## 3 Results and Discussion
### The Effects of Pressure Angle on Scuffing Load Capacity  
#### 3.2.1.  
Gearsets Geometry Parameters Planning  
The subsequent study examines the effects of varying pressure angles on a number of key variables, including tooth surface sliding velocity, specific sliding, load distribution, and flash temperature. These variables are considered under a constant center distance. The specific parameters for the five sets of gear pairs are outlined in Table 7. Each gear pair has a center distance of 87 mm, with the number of teeth consistently set at 26 and 75, a helix angle of 20\({}^{\circ}\) to the right, and a normal module of 1.62 mm. The pressure angles are systematically varied as 16\({}^{\circ}\), 17.5\({}^{\circ}\), 19.5\({}^{\circ}\), 21.5\({}^{\circ}\), and 23\({}^{\circ}\) across the five sets. In the design process, the guiding principle for determining the variation coefficient, tooth tip height, and tooth root height coefficients is to achieve a balance in the sliding rates between the large and small wheels.  
\begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline
**Gearset** & **Symbol** & **A16** & \multicolumn{2}{c}{**A17.5**} & \multicolumn{2}{c}{**A19.5**} & \multicolumn{2}{c}{**A21.5**} & \multicolumn{2}{c}{**A23**} \\ \hline \hline \multirow{2}{*}{\begin{tabular}{c} Gear \\ Tooth number \\ Normal module \\ \end{tabular} } & \multirow{2}{*}{\(z\)} & \multirow{2}{*}{26} & \multirow{2}{*}{75} & \multirow{2}{*}{26} & \multirow{2}{*}{275} & \multirow{2}{*}{26} & \multirow{2}{*}{275} & \multirow{2}{*}{26} & \multirow{2}{*}{275} & \multirow{2}{*}{26} & \multirow{2}{*}{275} \\  & & & & & & & & & & & \\ \hline \multirow{2}{*}{\begin{tabular}{c} Gear ratio \\ Pressure angle \\ \end{tabular} } & \multirow{2}{*}{\(a_{\text{n}}\)} & \multirow{2}{*}{\(16^{\circ}\)} & \multirow{2}{*}{\(17.5^{\circ}\)} & \multirow{2}{*}{\(19.5^{\circ}\)} & \multirow{2}{*}{\(21.5^{\circ}\)} & \multirow{2}{*}{\(23^{\circ}\)} & \multirow{2}{*}{\(23^{\circ}\)} \\  & & & & & & & & & \\ \hline \multirow{2}{*}{\
\begin{tabular}{c} Face width \\ Center distance \\ \end{tabular} } & \multirow{2}{*}{\(a\)} & \multirow{2}{*}{\(b\)} & \multirow{2}{*}{\(\begin{array}{c}\\ 87 mm \\ \end{tabular} }\) & \multirow{2}{*}{\(a\)} & \multirow{2}{*}{\(0.408\)} & \multirow{2}{*}{\(-0.445\)} & \multirow{2}{*}{\(0.308\)} & \multirow{2}{*}{\(-0.345\)} & \multirow{2}{*}{\(0.208\)} & \multirow{2}{*}{\(-0.245\)} & \multirow{2}{*}{\(0.208\)} & \multirow{2}{*}{\(-0.245\)} \\  & & & & & & & & & \\ \hline \multirow{2}{*}{
\begin{tabular}{c} Tip diameter \\ Root diameter \\ \end{tabular} } & \multirow{2}{*}{\(d_{\text{a}}/\text{mm}\)} & \multirow{2}{*}{\(50.26\)} & \multirow{2}{*}{\(132.08\)} & \multirow{2}{*}{\(49.9\)} & \multirow{2}{*}{\(132\)} & \multirow{2}{*}{\(49.6\)} & \multirow{2}{*}{\(132.7\)} & \multirow{2}{*}{\(49.5\)} & \multirow{2}{*}{\(132.8\)} & \multirow{2}{*}{\(49.3\)} & \multirow{2}{*}{\(132.6\)} \\  & & & & & & & & & & \\ \hline \hline \end{tabular}
\end{table}
Table 7: Gearset parameters of variable pressure angle.  
Figure 7: The tooth contact flash temperature and scuffing safety factors. (**a**) Contact flash temperature; (**b**) scuffing safety factors.