| 摘要 |
PURPOSE: To provide a portable power tool having a motor speed control circuit capable of substantially increasing effective torque output to a motor of a specified size and a gear train. CONSTITUTION: This power tool is provided with a gear train 20 connecting an output spindle of a motor 16 to a tool bit installation chuck 22, and the gear train 20 has loosening of such a degree that torque from the motor 16 is absorbed before it is transmitted to a tool bit. A control circuit 12 of the power tool alternately puts the motor 16 on and off by pulses of which off time has such a sufficient length as to relax the gear train 20, so that motor 16 can make a running start when power is applied again. For transition into a ratcheting action mode, various ways for detection of a current of a specified threshold value, detection of a specified increase of a motor current, detection of a specified reduction speed of the motor current, etc. are disclosed. |
