Study On Modeling And Simulation Of Steering System For Subjective Evaluation

Dynamic simulation of virtual prototype and concurrent engineering are the core of automotive digital development, which is the most revolutionary technique advance following Ford's assembly line production and Toyota's lean production. The application of virtual prototyping technology to build vehicles digital platform can greatly reduce the costs of product development, shorten the product development cycle and know of product performance in advance, all of which can supply strong technical support for full-vehicle development.Now in digital design of vehicle virtual prototype, the steady performance can be analyzed, but the dynamic process can not be studied. The matching of vehicle depends on subjective evaluation of professional driver according to some criterion. The main reason is the steady performance of vehicle can be described by vehicle model, but the dynamic process can be not, so the full digital design can not be realized in vehicle product development.Most of the existing vehicle dynamics models mainly describe the inherent open-loop characteristics of the vehicle. And the steady state performance of both objective evaluation and the test vehicle can achieve very high consistency, which can be used as objective evaluation for the main performance of vehicles. But there is no generally accepted unified objective evaluation system to evaluate the handling and stability of the vehicle at present. The final evaluation criteria of the vehicle are still decided by subjective evaluation. The current objective criteria are mostly for steady-state performance, while some phenomenon that irrelevant with steady-state performance may occur, especially during the vehicle dynamic driving process. With the rising vehicle speed, the vehicle's frequency response band broadens and the assembly interactions intensifies and more and more dynamic phenomenon occurs during low-speed driving conditions. Current objective indicators can effectively describe the main performance in the vehicle steady-state driving conditions, but can't describe the undesirable phenomena during dynamic process, and the anomalies can only be evaluated by subjective indicators in the real vehicle development.Therefore, in order to improve the application use of vehicle dynamics model, the vehicle dynamics model must be improved so that it can not only accurately predict steady-state performance of vehicles, but also analyze the dynamic process of vehicles, which can make it useful for promoting automotive technique and competitiveness of enterprises, which in turn can also contribute significantly to the promotion of vehicle virtual prototype technology and further development.This dissertation is mainly focus on research of steering system for dynamic process of vehicle model. There is shortcoming existed in dynamic process of vehicle stability: a poor anti-interference ability for straight line driving is showed in vehicle deviation by small disturbances; the difference of returnability between vehicle model and actual vehicle is showed in deviation from the driving course, the coordination of stability is inaccurate; the information of road feel in vehicle on-center performance is insufficiency. Focus on the above issue, the key points and difficulties of research are the modeling of key factors which influence the vehicle stability: the integrative steering system; the static and slip friction model; the wheel model considering elastic belt; the differential model based-on structure. Based on validation of coherence in steady performance of the vehicle model, the dynamics simulation of typical stability conditions which included vehicle on-center and linear retention are studied. Making a comprehensive view, there are several parts in the dissertation.First of all, based on the study of the development of vehicle model at home and abroad and the engineering requirement of vehicle enterprises for virtual prototype technology, the reason of vehicle digital design can not be full realized is analyzed. Limited to time, the key factors of steering system influent on dynamic process of vehicle stability are studied and the intention and technology exploration route of this dissertation are defined.In addition, the key factors on dynamic simulation of vehicle stability are studied as follows: (1) the integrative steering system is set up which can described the relation between left and right wheel and estimate the state of motion accurately. The elaborate steering system can provide foundation for research on the influence on vehicle stability by other steering system characteristics. (2) Stick-slip friction model is embedded into steering system which can simulate the vehicle anti-disturbance ability. (3) The wheel model considering the flexibility of tire carcass is established. The model constructed a dynamics system which constituted by the carcass and tire contact patch. The slip rate of tire is calculated accurately and the relation between brake and rolling resistance is kept by carcass flexibility. Considering the flexibility characteristic of tire carcass, it describe the filtering effect for the tire and using the stick-slip friction algorithm to calculate the static and dynamic friction force between tire and ground. (4) The differential model based on structure is set up which can reflect the real condition of the different rotation between left and right wheel. The model can provide the help for matching powertrain and other subsystems.Secondly, the vehicle dynamics model is established and the consistency of steady-state performance of the model and physical prototypes is verified by contrast with the experimental data. Even the model maintains a good consistency in steady-state performance with the physical prototypes, the lack of the key factors can cause inaccurateness in the vehicles stability dynamic simulation.Thirdly, the key factors are embedded into the vehicle model for dynamic simulation of the vehicle's line keeping performance. By exerting each kind of small disturbance in the actual vehicles travel process, the anti-interference ability of vehicles is verified. Due to the key factors embedded in model, the small disturbance input of the steering wheel and the road, the structural asymmetry by machining and assembly tolerances, and the different wheels rotation speed and so on would not give rise to the negative response to vehicles. The influences of the various characteristics of the steering system in vehicle returnability are analyzed, thus the reference suggestion for steering system's reasonable design and the match are provided.Finally, the simulation of the vehicles on-center performance is carried on. Based on summarizing the achievement of domestic and foreign about the vehicles on-center performance, the new testing methods are supplemented which can reflect the vehicles on-center performance comprehensively. With the static friction and flexibility of tire carcass embedded in the steering system, the"road feel"and steering sensitivity of the steering wheel middle position are analyzed and the relations between the flexibility of the tire and the dead zone of the on-center are studied.In summary, with the help of existing theoretical methods and simulation conditions, and the foundation of investigates and studies in the domestic and foreign research results, vehicle dynamic model is established comprehensively according to the technology route of the paper. The model can describe the typical stability dynamic simulation process for line keeping and the on-center and so on. The fidelity of the vehicle dynamics model is improved greatly.