| The quality of NVH(Noise Vibration and Harshness)is the most direct embodiment of vehicle performance,and is increasingly valued by customers and manufacturers.In the start of the manual transmission,the vehicle often produces an obvious amplitude and discomforting vibration,which is mainly expressed as the judder in the longitudinal direction of the body,which is called the start judder.The problem of starting judder not only affects the riding comfort,but also accelerates the aging and fatigue damage of related components,and shortens the service life of components.Meanwhile,starting judder increases the possibility of inexperienced driver misoperation,and affects the safety of vehicle driving.Therefore,controlling the starting judder is one of the important problems in the NVH performance optimization.This project is based on the actual project.From the theoretical and experimental point of view,the simulation analysis and evaluation of starting judder were studied,and the main research contents are as follows:(1)The classic model of belt friction and the equivalent model of transmission system were established and the mechanism of starting judder was analyzed,including the condition of starting jitter,the source of excitation and the path of transmission,etc.The results showed that the self excited vibration caused by the negative gradient of the friction coefficient of the clutch,the forced vibration induced by the periodic fluctuation of the clutch friction and the too close to the induced resonance of the modal frequency of the transmission system are the three main reasons for the start judder.(2)Based on the test conditions of China Automotive Technology Research Center,completed the judder test and subjective evaluation.The 5 rear drive MPV and 5 front drive SUV models were selected respectively,and 9 models and 10 vehicles were tested for starting judder.Meanwhile,a number of engineers who have long been engaged in the performance optimization of the vehicle NVH were selected,and the “5 grade scale” grade scoring method was used to evaluate the starting judder of the test vehicles.(3)After elaborating the characteristics of the key components,such as the friction characteristics of the clutch,the two stage torsion nonlinear characteristics and the transmission mode,a set of equivalent vehicle dynamic model including the power assembly system,the suspension system and the body was set up.In the modeling process,the equivalent transformation principle of the model and the parameters needed to establish the equivalent vehicle dynamics model were discussed in detail.Finally,comparing the actual vehicle test data with the model simulation analysis data,the rationality and accuracy of the equivalent vehicle dynamic model established by this project was verified.(4)The evaluation index of starting judder for engineering practice was put forward,and the evaluation criteria of starting judder was established.On the basis of full consideration of the three direction response of the start judder,a universal evaluation index,which can measure the starting judder and reflect the mutual mapping relationship with the subjective evaluation,was proposed in view of the different subjective feelings produced by the judder.The correlation analysis between the objective evaluation index and the subjective evaluation result was carried out by using the Pearson correlation coefficient.First,the first round correlation analysis were made for the response index of the body XYZ direction and the subjective evaluation,and the correlation coefficient was determined as the weight coefficient in the corresponding direction.Then the XYZ direction of the body was proposed to synthesize a weighted finger to the response index.Second rounds of correlation analysis were carried out with the subjective evaluation results,and the feasibility of the indexes was analyzed from the results of the two rounds of correlation analysis.The results showed that the objective evaluation index of starting judder proposed by this project was highly correlated with the subjective evaluation results,which proved the feasibility of the index.Finally,the objective evaluation index of starting judder was proposed to synthesize a comprehensive evaluation index,and the correlation analysis was carried out again.The results showed that the comprehensive evaluation index of starting judder was also highly correlated with the subjective evaluation results.(5)A software package for starting judder was developed,and the vehicle design parameters that affect starting judder were analyzed.According to the actual demand of the project,the software package for starting judder automatic calculation was developed with MATLAB software,including the modal calculation software of the transmission system,the automatic test data calculation software and the starting judder analysis software.Meanwhile,the influence of vehicle design parameters on starting judder was analyzed,which provides a reference for the design of key components such as clutch and transmission system.The innovation points of the subject:(1)The objective evaluation index of starting judder was put forward.On the basis of full consideration of the XYZ three direction response of the body,this paper put forward three subjective evaluation indexes,which can measure the starting judder degree,and can reflect the mutual mapping relationship with the subjective evaluation,and can be used to evaluate directly.On this basis,a comprehensive evaluation index for starting judder was put forward,and the evaluation system of starting judder was further improved.(2)An automatic calculation software for starting judder with friendly human-machine interaction interface had been developed.The software can analyze the contribution degree of the vehicle design parameters to the starting judder,that is,to reflect the impact of the key parameters on the starting judder.It can predict the starting judder in the early stage of vehicle development and point out the direction of vehicle development ahead of time. |
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