Patent ID: 8826765

Claim:
A helical gear including a hub mounted on a rotation shaft and having a rotation center, a disk extending from said rotation center of said hub towards an outer side in a radial direction, and a rim provided at an outer side of said disk, said rim including a plurality of teeth at an outer peripheral face, said disk including a plurality of opening perimeter walls defining through holes provided along a perimeter of said hub, said opening perimeter wall including a first arc side face located at a leading end side in a direction of rotation, concave towards said leading end side in the direction of rotation, and having a distance from an arc center as a first radius, and said first arc side face including a side face at a side of said rotation center of said hub, located at a position with a distance from said arc center differing from a length of said first radius, on a verge of a virtual arcuate line centered about the rotation center of said hub and passing through said arc center.