某SUV车内低频轰鸣声的分析与控制

Analysis and Control of Low-frequency Roaring Sound inside an SUV

针对某运动型多用途汽车(sport utility vehicle,SUV)在开发后期路测时出现的车内低频轰鸣声问题,采用测试和计算机辅助工程(computer aided engineering,CAE)仿真分析,提出合理的优化方案。首先,通过激励源、传递路径及响应端的快速排查,确认问题频率和部件为30 Hz尾门的呼吸及外板中间弯曲模态。对标实车测试模态结果,建立仿真分析整车模型,设定车内尾门到主驾的噪声传递函数(noise transfer function,NTF)优化目标值(78 dB),计算NTF及尾门的工作模态变形,从而识别出尾门结构弱点。提出一种复合材料的车身加强件(composite body solutions,CBS)优化方案,即对尾门弱点处内外钣金之间加装复合材料支架提高尾门刚度,使其NTF值达标,其优化效果与加装吸振器一致。且CBS方案增重仅0.4 kg,不影响尾门系统。同时计算CBS方案实施前后钣金等效辐射声功率,结果显示CBS方案在问题频率处声压级下降5 dB左右,验证了其可行性。最后制作了CBS样件并安装,进行实车路况测试与主观评价,整体主观优化明显,评估可接受。工况测试的客观数据显示关键峰值30 Hz附近声压级下降5 dB,验证了方案的有效性。

Aiming at the problem of low-frequency roaring sound in an sport utility vehicle(SUV)during road testing in the later development stages.A reasonable optimization scheme is proposed based on actual vehicle and computer aided engineering(CAE)simulation analysis.Firstly,through rapid investigation along the excitation source,transmission path,and response end,it was confirmed that the problem frequency and components were the liftgate breathing mode of the 30 Hz and the bending mode in the middle of the outer plate.Based on the modal results of the actual vehicle testing,a simulation model was established,and the noise transfer function(NTF)optimization target value(78 dB)was set from the liftgate to the driver inside the vehicle.The NTF and the working mode deformation of the vehicle liftgate were calculated to identify the structural weaknesses of the liftgate.A composite body solutions(CBS)optimization scheme is proposed to improve the stiffness of liftgate,which involves adding composite material brackets between the inner and outer sheet at the weak points of the tailgate.Compared to CBS and the installation of vibration absorbers,they have a consistent effect.And the CBS scheme only increases weight by 0.4 kg,which does not affect the liftgate system,so as not to affect the development cycle.Moreover,the equivalent radiated sound power of the sheet metal before and after the implementation of the CBS scheme was calculated,and the results showed that the sound pressure level of the CBS scheme decreased by about 5 dB at the problem frequency,verifying its feasibility.Finally,create CBS samples and install them for on-site road condition testing and subjective evaluation.The overall subjective optimization is obvious and the evaluation is acceptable.The objective data of the working condition test shows a 5 dB decrease in sound pressure near the critical peak of 30 Hz,verifying the effectiveness of the scheme.