3D Computer vision contact patch measurements inside off-road vehicle tyres

Abstract

The interaction between tyres and terrain is one of the most studied areas in the vehicle dynamics and terramechanics research communities because it is the only region where excitation forces act on the vehicle if aerodynamics is not considered. The tyre area which deforms against the ground is called the contact patch. Measuring the contact patch has been accomplished statically in the past; however, measurement while a wheel rotates has proven difficult. A number of attempts to measure carcass deformation from inside the tyre have succeeded in measuring small areas or single points but full field measurement has never been attempted. This study describes the design and testing of a system which uses stereo cameras and image correspondence to measure the deformation of the inside of the tyre carcass in the contact region completely. The system includes a stabilisation mechanism which prevents the cameras from rotating, ensuring that the cameras view the inside of the contact region at all times. Software to capture and process the images captured is developed and tested to ensure measurement accuracy. The 3D results produced by the software are compared to one another where possible and any trends or problems are discussed. Results indicate that the full 3D displacement field in the contact region can be measured accurately. The information produced is expected to be extremely valuable for development and validation of tyre and vehicle dynamics models.