Design and performance test of the omnidirectional leveling system for crawler work machine in hilly areas

Stability of body inclination, work quality and safety can be required during agricultural machinery operation in hilly and mountainous areas. In this study, an omnidirectional leveling system was designed for the crawler work machine. A structural scheme was also proposed with an articulated omnidirectional leveling system using a “three-layer frame”. The leveling hydraulic circuit was provided for the working principle of the omnidirectional leveling system. Secondly, a sensitivity analysis was conducted on the omnidirectional leveling performance, including the key structural parameters L_AE, L_BC, L_CD, L_HO, L_IJ, and L_IJ. The results showed that the displacement of the lateral leveling cylinder increased with the increase of L_AE and L_CD, whereas, decreased with the increase of L_BC. The displacement of the longitudinal leveling cylinder increased with the increase of L_JK and L_IJ, while decreasing with the increase of L_HO. The average thrust of the lateral leveling hydraulic cylinder decreased with the increase of L_AE and L_CD, but the leveling time increased. By contrast, the average thrust of the longitudinal leveling hydraulic cylinder increased with the increase of L_JK, but the leveling time decreased. A multi-objective genetic algorithm (GA) was designed to optimize the key structural parameters, taking the key structural parameters of the omnidirectional leveling system as the optimization variables, and the average thrust of the hydraulic cylinder and leveling time as the optimization objectives. Then, the overturning model was established for the omnidirectional leveling crawler work machine. The overturning stability of the whole machine was verified to analyze the static lateral limit overturning angle, static longitudinal limit overturning angle, and dynamic limit driving speed of the crawler work machine. The lateral and longitudinal limit overturning angles of the unleveled crawler work machine were 43.6°, and 60.7°, respectively, whereas, they were 46.7°, and 68.9°, respectively, after leveling. The lateral/longitudinal limit overturning angles after leveling increased by 7.1% and 13.5%, respectively. There was an increase in the maximum driving slope of the crawler work machine, compared with the non-leveling one. The limit driving speed of the crawler work machine to do circular motion on a flat road surface was 4.3 m/s, when the radius of circular motion was 2 m. Once the slope was 20°, the dynamic limit driving speeds were 2.9 and 3 m/s for the unleveled and omnidirectional leveling crawler work machine, respectively, which increased by 3.4%. Finally, an omnidirectional leveling performance test was conducted to verify the system effectiveness. The test results indicated that the lateral and longitudinal leveling times were 3.4 and 3.6 s, respectively, under static testing. By contrast, the maximum body inclination angle of the omnidirectional leveling crawler work machine decreased outstandingly and then quickly leveled under dynamic testing. The body inclination angle can be maintained within ±1.5° on the flat road and after leveling, which fully met the performance requirements of hilly and mountainous areas.