Solving NVH Problem in Prototype Van: Analysis & Results

[harvi101]

please help me to solve this problem

Figure shows noise results for a prototype van measured on a rolling road. the vehicle had a four cylinder in line engine. the engine speed was varied in 3rd gear from just above stall to about 4500 rpm. the sound pressure at the representative interior position was measured in dB using standard reference, namely 20 micro Pa. figure shows the overall noise level and also the component associated with second harmonic of the engine speed.

1. the noise peak at 3600 rpm is due to an acoustic resonance with a stand ing wave between the floor and roof of the van. what is the frequency of this resonance and what is the vertical dimension of the van interior.
2.sketch a graph of the microphone signal at 3600 rpm. (it should include the time and sound pressure axes )
3. comment on the overall results in the figure indicating if they are acceptable or if they indicate a specific NVH problem.

http://img25.imageshack.us/img25/5412/p25031015160001.jpg

 

[Navin A S]

1. The frequency of the acoustic resonance at 3600 RPM is approximately 600 Hz, and the vertical dimension of the van interior is approximately 2 meters.2. The graph of the microphone signal at 3600 RPM would look like a sine wave with a frequency of 600 Hz and an amplitude of about 75 dB.3. The overall results in the figure indicate that there is an NVH problem, as the second harmonic component is significantly higher than the overall noise level. This suggests that the engine vibration is being amplified due to the resonance at 3600 RPM.