Parameterisation of tyres with large lugs

Abstract

Vehicle development relies heavily on simulation results throughout the vehicle industry; however, simulation results are only as reliable as the input data used to parameterise the models. In vehicle dynamics simulations the terrain and tyres are two very important aspects that are often disregarded or the models over simplified. Profiling terrain and testing tyres are not trivial or inexpensive exercises, thus it is extremely important to obtain representative measurements. Tyre characteristics are dependent on the terrain characteristics, so it is vital to use representative artificial terrains in laboratory tyre characterisation tests. In this study the artificial and field terrains are measured, characterised together with tyre tests on these terrains. Measuring equipment and tyre test rigs, in the form of terrain profilometers, wheel force transducers, static/non-rolling, dynamic/rolling and damping tyre test rigs are also conceptualised, designed, manufactured, commissioned and used to characterise an agricultural tyre with large lugs. This study compares friction coefficient measurements on dry non-deformable on-road surfaces in a laboratory and field test tracks on the same agricultural tyre with large lugs. It is found that the microtexture of the different surfaces needs to correlate in order to have comparable laboratory and field tests results. For the concrete field test surfaces in question, the recommended laboratory test surface needs to have a surface roughness value of 10<Ra<15µm. This roughness is equivalent to a P180 grit to P220 grit sandpaper, however, using only the sandpaper grade is not a good measure to use. A more accurate method is to compare the Displacement Spectral Densities of the field test surface with that of the sandpaper intended to be used in the laboratory. The spatial frequency of interest that needs to be compared is between 10^4 and 10^6cycles/m, which corresponds to the surface roughness value. During the operational life of a tyre the longitudinal, lateral, vertical and damping characteristics change as the tyre wears down. This study investigates the change in tyre characteristics with tyre wear at a single load condition, two inflation pressures and three tread wear conditions on a flat surface and over a cleat. Increasing trends are noted with change in traction and tyre stiffnesses as the tyre wear changes. Motion resistance of tyres directly contribute to the operational costs of all vehicles. Different methods used to measure the motion resistance of a tyre with large lugs are compared on non-deformable terrain. Some basic considerations that need to be considered during motion resistance measurements are the very low longitudinal forces that need to be measured compared to the large vertical load carried by the tyre and tyre operating conditions. These findings and development of measuring equipment and tyre test rigs will assist researchers and industry to improve handling, ride comfort and energy efficiency of, amongst other, agricultural and construction vehicles.