In this manuscript, a modular sideslip angle and road grade estimation scheme for four-wheel drive (4WD) vehicles is proposed. The longitudinal tire forces are estimated based on disturbance observer, then the lateral tire forces are computed using the estimation of longitudinal tire forces as inputs based on the dugoff tire model. In the following, the full-dimensional nonlinear observer is designed to estimate the vehicle velocities, which fits for different road grade. In the following, the sideslip angle is obtained. In order to specify the effectiveness of the proposed modular estimation scheme, simulations of double lane change maneuver on low friction coefficient road for 4WD vehicle running are carried out. The simulation results verify that the proposed integrated observer could obtain accurate estimation results of sideslip angle, vehicle velocities, and road grade.
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