Development of an Analytical Method for Rear Differential Gear Whine Noise Utilizing Principal Component Contribution by OTPA and CAE 2019-01-1555

The progress of vehicle electrification has reduced engine noise and the improvement of rear differential gear whine noise has become more important for customer satisfaction. Rear differential gear whine noise is a result of the vibration generated by the transmission error of the gears transmitted to the cabin from various paths. As several components have a contribution, identifying key paths to develop an effective countermeasure becomes time consuming.

Operational transfer path analysis (OTPA) is one of the TPA methods to determine the main path and contributing part using only the operational data. However, in cases where many reference points are set on the same frame or body, the contribution becomes similar because of high correlation between the reference data set. As a result, finding the main transfer path becomes difficult. To overcome this issue, the principal component (PC) contribution obtained from the correlated reference signals was established by modifying the OTPA process. Through this process, important vibration behavior of the target structure can be obtained as the high contributing PC mode. In this paper, this approach was applied to a vehicle and verified. In addition, for applying the method, enormous signals at the reference and response points are necessary to be recorded simultaneously. This issue makes the method difficult to be applied especially to the high frequency phenomenon. This issue was solved by using frequency responses calculated from finite element (FE) models which were converted to transient data by inverse fast Fourier transform (FFT). After obtaining sufficient amount of data by using simulation, the data was used to identify the high contributing PC modes and the vibration modes. Using these findings, the vehicle was retrofitted, the vibration and sound pressure levels were confirmed to decrease and the effectiveness of the developed method was verified.