Patent ID: 7882899

Claim:
A power tool capable of variable output speed comprising: a housing; a motor contained in the housing for outputting rotary power; an output shaft; a gear transmission mechanism disposed between the motor and the output shaft for transmission of the rotary power of the motor to the output shaft at each of a plurality of gear reduction ratios including a low gear reduction ratio and a high gear reduction ratio, wherein the gear transmission mechanism comprises: a first gear train and a second gear train; a movable member variably engaged with one or both of the first gear train and the second gear train, wherein the movable member is movable between a first position corresponding to the low gear reduction ratio and a second position corresponding to the high gear reduction ratio, wherein the movable member has a rotational speed at the first position; and a control system operatively associated with the movable member which is capable of determining an operating characteristic indicative of a load applied to the output shaft, wherein the control system is operative to actuate the movable member to move from the first position to the second position and to reduce the rotational speed of the movable member when the operating characteristic reaches or exceeds a predetermined value.