Patent ID: 7451668

Claim:
A starter for cranking an internal combustion engine, the starter comprising: an electric motor including an armature connected to the armature shaft; a planetary gear speed reduction device composed of: a sun gear integrally formed with the armature shaft; a plurality of planetary gears, each having a same number of teeth, engaging with the sun gear and orbiting around the sun gear; an internal gear engaging with the planetary gears; and a planetary gear carrier rotatably supporting the planetary gears thereon, wherein a rotational speed of the armature is reduced and a rotational torque of the armature is transmitted to the planetary gear carrier by restricting rotation of the internal gear; an output shaft rotating together with the planetary gear carrier; a pinion gear, to which a rotational torque of the output shaft is transmitted, for cranking the internal combustion engine; and an excessive-torque-absorbing device including: a plurality of rotatable disks that form the internal gear, each rotatable disk having a same number of teeth engaging with teeth of the planetary gears; a plurality of fixed disks laminated alternately with the rotatable disks; and a resilient member for pressing the laminated rotatable disks and the fixed disks in the axial direction, wherein the rotational torque of the armature is absorbed, by causing slippage between the rotatable disks and the fixed disks only when the rotational torque of the armature exceeds a predetermined level, wherein: gear teeth of the internal gear are formed on the rotatable disks; the excessive-torque-absorbing device further includes a cylindrical casing having inner grooves extending in the axial direction and forming projections on an outer periphery of the cylindrical casing; each fixed disk includes projections formed on an outer periphery thereof; and the projections of the fixed disks are engaged with the inner grooves of the cylindrical casing, so that the fixed disks are movable in the axial direction and not rotatable in the cylindrical casing.