NVH Analysis And Optimization Of Automobile Driven Rear Axle

With the development of the body NVH technology, chassis NVH issues standout. As an important part of the power transmission system, drive rear axle not onlybear the excitation passed over by the engine, but also affected by the bending andtwisting of spring mass and road excitation, while it is also generating unbalanceimpact during operation by itself. So the rear axle is both the excitation source andalso a transmission path, NVH issues are very important, but quite complex, too.Aiming at the problem of excessive noise of a vehicle rear axle in the43km/huniform linear condition, the paper made corresponding analysis and optimization tothe NVH problem.Through early other related analysis, the rear axle noisy problem was mainlycaused by the rear axle itself. The paper analyzed internal excitation source of rearaxle noise, combined with the experience of previous research, found that gearmeshing of final drive produced greater impact which caused rear axle vibration,resulting in greater noise. Ignored the fluence on the force distribution duringoperation, the article made a force analysis to the gear meshing of final drive and thegear mounting shaft at first, as the circumference force of the driving gear was1N,got bearing force distribution ratio of gear mounting shaft.What’s more, through themodal analysis of the rear axle housing,comparing the main vibration frequency withmesh frequency， then found that the main reason of the excessive noise wasresonance caused by the gear of final drive meshing frequency of and third modalfrequency of the rear axle housing were277Hz. Finally, taking each bearing force asthe excitation, calculated rear axle housing vibration response.The vibration response mapped to the boundary element mesh as boundaryconditions, for sound radiation analysis of rear axle housing using the directboundary element method, obtained the distribution and the size of radiated soundfield under the main modal frequencies. The main radiation area are differentialhousing,rear axle bow and the back cover and the surface acoustic field of rear axlehousing is lager at277Hz, the maximum sound pressure levels up to69.9dB. A pointsource defined in the meshing point of final drive, field point of point set establishedon all sides250millimetre away from the center of rear axle housing, Calculated thesound transmission loss which is at least18dB,so meshing noise of final drive can bewell isolated from the rear axle housing. The differential housing,rear axle bow and the back cover main acousticradiation area as the design variable space,made topology optimizations based onmodal and vibration response respectively. Since mode can not be avoided,only tochange the frequency,low speed conditions corresponding to the low meshingfrequency,through the third modal frequency decreased,The correspondingverification analysis of improved rear axle housing according to the topologyoptimization show both radiated noise or vibration response has a certain degree ofreduction. In the actual low speed conditions,due to the reduction of the impact of themeshing, the effect will be more obvious.Through force analysises to the gear meshing of final drive and the gearmounting shaft, calculated the bearing load by unit of1N circumference force of thedriving gear. Do not force it come to the actual acoustic radiation, which has noeffect on the final optimization, eliminating the need for complex software analysis,avoiding model errors of software analysis. By using topology optimization to guidestructure change, avoided the blindness of optimization, and achieved good results. Inthis paper, the method also has some reference value to other rear axle analysises.