Effective Verification Of 5-DOF Model For Vehicle Stability And The Stable Headway Prediction Of Vehicles In Fleet

When driving on the high-speed and steering condition,the driver's continued acceleration,release the acceleration pedal or depress the brake pedal all of a sudden,may cause serious slippage,yaw and other unstable movements of the vehicle system,resulting in serious traffic accidents.In order to reduce the traffic accident rate,and realize the stability control of the vehicle system under the limit conditions mentioned above.Related research such as the vehicle system stability analysis and control based on the nonlinear vehicle and tire model have made some great achievements recently.Among the research,the representative five-degree-of-freedom stability analysis model can analyze the influence of driving and steering on the handling stability,and has good theoretical explanation and engineering application prospect.However,because of the high risk of stability tests,the validity of the five degrees of freedom model is just achieved by the simulation experiment method,and lacks the physical experiment to verify.Solving the validity verification problem of the five-degree-of-freedom stability model becomes the main bottleneck of the stability theory to the engineering practice.Therefore,the validity verification of the five-degree-of-freedom stability model is the main work in this paper,and then introduces vehicle five-degree-of-freedom stability model into the fleet system to predict the stable headway of vehicles in the fleet,promoting the five degrees of freedom stability model into engineering applications.The main research contents as follows:(1)The stability of the high-speed and steering vehicle system is analyzed respectively under the driving condition and braking condition.In the driving condition,the 5DOF(five-degree-of-freedom)nonlinear vehicle model is introduced.The influence of the change of the driving torque on the stability of the high-speed and steering vehicle system is studied.In the engine braking condition,the analytic expression of the engine braking torque is introduced firstly,and then the 5DOF vehicle model is established for the engine braking condition.After the accuracy verification of the 5DOF vehicle model under the engine braking condition,the stability of the high-speed and steering vehicle under the engine braking condition is also analyzed.Finally,the instability of the high-speed and steering vehicle system both on the driving condition and engine braking condition is proved to be the chaotic motion with the numerical methods of the Poincare section and power spectral density.As well,the instability mechanism is revealed.(2)According to the situation that the vehicle movement characteristics in the simulation of the 5DOF vehicle model in the engine braking condition are inconsistent with the actual vehicle movement states,the rolling resistance is introduced.Therefore,the influence of rolling resistance on the dynamic characteristics of the high-speed and steering vehicle is studied,and results show that the 5DOF vehicle model including the rolling resistance is proved rational.Then the vehicle system model with rolling resistance is used to analyze the dynamic characteristics of vehicle system at different front wheel angle input.(3)The vehicle system model effectiveness and its dynamic characteristics are verified by using a model car which is driven by the motor and the ratio is 1: 5.First of all,in order to carry out the experimental verification work on the model car,the basic parameters of the model car are needed to be measured by experimental method,so as to carry out the simulation analysis and experimental verification using the parameters of the model car.Secondly,based on the basic parameters of the model car,the sliding test is designed to verify the effectiveness of the 5DOF vehicle model including rolling resistance.Finally,based on the tire characteristics analysis of the model car on different adhesion coefficient pavements,the icy road is selected to carry out the experimental verification of the model car on the driving condition.Because of the limitation of the experimental conditions,the simulation experiment of the model car under the electromotor braking condition is carried out on the dry asphalt pavement,and the actual experiment of the model car is carried out under the electromotor braking condition in the artificial lawn experimental site.(4)The stable headway of vehicles in fleet under the driving condition and the engine braking condition are predicted respectively based on the 5DOF vehicle model.Firstly,a following controller is proposed for the steering following fleet which is composed of a longitudinal controller based on the constant time-gap policy and a lateral controller based on the PO(Position-Orientation)driver model.Secondly,on the basis of the stability analysis and control effect verification of the longitudinal controller and the lateral controller of the following controller,the sinusoidal path following experiment is carried out to verify the control effect of the following controller under complex path and limit conditions.Finally,the two vehicles following on the sinusoidal path is extended to the situation of multiple vehicles following to be analyzed.The following characteristics and stability of the fleet with different initial speeds are simulated and studied.The stable headway required for vehicles in the fleet is predicted by the method of simulation experiment under the driving condition and engine braking condition,respectivly.