| 摘要 |
A system and method for reducing the cost of producing a brushless DC motor ( 58 ) is presented. The brushless DC motor ( 58 ) provides higher power density and efficiency with an increased tool run time. The brushless DC motor ( 58 ) includes a rotor assembly ( 72 ) that has an unmagnetized permanent magnet ( 74 ) affixed to a shaft. The permanent magnet ( 74 ) remains unmagnetized until the motor is partially assembled. A plurality of coils ( 94 ) for producing a magnetic field are wound about the rotor assembly ( 72 ). The coils ( 94 ) include end turns that enclose the rotor assembly ( 72 ) such that the rotor assembly ( 72 ) is not removable. Since the windings ( 94 ) are wound with the rotor assembly ( 72 ) already enclosed, the windings ( 94 ) do not require large end coils to allow subsequent insertion of the rotor ( 72 ). Minimizing the end coils reduces the length of wire required per turn, thereby reducing the resistance of the winding ( 94 ). Also, since the permanent magnet ( 74 ) is unmagnetized when the coils ( 94 ) are wound around the rotor assembly ( 72 ) the winding process is simplified by not coupling energy into the wire which would influence the winder operation. The wound assembly is inserted into a stator stack ( 96 ) comprised of magnetic material that provides a magnetic flux return path for the magnetic flux generated by the permanent magnet ( 74 ). Using an unmagnetized permanent magnet ( 74 ) facilitates easy insertion of the wound assembly into the stator stack ( 96 ), reduces the accumulation of magnetic debris during the manufacturing process, and permits the motor assembly to be sealed prior to magnetizing the permanent magnet ( 74 ).
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