The Study About Optimizing Of Noise Emission And Sound Quality From The Front Of YC4561 Diesel Engine In IDLE Speed

The article introduced the study of noise emission from the front of YC4561 in idle speed. The noise of YC4561 in idle speed have a obvious knocking sound "ta ta ta". The topic explored from two aspects:the noise source and the noise transmission path. In order to reduce the noise emission and improve the sound quality, the GE420 just like YC4561 as a benchmark machine in the process of study.The following works were done in this topic:The first point:the test of noise and sound quality and noise source identification in idle speedThe noise of YC4561 and GE420 in idle speed was tested by 9 points method of engineering and found that the noise from the gearbox cover front of engine was bigger than other place. And the sound pressure level value of YC4561 was bigger than GE420. The spectrum of the noise was analyzed, and found that YC4561’s noise value in 2kHz band of(one third octave) was maximum. The location of the noise on 2kHz band front of engine was found by sound intensity method, which was in the top of the gearbox cover opposite to the timing gear.The objective parameters of sound quality such as loudness roughness sharpness impulsiveness were tested according to the standard of Q/YC3094-2011.From the test result, the sound quality of GE420 was better thanYC4561.The second point:modal calculation and modal test of gearbox coverThe first ten order free modal parameter of natural frequency and modal shape of the gearbox cover were calculated. And compared with modal test result, the correctness of the finite element model was verified. In addition, the modal of the gearbox cover in installed state was tested. According to the result, the boundary condition of finite model was created. And the feasibility of constraints boundary condition was verified by comparing with modal calculation and modal test. The modal of gearbox cover after optimization was calculated in the boundary condition above, and the natural frequency of one modal shape which have a great influence on noise emission was found. Comparing to modal test result, the relative error rate was 6.97%,which meet the engineering accuracy requirements.The third point:the optimized schemes and validationThree optimized schemes were proposed:anti-backlash timing gear, opening hole upper of the gearbox cover and instead of plastic, and using plastic gearbox cover. There have noise and sound quality test of three kinds of schemes. And, found that there had a great influence on noise emission and sound quality by changing the timing gear schemes. And through this scheme, the knocking noise of "ta ta ta" disappeared. Therefore, It can judge that the knocking noise was produced by gear engagement. The other two schemes also can improve the noise quality to some degree, but the improve effects are far less than changing timing gear scheme.