Patent ID: 7821217
Filing Date: 2010-10-26
Classification: H02P

Abstract:
1. A method of controlling a power tool, comprising: providing a power tool with an electronically commutated motor for driving a working implement of the power tool; using a gear reduction unit in communication with an output of the electronically commutated motor, which in turn drives the working implement; using an electronic control system to implement a field weakening control technique to limit a back electromotive force (EMF) generated by the electronically commutated motor, the electronic control system determining a phase advance angle for a current supplied to the electronically commutated motor to implement a degree of field weakening; and using the field weakening control technique to control a resultant torque generated by the electronically commutated motor by controlling the phase advance angle of the current applied to the electronically commutated motor so that at least one of a substantially constant power output and a substantially constant efficiency is achieved over a desired operating speed range of the electronically commutated motor.