## 3 Results and Discussion
### The Effects of Pressure Angle on Scuffing Load Capacity
#### 3.2.2 Comparison of Contact Ratio, Specific Sliding, and Load-Carrying Capacity  
Figure 8 illustrates the contact ratio and bending safety factor for the five gear sets described. It can be observed that the total contact ratio \(\epsilon_{\gamma}\) decreases in a linear fashion with an increasing pressure angle, falling from 4.579 to 4.184, which represents an 8.6% reduction. The transverse contact ratio \(\epsilon_{\alpha}\) exhibits the most pronounced decline, whereas the overlap ratio \(\epsilon_{\beta}\) remains unaltered. It is evident that an increase in pressure angle has a detrimental effect on the enhancement of gear contact ratios, which subsequently impacts the smoothness of gear motion and other NVH performance indicators.  
Figure 8(b) depicts the correlation between the pressure angle and the tooth root bending safety factor for the G2675 gearset, with all other variables maintained at a constant value except for the pressure angle. As the pressure angle increases from 16\({}^{\circ}\) to 23\({}^{\circ}\), the bending safety factor under peak load conditions decreases from 1.43 to 1.32. It is noteworthy that the safety factor for gearsets with a pressure angle of 21.5\({}^{\circ}\) or less remains relatively stable, whereas a significant decline is observed for the 23\({}^{\circ}\) gearset. In order to ensure that the tooth root bending safety factor is at least 1.2, it would be advisable to limit the pressure angle to 23\({}^{\circ}\). Furthermore, the safety factor would fall below the permissible value. Moreover, an elevated pressure angle gives rise to augmented radial forces on the gear, which, in turn, intensifies the load on the bearings and may potentially diminish their fatigue life.  
Figure 9 illustrates the correlation between sliding velocity and specific sliding in relation to pressure angle. Irrespective of whether the point in question is situated below or above the pinion's pitch circle during the tooth exit phase, the sliding velocity is observed to decrease in accordance with the increase in pressure angle. This trend is reflected in the corresponding specific sliding. A significant distinction is that the sliding velocity at the instantaneous contact point demonstrates a linear increase in the diameter distance from this point to the pitch circle. In contrast, the specific sliding at the instantaneous contact point displays a nonlinear increase with increasing diameter distance. Furthermore, the rate of change in the specific sliding is more pronounced below the pitch circle and more gradual above it.  
Table 8 presents the tooth surface pressure distribution for five gear sets with varying pressure angles. The left column indicates peak speed conditions, while the right column indicates peak torque conditions. In conditions of peak speed, the tooth surface pressure remains relatively stable with an increasing pressure angle, with a minimum of 872.2 MPa and a maximum of 883.4 MPa and with fluctuations within a 1.3% margin. In contrast, under peak torque conditions, tooth surface pressure decreases with an increase in pressure angle from a maximum of 2592.9 MPa to a minimum of 2062 MPa, representing a 20.5% reduction. Additionally, the load distribution across the tooth surface becomes increasingly uniform. In these gear sets, where the pressure angle is variable, the contact ratio is inversely correlated with the pressure angle. However, the contact pressure under peak  
Figure 8: The tooth contact ratio and bend safety factors for variable modulus. (**a**) Contact ratio; (**b**) tooth bend safety factors.