Evaluation of root stresses of a rattling gear pair

Abstract

Gear rattle is a major noise problem in certain powertrains systems, especially those that are driven by internal combustion engines such as timing gear drives, engine balancers or manual transmissions. Teeth lose contact intermittently to commit impacts along the drive and coast sides of the gear pairs having backlash. Most of the studies on this topic focused exclusively on the noise and vibration consequences of rattle with a very little attention given to its influence on system durability. This study presents an experimental investigation of tooth root stresses of a spur gear pair during periodic and chaotic rattling motions caused by a harmonically time-varying input torque. Root stresses of certain teeth of one of the gears are measured in the instances when these teeth are in gear mesh zone when impacts occur. Changes to root stress time histories due to drive and coast-side impacts are documented to show that root stress amplitudes are increased significantly by impacts. Measurements also indicate that most impacts generate families of fully-released strain peaks that contribute the fatigue damage along the drive and coast sides root fillets. A deformable-body model was shown to simulate the experiments accurately, so that it can be used to predict statistical distributions for root stress duty cycles for estimation of fatigue lives of rattling gears.