A known embedded magnet motor including a rotor core being embedded with permanent magnets is disclosed in JP2007-6857A (hereinafter referred to as Patent reference 1). An intermediate portion of the permanent magnet of the embedded magnet motor is formed thick and gradually comes to be thinner towards opposing end portions of the magnet. Thus, the thicker the permanent magnet is (can be the thickest at the intermediate portion), the more difficult it is for a magnetic flux to pass through. As a result, the magnetic flux passing in a q-axis direction is apt to pass through the rotor while the magnetic flux being formed by an armature winding and passing in a d-axis direction passes through the rotor with difficulty. Accordingly, because the difference in amount between a q-axis inductance Lq and a d-axis inductance Ld is increased, a reluctance torque (a torque of an attraction force being generated between the magnetic field from a stator core and a salient pole of the rotor core) can be increased. The d-axis serves as a direction of a main magnetic flux. The q-axis serves as a direction electrically orthogonal to the d axis. The reluctance torque is proportional to the difference in amount between the q-axis inductance Lq and the d-axis inductance Ld.
According to the embedded magnet motor disclosed in Patent reference 1, the rotor core is formed in a round shape when seen from an axial direction of the rotor core.
However, according to the embedded magnet motor disclosed in Patent reference 1, because the intermediate portion of the permanent magnet is formed thick and gradually comes to be thinner towards the opposing end portions of the magnet, a rectangular permanent magnet is required to be processed. Accordingly, the yield rate of the permanent magnet comes to be decreased. In addition, because the rotor core is formed in the round shape when seen from the axial direction of the rotor core, the waveform of an induced voltage being generated by the armature winding comes to be largely deformed from a sinewave.
A need thus exists for an embedded magnet motor and a rotor of the embedded magnet motor which is not susceptible to the drawback mentioned above.