Study On Real-Time Road Roughness Modeling For Quality Vehicle Dynamics

The traditional vehicle dynamics model has a narrow band, it is mainly oriented to the steady state problems. It is not accurate enough to simulate the high frequency vibration which has a great impact on the vehicle dynamic load calculation and the coupling of power transmission system and chassis system. An important feature of the quality vehicle dynamics model is that it is for the transient dynamics simulation, the band will expand to 100 Hz, which means that the need to join the simulation model of high frequency vibration. Usually, the uneven pavement is the basic input of the vehicle vibration, one of the main sources of the high frequency vibration is the model.The vehicle simulator in our lab is a large test equipment which is based on the humanvehicle—environment(HVE) closed-loop system experimental investigation with the support of advanced technology such as hydraulic, electronic, simulation and control. Vehicle motion simulate technology of high quality is the basic of vehicle simulator. Compared with other software simulation, the greatest significance of the vehicle simulator is adding real driver, the real driver randomness and subjective feelings into the closed-loop system simulation thus to achieve more accurate closed-loop evaluation. However, the road model of the simulator is only in the form of road simulation and does not have the simulation of road roughness. The simulation of high frequency vibration components is missing, so passengers do not feel the high frequency vibration caused by the road roughness.In this paper, based on real-time road roughness modeling for quality vehicle dynamics, the mathematical model of the single wheel road roughness excitation and of four wheel road roughness excitation are founded. After model validation, this model is used to simulate the random road excitation on the vehicle simulator, and then simulates the ride comfort simulation of the car.The structure of the paper is as follows:First of all, with full investigation on the mathematics methods about single wheel road roughness excitation modeling, we know that road roughness excitation model can be divided into four categories: PSD analysis model, time series model, fractal analysis model and wavelet analysis model. The application of PSD analysis model and time series model is more general. This paper, PSD analysis model based on inverse Fourier transform is used. This model has the characters of the briefness, simple operation, little account and more importantly accuracy through comparing these PSD curves and standard PSD curves.In this paper, random road excitation simulation based on inverse Fourier transform is mainly studied and the basic idea of this method is that we can deal with the amplitude spectrum which can be obtained from the known PSD and then phase spectrum can be calculated by the random phase method. The amplitude spectrum and the phase spectrum constitute the frequency spectrum. Random road excitation can be calculated from the frequency spectrum by means of inverse Fourier transform. Following this thought, the mathematical model of the single wheel road roughness excitation is founded in this paper.During driving, the amplitude and phase difference of the left and right wheel road roughness will cause the car’s body rolling angle vibration. Research shows that the left and right wheel road roughness is not irrelevant, the coherence between them is decided by the road grade and vehicle parameters. In order to improve the accuracy of the model, considering the coherence of the input of the left and right sides of the road, this paper founds a mathematical model of the four wheel road roughness excitation in both time domain and spatial domain based on the single wheel drive model. The main points and process of modeling are discussed in detail. Based on the software of MATLAB, the model is proved to be correct through comparing with standard PSD curves and can be used for simulation.Finally, convert the model into C code and put it into the road model of the vehicle simulator to simulate four channel vibration input. After model validation, the paper simulates the ride comfort of the car at high speed. The result of the simulation suggests that the random road excitation method based on the inverse Fourier transform which is applied to the vehicle simulator model is correct and feasible.