Vehicle Interior Noise Identification And Control Based On Transfer Path Analysis

The characteristic of vehicle interior noise is one of important evaluation targets of riding comfort. The loud interior noise not only impact the feeling and health of passengers, disturb the talk in vehicle, but also confuse user identifying the sound signal of vehicle, which will be likely to course traffic accident sometime. So decreasing vehicle interior noise to improve ride comfort has been a very important tache in product development. Works in this thesis are based on the research of FAW Research & Design Center technology development project " Research on Vehicle NVH Matching and Control Technology ". In the thesis, research on reducing interior noise for an indigenous car are performed and a vehicle model basing on noise transfer path is established to simulate interior noise. Compared simulation results with road test results, the major sources of interior noise are identified. Some structures were modified and some measures were applied, which had made a good progress in reduction of interior noise.Firstly, the theories of transfer path analysis are discussed and some formulas are deduced to identify the relation between system and substructure. Path contribution transfer function and excitation transmissibility function are put forward to identify the characteristics of coupled vehicle system, which will be used to control system response when external excitation are applied on system.Next, with the composing analysis of interior noise, combining the real status of test car, a vehicle interior noise simulation model based on transfer path analysis is established. Every path of structureborne noise and airborne noise is analyzed, while the measure method of transfer functions and key points are discussed.The noise investigation is the first step of the interior noise reduction. According to state standard GB/T 18697-2002, lots of interior noise road tests for the pattern car are performed. The noise levels, sound field distribution,frequency spectrum and so on are analyzed, as a result, 100~500Hz is regard to be the most important frequency range of interior noise reduction for the car.Through the measure of every parameter that model need, interior noise is synthesized in the model. Comparing the simulating result with real measure result in different work situation, the simulation model is verified to be available for analyzing interior noise.Interior noise transfer path analysis discover that structureborne noise have important impact in middle-low frequency noise. From path contribution transfer function analysis, mount transmissibility function analysis and frequency segment total contribution analysis, the most important transfer paths and components are identified, pointing out that the vibration isolation of mount and the noise-borne characteristic of body need to be improved for interior noise reduction.Vehicle noise reduction includes some techniques, for example, sound absorption, sound insulation, vibration isolation, damping, etc. These means are researched and some measures are applied on real vehicle:â‘ A engine-mount system model with six degrees-of-freedom is established and old mount system is renewedly optimized. The result indicate that the new mount obviously improve vibration isolation and decrease interior noise.â‘¡Modal experiment of vehicle body roof is performed to identify the unsubstantial position. With the increase of roof bolster rigidity and damping handle, the noise from unsubstantial structure radiating is weakened.â‘¢suitable sound absorption material is selected and new trim structure is adopted, as a result, the noise absorption capability of interior trim is improved and interior noise is accordingly decreased.Applying the above improvement on original car, some road tests including constant speed and acceleration are preformed. The results prove, with these improvement, the interior noise of the car is reduced by 3~5 dB(A), exceeding scheduled project target which is set at 2~3dB(A).In this thesis, according to the relation of transfer function between system and substructures, a vehicle interior noise simulation model based on transfer path analysis is established. The research process which include road test analyzing, interior noise modeling, major noise source identifying, noise reduction optimizing and so on, form an integrated technique of vehicle interior noise identification and control.