US Patent 7451668 Starter having excessive-torque-absorbing device

A starter for cranking an internal combustion engine includes an electric motor, a planetary gear speed reduction device for reducing a rotational speed of the electric motor and an excessive-torque-absorbing device. The excessive-torque-absorbing device is composed of plural rotatable disks that form an internal gear of the speed reduction device, plural fixed disks and a disk spring. Both disks are alternately laminated and pressed in the laminated direction by the disk spring. When a rotational torque of the electric motor to be transmitted to a pinion gear of the starter exceeds a predetermined level, slippage occurs between the rotatable disks and the fixed disks, and thereby the excessive torque is absorbed.