Electric motor capable of reducing cogging torque

Abstract

An electric motor including a rotor including magnetic pole units and a stator including slots facing an outer peripheral surface of the rotor. Each of the magnetic pole units is bulged to an outside in a radial direction so that a waveform of a magnetic flux density generated from the rotor is a sine wave shape, and a concave part or convex part which is small enough to prevent changing of a waveform cycle of cogging torque determined by a least common multiple of the number of slots and the number of magnetic poles of the rotor, is formed at a central part in a circumferential direction of an outer peripheral surface in each of the magnetic pole units.

1 . An electric motor comprising:
 a rotor including magnetic pole units; and   a stator including slots facing an outer peripheral surface of the rotor, wherein,   each of the magnetic pole units is bulged to an outside in a radial direction so that a waveform of a magnetic flux density generated from the rotor is a sine wave shape, and   a concave part or convex part is formed at a central part in a circumferential direction of an outer peripheral surface in each of the magnetic pole units, the concave part or convex part being small enough to prevent changing of a waveform cycle of cogging torque determined by a least common multiple of the number of slots and the number of magnetic poles of the rotor.   
     
     
         2 . The electric motor according to  claim 1 , wherein a depth of the concave part or a height of the convex part is equal to or less than 0.1 mm. 
     
     
         3 . The electric motor according to  claim 1 , wherein the outer peripheral surface of each of the magnetic pole units is set by adding a correction amount in the radial direction to a reference surface bulged to the outside in the radial direction so that the waveform of the magnetic flux density generated from the rotor is the sine wave shape. 
     
     
         4 . The electric motor according to  claim 3 , wherein the correction amount is set so that the concave part or the convex part is formed with a smooth curve. 
     
     
         5 . The electric motor according to  claim 3 , wherein the correction amount is set based on a function using, as a parameter, a phase in which a center in the circumferential direction of each of the magnetic pole units is 0°. 
     
     
         6 . The electric motor according to  claim 5 , wherein the function is any one of a sine function, a cosine function, and a hyperbolic cosine function. 
     
     
         7 . The electric motor according to  claim 1 , wherein the least common multiple of the number of magnetic poles of the rotor and the number of slots is equal to or less than 100.