Electric driven spanners

The utility model belonging to electric tools, in particular to an electric watch wrench, comprises an electric motor, a fly wheel, a centrifugal block and an output shaft. The electric watch wrench is characterized in that the motor is provided with a small gear which meshes with a buffer gear which is connected with the fly heel. Steel balls and a buffer spring are arranged between the buffer gear and the fly wheel and the two sides of the fly wheel are provided with the centrifugal block which is provided with a reset torsion spring. The output shaft is arranged in the middle of the fly wheel. The utility model is designed to separate the motor from the fly wheel, so the fly wheel drives the output shaft to impact the screw cap when the screw cap is unlocked and the screw cap transiently stops under the reaction force of the impact. Because the motor drives the buffer gear to rotate by the small gear, the buffer gear is separated from the fly wheel in the process of impact so the motor is not affected by the fly wheel, and the screw cap can be taken down with enough torques after the impact. The torque ratio of the utility model is 10% to 20% larger than that of the similar electric watch wrenches and besides the electric watch wrench needs small motor power, is small in volume, light in weight, more reliable in structure and convenient to use.