## 3 4F Integration Technology
### Fmeca-FHA Integration Model  
Due to the existence of safety failure modes and reliability failure modes in diesel engine systems, the previous fault input of this method is the FMECA-FHA analysis result at the system level. The FMECA describes the structure and function of the whole system. In addition, the FMECA can identify system-level reliability failure modes and evaluate the criticality of each failure mode. The failure modes are quantified by a risk priority number (RPN). In Formula (16), the RPN [48] is the product of three indicators (usually rated from 1 to 10): (1) severity \(S\), (2) the possibility of occurrence \(O\), and (3) fault detection \(D\). From a comparison of the PRN of each failure mode, the key failure modes are obtained. Therefore, this can be used as the basis for a system-level reliability evaluation of diesel engines.  
\[RPN=S\cdot O\cdot D. \tag{16}\]  
On the basis of the FMECA, the FHA of the FMECA-FHA model uses the rank comparability method [49] to rank the hazard degree of the diesel engine safety failure modes. According to MIL-STD-1180 (the US Army ground vehicle safety standard) [50], the following parameters are selected: \(v_{1}\) is the injury degree caused by the failure, \(v_{2}\) is the economic loss caused by the failure, and \(v_{3}\) is the maintenance cost caused by the failure. The frequency of failure \(v_{4}\) is taken as the index of the safety assessment. The score of each index is determined according to the scores from experts and the weight of the score is distributed according to the experience of the experts. The rank is calculated according to \(n\) evaluation indices (\(V_{i}=\{v_{1},v_{2},\ldots,v_{n}\}\)), from which the \(R_{i}\) of M failure modes is obtained. The \(RSR\) of each failure mode is calculated using Equation (17) and the cumulative frequency \(probit_{i}\) of each failure mode can be obtained. Finally, the ranking value \(\text{WRSR}_{i}\) of the hazard degree of the failure modes is calculated using Equation (18).  
\[RSR_{i}=\frac{1}{mn}\sum_{j=1}^{m}\ R_{ij} \tag{17}\]  
\[\text{WRSR}_{i}\text{= a+b}\times\text{Probit}_{i}, \tag{18}\]  
where a and b are constants.  
Finally, according to the analysis results of the FMECA-FHA integrated model, the most severe fault mode is used as the input for the FRACAS to judge the worst fault mode. The FMECA-FHA integrated model can simultaneously consider the reliability and safety problems in the primary stages of diesel engine design, making the system-level fault analysis of diesel engines more comprehensive. As shown in the schematic diagram of the FMECA-FHA model in Figure 9, the FHA carries out the safety analysis and modeling at the system/function level, while the FMECA carries out the reliability analysis and modeling at the system/function level. Finally, according to the severity principle, the severity of the fault mode is redivided. The failure modes of severity I and II are used as the input of the FIF.  
The fault cause analysis module in the FRACAS uses the FMECA-FHA model to replace the causes of the faults. The purpose of the FTA is to express the components within each subsystem graphically and quantitatively, while the FMECA conducts a fault cause analysis at the physical level for key components according to the quantitative results of the FTA. Section 2 proposed that an RDFTA can be applied as an alternative to an FTA in order to overcome the disadvantage of the maintenance rate not being considered in the analysis of repairable systems by a traditional dynamic FTA, thus bringing the calculation results of the RDFTA more in line with the actual situations of repairable systems. In the next section, the key findings of an application of 4F integration technology to the diesel engine reliability analysis method are introduced.