Numerical and Experimental Analysis of Manual Transmissions - Gear Rattle

Manual transmission gear rattle is the result of repetitive impacts of gear meshing teeth within their backlash. This phenomenon can occur under various loaded or lightly loaded conditions. It fundamentally differs from other transient NVH phenomena, such as clonk or thud, which are due to impulsive actions [1]. However, they all have their lowest common denominator in the action of contact/impact forces through lubricated contacts. Various forms of rattle have been cited, owing to the mechanism of manifestation and operating conditions [2, 3 and 4], among which drive rattle, creep rattle and over-run rattle can be found. In this work, a transmission model for creep rattle conditions has been developed taking into account the lubricated impacts of the gear teeth pairs during a meshing cycle and the friction between the contacting teeth flanks. Hertzian contact conditions are applied to the gear pair along the torque path and iso-viscous hydrodynamic lubrication is modelled for the lightly loaded gears. The model is further compared to experimental data, validating the results. The experimental and numerical signal analysis comprises short FFT.