Tire-Road Friction Estimation Using Slip-based Observers

In order to improve the security of the vehicles, the car industry focuses more and more on Active Safety. The objective is to introduce embedded electronic control systems to detect dangerous conditions, warn the driver and, in emergency situations, even take actions to avoid crash or at least reduce the violence of the impact. The tire-road friction coefficient which defines the maximum traction and braking capacities is very useful information for both the driver and electronic devices like ABS, ESP, roll-over prevention or collision mitigation. Unfortunately such a coefficient cannot be directly measured and has to be estimated from other available data. This thesis reviews the main directions followed by researchers around the world and then focuses on slip-based methods. The methods proposed in a few papers are implemented, compared and commented. Then some original solutions are proposed. First, a hybrid observer has been developed with the idea to classify roads into a few categories. The principle is very interesting and the implementation brings out many problems to take into consideration and some attempts of solutions.Secondly, a force observer and a tire friction model are combined. This natural approach works well in simulations