Research On Coordinated Motion Control Method For Road Vehicles After A Tire Blow-out

Since the automobile to be born, there has a history of more than one hundred years. During the history, traffic accidents killed more than sixty million people, and for tire blow-out only, it took the lives of more than ten million people. The invention of automobiles changes human life, but tire blow-out is always like the shadow accompanying with automobiles, especially when driving at high speeds, it often leads; to extremely serious accidents. The causes of tire blow-out are numerous and diversified, the occurrence of tire blow-out still cannot avoid completely so far, and how to ensure the driving safety through active control is a difficult problem still urgently need to be solved in the field of active safety research at home and abroad. In addition, with the progress of science and technology, intelligent automobile has gradually become one of the development directions of future automobiles, and how to handle the self-driving automobile after a tire blow-out is a very important problem which has its great practical significance since the intelligent driving technology is gradually popular. For this reason, the objective of this paper is to present reliable active control method for the high speed vehicle after a tire blow-out, it aims to improve driving safety of the high speed vehicle after a tire blow-out by lane-keeping and lateral stability control.By analyzing the impact of tire blow-out on the lateral dynamics of the automo-bile when running in the highway, this paper firstly presents the trajectory tracking and stability control method with double closed-loop structure for the vehicle after tire blow-out. According to the complex characteristics of the automobile such as multi-variable, time-varying parameters, and the existence of constrains such as the actuator satura-tion, a differential flatness based model predictive control method was adopted to control the front wheel angle for tracking the trajectory, and the differential brake control was adopted to offer an inner-loop control input and improve the lateral stability. By com-paring with the braking-alone control scheme and the steering-alone control scheme, the advantages of coordinated motion control scheme is discussed. Considering that most of the highway roads are straight (The turning radius of curved road is so larger that sometimes they can be approximate to straight), to simplify the controller design and implementation process and make the control system more convenient for engineering ap-plication, this paper proposes a novel constrained H∞ coordinated control approach for the path-following and driving stability problem of the road vehicles after a tire blow-out since the uncertainties/disturbances caused by a tire blow-out are difficult to be measured or estimated. In this control method, differential braking control and front wheel steering control are integrated together, the lateral dynamic change caused by a tire blow-out are considered as a disturbance, and the tire cornering stiffness is expressed in the form of additive uncertainty when establishing the model used for controller design. In order to ensure the driving safety of the vehicle after a tire blow-out, prevent too big the front wheel angle which may cause the tire to separate from the wheel rim, the front wheel angle is processed for the constraint condition of the controller. This is because that once the wheel rim touches the ground when the vehicle is running at high speed, a rollover accident could easily occur. The influence of different braking force distribution scheme for the control effect are discussed in detail in order to lay the foundation for the following research work. In order to further improve the control performance, make the controller not only can be used in the straight road condition but also the curved road condition, a nonlinear non-affine road vehicle model is established, and a novel nonlinear tri-step coordinated motion control method for road vehicles after a tire blow-out is presented in this paper. The closed-loop control system is designed to be the standard second order system, and the stochastic algorithm is used to study the regularities of parameter distri-bution with respect to the system performance, and this can provide some guidance for engineering realization. For purpose of simplifying the design process of the controller, only several major flat tire characteristics were considered, and this led to a simplified nonlinear vehicle dynamic model. Considering the model uncertainties and some other disturbance, the robust stability of the closed-loop system is analyzed based on the input to state stability theory. To address the model uncertainty, measurement noise, estima-tion error and some other perturbation problems, an improved nonlinear robust tri-step coordinated motion optimal control method is proposed in the framework of input to state stability theory to enhance the system robustness. In order to achieve satisfactory control performance and be able to deal with the constraints of control problem, we coordinate the steering control and braking control by using the optimal control strategy.A high precision vehicle dynamic model after a tire blow-out is given in the high-fidelity vehicle dynamics simulation software veDYNA(?), and it is used as the plant to verify the performance of each controller. The simulation experiment results show that the methods proposed in this thesis can achieve satisfactory control effect in respect of lane-keeping and lateral stability. The coordinated motion control have both advantages of braking control and steering control. The front wheel angle is controlled in a small range, and the vehicle can track the desired path steadily. The traffic accidents, such as collision or roll over, can be avoided. The coordinated motion control methods proposed in this thesis provide the theoretical basis for the hardware-in-the-loop simulations and the real vehicle tests which will be carried out in the future.