ELECTRIC MOTOR AND MOBILITY DEVICE COMPRISING SUCH AN ELECTRIC MOTOR

Abstract

This electric motor (100) comprises: - a stator (102); - a rotor (104); - an output shaft (112) designed to be driven by the rotor (104); and - at least one bearing (122, 126) for guiding the output shaft (112). It further comprises: - an enclosure (114, 140; 202) electrically connected to an electrical ground (GND); and - a conductive grease (142) enclosed in the enclosure (114, 140; 202), a portion (138) of the output shaft (112) extending into the enclosure (114, 140; 202) so that the conductive grease (142) is in contact with both the output shaft (112) and the enclosure (114, 140; 202). Figure for abstract: Fig. 1

Description

Title of the invention: ELECTRIC MOTOR AND MOBILITY DEVICE COMPRISING SUCH AN ELECTRIC MOTOR Technical field of the invention

[0001] The present invention relates to an electric motor and mobility device comprising such an electric motor.

[0002] A mobility device is, for example, a land motor vehicle, a train, an aircraft or a drone. A land motor vehicle is, for example, a motor vehicle, a motorcycle, a motorized bicycle or a motorized wheelchair. Technological background

[0003] An electric motor typically comprises: - a stator; - a rotor; - an output shaft designed to be driven by the rotor; and - at least one output shaft guide bearing.

[0004] A stray current may appear through the bearing, in particular when the motor is driven by an inverter providing pulse width modulation commands. Indeed, in this case, the inverter includes switches operating at high frequency. However, because of the switching time of the switches, the inverter commands are unbalanced, which generates a common mode voltage with a high frequency at the neutral of the stator windings of the motor. The stator windings, the rotor and the bearings have a capacitive behavior and provide a grounding path for the common mode voltage. At least part of the stray current therefore appears along this path.

[0005] Furthermore, the presence of an asymmetric magnetic flux in the motor can induce a non-zero voltage at the shaft, which further causes at least part of the parasitic current.

[0006] However, the stray current can damage the bearing, in particular by causing electrical discharge machining (EDM) of the bearing. For example, electroerosion can lead to surface melting and the appearance of pitting defects on the bearing parts. In addition, the stray current may reduce the surface hardness of the bearing parts. These combined effects can lead to the formation of frosting in the bearing. In the long term, the surface of the bearing parts may appear light and dark with wavy damage.

[0007] This electroerosion increases the temperature of the bearing and can generate debris degrading the performance of the bearing lubricating grease.

[0008] To avoid this parasitic current through the bearing, the patent application in France published under number FR 3 029 705 A1 describes the use of a brush connecting the rotor to the electrical ground in order to redirect the parasitic current by bypassing the bearing. A problem with this solution is that the brush rubs against the output shaft so that the contact between the two wears over time, which degrades the redirection.

[0009] It may thus be desirable to provide an electric motor which makes it possible to overcome at least some of the aforementioned problems and constraints. Summary of the invention

[0010] An electric motor is therefore proposed comprising: - a stator; - a rotor; - an output shaft designed to be driven by the rotor; and - at least one output shaft guide bearing; characterized in that it further comprises: - an enclosure electrically connected to an electrical ground (GND); and - a conductive grease enclosed in the enclosure, part of the shaft of output extending into the enclosure so that the conductive grease is in contact with both the output shaft and the enclosure.

[0011] Thus, thanks to the invention, a low resistance electrical path is created through the conductive grease and the enclosure, making it possible to redirect the stray current from the output shaft to the electrical ground by bypassing the bearing. Furthermore, thanks to the use of the conductive grease, the use of a part rubbing against the output shaft and therefore the corresponding problems are avoided.

[0012] The invention may further comprise one or more of the following optional features, in any technically possible combination.

[0013] Optionally, the electric motor further comprises a housing into which the stator, the rotor and a portion of the output shaft extend, the stator being fixed to the housing, and the enclosure being electrically connected to electrical ground through the housing.

[0014] Also optionally, the housing partly forms the enclosure.

[0015] Also optionally, the portion of the output shaft extending into the enclosure is one end of the output shaft.

[0016] Also optionally, the housing has an external face provided with a cavity and an opening opening into the cavity, the output shaft passing through the opening so that the end of the output shaft extends into the cavity, the electric motor further comprising a cover closing the cavity, the housing and the cover forming the enclosure in which the conductive grease is present.

[0017] Also optionally, the enclosure is located in an interior space delimited by the housing.

[0018] Also optionally, the enclosure is located outside the housing.

[0019] Also optionally, the enclosure has two openings through which the output shaft passes through the enclosure.

[0020] Also optionally, the conductive grease comprises grease and metallic particles, for example iron, added to this grease.

[0021] A mobility device comprising an electric motor according to the invention is also proposed. Brief description of the figures

[0022] The invention will be better understood with the aid of the following description, given solely by way of example and with reference to the appended drawings in which: - [Fig.l] is a cross-sectional view of an electric motor according to a first exemplary embodiment of the invention, and - [Fig.2] is a cross-sectional view of an electric motor according to a second exemplary embodiment of the invention. Detailed description of the invention

[0023] With reference to [Fig.l], an electric motor 100 according to a first exemplary embodiment of the invention will now be described.

[0024] The electric motor 100 comprises a stator 102 and a rotor 104 designed to rotate relative to the stator 102 about an axis of rotation A. The rotor 104 extends for example in the stator 102. For example, the stator 102 comprises stator windings and / or the rotor 104 comprises rotor windings.

[0025] The electric motor 100 further comprises, for example, an inverter 110 designed to control the stator windings of the stator 102 in order to operate the electric motor 100. For example, the inverter 110 is designed to provide pulse width modulation commands.

[0026] The electric motor 100 further comprises an output shaft 112 designed to be driven by the rotor 104. For example, as in the illustrated example, the output shaft 112 is fixed to the rotor 104 and extends along the axis of rotation A.

[0027] The electric motor 100 further comprises, for example, a housing 114 delimiting an interior space in which the stator 102 and the rotor 104 extend, the stator 102 being fixed to the housing 114. The housing 114 is at least partly electrically conductive and connected to an electrical ground GND. The electrical ground is, for example, transmitted to the housing via its connection to the chassis of the vehicle, itself connected to the electrical ground GND.

[0028] The housing 114 has for example an opening 116 through which the output shaft 112 passes to exit the housing 114. The output shaft 112 thus has a portion 118 extending outside the housing 114, to which a mechanical load 120 can be fixed in order to be driven by the output shaft 112. The mechanical load 120 can also be connected to the electrical ground GND.

[0029] The housing 114 is for example provided with a first bearing 122 housed in the opening 116 and interposed between the housing 114 and the output shaft 112 to guide the output shaft 112. The first bearing 122 comprises for example a rolling bearing, for example a ball bearing as in the example illustrated.

[0030] The housing 114 is furthermore, for example, provided with a bottom 124 located opposite the opening 116 along the axis of rotation A and provided with a second bearing 126 for receiving the output shaft 112. The second bearing 126 is, for example, housed in a recess 130 provided in the bottom 124. The second bearing 126 comprises, for example, a rolling bearing, for example a ball bearing as in the example illustrated.

[0031] For example, as in the example illustrated, the housing 114 has an external face 132 provided with a cavity 134 located on the axis of rotation A. The housing 114 also has a second opening 136 extending between the recess 130 and the cavity 134.

[0032] The output shaft 112 thus passes, after the second bearing 126, through this second opening 136, so that one end 138 of the output shaft 112 extends into the cavity 134. The electric motor 100 then comprises a cover 140 closing the cavity 134, in which a conductive grease 142 has previously been placed. Thus, the second end 138 of the output shaft 112 is in contact with the conductive grease 142 which itself is in contact with the housing 114 and / or the cover 140. The conductive grease 142 comprises, for example, grease to which metallic particles, for example iron or copper, or carbon have been added. This is, for example, a silicone-based grease.

[0033] Thus, the housing 114 and the cover 140 together form an enclosure electrically connected to the electrical ground GND and containing the conductive grease 142, a part of the output shaft 112 (its second end 138 in the present case) extending into the enclosure 114, 140 in order to be in contact with the conductive grease 142.

[0034] There is therefore an electrical conduction path (thick line arrows) connecting the output shaft 112 to the electrical ground GND, this electrical conduction path passing successively through: the second end 138 of the output shaft 112, the conductive grease 142, possibly the cover 140 (when the latter is electrically conductive), the housing 114, and the electrical ground GND.

[0035] To ensure the sealing of the enclosure 114, 140, the electric motor 100 preferably comprises a seal 144 extending between the output shaft 112 and the cover 140, and more particularly between the output shaft 112 and a sleeve of the cover 140 projecting into the cavity 134.

[0036] With reference to [Fig.2], an electric motor 200 according to a second exemplary embodiment of the invention will now be described.

[0037] The electric motor 200 is identical to the electric motor 100 of [Fig.l], except for the differences below.

[0038] In this second embodiment, the electric motor 200 comprises an enclosure 202 having two openings 204, 206 facing each other through which the output shaft 112 passes to cross the enclosure 202. As in the first embodiment, the conductive grease 142 fills the enclosure 202 in order to be in contact with the output shaft 112. Preferably, to ensure the sealing of the enclosure 202, a seal 208, 210 is provided in each opening 204, 206, this seal extending between the output shaft 112 and the enclosure 202. The enclosure 202 is connected to the electrical ground GND for example through the housing 114. Alternatively, the enclosure 202 could be connected to the electrical ground GND while avoiding the housing, for example, at least one electrical wire.

[0039] The enclosure 202 may be located within the housing 114, as illustrated in [Fig. 2], or outside the housing 114.

[0040] In conclusion, it appears clearly that an electric motor such as those described previously makes it possible to redirect the parasitic current, without requiring a part in contact with the output shaft and rubbing against the latter.

[0041] It will also be noted that the invention is not limited to the embodiments described above. It will indeed appear to those skilled in the art that various modifications can be made to the embodiments described above, in light of the teaching which has just been disclosed to them.

[0042] For example, the enclosure could be located outside the housing, i.e. outside the interior space delimited by the latter. For example, the enclosure could be located between the housing and the mechanical load driven by the output shaft.

[0043] In the detailed presentation of the invention which is made above, the terms used must not be interpreted as limiting the invention to the embodiments set out in the present description, but must be interpreted to include all equivalents whose prediction is within the reach of those skilled in the art by applying their general knowledge to the implementation of the teaching which has just been disclosed to them.

Claims

Claims

1. Electric motor (100; 200) comprising: - a stator (102); - a rotor (104); - an output shaft (112) designed to be driven by the rotor (104); and - at least one bearing (122, 126) for guiding the output shaft (112); characterized in that it further comprises: - an enclosure (114, 140; 202) electrically connected to an electrical ground (GND); and - a conductive grease (142) enclosed in the enclosure (114, 140; 202), a portion (138) of the output shaft (112) extending into the enclosure (114, 140; 202) so that the conductive grease (142) is in contact with both the output shaft (112) and the enclosure (114, 140; 202).

2. An electric motor (100; 200) according to claim 1, further comprising a housing (114) into which the stator (102), the rotor (104) and a portion of the output shaft (112) extend, the stator (102) being fixed to the housing (114), and wherein the enclosure (114, 140; 202) is electrically connected to electrical ground (GND) through the housing (114).

3. An electric motor (100) according to claim 2, wherein the housing (114) partly forms the enclosure (114, 140).

4. An electric motor (100) according to any one of claims 1 to 3, wherein the portion (138) of the output shaft (112) extending into the enclosure (114, 140) is one end (138) of the output shaft (112).

5. An electric motor (100) according to claims 3 and 4 taken together, wherein the housing (114) has an external face (132) provided with a cavity (134) and an opening (136) opening into the cavity (134), the output shaft (112) passing through the opening (136) so that the end (138) of the output shaft (112) extends into the cavity (134), further comprising a cover (140) closing the cavity (134), the housing (114) and the cover (140) forming the enclosure (114, 140) in which the conductive grease (142) is present.

6. An electric motor (200) according to claim 1 or 2, wherein the enclosure (202) is located in an interior space defined by the housing (114).

7. An electric motor according to claim 1 or 2, wherein the enclosure is located outside the housing.

8. An electric motor (200) according to claim 6 or 7, wherein the enclosure (202) has two openings (204, 206) through which the output shaft 112 passes to traverse the enclosure (202).

9. An electric motor (100; 200) according to any one of claims 1 to 8, wherein the conductive grease (142) comprises grease and metallic particles, for example iron, added to this grease.

10. Mobility device comprising an electric motor (100; 200) according to any one of claims 1 to 9.

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