Patent ID: 6983810

Claim:
An electric power tool, comprising: a housing; a motor encased in the housing and having an output shaft producing a torque; a spindle provided at a front end of the housing, the spindle receiving the torque and capable of rotation; an epicycle reduction gear unit provided between the output shaft of the motor and the spindle, the epicycle reduction gear unit including front and rear internal gears axially arranged and independently rotatable with respect to each other, front and rear carriers, and gear sets each including a front planetary gear having a first diameter and a rear planetary gear having a second diameter different from the first diameter, the front and rear planetary gears being supported on the front carrier so as to revolve on inner peripheral surfaces of the front and rear internal gears, respectively; and switchover means slidably provided on outer peripheral surfaces of the internal gears and responsive to slide operation of the switchover means performed from outside of the housing for selectively prohibiting rotation of the internal gears relative to the housing, the switchover means being capable of coupling one of the two internal gears to the one of the carriers so as to permit integral rotation of the coupled internal gears with the coupled carriers, further wherein the switchover means enables the spindle to rotate at a first speed by prohibiting rotation of one of the internal gears relative to the housing; at a second speed by prohibiting rotation of the other of the internal gears relative to the housing; and at a third speed by simultaneously permitting rotation of one of the internal gears relative to the housing and coupling that rotation-permitted internal gear to one of the carriers.