As shown in Figure 1, it is the contour map of CHTE under different profile modification parameters of gear pair 3, and the minimum value area in the figure represents the best combination of profile modification parameters.

Figure 1 (a) shows the CHTE contour of gear pair 3 without tooth direction modification and under ideal installation condition, and its minimum value area is in good agreement with the result of inspection procedure, which proves the correctness of tooth profile modification procedure. Figure 1 (b) is the contour of CHTE after considering the influence of tooth profile modification drum and meshing tooth error. Its minimum value area moves to the right side of the reference result, that is, under the same range of tooth profile modification, the amount of optimal tooth profile modification increases.

Fig. 2 shows the best increment of profile modification caused by tooth direction modification drum and meshing tooth direction error. The asterisk in the figure indicates the actual amount of tooth direction modification and meshing tooth direction error of gear pair 3 under rated working condition. It can be seen that the tooth profile modification and the meshing tooth alignment error can soften the meshing stiffness of gear teeth, and the optimal tooth profile modification increases with the increase of them.