Abstract: It is an object of the invention to provide a technique to effectively prevent a power tool from being adversely affected when a battery is removed from the power tool. According to the present invention, a power tool is provided that includes a tool bit, a motor that drives the tool bit, a body that houses the motor, a battery detachably coupled to the body so as to supply driving current to operate the motor, a control device that controls the operation of the motor and a power circuit that leads the driving current from the battery to the motor. Within the power tool, the control device stops the motor prior to an interruption of the power circuit when the battery is disengaged from the body in order to prevent a large driving current from being passed through the power circuit. As a result, arc can be effectively prevented from being generated between the battery and the body of the power tool.

Abstract: It is an object of the present invention to provide a technique to increase efficiency of the output torque of the blushless motor to drive a power tool. A representative power tool may comprise a tool bit, a brushless motor to drive the tool bit, a battery to operate the brushless motor and a control device. The control device may operate the brushless motor by means of the battery. The control device may include an advance angle controlling section to control an advance angle of the brushless motor. According to the present teachings, the advance angle of the brushless motor may be determined based upon indexes that reflect working condition of the tool bit when the brushless motor is under the operation. By reflecting the working condition of the tool bit to the determination of the advance angle of the brushless motor, the brushless motor can be operated with higher efficiency under the various working condition such as a hard joint operation and a soft joint operation.