| Due to the requirements of environmental protection, coach noise emission is limited more stringent in the domestic and abroad.However,a majority of the coach noise can't satisfy with the limits of GB 1495-2002 national standard, how to reduce the pass-by noise of coaches will be very important for all coach manufactories. In this report, KLQ6795Q and KLQ6129 coaches were taken as the research models, which interior and exterior noise were studied deeply from the noise investigation, noise source identification, noise control strategy and noise control measures by systematical test and analysis.The noise investigation was first step of the coach noise reduction. The noise level, sound field distribution, frequency spectrum and sound transmission paths were separately got by road test and stationary test, as a result, we knew current situation of the coach noise.Acceleration pass-by noise of the coach is non-stationary signal so that a noise source identification technique based on the time-frequency distribution is better method. Using it, the noise source signal features were extracted from the time-frequency domain, and that we developed several kinds of the noise source identification methods, which based on the wavelet package, wavelet package with system of linear equations, Morlet wavelet transform. It was found that fan, oil pan and muffler are the most important noise sources in the pass-by noise of the coach.Interior noise of the coach is composed of the air-borne noise and structure-borne noise. Contributions of different noise sources to interior noise of the coach were got from the air-borne noise by the acoustic source decomposition and transfer function analysis. The fan noise is the biggest noise source in the coach interior noise,however,contributions of oil pan and muffler changed with different places and rotational speed. The influence of the coach structure dynamic performance to the coach interior sound field was got by the simulation calculation and vibration test analysis, and that found out reasons why the coach resonates at idle.The coach noise reduction can't leave some techniques, for example, sound absorption, sound insulation and vibration isolation, damping etc. These means were researched by the performance test and mechanism analysis, which had laid the theory basis and the technical support for the coach noise reduction.By means of the optimum design,we developed a high performances & low noise fan for cooling systems of KLQ6795Q,which reduced the near field noise by 2.51dB (A).Further design for the air-inlet grille, air duct and back hatch door of the cooling system,which reduced noise by 2～3dB(A) emitted by accelerating coach of KLQ6795Q.Several mufflers matched with King Long coach were tested, some problems were pointed out. Meanwhile, we developed a new-type muffler with good acoustic and impedance properties based on bench tests and structure optimization design, which main performance parameters can satisfied with the request of QC/T631-1999 automobile standard, which the insertion loss is 22.9dB (A), the power loss is 1.11%, and the exhaust back pressure is 14kPa.According to the oil pan noise emitting characteristics by the near field noise test, we developed a new style acoustic shield, which had both noise reduction and good heat radiation, meanwhile, flexible disassemble and assemble. The result indicated that it can maximally reduce noise by 1.5dB(A) emitted by accelerating coach of KLQ6795Q.Some optimum structure methods and key technologies were proposed and applied to the entire coach noise reduction,the noise level of the coaches were controlled effectively. Examination results of the the national authority department showed that exterior noise of KLQ6795Q was dropped by 4.6dB (A), has achieved second stage limiting value request of the GB1495-2002;and that interior noise of KLQ6129 was maximally dropped by 4.7dB (A), has achieved noise limiting value of the most luxurious coach. The theory basis and the reliable technical guarantee for coaches noise reduction were given from our reseach job .
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