Motor having rotor structure with grooves to reduce cogging torque

A motor comprising:

• a rotor;
• and
• a stator disposed to correspond to the rotor,
• wherein the rotor includes a rotor core and a magnet disposed on the rotor core,
• wherein the rotor core includes a first rotor core and a second rotor core, the first rotor core and the second rotor core being coaxially stacked in an axial direction,
• wherein the first rotor core includes a first region in which one part of the magnet is disposed,
• wherein the second rotor core includes a second region in which another part of the magnet is disposed,
• wherein the first region includes two grooves, the two grooves being disposed on an outer surface of the first rotor core and being symmetrically disposed with respect to a center of a width of an inner surface of the magnet in a circumferential direction,
• wherein the second region does not include a groove,
• wherein the first region and the second region are located adjacent to each other in the axial direction,
• wherein the two grooves are disposed on the outer surface of the first rotor core, the two grooves being symmetrically disposed with respect to the center of the width of the inner surface of the magnet in the circumferential direction,
• wherein the two grooves are disposed to an axial end of the first rotor core, and
• wherein a cogging torque waveform generated by the first rotor core and a cogging torque waveform generated by the second rotor core are opposite in phase.