Research On Sound Quality Evaluation And Control Technology Of Electric Vehicles

Due to the increasingly outstanding energy problems, electric vehicle is the current tide of automobile industrial development. Except for the performance indexes of energy conservation, security and less pollution, consumers have higher requirements on the comfort while choosing the vehicle. The automobile interior sound quality has become the important index that reflects the product quality most directly and influences the user's purchasing psychology. Electric vehicle uses electric motors that have no engine noise. Although the sound pressure level of interior sound is not very high, high- frequency electromagnetic noise in quiet interior environment will be harsher and makes people feel annoyed subjectively. That's because without the masking effect of engine, it's hard for customers to get used to the special sound character of electric vehicle when they have already been used to traditional vehicle sound. This not only reduces the vehicle's ride comfort, poor sound quality will also affect the customers' acceptance and the competitiveness the vehicle in the market. In the domestic country, the controlling technology of electric vehicle sound quality is barely blank. In the past, if we want to improve the sound quality of products, we need to spend take a very long cycle to develop a series of related experiences, usually after the release of new products, which not only wastes resources to great extent, but also extends the designing cycle of new products. Therefore, we need to set up a project and have a special topic for the comprehensive development and research, so as to reach the following targets. Firstly, lay the solid foundation to related research on electric vehicle products by domestic automobile manufacturers, such as the improvement of acoustic design and acoustic performance of new products. Secondly, adjust and optimize the sound quality controll ing ability and acoustic design standard of our domestic pure electric vehicle. Thirdly, improve the competitive level of the same product in the domestic and foreign markets.This paper takes Sound Quality Analytic Evaluation and Controlling Technology of FAW Pure Electric Vehicles(Jilin Technology Development Plan Project, Project N umber: 20126007)as the background. The evaluation mechanism of people 's subjective emotions on the sound quality of acoustic signals was researched, depending on the foreign research experiences of subjective evaluation methods of vehicles' sound quality, makes researches on subjective and objective evaluation technologies for C hinese people, build ing objective and quantitative model of intelligent subjective evaluation of elec tric vehicles, finding out the objective evaluation parameters that have great effect on subjective evaluation of electric vehicle sound quality, and study and predict the special electromagnetic vibra tion and noise of electric vehicle. Meanwhile, to analyze and study the acoustic contribution of the noise source and transfer path analysis of electric vehicles, the paper builds a model of interior sound quality electric vehicle, and find out the main noise source and trans fer path that affect interior sound quality. To meet the actual needs of customers, improve the acoustic quality of domestic electric vehicles, keep abreast with similar foreign models of high level and make corresponding improvement measures to improve interior acoustic quality, this paper takes passive control technology of sound quality and improves the interior sound quality of domestic electric vehicles. The following is the main study context of this paper.(1)Subjective and objective evaluation analysis on sound quality of electric vehicles. Firstly, the paper took electric vehicles of domestic brands as the object of study, compared it with foreign electromobile of the same level and made sample records of noise test on electric vehicles of different types. After filtering, 84 sound samples of in uniform conditions were recorded. The paper then made objective psychoacoustics evaluation on every sample. Then, a jury was organized to make subjective evaluation tests on interior sound samples. The evaluation method is international rating scales, which can provide data support to objective quantitative models of subjective evaluations after getting the subjective scores of sound quality through data validation of subjective evaluations. Finally, the paper took the sound sample of domestic electric vehicles in work condition of 50km/h as an example, and made a detailed analysis of sound quality.(2)Objective quantitative models of intelligent subjective evaluation on electric vehicles. Based on BP neural networks, through Genetic Algorithm(GA) and Simulated Annealing(SA) to optimize BP neural networks, the paper built the objective quantitative models of intelligent subjective evaluation on electric vehicles according to SAGA-BP neural network. The coefficient of correlation between prediction value of this model and the subjective evaluation value is 0.99594, which showed that psychoacoustics objective evaluation parameter of sound quality could be reflected in subjective valuation results through the models built. Through the comparison between the evaluation models of BP neural network and multiple linear regressions, SAGA-BP model could make precise predicted rating on interior sound quality. The deviation between actual rating and predicted rating of SAGA-BP neural network model is within 5%. Analysis of network weights showed that the parameters that affect subjective assessment result are sharpness, loudness, A-weighted sound pressure level and roughness in sequence. After the reconstruction of the model, the model rebuilt(input only included sharpness, loudness, A-weighted sound pressure level and roughness) had little predicted error with the previous one. This model is very useful that it can not only realize the valuation of interior sound quality of electric vehicles but also work as the valuation tool designed for electric vehicle acoustics.(3)The build of electromagnetic vibration and noise model of electric motor in electric vehicles. The paper built the simulation model of electromagnetic energy of electric motor and analyzed the characteristics of electromagnetic force of electric motor in electric vehicles in time-step finite element method. Built 3D finite element model o f electric motor in the electromobile and calculated the inherent frequency and modal shape of electric model. Building electromagnetic vibration and noise radiation model of electric motor had used multi-coupling numerical analysis of electromagnetism and structure and acoustics. Through multi-coupling stimulation of electromagnetic vibration and the comparison with actual test results, verifying the rectitude of electro magnetic vibration simulation was true. Through the stimulation of electromagnetic radiant noise, calculated the main frequency and amplitude of noise from electric motor effectively and made the analysis on the acoustic contribution of each plate, which provided the foundation for the prediction and suppression of electromagnetic vibration and noise of driving motor in electric vehicle.(4)The build of equivalent model of interior sound quality in electric vehicles. Equivalent model of interior sound quality in electric vehicles is based on synthesis technology of transfer path anlysis. The noise source of this model was composed of airborne noise source(electric motor and tires) and structural wave-reserved noise source(mounting system and suspension system). Through the build of equivalent model of interior sound quality in electric vehicles, the interior noise in different conditions was simulated. Compared its A-weighted sound level, sharpness, loudness and roughness with actual interior noise, and the error was less than 7%. The evaluations of sound quality of synthetic interior noise and actual noise are basically are basically the same and the error was within 0.1 level. This showed that the equivalent model of interior sound quality in electric vehicles was precise in prediction and the parameters of objective psychological acoustic evaluation were basically the same with the actual numbers. It can reflect the real psychoacoustic physical properties of interior noise, thus shows its rectitude. The analysis of contribution of sound quality of electric vehicles in the speed of 50km/h showed that suspension system had greater contribution to interior sound quality of electric vehicles.(5)Control of interior sound quality of electric vehicles. The study showed that the main source of interior noise of electric vehicle was the structural noise from vehicle body plates. The tires of the vehicle induce the vibration of suspension system, which then produce structural noise in body plates. Through the analysis on the shake of different plates of body made by the vibration of suspension system, the paper found that the ceiling and doors had more contribution to interior sound. Putting damping materials and sound-absorbing materials on doors and the ceiling could improve the characteristic frequency components that have bigger objective parameters. Through the control techniques of sound qualit y above, interior sound quality can be improved greatly.