# Leveling Control of Hillside Tractor Body Based on Fuzzy Sliding Mode Variable Structure
###### Abstract  
To address the issues that arise when auto-leveling the vehicle body of a hillside tractor under complex working conditions, an auto-leveling control system was developed based on a newly developed hillside tractor and four-point body leveling mechanism. In this approach, leveling accuracy and stability were improved by adopting a sliding mode variable structure control algorithm based on fuzzy switching gain adjustment to achieve real-time dynamic auto-leveling control. To obtain curves of front and rear axle leveling displacement, speed, flow, pressure and body tilting angle during the leveling process, AMEsim/Simulink co-simulation was used to simulate and analyze the control system. The simulation results revealed that the tractor achieves a good leveling effect under complex working conditions in hilly and mountainous areas; the tractor can remain within a \(\pm 2^{\circ}\) tilting angle range during the leveling process and can return to \(0^{\circ}\) after leveling, demonstrating good dynamic stability. To further assess the algorithm, a model of the system was submitted to live-testing on a custom-built auto-leveling test bench. Comparison of the test and simulation results revealed a close agreement between the two, indicating that the self-leveling control system and control algorithm developed in this study have high leveling accuracies. The results reported in this paper could provide assistance with or in reference to obtaining solutions to the problems of tractor body leveling in hilly and mountainous areas. h 2023 13 606 1 2023 1 2  
have the ability to work safely in hilly and mountainous areas with small slopes. The main leveling methods include reducing the center of gravity, manual leveling and automatic leveling. The hillside tractors with automatic leveling have the best working performance. Automatic leveling can maintain the level of the body in real time, and improve the stability of hillside tractors during operation. However, the rapidity, stability and accuracy of leveling continues to require improvement [4]. Therefore, hillside tractors require a fast acting and high-precision self-leveling system to adjust vehicle body posture in a timely and effective manner to ensure that the vehicle level remains within an allowable range [5]. In recent years, vehicle body self-leveling systems have begun to be developed. [PERSON] et al. designed a height-adjustable suspension mechanism that could level a chassis during vehicle movement to improve the obstacle-surmounting ability of the overall vehicle [6]; however, the system had a low leveling accuracy, which limited its application in tractors operating in hilly regions. In 2014, [PERSON] and [PERSON] jointly developed a two-degree-of-freedom (2 DOF) controller for combine harvester header height control based on the optimization of the control system. Simulation and test results revealed that a 2 DOF controller mounted on a harvester header outperformed an independent feedback controller in terms of leveling, but that the leveling actuator had a delay, which lead to limitations in the application of the feedback control of header height [7]. Northwest Agriculture and Forestry University developed a hillside crawler tractor with an automatic leveling function; however, random noise generated by body vibration resulted in a less-than-ideal filtering effect, resulting in a body automatic leveling accuracy of only 40% [8]. [PERSON] et al. of Jilin Agricultural Machinery Research Institute studied a hillside tractor leveling system whose dynamic stability needed to be improved [9]. Shanghai Jiaotong University and Shandong Wuzheng Group jointly developed a four-wheel drive tractor with leveling functionality, in which a swing mechanism was installed between the rear drive axle and wheels to enable the horizontal leveling of the vehicle body through the height difference generated by the side-to-side swing of the mechanism; however, the actual operational effect of this assembly awaits verification [10].