高含水率玉米临界损伤机理与低损收获优化OA

[Objective]During the harvest period of summer maize in the Huang-Huai-Hai region,the moisture content of the ker-nels is generally high(≥28%).These kernels exhibit biomechanical properties characterized by a fragile pericarp,a soft endo-sperm,and poor impact resistance.Existing mechanically driven harvesters struggle to achieve continuous and precise adjust-ment of the operating speed.This limitation often leads to severe fluctuations in the feeding rate,sudden load changes,and clogging in the threshing cylinder,ultimately resulting in high grain breakage and impurity rates.To overcome the bottleneck of direct mechanical harvesting for high-moisture maize kernels,there is an urgent need to develop novel harvesting equipment and key technologies.[Methods]In this study,a longitudinal axial-flow flexible maize kernel harvester based on a hydrostatic trans-mission(HST)system was designed.Based on the traction dynamics model of the entire machine,a closed HST system was constructed.By incorporating Hertz contact theory,an impact dynamics model for high-moisture maize kernels was estab-lished.Furthermore,a low-speed combined flexible threshing cylinder with a diameter of 600 mm and an accompanying vari-able-clearance concave device were developed.Taking the cylinder speed,concave clearance,and operating speed as experi-mental factors,and the grain breakage rate and impurity rate as response indicators,a three-factor,three-level field experiment was conducted.Design-Expert software was utilized for multivariate regression analysis and parameter optimization of the ex-perimental results.[Results]Simulation analysis indicated that the HST system,utilizing a variable-displacement pump and fixed-displacement motor,achieved stepless and precise regulation of the operating speed within the range of 0～8 km/h.This capability significantly reduced feeding fluctuations and provided steady-state material flow conditions for the stable operation of the threshing system.The critical breakage linear velocity threshold for the kernels was determined to be 18 m/s,establishing a low-loss linear velocity range of 15～17 m/s for the threshing elements.Field experiment results demonstrated that the cylinder speed had a highly significant effect on the grain breakage rate(P<0.01),and the concave clearance had a highly significant ef-fect on the impurity rate(P<0.01),with a significant interaction between the two factors.The optimal parameter combination was identified as follows:a cylinder speed of 480 r/min,a concave clearance of 43 mm,and an operating speed of 4.2 km/h.Under these working conditions,the grain breakage rate was 3.28%and the impurity rate was 1.75%,with relative errors be-tween the model-predicted and experimental values being less than 5%.[Conclusion]All performance indicators of the harvest-er comply with the national standard(GB/T 21962-2020)and outperform those reported in existing studies.This research pro-vided a theoretical basis and technical support for the development and promotion of direct kernel harvesting equipment for high-moisture maize in the Huang-Huai-Hai region.