Research Of The Identification Method For Vehicle Longitudinal Dynamics Characteristic

With the promotion of vehicle performance requirements for steering safety and comfort, many countries have a deep research on vehicle intelligent driver assist system. Adaptive Cruise Control system (ACC) is an important part of advanced vehicle control safety system development in the research of Intelligent Transportation System (ITS). Due to ACC has a huge potential for promoting vehicle passenger comfort and active safety, the researchers pay more and more attentions to studying it.The control system of vehicle longitudinal dynamics as the main control system of ACC, is to mainly control the longitudinal velocity of vehicle, namely it automatically control the vehicle's velocity and the distance between host car and preceding car or obstacles.The control system of vehicle longitudinal dynamics system as the main control system of ACC control system, include nonlinear components such as engine, powertrain, braking system and tire etc. The complexity of nonlinear model of vehicle longitudinal dynamics almost can't directly design a control law based on only a model. For the nonlinear control system is very complex, there are all limitations for some classical methods which is used to solve nonlinear control system, and these methods can't be the universal method of analyzing and designing nonlinear control system.During the process of vehicle steering, in order to control the behavior of systembetter, we can build the nonlinear mathematical model of vehicle longitudinal dynamics to obtain the important characteristic of system, then control and analyze the model. But this method will inevitably bring some uncertain factors. These uncertain factors are mainly caused by the shortage of system dynamics knowledge, system dynamics characteristic inherent and unknown parameters or error when simplifying the model.Therefore, the vehicle longitudinal dynamics characteristic takes on severe non-stationary (off-equilibrium) and nonlinearities. According to the nonlinear control system of vehicle longitudinal dynamics, linearization will be carried out at equilibrium operating point, the increment linear model will be built up, and the parameters of vehicle longitudinal dynamics characteristic will be calibrated and used in ACC control system.According to the whole theory and simulation of the paper, we have several conclusions as below:Firstly, introduce the base principle and composing of driver optimal preview acceleration model, and then present the hypothesis of steady preview and dynamics correction for driver model. Due to this model takes into full consideration of driving safety, legality and handiness as well as driver's self delay feature and strong nonlinearity of vehicle dynamics system, the increment linear model at equilibrium state will be built according to the small scope linearization theory. Secondly, In order to get the equilibrium state of 29-degree of freedom vehicle model, two PID controllers will be designed to control the longitudinal velocity and lateral acceleration. Lastly, 29-degree of freedom vehicle model will be controlled at different shifts and different equilibrium states through compilation the C plus programming.Firstly, the off-line identification algorithm based on the least square will be presented according to the increment linear model. Secondly, simulate in the 29-degree of freedom vehicle model through compilation the C plus programming and get the table of parameters for increment linear model. Lastly, the method of system identification for increment linear model will be verified in real car, then analysis and process the test results through compilation the Matlab Programming and verify the method's feasibilityof system identification in real car.After the system parameters of increment linear model for vehicle longitudinal dynamics being identified, the parameters will be applied to ACC control system as adjustment parameters. Firstly, the working principle of ACC and the control principle of ACC which is based on the optimal preview longitudinal acceleration model are introduced, the control adjustment algorithm of ACC based on the optimal preview longitudinal acceleration model is built. Secondly, several classical operating conditions of ACC will be simulated, and realized the preceding car followed.The creative work of this paper is to build the increment linear model of vehicle longitudinal dynamics model and the identification algorithm based on least square, the system's parameters are identified and used to ACC control adjustment, Meanwhile, the method of increment linearization model for solving the nonlinearities of vehicle longitudinal dynamics is verified through field test, and it will provide the method of solving the nonlinearities of vehicle longitudinal dynamics for succedent ACC research.