Patent ID: 7605513

Claim:
An electrical tool comprising: a housing formed with an air inlet duct and an air exhaust duct; a stator core fixed within the housing, the stator core including at least a first coil winding part and a second coil winding part opposing the first coil winding part, the stator core having axial ends and being formed with a center bore; a first coil wound on the first coil winding part; a second coil wound on the second coil winding part, and positioned opposite to the first coil; a rotor rotatably disposed in the center bore and between the first coil and the second coil, the rotor defining a circumferential direction and an axial direction; and a fan placed within the housing for taking air from the air inlet duct in the housing and discharging air through the exhaust duct to cool the first coil and the second coil; wherein the first coil and the second coil respectively include a pair of axial winding portions respectively running in the axial direction of the rotor, and a pair of circumferential winding portions projecting outward from the axial ends of the stator core while running along the circumferential direction of the rotor; wherein the first coil and second coil respectively include at least a first coil bundle formed of a plurality of turns including an innermost turn and an outermost turn and a second coil bundle formed of a plurality of turns including an innermost turn and an outermost turn, and at least one of a gap and a groove is formed by the first coil bundle and the second coil bundle in at least one of the circumferential winding portions, the first coil bundle being positioned radially inwardly of the second coil bundle in a radial direction of the rotor; and wherein the innermost turn of the first coil bundle has a first innermost peripheral length, and the innermost turn of the second coil bundle has a second innermost peripheral length, the first innermost peripheral length being different from the second innermost peripheral length.