| 摘要 |
<p>The present invention provides a tightening structure with which a reduction in processing steps is achieved without modifying the shape of a partner member and improvements in bolt strength and fatigue strength are achieved, and with which the fitting length of a thread ridge is not altered greatly in comparison with a conventional tightening structure such that a size reduction can be achieved, thereby contributing greatly to a reduction in the weight of a vehicle. A self-forming screw having a strength of 14T, which is manufactured by pre-heat treatment rolling and gradually self-forms an internal screw, is used as a tightening bolt, and a member having a prepared hole formed by casting alone or by forging alone, while not yet being subjected to screw formation, is used as a member into which the self-forming screw is screwed. Following tightening of an attachment member, the tightening structure has a percentage of thread engagement of 75 to 90% between the internal screw formed through self-forming and an external screw, and a fitting length of d to 2.2 d (in the case of a steel cast member or a steel forged member, d being the screw diameter), or of d to 2.5 d (in the case of an aluminum die-cast member) which is obtained between the screw and the prepared hole. Moreover, the screw is fastened through self-forming, and therefore no clearance is generated on a contact surface between the external screw and the internal screw.</p> |
