| “On-center” refers to a vehicle’s particular driving condition under which the lateralacceleration of a vehicle is less than0.1g–0.3g with small steering input. On-centerhandling has extraordinarily important influence to a vehicle’s security under high speedmobility. With the continuous improvement of road conditions and increase of vehicle’sspeed, on-center handling has drawn more attentions of consumers and car manufactures.Currently, the world’s major automobile manufacturers have different test methods andevaluation metrics to characterize on-center handling. ISO also has evaluation system ofon-center handling, but the number of metrics is so large that the focus is not clear enough.Since China has not formulated relevant national standards of on-center handling, Althougha small number of domestic automobile plants have been involved in the evaluation ofon-center handling, but limited to no mature evaluation system, its evaluation results stillcannot guide the vehicle development efficiently. Therefore, to establish a comprehensive,irredundant, and focused objective evaluation system for on-center handling is of greatsignificance to enhance the chassis development capability of China’s auto industry.This paper investigates lots of related evaluation methods of on-center handling, andcarried out the following studies focused on the weave test, which is most widely used for oncenter handling evaluation:1. The formulation of the evaluation index system Based on widely used weave test, objective metrics from on-center handling evaluationsystems of ISO, GM, MIRA, TRC, and Hyundai were summarized in this section, anddynamics analysis were carried out for each metrics. According to the differences of theperformance each metric reflected, all metrics were divided into four categories. All theindicators summarized were regarded as the basis of the evaluation index system, that canensure the comprehensiveness of the evaluation index system.Then, the preliminary analysis of the evaluation index system was carried out, and theapparently repeated indices were removed. On-center handling test was conducted for eightmodels based on the indices from preliminary selection. Through correlation analysis of thetest results, highly correlated metrics were picked. The indices with high level correlationreflect similar performances of vehicles, and are largely substitutable to each other. Based onthis, indices reflecting similar performances were removed. After the screening, there willbe no redundant metrics in the evaluation system.In vehicle’s development process, since the subjective evaluation is the final evaluationtools, it must be combined with subjective evaluation to analyze the importance of objectivemetrics. The subjective evaluation systems of Audi Corporation, Lotus Corporation, and Jilinuniversity have been studied in this thesis, and subjective metrics referring to on-centerhandling have been analyzed. The representative Lotus’s subjective evaluation system wasadopted for the eight models’ subjective evaluation tests. Combined with the consulting withsubjective evaluation engineers and the analysis of subjective evaluation results, the degreeof importance of the objective metric was determined. Finally, a comprehensive, irredundant,and focused on-center handling objective evaluation index system was built.2. Weave test data processingA data processing procedure was written with Matlab/M-File module for weavetest(ISO13674-1), including test data preprocessing and postprocessing.3Hz low-pass filterwith no phase delay and zero drift removing were achieved in pretreatment process; thecalculation method for each evaluation index was described in detail in the process of post-processing. This can be a reliable basis for follow-up vehicle development, and furtherimproved on-center handling objective evaluation system.3. Analysis of the objective indices from high-speed returnability testHigh-speed returnability test reflects on-center returnability, and has a high requirementof testing ground. Currently, the domestic testing ground cannot fully meet the testrequirement, there is a huge difficulty in the implementation process. High-speedreturnability test and weave test were carried out for eight models using the vehicledynamics simulation software-Carsim. Correlation analysis between the two tests found ahigh correlation of residual lateral motion. Finally, this paper compared the vibrationcharacteristic of the yaw rate between the step input test and high-speed returnability test,and high correlation of vibration frequency and damping of yaw rate was found. Theanalysis of this section laid a theoretical foundation for replacing high-speed returnabilitytest with other tests. |
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