Michael R Kunz

US Patent:

55264603, Jun 11, 1996

Filed:

Apr 25, 1994

Appl. No.:

8/232559

Inventors:

Angelo J. DeFrancesco - Glen Ellyn IL
Daniel M. Elligson - Millers MD
Michael P. Kunz - Hampstead MD

Assignee:

Black & Decker Inc. - Newark DE

International Classification:

H02P 729

US Classification:

388831

Abstract:

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.