We are seeking methods of selecting the Alternate Bending Factor (Ym) for highly loaded gears in automotive applications.


Alternate bending factor (Ym) is part of DIN 3990 and ISO 6336 gear analysis methods. The factor is defined for pulsating loads or pure alternating loads. For gears in automotive applications – especially for gearboxes of electrical or hybrid vehicles – there are no suitable methods of determining Ym-factor. Since gears are not mainly loaded in drive direction, they are also loaded in the coast direction with remarkable loads (recuperation).

There are three main ways to obtain load data from customers, therefore different approaches may be necessary.


Gear modulus in the range of 1 to 2.5 mm

Possible solution areas:

  • Selection of appropriate gear pair
  • Determination of time based meshing force characteristics with different drive/coast shares
  • FEA based damage analysis of tooth root area on coast and drive flank
  • Determination of alternate bending factors
  • Verification at test bench (simplified component tests)

Desired outcome of the solution:

Proposal of a method to select the correct Ym-factor for highly-loaded gears in drive and coast direction.

Field of use and intended applications:


Previously attempted solutions:

  • ISO 6336 – Measures the difference between lower and higher loaded flank, only works for a periodic signal
  • DIN 3990