Patent ID: 7109675

Claim:
A power tool, comprising: a motor, means for generating an elevated torque, wherein the elevated torque generating means is coupled to the motor and has an output shaft, wherein if a load acting on the output shaft is less than a predetermined value, rotating torque generated by the motor is directly transmitted to the output shaft and if a load acting on the output shaft exceeds the predetermined value, an elevated torque is generated by the elevated torque generating means and applied to the output shaft, wherein the elevated torque generating means comprises an oil pulse unit driven by the motor, a load shaft connected to the output shaft, a plurality of magnets disposed around an outer surface of either the output shaft or the load shaft so that the magnets integrally rotate with the output shaft or the load shaft, each magnet having a South pole and a North pole, wherein the South poles are disposed in an alternating relationship with the North poles, a first sensor fixedly disposed relative to the magnets, such that the first sensor will not rotate when the output shaft or load shaft rotates, wherein the first sensor latches its output signal to a first level when detecting a North pole magnetic field, and latches its output signal to a second level when detecting a South pole magnetic field, and a second sensor fixedly disposed relative to the magnets, such that the second sensor will not rotate when the output shaft or load shaft rotates, wherein the second sensor latches its output signal to the first level when detecting the North pole magnetic field, and latches its output signal to the second level when detecting the South pole magnetic field, wherein the output signal of the first sensor and the output signal of the second sensor are shifted by first phase when the output shaft or load shaft rotates in a direction of tightening a fastener, and are shifted by second phase when the output shaft or load shaft rotates in a direction of loosening the fastener.