Electric motor

Abstract

Electric motor (300) comprising: an annular stator core (1); a plurality of coils (2) arranged in a circumferential direction of the stator core (1); a tubular cover (3a) arranged at an end face in an axial direction of the stator core to surround coil ends of the coils (2) projecting from the end face in the axial direction of the stator core; a tubular housing (10) arranged outside the stator core (1) and outside the tubular cover (3a);and a thermally conductive resin section (4) arranged between each of the coil ends of the coils (2) and the cover (3a), the cover (3a) comprising: a first inner circumferential section (3a3) having on one side close to a first end face (3a1) facing the stator core (1) and having a first inner diameter; a second inner circumferential section (3a4) having on one side close to a second end face (3a2) opposite the first end face (3a1) and having a second inner diameter larger than the first inner diameter; and a stepped section (3a5) provided in a boundary section between the first inner circumferential section (3a3) and the second inner circumferential section (3a4), and wherein the cover (3a) has a linear expansion coefficient smaller than a linear expansion coefficient of the thermally conductive resin section (4).

Description

AreaThe present invention relates to an electric motor including a stator and a rotor mounted inside the stator.BackgroundIn recent years, demand for higher output and higher torque for industrial electric motors has increased to cope with reduction of cycle times in machining processes. In connection with the increase in power and torque of the electric motor, heat generated in a coil disposed in the stator becomes large. Therefore, it is necessary to efficiently dissipate the heat generated in the coil to the outside of the electric motor.Patent Literature 1 discloses a configuration of an electric motor that efficiently dissipates the heat generated in a coil to the outside of the electric motor. A stator of the electric motor disclosed in Patent Literature 1 includes an annular stator core, a plurality of coils spaced apart from each other in a circumferential direction of the stator core, a tubular cover surrounding coil ends of the respective coils, a heat conductive resin filled between the coil ends and the cover, and a housing disposed outside the stator core and the cover in a circumferential direction.The electric motor disclosed in Patent Literature 1 uses the heat conductive resin as a transmission member. Heat generated in the coil ends is transferred to the heat conductive resin portion, the cover, and the housing in this order, or is transferred to the heat conductive resin portion, the cover, the stator core, and the housing in this order. The heat transferred to the housing is dissipated to the environment.Patent Literature 2 discloses ring-shaped covers and heat conductive resin portions whose linear expansion coefficients are close to each other. Patent Literature 3 discloses, for a material of a heat conductive resin portion, a linear expansion coefficient slightly larger than that of a housing of an electric motor.Patent Literature 4 discloses other findings of a person skilled in the art.Citing listPatent LiteraturePatent Literature 1: JP 2010-68 699 APatent Literature 2: German Patent Application DE 10 2013 020 066 A1.Patent Literature 3: U.S. Patent Application US 2006 / 0 138 876 A1.Patent Literature 4: German Patent Application DE 10 2007 014 691 A1OverviewTechnical ProblemIn the electric motor disclosed in Patent Literature 1, during operation of the electric motor, the cover moves in an axial direction due to a difference in a linear expansion coefficient of the thermally conductive resin and the cover.Patent Literature 1 fails to disclose measures that prevent the movement of the cover. Therefore, due to the axial movement of the cover, a contact area between the heat conductive resin and the cover is reduced, and a gap is formed between the cover and an end surface of the stator core. Therefore, the amount of heat transferred from the heat conductive resin to the cover is reduced, and the amount of heat transferred from the cover to the stator core is also reduced. Therefore, the heat releasing performance is reduced.The present invention has been made in view of the above-described problems, and an object of the present invention is to provide an electric motor that suppresses the lowering of the heat dissipation performance.Solution of the ProblemIn order to solve the above-described problems and achieve the object, an electric motor is proposed having the features of the appended claim 1. Advantageous embodiments are specified in the dependent claims.Advantageous Effects of the InventionThe electric motor according to the present invention has an effect whereby it is possible to suppress the lowering of the heat releasing performance.Brief Description of the DrawingsFIG. 1 is a vertical cross-sectional view of an electric motor according to a first embodiment of the present invention. FIG. 2 is a vertical cross-sectional view of a stator of the electric motor according to the first embodiment of the present invention. FIG. 3 is a cross-sectional view taken in an arrow direction along a line III-III in FIG. 2. FIG. 4 is a cross-sectional view taken in an arrow direction along a line IV-IV in FIG. 2. FIG. 5 is a cross-sectional view taken in an arrow direction along a line V-V in FIG. 2. FIG. 6 is an enlarged view of one end side of the stator illustrated in FIG. 2. FIG. 7 is a perspective view of a cover illustrated in FIG. 6. FIG. 8 is a cross-sectional view of a stator of an electric motor according to a second embodiment of the present invention. FIG. 9 is a cross-sectional view taken in an arrow direction along a line IX-IX in FIG. 8. FIG. 10 is a cross-sectional view taken in an arrow direction along a line X-X in FIG. 8. FIG. 11 is a cross-sectional view taken in an arrow direction along a line XI-XI in FIG. 8. FIG. 12 is an enlarged view of one end side of the stator illustrated in FIG. 8. FIG. 13 is a cross-sectional view of a stator of an electric motor according to a third embodiment of the present invention. FIG. 14 is a cross-sectional view taken in an arrow direction along a line XIV-XIV in FIG. 13. FIG. 15 is a cross-sectional view taken along a line XV-XV in FIG. 13. FIG. 16 is a cross-sectional view taken in an arrow direction along a line XVI-XVI in FIG. 13. FIG. 17 is an enlarged view of one end side of the stator illustrated in FIG. 13.DESCRIPTION OF EMBODIMENTSAn electric motor according to embodiments of the present invention will be described below in detail with reference to the accompanying drawings. The present invention is not limited to the embodiments.First Embodiment.FIG. 1 is a vertical cross-sectional view of an electric motor according to a first embodiment of the present invention. FIG. 2 is a vertical cross-sectional view of a stator of the electric motor according to the first embodiment of the present invention. FIG. 3 is an arrow-directional cross-sectional view taken along a line III-III in FIG. 2, FIG. 4 is an arrow-directional cross-sectional view taken along a line IV-IV in FIG. 2, FIG. 5 is an arrow-directional cross-sectional view taken along a line V-V in FIG. 2, FIGS. 2 and 3 omit the illustration of a rotor 200 illustrated in FIG. 1. FIG. 6 is an enlarged view of one end side of the stator illustrated in FIG. 2. FIG. 7 is a perspective view of a cover illustrated in FIG. 6.A configuration of an electric motor 300 according to the first embodiment will be described below with reference to FIGS. 1 to 7.The electric motor 300 includes a stator 100, the rotor 200 disposed inside a stator core 1 constituting the stator 100, and a tubular housing 10 disposed outside the stator core 1 in a radial direction.The stator core 1 is formed by stacking a plurality of thin annular plates stamped from electromagnetic sheets. The stator core 1 has a cavity 11 therein.The stator core 1 has a plurality of slots 12 arranged in a circumferential direction as illustrated in FIG. 3. A coil 2 is disposed in each of the slots 12.A resin portion 4, which is a heat conductive resin portion, is provided between the coil 2 disposed in each of the slots 12 and an inner circumferential surface of the respective slot 12. The material for the resin portion is epoxy resin or unsaturated polyester resin. The resin portion 4 is the above-described cured material filled in each of the cuts 12.A coil end 2 aprotrudes at an end of each of the coils 2 from an end surface 1 aof the stator core 1 in an axial direction. The axial direction is a direction in which a line C of a central rotation axis extends.A tubular cover 3 athat surrounds the coil ends 2 ais disposed on the one end surface 1 aof the stator core 1.The cover 3 ais made of a material having a linear expansion coefficient smaller than a linear expansion coefficient of the resin portion 4.The material for the cover 3a is an aluminum alloy, a corrosion-resistant austenitic alloy, a copper alloy, cast iron, steel or an iron alloy.As the aluminum alloy for the material of the cover 3 a, A6063 used for extrusion and A5056 used for bars can be used.As the corrosion-resistant austenitic alloy for the material of the cover 3a, SUS303 or SUS304 may be used.As the copper alloy for the material of the cover 3a, chromium copper or beryllium copper may be used.As the cast iron for the material of the cover 3 a, gray cast iron such as FC200 or spheroidal graphite iron cast iron such as FCD400 may be used.As the steel for the material of the cover 3 a, carbon steel such as SC 450 and a mechanical structural carbon steel pipe such as STKM may be used.As the iron alloy for the material of the cover 3 a, chromium-molybdenum steel such as SCM may be used.The cover 3 ais attached to the one end surface 1 aof the stator core 1.In the first embodiment, a notch is formed in advance on the one end surface 1 aof the stator core 1, and a protrusion is formed on an end surface of the cover 3 a. The cover 3 ais attached to the stator core 1 by fitting the protrusion of the cover 3 ainto the notch of the stator core 1. The cover 3 afixed to the one end surface 1 aof the stator core 1 is manufactured such that the outer diameter of the cover 3 ais equal to the outer diameter of the stator core 1.A resin portion 4 awhich is a heat conductive resin portion covering each of the coil ends 2 ais formed on the one end side of the stator core 1. The material for the resin portion 4a is unsaturated polyester resin. The resin portion 4a is cured unsaturated polyester resin filled between the coil end 2a and the cover 3a.The resin portion 4 ais formed outside the coil end 2 ain a radial direction between the coil end 2 aand the cover 3 a. Also, the resin portion 4 ais formed inside the coil end 2 ain the radial direction. Further, the resin portion 4 ais formed on a tip side of the coil end 2 ain the axial direction.The resin portion 4 ais in close contact with the entire outer circumferential surface of each of the coil ends 2 aand is also in close contact with the entire inner circumferential surface of the cover 3 a. A surface of the resin portion 4 aon the stator core 1 side is in contact with the one end surface 1 aof the stator core 1.A coil end 2 bat the other end of each of the coils 2 protrudes from the other end surface 1 bof the stator core 1 in the axial direction.A tubular cover 3 bsurrounding the coil ends 2 bis disposed on the other end surface 1 bof the stator core 1.The cover 3 b, which is made of an identical material to the cover 3 a, is attached to the other end surface 1 bof the stator core 1.In the first embodiment, a notch is formed in advance on the other end surface 1 bof the stator core 1, and a protrusion is formed on one end surface of the cover 3 b. The cover 3 bis attached to the stator core 1 by fitting the protrusion of the cover 3 bto the notch of the stator core 1. The cover 3 bmounted on the other end surface 1 bof the stator core 1 is made such that the outer diameter of the cover 3 bis equal to the outer diameter of the stator core 1.A resin portion 4 b, which is a heat conductive resin portion covering each of the coil ends 2 b, is formed on the other end side of the stator core 1. The material for the resin portion 4 bis unsaturated polyester resin. The resin portion 4 bis cured unsaturated polyester resin filled between the coil end 2 band the cover 3 b.The resin portion 4 bis formed outside the coil end 2 bin the radial direction between the coil end 2 band the cover 3 b. Also, the resin portion 4 bis formed inside the coil end 2 bin the radial direction. Further, the resin portion 4 bis formed on a tip side of the coil end 2 bin the axial direction.The resin portion 4 bis in close contact with the entire outer circumferential surface of each of the coil ends 2 band is also in close contact with the entire inner circumferential surface of the cover 3 b. One surface of the resin portion 4 bon the stator core 1 side is in contact with the other end surface 1 bof the stator core 1.The coil 2 has undergone an insulation process and is connected to a lead wire 20. Power is supplied to the coil 2 via the lead wire 20.The rotor 200 includes a rotor core 5 formed by stacking a plurality of thin annular plates stamped from electromagnetic sheets, and an aluminum conductor 6 annularly disposed in a cut of the rotor core 5 and on a tip side of the rotor core 5 in the axial direction.The rotor 200 is disposed in the cavity 11 of the stator core 1 coaxially with an axial center of the stator core 1.The tubular housing 10 is disposed outside each of the two covers 3 aand 3 bin the radial direction, and is also disposed outside the stator core 1 in the radial direction.The inner diameter of the housing 10 is equal to the outer diameter of the stator core 1. the outer diameter of each of the covers 3 aand 3 bis equal to the inner diameter of the housing 10.The stator core 1 is disposed inside the housing 10 by a shrink fit or an expansion fit.A configuration of the cover 3 ais specifically described below.In FIGS. 6 and 7, the cover 3 aincludes a first inner peripheral portion 3 a 3 provided on a side near a first end surface 3 a 1 facing the stator core 1, and has a first inner diameter and a second inner peripheral portion 3 a 4 provided on a side near a second end surface 3 a 2 opposite to the first end surface 3 a 1 and has a second inner diameter larger than the first inner diameter.The cover 3 aalso includes a stepped portion 3 a 5 provided in a boundary portion between the first inner peripheral portion 3 a 3 and the second inner peripheral portion 3 a 4. In the first embodiment, one surface of the stepped portion 3 a 5 is formed as a flat surface that is parallel to the one end surface 1 aof the stator core 1.The cover 3b shown in Fig. 1 is configured similarly to the cover 3a.A heat transfer path during operation of the electric motor 300 will be described below.Heat generated at the coil end 2 aduring operation of the electric motor 300 is released to the resin portion 4 a. The heat given to the resin portion 4a is given to the cover 3a.A portion of the heat that has been dissipated to the cover 3 ais dissipated to the stator core 1 via a contact surface between the cover 3 aand the stator core 1. The heat that has been dissipated to the stator core 1 is transferred to the housing 10 via an outer circumferential surface of the stator core 1 and released from the surface of the housing 10.Also, a portion of the heat that has been dissipated to the cover 3 ais dissipated to the housing 10 via a contact surface between the cover 3 aand the housing 10. The heat emitted to the housing 10 is released from the surface of the housing 10.During the operation of the electric motor 300, both the cover 3 aand the resin portion 4 aexpand due to the heat generated at the coil end 2 a.Since the cover 3 aand the resin portion 4 adiffer in linear expansion coefficient, thermal expansion difference occurs between the cover 3 aand the resin portion 4 a. The resin portion 4a expands more than the cover 3a. Therefore, a force acts on the cover 3a which is in close contact with the resin portion 4a to move the cover 3a in the direction opposite to the stator core 1.According to the electric motor 300 of the first embodiment, the movement of the cover 3 ais restricted by the stepped portion 3 a 5 even if this difference in thermal expansion arises. That is, because the resin portion 4 ais present at a position opposite to the stepped portion 3 a 5, the axial movement of the cover 3 ais restricted.Therefore, it is possible to suppress the decrease in the contact area between the resin portion 4 aand the cover 3 a. Also, it is possible to suppress generation of a gap between the first end surface 3 a 1 of the cover 3 aand the one end surface 1 aof the stator core 1.Therefore, a reduction in the amount of heat transferred from the resin portion 4 ato the cover 3 ais suppressed. Further, a reduction in the amount of heat transferred from the cover 3 ato the stator core 1 is suppressed. Consequently, a reduction in output can be suppressed.The cover 3 bshown in FIGS. 1 and 2 can be configured in the same manner as the cover 3 a. With this configuration, the axial movement of the cover 3 bis restricted, so that the quality of the stator 100 can be further improved compared to the case where the stepped portion 3 a 5 is provided only in the cover 3 a.In the first embodiment, the stepped portion 3 a 5 is formed as a flat surface that is parallel to the one end surface 1 aof the stator core 1. Alternatively, the surface of the stepped portion 3 a 5 may be inclined with respect to the one end surface 1 aof the stator core 1. In any case, it is possible to achieve an effect of ensuring engagement between the cover 3 aand the resin portion 4 a, as compared with the inclined surface, when the surface of the stepped portion is formed as a flat surface that is parallel to the one end surface 1 aof the stator core 1.Second EmbodimentFIG. 8 is a cross-sectional view of a stator of an electric motor according to a second embodiment of the present invention. FIG. 9 is an arrow-directional cross-sectional view taken along a line IX-IX in FIG. 8, FIG. 10 is an arrow-directional cross-sectional view taken along a line X-X in FIG. 8, FIG. 11 is an arrow-directional cross-sectional view taken along a line XI-XI in FIG. 8, FIG. 12 is an enlarged view of an end side of the stator illustrated in FIG. 8.A stator 100- 1 of the second embodiment includes covers 3 a- 1 and 3 b- 1 instead of the covers 3 aand 3 bof the first embodiment. In the following descriptions, elements corresponding to those of the first embodiment are denoted by the corresponding reference numerals and their description is omitted, and only different elements will be described. Since the cover 3 a- 1 and the cover 3 b- 1 are configured in the same manner, a configuration of the cover 3 a- 1 will be described below, and a description of the cover 3 b- 1 will be omitted.The cover 3 a- 1 includes the first inner peripheral portion 3 a 3, the second inner peripheral portion 3 a 4, and the stepped portion 3 a 5, similarly to the cover 3 aof the first embodiment.The cover 3 a- 1 further includes a protrusion 7. the protrusion 7 is disposed between the stepped portion 3 a 5 and the second inner peripheral portion 3 a 4 and protrudes inward from the second inner peripheral portion 3 a 4 in the radial direction of the cover 3 a- 1. The number of the protrusions 7 may be one or more.FIG. 11 shows a configuration example of the cover 3 a- 1 including four protrusions 7. The four protrusions 7 are spaced apart from each other in the circumferential direction of the stator core 1, and project inward from the second inner peripheral portion 3 a 4 in the radial direction of the cover 3 a- 1.In this configuration of the cover 3 a- 1, the resin portion 4 abeing filled inside the cover 3 a- 1 is in close contact with the first inner peripheral portion 3 a 3, the second inner peripheral portion 3 a 4, the stepped portion 3 a 5, and the protrusion 7 of the cover 3 a- 1.Axial movement of the cover 3 a- 1 is restricted by the resin portion 4 athat is in close contact with the stepped portion 3 a 5 and the protrusion 7.Further, rotation of the cover 3 a- 1 in the circumferential direction caused by vibration generated in operation of the electric motor 300 is prevented by the protrusion 7.By providing two or more protrusions 7, it is possible to more certainly prevent rotation of the cover 3 a- 1 in the circumferential direction, as compared with the case of providing one protrusion.The cover 3 b- 1 shown in FIGS. 8 and 9 can be configured in the same manner as the cover 3 a- 1 of the second embodiment. With this configuration, axial movement of the cover 3 b- 1 is restricted, and rotation of the cover 3 b- 1 in the circumferential direction is prevented. Therefore, the quality of the stator 100- 1 can be further improved compared to the case where the stepped portion 3 a 5 and the protrusion 7 are provided only in the cover 3 a- 1.Third EmbodimentFIG. 13 is a cross-sectional view of a stator of an electric motor according to a third embodiment of the present invention. FIG. 14 is an arrow-directional cross-sectional view taken along a line XIV-XIV in FIG. 13, FIG. 15 is an arrow-directional cross-sectional view taken along a line XV-XV in FIG. 13, FIG. 16 is an arrow-directional cross-sectional view taken along a line XVI-XVI in FIG. 13, FIG. 17 is an enlarged view of one end side of the stator illustrated in FIG. 13.A stator 100- 2 of the third embodiment includes a cover 3 a- 2, 3 b- 2 instead of the cover 3 a, 3 bof the first embodiment. In the following descriptions, elements corresponding to those of the first embodiment are denoted by the corresponding reference numerals and their description is omitted, and only different elements will be described. Since the cover 3 a- 2 and a cover 3 b- 2 are configured in the same manner, a configuration of the cover 3 a- 2 will be described below, and a description of the cover 3 b- 2 will be omitted.The cover 3 a- 2 includes the first inner peripheral portion 3 a 3, the second inner peripheral portion 3 a 4, and the stepped portion 3 a 5, similarly to the cover 3 aof the first embodiment.The cover 3 a- 2 further includes a protrusion 8, and the protrusion 8 is disposed on the second inner peripheral portion 3 a 4 and protrudes inward from the second inner peripheral portion 3 a 4 in the radial direction of the cover 3 a- 2. The number of the protrusions 7 may be one or more.FIGS. 16 and 17 show a configuration example of the cover 3 a- 2 including four protrusions 8. The four protrusions 8 are spaced apart from each other in the circumferential direction of the stator core 1, and project inward from the second inner peripheral portion 3 a 4 in the radial direction of the cover 3 a- 2.In this configuration of the cover 3 a- 2, the resin portion 4 abeing filled inside the cover 3 a- 2 is in close contact with the first inner peripheral portion 3 a 3, the second inner peripheral portion 3 a 4, the stepped portion 3 a 5, and the protrusion 8 of the cover 3 a- 2.Axial movement of the cover 3a-2 is restricted by the resin portion 4a which is in close contact with the stepped portion 3a5 and the protrusion 8.Further, rotation of the cover 3 a- 2 in the circumferential direction caused by vibration generated in operation of the electric motor 300 is prevented by the protrusion 8.By providing two or more protrusions 8, as compared with the case of providing one protrusion, it is possible to more certainly prevent rotation of the cover 3 a- 2 in the circumferential direction.However, there are the following problems in the case where an annular region continuous in the circumferential direction is provided on the second inner peripheral portion 3 a 4 instead of the protrusions 8.(1) An annular groove is formed between the annular region and the stepped portion 3a5. When the resin portion 4 ais filled in the groove, shear stress occurs on the resin portion filled in the groove due to a difference in thermal expansion between the cover 3 a- 2 and the resin portion 4 agenerated during operation of the electric motor 300. This shear stress causes a crack in the resin portion 4 a.(2) When the crack is generated, it is difficult to transfer heat in the resin portion 4 a, causing a reduction in output.(3) When the crack is generated, a portion of the resin portion 4 ais broken and falls into the electric motor 300, which may result in a problem in operation.Because the protrusion 8 is provided in the stator 100- 2 of the third embodiment, axial movement of the resin portion 4 athat expands upon operation of the electric motor 300 is not limited and can expand toward the second end surface 3 a 2 of the cover 3 a- 2. Thereby, the shear stress caused by the difference in thermal expansion is reduced and no crack is generated in the resin portion 4 a. Consequently, the quality of the electric motor 300 is improved.The cover 3 b- 2 shown in FIGS. 13 and 14 can be configured in the same manner as the cover 3 a- 2 of the third embodiment. With this configuration, the axial movement of the cover 3 b- 2 is restricted, and rotation of the cover 3 b- 2 in the circumferential direction is prevented. Therefore, the quality of the stator 100 can be further improved compared to the case where the stepped portion 3 a 5 and the protrusion 8 are provided only in the cover 3 a- 2.The stator core of the first to third embodiments is not limited to a stator core formed by stacking a plurality of electromagnetic plates. The stator core may be an integrated core obtained by machining a steel material into a cylindrical shape, a resin core obtained by hardening a mixture of resin and iron powder, or a dust core obtained by compression molding magnetic powder. The type of core is selected depending on the purpose and intended use.The rotor 200 according to the first to third embodiments may be a rotor for an induction motor or a rotor for a synchronous motor.The shapes of the protrusions 7 and 8 of the second and third embodiments are not limited to those shown in the drawings. The protrusions 7 and 8 may have any shapes as long as they protrude inward from the second inner peripheral portion 3 a 4 in the radial direction of the covers 3 a- 1 and 3 a- 2. The protrusions 7 and 8 may each have a shape with a rounded tip. The shape of each of the protrusions 7 and 8 may be a wedge shape, and the extension of the tip decreases from the second inner peripheral portion 3 a 4 toward the inner side in the radial direction of the cover 3 a- 1 or 3 a- 2. It is sufficient that the radial direction extension of each of the projections 7 and 8 is adjusted so that the projection 7 or 8 does not come into contact with the coil end 2a. The extension of each of the protrusions 7 and 8 in the axial direction may be equal to the length from the stepped portion 3 a 5 to the second end surface 3 a 2, or less than the length from the stepped portion 3 a 5 to the second end surface 3 a 2.The configurations described above in the embodiments are only examples of the content of the present invention. The configurations may be combined with other well-known techniques, and a part of each configuration may be omitted or adapted without departing from the gist of the present invention.List of Reference Numerals1 Stator core, 1 aone end surface, 1 bthe other end surface, 2 coil, 2 a, 2 bcoil end, 3 a, 3 a- 1, 3 a- 2, 3 b, 3 b- 1, 3 b- 2 cover, 3 a 1 first end surface, 3 a 2 second end surface, 3 a 3 first inner peripheral portion, 3 a 4 second inner peripheral portion, 3 a 5 stepped portion, 4, 4 a, 4 bresin portion, 5 rotor core, 6 aluminum conductor, 7, 8 protrusion, 10 housing, 11 cavity, 12 indentation, 20 lead wire, 100, 100- 1, 100- 2 stator, 200 rotor, 300 electric motor.

Claims

An electric motor (300) comprising: an annular stator core (1); a plurality of coils (2) arranged in a circumferential direction of the stator core (1); a tubular cover (3a) arranged on an end surface in an axial direction of the stator core to surround coil ends of the coils (2) protruding from the end surface in the axial direction of the stator core; a tubular housing (10) arranged outside the stator core (1) and outside the tubular cover (3a); and a heat conductive resin portion (4) disposed between each of coil ends of the coils (2) and the cover (3a), the cover (3a) comprising: a first inner peripheral portion (3a3) having a side close to a first end surface (3a1) facing the stator core (1) and a first inner diameter; a second inner peripheral portion (3a4) disposed on a side close to a second end surface (3a2) opposite the first end surface (3a1) and a second inner diameter larger than the first inner diameter; and a stepped portion (3a5) provided in a boundary portion between the first inner peripheral portion (3a3) and the second inner peripheral portion (3a4), and wherein the cover (3a) has a linear expansion coefficient smaller than a linear expansion coefficient of the heat conductive resin portion (4).The electric motor (300) according to claim 1, wherein the cover (3a) has a protrusion that is disposed between the stepped portion (3a5) and the second inner peripheral portion (3a4) and protrudes inward from the second inner peripheral portion (3a4) in a radial direction of the cover (3a).The electric motor (300) according to claim 1, wherein the cover (3a) includes a plurality of protrusions (7) that are disposed between the stepped portion (3a5) and the second inner peripheral portion (3a4) and spaced apart from each other in the circumferential direction of the stator core and protrude inward from the second inner peripheral portion (3a4) in a radial direction of the cover (3a).The electric motor (300) according to claim 1, wherein the cover (3a) includes a protrusion (7) that is disposed on the second inner peripheral portion (3a4) and protrudes inward from the second inner peripheral portion (3a4) in a radial direction of the cover (3a).The electric motor (300) according to claim 1, further comprising protrusions (7) disposed on the second inner peripheral portion (3a4), spaced apart from each other in the circumferential direction of the stator core (1), and protruding inward from the second inner peripheral portion (3a4) in a radial direction of the cover (3a).The electric motor (300) according to any one of claims 1 to 5, wherein the stepped portion (3a5) is formed as a flat surface parallel to the end surface in the axial direction of the stator core (1).

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