The exhaust of a full-feeding type combine harvester after threshing is composed of relatively longer straw, which results in difficulty for later stage field operations of scattering the straw to the cropland uniformly, and fully incorporating the straw into the soil. Longer straw is also easy to wind on the shaft of a rotary tiller in the process of cultivation, stuffing the openers of a sowing machine in the process of growing. As longer straw was not fully mixed with soil, the porosity of the soil became high, water loss became quick, and the seeds were to be sowed into the straw, not into the soil as well. Thus, the crop will be dried to death in the summer or be frozen to death in the winter, for the crop could not root steadily in the soil. If the currently applied straw shredding device is taken into concern, one has to face with the additional complexity of the structure, and the limited universality of the system, because there is no sufficient space to arrange the transmission system of the shredding device, and the shredding device can not be modified and fixed easily on the straw outlet of the machine. In order to facilitate the later operation of threshed straw returning back to the cropland by collecting the straw into the ditch, a flow-guiding shredder was developed and the shredder was assembled in the cover of a modified 4LL-1.8 full-feeding combine harvester based on analyzing the original structure of the threshing device. The operating performance of the modified threshing mechanism was tested. The field trial proved that, after threshing, the modified threshing unit could shred the straw effectively. The length of the cut straw can be adjusted by changing the angle,α, between straw-cutting knife and the axis of the roller. Moreover, the length of the shredded straw turned shorter with the increasing of the angle,α, gradually. The changing trend of the length of threshed straw was consistent with the theoretical analysis. Ifαwas kept no less than 60º, the length of the shredded straw was controlled within a length of 200 mm, and at least 90% of the straw feeding into a ditch was attainable. The modified threshing device will both satisfy the straw-cutting and ditch-feeding demand for the machine design and allow the subsequent field work to be operable. The proposed construction of the threshing mechanism is simple in design but effective in working, which can be used as a reference for other similar designs.%针对全喂入联合收割机存在脱粒后排出的秸秆较长，不利于还田利用，甚至影响后续耕种及作物生长，而现有配套秸秆切碎装置结构复杂、通用性差等问题，该文设计了导流型碎草刀，并对4LL-1.8型全喂入联合收割机的脱粒装置进行了改进。田间试验表明，改进后的脱粒装置在完成作物脱粒后，可对秸秆进行切碎。通过调整碎草刀与滚筒轴夹角α的大小，可有效改变切碎秸秆长度。当α大于等于60°时，切碎秸秆长度小于200 mm，秸秆入沟率不小于90%，满足秸秆切碎及集沟还田要求，并利于后续作业。该装置结构简单、切碎效果良好，可为同类机具改进设计提供借鉴。
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