塑料缸盖罩透射及结构辐射噪声

为了研究缸盖罩透射噪声及结构辐射噪声之间的关系，对某典型四缸汽油机的塑料缸盖罩在最大功率工况下（6 000 r/m）靠近螺栓处的表面振动速度进行测量，利用多体动力学计算整机振动得到该处振动速度结果并与试验进行对比，证明计算结果与试验基本吻合，通过该仿真结果计算出缸盖罩声压级.利用覆盖法对能对顶面声压带来影响的部件进行屏蔽，只保留缸盖罩不屏蔽，对缸盖罩在相同工况下进行声压级的测量.将计算所得声压级（结构辐射噪声）与测试所得声压级（总辐射噪声）结果进行对比分析.结果表明，透射噪声主要分布于频率1 500~3 000 Hz，结构辐射噪声主要分布于500~1 500 Hz利用有限元法及边界元法计算缸盖罩隔声量对该结论进行验证，得到缸盖罩隔声量在1 500~3 000 Hz处迅速下降，与分析结果吻合.

Research on transmission and structural radiation noise of plastic engine cover

To obtain the relationship between transmission and structural radiation noise, the vibration velocity near bolts of a plastic engine cover of typical 4-cylinder gasoline engine was measured in the max power work case (6 000 r/min). Multi-body dynamics method was used to calculate the surface velocity of the engine cover and the calculation result matched the test result and was used to calculate the sound pressure level. Every part of the engine top except the engine cover was covered and the sound pressure level of the top was tested in the same work case. The sound pressure level results from calculation (structural radiation noise) and test (total radiation noise) were compared and analyzed. The conclusion is that structural radiation contributes more in 500~1 500 Hz while transmission noise contributes more in 1 500~3 000 Hz. The transmission loss of the plastic engine cover was also calculated FEM& BEM and the result shows the loss decreases rapidly in 1 500~3 000 Hz and the situation matched the conclusion that transmission noise contributes more in 1 500~3 000 Hz.