Control of four-wheel steering vehicles based on composite model free observer

Abstract

Four-wheel steering (4WS) is an advanced technology for automotive chassis, which is more flexible and redundant than conventional front wheel steering. For a 4WS vehicle, the accuracy and stability of steering control must be guaranteed, so the main difficulty is the model nonlinearity during driving. To deal with the problems, a novel composite model free observer (CMFO) is designed. The nominal parameters are used to model the 4WS vehicles, and the data-driven method is used to improve observation accuracy. Then a CMFO based controller is designed to control the lateral dynamics of 4WS vehicles. The stability of the proposed control scheme is proved by theoretical derivation, and experiments are carried out to compare the performance between the CMFO based controller, model free adaptive controller (MFAC) and linear quadratic regulator (LQR). The mean absolute error (MAE) values of CMFO are reduced by 75.56% and 44.49% compared with those of LQR and MFAC, respectively.