scope:

The face load factor KHβ, which in rating equations represents the load distribution over the common face width in meshing gears, is one of the most important items for a gear strength calculation. In the international standard for cylindrical gear rating, the ISO 6336-1 [1], using method C, some formulas are proposed to get a value for this factor. But as the formulas are simplified, the result is often not very realistic. Also AGMA 2001 (or AGMA 2101) [2] proposes a formula for KHβ, different from ISO 6336, but again not always appropriate. Therefore a note in AGMA stipulates, that "it may be desirable to use an analytical approach to determine the load distribution factor".

In the last edition of ISO 6336 (2006), a new annex E was added: "Analytical determination of load distribution". This annex is entirely based on AGMA 927-A01 [3]. It is a well-documented procedure to get a direct and precise number for the face load factor.

Today an increasing number of gear designers are using tooth contact analysis (TCA) methods [4] to get precise information over the load distribution on the full gear flank. Contact analysis is very time consuming and does not permit to get a value for KHβ, as defined by the ISO or AGMA standard. A contact analysis result combines different factors of ISO 6336 as KHβ, KHα, Zε, Zβ, ZB, ZD and buttressing effects, etc., thus to 'extract' KHβ from a TCA is not possible.

The use of the algorithm, as proposed by AGMA 927, is a good solution to get proper values for KHβ; it is simpler and therefore much quicker than a contact analysis calculation. The paper explains how this algorithm can be applied for classic gear pair rating procedure, for ratings with complex duty cycles and even for planetary systems with interdependent meshings between sun, all planets and ring.