US Patent 9308630 Impact screwdriver

An impact screwdriver includes a housing, a battery arranged in the housing, an electric motor arranged inside the housing, a transmission part driven by the electric motor and an impacting part, the impacting part including a hammer, an anvil matched to and hammered by the hammer, and an output shaft revolved by the anvil, wherein the rated voltage of the battery is less than or equal to 4.25V, the impact frequency of the hammer and the anvil is at least 30 Hz, and the ratio of the output torque (Nm) of the output shaft to the rated voltage of the battery is 1.8˜4.5.