Patent ID: 12237745

DETAILED DESCRIPTION

A stator according to one aspect of the present disclosure includes: a stator core having an annular shape in which a plurality of teeth protrude in a radial direction from an inner peripheral surface of the stator core and are arranged in a circumferential direction; an insulator that covers the teeth; and a winding wound around the teeth with the insulator interposed between the winding and the teeth. Each of the teeth includes: a pair of long side surfaces extending in a direction along a central axis of the stator core; a pair of short side surfaces adjacent to the long side surfaces and extending in a direction intersecting the central axis; and a through-hole portion penetrating through the teeth from one short side surface to the other short side surface. The insulator includes: a pair of long side surface-covering portions that cover the pair of respective long side surfaces; a pair of short side surface-covering portions that cover the pair of respective short side surfaces; and a through-hole filling portion with which the through-hole portion is filled. The long side surface-covering portions and the short side surface-covering portions adjacent to each other are integrated with each other. The pair of short side surface-covering portions are integrated with each other through the through-hole filling portion. Each of the long side surface-covering portions includes an opening portion that is open while exposing a respective long side surface. A thermally conductive substance that is more thermally conductive than the insulator is provided on a portion of the long side surface exposed by the opening portion.

According to this configuration, a stator according to one aspect of the present disclosure includes: a stator core having an annular shape in which a plurality of teeth protrude in a radial direction from an inner peripheral surface of the stator core and are arranged in a circumferential direction; an insulator that covers the teeth; and a winding wound around the teeth with the insulator interposed between the winding and the teeth. Each of the teeth includes: a pair of long side surfaces extending in a direction along a central axis of the stator core; a pair of short side surfaces adjacent to the long side surfaces and extending in a direction intersecting the central axis; and a through-hole portion penetrating through the teeth from one short side surface to the other short side surface.

The insulator includes: a pair of long side surface-covering portions that cover the pair of respective long side surfaces; a pair of short side surface-covering portions that cover the pair of respective short side surfaces; and a through-hole filling portion with which the through-hole portion is filled. Each of the long side surface-covering portions includes an opening portion that is open while exposing a respective long side surface. A thermally conductive substance that is more thermally conductive than the insulator is provided on a portion of the long side surface exposed by the opening portion.

For this reason, heat is easily transferred from the winding to the stator core. Each of the long side surface-covering portions includes the opening portion. However, the long side surface-covering portions and the short side surface-covering portions adjacent to each other are integrated with each other, and the pair of short side surface-covering portions are integrated with each other through the through-hole filling portion. For this reason, rigidity of the insulator and of the stator core may be secured.

In this case, each of the pair of long side surface-covering portions comprises two opening portions that are open at boundaries with the pair of short side surface-covering portions adjacent to each other such that the short side surface-covering portions and each of the long side surfaces are on the same plane when viewed from the direction along the central axis, and each of the pair of long side surface-covering portions may cover the respective long side surface between the two opening portions.

According to this configuration, each of the pair of long side surface-covering portions includes two opening portions that are open at boundaries with the pair of short side surface-covering portions adjacent to each other such that the short side surface-covering portions and each of the long side surfaces are on the same plane when viewed from the direction along the central axis. For this reason, when the insulator is insert-molded around the teeth of the stator core inserted into a die, an undercut is unlikely to be generated, and manufacturing is facilitated. In addition, since each of the pair of long side surface-covering portions covers the long side surface between the two opening portions, a distance between the teeth and the winding wound around the teeth with the insulator interposed therebetween may be stabilized.

In the following description, with reference to the drawings, the same reference numbers are assigned to the same components or to similar components having the same function, and overlapping description is omitted. An electric motor including an example stator1shown inFIG.1is applied to, for example, a two-stage turbocharging system that requires transient response and wide range performance, in a turbocharged engine for a 48V mild hybrid system. The electric motor including the stator1according to the present example realizes an electric compressor of the two-stage turbocharging system and an electrically-assisted turbo that regenerates an extra turbine output during high load.

As shown inFIGS.1,2A,2B,2C, and3, the stator1includes a stator core2, an insulator4, and a winding5. In the stator core2, a plurality of teeth3protrude in a radial direction R from an inner peripheral surface of the stator core2having an annular shape, and are arranged in a circumferential direction C. The stator core2is divided into a plurality of core pieces in the circumferential direction C, each corresponding to one of the teeth3. As shown inFIGS.2A,2B,2C, and3, the stator core2includes a plurality of steel plates stacked in a direction along a central axis X of the stator core2.

The insulator4covers the teeth3. The insulator4is a molded part made of synthetic resin. The insulator4is formed by an insert molding method in which the insulator4is directly molded over the teeth3of the stator core2. The winding5is wound around the teeth3with the insulator4interposed therebetween. The winding5is wound around one of the teeth3by concentrated winding. The winding5is a substantially thick single copper wire having a diameter of approximately several mm to reduce copper loss.

Each of the teeth3has a pair of long side surfaces6(e.g. right long side surface6R and left long side surface6L; right surface and left surface) extending in a direction along the central axis X of the stator core2. In addition, each of the teeth3has a pair of short side surfaces7(e.g. top short side surface7T and bottom short side surface7B; top surface and bottom surface) that are adjacent to the long side surfaces6R and6L and that extend in a direction intersecting the central axis X, namely, in the circumferential direction C. The direction along the central axis X may not be a direction parallel to the central axis X, as long as it is not a direction orthogonal to the central axis X. In addition, the direction intersecting the central axis X may not be the direction orthogonal to the central axis X, as long as it is not a direction parallel to the central axis X. In addition, the direction in which each of the long side surfaces6R and6L and the short side surfaces7T and7B extends may be the same over the entirety thereof or may vary depending on the position thereon.

Each of the teeth3includes a through-hole portion8penetrating therethrough from one short side surface7T to the other short side surface7B. In the present example, in order to regain a volume of each of the teeth3reduced by providing the through-hole portion8, a width of each of the teeth3in the circumferential direction C is wider by a width of the through-hole portion8in the circumferential direction C than that of each of teeth30of a comparative stator core20as shown inFIGS.4A,4B, and4C. In addition, as shown inFIGS.2B and2C, each of the teeth3of the present example includes a reduced width portion16in the vicinity of a tip portion of the inner peripheral surface of the stator core2. A width of the reduced width portion16in the circumferential direction C is reduced from the inside of the stator core2to the outside of the stator core2(e.g., reduced in a direction from a side of inner circumference of the stator core2to a side of outer circumference of the stator core2). In addition, each of the teeth3of the present example includes an increased width portion17which is provided on the outside of the stator core2with respect to the reduced width portion16. A width of the increased width portion17in the circumferential direction C is increased from the inside of the stator core2to the outside of the stator core2(e.g., increased in a direction from a side of inner circumference of the stator core2to a side of outer circumference of the stator core2). Namely, in each of the teeth3of the present example, a constriction (e.g. neck) is formed in the vicinity of the tip portion when viewed from the direction along the central axis X of the stator core2. In addition, the through-hole portion8is formed closer to the outer circumference of the stator core2than the reduced width portion16.

As shown inFIGS.2A,2B,2C, and3, the insulator4includes a pair of long side surface-covering portions9(e.g. right long side surface-covering portion9R and left long side surface-covering portion9L; right insulating portion and left insulating portion) that cover the pair of respective long side surfaces6(e.g. the right long side surface-covering portion9R covers the right long side surface6R and the left long side surface-covering portion9L covers the left long side surface6L). In addition, the insulator4includes a pair of short side surface-covering portions10(e.g. top short side surface-covering portion10T and bottom short side surface-covering portion10B) that cover the pair of respective short side surfaces7(e.g. the top short side surface-covering portion10T covers the top short side surface7T and the bottom short side surface-covering portion10B covers the bottom short side surface7B). In addition, the insulator4includes a through-hole filling portion11with which the through-hole portion8is filled. Further, the insulator4includes a base portion-covering portion12(base insulating portion) that covers a base portion of each of the teeth3, and a tip portion-covering portion13(tip insulating portion) that covers the tip portion of each of the teeth3.

As shown inFIG.2A, the long side surface-covering portions9and the short side surface-covering portions10adjacent to each other are integrated with each other through the base portion-covering portion12and through the tip portion-covering portion13. As shown inFIG.3, the pair of short side surface-covering portions10are integrated with each other through the through-hole filling portion11. As shown inFIGS.2A,2C, and3, each of the long side surface-covering portions9R and9L includes two opening portions14(e.g. top opening portion14T and bottom opening portion14B) those are open while exposing the long side surfaces6R and6L partially. Six openings are formed in the insulator4of the present example. Four of the six openings are two opening portions14T and14B which expose the long side surface6R and two opening portions14T and14B which expose the long side surface6L. One of the six openings is an opening that exposes a part of the tip portion of each of the teeth3at the tip portion-covering portion13. The last one of the six openings opens on a side of the outer circumference of the stator core2along a shape of the base portion of each of the teeth3at the base portion-covering portion12when it is assumed that there is no stator core2.

As shown inFIG.3, each of the pair of long side surface-covering portions9R and9L includes two opening portions14T and14B that are open at boundaries with the pair of short side surface-covering portions10T and10B adjacent to the pair of long side surface-covering portions9R and9L such that the short side surface-covering portions10T and10B and each of the long side surfaces6R and6L are on the same plane when viewed from the direction along the central axis X. The top opening14T exposes the right long side surface6R from a top end to a middle portion. The bottom opening14B exposes the right long side surface6R from a bottom end to the middle portion. The top opening14T exposes the left long side surface6L from a top end to a middle portion. The bottom opening14B exposes the left long side surface6L from a bottom end to the middle portion. As shown inFIGS.2A,2B, and3, each of the pair of long side surface-covering portions9R and9L covers the long side surface6R and6L respectively between the two opening portions14. The right long side surface-covering portion9R covers the right long side surface6R at the middle portion. The left long side surface-covering portion9L covers the left long side surface6L at the middle portion. The short side surface-covering portions10T and10B have a sufficient thickness such that the winding5which is substantially thick and difficult to bend is not in contact with the long side surfaces6R and6L exposed at the opening portions14. The short side surface-covering portions10T and10B are formed without an opening.

As shown inFIGS.2A,2C, and3, a thermally conductive substance15that is more thermally conductive than the insulator4is provided on portions of each of the long side surfaces6R and6L exposed by the opening portions14T and14B. The thermally conductive substance15is a paste-like thermally conductive compound such as silicone grease. The thermally conductive substance15is provided on the portions of each of the long side surfaces6R and6L exposed by the opening portions14T and14B, by applying the paste-like thermally conductive compound to the opening portions14T and14B.

Generally, a thermal conductivity of the insulator4is approximately 0.3 to 0.5 W/mK. On the other hand, a thermal conductivity of the thermally conductive substance15is approximately 2 W/mK. When the winding5is wound around each of the teeth3, the thermally conductive substance15is crushed by the winding5. A space between the winding5and each of the teeth3of the stator core2is filled with the thermally conductive substance15, so that heat is more easily transferred from the winding5to the stator core2.

As shown inFIGS.2C and3, only a space between a first layer of the winding5wound in a plurality of layers and each of the teeth3may be filled with the thermally conductive substance15. Since the winding5that is substantially thick and difficult to bend, the first layer of the winding5wound in the plurality of layers does not cover (e.g. follow) each of the teeth3and the insulator4over the entire circumference. For this reason, the space between at least the first layer of the winding5and each of the teeth3may be filled with the thermally conductive substance15.

On the other hand, since winding radiuses of the winding5in second and subsequent layers are definitely larger than the radius of the first layer over the entire circumference, the winding5of the first layer and the winding5of the second and subsequent layers are in close contact with each other. When the turns of the winding5are in contact with each other, heat is easily transferred between the turns of the winding5. For this reason, only the space between the first layer of the winding5wound in the plurality of layers and each of the teeth3may be filled with the thermally conductive substance15.

In the above-described electric motor including the stator1according to the present example, an output of an ordinary turbocharger with a similar size is approximately 4.5 kW to 8 kW, so that water cooling may be basically applied. Since a centrifugal compressor is involved, the electric motor is driven at an ultra-high speed (a maximum speed of 80 k rpm for an electric compressor and a maximum speed of 200 k rpm for an electrically-assisted turbo), and low inductance design is applied to drive the electric motor with 48 V. Since this means a reduction in magnet torque, an amount of the electric current for generating the foregoing output is as large as approximately 150 A at its maximum. Therefore, copper loss is a main loss of the electric motor from which heat has to be removed. Since an allowable temperature of the winding is limited to approximately 180° C. to realize an economical electric motor, a design challenge is to reduce thermal resistance from the winding to cooling water.

Generally, in such an electric motor with a small size and a high output, a contact area between the winding and the stator core is increased and thermal resistance is lowered by winding the winding around the stator core and then by pouring and curing a casting resin having a high fluidity such as epoxy resin or silicone of which thermal conductivity is increased. However, in this method, a large amount (100 g or more) of the casting resin that is expensive is used, and a curing time (approximately 30 to 60 minutes in the case of thermal curing) is needed. For this reason, the cost for components increases.

As a simpler method, for example, as in Japanese Unexamined Patent Publication No. 2001-128402, it is proposed that a part of the insulator that covers the stator core is made of an insulating resin with a high thermal conductivity. In addition, a method is proposed in which the insulator is divided into two pieces in the direction along the central axis and the long side surfaces are replaced with thermally conductive sheets. However, in both of the proposals, since a hole portion is provided in a part of the insulator or the insulator itself is separated from the stator core, the rigidity of the stator core and the insulator decrease.

InFIGS.4A,4B, and4C, the degree of close contact between an insulator40and the stator core20is increased by the insert molding method in which the insulator40is directly molded over the teeth30of the stator core20. In this method, since insert molding resin of the insulator40increases rigidity of the stator core20, the winding5may be wound around the teeth30with high tension. For this reason, a substantially thick single copper wire may be employed as the winding5, and reliability of a connection portion of the winding5may be improved while handling a large electric current.

However, since the winding5that is substantially thick and wound around the teeth30is difficult to bend and has difficulty in covering (e.g., following) the teeth30and the insulator40, as shown inFIG.4C, the winding5and the insulator40are in close contact with each other only in the vicinity of the boundaries between the long side surface-covering portions9and the short side surface-covering portions10, and contact therebetween at other portions is not obtained. For this reason, heat transfer from the winding5to the stator core20becomes difficult, and heat removal capability is insufficient.

On the other hand, as shown inFIGS.1,2A,2B,2C, and3, in the present example, in the stator1including the stator core2having an annular shape in which the plurality of teeth3protrude in the radial direction R from the inner peripheral surface of the stator core2and are arranged in the circumferential direction C; the insulator4that covers the teeth3; and the winding5wound around the teeth3with the insulator4interposed between the winding5and the teeth3, each of the teeth3has the pair of long side surfaces6R and6L extending in the direction along the central axis X of the stator core2, the pair of short side surfaces7T and7B extending in the direction intersecting the central axis X, and the through-hole portion8penetrating through each of the teeth3from one short side surface7T to the other short side surface7B.

The insulator4includes the pair of long side surface-covering portions9R and9L that cover the pair of respective long side surfaces6R and6L, the pair of short side surface-covering portions10T and10B that cover the pair of respective short side surfaces7T and7B, and the through-hole filling portion11with which the through-hole portion8is filled. Each of the long side surface-covering portions9R and9L includes two opening portions14T and14B those are open while exposing the long side surface6R and6L partially. The thermally conductive substance15that is more thermally conductive than the insulator4is provided on a portion of each of the long side surfaces6R and6L exposed by the opening portions14T and14B.

For this reason, heat is transferred from the winding5to the stator core2. Each of the long side surface-covering portions9R and9L includes two opening portions14T and14B. However, the long side surface-covering portions9R and9L and the short side surface-covering portions10T and10B adjacent to each other are integrated with each other, and the pair of short side surface-covering portions10T and10B are integrated with each other through the through-hole filling portion11. For this reason, rigidity of the insulator4and of the stator core2may be secured.

The resin clings to the teeth3due to molding shrinkage of the resin, so that the rigidity of the insulator4is maintained. When the insulator4surrounds the entire periphery of the teeth3, the insulator4has a closed cross section, and the rigidity of the insulator4becomes the rigidity of the teeth3itself, so that the rigidity is maximized.

On the other hand, when a hole portion is drilled in the long side surfaces6, the hole portion opens on the entirety of the long side surfaces6of the teeth3due to restrictions on molding (die removal), so that the insulator4clings to the teeth3only through the short side surfaces7. Therefore, the amount of the material supporting the insulator4in the vicinity of the boundaries between the long side surface-covering portions9and the short side surface-covering portions10is minimized, and the rigidity decreases.

However, in the present example, the through-hole portion8is provided inside the stator core2(the teeth3), and the short side surface-covering portions10T and10B located on the short side surfaces7of the teeth3are connected to each other by the resin of the through-hole filling portion11with which the through-hole portion8is filled, so that the insulator4clings to the teeth3with such a surface area that enables the insulator4to surround the periphery of the teeth3, so that the rigidity may be relatively well maintained.

As described above, since the winding5that is substantially thick is difficult to bend and has difficulty in covering (following) the teeth3and the insulator4, the winding5and the insulator4are in close contact with each other only in the vicinity of the boundaries between the long side surface-covering portions9R and9L and the short side surface-covering portions10T and10B. Therefore, when the insulator4is in contact with the winding5only in the vicinity of the boundaries, the insulator4at locations other than the vicinity of the boundaries is removed, and the space between the teeth3and the winding5is filled with the thermally conductive substance, so that heat may be transferred from the winding5to the stator core2.

In addition, according to the present example, each of the pair of long side surface-covering portions9R and9L includes the two opening portions14T and14B that are open at the boundaries with the pair of short side surface-covering portions10T and10B adjacent to each other such that the short side surface-covering portions10and each of the long side surfaces6are on the same plane when viewed from the direction along the central axis X. (e.g., the short side surface-covering portion10T and the long side surfaces6R are on the same plane when viewed from the radial direction R; the short side surface-covering portion10T and the long side surfaces6L are on the same plane when viewed from the radial direction R; the short side surface-covering portion10B and the long side surfaces6R are on the same plane when viewed from the radial direction R; the short side surface-covering portion10B and the long side surfaces6L are on the same plane when viewed from the radial direction R). For this reason, when the insulator4is insert-molded around the teeth3inserted into a die, an undercut may be unlikely to be generated, and manufacturing may be facilitated. In addition, since each of the pair of long side surface-covering portions9R and9L covers the long side surface6R and6L between the two opening portions14T and14B, a distance between the teeth3and the winding5wounds around the teeth3with the insulator4interposed therebetween may be stabilized.

Namely, when the insulator4is molded over the teeth3by insert molding, in consideration of that a division direction of the molding die is the direction along the central axis X, in order to prevent an undercut from being generated, the opening portions14may be open such that the short side surface-covering portions10and each of the long side surfaces6are on the same plane when viewed from the direction along the central axis X. In this case, the proximity of the winding5and the long side surfaces6may be considered.

Therefore, in the present example, the opening portions14are disposed only at locations where the winding5is not in contact with the teeth3. The insulator4is molded on the short side surfaces7T and7B and central portions of the long side surfaces6R and6L. Accordingly, as shown inFIG.3, since the winding5is wound around the teeth3in a hexagonal shape or in an octagonal shape when viewed from the radial direction R, the distance between the teeth3and the winding5is stabilized. In addition, since the winding5is pressed against the teeth3by tension, the amount of use of the thermally conductive substance15is reduced, and the ease of heat transfer is stabilized.

Further, in the present example, since the winding5that is substantially thick is difficult to bend, while guiding the bending of the winding5to the middle, a thickness margin is provided with respect to each of the short side surfaces7of the teeth3at the opening portions14that are undercut removal portions, so that the winding of the winding5around the teeth3may be stabilized while avoiding contact between the winding5and the long side surfaces6of the teeth3.

It is to be understood that not all aspects, advantages and features described herein may necessarily be achieved by, or included in, any one particular example. Indeed, having described and illustrated various examples herein, it should be apparent that other examples may be modified in arrangement and detail. For example, the thermally conductive substance15may be a sheet-shaped thermal conductor sandwiched between the winding5and the teeth3, instead of being a thermally conductive compound. In addition, the thermally conductive substance15may be a molding material (potting material) with which the entirety of the electric motor including the opening portions14is filled.