Research On Vehicle Handling Stability Margin Based On Lyapunov Exponent And Dissipated Energy

The vehicle handling stability has always been a research hotspot in the field of vehicle dynamics,and it is a major performance that determines the safe driving of high-speed vehicles.It is known as the "lifeline of high-speed vehicles".When the vehicle is driving under extreme conditions such as snow and ice,off-road surface,and strong lateral wind disturbances,the driving skills of the driver and the performance of the vehicle are extremely severe tests.A small operation error or external interference can easily cause traffic accidents.Therefore,if the vehicle handling stability margin can be given from the theoretical research level of vehicle dynamics,and a quantitative description of the vehicle handling stability will be achieved,it will provide important theoretical basis for the structural design and stability controller design of the vehicle.For the theoretical research of vehicle handling stability,nonlinear analysis methods are the current mainstream technical means,and the relatively mature research results have been widely recognized and applied to engineering practice.However,classical analysis methods such as Lyapunov function method and phase plane method have all obtained qualitative conclusions,and there is still no clear quantitative analysis method.In response to this problem,on the basis of a large amount of literature reading work,based on the two theories of Lyapunov exponent and dissipated energy,this paper takes the stability region of the vehicle system as the research object,and explores the quantitative calculation method of the vehicle handling stability margin,the main research work is as follows:(1)In the ISO coordinate system,a 5-DOF nonlinear vehicle model with driving torque is established,analyzed the global phase space energy characteristics of the vehicle system,and proposed a method for distinguishing the stable state from the unstable state by using the energy change in the vehicle steering process,which effectively solved the stability region of the vehicle system.(2)The method of Lyapunov exponent is used to analyze the effect of different driving conditions on vehicle handling stability.According to the solution results of the largest Lyapunov exponent and the sum of Lyapunov exponents,reveals that there are differences in the handling stability of different states in the stability region.And based on the largest Lyapunov exponent,two calculation methods of vehicle handling stability margin were constructed,which achieved quantitative calculation.(3)The energy dissipation process of the vehicle system is researched.According to the solution results of the dissipated energy,the regular ensemble theory in statistical physics is used for reference.By analogy of physical phenomena,established a stable probability density expression method based on dissipated energy,and the calculation method of vehicle handling stability margin is defined from the perspective of probability,and analyzed the changes of vehicle system handling stability margin under different driving conditions.(4)The solution results of the two methods are comprehensively analyzed,the theoretical calculation method based on dissipated energy is selected as the research focus of the follow-up work of this paper,and a random test scheme is designed to verify the correctness of the theoretical calculation results of the handling stability margin.