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Several analytical tools exist for estimating a driveshaft’s critical speed, from simple elementary beam theory to sophisticated FEA models. Ultimately, nothing is better than a test, because no one will argue with the outcome from a well-designed measurement. Impact response measurements are easy, but they tend to over predict the critical speed. A test which sweeps the shaft speed up until failure is telling, but the speed causing failure is strongly dependent on even small amounts of variation in rotor unbalance. Waterfall plots of shaft displacement measurements offer the best indication of critical speed, however sometimes the resonance isn’t unmistakable or multiple resonances exist, making the critical speed unclear. A method less susceptible to system variation is offered here, fitting shaft orbit measurements to the theoretical single degree of freedom equation.

Gear rattle noise is a common issue in manual gear transmissions and is often difficult to resolve. This paper discusses a methodology involving development of a simulation model for noise prediction and subsequent design of experiments (DOE) analysis to select optimal design parameters to reduce rattle noise. A one-dimensional torsional vibration simulation model for a tractor driveline was developed and was correlated with experimental measurements. This correlated model was used to calculate the torque variation between the gear pairs based on engine excitations. The standard deviation of this mesh torque was used as a metric and was correlated to noise ratings assigned by experts during experimental evaluation. Using this metric as the response variable, a DOE was conducted to determine the contributing factors and their influence on the rattle noise. Optimal design parameters were selected to achieve target value on the rattle metric.