate / end cover separates the gear mechanism module 12 from the electric motor module 11. The rotor shaft 23 extends through the support plate / end cover into the gear mechanism module 12 and is coupled to a gear mechanism within the gear mechanism module 12.A gear portion or pinion is formed at the axial end of the rotor shaft 23 coupled to the gear mechanism module 12. An end of the rotor shaft 23 remote from the gear mechanism module 12 is rotatably supported by the main housing 20 via a bearing.

[0010] The transmission mechanism module 12 is connected to one end of the electric motor module 11. In this example, the transmission mechanism module 12 may include a housing 30 and a transmission mechanism provided within the housing. The transmission mechanism includes, for example, a reduction gear (not shown) and a differential 32. In this example, the reduction gear includes a large-diameter drive gear and a small-diameter driven gear. The drive gear and driven gear are attached to the same transmission shaft and thus rotate as a whole. The gear portion or pinion of the rotor shaft 23 engages the drive gear of the reduction gear, while the driven gear of the reduction gear transmits power to the differential 32.The driven gear of the reduction gear engages with a gear / toothing 31 on a differential housing of the differential 32, thus driving the differential 32 to rotate. The differential 32 is rotatably mounted to a housing of the transmission mechanism module 12 via a bearing. The differential 32 comprises two output shafts (half-shafts), one of which passes coaxially through the hollow rotor shaft 23 of the rotor of the electric motor and is thus arranged coaxially within the rotor shaft 23. The output shaft 33 is rotatably supported at an end facing away from the transmission mechanism module 12 via a bearing. An axially extending annular gap is defined between the rotor shaft 23 and the output shaft 33 arranged coaxially within the rotor shaft 23. As described below, the annular gap serves as a flow space through which a lubricating fluid can flow.It should be noted that the transmission mechanism of the electric drive 10 according to the present invention is not limited to the reduction gear and the differential 32, but may be any other transmission mechanism obvious to those skilled in the art.

[0011] A cooling system of the electric drive 10 of the present invention will be discussed in more detail below.

[0012] In summary, the cooling system of the electric drive 10 directs a lubricating fluid within the gear mechanism module 12 into an end of the flow space between the rotor shaft 23 and the output shaft 33 arranged coaxially within the rotor shaft 23, which end is remote from the gear mechanism module 12, so that the lubricating fluid flows through the flow space between the rotor shaft 23 and the output shaft 33 and finally flows back into the gear mechanism module 12 via the other end of the flow space facing the gear mechanism module 12.

[0013] According to the exemplary embodiment of the present invention, a lubricating fluid channel is formed in the main housing 20 of the electric motor module 11, said channel comprising a first channel portion 41 and a second channel portion 42. A first end of the first channel portion 41 is fluidly communicating with the transmission mechanism module 12, and a second end of the first channel portion 41 is coupled to an inlet of a pump. A first end of the second channel portion 42 is coupled to an outlet of a pump, and a second end of the second channel portion 42 is fluidly communicating with the flow space between the rotor shaft 23 and the output shaft 33. According to the present invention, the pump can be integrated into the electric drive 10 or arranged externally of the electric drive 10, and it can be a mechanical pump or an electronic pump.The lubricating fluid channel does not necessarily have to be formed in the main housing 20 of the electric motor module 11 and can rather be provided by a pipe provided outside the electric drive 10.

[0014] As shown in the drawing, the output shaft 33 extends beyond the rotor shaft 23 at an end facing away from the gear mechanism module 12. Furthermore, a support element 50 is provided at this end, which surrounds the rotor shaft 23 and the output shaft 33. A first sealing element 61 is provided between the support element 50 and the rotor shaft 23, and a second sealing element 62 is provided between the support element 50 and the part of the output shaft 33 extending beyond the rotor shaft 23, so that a cavity 70 that is in fluid communication with the flow chamber is formed between the rotor shaft 23, the output shaft 33, and the support element 50. Furthermore, a through-hole 51 that can connect the cavity 70 to the environment is formed in the support element 50. Specifically, the through-hole 51 is in fluid communication with the second end of the second channel section 42.

[0015] The support element 50 can be formed integrally with the main housing 20 of the electric motor module 11. Furthermore, the support element 50 can be connected to the main housing 20 of the electric motor module 11 and includes a bearing seat of the bearing for the output shaft 33. The bearing of the rotor shaft 23 is supported by the main housing 20. The first sealing element 61 and the second sealing element 62 are arranged in the axial direction between the bearing for the rotor shaft 23 and the bearing for the output shaft 33. Thus, the first sealing element 61 and the second sealing element 62 can be arranged close enough to each other to achieve a desired, small-sized cavity 70.

[0016] A radial gap between the rotor shaft 23 and the output shaft 33 is typically set to 2.5 to 5 mm, and to achieve the optimal technical effect, a radial distance between the first sealing element 61 and the second sealing element 62 may be set to 7 to 10 mm. The volume of the cavity 70 is preferably set to 0.01 to 0.02 L.

[0017] The small-sized cavity 70 achieves the following technical effects: 1. Due to the small volume of the cavity, the cavity can be quickly filled with the lubricating fluid, so that a lubrication / cooling circuit can be quickly established and the rotor can be quickly cooled. 2. In the radial direction, the cavity has a small dimension, so that the maximum pressure during operation can be reduced and thus the pressure at the location of a shaft sealing element can be reduced, which is convenient for the shaft sealing element. 3. Due to the small dimension, the cavity can be quickly filled with the lubricating fluid and the amount of air mixed into the lubricating fluid is reduced, thereby reducing the risk of cavitation erosion and improving NVH behavior.

[0018] In Fig. 1The support element 50 is formed integrally with the main housing 20 of the electric motor module 11, and the bearing seat of the bearing for the output shaft 33 is formed by a separate component. However, the present invention is not limited thereto, and the bearing seat of the bearing for the output shaft 33 can alternatively be formed on the support element 50 for the first sealing element 61 and the second sealing element 62. As far as structurally and spatially possible, the support element 50 for the first sealing element 61 and the second sealing element 62 can also be formed by a separate component fastened relative to the main housing 20 of the electric motor module 11.

[0019] In the above embodiment, the first sealing element 61 is arranged in the radial direction between the support element 50 and the rotor shaft 23, while the second sealing element 62 is arranged in the radial direction between the support element 50 and the output shaft 33. However, the present invention is not limited thereto, and for example, the first sealing element 61 may alternatively be arranged in the axial direction between the support element 50 and the rotor shaft 23, as long as a cavity 70 fluidly communicating with the flow space between the rotor shaft 23 and the output shaft 33 can be formed between the rotor shaft 23, the output shaft 33, and the support element 50.

[0020] Although the specific embodiments of the present invention have been described above, those skilled in the art should understand that these are merely examples, and the scope of the present invention is defined by the appended claims. Those skilled in the art may make various changes and modifications to such embodiments without departing from the principles and spirit of the present invention, which changes and modifications also fall within the scope of the invention.

Claims

1. Electric drive (10), comprising - an electric motor module (11) and - a transmission mechanism module (11) connected to the electric motor module (11), wherein - the electric motor module (11) comprises a hollow rotor shaft (23) which is attached to a rotor (22) and transmits power to the transmission mechanism module (11), wherein - the transmission mechanism module (11) comprises an output shaft (33) which is arranged coaxially within the rotor shaft (23), wherein - the rotor shaft (23) and the output shaft (33) run along an axial direction of the electric motor module (11) and a flow space is delimited between the rotor shaft (23) and the output shaft (33), wherein - the output shaft (33) extends beyond the rotor shaft (23) at an end of the electric motor module (11) remote from the transmission mechanism module (11) in the axial direction, and wherein - a support element (50) which surrounds the rotor shaft (23) and the output shaft (33) is provided, wherein - a first sealing element (61) is provided between the support element (50) and the rotor shaft (23) and - a second sealing element (62) is provided between the support element (50) and the portion of the output shaft (33) extending beyond the rotor shaft (23), so that - a cavity (70) fluidically communicating with the flow space is formed between the rotor shaft (23), the output shaft (33) and the support element (50), and wherein - a through-hole (51), which connects the cavity (70) to the surrounding area, is formed in the support element (50), characterized in that - the first sealing element (61) and the second sealing element (62) are arranged between a bearing for the rotor shaft (23) and a bearing for the output shaft (33) in the axial direction.

2. Electric drive according to Claim 1, characterized in that the through-hole (51) is in fluidic communication with a lubricating fluid channel (41, 42).

3. Electric drive according to Claim 1 or 2, characterized in that the transmission mechanism module (11) comprises a reduction gear and a differential (32), wherein the rotor shaft (23) is coupled to a differential housing of the differential (32) via the reduction gear and the output shaft (33) is a half-shaft of the differential (32).

4. Electric drive according to any of Claims 1-3, characterized in that the support element (50) is connected to a main housing (20) of the electric motor module (11) and the support element (50) is provided with a bearing seat of the bearing for the output shaft (33).

5. Electric drive according to any of Claims 4, characterized in that the lubricating fluid channel (41, 42) is arranged in the main housing (20) of the electric motor module (11).

6. Electric drive according to any of Claims 2-5, characterized in that the electric drive (10) comprises a pump which pumps a lubricating fluid in the transmission mechanism module (11) into the through-hole (51) via the lubricating fluid channel (41, 42).

7. Electric drive according to any of Claims 1-6, characterized in that the first sealing element (61) is arranged between the rotor shaft (23) and the support element (50) in the axial or radial direction and the second sealing element (62) is arranged between the output shaft (33) and the support element (50) in the radial direction.

8. Electric drive according to any of Claims 1-7, characterized in that a radial gap between the rotor shaft (23) and the output shaft (33) is set in the range of from 2.5 to 5 mm and a radial distance between the first sealing element (61) and the second sealing element (62) is set in the range of from 7 to 10 mm.

9. Electric drive according to any of Claims 1-8, characterized in that the volume of the cavity (70) is set in the range of from 0.01 to 0.02 L.