Patent ID: 8084981

Claim:
A rechargeable electric power tool comprising a motor driven by a secondary battery as a power source, a switching element for regulating power supplied to the motor, a motor control unit for controlling rotation of the motor through the switching element, a lead wire for supplying a drive current to the motor therethrough and a trigger switch changed over by a user for turning on or off the drive current supplied to the motor through the lead wire, wherein a first temperature detection unit is arranged on the lead wire and a first temperature threshold value T th1 , a second temperature threshold value T th2 lower than the T th1 , a first preset temperature increase rate (ΔT/Δt) s1 and a third temperature threshold value T th3 lower than the T th2 are set for the first temperature detection unit, wherein, based on a temperature detection signal outputted from the first temperature detection unit, the motor control unit calculates a first calculated temperature increase rate (ΔT/Δt) by dividing a temperature elevation degree ΔT by a lapse time Δt, wherein, upon changeover of the trigger switch, the motor control unit determines magnitude relations between a detected temperature T 1 corresponding to the temperature detection signal outputted from the first temperature detection unit and the T th1 , the T th2 and the T th3 , and a magnitude relation between the (ΔT/Δt) and the (ΔT/Δt) s1 , wherein, if the detected temperature T 1 is determined to be greater than the T th1 or if the (ΔT/Δt) is determined to be greater than the (ΔT/Δt) s1 after the detected temperature T 1 has been determined to be greater than the T th2 and to be equal to or smaller than the T th1 , the motor control unit is set in a limited operation mode in which the motor control unit stops rotation of the motor or in which the revolution number of the motor is limited to a predetermined value or less, and wherein, if the detected temperature T 1 is determined to be smaller than the T th3 , the motor control unit releases the limited operation mode.