| With the rapid development of construction machinery industry, requests for the construction machine which has a higher integrated character are raised by people. Energy-saving and environment friendly has already become a prevailing trend. As the volume of exports of domestic construction machinery to US and European countries becomes bigger, there is now a problem we have to face—vibration and noise, we have to enhance the quality of our products to meet the impulsive standard of US and European countries. Therefore, there is an urgent need to reduce noise of construction machinery like excavator. The premier task is to find noise sources. For a crawler-type hydraulic excavat or powered by diesel engine, the main noise source is diesel engine. So it is of importance theoretical meaning and huge practical value to do a research on noise characteristic of excavator diesel engine.This thesis was based on a Project(2009AA045103) supported by the National High Technology Research and Development Program of China. The identification of noise source of4B2-38M34diesel engine equipped in SWE50G3excavator was developed by Sunward Intelligent Equipment Co., Ltd, as well as noise characteristic research. Surface radiated noise is the dominating part if there equips a muffler, so the analysis of noise source in this paper was focused on surface part of diesel engine. Noise characteristic analysis presented a dynamic connection among digging resistance, speed and noise for the load was transient and speed was fluctuated.The noise source of diesel engine was identified through the following approach:first, vibration modals and corresponding natural frequencies of different parts of diesel engine were obtained by finite element modal analysis. Second, according to the results of acoustic intensity and acoustic array, the biggest noise source was found through acoustic image identification technology, and then recorded noise signals. Third, the frequency domain of dominating noise was confirmed by using wavelet analysis. Then, signals in frequency domain of dominating noise was separated to get independent signals which were given by different noise sources, and then extracted the domain frequency from relevant independent signal. At last, main noise parts could be found after comparing the domain frequencies of vibration modals with independent signals'. It was confirmed that oil pan, valve cap, body, flywheel casing and cylinder head were main noise parts.The noise characteristic of diesel engine was researched through the following way:first, a three dimensional model of SWE50G3was obtained under Inventor environment, and construction parameters of the equipment were got. Second, kinematics and dynamics were analyzed and digging resistance calculation equation was deducted. Third, a test that the bucket dragged weight was conducted, the validity of calculation equation was verified by comparing the result of pull sensor with calculation digging resistance. Finally, actual digging resistance was obtained using obliquity signal and cylinder pressure signal measured in working condition. According to the digging resistance, speed and actual external radiated noise, a conclusion that actual external radiated noise increased as the accelerator became larger was received.Some measures to make a progress to diesel engine were proposed: rigid of oil pan, body, flywheel casing and cylinder head were enhanced by adding reinforce rib; rigid of valve cap was enhanced by optimizing its shape; crank equipped with a torque damper was also adopted to reduce transmission of force from the internal to the surface of diesel engine, decreasing the whole noise by2dB(A).
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