## 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  
According to the evaluation point of the AVL company for the high-grade bearing bush of civil vehicle engine, the peak oil film pressure in the bearing lubrication calculation results of the EXCITE software should be less than 100-150 MPa, the peak asperity contact pressure should be less than 50 MPa, and the minimum oil film thickness should be greater than 1.5 \(\mu\)m; for the bearing to work normally [60]. With the AVL evaluation method, the three indicators of peak oil film pressure, peak asperity contact pressure, and minimum oil film thickness are used as the basis for the main bearing lubrication evaluation. Table 5 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 9 main bearings in the time range of 0-0.9 s under normal conditions of a 16-cylinder V-type diesel engine. It can be seen from Table 5 that, according to the above evaluation point of the AVL Company for the peak oil film pressure index, each main bearing meets the requirement that the peak oil film pressure is less than 100-150 MPa in normal 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 normal conditions. Figure 7: The contrast between diesel engine calculation results (red curve) and test result (dark blue curve) on vertical acceleration of the diesel engine feet. Using the minimum oil film thickness index to evaluate, it can be found that there is a case where the minimum oil film thickness does not meet the requirement to be greater than 1.5 \(\upmu\)m, the 1.065 \(\upmu\)m of the second main bearing under normal condition. The second main bearing is in poor working condition. Based on the values in the AVL company's evaluation point, the minimum oil film thickness values in the above cases are not up to the recommended values. [PERSON] pointed out that, when calculating the bearing lubrication, the surface roughness of the main journal and the main bearing bush is taken according to the machining process parameters. It is the \"nominal\" roughness which reflects the surface conditions before running-in. In the actual environment, the influence of running-in on the surface roughness should be considered. After proper running-in, the surface roughness of the journal and the bearing bush is improved, and the minimum oil film thickness can be as small as the half of the sum of the surface roughness of the journal and the bearing bush, but the continuous angle cannot exceed 20% of the entire working cycle. This is a semi-dry friction state, and the bearing may still work normally [61]. The calculated surface roughness of the main journal of the 16-cylinder V-type diesel engine is 0.5 \(\upmu\)m, the surface roughness of the main bearing bush is 1 \(\upmu\)m, and the half of the sum is 0.75 \(\upmu\)m. It can be seen from Table 5 that the minimum oil film thickness of all main bearings exceeds 0.75 \(\upmu\)m. Next, the continuous angle of the relevant main bearing in a semi-dry friction state needs to investigate. The continuous time should not exceed 20% of the entire working cycle, which is 0.024 s in this research. As shown in Figure 8, it is the minimum oil film thickness curve of the second main bearing in 0-0.9 s in normal conditions. In Figure 8, the x-axis represents time in seconds, and the y-axis represents the minimum oil film thickness in microns. The EXCITE calculation algorithm is an iterative calculation, is affected by the initial value, and has a gradual convergence process. The result of the very high minimum oil film thickness at 0 s in Figure 8 is the numerical abnormalities caused by the initial value.