## 3 Case Study
### Calculation of Diesel Engine with Shock Absorbers in Normal Condition
#### 3.2.1 Main Bearing Lubrication of Diesel Engine with Shock Absorbers in Normal Condition
Among them, at 0.03875 s, the minimum oil film thickness is 1.065 \(\upmu\)m. It can be found from the calculation results that when the minimum oil film thickness is less than 1.5 \(\upmu\)m, it lasts from 0.0386706 s to 0.0388294 s, which lasts 0.0001588 s and is much lower than 20% of the entire working cycle (which is 0.024 s). Therefore, according to the evaluation criteria in Reference [61], the second main bearing under normal conditions can work normally. In normal conditions, among the nine main bearings, the second main bearing has the minimum oil film thickness and is in poor working condition. Figure 9a is the distribution map of the average oil film pressure of the second main bearing in 0-0.12 s in normal conditions. The x-axis represents the circumferential length of the inner surface of the main bearing bush, expressed in a circumferential angle of 0\({}^{\circ}\) to 360\({}^{\circ}\). Taking the vertical direction of the upper bearing bush as the starting position 0\({}^{\circ}\), the range of 0\({}^{\circ}\) to 90\({}^{\circ}\) and 270\({}^{\circ}\) to 360\({}^{\circ}\) is the upper bush, and the range of 90\({}^{\circ}\) to 270\({}^{\circ}\) is the lower bush. The y-axis represents the width of the bearing bush. The high oil film pressure distribution area on the bearing bush (the red, yellow, and green colors in Figure 9a) is concentrated near the \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Main Bearing**} & \multirow{2}{*}{**Peak Oil Film Pressure (MPa)**} & **Peak Asperity Contact** & **Minimum Oil Film** \\  & & **Pressure (MPa)** & **Thickness (\(\upmu\)m)** \\ \hline
1 & 61.166 & 5.044 \(\times\) 10\({}^{-7}\) & 4.2 \\
2 & 57.338 & 14.816 & 1.065 \\
3 & 53.517 & 0 & 4.693 \\
4 & 61.874 & 8.561 \(\times\) 10\({}^{-2}\) & 2.875 \\
5 & 56.926 & 1.469 \(\times\) 10\({}^{-3}\) & 3.593 \\
6 & 55.082 & 1.447 \(\times\) 10\({}^{-4}\) & 3.847 \\
7 & 63.852 & 9.141 \(\times\) 10\({}^{-3}\) & 3.322 \\
8 & 56.472 & 1.175 & 2.125 \\
9 & 54.5 & 4.58 & 1.527 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Lubrication calculation results of diesel engine in normal conditions. center of the lower bush at 180\({}^{\circ}\). It can also be seen that the distribution area of the high oil film pressure is wide, which is beneficial for the main journal to obtain a good oil film support in a wide angle of the lower bearing bush. Figure 9b shows the average asperity contact pressure distribution map of the second main bearing in 0-0.12 s in normal conditions. The x-axis represents the circumferential length of the bearing bush, and the y-axis represents the width of the bearing bush. The small green color zone in the Figure 9b represents the area where asperity contact occurs,  
Figure 8: The minimum oil film thickness curve of the second main bearing under normal conditions. Figure 9: Distribution map of the average oil film pressure and the average asperity contact pressure of the second main bearing in normal condition in 0 to 0.12 s. (**a**) Distribution map of the average oil film pressure of the second main bearing. (**b**) Distribution map of the average asperity contact pressure of the second main bearing. which only accounts for a very small proportion of the entire bearing bush area. The asperity contact position of the second main bearing is at the edge of the bearing shell near the 180\({}^{\circ}\) position of the lower bush. It can be seen from Figure 9 that the working state of the second main bearing is in safe condition. Integrating the evaluation points of the AVL company and reference [61], the peak oil film pressures of the nine main bearings are less than 100-150 MPa; the peak asperity contact pressures of the nine main bearings are less than 50 MPa. Although the minimum oil film thickness is lower than 1.5 \(\upmu\)m in one case, it still exceeds half of the sum of the roughness of the main journal and the main bearing, and the continuation time is much lower than 20% of the entire working cycle.