Patent ID: 8334626

Claim:
A power tool having a cooling unit, the cooling unit comprising a fan wheel supported on an armature shaft of a motor of the power tool, wherein the fan wheel is rotatable separately from the armature shaft; wherein the cooling unit comprises: a torque transfer arrangement that is selectively coupleable with the armature shaft and with the fan wheel, and that is displaceable between a first position wherein the torque transfer arrangement does not couple the armature shaft and the fan wheel and a second position wherein the torque transfer arrangement operably couples the armature shaft and the fan wheel; and an actuator that moves the torque transfer arrangement between the first position and the second position so as to selectively transfer the rotation of the armature shaft to the fan wheel to respectively achieve, during operation of the power tool, a first mode wherein the fan wheel is not driven along with rotation of the armature shaft and a second mode wherein the fan wheel is driven along with rotation of the armature shaft; wherein the actuator comprises a responsive element that responds to a motor parameter comprising one of: a motor temperature and a motor load, and moves the torque transfer arrangement from the first position to the second position in response to a change of the motor parameter.