Design and physical model experiment of body leveling system for roller tractor in hilly and mountainous region

Abstract: Hilly tractor is difficult to maintain level, and easy to tip over in complex working conditions. In order to solve this problem, promote the rapid development of agricultural mechanization and improve the farmers' production conditions in hilly areas of China, a new leveling system of tractor body is proposed relying on "intelligent agricultural machinery and equipment", the national key research and development plan. Structural design, hydraulic system design, kinematics and dynamics simulation were included in this paper. The leveling system was mainly composed of central transmission assembly, leveling cylinder assembly, steering knuckle assembly, wheel transmission assembly and tyre. The power of the engine was transferred to the cylinder assembly through the central transmission assembly, then the power was transferred to a pair of bevel gear pairs in the steering knuckle assembly by leveling the cylinder, and finally the power was transferred to the wheels through the wheel transmission assembly. The hydraulic system was mainly composed of a gear oil pump, a filter, 4 electromagnetic proportional selector valves and 4 leveling cylinders. To achieve the leveling of the body, it needs to adjust the input flow of the cylinder by controlling the input current of the electromagnetic proportional valve. Three-dimensional (3D) model was built by CATIA (computer aided three-dimensional interactive application) according to vehicle design parameters. A multi-body dynamics model of a hilly tractor equipped with the leveling system was established using the digital virtual prototype technology, i.e. the automatic dynamic analysis of mechanical systems (ADAMS), to simulate the kinematics and dynamics. The changing curves between attitude angles (i.e. pitch angle and roll angle) of the vehicle body and displacement, velocity of the leveling hydraulic cylinder rod were analyzed through kinematics simulation. The result shows that the leveling mechanism can achieve leveling movement and there is no interference between working parts. The attitude angle of vehicle body changes within 5°, indicating that the leveling system has good stability performance. The key data such as dynamic loading and torque of each cylinder and other key parts were analyzed through dynamics simulation. For example, the lateral bending moment of the front axle cylinder rod is gradually reduced from 449.3 to 327.7 N·m, and the lateral bending moment of the rear axle cylinder rod is gradually reduced from 1 259.2 to 814.3 N·m. The strength and stiffness requirements of the components can be satisfied after checking and calculating the endurance strength, which proves the correctness of the designed leveling mechanism of the hilly tractor body. A tractor body test bench including a model vehicle equipped with the leveling system was built to examine the leveling system. Through the comparative analysis of experiment and simulation, the maximum error is 15%, and the maximum average error is less than 10.20%, so the accuracy of the simulation method of tractor body leveling system is verified, which provides an effective theoretical support for the design of the tractor body leveling system.