1. Field of the Invention
The present disclosure relates generally to a fan motor, a brushless direct current (BLDC) motor, and a rotor for the BLDC motor.
2. Description of Related Art
BLDC motors are typically brushless motors that have a stator and a rotor mounted inside the stator. Generally the stator includes a plurality of salient poles and coils wound therearound. The rotor includes one or more magnets installed thereon.
Among BLDC motors, an internal permanent magnet (IPM) BLDC motor is a motor that has a magnet installed inside the rotor. Depending on an installation position of the magnet and a shape of the rotor through which lines of a magnetic field of the magnet pass, a back electromotive force (EMF) coefficient and a cogging torque significantly vary.
The back EMF is a factor in evaluating performance of the BLDC motor, and a factor in evaluating a torque component due to magnetic force generated by the magnet. The cogging torque is an amount of torque generated when the rotor moves to an equilibrium state where a magnetic energy is minimal in a mutual relation of the magnet and the stator, regardless of a current. The cogging torque is a factor that generates vibration and noise during the rotation of the rotor.
Various methods have been tried to provide a BLDC motor that is configured to generate a large torque such that loss of the back EMF coefficient can be reduced to the maximum, and to make the cogging torque as small as possible in order to reduce vibration and noise generated during the rotation of the BLDC motor. However, the various methods according to the related art either cannot obtain sufficient torque, or generate too much vibration and noise.