Study On Road, Human And Objective Evaluation Of Automotive Ride Comfort

For the vehicle ride analysis in China, the objective evaluation result can not reflect the actual characteristics of the vehicle well. Aim to improve the vehicle ride simulation and evaluation, the following four aspects are studied. They are road irregularity modeling, Chinese human biodynamic model, frequency weighting filter design and development of the vertical weighting factor for Chinese.Road irregularity is the main excitation of a vehicle and it directly effects the objective evaluation result of a vehicle. Road roughness modeling need deep study of the characteristics of the highway. In order to clarify the spatial statistics calculation of road roughness and find out the relations among several important power spectral densities(PSD), Parseval’s theorem and Wiener-Khintchine theorem are employed in this study. Based on these theorems, this paper obtained the calculation formulas of spatial autocorrelation and PSD functions, and gave a detailed derivation of the conversion relationships among spatial displacement, velocity and acceleration PSD. The paper also found out different relationships between spatial frequency PSD and angular frequency PSD according to different patterns of Fourier transform. Besides, due to lack of strictly theoretical analysis of PSD discretization for road irregularity modeling, the paper thoroughly analyzed it on the basis of the frequency domain convolution theorem and the principles of six kinds of Fourier transform. Also, it pointed out the irrational PSD verifying method in the literatures. In addition, it proved that Welch’s spectrum estimation method produces different kinds of road PSD depending on different parameter – the spatial or temporal sampling frequency. Results show that the analysis and derivation are right and they can be applied to road irregularity modeling and vehicle ride comfort analysis.Human body is a complex vibration system and it should be taken into account for the ride comfort analysis. National and international standards recommend the use of the lumped models and it is necessary to study the characteristics described by them. Three widely used biodynamic response functions(driving-point mechanical impedance, apparent mass and seat-to-head transmissibility) of the seated human models are analyzed in an attempt to obtain some general regularity about the primary resonant frequency and magnitude. The differentiation and vibration theory are employed. These analyses shows that the primary resonant frequency of the seated human body derived from the vertical driving-point mechanical impedance dooms to be higher than those derived from the apparent mass and the seat-to-head transmissibility function. Parallel multi-degrees-of-freedom models can be simplified as one single-degree-of-freedom model with a rigid support for the study of the primary resonant frequency, and these resonant frequencies derived from the seat-to-head transmissibility must be higher than those from the apparent mass, although they are very close. The magnitude of the seat-to-head transmissibility of parallel multi-degrees-of-freedom models is larger than that of the normalized apparent mass for frequencies less than about 2 times the first modal frequency. These regularities about the primary resonant frequency and magnitude are still applicable for in series models, while there is a little distinction. The two-degrees-of-freedom parrellel model for Chinese is used to study the effect of human body on automotive ride comfort evaluation.Few study gives guidance to design weighting filters according to the frequency weighting factors, and the additional evaluation method of automotive ride comfort is not made good use of in some countries. Based on the regularities of the weighting factors, a method is proposed and the vertical and horizontal weighting filters are developed. The whole frequency range is divided several times into two parts with respective regularity. For each division, a parallel filter constituted by a low- and a high-pass filter with the same cutoff frequency and the quality factor is utilized to achieve section factors. The cascading of these parallel filters obtains entire factors. These filters own a high order. But, low order filters are preferred in some applications. The bilinear transformation method and the least P-norm optimal infinite impulse response(IIR) filter design method are employed to develop low order filters to approximate the weightings in the standard. In addition, with the window method, the linear phase finite impulse response(FIR) filter is designed to keep the signal from distorting and to obtain the staircase weighting. For the same case, the traditional method produces 0.330 7 m·s–2 weighted root mean square(r.m.s.) acceleration and the filtering method gives 0.311 9 m·s–2 r.m.s. The fourth order filter for approximation of vertical weighting obtains 0.313 9 m·s–2 r.m.s. Crest factors of the acceleration signal weighted by the weighting filter and the fourth order filter are 3.002 7 and 3.011 1, respectively. This paper proposes several methods to design frequency weighting filters for automotive ride comfort evaluation, and these developed weighting filters are effective.Weightings in GB/T4970-2009 are from ISO 2631-1:1997. They are developed based on the Western and they may not suitable for Chinese because the ethnic differences. An experiment is conducted for the purpose of developing vertical weighting factors for Chinese young male. Fifteen Chinese young male subjects were involved in the experiment which lasted almost two months. Each subject had been tested for many times at different time of different date. According to the Stevens’ power law, the equivalent comfort contours are devised. Based on these comfort contours, the vertical weighting factors between 2 Hz and 16 Hz for Chinese young male are developed.