Abstract
In order to address the issues of large inclination angles and poor pass ability encountered by small-scale combine harvesters operating in hilly regions，a design and experimental study were conducted on an automatic lifting hydraulic system for the combine's chassis. This research developed the overall structure of the automatic lifting hydraulic system for the chassis，designed and selected key components such as hydraulic cylinders with built-in displacement sensors and directional proportional valves，and proposed methods for leveling and lifting the chassis by extending or retracting the hydraulic cylinders based on the transverse inclination angle. The study employed two leveling modes：automatic and manual，to level the chassis. The hydraulic system was simulated using AMEsim software，revealing stable pressure and flow within the hydraulic cylinders during direction reversing，along with smooth displacement velocity. A leveling control strategy centered on a PLC controller and PID control method was designed，which adjusted the length of the hydraulic cylinders to regulate the chassis's attitude and to conduct a static leveling experiment. Results indicated the proportional directional valve，when adjusted to a position between 20% and 45%，it can effectively regulate the velocity of both the extension and retraction movements of the hydraulic cylinders. The adjustment time increased with larger inclination angles，but the overall adjustment error remained below 0.5° within an inclination range of 7.7°，which can meet the requirements for transverse leveling of the combine harvester's chassis. This research introduced a hydraulic system and control method to realize leveling based on the transverse angle，providing a reference for the design of the chassis leveling hydraulic system for small-scale combine harvesters.
