| Along with the rapid development of the high-grade highway,the average vehicle speed tends to be higher and higher,which potentially threatens the vehicle driving safety.Tire,as the only contact component between road and vehicle,has great impact on the maneuverability and safety of the vehicle.There exists the obvious off-tracking and yaw motions for the vehicle after a tire blowout,and drift out and spin may occur in the critical cases,which has negative effects on the road traffic and passengers' safety.Under such situations,it is difficult for human driver to make the effective decision-making and corrective action because of nervousness and inexperience,and the existed studies imply that driver's excessive and/or incorrect operation is the principal contributor that causes serious traffic injury.Besides,the redistribution of vertical loads caused by decrease of effective radius of wheel after a tire blowout,together with system inherent uncertainties and safety constraints,and these make it hard for the traditional active safety control system to achieve the expected control effect for the vehicle.In addition,the rapid development of drive distributed electric vehicle and its superiorities in architecture and performance bring new opportunities for the active safety control of the vehicle after a tire blowout.Meanwhile,the unsprung mass of the whole vehicle has significantly increased due to the introduced distributed motors,which will aggravate the vertical dynamic response of the system.To this end,this dissertation devotes to propose an automated hazard escaping control scheme for the distributed drive electric vehicle after a tire blowout on highway considering the reconfiguration of the vertical loads,and the details are as follows:Firstly,an eight degree of freedom(DOF)vehicle dynamics model that includes four wheels' rotation dynamics and longitudinal,lateral,yaw and roll dynamics of the vehicle body is developed.Combining the standard commercial vehicle simulation platform CarSim,a CarSim-Simulink co-simulation model is constructed with consideration of wheels' rotation dynamics,and the effectiveness of eight DOF and co-simulation models is confirmed under lane change and double lane change test maneuvers based on the standard vehicle model in CarSim.Based upon the reported mechanical property variations after a tire blowout on highway and the verified co-simulation model,a CarSim-Simulink co-simulation model for the tire blow-out vehicle is presented.Vehicle kinematic and dynamic characteristics are analyzed via the co-simulation model,and the effectiveness of the model is discussed.Based on the verified vehicle body and flat tire models,together with the induced vertical load transfer after a tire blowout,the blow-out vehicle dynamic simulation model is established including vertical load reconfigurations,which offers the foundation for the hazard escaping control system design of the tire blow-out vehicle.Secondly,facing the requirements of both driving state parameter acquisition and quick stopping,a coordinated primary and auxiliary braking wheels emergency braking control scheme is proposed for the tire blow-out vehicle integrating with a nonsingular terminal sliding mode state observer.To acquire the state parameters used for controller design,a nonlinear tire model based nonsingular terminal sliding mode observer is developed for achieving the fast and robust observation of the state parameters.Based on the observed state signals,a yaw-moment controller used to correct the driving directionality of the vehicle with a tire blowout is designed,by which the required primary braking wheel moment can be obtained.In addition,to exert potential braking capacity of two remaining effective wheels apart from the primary and tire blow-out wheels,the maximum allowable braking force between the two wheels is deduced taking the vertical load reconfigurations into account,which can be used to realize quick stopping.Aiming at the distributed drive feature of the system,a constrained weighted least square based reconfigurable tire force distributor is developed for allocating the target yaw moment and the braking force,and driving directionality and quick stopping objectives of the tire blow-out vehicle can be coordinately achieved.Thirdly,aiming at the problem that emergency braking is extremely easy to trigger the rear-end accident in the complex traffic surroundings,a car-following control scheme for the vehicle after a tire blowout on highway is proposed.To implement the active intervention for the longitudinal motion of the vehicle after a tire blowout on highway,a sliding mode control based longitudinal velocity controller is designed considering the sharply increased rolling resistance and its uncertainty.Meanwhile,a model predictive control(MPC)based lateral stability controller is developed to enhance the lateral stability because of its multi-step prediction,rolling optimization and feedback compensation features.Longitudinal velocity and lateral stability controllers as well as the developed torque distributor constitute the integrated control-distribution car-following scheme.Furthermore,aiming at the exogenous disturbances of highway surroundings and the real-time responses requirements of distributed drive system,a robust tube MPC(RMPC)based lateral stability controller and a pseudo-inverse(PI)based reconfigurable tire force allocator are separately developed under car-following scheme to enhance the robustness and real-time property of the control system,and comparison results validate the effectiveness and advantage of the proposed car-following control methods.Finally,a polynomial theory based lane change trajectory planner is presented for the blow-out vehicle taking the vehicle dynamics features into account,and the hazard escaping scheme of the system is given.Considering the dynamics features and safety space constraints,a quintic polynomial based lane change trajectory planning method is investigated.Integrating with car-following and emergency braking control study,system hazard escaping trajectory planning method is discussed.Assimilating the three stages of car-following,lane change and emergency braking maneuvers,a hazard escaping control strategy of coordinating trajectory planning,trajectory tracking and torque distribution modules is proposed.Simulation results of lane change trajectory planning demonstrate that the planned trajectory with the proposed method has the considerable continuation and smoothness,which can satisfy the requirements of system dynamic constraints and actuator characteristics,and system hazard escaping simulation results validate the feasibility and effectiveness of the proposed control strategy and approaches.Outcomes of this dissertation provide a feasible method to solve driving safety problem of the vehicle after a tire blowout considering the vertical load transfer and system safety constraints,which can offer theoretical reference and technical support for method design of the similar fail-safe system,and it is helpful to promote the development of vehicle active safety collaborative control technique. |
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