Patent ID: 7051820

Claim:
An electrically powered rotary hammer comprising: a hollow cylindrical spindle mounted rotatably within a housing of the hammer with a tool holder arrangement located at a forward end of the spindle for releasably holding a tool or bit so as to enable limited reciprocation of the tool or bit; an air cushion hammering mechanism located within the spindle for generating repeated impacts on the tool or bit; and a rotary drive mechanism comprising a spindle drive gear mounted rotatably around the spindle for rotationally driving the spindle via an overload clutch, characterised in that the overload clutch comprises: a clutch ring rotatably mounted around the spindle so as to have limited rotational movement with respect to the spindle drive gear and so as to be rotatably driven by the spindle drive gear via at least one spring element; and at least one locking member carried by the clutch ring so as to be shiftable with respect to the clutch ring from a first position, in which the locking member transmits rotary drive from the clutch ring to the spindle, to a second position wherein the locking member does not transmit rotary drive to the spindle; arranged such that below a predetermined torque threshold the spring element maintains the spindle drive gear and the clutch ring in a first relative rotational position in which the spindle drive gear locks the locking member in the first position and such that above the torque threshold the spring element deforms and the spindle drive gear and the clutch ring move into a second relative rotational position wherein the locking member moves into the second position.