## 1 Introduction  
China is a large agricultural country. According to the reference [1] statistics, China's agricultural planting area reached 1.167 \(\times\) 10\({}^{8}\) hectares in 2020. Tractors are one of the critical equipment types in the process of crop planting, harvesting, spraying, etc. The number of tractors held and sold gradually increases with the increase of the planting area. With the increasing agricultural area circulation in China, more and more small farms have been established. The demand for large and medium horsepower tractors is increasing. For example, China's production of large and medium horsepower tractors was 3.46 \(\times\) 10\({}^{5}\) units, an increase of 23% compared to the previous year [1]. Additionally, the Chinese government formulated a special law to promote agricultural mechanization.  
In China, the hydraulic linkage is widely used in large and medium-sized tractors, connected with rotary tiller, riding machine, seeder, and other agricultural machinery through the lower link [2; 3; 4; 5]. The performance of hydraulic linkage directly affects the working quality and efficiency of the tractor in the field, such as depth of the rotary blade,sowing depth, etc. [4; 6; 7]. With the promotion of precision agriculture, the loading-lifting performance of the hydraulic linkage also affects the operation accuracy of agricultural machinery. Hence, it is required to test the load-bearing and lifting performance of the hydraulic linkage during the production process of the tractor [8; 9; 10]. Many methods have been developed to test the loading and lifting performance of tractor hydraulic linkages, such as the weight loading method, orifice loading method, and hydraulic loading method [11; 12; 13]. As the lower link in the hydraulic linkage system can swing horizontally in the horizontal direction, the existing test method requires an artificial connection between the test mechanism and the hydraulic linkage. This will reduce the test efficiency, precision, and safety factor, and easily cause casualties and other shortcomings [11; 14]. Additionally, these methods cannot achieve continuous loading of the hydraulic linkage. The research team investigated some tractor manufacturers (for example, YtG Group Corporation, which has a complete tractor product series in China), and found that it takes 10 to 15 min to test the hydraulic linkage. Meanwhile, these methods also need to dig trenches on the test site, which further decreases the safety of the tractor test. In recent years, with the introduction of \"Made in China 2025\" and some key science and technology plans in China, intelligent agricultural machinery equipment is one of the key development areas in these plans [15]. Therefore, there is an urgent need for a new method in the engineering field to actively connect the tractor lower link to improve the test efficiency and safety of the tractor hydraulic linkage.  
In order to realize the intelligent test of the hydraulic linkage of the tractor before leaving the factory, the study proposed an automatic test device for the load-bearing and lifting performance of the hydraulic linkage. The designed tractor hydraulic linkage hook test device was analyzed from the kinematics and mechanics. Based on the analysis results, the automatic test device for load-bearing and lifting performance of the hydraulic linkage was optimized and developed. Additionally, a test of the hooking, loading, and lifting performance was carried out. The research can provide a reference for the tractor to develop a hydraulic linkage hooking test device, realize the unmanned hooking during the test process. Additionally, the safety and efficiency of the tractor hydraulic linkage test are improved, and the detection cost is reduced. The present study can provide a reference for the design of lifting devices of other types of tractors.