Numerical and experimental comparative study of strength-optimised AGMA and FZG spur gears

In standard gear pairs there is typically a discrepancy between the bending strength of the pinion and the wheel, with the pinion being the weakest. Smaller pinion tooth numbers, typical of automotive gearing, further increase this problem and different optimised design solutions, based on long addendum modifications, have been proposed by the American Gear Manufacturers Association (AGMA) and the German organisation for gear research Forschungsstelle für Zahnräder und Getriebebau (FZG). AGMA favours a compromise between the strength of the pinion and the wheel (balanced bending strength), while FZG strengthens both pinion and wheel using bigger addendum modifications and a correspondingly bigger centre distance (maximum bending strength with balanced sliding velocities). A comprehensive comparison of the two methods does not exist in the literature because the shifting employed by the FZG recommendation exceeds the normal tabulated J-factor ranges and, because of the large number of design variables involved (i.e., number of teeth, pinion and wheel shift etc.). This paper uses non-dimensional modelling to decrease the number of independent design variables in conjunction with Boundary Element Analysis and photoelasticity measurements to compare the bending strength of all AGMA and FZG designs in the region of their intended use.