Effect of addendum on contact strength, bending strength and basic performance parameters of a pair of spur gears

This paper investigates effect of addendum on tooth contact strength, bending strength and basic performance parameters of spur gears. Face-contact model of teeth, mathematical programming method (MPM) and three-dimensional (3D), finite element method (FEM) are used together to conduct loaded tooth contact analyses (LTCA), deformation and stress calculations of spur gears with different addendums and contact ratios. Tooth load, load-sharing rate, contact stress, root bending stress, transmission error and mesh stiffness of the spur gears are analyzed. Effects of addendum and contact ratio on gear strength and basic performance parameters are also discussed.It is found that contact stress distributed on tooth surface along the profile is asymmetrical around the geometrical contact point of the gears when the geometrical contact point is far away from the pitch point, especially at the tip or root contacts. The maximum contact stress is also not exactly at the geometrical contact point. Hertz formula can only calculate the tooth contact stress approximately. FEM can be used to conduct precise analysis of the tooth contact stress.It is also found that increment of addendum can increase number of contact teeth, then this increment can reduce tooth contact stress and root bending stress, generally speaking. But this increment also makes the tooth depth long and lets the tooth be deformed easily. So, this increment can reduce tooth contact stress, but there is no guarantee that this increment can certainly reduce tooth root bending stress. Also, increment of the addendum makes the values of “T” and “V” in the so-called value of “PVT” great. So, scoring strength calculations of the tooth tip and root becomes more important when to use high contact ratio gears (HCRG) with long addendum.Finally, strength calculations of HCRG with misalignment error, lead crowning and thin-walled thickness are discussed simply in this paper.