Black Decker Inc.

Daniel M Elligson

Michael P Kunz

Angelo J DeFrancesco

An impact wrench having a speed limiting control circuit to allow an operator of the wrench to controllably limit the maximum speed of the wrench to a predetermined value when a trigger thereof is fully engaged. The impact wrench includes a manually adjustable speed limiting control protruding from an outer surface of the impact wrench which is conveniently manually adjustable. The speed limiting control is coupled to the wiper arm of a speed limiting potentiometer which is electrically coupled to a speed control circuit within the impact wrench. The speed limiting potentiometer limits the maximum speed of the motor of the impact wrench (and thus the maximum torque which can be generated by the impact wrench 10) to an operator selected percentage of the maximum motor speed which would otherwise be produced when the trigger is fully engaged. In the preferred embodiment the speed limiting potentiometer is electrically coupled in series between a capacitor and speed control potentiometer, which are each coupled to a 555 CMOS timer which controls the duty cycle of an FET used to drive the motor. The speed limiting potentiometer enables the operator to further limit the maximum duty cycle of the output of the timer, which is a pulse-width-modulated like output, to a percentage of that which would otherwise be produced when the trigger is fully engaged.

Impact wrench having speed control circuit

In an electrically powered combination screwdriver/drill opposing halves of a ratchet type torque tranmsitting clutch are normally biased axially apart by a compression spring. The output half of the clutch is fixed on the output spindle of the tool which is free to move axially within limits. For screwdriving operation, operator bias of the tool against the workpiece overcomes the spring, retracting the output spindle and bringing the clutch halves into engagement. An adjustable stop in the nose of the tool limits axially rearward movement of the output spindle and hence depth of engagement of the clutch teeth, thus providing a variable limit on torque transmitted. For the drilling mode, the rearward half of the clutch is cammed forward so that the clutch is firmly engaged for continuous rotation of the output spindle without specific torque limitation. An operator may switch from drilling mode to screwdriving mode and back without disturbing the torque limit adjustment of the screwdriving mode.

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Millers, MD, United States of America

Daniel M Elligson