Mazda Motor Corporation

Hiroshi Shinagawa

Yutaka Fujii

Tatsumi Makimae

After it is tightened with a snug torque T, a bolt is tuned by a total turning angle &#x3b8;equivalent to the sum of an initial-set turning angle &#x3b8;and a corrective additional-turning angle (&#x3b8;+&#x3b8;). The corrective additional-turning angle (&#x3b8;+&#x3b8;) is the sum of a first corrective additional-turning angle &#x3b8;and a second corrective additional-turning angle &#x3b8;, the first corrective additional-turning angle &#x3b8;being to compensate for a situation where a bolt turning angle &#x3b8;corresponding to the snug torque &#x3b8;on an extension line of the bolt tightening torque properties Cin a late tightening stage II is different from a bolt turning angle &#x3b8;corresponding to the actual snug torque T, the second corrective additional-turning angle &#x3b8;being to compensate for a decrease of an effective bolt axial force that is caused by an existence of the initial tightening stage I.

Bolt tightening method and bolt tightening apparatus

According to a bolt tightening method and a bolt tightening apparatus of the invention, a bolt is tightened by using a bolt tightening device, in which torque gradients expressed in terms of the ratio of a tightening torque exerted on the bolt to its turning angle are calculated by successively detecting the tightening torque at intervals of a specific bolt turning angle and calculating an average of individual torque gradient values by first and second torque gradient calculators, and the amount of tightening of the bolt is controlled by a tightening amount controller based on the average of the individual torque gradient values calculated.

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Hiroshima, Japan

Hiroshi Shinagawa