行间耕播机弹性可覆土镇压轮性能有限元仿真分析及试验

Finite element analysis of performance on elastic press wheel of row sowing plow machine for covering with soil and its experiment

为提高播种机的播种及镇压性能,解决播种作业中覆土后即时镇压的难题,结合橡胶类材料的变形理论与轮胎力学的研究基础,建立基于种沟沟型的理论模型,并设计出一种具有覆土功能的弹性镇压轮,镇压轮横截面由顶端连通的两个腔室组成,通过镇压轮侧缘与种沟接触产生的挤压力以同时实现覆土和镇压作业。利用ABAQUS软件对镇压轮进行有限元仿真分析,考察其覆土及镇压性能,通过有限元仿真分析证实该模型可行有效。通过与双圆盘覆土器和传统橡胶镇压轮的田间对比试验测得,该文所设计的弹性可覆土镇压轮作业后种子平均覆土深度为34 mm,变异系数为15.68%,镇压后种子上方距离地表5 cm的土壤紧实度为33.5 k Pa,变异系数为13.97%,应用双圆盘覆土器和传统橡胶镇压轮作业后种子平均覆土深度为35.3 mm,变异系数为17.51%,镇压后种子上方距离地表5 cm的土壤紧实度为26.5 k Pa,变异系数为15.32%,田间对比试验证实弹性可覆土镇压轮和双圆盘覆土器均可满足玉米播种作业对覆土深度的要求,但弹性可覆土镇压轮对土壤的镇压强度大于传统橡胶镇压轮,同时由覆土深度变异系数和镇压强度变异系数可以看出,弹性可覆土镇压轮在作业过程中的覆土深度稳定性和镇压强度稳定性均优于双圆盘覆土器和传统橡胶镇压轮。

The soil coverer and the press wheel are the main parts of the corn planter, and their performances are directly related to the growth and the output of the corn. The operation of soil compaction immediately after the soil covering can improve the soil moisture content and reduce soil evaporation. The application of elastic material in the press device also has a positive effect on solving the phenomenon of soil adhesion during the operation of seeding. In order to improve the performances of seeding and soil compaction of the corn planter under conservation tillage, an elastic press wheel with the function of covering soil was designed through the combination of the deformation theory of rubber material and the tire mechanics to solve soil covering and soil compaction simultaneously after corn planting. The force of contact unit during the operation process of press wheel was analyzed, a theoretical model of the press wheel was built up based on shape characteristics of furrows, and an elastic press wheel with a double-cavity structure was presented. Depending on the extrusion force caused by the contact between the lateral edge of press wheel and furrows realize the functions of soil covering and soil compaction simultaneously. The structural parameters of the elastic press wheel with the material of styrene butadiene rubber（SBR） was determined through the analysis of the theoretical mode as follows： the diameter, the width and the thickness of the press wheel were 500, 180 and 8 mm, respectively; the width of cross section of single-cavity of the press wheel was 70 mm, the cross section of single-cavity of the press wheel was composed with the curvature radius of the lateral edge of the press wheel respectively ρ1, ρ2 and ρ3, which were 30, 135 and 60 mm separately; the internal pressure of the press wheel was 500 Pa, and the external load during working was 475 N. The theoretical model was confirmed by the finite element simulation based on ABAQUS through analyzing the stress, strain and displacement of soil, contact area and vertical contact force. The simulation results showed that the elastic press wheel could realize these objectives of soil covering and soil compaction with less disturbance of the soil and better working stability. A field experiment was conducted to validate the theoretical model and the elastic press wheel＇s functions of soil covering and soil compaction, and the results showed that the soil covering depth of seed after compacting operation was 34 mm, the coefficient of variation of the seed＇s soil covering depth after compacting operation was 15.68%, the soil compactness was 33.54 KPa in the top 50 mm soil layer of the seed furrow, and the coefficient of variation was 13.97%, which indicated that the elastic press wheel would work effectively in the functions of soil covering and soil compaction. An additional comparative experiment was carried out between the elastic press wheel presented in the paper and the double-disc coverer and rubber press wheel widely used in precision planter, and the desired soil covering depth of seed was both obtained in the corn planting, but the corn planter equipped with elastic press wheel worked more effectively in the functions of soil compaction, and our result indicated that the corn planter equipped with elastic press wheel could also result in good performances on the stability of soil covering and soil compaction. Therefore, this method and the theoretical model are demonstrated to be practical and feasible, and the elastic press wheel presented in the paper can achieve the expected target of the soil covering and soil compaction with good performance of working stability.