The modification length and modification curve need to be selected for the modification along the tooth profile direction. In the meshing process of straight bevel gear, the modification length will be affected by many factors, such as manufacturing error, tooth deformation, coincidence degree, etc. Therefore, the modification length should be selected in combination with the actual transmission situation of straight bevel gear. For straight bevel gear transmission under different load conditions, short modification and long modification show different degrees of advantages. Through a large number of tooth profile modification studies, it can be seen that the long modification of helical gears with large axial coincidence and large helix angle can obtain ideal modification effect; Better modification results can be obtained by short modification of straight bevel gear and helical gear with small helix angle. The short modification is adopted for the straight bevel gear. According to the dimensional parameters of the straight bevel gear, the appropriate modification length is calculated with the help of the finite element method.
Compared with the straight-line modification, the curve modification can make a tangent transition with the previous involute, and the change of the curve is also continuous with the change of the previous involute. Therefore, the curve modification can more effectively improve the transmission performance and vibration performance of straight bevel gear and reduce the dynamic load. However, the straight-line modification can not make a good transition with the previous tangent, and the intersection point with the involute is a sharp angle. Therefore, the arc curve is adopted for the involute modification of straight bevel gear.
The modification area in the tooth direction should be determined according to the effective contact area of the tooth, so as to complete the modification of straight bevel gear according to the predetermined load distribution law of the tooth surface. According to the straight bevel gear standard GB / t11365-1989, the effective contact area of straight bevel gear pair can be obtained.
For the involute straight bevel gear analyzed in this paper, the effective modification areas are 35% ~ 65% along the tooth length direction and 40% ~ 70% along the tooth height direction.