## 5 Case Analysis
### EPS Performance Evaluation under Multi-Level System
#### 5.1.2 Combined Weight of Each Factor in EPS System  
In order to consult the relevant structural design data and operation parameters, nine industry experts, designers, and maintenance personnel were hired. First, authoritative experts were invited to judge the importance of each indicator according to the index scaling criteria outlined in Table 1, and the subjective weight of each indicator was calculated according to Equations (1)-(4). Then, the experts scored the actual situation of each indicator of the project, and the objective weight was calculated according to Equations (7) and (8).  
According to Equations (11) and (12), the linear combination coefficients \(\alpha_{1}\) = 0.524 and \(\alpha_{2}\) = 0.476 of the factor layers, as well as \(\alpha_{1}\) = 0.308 and \(\alpha_{2}\) = 0.692 of the state layer, are obtained. Then, the combination weight value of each index could be obtained, as shown in Tables 3 and 4.  
As can be seen from Tables 3 and 4, steering portability (\(A\)) and steering returnability (\(B\)) have the most obvious influence on the working performance of the EPS, followed by the steering wheel middle area performance (\(C\)); in addition, the assisting characteristic (\(E\)) is smaller than that of the steering wheel vibration (\(D\)).  
Steering portability (\(A\)) is a key index. On the one hand, good steering portability can make the vehicle easier to drive and provide a better handling performance, which is very important for daily driving and emergency handling. It can help drivers cope better with emergencies and improve the safety of driving. On the other hand, it can also reduce the driver's driving fatigue and provide a more pleasant driving experience. At the same time, it can also improve the brand image of automobile manufacturers and increase the trust of consumers. In the subordinate hierarchy of \(A\), vehicle speed (\(A_{4}\)) has the greatest degree of influence, and the other four factors have the same degree of influence; as such, this parameter should be paid more attention to when evaluating the working performance of the EPS.  
Steering returnability (\(B\)) refers to the ability of the vehicle to automatically return to the straight-line driving state after steering control, which is also important for the handling, stability, and safety of the vehicle. A good steering performance ensures that the driver can easily restore the vehicle to a straight line after steering, reducing the risk of driver fatigue and difficult handling. Usually, the steering alignment performance of vehicles can be improved by adjusting the settings of the suspension system, adjusting the parameters of the steering system, selecting the appropriate tire type and specifications, and equipping the system with an electronic auxiliary system. Moreover, the regular maintenance of the steering system and suspension system of vehicles is the key to maintaining the alignment performance. In the subordinate hierarchy of B, a slight rotation at high speeds (\(B_{3}\)) and slow normal steering (\(B_{4}\)) are more obvious, and these two performance indicators should therefore be paid more attention to.  
Similarly, lateral acceleration (\(C_{1}\)) is associated with the steering wheel middle area performance (\(C\)), the mechanical mechanism design (\(E_{2}\)) is associated with the assisting characteristic (\(E\)), and the roughness of the road surface (\(D_{2}\)) is associated with the steering wheel vibration (\(D\)); these are also important performance indicators that need more attention.