Patent ID: 7608956

Claim:
A starter for an engine comprising: a casing including an end frame, the end frame having a bearing mount chamber formed therein; an electric motor disposed within the casing, the electric motor including an armature, a commutator, and brushes, the armature being equipped with an armature shaft to produce torque for starting an engine, the commutator being retained on the armature shaft through an insulator to have a cylindrical commutator surface rotatable in a direction of rotation of the armature shaft, the brushes slidably riding on the commutator surface in electrical contact therewith; a speed reducer working to reduce a speed of rotation of said electric motor; a porous metallic sleeve bearing which retains an end of the armature shaft to be rotatable; a plurality of protrusions extending on the commutator surface substantially in parallel to each other in a direction of rotation of the commutator surface; and urging mechanisms each of which works to urge a surface of one of said brushes into constant engagement with said protrusions to establish the electrical contacts between the brushes and the commutator surface and minimize movement of the armature shaft relative to said bearing, wherein the insulator is mounted directly on the armature shaft and extends along a length of the armature shaft to have an end placed over an outer periphery of the end of the armature shaft, the commutator extends along the length of the armature shaft over the outer periphery of the end of the armature shaft, the porous metallic sleeve bearing is installed in the bearing mount chamber of the end frame in contact with the end of the armature shaft and retains the end of the armature shaft to be rotatable, and the bearing mount chamber is located inwardly of the end of the insulator in a radius direction of the armature shaft, and wherein said speed reducer is implemented by a planetary gear speed reducer which includes a sun gear formed on an end of the armature shaft opposed to the end retained by said bearing and planet gears placed in mesh with the sun gear.