Patent ID: 8607891
Filing Date: 2013-12-17
Classification: B25B

Abstract:
1. An electrical power tool comprising: a tool main body portion that contains an electric motor as a drive source and a speed change device for decelerating rotative power of the electric motor and outputting the same to a spindle; a handle portion that is protruded laterally from the tool main body portion; and a battery pack as a power source that is attached to a distal end of the handle portion, wherein the speed change device is capable of changing a reduction ratio thereof and capable of automatically switching between a high speed low torque mode in which a high speed low torque is output and a low speed high torque mode in which a low speed high torque is output, based on an external torque applied to the spindle, thereby outputting the rotative power, and a distance from a rotation axis of the spindle to a center of gravity of the battery pack and a mass of the battery pack are preset such that a moment of inertia around the rotation axis of the spindle is greater than a reaction around the rotation axis of the spindle that is produced when the high speed low torque mode is changed to the low speed high torque mode in the speed change device.