The Torque–Tension Behaviour of 22 × 1.5 mm Bolts for Fixing Spigot-Located Wheels on Heavy Commercial Vehicles

Abstract

Threaded fasteners are generally used to secure wheels on to vehicles. However, in the case of heavy commercial vehicles, in recent years there has been a problem of ensuring the integrity of wheel fixings (1, 2). Notwithstanding a change of wheel centring from conically ended nuts to a central hub spigot, essentially the same wheel fixing system is used nowadays as was developed when the operational duty cycles were much lower, for example 80 kN versus 130 kN maximum regular axle loads, increased mileages, markedly improved braking performance, higher speeds, better tyre/road coefficients and greater cornering forces. Consequently a new British Standard concerned with quality control of the components used for commercial vehicle wheel fixings has been published (3). The purpose of the present work is to report the results of an investigation into some of the factors which can affect the performance of the main type of commercial vehicle wheel fastener, in particular the effects of fastener friction on the pre-load. Experiments have been performed on 22 × 1.5 mm wheel bolts and nuts under four different conditions, namely ‘as received’, degreased, heat-cycled and re-lubricated, at torques up to 800 N m. The results showed a substantial decrease, of up to 60–70 per cent, in axial tension for both degreased and heat-cycled conditions, when compared with the ‘as received’ performance. Full recovery was found to be achievable simply by re-lubricating with engine oil. The theoretical torque-tension model (4) was modified to account for the nut–washer geometry and used to determine effective friction coefficients. These, and the other limited published data (5–7) were used to define performance boundaries. A comparison is made between the data presented herein and the quality determining performance as specified in the new British Standard (3).