Rotor and dynamo-electric machine having the same

1. A rotor for a dynamo-electric machine, comprising:

a shaft;

a rotor core that is fitted to the shaft and is fixed to the shaft; and

a plurality of permanent magnets that are located on a radially outer side of the rotor core and are intermittently arranged in a circumferential direction while the plurality of permanent magnets is fixed to the rotor core at a plurality of predetermined portions, respectively, of the rotor core, wherein:

one of each permanent magnet and a corresponding one of the plurality of predetermined portions of the rotor core, which are radially opposed to each other, includes a projection that projects toward the other one of each permanent magnet and the corresponding one of the plurality of predetermined portions of the rotor core;

an inner peripheral surface of each permanent magnet, which is radially opposed to the corresponding one of the plurality of predetermined portions of the rotor core, includes:

a primary contacting portion that contacts the corresponding one of the plurality of predetermined portions of the rotor core at a circumferential location, which corresponds to the projection; and

two primary non-contacting portions that do not contact the rotor core and are located on two circumferentially opposite sides, respectively, of the primary contacting portion, wherein:

each of the plurality of predetermined portions of the rotor core includes the projection, which projects toward the corresponding one of the plurality of permanent magnets;

each of the plurality of permanent magnets includes a recess, which is radially opposed to the projection of the corresponding one of the plurality of predetermined portions of the rotor core;

a bottom surface of the recess of each of the plurality of permanent magnets forms the primary contacting portion, which contacts the projection of the corresponding one of the plurality of predetermined portions of the rotor core;

a circumferentially outer end of each of the two primary non-contacting portions in the inner peripheral surface of each permanent magnet is separated from the rotor core by a gap formed between each of the two primary non-contacting portions and the rotor core, and

each of the two primary non-contacting portions in the inner peripheral surface of each permanent magnet is bent radially inward relative to the primary contacting portion of the permanent magnet.

2. The rotor according to claim 1 , wherein:

a total number of the plurality of permanent magnets is 2p where p denotes an integer number;

the rotor core includes a polygonal portion that has a cross section, which is taken in a direction perpendicular to an axial direction and is configured into a polygonal shape having a plurality of corners, wherein a total number of the plurality of corners is 4p where p denotes the integer number; and

each of the plurality of predetermined portions of the rotor core, which is placed in a corresponding one of a plurality of sides of the polygonal portion, includes the projection, which projects toward the corresponding one of the plurality of permanent magnets.

3. The rotor according to claim 1 , further comprising a tubular cover, which is fitted to an outer peripheral surface of each of the plurality of permanent magnets, wherein:

the outer peripheral surface of each of the permanent magnets, which is radially opposed to the tubular cover, includes:

a secondary contacting portion that is located in a circumferential center portion of the outer peripheral surface of the permanent magnet and contacts the tubular cover; and

two secondary non-contacting portions that do not contact the tubular cover and are located on two circumferentially opposite sides, respectively, of the secondary contacting portion.

4. The rotor according to claim 3 , wherein the primary contacting portion and the secondary contacting portion in each of the plurality of permanent magnets are placed at a circumferential position, at which an urging load of the tubular cover exerted against the permanent magnet is maximum along a circumferential extent of the permanent magnet.

5. The rotor according to claim 3 , wherein:

the shaft and the rotor core are rotatable about a rotational axis;

a first angle is defined about the rotational axis between one circumferential end and another circumferential end of the primary contacting portion of each of the plurality of permanent magnets;

a second angle is defined about the rotational axis between one circumferential end and another circumferential end of the secondary contacting portion of each of the plurality of permanent magnets; and

the first angle is equal to or smaller than the second angle.

6. The rotor according to claim 5 , wherein when the second angle is set to be a predetermined electrical angle, which is equal to or larger than 75 degrees and is equal to or smaller than 150 degrees.

7. The rotor according to claim 3 , wherein:

the tubular cover is press fitted to the outer peripheral surface of each of the plurality of permanent magnets; and

each of the plurality of permanent magnets is urged against the rotor core by the tubular cover to fix each of the plurality of permanent magnets to the rotor core.

8. The rotor according to claim 3 , wherein:

the tubular cover is press fitted to the outer peripheral surface of each of the plurality of permanent magnets; and

each of the plurality of permanent magnets is urged against the rotor core by the tubular cover and is bonded to the rotor core with a bonding agent, which is radially placed between each of the two primary non-contacting portions of the permanent magnet and the rotor core, to fix each of the plurality of permanent magnets to the rotor core.

9. The rotor according to claim 1 , wherein:

each of the plurality of permanent magnets or the corresponding one of the plurality of predetermined portions of the rotor core, which are radially opposed to each other, has a wall portion that corresponds to the primary contacting portion, and the wall portion includes a groove; and

each of the plurality of permanent magnets is fixed to the rotor core with a bonding agent received in the groove of the wall portion.

10. The rotor according to claim 1 , wherein the rotor is used in a drive electric motor of a vehicle electric power steering apparatus.

11. A dynamo-electric machine comprising:

the rotor according to claim 1 ; and

a stator that is placed on a radially outer side of the rotor, wherein a number of slots per pole per phase at the stator is 2.