Development of tightening apparatus with multiple shafts and torque control mechanism for wheel bolts of large vehicles

One of the major causes of the tire coming-off accident of large vehicles is that wheel bolts, which clamp inner and outer wheels to the hub, are not necessarily tightened with prescribed torque. The amount of torque is a practical index to clamp the joint with its target bolt preload. In the past, tightening operation was conducted by an impact wrench, which cannot control the tightening torque with sufficient accuracy. In order to reduce the number of such accidents, the use of a manual torque wrench has strongly been recommended since 2003 by Ministry of Land, Infrastructure, Transport and Tourism. However, the tire coming-off accident still occurs rather frequently. That is because all the tires of large vehicles have not always been tightened using manual torque wrenches due to the low working efficiency, since the total number of tightening operation is usually 80 times and higher when clamping a lot of wheel bolts one by one. In this study, tightening apparatuses with torque control mechanism, especially designed for wheel bolts of large vehicles, are developed aiming at the extermination of tire coming-off accidents. A tightening device, called "air wrench", is used as the key device to design the tightening apparatuses. Air wrench has been used to tighten large bolts with prescribed torque in some industrial fields. First, the performance of air wrench is examined concerning the accuracy of bolt preloads and the scatter in coefficients of friction at mating surfaces. Then, tightening apparatuses equipped with two or four air wrenches are designed, which can tighten two or four wheel bolts simultaneously. It is shown that the developed tightening apparatuses provide high working efficiency and low scatter in bolt preloads.