## 6 Conclusions  
In this paper, a novel reconfiguration method was applied based on the connectivity between bus chassis modules, and was subsequently used to guide the reconfiguration process. The following conclusions were reached:  
Figure 16: (**a**) Bus chassis without a replaced front suspension frame module; (**b**) Bus chassis with a replaced front suspension frame module.  
Figure 15: (**a**) Connections between the front suspension frame module and the middle frame module (without reconfiguration); (**b**) Connections between the front suspension frame module and the middle frame module (with reconfiguration).  
The digital expression of the chassis module interface provides criteria for assessing the connectivity between modules. Connectivity between modules can be identified quickly and accurately through the parent and child relationship using the matrices of the digital expression for the interface. This greatly improves the efficiency of the modular design. At the same time, the connection criterion perlects the digital expression method of the module interface and improves the implementation of the digital expression method.
2. A reconfiguration method for modules, based on the digital expression of the module interface, was proposed and implemented for a real-world case bus chassis. This method is oriented to the connectivity between modules. It relies on the guidance of their reconfiguration of the module through the digital operation, step by step. This improves the versatility and interchangeability of the module. The method could be applied in the future to the reconfiguration of a product module with a similar truss structure.
3. In the actual process of product design, the module reconfiguration method based on the interface digital expression method can quickly determine whether the original module can be borrowed and applied through the numerical relationship of the interface matrix, and show module reconfiguration through the numerical relationship. The borrowing or reconfiguration of original modules greatly reduces the development cost of new modules and products and plays an important role in helping enterprises to implement platform and diversified products.
4. In addition, in this study, the specific connection methods for the interface in the manufacturing process, such as the welding process for the bus chassis frame and the welding strength, were not discussed, and further research is needed in the future.  
In this study, the reconfiguration and replacement of the front suspension frame module of a bus chassis was used as an example to illustrate the validity and effectiveness of the proposed method.  
The present study mainly describes the methodology and discusses the implementation of this method in a bus chassis based on homogeneous materials with various interfaces. However, the following factors need to be considered in the future:  
1. The strength and stiffness of bus chassis modules should be investigated to identify the effect of reconfiguration on mechanical behavior.
2. The connections between hybrid material linkages should be further investigated, as the welding parameters and the connection techniques may be different.
3. The implementation of this method in manufacturing requires a comprehensive study, including consideration of the assembly sequence and associated equipment.  
Conceptualization, Q.P. and M.R.; methodology, Q.P., X.M. and S.L.; validation, X.M. and S.L.; writing--original draft preparation, X.M. and S.L.; writing--review and editing, Q.P., M.R. and F.H.; supervision, M.R. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the National Natural Science Foundation of China under Grant 51505403; the 2011 Program of Bus and Specialty Vehicle Research & Design Collaborative Innovation Centre in Fujian Province under Grant 2016 AYF004; and the National High-End Expert Programme (HEEP) under Grant GDT20183600413.  
Not applicable.  
The authors declare no conflict of interest.