Abstract
This paper considers the origin and implications of higher-order (non-linear) cumulant spectral signatures generated by a hypoid gear assembly in a light utility van. This analysis demonstrates that the hypoid gear silencing problem is qualitatively and quantitatively different than the problems in gear design, both nominal and detailed, in particular:
• The production of sound by final drive gear trains is an extremely inefficient process; therefore, the vibration components which dominate sound generation are negligible quantities in typical gear design trade-offs. The usual silencing adjustments often shift but do not remove the offending source.
• Human hearing is acutely sensitive to the phase-coherent sinusoidal oscillations with modulated sidebands produced by hypoid gear trains. Modifications which reduce signature energy in a specific narrow band component may have no useful effect on perceived acoustic annoyance.
• Final drive measurements capture transient, stochastically modulated hypoid gear signatures confounded by highly correlated, non-Gaussian interference. Experimental design to explicitly measure the transient drive signals and the sources of correlated inference is essential for useful results.
• Emerging higher-order spectral analysis methods require long measurement ensembles to achieve appropriate resolution bandwidth and statistical convergence. Efficient data handling architecture for long, replicated ensembles is a pragmatic necessity.
