Two Degree of Freedom/H_∞Controller Synthesis for Active Four Wheel Steering Vehicles

Abstract

This paper proposes an active front and rear wheel steering control system that simultaneously achieves both lateral acceleration and yaw rate responses always desirable regardless of changes in vehicle dynamics. First, this paper describes a method to accurately estimate physical parameters in the four wheel steering vehicle model, including the dynamics of a steering actuator, by applying the maximum likelihood estimation method. Next, the structure of the proposed front and rear steering control system is described. This control system has for its purpose to coincide both the lateral acceleration and yaw rate responses of the vehicle with the responses of the respective desirable reference models, as well as to make it a robust system against changes in vehicle dynamics and external disturbances. To achieve both objectives, a two-degree-of-freedom control system theory is employed. Then the paper shows the viability of the proposed steering control system through computer simulations. Finally, the results of proving ground tests carried out with a test vehicle equipped with a front and rear wheel steering mechanism driven by the digital computer and electric powered actuator are shown. From these results, it was confirmed that the proposed active front and rear wheel steering control system would contribute greatly to the improvement of vehicle handling qualities and preventive safety.

Comparisons of vehicle stability controls based on 4WS, Brake, Brake-FAS and IMC techniques

“…For vehicle active control, vehicle yaw rate and sideslip angle are usually chosen as control targets, and braking and/or active steering are usually applied to fulfil control strategies. In recent years, four-wheel-steering (4WS) control is widely studied [1][2][3][4][5][6][7] with the development of steer-by-wire technologies. However, braking control is still indispensable and would be much more effective when combined with active steering [8][9][10][11].…”

Comparisons of 4WS and Brake-FAS based on IMC for vehicle stability control

“…In recent years, four-wheel-steering (4WS) control is widely studied [1][2][3][4][5][6][7][8] with the development of steer-by-wire technologies. However, braking control is still indispensable and would be much more effective when combined with active steering [9][10][11][12].…”

Dimensionless robust control with application to vehicles

“…A few to be briefly mentioned here include robust yaw rate control [6] and robust lateral positioning using one [7], [8] or more [9]- [11] driver inputs. In developing controllers for these plants, the particular nominal model and uncertainty representation must be selected.…”