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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.

In this paper, a direct correlation between transmission gear rattle experiments and numerical models is presented, particularly focusing on the noise levels (dB) measured from a single gear pair test rig. The rig is placed in a semi-anechoic chamber environment to aid the noise measurements and instrumented with laser vibrometers, accelerometers and free field microphones. The input torsional velocity is provided by an electric motor, which is controlled by a signal generator, aiming to introduce an alternating component onto the otherwise nominal speed; thus, emulating the engine orders found in an internal combustion engine. These harmonic irregularities are conceived to be the triggering factor for gear rattle to occur. Hence, the rig is capable of running under rattling and non-rattling conditions. The numerical model used accounts for the gear pair's torsional dynamics, lubricated impacts between meshing teeth and bearing friction.