Yoke of planetary gear-type starter manufacturing apparatus therefor manufacturing method thereof

A cylindrical yoke for a planetary gear type starter including an electric motor with an armature and a rotary shaft, and a starter output shaft having a flange portion formed at one end and operatively connected with the rotary shaft through a planetary gear mechanism having a sun gear, a plurality of planetary gears and a ring gear, said cylindrical yoke comprising:

• a hollow cylindrical body acting as a field magnet of the electric motor;
• a side wall portion formed integrally with said hollow cylindrical body and having an opening at a center of said side wall portion concentric with said hollow cylindrical body for rotatably supporting the starter output shaft;
• an inner peripheral gear portion formed on an inner periphery of said hollow cylindrical body, said inner peripheral gear portion acting as the ring gear and being adapted to be in meshing engagement with the planetary gears;
• and
• an enlarged-thickness annular portion formed integrally with said hollow cylindrical body between said inner peripheral gear portion and said side wall portion;
• wherein the armature of the electric motor and the planetary gears provided on the flange portion of the starter output shaft are accommodated in said hollow cylindrical body.