# Leveling Control of Hillside Tractor Body Based on Fuzzy Sliding Mode Variable Structure
## 6 Conclusions  
This paper presented a vehicle body auto-leveling control system for hillside tractors and presented the results of simulation and testing using a custom-built auto-leveling test bench. The proposed fuzzy sliding mode variable structure control was simulated using software and tested using the auto-leveling system. Our primary conclusions are as follows:  
1. The proposed vehicle body leveling control system, which employs a fuzzy sliding mode variable structure control algorithm designed and built according to the functional requirements of the leveling system, is capable of real-time adjustment of controller parameters, guaranteeing a vehicle leveling effect.
2. Data curves produced by measurements of front and rear axle leveling displacement, speed, flow, pressure, and body tilting angle during the tractor leveling process obtained through AMEsim/Simulink simulation reveal that the tractor has a good leveling effect under complex working conditions in hilly and mountainous areas.  
Figure 16: Comparison of field pavement spectrum excitation test and simulation data. (**a**) Front axle displacement speed. (**b**) Rear axle displacement speed. (**c**) Vehicle body real-time tilting.  
The tilting angle of the tractor is kept within a \(\pm 2^{\circ}\) range during the leveling process and can return to \(0^{\circ}\) after leveling, indicating good dynamic stability.
3. The proposed control method was used to carry out functional tests on an auto-leveling test bench, with the results confirming the correctness, accuracy, and reliability of the vehicle body auto-leveling control system and fuzzy sliding mode variable structure control algorithm. The test-confirmed results obtained in this study provide a theoretical basis for the design of auto-leveling control systems for hillside tractors.
4. The tractor body leveling control of the sliding mode variable structure control algorithm, based on fuzzy switching gain adjustment, still exhibits some chattering and a singularity under an excitation signal with a large variation amplitude. Therefore, the control parameters can be optimized to further improve the body leveling response speed and control accuracy. Owing to the incomplete consideration of the influencing factors and parameters during the modeling process, a certain error is presented in the actual condition of the tractor leveling. If the actual model of the tractor can be used for the simulation in the follow-up study, the error of the electromechanical-hydraulic joint simulation can be reduced further.  
Conceptualization, H.P. and W.M.; methodology, H.P. and Z.Y.; software, H.P. and Z.W.; validation, H.P.; formal analysis, H.P. and Z.Y.; investigation, H.P. and Z.W.; resources, W.M.; data curation, Z.Y.; writing--original draft preparation, H.P.; writing--review and editing, W.M. and Z.Y.; visualization, H.P.; supervision, Z.Y.; project administration, Z.Y.; funding acquisition, W.M. All authors have read and agreed to the published version of the manuscript.  
Not applicable.  
The data presented in the study are available on request from the corresponding author.  
The authors would also like to thank the anonymous reviewers for their constructive comments.  
The authors declare that they have no conflict of interest.