Acoustic Performances Analysis And Application Of Porous Polyurethane Composites Foams In Vehicle

Recently,with the continuous improvement of automobile technology and manufacturing process,the automobile industry has developed rapidly in the direction of high speed and light weight.The interior noise has became one of the signatures of passenger vehicles,and automotive manufactures have put tremendous efforts to reduce the overall noise and vibration of vehicles,for it is desirable for vehicle occupants to experience low noise levels.The vehicle acoustic packages,such as sound absorbing materials,are used throughout a vehicle to reduce interior noise level and meet the expectation of customer.Polyurethane foams(PU foams),as one of the sound absorbing materials for vehicle interior acoustics,have been widely applied in vehicle applications because of their advantages in lightweight,thermal insulation,sound absorption,processing and molding,and low cost.Therefore,it is very important to study the sound absorption and noise reduction of the porous polyurethane materials to improve the noise environment inside the vehicle.First of all,four additives of the polyurethane foams were chosen to optimize the acoustic properties of PU foams by using design of experiment(DOE).Sound absorption coefficient and transmission loss were both chosen as target objectives.The best combination and critical factors affecting the acoustic properties was determined by using signal-to-noise ratio analysis(S/N analysis)and analysis of variance(ANOVA).In order to further improve the acoustical properties of PU foams,the plant-polyurethane composites foams were prepared by taking the crop byproducts-bamboo leaves and wheat straws as fillers.The effect of bamboo leaves,bamboo chips and wheat straw on the cell morphology,airflow resistivity,sound absorption,transmission loss and mechanism was analyzed and discussed.The results showed that adding bamboo leaves and wheat straws into PU foams can achieve a noticeable improvement of sound absorption properties,especially in low-frequency region(100-400Hz);they also exhibited the best sound insulation in the whole frequency and achieved the significant improvement of transmission loss which was 7d B.Finally,a full vehicle SEA(Statistical Energy Analysis)model was developed to evaluate the plant-polyurethane composite foams' application effect on the interior noise level.The PU composites foams were used in sound packages of vehicle dash and floor to improve the acoustical properties,the simulation analysis in a full vehicle SEA model was conducted to measure the sound pressure level of driver's head cavity,the analytical results revealed that the PU composites foams has superior performance over the conventional sound materials,and this study will aid in providing guidelines in the interior noise control of vehicle.