Patent ID: 8454445

Claim:
A power transmission comprising: a driven body, a drive body; wherein said drive boding drives said driven body; and wherein said driven body and said drive body are rotated in the same direction, a coupling portion, through which torque of said drive body is transmitted to said driven body and transmission of torque from said drive body is interrupted when a driving load of said driven body exceeds a predetermined level, comprising: a positive torque transmission member for transmitting torque in a direction of forward rotation and interrupting transmission of torque from said drive body by fracturing when said driving load of said driven body exceeds said predetermined level and a negative torque transmission member for transmitting torque in a direction of reverse rotation, wherein said positive torque transmission member is different from said negative torque transmission member, and a surface layer comprised of a different kind of material from a material composing said positive and negative torque transmission members is formed integrally on a surface of at least one of said positive and negative torque transmission members and is interposed at a contact portion between said positive torque transmission member and said negative torque transmission member.