Estimation of road inclination and bank angle in automotive vehicles

We extend an observer design for estimation of the vehicle sideslip angle on horizontal surfaces to include estimation of the road inclination angle and the road bank angle. The design makes use of a nonlinear road-tire friction model, and the nonlinearity of the road-tire friction forces are taken into account in the theoretical analysis of the design. Using an absolute-stability argument we show that, under a set of technical assumptions, the origin of the observer error dynamics is globally exponentially stable. Taking unknown road-surface conditions into account, we discuss simultaneous estimation of the road bank angle and a road-tire friction parameter, which is complicated by the dependence of the friction-parameter estimation on lateral excitation of the vehicle. To improve performance on low-friction surfaces, we modulate the observer gains based on a set of practical conditions. Using experimental data from a passenger car, we investigate the performance of the approach.