## 4 Orthogonal Experiment Analysis
### Model Validation and Orthogonal Experiment Analysis
An orthogonal experimental design reduces the number of experiments that would otherwise be conducted from \(3^{6}\) to \(27\), thereby improving the efficiency of the study. Table 4 lists the influencing factors of the orthogonal experiment, and 6 factors with three levels were considered. Table 5 presents the simulation results of the orthogonal experiment. Figure 10 illustrates the comparison of the influence of each factor and its level on the evaluation indices based on the simulation results of the orthogonal method. Figure 9: (a) Oil film pressure distribution in left piston pin boss. (b) Oil film pressure distribution in small-end bushing. (c) Oil film pressure distribution in right piston pin boss. A range analysis method was used to assess the size of the effect of each factor on the evaluation indices, and the range was calculated using Equation (14). \[R=\max\{h_{1},h_{2},h_{3}\}-\min\{h_{1},h_{2},h_{3}\} \tag{14}\]  
where \(\max\{h_{1},h_{2},h_{3}\}\) is the maximum value of the average MOFT, average friction power, and MOFP in the corresponding graph, and \(\min\{h_{1},h_{2},h_{3}\}\) is the minimum value of the average MOFT, average friction power, and MOFP in the corresponding graph. The larger the range, the greater the influence of the factor on the evaluation index. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Factors** & **Level 1** & **Level 2** & **Level 3** \\ \hline Oil temperature A/\({}^{\circ}\)C & 100 & 80 & 60 \\ Oil supply pressure B/bar & 12 & 8 & 4 \\ Bushing roughness C/\(\upmu\)m & 1 & 0.6 & 0.2 \\ Piston pin roughness D/\(\upmu\)m & 1 & 0.6 & 0.2 \\ Bearing clearance E/\(\upmu\)m & 20 & 15 & 10 \\ Rotational speed F/(r\(\cdot\)min\({}^{-1}\)) & 500 & 1000 & 1500 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Orthogonal experiment table. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline \multirow{2}{*}{**NO. **} & \multicolumn{6}{c}{**Factor Level**} & \multirow{2}{*}{**MOFT/\(\upmu\)m**} & \multicolumn{2}{c}{**Friction**} \\  & **A** & **B** & **C** & **D** & **E** & **F** & **Power/W** & **MOFP/MPa** \\ \hline
1 & 1 & 1 & 1 & 1 & 1 & 1 & 0.23 & 179.19 & 399.27 \\
2 & 1 & 1 & 1 & 1 & 2 & 2 & 0.34 & 78  
This comparison indicates that the factors that influence MOFT from weak to strong are E (clearance), F (engine speed), C (bushing surface roughness), A (lubricant temperature), D (piston pin surface roughness), and B (oil supply pressure). From weak to strong, friction power is influenced by E (clearance), D (piston pin surface roughness), C (bushing surface roughness), A (lubricant temperature), F (engine speed), and B (oil supply pressure). The factors that influence the MOFP from weak to strong are E (clearance), C (bushing surface roughness), F (engine speed), B (oil supply pressure), A (lubricant temperature), and D (piston-pin surface roughness). According to the above conclusions, to increase the analysis efficiency, clearance, bushing roughness, and engine speed were chosen as the influencing factors, and a suitable range of variables was chosen based on the engineering reality to further analyze the influence law of the main influencing factors on lubrication performance.