Decomposing Theory And Experimental Study Of Noise Source For Accelerating Vehicle

China government constituted and enacted The Law of Prevention of Circumference Noise Pollution in 1996, which prescribed prohibiting the manufacture, sale or import the vehicle of the noise exceeding the limits. Later, National Standard GB1495-2002 Limits and Measurement Methods for the Exterior Noise Emitted by Accelerating Vehicles were published in 2002 to further control and standardize the measurements of the exterior noise of accelerating vehicles.The purpose of the thesis is to offer an effective method of the noise emitted by accelerating vehicles speculation and noise source decomposition, which can simulate and predict the exterior noise of accelerating vehicles according to the general layout construction of products, the characteristic of noise of the assembly components matching products and matching relations of power system when the product is still in the early stage of development. It also can confirm the noise limits of the assembly bench according to the developmental targets of vehicles noise (noise limits). Thus, the method can effectively realize active control of automotive product, shorten the cycles and reduce the cost of product development.Firstly, in the part of characteristic introduction on the main noise source of vehicles, we summarize the production mechanism of vehicle assembly individual noise. In addition, the characteristic of radiation, the feature of frequency and the influence factors of noise level of vehicle assembly individual noise are introduced and analyzed. According to the characteristic of individual noise, the information on assembly individual bench noise test techniques is given. For example, the description of simplified surface of assembly test, the coordinate system of sensor monitoring points, the depiction of the condition of assembly test (running speed and load), the description of spatial location of anechoic rooms,bench test and assembly components and the description of noise measurement.With the help of China FAW Group technical center, the individual bench noise tests of vehicle assembly are accomplished and much valuable information is achieved. Main experimental projects are described as follows:1. The engine noise test on the condition of o2 engine with stable running speed (external characteristic).2. The engine noise test on condition of o2 engine accelerated.3. The engine noise test on the condition of o3 engine with stable running speed (external characteristic).4. The engine noise test on condition of o3 engine accelerated.5. The power assembly noise test on the condition of o2 engine with stable running speed (external characteristic).6. The power assembly noise test on the condition of o2 engine accelerated.7. The exhaust noise test on condition of engine with stable running speed (external characteristic).8. The exhaust noise test on condition of engine accelerated.9. The exhaust noise test of blank pipe on condition of engine with stable running speed (external characteristic).10. The exhaust noise test of blank pipe on condition of engine accelerated.11. The noise emitted by muffler test on condition of engine with stable running speed (external characteristic).12. The noise emitted by muffler test on condition of engine accelerated.13. The induction noise test on condition of engine with stable running speed (external characteristic).14. The induction noise test on condition of engine accelerated.15. The rear axle noise test on condition of engine with stable running speed (external characteristic).16. The rear axle noise test on condition of engine accelerated. 17. The fan noise test on condition of engine with stable running speed (external characteristic).18. The fan noise test on condition of engine accelerated.19. The tread noise test on condition of engine with stable running speed (external characteristic).20. The tread noise test on condition of engine accelerated.On the above tests, sensor quantities and location of monitoring points vary with the radiation characteristics of vehicle assembly individual. There are five monitoring points in the bench noise test of o2 engine, three monitoring points in that of rear axle, fan and tire, one monitoring point in that of muffler bench, three monitoring points in that of power assembly bench and nine monitoring points in that of engine bench due to connect to the gearbox during the testing.On the noise testing of vehicle assembly individual, the Sound Pressure Level (SPL) of vehicle assembly individual under specified conditions (running speed and load) is measured. In this thesis, the Microphone model of vehicle assembly individual is established, which is a model of processing and analyzing data achieved by sensors. The SPL of the bench noise test can be speculated under random conditions using the model. To the above purpose, the theory of regression analysis, in which we can establish the fundamental relation among the variables from a sample data, verify the credibility of the relation, verdict whose variables have a marked influence are applied. Then the SPL of vehicle assembly individual can be predicted and controlled using the achieving relation.To further analyze the noise source information of vehicle assembly individual equivalent sound source model are established in the thesis. According to different geometry of the assembly noise source, equivalent point source and equivalent line source are established, respectively. The model is obtained by least square method on the base of the Microphone model, the aim of which is to predict the SPL of vehicle assembly individual under random conditions and spatial location.With B&K SPC (Source, Path and Contribution) theory, we achieve the algorithm of transfer function and contribution, and establish a model of the noise emitted by accelerating vehicles. The passby noise SPL of vehicle and the vehicle assembly individual contributions to the exterior noise are predicted using this model. To verify the validity of the model, three comparison experiments are done, which are the comparison between predicted value and measured value. The relative deviation of the three experiments is less than 2 dB, which is in accord with the engineering request. The work has received recognition of China FAW Group technical center.Finally, based on the spatial transformation within sound field and the analysis of the vehicle assembly individual contributions to the exterior noise, the acceptable value of the bench noise testing of assembly individual is further predicted using the noise characteristic of assembly under given conditions and the active control of vehicle noise is realized at last. These results possess fundamental significance on vehicle assembly bench noise test.