Electric motor
Patent Information
- Authority / Receiving Office
- DE · DE
- Patent Type
- Patents
- Current Assignee / Owner
- ZF FRIEDRICHSHAFEN AG
- Filing Date
- 2021-07-21
- Publication Date
- 2026-07-30
AI Technical Summary
Existing electric motors face issues with harmful bearing currents leading to spark formation and component degradation due to electrical charge transfer across gaps, which conventional shaft grounding rings attempt to address but often cause friction and are complex.
A novel electric motor design uses a singular electrically conductive contact ring to ground the rotor shaft, eliminating the need for brush-like fibers and reducing friction by positioning it at a location with a small contact surface, or employs a series connection of contact rings for a simpler and more efficient current path.
The solution effectively dissipates harmful currents without significant friction, simplifying assembly, reducing costs, and enhancing the motor's operational efficiency by minimizing current flow through bearings and gears.
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Abstract
Description
[0001] The invention relates to an electric motor, in particular for a vehicle drive, with a housing and a rotor shaft which is rotatably mounted in the housing via bearings, wherein the rotor shaft is electrically grounded via the housing.
[0002] During the operation of electric motors, various types of currents are generated within the motor. It is known from the prior art that rotor shafts of electric motors are grounded to prevent damaging bearing currents. If electrical charge is transferred across a gap between two components, sparking can occur. This can lead to lubricant deposits or pitting corrosion on components. Shaft grounding rings are typically used to provide a current path from the rotor shaft to the housing. Such shaft grounding rings usually have brush-like fibers arranged between several ring discs and in contact with the rotor shaft to dissipate the harmful currents without generating significant friction.
[0003] The purpose of the invention is to create an electric motor with a novel grounded rotor shaft.
[0004] The problem is solved by an electric motor, particularly for vehicle propulsion, comprising a housing and a rotor shaft rotatably mounted in the housing via bearings. The housing and rotor shaft are electrically connected to each other via a single, electrically conductive contact ring for grounding the rotor shaft. The use of a single, electrically conductive contact ring results in a particularly simple design for grounding the rotor shaft, as a shaft grounding ring is no longer required.
[0005] Preferably, the rotor shaft is a hollow shaft with an internal channel for oil or coolant, and the housing has an inlet nozzle that projects into an inlet opening of the channel, with the contact ring positioned between the rotor shaft and the inlet nozzle. This results in a particularly easy-to-assemble design, as the inlet nozzle can simply be inserted into the inlet opening. Furthermore, this arrangement positions the contact ring at a point where its contact surface has a very small diameter, thus significantly reducing the frictional torque generated at the contact ring.
[0006] In one embodiment, a receptacle for the contact ring is formed in the rotor shaft or in the inlet nozzle.
[0007] In one embodiment, the contact ring seals the oil or coolant channel at an axial end region of the hollow shaft. This eliminates the need for an additional seal for the oil or coolant channel in this axial end region, thus simplifying the design and saving costs.
[0008] The problem is further solved by an electric motor with a housing and a rotor shaft, which is rotatably mounted in the housing via bearings, wherein the housing and the rotor shaft are electrically connected to each other via a series connection of singular electrically conductive contact rings. The use of a series connection of singular electrically conductive contact rings also eliminates the need for a conventional shaft grounding ring.
[0009] In one embodiment, a planetary gear unit is coupled to the rotor shaft, with a first, singular contact ring arranged between the rotor shaft and a planet carrier, and a second, singular contact ring arranged between the planet carrier and the housing, allowing current to flow from the rotor shaft via the planet carrier to the housing. This arrangement enables a particularly simple series connection.
[0010] Preferably, the contact ring is made of steel or gray cast iron, i.e., a readily available electrically conductive material. Gray cast iron also exhibits very good emergency running properties.
[0011] In one version, the contact ring is made of an electrically conductive polymer. This makes it particularly easy to achieve a sealing effect with the contact ring.
[0012] Preferably, the contact ring has a square cross-section. This allows for very simple manufacturing of both the contact ring and the receptacle for the contact ring. For example, the contact ring can have a rectangular cross-section. Other cross-sectional shapes, such as trapezoidal or round, are also possible.
[0013] In another version, the contact ring has lubrication or oil pockets. This allows lubricating oil to be guided in a targeted manner via the contact ring.
[0014] In one embodiment, the contact ring is held solely by a groove in the rotor or the housing. This results in a particularly simple and cost-effective design.
[0015] Further features and advantages of the invention will become apparent from the following description and from the accompanying drawings, to which reference is made. The drawings show: - Fig. 1. A sectional view of an electric motor with shaft grounding ring, - Fig. 2 the detail II from Fig. 1 with a state-of-the-art wave grounding ring, - Fig. 3 an enlarged view of a first embodiment of an electric motor according to the invention with a contact ring in a rotor shaft, - Fig. 4 an enlarged view of a second embodiment of an electric motor according to the invention with a contact ring in an inlet nozzle and - Fig. 5 an enlarged view of a third embodiment of an electric motor according to the invention with a series connection of contact rings.
[0016] Fig. Figure 1 shows an electric motor 10 for a vehicle drive with a housing 12 in which a rotor shaft 14 is rotatably mounted via bearings 16, which are designed here as ball bearings.
[0017] A gearbox 18 is coupled to one axial end region of the rotor shaft 14 and a pulse disk 20 for determining the speed is attached to the other axial end region.
[0018] The electric motor 10 is designed here as an asynchronous motor with rotor and stator, with the gearbox 18 being a planetary gearbox. However, it is also conceivable that other types of electric motors and gearboxes could be used.
[0019] The rotor and stator of the electric motor 10 are arranged here in a separate motor compartment 24, which is sealed by shaft seals 22. The rotor is coupled to the rotor shaft 14, which is designed here as a hollow shaft with an oil-carrying channel 26. The two axial end sections of the rotor shaft 14 project into oil chambers 28, which are formed on axially opposite sides of the housing 12, with the oil-carrying channel 26 connecting the two oil chambers 28 fluidically. The lower section of the oil chambers 28 serves as an oil reservoir.
[0020] On the side of the rotor shaft 14 facing away from the gearbox 18, an oil inlet nozzle 30 is arranged, which projects into an oil inlet opening 32 of the rotor shaft 14, so that the oil inlet nozzle 30 and the oil-carrying channel 26 of the rotor shaft are fluidically connected. The oil inlet nozzle 30 is formed on the housing 12 of the electric motor 10.
[0021] The arrangement for grounding the rotor shaft 14 according to the prior art, with a shaft grounding ring 34, is described in Fig. Figure 2 shows an enlarged view. The shaft grounding ring 34 is arranged in the housing 12 and provides current paths from the rotor shaft 14 to the housing 12 via brush-like fibers 36. The brush-like fibers 36 are arranged between several ring disks 38, which are arranged in a base body 40. The shaft grounding ring 34 is arranged in a receptacle in the motor compartment 24.
[0022] Fig. Figure 3 shows an enlarged view of the axial end region of the rotor shaft 14, facing away from the gearbox 18, with the oil inlet nozzle 30 projecting into the oil inlet opening 32 of the rotor shaft 14. A single electrically conductive contact ring 42 is arranged between the rotor shaft 14 and the oil inlet nozzle 30 of the housing 12, thus providing a current path from the rotor shaft 14 to the housing 12 without the need for a shaft grounding ring 34. This eliminates the need for multiple ring disks or fibers. A single ring performs the complete function of the many parts of the shaft grounding ring 34.
[0023] When the electric motor 10 is operated, currents, e.g. capacitive or circulating currents, can be generated that flow from the rotor shaft 14 to the housing 12. The contact ring 42 provides a current path from the rotor shaft 14 to the housing 12 and grounds the rotor shaft 14.
[0024] The contact ring 42 is made of an electrically conductive material, and the current path provided via the contact ring 42 has a lower electrical resistance than the current path via the bearings 16 or the gears of the gearbox 18. Therefore, current generated in the rotor shaft 14 during operation of the electric motor 10 flows from the rotor shaft 14 to the housing 12 via the contact ring 42, rather than via the bearings 16 or the gears of the gearbox 18. The contact ring 42 can be made of, for example, steel, cast iron, or an electrically conductive polymer.
[0025] Here, the contact ring 42 is received in a groove in the rotor shaft 14. In an alternative embodiment, the contact ring 42 can be received in a groove in the oil inlet nozzle 30 (see Fig. 4) However, it is also conceivable that the contact ring 42 is arranged at a different location in the electric motor 10 between the rotor shaft 14 and the housing 12. The arrangement between the oil inlet nozzle 30 and the rotor shaft 14 has the advantage that the contact ring 42 can be designed with a particularly small diameter friction surface, thus reducing friction during operation.
[0026] In the illustrated embodiments, the contact ring 42 has a rectangular cross-section.
[0027] However, it is also conceivable that the contact ring 42 has a different cross-section that is easy to manufacture, e.g. a trapezoidal or round cross-section.
[0028] Furthermore, in the illustrated embodiment, the contact ring 42 seals the oil-carrying channel 26 at an axial end region.
[0029] Fig. Figure 5 shows another embodiment of the electric motor 10 with a series connection of singular electrically conductive contact rings 42. Since the basic principle is the same as that of the embodiments of Fig. 3 and Fig. Since 4 corresponds to this, only the differences will be explained below.
[0030] In the embodiment according to Fig. 5 Two contact rings 42 are arranged in the electric motor 10.
[0031] A first contact ring 42 is arranged between the rotor shaft 14 and the gearbox 18, and a second contact ring 42 is located between the gearbox 18 and the housing 12. The first contact ring 42 is received in a groove at the axial end region of the rotor shaft 14, to which the gearbox 18 is coupled, and forms an electrical connection from the rotor shaft 14 to a planet carrier 46 of the gearbox 18. The contact ring 42 is positioned between the rotor shaft 14 and the gearbox 18 such that it has the smallest possible diameter at the friction surface.
[0032] The second contact ring 42 is mounted in a receptacle between the housing 12 and a mounting flange 48 of the planet carrier 46.
[0033] These two contact rings 42 form a series connection of contact rings 42, thereby providing a current path so that current can flow from the rotor shaft 14 via the planet carrier 46 to the housing 12. Reference symbol list 10 Electric motor 12 cases 14 Rotor shaft 16 warehouses 18 gearboxes 20 Impulse disc 22 shaft seals 24 Engine compartment 26 Channel 28 oil chambers 30 oil inlet nozzles 32 Oil inlet opening 34 Wave grounding ring 36 fibers 38 ring discs 40 basic shapes 42 Contact ring 44 Lubrication channel 46 planetary carriers 48 Mounting flange
Claims
[1] Electric motor, in particular for a vehicle drive, with a housing (12) and a rotor shaft (14) which is rotatably received in the housing (12) via bearings (16), wherein the housing (12) and the rotor shaft (14) are electrically connected to one another via a singular electrically conductive contact ring (42) for earthing the rotor shaft (14) [2] Electric motor according to claim 1, characterized by that the rotor shaft (14) is a hollow shaft and has an oil or coolant-carrying channel (26) in its interior and the housing (12) has an inlet nozzle (30) which projects into an inlet opening (32) of the channel (26), wherein the contact ring (42) is arranged between the rotor shaft (14) and the inlet nozzle (30). [3] Electric motor according to claim 2, characterized by that a receptacle for the contact ring (42) is formed in the rotor shaft (14) or in the inlet nozzle (30). [4] Electric motor according to claim 2 or 3, characterized bythat the contact ring (42) seals the oil or coolant-carrying channel (26) at an axial end region of the rotor shaft (14). [5] Electric motor, in particular according to one of the preceding claims, with a housing (12) and a rotor shaft (14) which is rotatably received in the housing (12) via bearings (16), wherein the housing (12) and the rotor shaft (14) are electrically connected to one another via a series connection of singular electrically conductive contact rings (42). [6] Electric motor according to claim 5, characterized by that a planetary gear (18) is coupled to the rotor shaft (14), wherein a first, singular contact ring (42) is arranged between the rotor shaft (14) and a planet carrier (46) and a second, singular contact ring (42) is arranged between the planet carrier (46) and the housing (12), so that current can flow from the rotor shaft (14) via the planet carrier (46) to the housing (12). [7] Electric motor according to one of the preceding claims, characterized by that the contact ring (42) is made of steel or grey cast iron. [8] Electric motor according to one of the preceding claims, characterized by that the contact ring (42) consists of an electrically conductive polymer. [9] Electric motor according to one of the preceding claims, characterized by that the contact ring (42) has a square cross-section. [10] Electric motor according to one of the preceding claims, characterized by that the contact ring (42) is held exclusively by a groove in the rotor shaft (14) or in the housing (12).