Page 271 - Gear Technology Solutions

Figure 21: Load sharing ratio comparison

Selective crowning increases the effective contact ratio, which reduces in the
example the maximal contribution to 60% of the input torque, while the neigh-
boring tooth pairs doubled their contribution. The selective crowning optimized
hypoid gearset has an estimated increase in power density of 80%/60% 0
1.33-fold.

18.5 Summary

Spiral bevel and Hypoid gearsets have very individual contact geometries,
which already change by adding or subtracting one single tooth (in particular
on the pinion). This is the reason why automated selective crowning applica-
tions are not possible. In the case of conventional designs, the GEMS soft-
®
ware provides an automated approach to create excellent basic geometries
and also generates very good contact conditions which are based on circular
length and profile crowning as well as flank twist (bias). A gear engineer can
control the contact geometry with only a few control factors to achieve the de-
sired path of contact bias and a low motion error.

However, these conventional designs have a contact ratio of 1.0 in case of no
load and motion errors in the range of 50 microradians and more. In order to
reduce motion errors below 50 microradians, length and profile crowning have
to be chosen very low, which results in a high deflection sensitivity.

The development of a selective crowning Ease-Off allows a motion error below
50 microradians, increases the load sharing contribution and is less sensitive
to deflections than a conventional Ease-Off design. A GEMS design is a good
starting point for selective crowning developments. The investment of some
additional time to conduct the steps described in chapter 3.4 is justified if the
gearset is required to have the highest possible power density combined with
excellent NVH properties.

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