The sliding coefficient is an important parameter to measure the relative sliding degree between the tooth surfaces of the meshing helical gear pair. Because sliding will lead to scuffing failure or even wear of the tooth surface, causing serious consequences, it is necessary to study the sliding coefficient of the helical gear, so as to improve its ability to resist scuffing and wear.
Generally, the helical gear mesh is perfect when the sliding coefficient is at (- 1, 1), good when it is at (- 3, 3), and poor when it is at (- ∞, – 3) and (3,+∞). As shown in the figure, the sliding coefficient curves of the helical gear pair No. 0 without modification, No. 1 optimization scheme and No. 9 optimization scheme show that the sliding coefficients are all between (-0.95, 0.49) and the meshing performance is perfect, but the optimization modification does not cause the sliding coefficient change of the helical gear, so it can be considered that the above optimization modification methods have little impact on the sliding degree between the helical gear pair teeth. In addition, it can be found from the figure that the slip coefficient of big and small gears is close (red line, green line), so that the relatively balanced helical gear slip rate can keep the wear degree of the two helical gears consistent in the transmission process, thus improving the utilization rate of helical gears.
| Original plan | Plan 1 | Plan 2 | |
| Number of teeth Z1 | 30 | 32 | 34 |
| Number of teeth Z2 | 51 | 49 | 47 |
| Slip coefficient ζ1 | （-0.95，0.49） | （-0.89，0.49） | （-0.84，0.49） |
| Slip coefficient ζ2 | （-0.94，0.49） | （-0.94，0.49） | （-0.95，0.46） |
| Tooth ratio | 1.7 | 1.53 | 1.38 |
Of course, if there is a higher requirement for the anti scuffing and anti wear ability of the gear, it can be achieved by properly adjusting the ratio of the number of teeth of the big and small gears. As shown in the table, the absolute value of the sliding coefficient can be reduced by appropriately reducing the gear number ratio when the center distance and the modification coefficient remain unchanged.