Patent ID: 8302702

Claim:
A torque sensing unit for a power tool having a housing, a rotation motor, and a planetary reduction gearing with a ring gear, the torque sensing unit comprising: a torque transferring element interposed between the ring gear and the housing for transferring a reaction torque exerted on the ring gear to the housing, the torque transferring element including at least one strain sensor for delivering electric signals in response to the transferred reaction torque magnitude, and wherein: the torque transferring element is substantially annular in shape and has an axial length substantially smaller than its radial dimensions, the torque transferring element is arranged with its geometric axis coinciding with the geometric axis of the ring gear; and wherein the torque transferring element further comprises: a first pair of external engagement portions for co-operation with grooves in the housing; a second pair of external engagement portions for co-operation with pockets in the ring gear, said first and second pairs of engagement portions being angularly spaced relative to each other; and at least one pair of weak deformation zones located between said first and second pairs of engagement portions and arranged to be exposed to bend stresses by the reaction torque transferred by the torque transferring element, and wherein said at least one strain sensor is attached to one of said deformation zones.