Tire longitudinal grip estimation for improved safety of vehicles in off-road conditions

We describe an on-line observer that allows to monitor the soil-tire contact longitudinal stiffness of off-road vehicles equipped with low cost sensors. The knowledge of such a value is a milestone in the development of active security devices, or at least a mean to inform the driver about the longitudinal stability of his vehicle. Indeed, these vehicles are frequently subject to ground changes and high slopes, causing fatal losses of control - slipping, rollover, etc. - every year. The observer has been tested and validated on a grape harvester in various conditions and its output evaluated with respect to an estimation based on expensive but precise sensors. These experimental results show that the driver can be informed in real-time about the longitudinal stability of his vehicle and alerted about critical situations.