## 3 Case Study
### Calculation of Diesel Engine with Shock Absorbers in Impact Condition
#### 3.3.1 Main Bearing Lubrication of Diesel Engine with Shock Absorbers in Impact Condition  
Table 6 lists the value of the maximum of peak oil film pressure, the maximum of peak asperity contact pressure, and the minimum value of the minimum oil film thickness of the nine main bearings in the time range of 0-0.9 s under external impact conditions of the 16-cylinder V-type diesel engine. It can be seen from Table 6 that, according to the evaluation point of the AVL Company for the peak oil film pressure index, each main bearing meets the requirement that 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 (\(\mu\)m)** \\ \hline
1 & 66.984 & 5.773 & 4.083 \\
2 & 57.195 & 14.372 & 1.081 \\
3 & 55.74 & \(\Diamond\) & 4.759 \\
4 & 62.114 & \(8.273\times 10^{-2}\) & 2.883 \\
5 & 59.696 & \(4.693\times 10^{-3}\) & 3.43 \\
6 & 56.478 & \(1.97\times 10^{-4}\) & 3.818 \\
7 & 80.243 & 0.864 & 2.229 \\
8 & 59.023 & 1.808 & 1.971 \\
9 & 64.28 & 11.677 & 1.093 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Lubrication calculation results of diesel engine with shock absorbers in external shock conditions. Figure 11: Under normal conditions, the maximum crankshaft stress is 364 MPa at 0.177937 s, which is located at the eighth crank pin. peak oil film pressure is less than 100-150 MPa in external shock conditions. Evaluated by the peak asperity contact pressure index, each main bearing meets the requirement that the peak asperity contact pressure is less than 50 MPa in external shock conditions. Using the minimum oil film thickness index to evaluate, it can be found that there are two cases where the minimum oil film thickness does not meet the requirement (to be greater than 1.5 \(\upmu\)m), the 1.081 \(\upmu\)m of the second main bearing, and the 1.093 \(\upmu\)m of the ninth main bearing under impact conditions. Based on the values in the AVL company's evaluation point, the minimum oil film thickness values in the above two cases are not up to the requirements. According to the evaluation criteria in Reference [61], as shown in Figure 12, it is the minimum oil film thickness curve of the second main bearing in 0-0.9 s in impact conditions. Among them, at 0.03875 s, the minimum oil film thickness is 1.081 \(\upmu\)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). As shown in Figure 13, it is the minimum oil film thickness curve of the ninth main bearing in 0-0.9 s in the impact condition, where at 0.6936 s, the minimum oil film thickness is 1.093 \(\upmu\)m. It can be found from Figure 13 that when the minimum oil film thickness is less than 1.5 \(\upmu\)m, it lasts from 0.692798 s to 0.694385 s, which lasts for 0.001587 s and is much lower than 20% of the entire working cycle (that is 0.024 s). Therefore, according to the evaluation criteria in Reference [61], the second and ninth main bearings under impact conditions can work normally. In shock conditions, among the nine main bearings, the second and ninth main bearings have an oil film thickness less than 1.5 \(\upmu\)m and are in poor working conditions. Figure 12: The minimum oil film thickness curve of the second main bearing under impact condition. Figure 13: The minimum oil film thickness curve of the ninth main bearing under impact condition. Figure 14a is the distribution map of the average oil film pressure of the second main bearing in 0-0.12 s in shock conditions. It can be seen that the distribution position of the high oil film pressure area is concentrated near the center position of the lower bush at 180\({}^{\circ}\). The distribution area of the high oil film pressure is wide and is beneficial for the main journal working better in the lower bearing bush.