Sound quality is a very important performance for a new development vehicle. Poor sound quality will downgrade the subjective evaluation to the production by customers. In this paper, the roughness of interior noise of a SUV with a 1.5L turbo-charged gasoline engine was found during acceleration from 1500r/min to 4000r/min. By subjective evaluation and spectrum analysis, the noise around 275Hz was found contribute most to the noise roughness, and the half order noise around the frequency band represented a modulation phenomenon. Then, all possible noise vibration sources and transfer paths were studied separately.
Firstly, the interior noise was measured on the condition that inlet and exhaust noise sources were deadened. the results showed that air-born noise had merely no contribution to the interior roughness. So the half orders noise was judged to be structure born noise. Secondly, the vibration of powertrain mounts were measured both on the engine side and body side, the test results showed that the spectrum features of vibration on transmission mount bracket coincided well with the interior noise spectrum feature.
The results proved that the half orders vibration of engine transfer to the car body though gearbox mount. Finally the mode of powertrain was measure by impacting test, and there was a global torsional mode frequency of powertrain about 275Hz, and the position of transmission was sensitive to this mode. So it can be concluded that the combustion force caused the resonance of powertrain torsional mode, and the vibration transferred into cabin though transmission bracket given rise to the interior roughness. Two feasible methods were used to reduce the vibration transfer from engine to the car body. The first one was to optimize the powertrain mount system by reducing the dynamic stiffness of transmission mount rubber. Then dynamic stiffness of transmission mounting attachment points on car body side was enhanced by adding welding points. And the test results proved that the roughness of interior noise was effectively decreased and sound quality was improved during acceleration.
Dr. Yan Jin, China Automotive Engineering Research Institute Co. Ltd, CHINA