Grounding of a rotor of an electric machine

Abstract

An electric machine (120) comprises a housing (225) and a rotor (205) which is rotatably mounted in the housing (225) about an axis of rotation (215). A recess (230) is provided in the housing (225) at an axial end of the rotor (205), in which a terminal element (235) is removably mounted. An earthing contact (280) is arranged axially between the terminal element (235) and the rotor (205).

Description

[0001] The present invention relates to the grounding of a rotor of an electrical machine. In particular, the invention relates to the grounding of a rotor of an electric drive motor for a motor vehicle.

[0002] A motor vehicle comprises an electric machine that can be operated with energy from an electrical energy storage device in order to drive the motor vehicle. The electric machine comprises a housing with a stator and a rotor. The rotor is mounted relative to the stator or the housing so as to be rotatable about an axis of rotation. To prevent an electrical potential difference from building up between the rotor and the housing, an earth contact can be provided. The earth contact comprises a first and a second side that are electrically connected to one another but separated from one another with regard to torque. The bearing is attached to the electric machine in such a way that one side is connected to the rotor and the other to the housing.

[0003] Various proposals have been made for attaching a grounding contact to an electrical machine. CN 214 506 818 U proposes a grounding contact attached to an axial end of a rotor of an electrical machine. The grounding contact comprises a rolling bearing between the rotor and the housing, which is axially preloaded by an elastic element.

[0004] However, it has been shown that rolling bearings are prone to corrosion when exposed to an electric current. It has therefore been proposed to use a grounding contact comprising two axially pressed-together elements arranged along the axis of rotation. However, such a bearing is subject to a certain degree of frictional wear, and it may be necessary to inspect one of the contact partners at predetermined intervals and replace it if necessary. Until now, this required opening the housing of the electrical machine to gain access to the grounding contact. Particularly when the electrical machine is housed in a common housing with other elements, servicing the grounding contact can be complex.

[0005] One object underlying the present invention is to provide an improved technique for grounding a rotor of an electrical machine. The invention achieves this object by means of the subject matter of the independent claims. Subclaims specify preferred embodiments.

[0006] According to a first aspect of the present invention, an electric machine comprises a housing and a rotor mounted in the housing for rotation about a rotational axis. A recess is provided in the housing at one axial end of the rotor, in which a termination element is removably mounted. A grounding contact is arranged axially between the termination element and the rotor.

[0007] Access to the grounding contact can be facilitated by removing the end cap from the housing. Opening the housing may not be necessary to service the grounding contact. In many applications, it may not be necessary to remove the housing with the electrical machine from a surrounding structure. Available space can be advantageously used to install the grounding contact. The end cap may protrude only slightly or not at all beyond the enclosure's perimeter.

[0008] The grounding contact can comprise a first and a second side that are electrically connected to one another but separated from one another with respect to torque. It is preferred that the first and the second side form an electrical abutment contact that does not comprise a rolling element. In particular, the first and the second side can be pressed axially against one another in order to establish electrical contact with as little friction as possible. One side can comprise a wear-resistant end plate and the other an electrical conductor that is designed as a wearing part. For example, a carbon pin can be used for this purpose. To compensate for axial mechanical wear, one of the sides can be pressed against the other by means of an axially acting elastic element.

[0009] Such a grounding contact can achieve improved electrical equipotential bonding between the rotor and the housing without risking electrical corrosion of a rolling bearing. Due to the improved maintainability of the grounding contact, its use can also be beneficial in highly loaded or continuously loaded electrical machines.

[0010] It is further preferred that the grounding contact is axially separable between the first and second sides. One of the two sides can be captively connected to the termination element. Separation can be achieved, in particular, without the use of tools. The first and second sides can be held together by contact, and one of the sides can be removed after the termination element has been removed from the housing. This side can be designed as a wear element so that it can be easily inspected or replaced. The other side of the grounding contact can remain in the housing.

[0011] It is further preferred that the closing element is held in the recess by means of a thread. The thread more preferably runs coaxially to the axis of rotation. An internal thread is preferably provided in the recess and an external thread on the closing element. In this way, the closing element can be securely held on the housing and easily removed if necessary. The thread allows axial surface pressure between an outer section of the closing element and the housing. In this area, for example, a flat gasket can be used to prevent a fluid contained in the housing from escaping. In another embodiment, an axial or radial annular groove can be provided on the closing element, into which an O-ring can be inserted, which seals the closing element against the housing.

[0012] Further preferably, an axial connecting element is provided between the end element and the grounding contact. The grounding bearing can thus be arranged at a greater axial distance from the housing. This can be electrically or mechanically more advantageous, and the connecting element can be used for another purpose, in particular for guiding a fluid in the axial direction, as described in more detail herein.

[0013] The connecting element is preferably attached to the end element with a clearance fit. In a preferred embodiment, the connecting element is removably attached to the end element. More preferably, the connecting element is held non-rotatably on the end element. A rotational position can be determined by positive locking. A torque transmitted via the grounding contact despite the decoupling can thus be supported against the end element or the housing. For example, a radial projection can be formed on the connecting element and a radial receptacle for the projection can be formed on the end element. This connection can allow axial play between the connecting element and the end element.

[0014] More preferably, the connecting element comprises an axial bore, wherein the closing element comprises a fluid channel through which a fluid can enter in the radial direction and exit in the axial direction of the bore. A fluid line through which fluid can flow towards a radial end of the fluid channel can be provided on the housing. The fluid line can be attached to the housing or formed in a housing component. An annular channel can be provided between the fluid line and the fluid channel in order to compensate for a rotational orientation of the closing element relative to the housing. The fluid can be provided for cooling and / or lubricating the electrical machine. The fluid preferably comprises a liquid, in particular oil.

[0015] The rotor of the electric machine preferably comprises a coaxial bore into which the connecting element extends. The connecting element can have at least one radial recess for radially discharging fluid from the bore to the rotor. The rotor can thus be supplied with fluid at any axial location for lubrication or cooling. Fluid escaping from the radial recess can flow away in the axial direction in a region between the connecting element and the rotor.

[0016] The flow of fluid after it exits the connecting element can increase with the rotor's speed. A fluid barrier can be provided between the connecting element and the rotor to reduce the flow of fluid toward the closure element. The fluid barrier is preferably located between the closure element and a radial recess. This can promote the flow of fluid toward the grounding contact.

[0017] In a further embodiment, an elastic element is provided to exert an axial force between the end element and the connecting element. The elastic element can comprise, for example, a wave spring. The connecting element can be accommodated in a rolling bearing in the area of ​​the grounding contact to support it radially. The rolling bearing can be axially preloaded by means of the elastic element to ensure favorable support.

[0018] According to a further aspect of the present invention, a grounding device for an electrical machine is provided. The electrical machine comprises a housing and a rotor mounted in the housing for rotation about a rotational axis. The housing has a recess at one axial end of the rotor. The grounding device comprises a terminal element configured to be removably mounted in the recess and a grounding contact mounted axially between the terminal element and the rotor.

[0019] An electric drive axle comprises an electric machine as described herein. Furthermore, the electric drive axle may comprise a transmission. In one embodiment, the drive axle is configured to be connected to another drive machine, in particular an internal combustion engine. Torques from the electric machine or the other drive machine can be provided at an output shaft.

[0020] According to yet another aspect of the present invention, a motor vehicle comprises an electric drive axle as described herein.

[0021] The invention will now be described in more detail with reference to the accompanying figures, in which: Fig. 1 an electrically powered motor vehicle; Fig. 2 an earthing device on an electrical machine; and Fig. 3 shows an earthing device from a further perspective.

[0022] Fig. 1 shows a motor vehicle 100 with an electric drive 105. The electric drive 105 comprises an electric drive axle 110, which acts on a drive wheel 115 of the motor vehicle 100. The drive axle 110 comprises an electric machine 120, which can be operated using electrical energy from an energy storage device 125. A current converter 130 is provided to convert a direct voltage, typically provided by the energy storage device 125, into one or more alternating voltages.

[0023] Fig. 2 shows a grounding device 200 on an electrical machine 120. The electrical machine 120 comprises a rotor 205 and a stator 210, which are mounted rotatably relative to each other with respect to a rotational axis 215. Only a rotor shaft 220 is connected to the rotor 205 in Fig. 2. The stator 210 is mounted in a rotationally fixed manner relative to a housing 225 and in Fig. 2 not visible.

[0024] A recess 230 is provided on the housing 225 coaxially to the axis of rotation 215. A closure element 235 is arranged in the recess 230. Preferably, the recess 230 is round and has an internal thread; the closure element 235 has a corresponding external thread. A seal 240 can be provided between the closure element 235 and the housing 225. In the illustrated embodiment, a contact surface perpendicular to the axis of rotation 215 is formed on an outer side of the housing 225, wherein the closure element 235 has a collar that projects beyond the contact surface. An axial groove extending around the axis of rotation 215 is formed in the collar, into which an O-ring can be inserted as a seal 240.

[0025] An axial end of a connecting element 245 is received in the closure element 235. The connecting element 245 is preferably hollow and comprises an axial bore 250. More preferably, the connecting element 245 is designed in the manner of a tube. The closure element 235 comprises a fluid channel 255, which preferably enters radially into the closure element 235 and exits axially in the direction of the connecting element 245. A fluid line 260 can be provided in or on the housing 225, through which, for example, a flow of oil can be effected towards the closure element 235 during operation of the electric machine 120. The oil can flow from the fluid line 260 through the fluid channel 255 and into the bore 250 of the connecting element 245. The fluid can exit at an end of the connecting element 245 remote from the closure element 235.

[0026] A radial recess 265 may be provided on the connecting element 245, through which fluid can enter a space radially between the connecting element 245 and the rotor shaft 220. To control the flow of fluid from this space and, in particular, to promote axial outflow toward the grounding contact 280, a fluid barrier 270 may be provided in an axial region between the recess 265 and the closure element 235. The fluid can cool the rotor shaft 220 radially from the inside.

[0027] To torque-lock the connecting element 245 to the closure element 235, the connecting element 245 can have a radial projection 275 that engages in a corresponding recess on the closure element 235. Furthermore, an elastic element 278 can be provided, which acts axially between the connecting element 245 and the closure element 235. In the illustrated embodiment, the elastic element 278 is supported axially on the projection 275 on the connecting element 245. In the present case, the elastic element 278 is formed from one or more wave springs that encircle the connecting element 245.

[0028] At an axial end remote from the closure element 235, the connecting element 245 carries a grounding contact 280 having a first side 285 and a second side 290. The second side 290 is electrically and mechanically formed on the rotor 205 or connected thereto. The second side 290 is preferably made of a wear-resistant material such as steel. The first side 285 is further preferably designed as a wearing part, in particular in the form of an electric brush with a carbon pin that is electrically connected to the connecting element 245 by means of a flexible stranded wire. The carbon pin can be pressed against the first side 285 by means of a coaxial elastic element, here for example in the form of a cylindrical spring. Fluid accommodated in a space between the hollow rotor shaft and the connecting element 245 can flow to a predetermined extent through the grounding contact 280, thus reducing wear.A typically significantly larger portion of the fluid flow can exit axially and be spun off the rotor 215. Alternatively, the fluid can be collected in a fluid channel that can direct the fluid to a cooling or lubrication point, for example, a bearing of the rotor shaft 220 opposite the stator 210 or the housing 225.

[0029] Further preferably, a roller bearing 295 is provided in this area to radially support the first side 285 of the grounding contact 280 or an end of the connecting element 245 remote from the end element 235. The roller bearing 295 can be axially preloaded by means of the elastic element 278 in the area of ​​the end element 235. This allows the roller bearing 295 to be operated in an O-arrangement, which is advantageous for position control of the connecting element 245. The elasticity of the element 278 can compensate for a thermally induced change in length of the connecting element 245.

[0030] If the end element 235 is removed from the recess 230 of the housing 225, the connecting element 245 can be removed together with the first side 285 of the grounding contact 280. The grounding contact 280 can be easily inspected or replaced in this way. For this purpose, in particular, the wearing part of the first side 285 can be replaced. The first side 285, together with the connecting element 245, can then be inserted through the recess 230 in the housing 225 and secured thereto by means of the end element 235.

[0031] The illustrated grounding device 200 can fulfill a mechanical, electrical, and / or hydraulic requirement in an improved manner. Advantageously, the grounding device 200 can facilitate inspection or maintenance and, in particular, enable the replacement of a grounding contact without dismantling a housing 225.

[0032] Fig. 3 shows a grounding device 200 of the type of Fig. 2 from a different perspective. The rotation axis 215 is tilted relative to the plane of the drawing. At its right end, the rotation axis 215 runs toward the viewer.

[0033] It can be seen that an annular channel 305 is formed between the fluid line 260 and the fluid channel 255. The fluid line 260 is presently part of the housing 225, but can also be designed as a separate element. The fluid line 260 ends in the annular channel 305, and an inlet of the fluid channel 255 begins there. The annular channel 305 allows the closure element 225 to be oriented in any desired direction around the rotation axis 215 to enable fluid passage from the fluid line 260 into the fluid channel 255.

[0034] The illustrated portion of the housing 225 may, for example, comprise a housing cover, which may, for example, be made of light metal casting.

[0035] In a right-hand section of the illustration, the rotor shaft 220 has a toothing 310 for engagement with a gear of a transmission. The toothing 310 is preferably designed as a helical toothing and can act on a drive gear 115 via the transmission. Reference symbol 100 motor vehicles 105 electric drive 110 electric drive axle 115 drive wheel 120 electric machine 125 energy storage units 130 current transformers 200 Earthing device 205 Rotor 210 Stator 215 axis of rotation 220 rotor shaft 225 housings 230 recess 235 End element 240 Seal 245 connecting element 250 bore 255 Fluid channel 260 Fluid line 265 recess 270 Fluid barrier 275 lead 278 elastic element 280 Earthing contact 285 first page 290 second page 295 rolling bearings 305 Ring Canal 310 Gearing QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] CN 214 506 818 U

[0003]

Claims

[1] An electric machine (120) comprising a housing (225) and a rotor (205) which is mounted in the housing (225) so as to be rotatable about a rotational axis (215); wherein the housing (225) has a recess (230) at an axial end of the rotor (205); further comprising - a closure element (235) removably mounted in the recess (230); and - an earthing contact (280) arranged axially between the end element (235) and the rotor (205). [2] The machine (120) of claim 1, wherein the ground contact (280) comprises a first (285) and a second side (290) that are electrically connected to each other but separated from each other with respect to torque. [3] The machine (120) of claim 2, wherein the ground contact (280) is axially separable between the first (285) and second sides (290). [4] Machine (120) according to one of the preceding claims, wherein the closure element (235) is held in the recess (230) by means of a thread. [5] Machine (120) according to one of the preceding claims, further comprising an axial connecting element (245) between the terminating element (235) and the grounding contact (280). [6] Machine (120) according to claim 5, wherein the connecting element (245) is non-rotatably attached to the end element (235). [7] Machine (120) according to one of claims 5 or 6, wherein the connecting element (245) has an axial bore (250); and the closing element (235) comprises a fluid channel (255) through which a fluid can enter in the radial direction and exit in the axial direction of the bore. [8] The machine (120) of claim 7, wherein the rotor (205) has a coaxial bore into which the connecting member (245) extends; wherein the connecting member (245) has at least one radial recess (265) for radially discharging fluid from the bore (250). [9] Machine (120) according to claim 8, wherein a fluid barrier (270) is provided between the connecting element (245) and the rotor (205) to reduce a flow of fluid towards the closure element (235). [10] Machine (120) according to one of claims 5 to 9, wherein an elastic element (278) is provided to cause an axial force between the closure element (235) and the connecting element (245). [11] Grounding device (200) for an electrical machine (120) having a housing (225) and a rotor (205) which is mounted in the housing (225) so as to be rotatable about a rotational axis (215); wherein the housing (225) has a recess (230) at an axial end of the rotor (205); wherein the grounding device (200) comprises the following elements: - a closure element (235) adapted to be removably mounted in the recess (230); and - an earthing contact (280) mounted axially between the end element (235) and the rotor (205). [12] Electric drive axle (110) comprising an electric machine (120) according to one of claims 1 to 10. [13] Motor vehicle (100) comprising an electric drive axle (110) according to claim 12.

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