Stator for electric rotating machine

1. A stator for an electric rotating machine, the stator comprising:

a stator core that includes an annular yoke portion, a plurality of tooth portions and a plurality of slots, each of the tooth portions extending radially inward from a radially inner periphery of the yoke portion, the tooth portions being arranged in a circumferential direction of the yoke portion at predetermined intervals, each of the slots being formed between a circumferentially-adjacent pair of the tooth portions; and

a stator coil that is mounted on the stator core so as to have a plurality of in-slot portions each of which is received in a corresponding one of the slots of the stator core,

wherein

the tooth portions of the stator core are separately formed from and assembled to the yoke portion,

the stator core further comprises a plurality of connecting portions each of which circumferentially extends to connect a corresponding circumferentially-adjacent pair of the tooth portions,

each of the slots of the stator core is partitioned by a corresponding one of the connecting portions into a radially-outer section and a radially-inner section, and

the stator coil is mounted on the stator core so that:

in each of the radially-outer and radially-inner sections of the slots, there is received at least one of the in-slot portions of the stator coil,

for each of the slots, the at least one in-slot portion received in the radially-outer section of the slot creates a first magnetic field while the at least one in-slot portion received in the radially-inner section of the slot creates a second magnetic field, and

the magnitudes of the first and second magnetic fields are equal to each other, but the directions of the first and second magnetic fields are opposite to each other at the corresponding connecting portion by which the slot is partitioned.

2. The stator as set forth in claim 1 , wherein each of the slots is equally partitioned by the corresponding connecting portion so that the area of a cross section of the radially-outer section perpendicular to the axial direction of the yoke portion is equal to that of the radially-inner section perpendicular to the axial direction.

3. The stator as set forth in claim 1 , wherein the yoke portion has a plurality of recesses that are formed in a radially inner surface of the yoke portion and spaced at predetermined intervals in the circumferential direction of the yoke portion,

each of the tooth portions has a protrusion formed at a radially outer end thereof, and

the tooth portions are assembled to the yoke portion by fitting the protrusions of the tooth portions respectively into the recesses of the yoke portion.

4. The stator as set forth in claim 1 , wherein the tooth portions are assembled to the yoke portion by press-fitting radially outer surfaces of the tooth portions to a radially inner surface of the yoke portion.

5. The stator as set forth in claim 1 , wherein the tooth portions are shaped so that each of the slots formed between the tooth portions has a constant circumferential width in a radial direction of the yoke portion.

6. The stator as set forth in claim 1 , wherein the tooth portions are so shaped as to have a constant circumferential width in a radial direction of the yoke portion.

7. The stator as set forth in claim 1 , wherein the following dimensional relationship is satisfied: a≧b>d, where a is the maximum width of each of the in-slot portions of the stator coil in a width-wise direction of the corresponding slot, b is the maximum thickness of each of the in-slot portions of the stator coil in a radial direction of the stator core, and d is the radial thickness of the connecting portions of the stator core.

8. The stator as set forth in claim 1 , wherein all of the tooth portions and connecting portions of the stator core together make up a stator tooth ring,

the stator tooth ring is formed of a plurality of magnetic steel sheets that are laminated in the axial direction of the yoke portion,

the radial thickness of the connecting portions is set to be greater than the thickness of the magnetic steel sheets.