Stator for electric motor

A stator for an electric motor includes: (a) a tubular stator core having slots provided through the stator core in a direction of a rotation axis of the stator core; (b) coils inserted through the slots; (c) a conductive member electrically connected to the coils; (d) a temperature sensor attached to the conductive member; and (e) a resin portion provided to cover at least a part of the conductive member and at least a part of the temperature sensor. The conductive member is provided with a hole that extends in the direction of the rotation axis of the stator core. The temperature sensor is inserted, at least its portion, in the hole.

This application claims priority from Japanese Patent Application No. 2022-027246 filed on Feb. 24, 2022, the disclosure of which is herein incorporated by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to a structure for attaching a temperature sensor to a stator for an electric motor.

BACKGROUND OF THE INVENTION

JP-2021-114877A discloses a structure for attaching a temperature sensor to a stator, which is to constitute a part of an electric motor. Specifically, in the structure disclosed in this Japan Patent Application Publication, the temperature sensor is attached to a conductive member connected to a stator coil that is attached to a stator core. Further, in the disclosed structure, distal end portions of the stator coil protruding from the stator core in a direction of a rotation axis are welded to each other, and the welded portions are covered with resin so as to assure insulation of the welded portions. Moreover, the temperature sensor as well as the distal end portions of the stator coil is covered with the resin, for avoiding an element portion of the temperature sensor from being in contact with a refrigerant such as coolant oil, such that a temperature value measured by the temperature sensor does not become lower than an actual coil temperature value.

SUMMARY OF THE INVENTION

By the way, in the structure for attaching the temperature sensor, disclosed in the above-identified Japan Patent Application Publication, the conductive member is bent so as to include opposed portions opposed to each other, and the temperature sensor is held between the opposed portions of the conductive member, so that a thickness of a portion in which the temperature sensor is attached is increased, thereby problematically resulting in increase in size and increase in amount of the resin required to cover the temperature sensor and the conductive member.

The present invention was made in view of the background art described above. It is therefore an object of the present invention to provide a stator for an electric motor, wherein the stator includes a temperature sensor attached to a conductive member and covered with resin, and wherein the stator has a structure capable of suppressing increase in size and increase in amount of use of the resin.

The object indicated above is achieved according to the following aspects of the present invention.

According to a first aspect of the invention, there is provided a stator for an electric motor. The stator includes: (a) a tubular stator core having slots provided through the stator core in a direction of a rotation axis of the stator core; (b) coils inserted through the slots; (c) a conductive member electrically connected to the coils; (d) a temperature sensor attached to the conductive member; and (e) a resin portion provided to cover at least a part of the conductive member and at least a part of the temperature sensor. The conductive member is provided with a hole that extends in the direction of the rotation axis of the stator core. The temperature sensor is inserted, at at least its portion, in the hole.

According to a second aspect of the invention, in the stator according to the first aspect of the invention, the temperature sensor includes a base portion and a protrusion portion protruding from the base portion, wherein the protrusion portion of the temperature sensor is inserted in the hole.

According to a third aspect of the invention, in the stator according to the first or second aspect of the invention, the at least the portion of the temperature sensor is interference-fitted in the hole.

According to a fourth aspect of the invention, in the stator according to any one of the first through third aspects of the invention, the conductive member is a neutral busbar.

In the stator according to the first aspect of the invention, the temperature sensor is inserted in the hole provided in the conductive member, so that a thickness of a portion covered by the resin portion can be reduced by a distance by which the temperature sensor is inserted in the hole. Consequently, it is possible to reduce an amount of use of resin required to form the resin portion and to suppress increase of a size of the stator or the electric motor.

In the stator according to the second aspect of the invention, the protrusion portion protruding from the base portion is inserted in the hole. Thus, the distance by which the temperature sensor is inserted in the hole, i.e., a length of a portion of the temperature sensor which is inserted in the hole, can be made always constant.

In the stator according to the third aspect of the invention, the at least the portion of the temperature sensor is interference-fitted in the hole. Thus, it is possible to prevent the temperature sensor from being removed from the hole after the temperature sensor is attached to the neutral busbar. Further, since the temperature sensor is in close contact with the neutral busbar, it is possible to improve temperature followability of the temperature sensor.

In the stator according to the fourth aspect of the invention, the conductive member is the neutral busbar. Thus, it is possible to improve an accuracy of detection of the temperature of the electric motor, by detecting a temperature of the neutral busbar to which an electric current is constantly applied during running of a vehicle.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

There will be described embodiments of the present invention in details with reference to drawings. It is noted that figures of the drawings are simplified or deformed as needed, and each portion is not necessarily precisely depicted in terms of dimension ratio, shape, angle, etc., for easier understanding of each of the embodiments.

First Embodiment

FIG.1is a view of an electric motor MG that is to be provided in a vehicle in an embodiment of the present invention, as viewed in a direction of a rotation axis CL of the electric motor MG. The electric motor MG is disposed in a casing12as a non-rotary member, such that its center lies on the rotation axis CL. The electric motor MG includes a rotor14disposed to be rotatable about the rotation axis CL and a stator16disposed on an outer peripheral side of the rotor14.

The rotor14has a cylindrical shape, and is rotatably held by the casing12through bearings (not shown) that are disposed on respective opposite sides of the rotor14in a direction of the rotation axis CL. The stator16has a tubular shape, and is fixed to the casing12through screw bolts (not shown). Thus, the stator16is unrotatably fixed to the casing12. A predetermined amount of clearance is defined between the rotor14and the stator16in a radial direction of the rotor14and the stator16.

A plurality of magnets14aare provided inside the rotor14. The stator16includes a tubular stator core18disposed around the rotation axis CL and a plurality of stator coils20extending through the stator core18in the direction of the rotation axis CL. Each of the stator coils20is provided by a conductive wire which has a rectangular cross-sectional shape and which is covered with an insulation film (not shown). A length of a side of each of the stator coils20is substantially equal to a width of each of slots22. It is noted that the stator coils20correspond to “coils” recited in the appended claim.

The stator core18is constituted by a plurality of electromagnetic steel plates that are laminated on each other, so as to have a tubular shape. The plurality of slots22are provided in the stator core18such that slots22are arranged radially as viewed in the direction of the rotation axis CL. Each of the slots22is a cutout extending in the radial direction from an inner circumferential surface of the stator core18toward an outer circumferential surface of the stator core18. The slots22are located at equal angular intervals in a circumferential direction of the stator core18, and extend through the stator core18in the direction of the rotation axis CL.

Each of the slots22receives corresponding ones of the plurality of stator coils20which are inserted through each slot22and which are arranged in the radial direction as viewed in the direction of the rotation axis CL. Each of the stator coils20, which extends through the stator core18in the direction of the rotation axis CL, has substantially a U-shape so that a pair of end portions of each stator coil20protrudes from an axial end face of the stator core18in the direction of the rotation axis CL. The end portions protruding from the axial end face of the stator core18are bundled to constitute a coil end24as indicated by one-dot chain line inFIG.1. In the coil end24, one of the end portions of each of the stator coils20and one of the end portions of another of the stator coils20are welded to constitute a welded portion26(seeFIG.2).

In a state in which the electric motor MG is installed in the vehicle, a coolant pipe28is located above the coil end24in a vertical direction of the vehicle, as shown inFIG.1. A coolant oil (coolant fluid), which is cooled by passing through an oil cooler30, is pumped up by a mechanical oil pump32so as to be supplied to the coolant pipe28that extends in the direction of the rotation axis CL.

InFIG.1, arrows indicate flow of the coolant oil. The coolant pipe28is provided with a plurality of oil release holes34, so that the coolant oil is released through the oil release holes34. The coolant oil released from the oil release holes34scatters toward the coil end24. The coolant oil adhering to the coil end24is moved downward along the coil end24as indicated by the arrows, and the coil end24is cooled at this time. Further, the coolant oil, which reaches a lower portion of the coil end24and is moved to a bottom of the casing12, is cooled by the oil cooler30, and is supplied to the coolant pipe28again through the mechanical oil pump32. In this way, the coolant oil is circulated inside the casing12while cooling the coil end24.

FIG.2is a view showing a cross section taken in line A-A inFIG.1, in a simplified manner. InFIG.2, a vertical direction of the drawing sheet corresponds to the direction of the rotation axis CL while a horizontal direction of the drawing sheet corresponds to the radial direction of the radial direction of the rotor14and the stator16. As shown inFIG.2, the coil end24is constituted by the end portions of the stator coils20, which protrude from the axial end face of the stator core18. In a distal end portion of the coil end24, one of the end portions of each of the stator coils20and one of the end portions of another of the stator coils20are welded to constitute the welded portion26. Each of the coil end24and the welded portion26has an annular body whose center lies on the rotation axis CL.

A neutral busbar36is provided to be electrically connected to the stator coils20, and connect among a U-phase coil, a V-phase coil and a W-phase coil that constitute the stator coils20, so as to constitute a neutral point of a Y connection of the three phase coils. Further, a temperature sensor38is attached to the neutral busbar36, so as to detect a temperature of the electric motor MG. During an operation of the vehicle (including during stop of the vehicle as well as during running of the vehicle), an electric current is constantly supplied to the neutral busbar36, so that an accuracy of detection of the temperature of the electric motor MG can be improved owing to the arrangement in which the temperature sensor38is attached to the neutral busbar36. Further, since the temperature sensor38is provided within a space defined between the neutral busbar36and the stator core18, it is possible to prevent increase of a size of the electric motor MG due to the provision of the temperature sensor38. It is noted that the neutral busbar36corresponds to “conductive member” recited in the appended claims.

Further, in order to assure insulation of the welded portion26that is constituted by the distal end portions of the stator coils20that are welded to one another, the welded portion26is covered with a resin portion made40of resin. Moreover, the neutral busbar36and a part of the temperature sensor38, as well as the welded portion26, are covered with the resin portion40, so as to prevent contact of the coolant oil with a vicinity of a thermistor element portion48(seeFIG.3) of the temperature sensor38attached to the neutral busbar36, for avoiding reduction of the accuracy of the detection of the temperature of the temperature sensor38. Thus, the resin portion40covers the welded portion26, the neutral busbar36and the part of the temperature sensor38.

As described above, the temperature sensor38is partially covered with the resin portion40, so that a temperature value measured by the temperature sensor38is unlikely to be reduced by the coolant oil. However, the coverage of the temperature sensor38with the resin increases a thickness of the resin portion40measured in the direction of the rotation axis CL (that is represented by “L1” inFIG.2), thereby resulting in increase of an amount of use of the resin. Further, where there is a limitation of a length of the electric motor MG in the direction of the rotation axis CL due to a restriction required for installing the electric motor MG in the vehicle, an axial length of the coil end24(that is represented by “L2” inFIG.2) in the direction of the rotation axis CL, which can be cooled by the coolant coil, is made small relative to the thickness of the resin portion40, thereby resulting in reduction of a surface area of the coil end24with which the coolant oil can be in contact. The reduction of the surface area of the coil end24leads to reduction of a cooling performance of the stator coils20. In connection with this, there is a risk that the output torque of the electric motor MG could be problematically limited due to the temperature restriction of the stator coils20.

For avoiding the above-described problems, the temperature sensor38is inserted, at least its portion, in a round hole46that is provided to extend through the neutral busbar36.FIG.3is a cross sectional view taken in line B-B inFIG.2. InFIG.3, a vertical direction of the drawing sheet corresponds to the direction of the rotation axis CL.FIG.3further includes a cross sectional view of the temperature sensor38taken in line C-C. It is noted that the round hole46corresponds to “hole” recited in the appended claims.

The temperature sensor38includes the above-described thermistor element portion48and a sensor casing50provided to protect the thermistor element portion48. The thermistor element portion48is provided in the sensor casing50made of resin. Further, two lead wires52a,52bare connected to the thermistor element portion48.

The sensor casing50includes a plate-like base portion54having a predetermined thickness and a protrusion portion56protruding perpendicularly from the base portion54by a distance larger than a thickness of the neutral busbar36, as shown inFIG.3. Thus, the sensor casing50has a convex shape (stepped cylindrical shape) as a whole. The neutral busbar36has the predetermined thickness in the direction of the rotation axis CL. The neutral busbar36is provided with the round hole46extending in the direction of the rotation axis CL, i.e., a thickness direction of the neutral busbar36.

The protrusion portion56of the temperature sensor38is inserted in the round hole46provided in the neutral busbar36and having a circular cross-sectional shape. The temperature sensor38is inserted in the round hole46so as to be positioned relative to the neutral busbar36in a position that makes the base portion54of the sensor casing50brought into contact with the neutral busbar36.

Therefore, as shown inFIG.2, the thickness L1of the resin portion40can be reduced by a distance L3by which the temperature sensor38is inserted in the round hole46, thereby making it possible to reduce the amount of use of the resin required to form the resin portion40. Further, even in a case in which, due to an issue of mountability of the electric motor MG, there is a limitation on a length of a portion of the electric motor MG, which protrudes from the stator core18in the direction of the rotation axis CL, the axial length L2of the coil end24, which can be cooled by the coolant coil, can be made large relative to the thickness L1of the resin portion40, because the thickness L1can be reduced as described above. Consequently, the surface area of the coil end24with which the coolant oil can be in contact is increased whereby the electric motor MG can be cooled by the coolant oil with an improved cooling performance. In this connection, it is possible to reduce a limitation on an output of the electric motor MG due to heat generated by the electric motor MG, and to make the electric motor MG more compact in size.

FIG.4is a view showing a process of forming the resin portion40, i.e., a process of covering the welded portion26, the neutral busbar36and the temperature sensor38, with the resin portion40, when the electric motor MG is to be manufactured. InFIG.4, a downward direction of the drawing sheet corresponds to a downward direction during the covering process. When the resin portion40is to be formed, a mould42is filled with a liquid resin, and the welded portion26, the neutral busbar36and the temperature sensor38(that is attached to the neutral busbar36) are immersed into the liquid resin in the mould42. Then, with the liquid resin being cured, the resin portion40is formed such that the welded portion26, the neutral busbar36and the temperature sensor38are covered by the formed resin portion40.

FIG.5is a view showing a dimensional relationship between the temperature sensor38and the neutral busbar36in a state before the temperature sensor38is inserted in the round hole46of the neutral busbar36. In this state before the protrusion portion56of temperature sensor38is inserted in the round hole46, an outside diameter d1of the protrusion portion56is slightly larger than an inside diameter d2of the round hole46. Thus, upon insertion of the protrusion portion56of temperature sensor38into the round hole46of the neutral busbar36, the protrusion portion56is press-fitted in the round hole46, so that the protrusion portion56is interference-fitted in the round hole46, namely, the temperature sensor38is fixed to the neutral busbar36with an interference fit, after the protrusion portion56of temperature sensor38has been inserted into the round hole46of the neutral busbar36. It is noted that the difference between the outside diameter d1of the protrusion portion56and the inside diameter d2of the round hole46is set to a suitable value that makes the protrusion portion56be interference-fitted in the round hole46after the insertion of the protrusion portion56into the round hole46.

As described above, when the resin portion40is to be formed, the welded portion26, the neutral busbar36and the temperature sensor38(that is attached to the neutral busbar36) are immersed into the liquid resin in the mould42. In this instance, the temperature sensor36is fixed in the round hole46of the neutral busbar36with the interference fit, so that it is possible to prevent the temperature sensor38from being deviated from a predetermined position relative to the neutral busbar36during formation of the resin portion40, thereby resulting in an improved manufacturability. Further, since the resin comes into close contact with the neutral busbar36in vicinity of the thermistor element portion48, the resin or air is unlikely to enter between the temperature sensor38and the neutral busbar36so that it is possible to suppress thermal resistance that could be increased by presence of the resin or air between the temperature sensor38and the neutral busbar36, and accordingly to improve temperature followability of the temperature sensor38.

As described above, in the present embodiment, the temperature sensor38is inserted in the round hole46provided in the neutral busbar36, so that the thickness L1of the portion covered by the resin portion40can be reduced by a distance by which the temperature sensor38is inserted in the round hole46. Consequently, it is possible to reduce the amount of use of the resin required to form the resin portion40and to suppress increase of the size of the stator16or the electric motor MG.

In the present embodiment, the protrusion portion56protruding from the base portion54is inserted in the round hole46. Thus, the distance by which the temperature sensor38is inserted in the round hole46, i.e., a length of a portion of the temperature sensor38which is inserted in the round hole46, can be made always constant. Further, the temperature sensor38is interference-fitted in the round hole46, thereby making it possible to prevent the temperature sensor38from being removed from the round hole46after the temperature sensor38is attached to the neutral busbar36. Still further, since the temperature sensor38is in close contact with the neutral busbar36, it is possible to improve the temperature followability of the temperature sensor38. Moreover, since the temperature sensor38is attached to the neutral busbar36to which an electric current is to be constantly applied during running of the vehicle, it is possible to improve the accuracy of detection of the temperature of the electric motor MG by the temperature sensor38.

There will be described another embodiment of this invention. The same reference signs as used in the above-described embodiment will be used in the following embodiment, to identify the practically corresponding elements, and descriptions thereof are not provided.

Second Embodiment

FIG.6is a view showing a neutral busbar80and a temperature sensor82attached to the neutral busbar80in this second embodiment of the invention. The constructions other than the neutral busbar80and the temperature sensor82are the same as those in the above-described first embodiment, so that the description thereof is not provided. It is noted that the neutral busbar80corresponds to “conductive member” recited in the appended claims.

As shown inFIG.6, the temperature sensor82is inserted in a quadrangle hole84provided in the neutral busbar80. The quadrangle hole84is formed to have a square cross-sectional shape. It is noted that the quadrangle hole84corresponds to “hole” recited in the appended claims.

The temperature sensor82includes the above-described thermistor element portion48and a sensor casing86provided to protect the thermistor element portion48. The sensor casing86includes a plate-like base portion88having a predetermined thickness and a protrusion portion90protruding perpendicularly from the base portion88by a distance larger than a thickness of the neutral busbar80. Thus, the sensor casing86has a convex shape (stepped shape) as a whole.FIG.6further includes a cross sectional view of the protrusion portion90of the temperature sensor82taken in line D-D. As shown in the cross sectional view taken in the line D-D, the protrusion portion90is formed to have a quadrangle (square) contour, so that the protrusion portion90of the temperature sensor82can be inserted into the quadrangle hole84of the neutral busbar80. The protrusion portion90passes through the quadrangle hole84of the neutral busbar80in a state in which the temperature sensor82is attached to the neutral busbar80. Thus, the hole (quadrangle hole84) of the neutral busbar80in which the temperature sensor82is inserted is formed to have a rectangular cross-sectional shape, and the protrusion portion (protrusion portion90) of the temperature sensor82is formed to have a rectangular cross-sectional shape corresponding to the cross sectional shape of the quadrangle hole84. In the present second embodiment as in the above-described first embodiment, with the protrusion portion90of the temperature sensor82being inserted in the quadrangle hole84of the neutral busbar80, the thickness L1(seeFIG.2) of the resin portion can be reduced by a distance by which the protrusion portion90is inserted in the quadrangle hole84. Consequently, it is possible to make it possible to reduce the amount of use of the resin required to form the resin portion, and to increase the surface area of the coil end24with which the coolant oil can be in contact, so that the electric motor MG can be cooled by the coolant oil with an improved cooling performance.

Further, in this state before the protrusion portion90of temperature sensor82is inserted in the quadrangle hole84, a length s1of a side of the protrusion portion90that is shaped to a quadrangular prism is slightly larger than a length s2of a side of the quadrangle hole84. Thus, upon insertion of the protrusion portion90of temperature sensor82into the quadrangle hole84of the neutral busbar80, the protrusion portion90is press-fitted in the quadrangle hole84, so that the protrusion portion90is interference-fitted in the quadrangle hole84, namely, the temperature sensor82is fixed to the neutral busbar80with an interference fit, after the protrusion portion90of temperature sensor82has been inserted into the quadrangle hole84of the neutral busbar82. Consequently, it is possible to prevent the temperature sensor82from being deviated from a predetermined position relative to the neutral busbar80during manufacturing process, and to make the temperature sensor82and the neutral busbar80being in close contact with each other whereby the temperature followability of the temperature sensor82can be improved. Thus, the present second embodiment also provides substantially the same effects as the above-described first embodiment.

While the preferred embodiments of this invention have been described in detail by reference to the drawings, it is to be understood that the invention may be otherwise embodied.

For example, in the above-described first embodiment, the round hole46provided in the neutral busbar36has a perfect circular shape in its cross section. However, the round hole46may be formed to have an elliptical-circular shape in its cross section. Further, in conformity with the shape of the round hole46, the protrusion portion56may be formed to have an elliptical-circular shape in its cross section. In the above-described second embodiment, the quadrangle hole84provided in the neutral busbar80has a square shape in its cross section. However, the quadrangle hole84may be formed to have a rectangular shape in its cross section. Further, in conformity with the shape of the quadrangle hole84, the protrusion portion90may be formed to have a rectangular shape in its cross section. Moreover, the hole provided in the neutral busbar does not necessarily have to be formed to have the circular or quadrangle shape in the cross section, but may be formed to have any other shape such as a triangular or trapezoid shape in the cross section. Similarly, the protrusion portion of the temperature sensor may be formed to have any cross sectional shape depending on the cross sectional shape of the hole of the neutral busbar.

In the above-described embodiments, each of the round hole46and quadrangle hole84of the neutral busbars36,80is a through-hole formed through the neutral busbar in the thickness direction. However, each of the holes46,84does not necessarily have to be a through-hole but may be a cutout or blind hole having a predetermined depth.

In the above-described embodiments, each of the round hole46and quadrangle hole84of the neutral busbars36,80is a through-hole formed through inside the neutral busbar in the thickness direction. However, each of the holes46,84may be constituted by a cutout or groove formed in an end surface of the neutral busbar, such that the temperature sensor is inserted or fitted in such a cutout or groove. In this modified arrangement, the cutout or groove serves as a hole in which the temperature sensor is inserted or fitted.

In the above-described embodiments, each of the sensor casings50,86of the temperature sensors38,82consists of a corresponding one of the base portions54,88and a corresponding one of the protrusion portions56,90so as to have a stepped shape as a whole. However, each of the sensor casings50,86does not necessarily have to have a stepped shape. In connection of this, the temperature sensor in its entirety may be inserted in the hole provided in the neutral busbar. That is, at least part of the temperature sensor should be inserted into the hole of the neutral busbar.

It is to be understood that the embodiments described above are given for illustrative purpose only, and that the present invention may be embodied with various modifications and improvements which may occur to those skilled in the art.

NOMENCLATURE OF ELEMENTS