# Reliability Optimization Design of Diesel Engine System Based on the GO Method
## 1 Introduction  
The engine is the key component of the vehicle system, whose reliability level directly affects the reliability level of the vehicle system. In recent years, domestic and foreign scholars have carried out reliability research on engine parts, management methods, reliability modeling, design and evaluation, and index distribution. [PERSON] et al. [1] proposed an innovative fuel pump design based on geared hypocycloid transmission and analyzed its strength to improve the reliability of the engine. [PERSON] et al. [2] proposed a comprehensive reliability analysis and management method for diesel engines based on 4F integration technology. [PERSON] et al. [3] summarized the idea of engine reliability design analysis. [PERSON] et al. [4] evaluated the reliability of fuel cell engines using the point estimation method of uniformly minimum variance unbiased estimation and the interval estimation method of the shortest confidence interval. Focusing on the main engine and typical components of the fuel flow regulator, [PERSON] et al. [5] conducted reliability modeling and allocation of failure rate index by combining fuzzy comprehensive evaluation theory and fuzzy reasoning method. However, there are few research studies on the reliability modeling and optimization design of the whole engine system, and with the higher requirements for vehicle reliability design, increasingly more attention is being paid to engine reliability design. Moreover, the system reliability optimization design considering the trade-off between reliability and resources has become an essential topic in diesel reliability engineering. At present, the main challenges facing the reliability optimization design of engine systems are described as follows. (1) How does the reliability optimization design model reflect the real structure, operating principle, and functional composition of system (the existing research focuses mainly on the single function of system, without the function differences of system)? (2) How can the system reliability index be assigned directly to the design unit following the complex characteristics of system? (3) The margin design should be adopted for the complex correlation of the system. Thus, how to providea reasonable means to distribute margin requires consideration. Additionally, system reliability allocation and reliability modeling and analysis are complementary to each other, and this should be repeated in each stage of design. Hence, the reliability models and analysis methods highly related to the system and the reliability allocation methods applicable to different design requirements can not only integrate the tendencies of different methods but also reduce the low-cycle times of the process so as to achieve twice the result with half the effort. At present, the common reliability modeling and analysis methods of diesel engine systems comprise reliability block diagram (RBD) [6], fault tree [7], FMECA [8], and the GO method [9]. RBD is a top-down reliability analysis method representing the reliability function relationship between systems and components. However, its model has limited ability to demonstrate the system's functional structure, working principle, and system characteristics, such as feedback, multi-function, multi-state, and complex correlation. FTA analyzes the cause of the failure step by step through the specific events (unexpected events) of the system from the perspective of the failure, establishes the fault tree model, finds the weak link of the system according to the fault tree model, and conducts a qualitative and quantitative evaluation. Nonetheless, its modeling is significantly influenced by human subjective experience, and it is difficult to indicate the functional structure, working principle, and system characteristics of the system using the fault tree. FMECA is a qualitative reliability analysis method.