| 摘要 |
A starter motor with a planetary speed reduction gear in which a bolt for securing an electric motor unit to a front bracket passes at an outer circumference of an internal gear constituting a planetary speed reduction gear. The internal gear is provided in its outer circumference with a recessed groove with its bottom located on a radial axis passing through the center of one of the teeth of the internal gear and extending in the axial direction, and that a stem of the bolt is partly engaged by the recessed groove. Also, the internal gear may be provided in its outer circumference with an axially-extending threaded hole having a center located on a radial axis passing through the center of one of the teeth of the internal gear and formed in the end face of the frame, the threaded hole being located at a position in which its inner thread portion contacts with an imaginary circle having a radius equal to a thickness dimension of the rim portion necessary for the mechanical strength from the corner portion of the deddendum of the teeth, and that the threaded hole is thread-engaged by a tip threaded portion of the bolt.
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