Electric rotating machine

An electric rotating machine includes a rotor and a stator. The rotor has a plurality of pairs of magnetic poles. The stator includes a stator core and a stator coil that is comprised of a plurality of phase windings wound on the stator core. The stator core has, for each of the phase windings of the stator coil, n circumferentially-consecutive single-phase slots, in which only the phase winding is received, per magnetic pole of the rotor, where n is a natural number not less than 2. Each of the phase windings of the stator coil has first to kth sections that are sequentially arranged from one end to the other end of the phase winding, where k is a natural number not less than 2. The first section is received in different ones of the single-phase slots for the phase winding from the kth section.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based on and claims priority from Japanese Patent Applications No. 2011-208278 filed on Sep. 24, 2011, No. 2012-15596 filed on Jan. 27, 2012, and No. 2012-148570 filed on Jul. 2, 2012, the contents of which are hereby incorporated by reference in their entireties into this application.

BACKGROUND

1. Technical Field

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

2. Description of the Related Art

There are known electric rotating machines which include a rotor and a stator. The rotor has a plurality of pairs of magnetic poles that are arranged in a circumferential direction of the rotor. The stator includes a stator core and a stator coil. The stator core has a plurality of slots, which are arranged in a circumferential direction of the stator core, and is radially opposed to the rotor. The stator coil is comprised of a plurality of phase windings each of which is wound on the stator core so as to be inserted in corresponding ones of the slots of the stator core.

Moreover, to secure high output of the electric rotating machine, the stator core is configured to have, for each of the phase windings of the stator coil, a plurality of circumferentially-consecutive single-phase slots, in which only the phase winding is received, per magnetic pole of the rotor.

For example, Japanese Patent Application Publication No. 2000-69729 (to be simply referred to as Patent Document 1 hereinafter) discloses a three-phase stator coil that is wave-wound on a stator core that has two single-phase slots per phase winding of the stator coil and per magnetic pole of the rotor.

More specifically, as shown inFIG. 26A, the stator coil is comprised of a U-phase winding, a V-phase winding and a W-phase winding. Each of the U-phase, V-phase and W-phase windings includes a first section (a), a second section (b), a third section (c) and a fourth section (d). The four sections (a)-(d) are sequentially arranged from a terminal of the phase winding at one end of the phase winding to a neutral point of the stator coil at the other end of the phase winding. Further, taking only the U-phase winding as an example, as shown inFIG. 26B, the first section (a) and the fourth section (d) of the U-phase winding are received in the same single-phase slots U1of the stator core, while the second section (b) and the third section (c) of the U-phase winding are received in the same single-phase slots U2of the stator core. That is, the first and fourth sections (a) and (d) are received in different ones of the single-phase slots for the U-phase winding from the second and third sections (b) and (c). Here, the single-phase slots U1are circumferentially spaced from one another by one magnetic pole pitch (i.e., a pitch between the N and S magnetic poles of the rotor); the single-phase slots U2are also circumferentially spaced from one another by one magnetic pole pitch; each of the single-phase slots U1is positioned immediately adjacent to one of the single-phase slots U2. In addition, it should be noted that the V-phase and W-phase windings of the stator coil are wound on the stator core in the same manner as the U-phase winding.

Japanese Patent Application Publication No. 2004-64914 (to be simply referred to as Patent Document 2 hereinafter) discloses a three-phase stator coil that is wound on a stator core in a manner that is a hybrid of a lap winding manner and a wave winding manner. The stator core has three single-phase slots per phase winding of the stator coil and per magnetic pole of the rotor. Further, in each slot of the stator core, the stator coil is received in six layers in a radial direction of the stator core. More specifically, the stator coil is first lap-wound around the stator core so as to fill the radially-inside four layers in each slot of the stator core and then wave-wound around the stator core so as to fill the radially-outside two layers in each slot of the stator core. Furthermore, each phase winding of the stator coil includes first to sixth sections. For each phase winding of the stator coil, the first section and the sixth section (i.e., the last section) of the phase winding are received in the same single-phase slots for the phase winding.

That is, in both Patent Document 1 and Patent Document 2, for each phase winding of the stator coil, the first and the last sections of the phase winding are received in the same single-phase slots for the phase winding.

INVESTIGATION BY THE INVENTORS

The inventors of the present invention have investigated the reason why the configurations of receiving the first and the last sections of each phase winding in the same single-phase slots for the phase winding have so far been used in the art.

Specifically, in terms of minimizing the protruding heights of coil ends of the stator coil from corresponding axial end faces of the stator core, it is preferable to locate all of the terminals and neutral point of the stator coil radially outside of the stator core. Here, the coil ends denote those parts of the stator coil which are located outside of the slots of the stator core and respectively protrude from the corresponding axial end faces of the stator core.

Further, for locating all of the terminals and neutral point of the stator coil radially outside of the stator core, it is necessary to arrange an even number of bridging wires to radially cross over one coil end of the stator coil. In particular, when the stator core has two single-phase slots per phase winding of the stator coil and per magnetic pole of the rotor, it is necessary to arrange either zero (i.e., no) or six (i.e., two per phase winding) bridging wires to cross over the coil end of the stator coil.

In cases where the number of bridging wires radially crossing over the coil end is equal to zero, the phase windings of the stator coil overlap each other in six layers in the axial direction of the stator core regardless of the positions of the sections of the phase windings in the slots of the stator core. Moreover, in those cases, the number of types (or shape patterns) of the bridging wires used in the stator coil is equal to nine.

More specifically,FIG. 27Aillustrates a case where for each phase winding of the stator coil, the first section (a) and the fourth section (d) of the phase winding are received in the same single-phase slots while the second section (b) and the third section (c) of the phase winding are received in the same single-phase slots.FIG. 27Billustrates another case where for each phase winding of the stator coil, the first section (a) and the second section (b) of the phase winding are received in the same single-phase slots while the third section (c) and the fourth section (d) of the phase winding are received in the same single-phase slots. In either of those cases shown inFIGS. 27A-27B, six different types of bridging wires are arranged on the radially inner periphery of the stator coil to bridge corresponding pairs of the first to the fourth sections (a)-(d) of each phase winding of the stator coil. On the other hand, three different types of the bridging wires are arranged on the radially outer periphery of the stator core to bridge corresponding pairs of the first to the fourth sections (a)-(d) of each phase winding of the stator coil. However, there is no bridging wire that radially crosses over the coil end of the stator coil. Accordingly, the total number of types of the bridging wires used in the stator coil is equal to nine. Further, the bridging wires of the stator coil overlap each other in six layers in the axial direction of the stator core.

In addition, it should be noted that though there are depicted six bridging wires inFIGS. 27A-27Bas extending on the radially inside of the stator core, those bridging wires actually extend over the coil end of the stator coil without protruding radially inward from the stator core. It also should be noted that the number of bridging wires radially crossing over the coil end cannot be equal to zero in cases where for each phase winding of the stator coil, the first section (a) and the third section (c) of the phase winding are received in the same single-phase slots while the second section (b) and the fourth section (d) of the phase winding are received in the same single-phase slots.

On the other hand,FIGS. 28A-28Cillustrate three cases where the number of bridging wires radially crossing over the coil end is equal to six.

More specifically,FIG. 28Cillustrates a case where for each phase winding of the stator coil, the first section (a) and the second section (b) of the phase winding are received in the same single-phase slots while the third section (c) and the fourth section (d) of the phase winding are received in the same single-phase slots. In this case, there are six bridging wires that radially cross over the coil end of the stator coil. Further, all the bridging wires used in the stator coil overlap each other in six layers in the axial direction of the stator core. In addition, the total number of types of the bridging wires used in the stator coil is equal to eight.

FIG. 28Billustrates another case where for each phase winding of the stator coil, the first section (a) and the third section (c) of the phase winding are received in the same single-phase slots while the second section (b) and the fourth section (d) of the phase winding are received in the same single-phase slots. In this case, there are six bridging wires that radially cross over the coil end of the stator coil. Further, all the bridging wires used in the stator coil overlap each other in four layers in the axial direction of the stator core. In addition, the total number of types of the bridging wires used in the stator coil is reduced to five.

FIG. 28Aillustrates still another case where for each phase winding of the stator coil, the first section (a) and the fourth section (d) of the phase winding are received in the same single-phase slots while the second section (b) and the third section (c) of the phase winding are received in the same single-phase slots. In this case, there are six bridging wires that radially cross over the coil end of the stator coil. Further, all the bridging wires used in the stator coil overlap each other in four layers in the axial direction of the stator core. In addition, the total number of types of the bridging wires used in the stator coil is further reduced to four.

Among all the stator configurations shown inFIGS. 27A-27Band28A-28C, the configuration shown inFIG. 28Ais most preferable in terms of minimizing the axial length of the stator coil and facilitating the manufacture of the stator. Accordingly, for the above reason, the configurations of receiving the first and the last sections of each phase winding in the same single-phase slots for the phase winding have been widely used in the art.

However, the inventors of the present invention also have found a problem with stator coils of electric rotating machines.

Specifically, for an electric motor, when a square wave voltage, whose maximum voltage is equal to V0as shown inFIG. 29, is applied between the terminals of phase windings of the stator coil of the motor, the actual maximum phase-to-phase voltage of the stator coil (i.e., the actual maximum voltage across any two of the phase windings of the stator coil) exceeds V0due to voltage surge as shown inFIG. 30.

FIG. 31illustrates the change in the amplification ratio of the actual maximum phase-to-phase voltage of the stator coil to the maximum voltage V0with frequency.

It can be seen fromFIG. 31that the amplification ratio reaches its peak when the stator coil has a resonant frequency with respect to harmonic components of the square wave voltage applied between the terminals of the phase windings of the stator coil.

Further, when the maximum phase-to-phase voltage of the stator coil is amplified, there may occur necessity to increase the phase-to-phase clearance of the stator coil (e.g., by increasing the thickness of insulating coats of the phase windings of the stator coil) and thereby improve electrical insulation between the phase windings, so as to prevent short circuits from occurring between the phase windings.

SUMMARY OF THE INVENTION

According to one exemplary embodiment, an electric rotating machine is provided which includes a rotor and a stator. The rotor has a plurality of pairs of magnetic poles that are arranged in a circumferential direction of the rotor. The stator includes a stator core and a stator coil. The stator core has a plurality of slots, which are arranged in a circumferential direction of the stator core, and is radially opposed to the rotor. The stator coil is comprised of a plurality of phase windings each of which is wound on the stator core so as to be inserted in corresponding ones of the slots of the stator core. Further, according to this embodiment, the stator core has, for each of the phase windings of the stator coil, n circumferentially-consecutive single-phase slots, in which only the phase winding is received, per magnetic pole of the rotor, where n is a natural number greater than or equal to 2. Each of the phase windings of the stator coil has k sections including a first section and a kth section, where k is a natural number greater than or equal to 2. The first to the kth sections are sequentially arranged from one end to the other end of the phase winding. The first section is received in different ones of the single-phase slots for the phase winding from the kth section.

With the above configuration, the negative mutual inductance between the first and the kth sections can be minimized, thereby minimizing the decrease in the total inductance of the stator coil due to the negative mutual inductance. Consequently, it is possible to lower both the resonant frequency and the resonance peak of the stator coil. As a result, it is possible to lower the maximum phase-to-phase voltage of the stator coil, thereby shortening the necessary phase-to-phase clearance of the stator coil for ensuring electrical insulation between the phase windings of the stator coil.

According to another exemplary embodiment, an electric rotating machine is provided which includes a rotor and a stator. The stator includes a stator core and a stator coil. The stator core has a plurality of slots, which are arranged in a circumferential direction of the stator core, and is radially opposed to the rotor. The stator coil is comprised of a plurality of phase windings each of which is wound on the stator core so as to be inserted in corresponding ones of the slots of the stator core. Further, according to this embodiment, each of the phase windings of the stator coil includes k sections that are sequentially arranged from one end of the phase winding to the other end of the phase winding, where k is a natural number greater than or equal to 2. Each of the k sections is wound on the stator core in such as a manner that a circumferential advancing direction of the section is reversed for each completion of a circumferential advancement of 360°/k.

With the above configuration, for each of the phase windings of the stator coil, the k sections of the phase winding can be separately received in different ones of the corresponding slots to the phase winding from each other. Consequently, it is possible to weaken the magnetic coupling between the k sections of the phase winding, thereby minimizing the negative mutual inductances therebetween. Thus, it is possible to minimize the decrease in the total inductance of the stator coil due to the negative mutual inductances, thereby lowering both the resonant frequency and the resonance peak of the stator coil. As a result, it is possible to lower the maximum phase-to-phase voltage of the stator coil, thereby shortening the necessary phase-to-phase clearance of the stator coil for ensuring electrical insulation between the phase windings of the stator coil.

According to yet another exemplary embodiment, an electric rotating machine is provided which includes a rotor and a stator. The stator includes a stator core and a stator coil. The stator core has a plurality of slots, which are arranged in a circumferential direction of the stator core, and is radially opposed to the rotor. The stator coil is comprised of a plurality of phase windings each of which is wound on the stator core so as to be inserted in corresponding ones of the slots of the stator core. Further, according to this embodiment, each of the phase windings of the stator coil is comprised of j sub-windings that are connected in parallel with each other between opposite ends of the phase winding, where j is a natural number greater than or equal to 2. Each of the sub-windings includes k sections that are sequentially arranged from one end of the sub-winding to the other end of the sub-winding, where k is a natural number greater than or equal to 2. Counting from one end of the phase winding, the same-numbered sections of the sub-windings of the phase winding are received in the same ones of the corresponding slots to the phase winding so as to be proximate to one another in the corresponding slots.

With the above configuration, for each of the phase windings of the stator coil, the first sections of the sub-windings of the phase winding can be radially separated from the kth sections of the sub-windings, thereby weakening the magnetic coupling between the first sections and the kth sections. Consequently, it is possible to minimize the decrease in the total inductance of the stator coil due to the negative mutual inductances between the first sections and the kth sections, thereby lowering both the resonant frequency and the resonance peak of the stator coil. As a result, it is possible to lower the maximum phase-to-phase voltage of the stator coil, thereby shortening the necessary phase-to-phase clearance of the stator coil for ensuring electrical insulation between the phase windings of the stator coil.

According to still another exemplary embodiment, an electric rotating machine is provided which includes a rotor and a stator. The rotor has a plurality of pairs of magnetic poles that are arranged in a circumferential direction of the rotor. The stator includes a stator core and a stator coil. The stator core has a plurality of slots, which are arranged in a circumferential direction of the stator core, and is radially opposed to the rotor. The stator coil is comprised of a plurality of phase windings each of which is wound on the stator core so as to be inserted in corresponding ones of the slots of the stator core. Further, according to this embodiment, the stator core has, for each of the phase windings of the stator coil, 2j circumferentially-consecutive single-phase slots, in which only the phase winding is received, per magnetic pole of the rotor, where j is a natural number greater than or equal to 2. Each of the phase windings of the stator coil is comprised of j sub-windings that are connected in parallel with each other between opposite ends of the phase winding. Each of the sub-windings consists of a first half on the side of one end of the phase winding and a second half on the side of the other end of the phase winding. For each of the phase windings of the stator coil, all the first and second halves of the sub-windings of the phase winding are separately received in different ones of the single-phase slots for the phase winding from each other.

With the above configuration, for each of the sub-windings of the phase windings of the stator coil, the first and second halves of the sub-winding are respectively received in two different single-phase slots for the phase winding. Consequently, it is possible to weaken the magnetic coupling between the first and second halves of the sub-winding, thereby minimizing the negative mutual inductance therebetween. Thus, it is possible to minimize the decrease in the total inductance of the stator coil due to the negative mutual inductance, thereby lowering both the resonant frequency and the resonance peak of the stator coil. As a result, it is possible to lower the maximum phase-to-phase voltage of the stator coil, thereby shortening the necessary phase-to-phase clearance of the stator coil for ensuring electrical insulation between the phase windings of the stator coil.

DESCRIPTION OF EMBODIMENTS

Exemplary embodiments will be described hereinafter with reference toFIGS. 1-25. It should be noted that for the sake of clarity and understanding, identical components having identical functions in different embodiments have been marked, where possible, with the same reference numerals in each of the figures and that for the sake of avoiding redundancy, descriptions of the identical components will not be repeated.

First Embodiment

FIG. 1shows the overall configuration of an electric rotating machine1according to a first embodiment. The electric rotating machine1is designed to be used in a motor vehicle to function as an electric motor.

As shown inFIG. 1, the electric rotating machine1includes a housing10, a rotor14and a stator20. The housing10is comprised of a pair of substantially cup-shaped housing pieces10aand10bwhich are jointed together at the open ends thereof. The housing10has a pair of bearings11and12mounted therein, via which a rotating shaft13is rotatably supported by the housing10. The rotor14is received in the housing10and fixed on the rotating shaft13. The stator20is fixed in the housing10so as to surround the radially outer periphery of the rotor14.

The rotor14includes a plurality of permanent magnets that are embedded at predetermined positions in the rotor14. The permanent magnets form a plurality of pairs of N and S magnetic poles on the radially outer periphery of the rotor14to face the radially inner periphery of the stator20. The magnetic poles are spaced from one another at a predetermined pitch in the circumferential direction of the rotor14. Further, the polarities of the magnetic poles alternate between north (N) and south (S) in the circumferential direction. In addition, the number of the magnetic poles can be suitably set according to the design specification of the electric rotating machine1. For example, in the present embodiment, the number of the magnetic poles is set to be equal to eight (i.e., four N poles and four S poles).

Referring now toFIG. 2, the stator20includes a substantially annular stator core30and a three-phase stator coil40that is comprised of a U-phase winding, a V-phase winding and a W-phase winding.

The stator core30is formed by, for example, laminating a plurality of core sheets (or steel sheets) in the axial direction of the stator core30. The stator core30has a plurality of slots31that are formed in a radially inner surface of the stator core30and spaced from one another in the circumferential direction of the stator core30at a constant pitch. Each of the slots31extends in the axial direction of the stator core30so as to penetrate the stator core30in the axial direction and has a substantially rectangular cross section perpendicular to the axial direction. For each of the slots31, the depth-wise direction of the slot31is coincident with a radial direction of the stator core30.

In the present embodiment, there are provided two slots31(or n slots31, where n is equal to 2) per magnetic pole of the rotor14that has the eight magnetic poles and per phase of the three-phase stator coil40. That is, the stator core30has, for each of the U-phase, V-phase and W-phase windings of the stator coil40, two circumferentially-consecutive single-phase slots, in which only the phase winding is received, per magnetic pole of the rotor14. Accordingly, the total number of the slots31provided in the stator core30is equal to 48 (i.e., 2×3×8).

Each of the U-phase, V-phase and W-phase windings of the stator coil40is formed by inserting a plurality of substantially U-shaped electric conductor segments50into corresponding slots31of the stator core30from one axial side of the stator core30and welding corresponding pairs of free ends of the electric conductor segments50on the other axial side of the stator core30. Each of the electric conductor segments50is obtained by bending a rectangular electric conductor, which has an insulating coat (not shown) covering its outer surface, into a substantially U-shape. Each of the electric conductor segments50has, at each free end thereof, an exposed portion (not shown) where the insulating coat is removed from the electric conductor segment50. Corresponding pairs of the exposed portions of the electric conductor segments50are jointed together by welding to form a joint (or weld)56therebetween.

More specifically, as shown inFIG. 3, each of the electric conductor segments50is substantially U-shaped to include a pair of straight portions51that extend parallel to each other and a turn portion52that connects ends of the straight portions51on the same side. The turn portion52includes an apex part53that is formed at the center of the turn portion52so as to extend parallel to a corresponding one of axial end faces30aof the stator core30. The turn portion52also includes a pair of oblique parts54that are formed respectively on opposite sides of the apex part53so as to extend obliquely at a predetermined angle with respect to the corresponding axial end face30aof the stator core30. In addition, inFIG. 3, the reference numeral24denotes an insulator that is arranged to electrically insulate the stator coil40(or the electric conductor segments50) from the stator core30.

Further, as shown inFIG. 3, in the present embodiment, the electric conductor segments50forming the stator coil40include a plurality of pairs of first and second electric conductor segments50A and50B. For each pair of the first and second electric conductor segments50A and50B, the straight portions51of the first electric conductor segment50A are inserted in different ones of the slots31of the stator core30from those of the second electric conductor segment50B. More specifically, the slots31in which the straight portions51of the first electric conductor segment50A are inserted are respectively adjacent to those in which the straight portions51of the second electric conductor segment50B are inserted.

For example, for that pair of the first and second electric conductor segments50A and50B which is shown on the right upper side inFIG. 3, the first electric conductor segment50A has its right-side straight portion51inserted in the sixth layer (i.e., the radially outermost layer) of one slot31A and its left-side straight portion51inserted in the fifth layer of another slot (not shown) that is positioned counterclockwise of the slot31A by one magnetic pole pitch (i.e., a pitch between the N and S magnetic poles of the rotor14). On the other hand, the second electric conductor segment50B has its right-side straight portion51inserted in the sixth layer of one slot31B that is positioned counterclockwise of and immediately adjacent to the slot31A and its left-side straight portion51inserted in the fifth layer of another slot (not shown) that is positioned counterclockwise of the slot31B by one magnetic pole pitch. That is, the first and second electric conductor segments50A and50B are circumferentially offset from each other by one slot pitch.

In addition, in each of the slots31of the stator core30, there are inserted an even number of the straight portions51of the electric conductor segments50. More specifically, in the present embodiment, in each of the slots31of the stator core30, there are inserted six straight portions51of the electric conductor segments50so as to be radially stacked in six layers in the slot31.

For each of the electric conductor segments50, free end parts of the straight portions51of the electric conductor segment50, which protrude outside of the corresponding slots31on the other axial side of the stator core30, are twisted respectively toward opposite sides in the circumferential direction of the stator core30so as to extend obliquely at a predetermined angle with respect to the corresponding axial end face30aof the stator core30. Consequently, each of the free end parts of the straight portions51is transformed into an oblique part55that extends in the circumferential direction of the stator core30for substantially half a magnetic pole pitch (seeFIG. 2).

Further, on the other axial side of the stator core30, each corresponding pair of the oblique parts55of the electric conductor segments50are welded at their respective distal ends, forming a weld56therebetween and thereby being electrically connected to each other. More specifically, for each of the three phase windings41(i.e., the U-phase, V-phase and W-phase windings) of the stator coil40, all the electric conductor segments50which together make up the phase winding41are electrically connected in series with one another. As a result, as shown inFIGS. 4A-4C, each of the phase windings41is wave-wound around the stator core30by, for example, 6 turns in the circumferential direction of the stator core30.

In addition, each of the phase windings41of the stator coil40further includes, in addition to the substantially U-shaped electric conductor segments50as shown inFIG. 3, other electric conductor segments of different shapes (not shown). Those other electric conductor segments include: an electric conductor segment that has a terminal of the phase winding41integrally formed therein; an electric conductor segment that has a neutral point lead (i.e., a lead for being connected to the neutral point of the stator coil40); and electric conductor segments each having a connection portion for connecting two consecutive turns (e.g., the first and second turns) of the phase winding41.

Referring further toFIG. 5A, in the present embodiment, the three phase windings41of the stator coil40are Y-connected to define the neutral point44therebetween. In other words, the U-phase, V-phase and W-phase windings41of the stator coil40are jointed and thus electrically connected to each other at the neutral point44.

Moreover, each of the U-phase, V-phase and W-phase windings41of the stator coil40includes 2n sections, where n is a natural number greater than or equal to 2.

More specifically, in the present embodiment, each of the phase windings41of the stator coil40includes a first section (a), a second section (b), a third section (c) and a fourth section (d), which are sequentially arranged from the terminal43of the phase winding41at one end of the phase winding41to the neutral point44of the stator coil40at the other end of the phase winding41. That is, in the present embodiment, n is equal to 2. Further, each of the first to the fourth sections (a)-(d) is wave-wound on the stator core30.

Furthermore, for each of the phase windings41, the first section is received in different ones of the single-phase slots31for the phase winding41from the 2nth section. Moreover, counting from the terminal43side, the 2mth section is received in the same ones of the single-phase slots31for the phase winding41as the (2m−1)th section, where m is a natural number that satisfies 1≦m≦n.

More specifically, in the present embodiment, as shown inFIG. 5B, for the U-phase winding41, the first section (a) is received in the single-phase slots U1, while the fourth section (d) (i.e., the 2nth section) is received in the single-phase slots U2. Here, the single-phase slots U1are circumferentially spaced from one another by one magnetic pole pitch; the single-phase slots U2are also circumferentially spaced from one another by one magnetic pole pitch; each of the single-phase slots U1is positioned immediately adjacent to one of the single-phase slots U2. Further, since n is equal to 2, m is equal to 1 or 2. Therefore, the second section (b) (i.e., the 2mth section where m is equal to 1) is received in the same single-phase slots U1as the first section (a) (i.e., the (2m−1)th section where m is equal to 1). On the other hand, the fourth section (d) (i.e., the 2mth section where m is equal to 2) is received in the same single-phase slots U2as the third section (c) (i.e., the (2m−1)th section where m is equal to 2). In addition, it should be noted that though not graphically shown, the V-phase and W-phase windings41of the stator coil40are wound on the stator core30in the same manner as the U-phase winding41.

Moreover, in the present embodiment, on the one axial side (i.e., the lower side inFIG. 2) of the stator core30, all the turn portions52of the electric conductor segments50, which protrude from one axial end face30aof the stator core30, together make up a first coil end47of the stator coil40. On the other axial side (i.e., the upper side inFIG. 2) of the stator core30, all of the oblique parts55of the electric conductor segments50, which protrude from the other axial end face30aof the stator core30, and the joints56formed between the oblique parts55together make up a second coil end48of the stator coil40.

In addition, though not graphically shown, on the one axial side of the stator core30, the turn portions52of the electric conductor segments50are radially arranged in a given number of layers. On the other axial side of the stator core30, as shown inFIG. 2, the joints56formed between the oblique parts55of the electric conductor segments50are circumferentially arranged at given intervals and radially arranged in a given number of layers.

Furthermore, in the present embodiment, the maximum voltage applied between the terminals43of the U-phase, V-phase and W-phase windings41of the stator coil40is set, based on Paschen's Law, to be higher than or equal to 330V. In addition, as shown inFIG. 6, according to Paschen's Law, electric discharge may occur between electric conductors at the atmospheric pressure when the voltage across the electric conductors is not lower than about 330 V.

The above-described electric rotating machine1according to the present embodiment has the following advantages.

In the present embodiment, the electric rotating machine1includes the rotor core14and the stator20. The rotor14has four pairs of N and S magnetic poles that are arranged at a predetermined pitch in the circumferential direction of the rotor14(see,FIG. 5B). The stator20includes the stator core30and the stator coil40. The stator core30has the 48 slots31, which are arranged in the circumferential direction of the stator core30, and is radially opposed to the rotor14. The stator coil40is comprised of the U-phase, V-phase and W-phase windings41each of which is wave-wound on the stator core30so as to be inserted in the corresponding slots31of the stator core30. More specifically, the stator core30has, for each of the phase windings41of the stator coil40, n circumferentially-consecutive single-phase slots31, in which only the phase winding41is received, per magnetic pole of the rotor14, where n is a natural number not less than 2 (e.g., n=2 in the present embodiment). Each of the phase windings41of the stator coil40includes 2n sections (i.e., four sections in the present embodiment) that are sequentially arranged from the terminal43of the phase winding41to the neutral point44of the stator coil40. For each of the phase windings41, the first section (a) is received in different ones of the single-phase slots31for the phase winding41from the 2nth section (i.e., the fourth section (d) in the present embodiment).

With the above configuration, the negative mutual inductance between the first and the 2nth sections can be minimized, thereby minimizing the decrease in the total inductance of the stator coil40due to the negative mutual inductance. Consequently, as shown inFIG. 7, it is possible to considerably lower both the resonant frequency and the resonance peak of the stator coil40in comparison with the conventional configuration shown inFIG. 27A. As a result, it is possible to lower the maximum phase-to-phase voltage of the stator coil40, thereby shortening the necessary phase-to-phase clearance of the stator coil40for ensuring electrical insulation between the phase windings41of the stator coil40.

In addition, the resonant frequency fnof the stator coil40can be determined by the following equation:
fn1/2π√{square root over (LC)}
where L is the total inductance of the stator coil40and C is the earth capacitance between the stator coil40and the stator core30. Moreover, the total inductance L of the stator coil40is the sum of the self-inductance of the stator coil40and the mutual inductances between different sections of the stator coil40. Therefore, by minimizing the negative mutual inductance between the first and the 2nth sections in each phase winding41of the stator coil40, it is possible to minimize the decrease in the total inductance L of the stator coil40due to the negative mutual inductance.

In the present embodiment, for each of the phase windings41of the stator coil40, the 2mth section of the phase winding41is received in the same single-phase slots31for the phase winding41as the (2m−1)th section of the phase winding41, where m is a natural number that satisfies 1≦m≦n. For example, for the U-phase winding41, the first and second sections (a) and (b) are received in the same single-phase slots U1, while the third and fourth sections (c) and (d) are received in the same single-phase slots U2.

Consequently, it is possible to minimize the negative mutual inductances between the first and third sections (a) and (c) and between the second and fourth sections (b) and (d), thereby further lowering both the resonant frequency and the resonance peak of the stator coil40. As a result, it is possible to further lower the maximum phase-to-phase voltage of the stator coil40, thereby further shortening the necessary phase-to-phase clearance of the stator coil40for ensuring electrical insulation between the phase windings41.

In the present embodiment, for each of the phase windings41of the stator coil40, each of the first to the 2nth sections of the phase winding41is wave-wound on the stator core30.

With the above configuration, it is possible to easily form the stator coil40. Moreover, it is also possible to reliably obtain the effect of lowering both the resonant frequency and the resonance peak of the stator coil40.

In the present embodiment, each of the phase windings41of the stator coil40is formed of the substantially U-shaped electric conductor segments50that are respectively inserted in the corresponding single-phase slots31for the phase winding41and electrically connected in series with one another. On one axial side of the stator core30, each corresponding pair of the in-slot portions51of the electric conductor segments50are connected by one turn portion52. On the other axial side of the stator core30, each corresponding pair of the oblique parts55of the electric conductor segments50are joined together to form the joint56therebetween. All of the turn portions52connecting the in-slot portions51of the electric conductor segments50of the phase windings41together make up the first coil end47of the stator coil40on the one axial side of the stator core30. All of the oblique parts55of the electric conductor segments50of the phase windings41and the joints56formed between the oblique parts55together make up the second coil end48of the stator coil40on the other axial side of the stator core30.

With the above configuration, since each of the electric conductor segments50can be made short and thus be easily handled, it is possible to more easily manufacture the stator coil40in comparison with the case of forming each of the phase windings41of the stator coil40with a single continuous electric wire.

In the present embodiment, the maximum voltage applied between the terminals43of the phase windings41of the stator coil40is set to be higher than or equal to 330 V.

Specifically, as shown inFIG. 6, according to Paschen's Law, in the region where the discharge-starting voltage is not lower than about 330 V, the discharge-starting voltage has a positive correlation with the distance between the electric conductors. Accordingly, in the region, the necessary phase-to-phase clearance of the stator coil40for ensuring electrical insulation between the phase windings41also has a positive correlation with the maximum phase-to-phase voltage of the stator coil40. Therefore, setting the maximum voltage applied between the terminals43of the phase windings41as above, it is possible to shorten the necessary phase-to-phase clearance of the stator coil40by lowering the maximum phase-to-phase voltage of the stator coil40.

This experiment has been conducted to verify the effect of lowering the maximum phase-to-phase voltage of the stator coil40according to the first embodiment.

Specifically, in the experiment, an electric rotating machine was used in which: the stator core had two single-phase slots per phase winding of the stator coil and per magnetic pole of the rotor; and the phase windings of the stator coil were wave-wound on the stator core so as to be radially stacked in six layers in each slot of the stator core. Moreover, with the electric rotating machine, three different stator configurations were realized by changing the sequence of electrically connecting different sections of the phase windings of the stator coil.

The first configuration was the conventional one as shown inFIG. 27A. The second configuration was the conventional one as shown inFIG. 28A. In both the first and second conventional configurations, for each phase winding of the stator coil, the first section (a) and the fourth section (d) are received in the same single-phase slots as disclosed in Patent Document 1. On the other hand, the third configuration was the one according to the first embodiment and as shown inFIG. 8B.

With each of the three configurations, as shown inFIG. 8A, the phase-to-phase voltage was measured between the phase windings41at positions where the degree of resonance is high (e.g., at about the ¼-length positions from the respective terminals43in the phase windings41).

The measurement results of the experiment are shown inFIG. 9, in which the horizontal axis represents time and the vertical axis represents the phase-to-phase voltage. In addition, inFIG. 9, “APPLIED VOLTAGE” denotes the voltage applied between the terminals43of the phase windings41; “1ST CONVENTIONAL” denotes the first conventional configuration; “1ST EMBODIMENT” denotes the configuration according to the first embodiment; and “2ND CONVENTIONAL” denotes the second conventional configuration.

As seen fromFIG. 9, with the configuration according to the first embodiment, the fluctuation in the phase-to-phase voltage due to resonance was considerably reduced in comparison with the first and second conventional configurations. Moreover, with the configuration according to the first embodiment, the maximum phase-to-phase voltage was reduced by about 18% with respect to the voltage applied between the terminals43of the phase windings41. In comparison, with the first and second conventional configurations, the maximum phase-to-phase voltage exceeded the voltage applied between the terminals43of the phase windings41.

In this modification, as shown inFIGS. 10A and 10B, each of the phase windings41of the stator coil40is formed by joining eight continuous electric wires60, not by joining the electric conductor segments50as in the first embodiment.

Specifically, each of the electric wires60includes twelve in-slot portions (not shown), each of which is received in a corresponding one of the slots31of the stator core30, and eleven turn portions62that each connect a corresponding adjacent pair of the in-slot portions and are alternately located on opposite axial sides of the stator core30. Further, among the twelve in-slot portions, the first in-slot portion which is formed at one end of the electric wire60is received in the first layer (i.e., the radially innermost layer) of one slot31of the stator core30, while the twelfth in-slot portion which is formed at the other end of the electric wire60is received in the sixth layer (i.e., the radially outermost layer) of another slot31of the stator core30. Each of the electric wires60is wave-wound around the stator core30by, for example, 11/8 turns.

Moreover, in the modification, each of the phase windings41of the stator coil40includes, as in the first embodiment, four sections (i.e., 2n sections where n is equal to 2). The first to the fourth sections (a)-(d) are sequentially arranged from one end of the phase winding41to the other end of the phase winding41. The first section (a) is received in different ones of the single-phase slots31for the phase winding41from the fourth section (d). Further, the first and second sections (a) and (b) are received in the same ones of the single-phase slots31for the phase winding41, while the third and fourth sections (c) and (d) are received in the same ones of the single-phase slots31for the phase winding41. Furthermore, each of the first to the fourth sections (a)-(d) is wave-wound on the stator core30.

With the above configuration according to the modification, it is also possible to considerably lower both the resonant frequency and the resonance peak of the stator coil40. As a result, it is possible to lower the maximum phase-to-phase voltage of the stator coil40, thereby shortening the necessary phase-to-phase clearance of the stator coil40for ensuring electrical insulation between the phase windings41of the stator coil40.

In this modification, as shown inFIGS. 11A-11C, each of the phase windings41of the stator coil40is formed by joining a plurality of substantially U-shaped electric conductor segments50as in the first embodiment. However, each of the phase windings41is lap-wound on the stator core30, not wave-wound on the stator core30as in the first embodiment.

Specifically, in the modification, each of the phase windings41is lap-wound around the stator core30to have a plurality of in-slot portion pairs each of which is received in a corresponding one of the single-phase slots31for the phase winding41such that the two in-slot portions of the pair are superposed in the corresponding single-phase slot31.

Moreover, in the modification, each of the phase windings41of the stator coil40includes, as in the first embodiment, four sections (i.e., 2n sections where n is equal to 2). The first to the fourth sections (a)-(d) are sequentially arranged from one end of the phase winding41to the other end of the phase winding41. The first section (a) is received in different ones of the single-phase slots31for the phase winding41from the fourth section (d). Further, the first and second sections (a) and (b) are received in the same ones of the single-phase slots31for the phase winding41, while the third and fourth sections (c) and (d) are received in the same ones of the single-phase slots31for the phase winding41.

With the above configuration according to the modification, it is also possible to considerably lower both the resonant frequency and the resonance peak of the stator coil40. As a result, it is possible to lower the maximum phase-to-phase voltage of the stator coil40, thereby shortening the necessary phase-to-phase clearance of the stator coil40for ensuring electrical insulation between the phase windings41of the stator coil40.

Second Embodiment

This embodiment illustrates a stator20which has a similar configuration to the stator20according to the first embodiment; accordingly, only the differences therebetween will be described hereinafter.

In the present embodiment, as shown inFIG. 12, each of the phase windings41of the stator coil40is comprised of j sub-windings42that are connected in parallel with each other between the terminal43of the phase winding41and the neutral portion44of the stator coil40, where j is a natural number greater than or equal to 2. Moreover, each of the sub-windings42includes k sections that are sequentially arranged from one end of the sub-winding42on the terminal43side to the other end of the sub-winding42on the neutral point44side, where k is a natural number greater than or equal to 2. Furthermore, for each of the sub-windings42, the first to the (k/2)th sections of the sub-winding42are received in different ones of the single-phase slots31for the phase winding41from the (k/2+1)th to the kth sections of the sub-winding42.

Specifically, assume that j is equal to 2 and k is equal to 4. Then, as shown inFIG. 12, each of the phase windings41of the stator coil40is comprised of a first sub-winding42-1and a second sub-winding42-2that are connected in parallel with each other between the terminal43of the phase winding41and the neutral point44of the stator coil40. The first sub-winding42-1includes a first section (1a), a second section (1b), a third section (1c) and a fourth section (1d), which are sequentially arranged from one end of the first sub-winding42-1on the terminal43side to the other end of the first sub-winding42-1on the neutral point44side. The second sub-winding42-2includes a first section (2a), a second section (2b), a third section (2c) and a fourth section (2d), which are sequentially arranged from one end of the second sub-winding42-2on the terminal43side to the other end of the second sub-winding42-2on the neutral point44side.

Moreover, as shown inFIG. 13, for each of the phase windings41, the first and second sections (1a,1b,2a,2b) of the first and second sub-windings42-1and42-2are received in different ones of the single-phase slots31for the phase winding41from the third and fourth sections (1c,1d,2c,2d) of the first and second sub-windings42-1and42-2.

In addition, it should be noted that for the sake of simplicity, only the positions of the sections of the sub-windings of the U-phase winding41in the single-phase slots31for the U-phase winding41are shown inFIG. 13; and that the sections of the sub-windings of the V-phase and W-phase windings41are respectively positioned in the single-phase slots31for the V-phase and W-phase windings41in the same manner as those of the U-phase winding41.

With the above configuration of the stator20according to the present embodiment, for each phase winding41of the stator coil40, it is possible to weaken the magnetic coupling between the first and second sections (1a,1b,2a,2b) and the third and fourth sections (1c,1d,2c,2d) of the first and second sub-windings42-1and42-2of the phase winding41, thereby minimizing the negative mutual inductances therebetween. Consequently, it is possible to minimize the decrease in the total inductance of the stator coil40due to the negative mutual inductances, thereby lowering both the resonant frequency and the resonance peak of the stator coil40. As a result, it is possible to lower the maximum phase-to-phase voltage of the stator coil40, thereby shortening the necessary phase-to-phase clearance of the stator coil40for ensuring electrical insulation between the phase windings41of the stator coil40.

In addition, in the case of k being an odd number greater than 2, for each of the sub-windings42-1and42-2, the central section of the sub-winding may be received either in the same single-phase slots31as those sections of the sub-winding which are positioned upstream (i.e., on the terminal43side) of the central section or in the same single-phase slots31as those sections of the sub-winding which are positioned downstream (i.e., on the neutral point44side) of the central section.

Third Embodiment

This embodiment illustrates a stator20which has a similar configuration to the stator20according to the first embodiment; accordingly, only the differences therebetween will be described hereinafter.

In this embodiment, as shown inFIGS. 14 and 15, each of the phase windings41of the stator coil40includes k sections that are sequentially arranged from one end of the phase winding41on the terminal43side to the other end of the phase winding41on the neutral point41side, where k is a natural number greater than or equal to 2. Moreover, each of the k sections is wound on the stator core30in such as a manner that the circumferential advancing direction of the section is reversed for each completion of a circumferential advancement of 360°/k (i.e., an advancement in the circumferential direction of the stator core30corresponding to a mechanical angular range of 360°/k).

Specifically, assume that k=2. Then, as shown inFIG. 14, each of the phase windings41of the stator coil40includes a first section (a) on the terminal43side and a second section (b) on the neutral point44side. Moreover, each of the first and second sections (a) and (b) is wound on the stator core30in such a manner that the circumferential advancing direction of the section is reversed each time the section completes an advancement in the circumferential direction of the stator core30by 180°.

More specifically, as shown inFIG. 15, for each of the phase windings41, the first section (a) of the phase winding41is first two-layer-lap-wound on the stator core30so as to advance clockwise (i.e., rightward inFIG. 15) in the circumferential direction of the stator core30from a first slot31(not shown) to a second slot31(not shown) of the stator core30. The first slot31has a circumferential position corresponding to a mechanical angle of 0° (or 360°), while the second slot31has a circumferential position corresponding to a mechanical angle of 180°. That is, the first section (a) is first advanced clockwise in the circumferential direction of the stator core30by 180°. Consequently, as indicated with a solid line inFIG. 15, a first part (a1) of the first section (a) is received in two layers in each of those slots31the circumferential positions of which fall in the range of 0 to 180°. Then, the first section (a) is two-layer-lap-wound on the stator core30so as to advance counterclockwise (i.e., leftward inFIG. 15) from the second slot31to the first slot31. That is, the circumferential advancing direction of the first section (a) is reversed at the second slot31and the first section (a) is further advanced counterclockwise in the circumferential direction of the stator core30by 180°. Consequently, as indicated with a dashed line inFIG. 15, a second part (a2) of the first section (a) is also received in two layers in each of those slots31the circumferential positions of which fall in the range of 0 to 180°.

Moreover, the second section (b) of the phase winding41is first two-layer-lap-wound on the stator core30so as to advance counterclockwise from the first slot31to the second slot31. That is, the second section (b) is first advanced counterclockwise in the circumferential direction of the stator core30by 180°. Consequently, as indicated with a dashed line inFIG. 15, a first part (b1) of the second section (b) is received in two layers in each of those slots31the circumferential positions of which fall in the range of 180 to 360°. Then, the second section (b) is two-layer-lap-wound on the stator core30so as to advance clockwise from the second slot31to the first slot31. That is, the circumferential advancing direction of the second section (b) is reversed at the second slot31and the second section (b) is further advanced clockwise in the circumferential direction of the stator core30by 180°. Consequently, as indicated with a solid line inFIG. 15, a second part (b2) of the second section (b) is also received in two layers in each of those slots31the circumferential positions of which fall in the range of 180 to 360°.

In addition, in the present embodiment, for each of the first and second sections (a) and (b) of the phase windings (41), the circumferential advancing direction of the section is reversed only once and thus the section includes only the first and second parts. However, it should be noted that the circumferential advancing direction of the section may also be reversed a plurality of times and thus the section may include three or more parts.

With the above configuration of the stator20according to the present embodiment, for each of the phase windings41of the stator coil40, the first section (a) of the phase winding41can be separately received in different ones of the single-phase slots31for the phase winding41from the second section (b) of the phase winding41. Consequently, it is possible to weaken the magnetic coupling between the first section (a) and the second section (b) of the phase winding41, thereby minimizing the negative mutual inductance therebetween. Thus, it is possible to minimize the decrease in the total inductance of the stator coil40due to the negative mutual inductance, thereby lowering both the resonant frequency and the resonance peak of the stator coil40. As a result, it is possible to lower the maximum phase-to-phase voltage of the stator coil40, thereby shortening the necessary phase-to-phase clearance of the stator coil40for ensuring electrical insulation between the phase windings41of the stator coil40.

Comparative Example of Third Embodiment

In this comparative example, for each of the phase windings41of the stator coil40, each of the k sections of the phase winding41is wound on the stator core30in a different manner from the third embodiment.

Specifically, as shown inFIG. 16, for each of the phase windings41, the first section (a) of the phase winding41is first two-layer-lap-wound on the stator core30by one complete turn so as to advance clockwise (i.e., rightward inFIG. 6) in the circumferential direction of the stator core30by 360°. That is, the first section (a) is wound on the stator core30without reversing its circumferential advancing direction. Then, the second section (b) of the phase winding41is two-layer-lap-wound on the stator core30by one complete turn so as to advance counterclockwise (i.e., leftward inFIG. 16) in the circumferential direction of the stator core30by 360°. That is, the second section (b) is also wound on the stator core30without reversing its circumferential advancing direction.

Consequently, as indicated with a solid line inFIG. 16, the first section (a) is received in two layers in each of those slots31the circumferential positions of which fall in the range of 0 to 360°. Moreover, as indicated with a dashed line inFIG. 16, the second section (b) is also received in two layers in each of those slots31the circumferential positions of which fall in the range of 0 to 360°. Furthermore, the first part (a1) of the first section (a) and the second part (b2) of the second section (b) are received in the same slots31the circumferential positions of which fall in the range of 0 to 180°; the second part (a2) of the first section (a) and the first part (b1) of the second section (b) are received in the same slots31the circumferential positions of which fall in the range of 180 to 360°.

Accordingly, in the comparative example, for each of the phase windings41of the stator coil40, the first section (a) of the phase winding41is received in the same single-phase slots31for the phase winding41as the second section (b) of the phase winding41. Consequently, it is impossible to achieve the same advantages as the stator20according to the third embodiment.

Fourth Embodiment

This embodiment illustrates a stator20which has a similar configuration to the stator20according to the first embodiment; accordingly, only the differences therebetween will be described hereinafter.

In the present embodiment, as in the second embodiment (seeFIG. 12), each of the phase windings41of the stator coil40is comprised of j sub-windings42that are connected in parallel with each other between the terminal43of the phase winding41and the neutral portion44of the stator coil40, where j is a natural number greater than or equal to 2. Moreover, each of the sub-windings42includes k sections that are sequentially arranged from one end of the sub-winding42on the terminal43side to the other end of the sub-winding42on the neutral point44side, where k is a natural number greater than or equal to 2. Further, in the present embodiment, counting from one end of the phase winding41on the terminal43side, the same-numbered sections of the sub-windings42of the phase winding41are received in the same ones of the single-phase slots31for the phase winding41so as to be proximate to one another in the same single-phase slots31.

Specifically, assume that j is equal to 2 and k is equal to 4. Then, referring again toFIG. 12, each of the phase windings41of the stator coil40is comprised of a first sub-winding42-1and a second sub-winding42-2that are connected in parallel with each other between the terminal43of the phase winding41and the neutral point44of the stator coil40. The first sub-winding42-1includes a first section (1a), a second section (1b), a third section (1c) and a fourth section (1d), which are sequentially arranged from one end of the first sub-winding42-1on the terminal43side to the other end of the first sub-winding42-1on the neutral point44side. The second sub-winding42-2includes a first section (2a), a second section (2b), a third section (2c) and a fourth section (2d), which are sequentially arranged from one end of the second sub-winding42-2on the terminal43side to the other end of the second sub-winding42-2on the neutral point44side.

Moreover, as shown inFIG. 17, for each of the phase windings41, the first sections (1a,2a) of the first and second sub-windings42-1and42-2of the phase winding41are received in the same ones of the single-phase slots31for the phase winding41so as to be proximate to each other in the same single-phase slots31. The second sections (1b,2b) of the first and second sub-windings42-1and42-2of the phase winding41are received in the same ones of the single-phase slots31for the phase winding41so as to be proximate to each other in the same single-phase slots31. The third sections (1c,2c) of the first and second sub-windings42-1and42-2of the phase winding41are received in the same ones of the single-phase slots31for the phase winding41so as to be proximate to each other in the same single-phase slots31. The fourth sections (1d,2d) of the first and second sub-windings42-1and42-2of the phase winding41are received in the same ones of the single-phase slots31for the phase winding41so as to be proximate to each other in the same single-phase slots31. More specifically, in the present embodiment, in each of the single-phase slots31for the phase winding41, all of the sections of the first and second sub-windings42-1and42-2of the phase winding41are radially arranged from the radially outer side in the sequence of1a,2a,1b,2b,1c,2c,1d,2dor in the sequence of2a,1a,2b,1b,2c,1c,2d,1d.

With the above arrangement, for the first sub-winding42-1, the first and second sections (1a,1b) are radially separated from the third and fourth sections (1c,1d), thereby weakening the magnetic coupling between the first and second sections (1a,1b) and the third and fourth sections (1c,1d). Similarly, for the second sub-winding42-2, the first and second sections (2a,2b) are radially separated from the third and fourth sections (2c,2d), thereby weakening the magnetic coupling between the first and second sections (2a,2b) and the third and fourth sections (2c,2d). Consequently, it is possible to minimize the decrease in the total inductance of the stator coil40due to the negative mutual inductances between the first and second sections (1a,1b) and the third and fourth sections (1c,1d) of the first sub-winding42-1and between the first and second sections (2a,2b) and the third and fourth sections (2c,2d) of the second sub-winding42-2, thereby lowering both the resonant frequency and the resonance peak of the stator coil40. As a result, it is possible to lower the maximum phase-to-phase voltage of the stator coil40, thereby shortening the necessary phase-to-phase clearance of the stator coil40for ensuring electrical insulation between the phase windings41of the stator coil40.

In addition, for each of the phase windings41of the stator coil40, in each of the single-phase slots31for the phase winding41, all of the sections of the first and second sub-windings42-1and42-2of the phase winding41may also be radially arranged from the radially outer side in different sequences, for example in the sequence of1a,1b,2a,2b,1c,1d,2c,2d.

Fifth Embodiment

In the present embodiment, as in the fourth embodiment, for each of the phase windings41of the stator coil40, counting from one end of the phase winding41, the same-numbered sections of the sub-windings42of the phase winding41are received in the same ones of the single-phase slots31for the phase winding41so as to be proximate to one another in the same single-phase slots31.

Further, in the present embodiment, for each of the sub-windings42, the first to the (k/2)th sections of the sub-winding42are received in different ones of the single-phase slots31for the phase winding41from the (k/2+1)th to the kth sections of the sub-winding42.

Specifically, assume that j is equal to 2 and k is equal to 4 as in the fourth embodiment. Then, as shown inFIG. 18, for each of the phase windings41of the stator coil40, the first sections (1a,2a) of the first and second sub-windings42-1and42-2are received in the same ones of the single-phase slots31for the phase winding41so as to be proximate to each other in the same single-phase slots31. The second sections (1b,2b) of the first and second sub-windings42-1and42-2are received in the same ones of the single-phase slots31for the phase winding41so as to be proximate to each other in the same single-phase slots31. The third sections (1c,2c) of the first and second sub-windings42-1and42-2are received in the same ones of the single-phase slots31for the phase winding41so as to be proximate to each other in the same single-phase slots31. The fourth sections (1d,2d) of the first and second sub-windings42-1and42-2are received in the same ones of the single-phase slots31for the phase winding41so as to be proximate to each other in the same single-phase slots31.

Further, in the present embodiment, for each of the phase windings41of the stator coil40, the first and second sections (1a,1b,2a,2b) of the first and second sub-windings42-1and42-2are received in different ones of the single-phase slots31for the phase winding41from the third and fourth sections (1c,1d,2c,2d) of the first and second sub-windings42-1and42-2. More specifically, in one of the single-phase slots31for the phase winding41, the first and second sections (1a,1b,2a,2b) of the first and second sub-windings42-1and42-2are radially arranged from the radially outer side in the sequence of1a,2a,1a,2a,1b,2b,1b,2b. In another one of the single-phase slots31for the phase winding41, the third and fourth sections (1c,1d,2c,2d) of the first and second sub-windings42-1and42-2are radially arranged from the radially outer side in the sequence of1c,2c,1c,2c,1d,2d,1d,2d.

With the above configuration of the stator20according to the present embodiment, since the first and second sections (1a,1b,2a,2b) of the first and second sub-windings42-1and42-2are received in different ones of the single-phase slots31for the phase winding41from the third and fourth sections (1c,1d,2c,2d) of the first and second sub-windings42-1and42-2, it is possible to weaken the magnetic coupling between the first and second sections (1a,1b,2a,2b) and the third and fourth sections (1c,1d,2c,2d). Moreover, since the same-numbered sections of the first and second sub-windings42-1and42-2are received in the same single-phase slots31so as to be proximate to one another, all the sections of the sub-windings42can be arranged so that: the first and second sections (1a,1b) of the first sub-winding42-1are radially separated from each other; the third and fourth sections (1c,1d) of the first sub-winding42-1are radially separated from each other; the first and second sections (2a,2b) of the second sub-winding42-2are radially separated from each other; and the third and fourth sections (2c,2d) of the second sub-winding42-2are radially separated from each other. Consequently, it is possible to weaken the magnetic coupling between the sections (1a-1d) of the first sub-winding42-1and between the sections (2a-2d) of the second sub-winding42-2. Thus, it is possible to minimize the decrease in the total inductance of the stator coil40due to the negative mutual inductances between the sections (1a-1d,2a-2d) of the sub-windings42of the phase windings41, thereby lowering both the resonant frequency and the resonance peak of the stator coil40. As a result, it is possible to lower the maximum phase-to-phase voltage of the stator coil40, thereby shortening the necessary phase-to-phase clearance of the stator coil40for ensuring electrical insulation between the phase windings41of the stator coil40.

In addition, in the present embodiment, in the case of k being an odd number greater than 2, for each of the sub-windings42, the central section of the sub-winding42may be received either in the same single-phase slots31as those sections of the sub-winding42which are positioned upstream (i.e., on the terminal43side) of the central section or in the same single-phase slots31as those sections of the sub-winding42which are positioned downstream (i.e., on the neutral point44side) of the central section.

Sixth Embodiment

This embodiment illustrates a stator20which has a similar configuration to the stator20according to the first embodiment; accordingly, only the differences therebetween will be described hereinafter.

In the present embodiment, the stator core30has, for each of the phase windings41of the stator coil40, 2j circumferentially-consecutive single-phase slots31, in which only the phase winding41is received, per magnetic pole of the rotor14, where j is a natural number greater than or equal to 2. Moreover, each of the phase windings41of the stator coil40is comprised of j sub-windings42that are connected in parallel with each other between the terminal43of the phase winding41and the neutral portion44of the stator coil40. Further, each of the sub-windings42consists of a first half on the terminal43side and a second half on the neutral point44side. Furthermore, in each of the single-phase slots31for the phase winding41, there is received only a corresponding one of the first and second halves of the sub-windings42of the phase winding41.

Specifically, assume that j is equal to 2. Then, as shown inFIGS. 19 and 20, the stator core30has, for each of the phase windings41of the stator coil40, four circumferentially-consecutive single-phase slots31per magnetic pole of the rotor14. Accordingly, the total number of the slots31provided in the stator core30is equal to 96 (i.e., 4×3×8). Moreover, each of the phase windings41of the stator coil40is comprised of two sub-windings42, i.e., a first sub-winding42-1and a second sub-winding42-2that are connected in parallel with each other between the terminal43of the phase winding41and the neutral point44of the stator coil40. The first sub-winding42-1includes a first section (1a), a second section (1b), a third section (1c) and a fourth section (1d), which are sequentially arranged from one end of the first sub-winding42-1on the terminal43side to the other end of the first sub-winding42-1on the neutral point44side. The second sub-winding42-2includes a first section (2a), a second section (2b), a third section (2c) and a fourth section (2d), which are sequentially arranged from one end of the second sub-winding42-2on the terminal43side to the other end of the second sub-winding42-2on the neutral point44side.

Furthermore, taking the U-phase winding41as an example, as shown inFIG. 20, the first half of the second sub-winding42-2, which is comprised of the first and second sections (2a,2b) of the second sub-winding42-2, is received in the single-phase slots U1. The second half of the second sub-winding42-2, which is comprised of the third and fourth sections (2c,2d) of the second sub-winding42-2, is received in the single-phase slots U2. The first half of the first sub-winding42-1, which is comprised of the first and second sections (1a,1b) of the first sub-winding42-1, is received in the single-phase slots U3. The second half of the first sub-winding42-1, which is comprised of the third and fourth sections (1c,1d) of the first sub-winding42-1, is received in the single-phase slots U4.

That is, in the present embodiment, all the first and second halves of the first and second sub-windings42-1and42-2of the U-phase winding41are separately received in different ones of the single-phase slots U1-U4for the U-phase winding41from each other.

In addition, in the present embodiment, in each of the single-phase slots U1, the first and second sections (2a,2b) of the second sub-winding42-2are alternately arranged in eight layers. In each of the single-phase slots U2, the third and fourth sections (2c,2d) of the second sub-winding42-2are alternately arranged in eight layers. In each of the single-phase slots U3, the first and second sections (1a,1b) of the first sub-winding42-1are alternately arranged in eight layers. In each of the single-phase slots U4, the third and fourth sections (1c,1d) of the first sub-winding42-1are alternately arranged in eight layers.

Furthermore, as shown inFIG. 21, the difference in electrical angle between the first half of the second sub-winding42-2received in the single-phase slots U1and the first half of the first sub-winding42-1received in the single-phase slots U3is equal to 30°. The difference in electrical angle between the second half of the second sub-winding42-2received in the single-phase slots U2and the second half of the first sub-winding42-1received in the single-phase slots U4is also equal to 30°.

That is, in the present embodiment, the first and second sub-windings42-1and42-2are wound on the stator core30so as to be circumferentially offset from each other by 30° in electrical angle.

In addition, it should be noted that the first and second halves of the sub-windings42of the V-phase and W-phase windings41are respectively arranged in the single-phase slots31for the V-phase and W-phase windings41in the same manner as those of the U-phase winding41.

With the above configuration of the stator20according to the present embodiment, for each of the sub-windings42of the phase windings41of the stator coil40, it is possible to weaken the magnetic coupling between the first and second halves of the sub-winding42, thereby minimizing the negative mutual inductance therebetween. Consequently, it is possible to minimize the decrease in the total inductance of the stator coil40due to the negative mutual inductance, thereby lowering both the resonant frequency and the resonance peak of the stator coil40. As a result, it is possible to lower the maximum phase-to-phase voltage of the stator coil40, thereby shortening the necessary phase-to-phase clearance of the stator coil40for ensuring electrical insulation between the phase windings41of the stator coil40.

Moreover, since the sub-windings42are circumferentially offset from each other by an electrical angle of 30° (i.e., 60°/j, where j is equal to 2) in each of the phase windings41of the stator coil40, it is possible to reduce variation in magnetomotive force in the circumferential direction of the stator core30, thereby lowering the level of magnetic noise in the stator20.

In addition, it is possible to modify the stator20according to the present embodiment such that each of the phase windings41of the stator coil40is formed by joining a give number of continuous electric wires instead of joining the U-shaped electric conductor segments50. It is also possible to modify the stator20according to the present embodiment such that each of the phase windings41is lap-wound around the stator core30instead of being wave-wound around the stator core30.

This experiment has been conducted to verify the effect of reducing magnetic noise according to the sixth embodiment.

Specifically, in the experiment, both the stator20according to the sixth embodiment and a stator20according to a comparative example were tested.

In the stator20according to the comparative example, as shown inFIG. 22, the stator core30has, for each of the phase windings41of the stator coil40, only one single-phase slot per magnetic pole of the rotor14. Further, each of the phase windings41is not comprised of parallel sub-windings as in the sixth embodiment.

FIG. 23shows the distribution of magnetomotive force in the stator20according to the sixth embodiment, which was measured in the experiment. On the other hand,FIG. 24shows the distribution of magnetomotive force in the stator20according to the comparative example, which was also measured in the experiment.

As seen fromFIGS. 23 and 24, in either of the stators20, the magnetomotive force varied in a cycle of 60° in electrical angle. The amount of variation in the magnetomotive force become maximum when electrical angle was changed from 0° to 30°. In addition, the larger the amount of variation in the magnetomotive force, the higher the level of the magnetic noise induced in the electric rotating machine1.

FIG. 25gives a comparison in magnetic noise level between the stator20according to the sixth embodiment and the stator20according to the comparative example. Here, the magnetic noise level was obtained by integrating the amount of variation in the magnetomotive force for the range of electrical angle from 0° to 60°.

It can be seen fromFIG. 25that the magnetic noise level in the stator20according to the sixth embodiment was lowered below half the magnetic noise level in the stator20according to the comparative example.

While the above particular embodiments have 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 first embodiment, each of the U-phase, V-phase and W-phase windings41of the stator coil40is configured to include 2n sections, where n is a natural number greater than or equal to 2. However, each of the U-phase, V-phase and W-phase windings41of the stator coil40may also be configured to include k sections, where k is a natural number greater than or equal to 2.

Moreover, in the first embodiment, the substantially U-shaped electric conductor segments50are used for forming the stator coil40. However, electric conductor segments of other shapes (e.g., substantially I-shaped electric conductor segments) may also be used, instead of the substantially U-shaped electric conductor segments50, for forming the stator coil40.

In the previous embodiments, the present invention is directed to the electric rotating machine1which is designed to function as an electric motor. However, the invention can also be applied to other electric rotating machines, such as an electric generator or a motor-generator that can functions both as an electric motor and as an electric generator.