1. Technical Field of the Invention
The present invention relates to an electric motor suitable for various types of brushless motors for use in industries, home appliances and vehicles, and in particular, to an electric motor suitable for driving compressors for vehicles and suitable for use as servomotors for vehicles.
2. Related Art
Recently, electric motors using permanent magnets as magnetic poles tend to suffer from cogging torque due to the enhancement of magnetic performances.
In this regard, a technique of contriving the shape of magnetic poles is put into practice to reduce cogging torque. However, such a technique raises problems of involving a high-precision press technique and producing a lot of scraps.
A patent document JP-A-2011-050216 discloses a technique of reducing cogging torque and torque ripple by using a specific arrangement of the magnetic poles of a rotor with respect to the teeth of a stator. According to this technique, one magnetic pole is composed of two permanent magnets arranged in a V-shape. The two permanent magnets forming one magnetic pole are arranged in a range which is defined by the center lines of the respective second teeth leftward and rightward of the tooth confronting the center of the magnetic pole.
However, the technique disclosed in JP-A-2011-050216 has a main purpose of reducing torque ripple and thus exerts only a low effect of reducing cogging torque. Further, the technique is only applicable to a type of motors in which one magnetic pole is composed of two permanent magnets (V-shaped arrangement).