Three-dimensional contact patch strain measurement inside rolling off-Road tyres

Abstract

The forces generated in the tyre contact-patch are important for vehicle dynamics analysis. The tyre contact patch is not directly visible due to the terrain. Measuring the strain in the contact patch region may give insight into the forces generated by the tyre as it deforms. Strain measurement in the contact patch is often limited to discrete points, using strain gauges or other techniques which limits data capture to once per revolution. In this study stereovision cameras are used to capture unique features in the pattern painted on the tyres inner surface. An in-tyre mechanically stabilized camera system allows the contact patch to be captured continuously and the stereovision cameras allow for full field measurement of the tyre inner surface. In post processing the features are tracked and triangulated to form point-clouds for each time step. Point-clouds are compared to determine the strain of common points in two directions. The system is applied to an agricultural tyre with large tread-blocks. The wheel is instrumented to measure pressure and forces. The tyre is tested statically in a series of tyre tests where the lateral, longitudinal and vertical displacement is controlled. The strain measured in the tyre contact patch region is compared to the forces measured at the wheel centre. It is noticed that as the measured forces increases so too does the magnitudes of the strains. Unique patterns are found in the contact patch strain for each test type. These patterns could be used to identify the type of forces experienced by the wheel while the strain magnitude could give an indication of the magnitude of the forces. Future work could allow for strain measurement in the contact patch as the tyre rolls over deformable terrain where displacement is not easily controlled.