Rotor of motor and fan driving motor including rotor

1. A rotor of a motor comprising:

four or more slots formed at an equal angular interval inside of the rotor in a circumferential direction of the motor; and

four or more permanent magnets inserted in the four or more slots, respectively, each of the slots being formed with:

a first inner wall surface which comprises a flat surface having a depth extending in parallel to the rotational axis and a width located between a rotational axis of the motor and an outer periphery of the rotor in a cross-section perpendicular to the rotational axis and extending in the cross-section perpendicular to an imaginary plane that includes the rotational axis and bisects the first inner wall surface in the cross-section;

a second inner wall surface which has a depth extending in parallel to the depth of the first inner wall surface and a width located in the cross-section radially outward of the first inner wall surface and extending in the cross-section in parallel with the width of the first inner wall surface; and

a pair of side wall surfaces shaped symmetrically in the cross-section with respect to the imaginary plane;

wherein the width of the second inner wall surface is longer than the width of the first inner wall surface in the cross-section,

wherein the pair of side wall surfaces each comprise a flux barrier wall surface extending in the cross-section from one end of the second inner wall surface to a terminal end of the flux barrier wall surface so that in each of the flux barrier wall surface, a radial distance in the cross-section between the outer periphery of the rotor and the flux barrier wall surface, which is measured at a location in the cross-section on the flux barrier wall surface, becomes wider as the location moves along the flux barrier wall surface away from the second inner wall surface in the cross-section, and

wherein the four or more permanent magnets are placed, respectively, in the four or more slots each having the pair of flux barrier wall surfaces and comprise sets of two or more permanent magnets adjacently arranged in circumferential series in each set, wherein in each set, the two or more permanent magnets have the same radially outward polarity.

2. The rotor of the motor according to claim 1 ,

wherein the flux barrier wall surface extends in an arcuate manner along its entire length so that both of the flux barrier wall surfaces are co-extensive in the cross-section along their entire lengths with a single imaginary circle running in the cross-section between the outer periphery of the rotor and the second inner wall surface, the imaginary circle having a center in the cross-section between the rotational axis and the first inner wall surface on a intersecting line between the imaginary plane and the cross-section.

3. The rotor of the motor according to claim 1 , wherein the slot further comprising a pair of positioning grooves each having first and second ends, the pair of positioning grooves each being continuous at its first end with one end of the first inner wall surface, and

wherein each of the side wall surface further comprises (i) a positioning wall surface extending in the cross-section form the second end of a positioning groove perpendicularly towards the second inner wall surface and terminating in the cross-section between the first and second inner wall surfaces and (ii) a connecting wall surface connecting a terminal end of the positioning wall surface and the terminal end of the flux barrier wall surface in the cross-section.

4. The rotor of the motor according to claim 1 , wherein the slot has grooves running in parallel to the rotational axis, respectively, at the ends of the first inner wall surface.

5. The rotor of the motor according to claim 1 ,

wherein there are a total of four slots arranged at a 90 degree interval in the circumferential direction of the rotor, and there are four permanent magnets placed, respectively, in the four slots, the four permanent magnets comprising two sets of two magnets adjacently arranged in circumferential series, and

wherein the two magnets in each set have the same radially outward polarity, the two sets have the opposite radially outward polarity, and two magnets in the different sets opposing to each other through the rotational axis have the opposite radially outward polarities.

6. The rotor of the motor according to claim 1 , wherein the permanent magnets inserted into the slots are made of a rare-earth element.

7. A fan driving motor comprising the rotor of the motor recited in claim 1 , the rotor being retained inside the stator for rotation relative to the stator,

wherein the rotor is formed with four slots arranged at equal angular intervals in a circumferential direction of the rotor, the permanent magnet is inserted in each of the four slots, and

wherein the stator is formed generally in a tubular shape and includes three teeth portions arranged at equal angular intervals in a circumferential direction of the stator, the three teeth portions each extending radially inward from an inner wall surface of the stator.