Abstract:

[Significance] Hilly and mountainous areas are characterized by complex topography, rugged roads, steep and narrow slopes, and fragmented, discontinuous farmland plots, making it difficult for traditional agricultural machinery to adapt to such conditions. These terrain-related limitations have become a major bottleneck restricting the development of agricultural mechanization and modernization in such areas. Therefore, the research, development, and promotion of agricultural machinery and equipment suitable for hilly and mountainous areas are urgently needed. As a key technology for improving the terrain adaptability and operation quality of agricultural machinery, chassis leveling has become a research focus in the field of agricultural machinery equipment. [Progress] A comprehensive review of research on evaluation indicators, leveling devices, and control systems for agricultural machinery chassis leveling is presented. This review focuses on summarizing the categories and applicable scopes of static and dynamic evaluation indicators and on analyzing the principles, performance characteristics, and applicable scenarios of two types of leveling mechanisms, namely, three-point support and four-point support. In this review, multisource information fusion schemes, such as attitude sensing, displacement measurement, load monitoring and terrain perception are summarized; the technical characteristics of chassis leveling control strategies, including the angle error control method and the position error control method, are expounded; and the evolutionary path of intelligent algorithms from traditional proportional-integral-derivative (PID) control to fuzzy control, sliding mode control, and neural networks is reviewed. Evaluation indicators, such as roll angle, pitch angle, leveling speed, mean tilt angle, and standard deviation of tilt angle, can provide a relatively comprehensive assessment of the operational performance of chassis leveling systems. Representative three-point support leveling devices include mechanisms based on lateral leveling, hydraulic differential-height adjustment, double guide columns, double parallel four-bar linkages, left-right eccentric wheel swing, and left-right transmission rocker arms. Representative four-point support leveling devices include adaptive balanced rocker suspension, four-point guide-column lifting mechanisms, Y-shaped adjustable suspension, four-hydraulic-cylinder leveling structures, hinged multi-link mechanisms, and articulated three-layer frames. These devices can determine the required compensation according to the inclination state of the chassis and then achieve body attitude adjustment through mechanical structures, hydraulic systems, and other actuating devices. By dynamically adjusting the vehicle body and operating components, they can effectively adjust the center of gravity of agricultural machinery and improve operational stability on sloping terrain. In addition, when integrated with high-precision sensors, intelligent control strategies, and efficient control algorithms, chassis leveling systems can achieve adaptive leveling under complex terrain conditions involving steep and narrow slopes. [Conclusions and Prospects] Existing chassis leveling technologies for agricultural machinery can basically satisfy the leveling requirements of large-scale machinery operating on broad and relatively gentle farmland and have already seen preliminary application. However, in the complex terrain of hilly and mountainous areas, the following limitations still exist: Chassis leveling models and performance evaluation standards have not yet been fully established; the reliability and general applicability of existing leveling devices remain insufficient; the degree of integration of chassis leveling control systems is still limited, and the intelligence and adaptability of control algorithms require further improvement; the false leg phenomenon remains difficult to identify, and engineering verification, practical promotion, and field application remain inadequate. In view of the current research status, existing problems, and future development demands, this paper proposes several priority directions for future study aimed at improving the adaptability of agricultural machinery to hilly and mountainous terrain. These include constructing leveling mechanisms and evaluation systems closely integrated with agronomic practices; developing highly reliable and universal chassis leveling devices; developing low-cost engineering verification and leveling technologies capable of suppressing the false-leg phenomenon. This review is expected to provide reference data for the research and development of advanced agricultural machinery equipment applicable to hilly and mountainous areas of China.

Key words: agricultural machinery chassis, complex terrain, leveling devices, control