Clutch torque control

In a power tool having a motor, a rotary drive input operated by the motor, a rotary drive output for driving a fastener, and a shut-off mechanism for interrupting power to the motor, a clutch torque control comprising

• rotary driving and driven clutch parts respectively drivingly connected to the drive input and drive output,
• resilient means exerting a biasing force continuously urging the driving and driven clutch parts toward one another,
• the driving clutch part and the driven clutch part being relatively axially movable against the force exerted by the resilient means and coaxially rotatable relative to one another,
• the driving and driven clutch parts including input and output cams each having complementary annular races in confronting relation to one another, the races of the cams including a like plurality of equally circumferentially spaced lobes,
• a clutch ball disposed within the races and between each adjacent pairs of lobes, the clutch balls cooperating with the lobes for normally establishing a releasable drive between the drive input and drive output and providing relative movement between the driving and driven clutch parts at a preset output torque established by the resilient means,
• the lobes each having a peak and cam ramps rising to its peak, the lobes being dimensioned and configured with profiles such that the lobes of the input cam are engageable with the clutch balls for rolling them simultaneously between matching cam peaks responsive to relative rotation of the clutch parts to axially displace the driving and driven clutch parts relative to one another against the biasing force of the resilient means for releasing the drive between the clutch parts and actuating the shut-off mechanism responsive to the drive output reaching said preset output torque,
• the clutch balls, upon engagement with a cam lobe, being disposed in the races in a base position, the clutch balls in base position being operative for transmitting said preset torque prior to relative axial movement of the driving and driven clutch parts, and
• the cam lobes being dimensioned and configured such that each of the clutch balls are in engagement with a peak of a cam lobe in said base position of the clutch balls prior to rolling over the cam lobes after said preset torque is transmitted.