Stator for electric rotating machine

A stator coil includes first to fourth in-slot portions and first and second turn portions. Both the first and third in-slot portions are received in one slot of a stator core, while both the second and fourth in-slot portions are received in another slot. The first and second turn portions both protrude from an axial end face of the stator core and respectively connect the pair of the first and second in-slot portions and the pair of the third and fourth in-slot portions. The second turn portion is located inside the first turn portion. When viewed along an axial direction of the stator core, the first and second turn portions extend so as to cross each other with a reference line C interposed therebetween; the reference line C is defined to extend along a circumferential direction of the stator core through an intersection between the first and second turn portions.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based on and claims priority from Japanese Patent Application No. 2012-7761, filed on Jan. 18, 2012, the content of which is hereby incorporated by reference in its entirety into this application.

BACKGROUND

1. Technical Field

The present invention relates to stators for electric rotating machines that are used in, for example, motor vehicles as electric motors and electric generators.

2. Description of Related Art

There is disclosed, for example in Japanese Unexamined Patent Application Publication No. H11-164504, a stator for an electric rotating machine which includes a stator coil formed by joining corresponding pairs of ends of electric conductor segments. The stator coil has a double annular structure. More specifically, the electric conductor segments forming the stator coil are comprised of a plurality of pairs of large and small U-shaped electric conductor segments. For each electric conductor segment pair, turn portions of the large and small electric conductor segments have substantially the same shape and are twisted in the same direction so as to extend in the same direction. Further, the turn portion of the small electric conductor segment is surrounded by the turn portion of the large electric conductor segment so as to extend on the inner side of the turn portion of the large electric conductor segment.

With the above structure, however, it may be difficult to effectively cool the turn portions of the small electric conductor segments. More specifically, as described previously, the turn portions of the large electric conductor segments have substantially the same shape and the same extending direction as those of the small electric conductor segments. Therefore, when cooling air is supplied from the radially inside to coil ends of the stator coil, which are made up of the turn portions of the large and small electric conductor segments, the cooling air first makes contact with the turn portions of the large electric conductor segments and then changes its course to pass by the turn portions of the large electric conductor segments. Consequently, the turn portions of the large electric conductor segments can be effectively cooled by the cooling air. However, the turn portions of the small electric conductor segments, which are located on the inner side of those of the large electric conductor segments, will be shielded from the cooling air by the turn portions of the large electric conductor segments. As a result, the turn portions of the small electric conductor segments may not be effectively cooled by the cooling air.

SUMMARY

According to an exemplary embodiment, there is provided a stator for an electric rotating machine which includes a hollow cylindrical stator core and a stator coil mounted on the stator core. The stator core has a plurality of slots formed along the circumferential direction of the stator core. The stator coil includes first to fourth in-slot portions and first and second turn portions. The first and second in-slot portions are respectively received in two different ones of the slots of the stator core. The third in-slot portion is received in the same slot as the first in-slot portion. The fourth in-slot portion is received in the same slot as the second in-slot portion. Both the first and second turn portions protrude from an axial end face of the stator core so as to be located outside the slots of the stator core. The first turn portion connects the first and second in-slot portions. The second turn portion connects the third and fourth in-slot portions. The second turn portion is located inside the first turn portion. Further, when viewed along the axial direction of the stator core, the first and second turn portions extend so as to cross each other with a reference line C interposed therebetween; the reference line C is defined to extend along the circumferential direction of the stator core through an intersection between the first and second turn portions.

With the above arrangement of the first and second turn portions, the second turn portion can be directly exposed to and thereby effectively cooled by cooling air that passes by the first turn portion after making contact with and thereby cooling the first turn portion. That is, it is possible to effectively cool both the first and second turn portions of the stator coil.

In a further implementation, the electric rotating machine includes a cooling fan to create a flow of the cooling air for cooling the stator coil. Each of the first and second turn portions includes an apex part that is positioned axially furthest from the axial end face of the stator core in the turn portion. The extending direction of the apex part of the first turn portion is substantially coincident with the flow direction of the cooling air, while the extending direction of the apex part of the second turn portion is transverse to the flow direction of the cooling air.

With the above arrangement, when the cooling air passes by the first turn portion, the apex part of the first turn portion can serve as a guide vane to guide the flow of the cooling air, thereby lowering the resistance of the stator coil to the flow of the cooling air and thus increasing the flow rate of the cooling air. Moreover, the apex part of the second turn portion can be more reliably exposed to the cooling air, thereby being more effectively cooled by the cooling air.

It is preferable that each of the first to the fourth in-slot portions has a substantially rectangular cross section. In this case, it is possible to maximize the space factors of the stator coil in the slots of the stator core and minimize the electrical resistance of the stator coil. Consequently, it is possible to lower the temperature of the entire stator coil.

The stator coil may be comprised of a plurality of substantially U-shaped electric conductor segments that are mounted on the stator core and electrically connected to one another. In this ease, it is possible to easily realize the above-described arrangement of the first and second turn portions of the stator coil.

Preferably, the first in-slot portion is located radially inside the third in-slot portion in one of the two slots of the stator core, while the second in-slot portion is located radially outside the fourth in-slot portion in the other slot. In this case, it is possible to reliably make the first and second turn portions cross each other.

DESCRIPTION OF EMBODIMENT

FIG. 1shows the overall configuration of an automotive alternator1according to an exemplary embodiment. The alternator1is designed to be used in a motor vehicle, such as a passenger car or a truck.

As shown inFIG. 1, the alternator1includes a rotor2, a stator3, a frame4, a rectifier5, a voltage regulator11and a pulley20.

The rotor2includes a rotating shaft6, a pair of Lundell-type magnetic pole cores21and a field coil24. The rotating shaft6is rotatably supported by the frame4. The rotating shaft6has the pulley20mounted on a front end portion (i.e., a left end portion inFIG. 1) thereof, so that it can be driven by an internal combustion engine (not shown) of the vehicle via the pulley20. Each of the magnetic pole cores21has a plurality of magnetic pole claws. The field coil24is made of, for example, an insulation-treated copper wire and wound into a hollow cylindrical shape. The magnetic pole cores21are fixed on the rotating shaft6with the field coil24held between the magnetic pole cores21. In addition, on a rear end portion (i.e., a right end portion inFIG. 1) of the rotating shaft6, there are provided a pair of slip rings via which field current is supplied to the field coil24during rotation of the rotor2.

The stator3includes a hollow cylindrical stator core31and a three-phase stator coil32mounted on the stator core31. The detailed configuration of the stator3will be described later.

The frame4has both the rotor2and the stator3retained therein so that the stator3surrounds the rotor2with a predetermined radial gap formed therebetween.

The rectifier5rectifies three-phase AC power outputted from the stator coil32into DC power and outputs the obtained DC power via output terminals thereof.

The voltage regulator11regulates the voltage of the DC power outputted from the rectifier5.

Moreover, in the present embodiment, the alternator1further includes a pair of cooling fans22and23that are respectively provided on axial end faces of the magnetic pole cores21of the rotor2. The cooling fans21and22suck cooling air into the alternator1via suction openings41formed in front and rear end walls of the frame4and discharge the cooling air out of the alternator1via discharge openings42formed in a circumferential wall (or side wall) of the frame4. With the cooling air, it is possible to cool the stator coil32, the rectifier5and the regulator11during operation of the alternator1. In addition, it should be noted that though not shown inFIG. 1, the discharge openings42are formed not only in a front part but also in a rear part of the frame4.

Next, the configuration of the stator3according to the present embodiment will be described in detail.

As shown inFIGS. 2-5, the stator core31has a plurality of slots310that are formed in the radially inner surface of the hollow cylindrical stator core31so as to be spaced from one another at equal intervals in the circumferential direction of the stator core31. Each of the slots310extends in the axial direction of the stator core31so as to axially penetrate the stator core31in the axial direction. In addition, for each of the slots310, the depth-wise direction of the slot310coincides with a radial direction of the stator core31.

The three-phase stator coil32is partially received in the slots310of the stator core31so as to have front-side and rear-side coil ends32F and32R. As shown inFIGS. 1-3, the front-side coil end32F protrudes from a front end face (or one axial end face) of the stator core31, while the rear-side coil end32R protrudes from a rear end face (or the other axial end face) of the stator core31.

In the present embodiment, the stator coil32is comprised of a plurality of electric conductor segments30mounted on the stator core31. Each of the electric conductor segments30is substantially U-shaped and has a substantially rectangular cross section perpendicular to its extending direction.

Specifically, before being mounted to the stator core31, each of the electric conductor segments30has a pair of straight portions extending parallel to each other and a turn portion that connects ends of the straight portions on the same side. In forming the stator coil32, the straight portions are axially inserted, from one axial side (i.e., the rear side inFIG. 1) of the stator core31, respectively into corresponding two of the slots310of the stator core31; the corresponding two slots310are positioned away from each other by one magnetic pole pitch. Then, free end parts of the straight portions, which respectively protrude outside the corresponding slots310on the other axial side (i.e., the front side inFIG. 1) of the stator core31, are bent so as to extend along the circumferential direction of the stator core31obliquely at a predetermined angle with respect to the axial end face of the stator core31. Thereafter, corresponding pairs of the free ends of the electric conductor segments30are joined by, for example, welding.

Consequently, in the resultant stator coil32, each of the electric conductor segments30has a pair of in-slot portions, a turn portion and a pair of end portions. The in-slot portions are respectively received in the corresponding two slots310of the stator core31and extend in the axial direction of the stator core31. The turn portion connects the in-slot portions on the one axial side of the stator core31. The end portions respectively extend from the in-slot portions on the other axial side of the stator core31.

In the present embodiment, as shown inFIG. 5, in each of the slots310of the stator core31, there are received four in-slot portions of the electric conductor segments30so as to be aligned with each other in the radial direction of the stator core31(or in the depth-wise direction of the slot310). Hereinafter, the four in-slot portions are sequentially referred to as an inside in-slot portion, an inside-center in-slot portion, an outside-center in-slot portion and an outside in-slot portion from the radially inside to the radially outside of the slot310. In addition, all the four in-slot portions received in the same slot310belong to the same phase of the stator coil32.

Moreover, the in-slot portions received in the slots310of the stator core31are electrically connected to one another in a predetermined manner, forming the stator coil32.

Specifically, as shown inFIG. 5, on the one axial side (i.e., the rear side inFIG. 1) of the stator core31, for each of the slots310, the inside in-slot portion331ain the slot310is connected, via a corresponding turn portion331c, to the outside in-slot portion331bin another one of the slots310which is positioned away from the slot310clockwise by one magnetic pole pitch. Moreover, the outside-center in-slot portion332ain the slot310is connected, via a corresponding turn portion332c, to the inside-center in-slot portion332bin that slot310which is positioned away from the slot310clockwise by one magnetic pole pitch. Furthermore, the turn portion331cthat connects the pair of the inside in-slot portion331aand the outside in-slot portion331bis located outside the turn portion332cthat connects the pair of the outside-center in-slot portion332aand the inside-center in-slot portion332b.

Consequently, on the one axial side of the stator core31, all the turn portions331cand332cof the electric conductor segments30together make up the rear-side coil end32R of the stator coil32, as shown inFIG. 2. Moreover, all the turn portions331ctogether make up an axially outer layer of the rear-side coil end32R, while all the turn portions332ctogether make up an axially inner layer of the rear-side coil end32R. That is to say, the rear-side coil end32R has a double annular structure.

On the other hand, on the other axial side (i.e., the front side inFIG. 1) of the stator core31, for each of the slots310, the inside-center in-slot portion332bin the slot310is connected to the inside in-slot portion331ain another one of the slots310which is positioned away from the slot310clockwise by one magnetic pole pitch. Moreover, the outside in-slot portion331bin the slot310is connected to the outside-center in-slot portion332ain that slot310which is positioned away from the slot310clockwise by one magnetic pole pitch.

More specifically, as shown inFIG. 3, the inside-center in-slot portion332band the inside in-slot portion331arespectively received in the two slots310, which are positioned away from each other by one magnetic pole pitch, are connected to each other by joining that end portion332eof one electric conductor segment30which extends from the inside-center in-slot portion332band that end portion331eof another electric conductor segment30which extends from the inside in-slot portion331a. In addition, the end portion332eand the end portion331eare joined, for example by TIG welding or ultrasonic welding, forming a joint333atherebetween. Moreover, the outside in-slot portion331band the outside-center in-slot portion332arespectively received in the two slots310, which are positioned away from each other by one magnetic pole pitch, are connected to each other by joining that end portion331dof one electric conductor segment30which extends from the outside in-slot portion331band that end portion332dof another electric conductor segment30which extends from the outside-center in-slot portion332a. In addition, the end portion331dand the end portion332dare joined, for example by TIG welding or ultrasonic welding, forming a joint333btherebetween.

Consequently, on the other axial side of the stator core31, all the end portions331d,331e,332dand332eof the electric conductor segments30and the joints333aand333bformed therebetween together make up the front-side coil end32F of the stator coil32, as shown inFIG. 3. Moreover, all the end portions331eand332eof the electric conductor segments30and the joints333aformed therebetween together make up a radially inner layer of the front-side coil end32F, while all the end portions331dand332dof the electric conductor segments30and the joints333bformed therebetween together make up a radially outer layer of the front-side coil end32F. That is to say, the front-side coil end32F also has a double annular structure.

Furthermore, in the present embodiment, as shown inFIG. 4, the electric conductor segments30forming the stator coil32are comprised of a plurality of pairs of large and small U-shaped electric conductor segments331and332; the small electric conductor segment332is located inside the large electric conductor segment331.

More specifically, the large electric conductor segment331includes one inside in-slot portion331a, one outside in-slot portion331b, one turn portion331cthat connects the inside in-slot portion331aand the outside in-slot portion331bon the rear side of the stator core31, one end portion331dthat extends from the outside in-slot portion331bon the front side of the stator core31, and one end portion331ethat extends from the inside in-slot portion331aon the front side of the stator core31. On the other hand, the small electric conductor segment332includes one outside-center in-slot portion332a, one inside-center in-slot portion332b, one turn portion332cthat connects the outside-center in-slot portion332aand the inside-center in-slot portion332bon the rear side of the stator core31, one end portion332dthat extends from the outside-center in-slot portion332aon the front side of the stator core31, and one end portion332ethat extends from the inside-center in-slot portion332bon the front side of the stator core31.

In operation of the alternator1, with rotation of the cooling fan23(seeFIG. 1), the cooling air flows through spaces formed between the turn portions331eand332cat the rear-side coil end32R of the stator coil32.

FIG. 6illustrates the extending directions of the turn portions331cand332cof the large and small U-shaped electric conductor segments331and332(or the stator coil32) according to the present embodiment as well as the flow direction W of the cooling air that cools the rear-side coil end32R of the stator coil32.

As shown inFIG. 6, the flow direction W of the cooling air is not coincident with any radial direction of the stator core31, in other words, is not perpendicular to the circumferential direction of the stator core31. Instead, the cooling air flows obliquely with respect to the circumferential direction of the stator core31, reaching the turn portions331cof the large electric conductor segments331that are located outside the turn portions332cof the small electric conductor segments332.

In the present embodiment, as described previously, for each pair of the large and small electric conductor segments331and332, the in-slot portion331aof the large electric conductor segment331is received in the same slot310as the in-slot portion332aof the small electric conductor segment332. The in-slot portion331bof the large electric conductor segment331is received in the same slot310as the in-slot portion332bof the small electric conductor segment332. The slot310receiving the in-slot portions331aand332ais positioned away from the slot310receiving the in-slot portions331band332bby one magnetic pole pitch. Further, the in-slot portion331aof the large electric conductor segment331is located radially inside the in-slot portion332aof the small electric conductor segment332, while the in-slot portion331hof the large electric conductor segment331is located radially outside the in-slot portion332bof the small electric conductor segment332(seeFIG. 5). Consequently, as shown inFIG. 6, when viewed along the axial direction of the stator core31, the turn portion331cof the large electric conductor segment331and the turn portion332cof the small electric conductor segment332extend so as to cross each other with a reference line C interposed therebetween; the reference line C is defined to extend along the circumferential direction of the stator core31through an intersection between the turn portions331cand332c.

With the above arrangement of the turn portions331cand332cof the large and small electric conductor segments331and332, the turn portions332cof the small electric conductor segments332can be directly exposed to and thereby effectively cooled by the cooling air that passes by the turn portions331cof the large electric conductor segments331after making contact with and thereby cooling the turn portions331c. As a result, it is possible to effectively cool the entire rear-side coil end32R of the stator coil32.

Further, as shown inFIGS. 4 and 6, in the present embodiment, each of the turn portions331cof the large electric conductor segments331has an apex part331c′ that is positioned axially furthest from the axial end face of the stator core31in the turn portion331c. Similarly, each of the turn portions332cof the small electric conductor segments332has an apex part332ethat is positioned axially furthest from the axial end face of the stator core31in the turn portion332c. For each of the turn portions331cof the large electric conductor segments331, the extending direction of the apex part331e′ of the turn portion331cis substantially coincident with the flow direction W of the cooling air. On the other hand, for each of the turn portions332cof the small electric conductor segments332, the extending direction of the apex part332e′ of the turn portion332cis transverse to the flow direction W of the cooling air.

With the above arrangement, when the cooling air passes by the turn portions331cof the large electric conductor segments331, the apex parts331c′ of the turn portions331ccan serve as guide vanes to guide the flow of the cooling air, thereby lowering the resistance of the rear-side coil end32R of the stator coil32to the flow of the cooling air and thus increasing the flow rate of the cooling air. Moreover, the apex parts332c′ of the turn portions332ccan be more reliably exposed to the cooling air, thereby being more effectively cooled by the cooling air.

In the present embodiment, the stator coil32is formed by joining corresponding pairs of the end portions331d,331e,332dand332eof the large and small U-shaped electric conductor segments331and332.

With the above formation of the stator coil32, it is possible to easily arrange the turn portions331cand332cas described above.

In the present embodiment, each of the large and small U-shaped electric conductor segments331and332is configured to have a substantially rectangular cross section. That is, each of the in-slot portions331a,331b,332aand332bof the large and small U-shaped electric conductor segments331and332has a substantially rectangular cross section perpendicular to the axial direction of the stator core31.

With the above configuration, it is possible to maximize the space factors of the in-slot portions331a,331b,332aand332bof the electric conductor segments331and332in the slots310of the stator core31and minimize the electrical resistance of the stator coil32. Consequently, it is possible to lower the temperature of the entire stator coil32.

While the above particular embodiment has been shown and described, it will be understood by those skilled in the art that various modifications, changes, and improvements may be made without departing from the spirit of the invention.

For example, in the previous embodiment, the present invention is directed to the stator3for the automotive alternator1. However, the invention can also be applied to stators for other electric rotating machines, such as a stator for an electric motor and a stator for a motor-generator that can function both as an electric motor and as an electric generator.

In the previous embodiment, the electric conductor segments30(i.e., the pairs of the large and small U-shaped electric conductor segments331and332) forming the stator coil32are configured to have a substantially rectangular cross section. However, the electric conductor segments30may also be configured to have cross sections of other shapes, such as a substantially circular cross section.

In the previous embodiment, the stator coil32is formed by joining corresponding pairs of the ends of the U-shaped electric conductor segments30. However, the stator coil32may also be formed by joining corresponding pairs of ends of a plurality of continuous electric wires that are wound around the stator core31and much longer than the electric conductor segments30.

In the previous embodiment, the stator3is obtained by assembling the U-shaped electric conductor segments30to the hollow cylindrical stator core31and joining corresponding pairs of the ends of the U-shaped electric conductor segments30. However, the stator3may also be obtained by: (1) winding a plurality of continuous electric wires around a flat band-shaped stator core; and (2) rolling the flat band-shaped stator core into a hollow cylindrical shape.