Inner-rotor-type motor

1. An inner-rotor-type motor, comprising:

a stator including a stator core and a coil, the stator core including a ring-shaped core-back portion and a plurality of main poles protruding radially inward from the core-back portion, the coil being wound around each of the plurality of main poles through an insulator;

a rotor rotatably arranged inside the stator to face tip ends of the plurality of main poles and provided with a rotor shaft extending along a center axis; and

cover members arranged to cover axial opposite sides of the stator and configured to hold bearings which support the rotor shaft; wherein

the core-back portion of the stator core has a square or substantially square shape;

the core-back portion includes side surfaces corresponding to four sides of a square;

the side surfaces of the core-back portion are configured to define motor outer surfaces;

the insulator includes two insulating members mounted to the stator core at the axial opposite sides thereof;

each of the two insulating members includes a plurality of slot insulating portions which covers the main poles and an octagonal or substantially octagonal frame portion which interconnects the plurality of slot insulating portions at an axial end surface side of the stator core;

each of the frame portions includes four outer surface portions flush or substantially flush with the motor outer surfaces of four sides of the core-back portion;

each of the cover members includes an end plate portion configured to define an end surface of the motor and provided with a bearing holding portion in a central region thereof, and four leg portions arranged in four corners of the end plate portion and configured to contact axial end surfaces of four corner portions of the stator core;

each of the outer surface portions of the frame portion of each of the insulating members is inserted between the leg portions of each of the cover members; and

each of the frame portions includes a base-side ring-shaped frame having a diameter slightly smaller than an outer diameter of the stator core, a tip-end-side ring-shaped frame having a diameter equal or substantially equal to the outer diameter of the stator core, and a ring-shaped thin portion which interconnects the base-side ring-shaped frame and the tip-end-side ring-shaped frame.

2. The motor of claim 1 , wherein a radial minimum thickness of the four sides of the core-back portion is a minimum value within a range permitted as a magnetic path in terms of a magnetic property, and a protruding length of each of the main poles is a minimum value which allows the coil to be wound around each of the main poles at a predetermined winding number.

3. The motor of claim 2 , wherein a ratio of an inner diameter of the stator core to a minimum outer diameter of the stator core is about 0.7.

4. The motor of claim 1 , wherein a tip end of the frame portion of each of the insulating members is configured to contact the end plate portion at least in the four outer surface portions.

5. The motor of claim 4 , wherein the tip-end-side ring-shaped frame corresponds to the four outer surface portions being flush or substantially flush with the motor outer surface of the core-back portion.

6. The motor of claim 1 , wherein claws locked to the outer surfaces of the four corner portions of the stator core at the outer side thereof are provided as a single monolithic member together with the leg portions of each of the cover members.

7. The motor of claim 1 , wherein fixing holes are provided in the four corner portions of the stator core and in the leg portions of each of the cover members, and each of the cover members is fastened to the stator core by screws inserted through the fixing holes of the stator core.

8. The motor of claim 1 , wherein each of the cover members has a 90° rotation symmetry shape.

9. The motor of claim 1 , wherein sections of the frame portion of each of the insulating members interposed between the four outer surface portions are arranged along inner sides of the leg portions of each of the cover members.

10. The motor of claim 1 , wherein a drawing-out hole of a lead wire connected to the coil or a connector mounting portion is provided on an outer surface portion of one of the insulating members.