1. Field of the Invention
The present invention relates to a brushless motor.
2. Description of Related Art
Japanese Unexamined Patent Publication No. 2008-86064A (corresponding to US 2008/0073995A) recites a brushless motor known as a 10-pole/12-slot brushless motor. In this brushless motor, teeth of a stator core are arranged one after another at 30 degree pitches, i.e., intervals (360 degrees/12=30 degrees) in the circumferential direction of the brushless motor, and magnetic poles of rotor magnets are arranged one after another at 36 degree pitches, i.e., intervals (360 degrees/10=36 degrees) in the circumferential direction.
In the above-described brushless motor, a difference (specifically, a difference of 6 degrees measured as the central angle) exists between the pitch of the teeth measured in the circumferential direction of the brushless motor and the pitch of the magnetic poles of the rotor magnets measured in the circumferential direction of the brushless motor. This difference poses the following disadvantage.
Generally, in order to implement a relatively high effective magnetic flux amount and a relatively high motor efficiency in the motor, desirably, a phase difference Δθ (see FIG. 5) between the phase of the electric current I flowing through the stator coil wound around the corresponding tooth and the phase of the magnetic flux φ applied from the rotor magnet to the stator coil should be 90 degrees, as is well known according to Fleming's left-hand rule.
As discussed above, in the case of the brushless motor recited in Japanese Unexamined Patent Publication No. 2008-86064A, the difference (the difference of 6 degrees measured as the central angle) exists between the pitch of the teeth and the pitch of the magnetic poles of the rotor magnets. Therefore, the phase difference between the phase of the electric current flowing through the stator coil wound around the corresponding tooth and the phase of the magnetic flux applied from the rotor magnet to the stator coil becomes 75 degrees, which is smaller than 90 degrees. Thereby, the effective magnetic flux amount may be disadvantageously reduced to reduce the motor efficiency.