Test And Study On Pass-by Noise Source Of Diesel Engine Vehicle

Nowadays,people pay more attention to noise, which is a kind of important environment pollution source. We make efforts to decrease the level of noise pollution. As an automobile manufacturer, we should control the pass-by noise to reach the national noise standard. Some research indicate that engine noise take about 60%～65% part of the whole noise. The efficient method of lowing down the pass-by noise is to control the engine noise, so it has great significance to do some research on the field.The reason for the pass-by noise is complicated and difficult to analyze. How to accurately find the main noise source is the problem of noise and vibration research field. Besides, it is crucial to put forward the economic and efficient measures aiming at each main noise source.Simply speaking, the pass-by noise includes various kinds of noise. We can divide the pass-by noise into two kinds-one is the noise source of the truck itself, which comprises the exhaust noise, inhaust noise and engine noise; the other is the friction noise, which contains road friction noise and aerodynamic noise.The testing truck's maximum noise appears on the third gear and at the speed of 17.4m/h. In this condition, the friction noise becomes less because of the low speed. Instead, when we do pass-by full-load truck noise experiment, the engine noise is the main reason.The engine noise is the most complicated and vital noise. It radiates from engine surface. Meanwhile, it contains the noise that produced by the process of fuel combustion and relevant mechanical parts. The noise of induction system is also one of the truck's main noise source, which is the noise of admission pipe. Its features is high temperature and speed. Furthermore, the temperature changes with the position of exhaust pipe. It has great significance for pass-by noise no matter the engine noise or the induction and exhaust system noise.We adopt the window method to identify the source of noise in order to make sure the effect of engine noise to pass-by noise. First, select suitable acoustics shielding materials, and then shield the main structure and parts, finally, gain the silent truck meeting noise separation test. Before recognizing the source of noise, the window method firstly measures silent truck's pass-by noise. Then remove the shield of one part which will be used to identify the noise source by order. The later minus the former is the final result.For the sake of obtaining the exact experiment result, we select the advanced pass-by noise data logger and use Matlab to program the data processing procedure which is suitable for our experiment. Finally, we got the conclusion that the muffler induction pipe, the muffler tailpipe, the muffler system and oil pan drain plug are the cause of noise. At the same time ,we find that controlling the noise of exhaust system is the shortcut to solve the problem.Through the contrast and analysis of two groups( silent truck and muffler plus exhaust tailpipe exposure) of experimental data, we find the max peak value frequency of 1/3 octave is 125Hz, which is the type of truck's exhaust system fundamental frequency. Therefore, it will directly lead to the high pass-by accelerating noise if the noise-eliminating effect on exhaust fundamental frequency is not good. In other words, if only we provide the right exhaust and noise-eliminating system, we could reduce the amplitude of exhaust system fundamental frequency in order to reduce the noise of whole truck.We choose four different kinds of impedance muffler to compare according to the team's order. Then, we match inhaust pipe and exhaust tailpipe of the muffler whose diameter is longer. After the analysis of experiment data, we take the third project which can decrease the level of pass-by noise and it meets the national standard.It proves that the window method to identify the engine pass-by noise source is effective and reliable, when we succeed on reducing the exhausting system noise.