【作者】 祁兵；

【导师】 张东兴；

【作者基本信息】 中国农业大学 ， 农业机械化工程， 2014， 博士

【摘要】 随着种子质量和裁培技术的提升,我国当前农业生产对精量播种产生了迫切的需求。气力式排种器由于种子适应性好、适应高速作业等优势,已成为精量排种器的发展方向。目前气力式排种器以单行排种为主,排种器无法与仿形机构分离,具有振动大、布局困难、调整繁琐等问题；气力式排种器充种性能受种群移动阻力影响较大,对于玉米等流动性差的种子充种效果不佳。针对这些问题,本文分析了充种区种群合理空间状态,提出了扰种式气流结构,结合集中排种与气送投种的特点,研制了一种中央集排气送式精量排种器。该排种器改变了气流进入种群的方向,利用气流扰动种群,气流由充种区下方进入,使充种区处于膨松状态,种子流动性好,充种性能可靠；利用正压滚筒充种,可实现一器多行作业,简化了播种机整体结构；利用气流输送远距离投种,实现了排种器与仿形机构的分离,振动干扰小,高速作业时优势尤为明显。论文建立了传统气流结构与扰种式气流结构的力学模型,研究了种群状态对充种性能的影响机理。基于流体力学绕流阻力原理,建立了正压径向充种过程的力学模型,得出了影响压附性能的主要因素及影响规律。提出占据面积比例并对清种过程进行分析,确定了影响清种的各项参数及相互关系。在理论分析基础上,对排种器关键部件进行结构设计,确定了主要结构参数。基于计算流体力学软件Fluent对排种器内部流场特性进行了数值模拟,考察了中央集排气送式排种器结构对内部流场分布的影响。分析了不同型孔数目、型孔直径下的充种区流场特性,结合理论分析,确定了合理的型孔数目。对排种器整体流场分布规律进行了仿真分析,计算结果显示不同排种行间的流场分布规律差异不大,充种区具有较高的压力及气流速度,符合设计要求。对试制的中央集排气送式精量排种器进行了台架试验。对4～5.5mm范围内的4种不同孔径进行了压力、转速试验,试验表明,低速作业时4.5mm孔径排种效果最好,所需压力略高,但高速作业漏播严重；5.5mm孔径充种性能及高速作业适应性最好,所需压力最低,但低速作业重播较多。考虑玉米播种对漏播容忍度低,确定孔径为5.5mm。为解决5.5mm孔径低速作业的重播问题,对清种装置进行了优化试验,确定了合理的清种距离为0.25mm。对优化后的排种器进行转速试验,优化后与优化前相比合格指数在低速段有大幅提高,高速作业时变化不大。与勺轮式、气吹式、气吸式排种器进行了排种性能对比,在4～12km/h的作业速度内中央集排气送式排种器平均合格指数最高,充种性能优越,能够较好的适应高速作业。更多还原

【Abstract】 With the fast development of seed quality and cultivation techniques, precision planting becomes a problem urgently to be solved in China. Pneumatic precision metering device, which is flexible to seed shape and adapts to high-speed operation, has been the development trend. As affording only one row’s sowing and cannot being separated from feeler mechanism, conventional pneumatic precision metering device has many shortcomings such as excessive vibration, layout difficulty and tedious manual adjustment. Besides, pneumatic metering device has poor performance when planting corn seeds which have hard fluidity. To solve these problems, the reasonable state of corn seeds were analyzed, a new airflow structure which could effectively reduce the moving resistances was presented. Based on the airflow structure, a centralized pneumatic metering device (CP) was designed.By the airflow structure of CP, the direction of the airflow is changed to blow the seeds in "boiling" movement which can reduce the seed-filling resistances, getting good seed-filling performance. CP makes a seeder more concise in structure as it distributes seeds to several sowing rows through a centre drum and a positive pressure system. A pneumatic conveying system is applied to throwing seeds, which enables the separation of the metering device from the placement system and reduces the vibration of the metering device obviously.In this paper, mechanical model of the new air flow structure was built to analyze the influence mechanism of seeds state to seed-filling. Main influence factors and their influence rules were acquired through the analysis of filling process in radial direction of the drum under positive pressure. Occupied area coefficient was presented, the process of seed-cleaning was analyzed to detect the affecting factors and the relation between them. Based on the theoretical analysis, the key structural parameters were confirmed.Numerical simulation of the fluid field characteristic of CP was carried out in Fluent to investigate the affect of the structure of CP. The number of holes was confirmed by the simulation of fluid model under different hole diameters and numbers. The whole flow field simulation showed that there is no apparent difference between different sowing rows and filling area has higher pressure, and pressure and velocity were high in filling area. The structure conforms to design requirements.The performance of CP was investigated under laboratory. The experiments of pressure and rotation speed under4kinds of hole diameters during4to5.5mm showed that:hole diameter of4.5mm had the best performance under low operating speed, and required slightly higher pressure, and miss rate was very high under high operating speed. Hole diameter of5.5mm was the best at seed-filling and flexibility of high-speed operation. Its required pressure was the lowest. But it had higher multiple rate under low operating speed. As precision planting of corn has a low tolerance for miss-seeding, hole diameter of5.5mm was selected. The experiments for the optimization of seed-cleaning device were conducted to solve the problem of multiple-seeding of the hole diameter of5.5mm, and the cleaning-distance was confirmed as0.25mm. The experiments of the optimized structure showed that:after the optimization, the single rate increased obviously under low operating speed and had no big change under high operating speed. The comparison with other3metering devices showed that CP had the highest single rate. CP has good seed-filling performance and adapts to the high-speed operation..更多还原