Analysis on Increase of Contact Ratio and its Effects on Involute Spur Gear Teeth

The influences of centre distance and tooth addendum increase on the contact ratio of involute spur gear sets are studied taking the major performance parameters such as bending strength, surface compressive strength and gear tooth deflection into account. In the first case, the contact ratio is intentionally varied between one and two by altering the center distance and for a given gear ratio, module and pressure angle. In the second case, for the same gear set, the contact ratio is increased by tooth extension within the permissible clearance limits on the addendum side avoiding interference. On either case, the influence of contact ratio on the performance parameters is analyzed. The results of the three dimensional FEM analyses from ANSYS are presented. For two sets of identical gears, when the contact ratio is increased in one set by tooth extension considerable improvement in the percentage engagement time is observed indicating improved performance capabilities.