Vibro-Acoustic Methods to Predict Chain Noise in Automotive Transfer Cases

The dynamic interactions between the chain links and sprocket during mesh are one of the predominant sources of noise in an automotive transfer case. This paper uses Vibro-Acoustic methods to predict chain-sprocket mesh noise using commercial numerical codes. Chain-sprocket excitations are simulated using a multi-body dynamics program at several speed steps. Subsequently, these dynamic forces are transformed from the time domain to frequency domain and used as an input to a finite element model of the transfer case. The surface velocities calculated due to these boundary conditions are used as an input to SYSNOISE, a vibro-acoustics program. The predicted sound pressure levels (SPL) and sound power levels (LW) from Sysnoise for each speed step are then compared with test data measured in a hemi-anechoic chamber. In addition, this paper also discusses the effects of “simplifying” the dynamic excitation forces due the chain-sprocket in order to reduce computation time. The results of these “simplifications” will then be presented, along with practical engineering guidelines, for predicting chain noise from a transfer case.