Flat Tire Vehicle Trajectory Control

Highway is a production of the process of social modernization, and because of its convenient, efficient and flexible transport characteristics, it attracts people with all ages. The tendency of rapid economic growth stimulated the rapid development of highway business, and the resulting social positive factors can be seen everywhere. However, after the ascendant in the good situation about highway, the increasingly severe traffic safety problems ensued.Just like the country's aorta, the highway connects the country's various regions, and it is the tache that the national economy developed rapidly. At the same time, it has also been an accident-prone area,where the life and property were caused immeasurable loss. Tire is the fulcrum between the force and the vehicle body, and through the tire the force of the ground affects the vehicle. The tire plays an important role in the car. However, the high speed of vehicles will increase the inside temperature of the tire,and the temperature of tire will become higher as the speed becoming faster. With the high temperature, friction and suddenly hitting by the road,the tire is extremely prone to bursting. In the highway traffic accidents, flat tire hold a large proportion.After the tire bursting, its performance changed tremendously,such as aspect ratio, rolling resistance force coefficient, radial stiffness, cornering stiffness coefficient, longitu-dinal slip stiffness coefficient and roll stiffness coefficient, etc. The deterioration of the mechanical properties of the tire is the fuse which cause instability in the running vehicle. However,after the tire bursting, the operation of the driver is crucial to the vehicle. Ac-company with the vehicle's front tire bursting,it is very difficult to turn the vehicle and the worse is that the vehicle could lose steering capabilities, or even rollover. When the rear tire bursting, the vehicle prone to drift and rollover. What the driver could manipu-late is only for the front wheel which is connected with the steering wheel. So,this paper mainly research on trajectory control for front tire bursting of the vehicle.This paper start from safe driving strategy for the flat-tire vehicle,and then analyzes the flat-tire vehicle's state and the influence of driver operation on the vehicle. After front tire bursting, if we do not take the brake, driving and steering operation, the vehicle will yaw to the flat-tire side. And the result is that the vehicle will run into another lane or crash barrier suddenly.At this time,because the unseating resistance decreases, braking action will lead the tire slip angle increases, then the tire is separated from the rim by force eventually.Besides that, if the turning action is too drastic, the tire will be also separated from the rim. After the tire from the rim, the rigid rim touches ground with sliding or rolling.If pavement is uneven or there are some obstacles encountered in the case, vehicle is extremely vulnerable to "Tripping".After puncture, for driving error in operational problems combined with flat-tire vehicle running simulation, we develop a safety evaluated criteria for flat-tire vehicle driving. The tire slip angle is the evaluated criteria of rollover.Vehicle's sideslip angle and yaw rate are as the evaluation criteria of running with stable state. The problem that whether the vehicle yaw badly or not could be judged by the position error between the vehicle and the road centerline. Based on the evaluated criteria of safe driving, a safe driving strategy comes out.The braking action may cause the vehicle fatal dangerous, so the appropriate turning action is crucial to safe driving. But flat tire causes turning resistance force increases, so that it is hard to make the reasonable operation of the steering wheel for the driver. Based on a simple model of vehicle dynamics which is said as the "bicycle" model of Vehicle, a flat tire vehicle dynamics model is established. It is in order to plan the vehicle's steering wheel angle reasonably. The Trajectory planning chooses the differential flatness method. By choosing reasonable flatness output,we can describe the vehicle state, run-time input, constraints and the necessary performance targets that the running vehicle must meet. By this way,the flat tire vehicle gets an ideal value of steering wheel angle.Finally, based on the differential flatness, we use MPC method to control the flat tire vehicle.The system state and input can be described by the flat output and its finite derivative,therefore, when the computer solves the system input, optimization process can greatly reduce the dimensions of space and increase solution speed under meeting the state constraints. When MPC is used for getting Optimal trajectory, the problem that steering wheel is not allowed to turn severely could be solved. For such restrictions of the executive body, predictive control can be a good idea. And this "walking to see" controller could deal with the real-time emergency of vehicle.For vehicles traveling on the highway, flat tire is an extremely dangerous condition. By the reason of that flat tire vehicle may yaw, drift or even rollover, the test in real vehicle is risky. In order to reflect the real driving environment on highway,in this paper, the vehicle dynamics simulation software,veDYNA, is used as the controlled object. Vehicle model in veDYNA has high degree of freedom,and parameters of model come from the engineering practice. It also offers specialized modules for the design of roads, so it has a high credibility.In the paper,there is some detailed analysis about the changing of tire performance impacting on the vehicle dynamics. The data used in vehicle simulation are based on the actual test of flat tire. It means that the safety evaluation criteria is high reliable and simulation results show that the proposed strategy meets the realistic driving. For flat tire vehicle,we use the differential flatness approach to plan the ideal value of vehicle steering wheel angle. Then, based on moving optimization method,the planed steering wheel angle is used to control the vehicle in real-time.The experimental results show that the method is very effective to control the vehicle with flat tire.However, the paper discussed the trajectory control for flat-tire vehicle just in the initial stage. The vehicle model which is chosen as precise veDYNA model,is much more different from the actual vehicle model. Especially,for different vehicles, different vehicle parameters need different effects. In the Next,we will embed real vehicle's parameters into the veDYNA model to improve the authenticity of the simulation. In the establishment of flat-tire Vehicle model, in order to simplify the model, changes of tire load is not considered. Besides that, steering wheel angle which is planned to control the vehicle may not be useful for no steering system modeling.