Abstract: In a motor, a raised portion arranged to project toward a rotor magnet is provided on an opposed surface of each tooth portion. This raised portion provided on an opposed surface of each tooth portion. This raised portion is provided at a substantial middle of the opposed surface in a circumferential direction. This allows a waveform of a cogging torque generated by the raised portions and a fundamental of a waveform of a cogging torque generated by slot openings to be substantially in opposite phases. Cogging torque generated by the slot openings can be thereby reduced, because of the cogging torque generated by the raised portion.

Abstract: A small, lightweight relative drive device is provided, which is capable of producing large torque. The relative drive device of a two-phase magnetic excitation type according to an aspect of the invention comprises first and second coil groups and a magnet group. The magnet group includes magnets disposed with alternating north and south poles facing the first and second coil groups. The first and second coil groups are disposed at positions that are out of phase with each other by an odd multiple of ?/2 in electrical angles. The coils in the first and second coil groups have substantially no magnetic material cores, and the relative drive device has substantially no magnetic material yoke for forming a magnetic circuit.

Abstract: A small, lightweight relative drive device is provided, which is capable of producing large torque. The relative drive device of a two-phase magnetic excitation type according to an aspect of the invention comprises first and second coil groups and a magnet group. The magnet group includes magnets disposed with alternating north and south poles facing the first and second coil groups. The first and second coil groups are disposed at positions that are out of phase with each other by an odd multiple of ?/2 in electrical angles. The coils in the first and second coil groups have substantially no magnetic material cores, and the relative drive device has substantially no magnetic material yoke for forming a magnetic circuit.

Abstract: When a brushless motor is rotated at low speeds (the answer of a step S12 is YES), the brushless motor is driven by exciting a first phase coil, a second phase coil and a third phase coil by a sine wave PWM system having a phase difference of 120.degree. from each other to perform a torque control. Since the crest value of the sine wave is controlled in response to torque greatly fluctuated by a load, an out-of-phase phenomenon which is apt to occur at low rotational speeds can be previously prevented. When the brushless motor is rotated at high speeds (the answer of the step S12 is NO), the brushless motor is driven by a square wave PWM system based on a three-phase 120.degree. conduction type. Since the out-of-phase phenomenon is apt to occur as a frequency is increased when the brushless motor is driven by the sine wave PWM system, the control system is switched to a square wave PWM system to prevent the out-of-phase phenomenon.