DE2919744

A power tool speed shifting mechanism includes a planetary gear set wherein the ring gear is connected to the driven member of a torque responsive disengageable clutch. The driving clutch member is keyed for rotation with the sun gear of the planetary gear set; and the ring gear is mounted in a one-way clutch to provide for unidirectional rotation of the entire planetary gear set at the speed of the sun gear when the torque responsive clutch is engaged. The one-way clutch is mounted in an axially movable but substantially nonrotatable member of a torque responsive coupling. In response to a predetermined torque being transmitted through the speed shifting mechanism the clutch members disengage to impose a reaction torque on the coupling through the ring gear and the clutch. Axial movement of the one coupling member together with the ring gear holds the clutch disengaged whereby the planet gear carrier then rotates at a reduced speed with respect to the sun gear.