Patent ID: 8171597

Claim:
A wiper motor for pivotally driving a wiper to and fro, the wiper motor comprising: a motor body that generates a rotational force; an output shaft that is coupled to the wiper so as to rotate the wiper; a transmission mechanism that transmits the rotational force from the motor body; and a clutch mechanism that transmits the rotational force from the transmission mechanism to the output shaft when the output shaft is subjected to a torque not larger than an engagement releasing torque, and lets the transmission mechanism run idle not to transmit the rotational force from the transmission mechanism to the output shaft when the output shaft is subjected to a torque equal to or larger than the engagement releasing torque, wherein the engagement releasing torque is specified as a value that is larger than a maximum output torque of the wiper motor, which is exerted when the output shaft is locked, wherein: the clutch mechanism includes an input disk that is arranged coaxially with the output shaft and rotationally driven by the rotational force generated by the motor body, a clutch disk that is installed to the output shaft coaxially with the output shaft so as to face the input disk and a biasing member that biases at least one of the input disk and the clutch disk to bring them close to each other; the clutch disk is integrally rotatable with the output shaft; the input disk has a first engaging portion on one side surface thereof to face the clutch disk; the clutch disk has a second engaging portion on one side surface thereof to be engaged with the first engaging portion of the input disk when the input disk and the clutch disk are in a predetermined relative angle and a clearance between the input disk and the clutch disk is minimized by the biasing means; the first and second engaging portions are formed so as to be disengaged from each other when a torque acting on the output shaft forcedly rotates the clutch disk with respect to the input disk in increasing the clearance between the input disk and the clutch disk against a biasing force of the biasing means; the engagement releasing torque is specified by at least one of: adjusted shapes of the first and second engaging portions; and adjusted biasing force of the biasing member; the second engaging portion of the clutch disk and the first engaging portion of the input disk are configured to maintain engagement therebetween to limit relative rotation between the clutch disk and the input disk when the torque, which is applied by the wiper onto the output shaft, is smaller than the engagement releasing torque; and the second engaging portion of the clutch disk and the first engaging portion of the input disk are configured to be disengaged from each other to enable the relative rotation between the clutch disk and the input disk when the torque, which is applied by the wiper onto the output shaft, is equal to or larger than the engagement releasing torque.