Abstract: A power tool and a motor drive circuit thereof are provided. The motor drive circuit includes an inverter, a controller and a current sensor. The inverter includes a plurality of semiconductor switches and configured to convert a voltage from a power supply into an alternating current for an electric motor. The controller is configured to output detecting signals and drive signals for the inverter. The current sensor is configured to sample a current flowing through the motor, the current comprising a plurality of driving current portions corresponding to the drive signals and a plurality of position detecting current portions corresponding to the detecting signals. The controller determines the drive signals at least based on the position detecting current portions of the current so as to control power modes of the semiconductor switches in the inverter in a starting stage of the motor.

Abstract: A brushless motor has a stator and an outer rotor. The stator includes a stator core having 6N teeth and 6N coils wound respectively around the teeth where N is an integer equal to or greater than 1. The rotor includes 6N±2 permanent magnets. The permanent magnets are arranged circumferentially around the stator core and face the teeth across an air gap. The radial thickness of the air gap is uneven along the circumferential direction of the motor.

Abstract: A power tool is provided. The power tool includes a housing, a working head extended from the housing, a brushless direct current motor configured to drive the working head, a battery, an inverter and a controller. The inverter includes a plurality of semiconductor switches and configured to convert a power from the battery into an alternating current power which is coupled to the brushless direct current motor. The controller is configured to output drive signals to control the semiconductor switches of the inverter based on a magnetic field position of the rotor obtained in a sensorless way.

Abstract: A power tool and a motor drive circuit thereof are provided. The motor drive circuit includes an inverter, a controller and a current sensor. The inverter includes a plurality of semiconductor switches and configured to convert a voltage from a power supply into an alternating current for an electric motor. The controller is configured to output detecting signals and drive signals for the inverter. The current sensor is configured to sample a current flowing through the motor, the current comprising a plurality of driving current portions corresponding to the drive signals and a plurality of position detecting current portions corresponding to the detecting signals. The controller determines the drive signals at least based on the position detecting current portions of the current so as to control power modes of the semiconductor switches in the inverter in a starting stage of the motor.

Abstract: An electric motor includes a stator and a rotor installed in the stator. The stator has a laminated stator core and at least two stator windings wound on the stator core. The stator core has at least two stator poles facing the rotor and at least two yokes connecting adjacent stator poles. T stator core is constituted by at least two separate members joined together. The at least two stator poles are only arranged at a single one of the at least two separate members.

Abstract: A starter motor for engine has a flywheel fixed to a shaft of the engine. A support is fixed relative to the engine. A space is formed between the flywheel and the support and a driving device is installed in the space. The driving device includes a stator fixed to the support and a rotor fixed to the flywheel.

Abstract: A solenoid includes a stationary member, a movable member being movable relative to the stationary member and spring disposed between the stationary member and the movable member. The stationary member includes a housing with an end wall and a side wall, a first permanent magnet attached to the end wall, a second permanent magnet attached to the side wall and a magnetic flux concentrator configured to concentrate a magnetic field generated by the second permanent magnet with a magnetic field generated by the first permanent magnet. The movable member includes a head inserted into the housing. The head is made of magnetically conductive material. The stationary member further includes a coil surrounding the head of the movable member. When the coil receives a pulse current, the movable member is driven from an extended/retracted position to a retracted/extended position.

Abstract: A relay has a driving device that includes a magnet portion, two electromagnets, a yoke portion fixed to the above elements, and a rocking armature. The magnet portion includes a ferrite permanent magnet polarized in a direction perpendicular to the yoke portion and a bearing surface facing way from the yoke portion. Each electromagnet includes an iron core fixed to the yoke portion and a coil wound thereon. The two iron cores are arranged at opposite sides of the magnet portion. The rocking armature includes two arms connected to each other with an included angle formed therebetween and a convex joint of the two arms. The convex joint abuts against the bearing surface and the rocking armature pivots about the convex joint between a first position and a second position in which the rocking armature contacts a respective one of the iron cores.

Abstract: A rotary solenoid (1) includes a stator (10), a rotor (40), and a torsion spring (50) connected between the stator (10) and the rotor (40). The stator (10) includes an armature (13) having three stator poles (14, 15) cooperatively defining a substantially cylindrical space (18) and a coil (19) wound about one of the stator poles (14). The rotor (40) includes a shaft (42) rotatably assembled to the stator (10) and a rotor core (44) fixed to the shaft (42) and received in the cylindrical space (18). The rotor core (44) has three rotor poles (43) corresponding to the stator poles (14, 15). The rotor (40) stays at a first position under the force of the torsion spring (50) and rotates to a second position under the force of the torsion spring (50) and the magnetic force of stator (10) when the coil (19) is powered.

Abstract: A rotary solenoid (1) includes a stator (10), a rotor (40), and a torsion spring (50) connected between the stator (10) and the rotor (40). The stator (10) includes an armature (13) having three stator poles (14, 15) cooperatively defining a substantially cylindrical space (18) and a coil (19) wound about one of the stator poles (14). The rotor (40) includes a shaft (42) rotatably assembled to the stator (10) and a rotor core (44) fixed to the shaft (42) and received in the cylindrical space (18). The rotor core (44) has three rotor poles (43) corresponding to the stator poles (14, 15). The rotor (40) stays at a first position under the force of the torsion spring (50) and rotates to a second position under the force of the torsion spring (50) and the magnetic force of stator (10) when the coil (19) is powered.

Abstract: A relay has a driving device that includes a magnet portion, two electromagnets, a yoke portion fixed to the above elements, and a rocking armature. The magnet portion includes a ferrite permanent magnet polarized in a direction perpendicular to the yoke portion and a bearing surface facing way from the yoke portion. Each electromagnet includes an iron core fixed to the yoke portion and a coil wound thereon. The two iron cores are arranged at opposite sides of the magnet portion. The rocking armature includes two arms connected to each other with an included angle formed therebetween and a convex joint of the two arms. The convex joint abuts against the bearing surface and the rocking armature pivots about the convex joint between a first position and a second position in which the rocking armature contacts a respective one of the iron cores.

Abstract: A brushless motor has a stator and an outer rotor. The stator includes a stator core having 6N teeth and 6N coils wound respectively around the teeth where N is an integer equal to or greater than 1. The rotor includes 6N±2 permanent magnets. The permanent magnets are arranged circumferentially around the stator core and face the teeth across an air gap. The radial thickness of the air gap is uneven along the circumferential direction of the motor.

Abstract: An electric motor includes a stator and a rotor installed in the stator. The stator has a laminated stator core and at least two stator windings wound on the stator core. The stator core has at least two stator poles facing the rotor and at least two yokes connecting adjacent stator poles. T stator core is constituted by at least two separate members joined together. The at least two stator poles are only arranged at a single one of the at least two separate members.

Abstract: A starter motor for engine has a flywheel fixed to a shaft of the engine. A support is fixed relative to the engine. A space is formed between the flywheel and the support and a driving device is installed in the space. The driving device includes a stator fixed to the support and a rotor fixed to the flywheel.