Threshing device is one of the important parts of combine harvesters, whose function determines the working performance, efficiency, and adaptability of the whole machine directly. Threshing gap refers to the clearance between the threshing elements of the drum and the concave grid. During field harvesting, the actual feeding rate shows a great fluctuation due to various biomechanical characteristics and growth density of different varieties of rice, which will deteriorate the threshing and separation performance of combine harvester (Toshikazu and Tatsuro, 2017;Alizadeh and Bagheri, 2009;Singh and Singh, 1981). Therefore, it is necessary to adjust the threshing gap in time according to various working conditions to ensure the operation stability of combine harvesters and improve its harvesting adaptability.Researchers have conducted a lot of studies on the effect of threshing gap on threshing performance, as well as its regulation mode. Scholars have established some basic models of threshing and separation process through comprehensive consideration of multiple factors that exist during the threshing process. They optimized
The threshing gap of the thresher device for rice combine harvester has to be adjusted in real time based on different feed rates to ensure the operation efficiency in the harvesting process. However, adjusting the threshing gap by changing the position of concave grid may result in unevenness of threshing gap of the thresher device and further impact on the fluidity of material in the thresher device; in addition, it is also unavailable to adjust the threshing gap by changing the drum diameter when the rice combine harvester is in operation. In view of the above and based on axial flow threshing drum, the design of a variable-diameter threshing drum available for overall and rapid drum diameter adjustment and the research on diameter adjustment device as well as electronic control self-locking device were introduced in this study. Besides, stress analysis was implemented to the diameter adjustment device to ensure the stability of the variable-diameter threshing drum. Field experiment was implemented to identify the difference between the impacts brought to the threshing performance (grain-entrainment loss rate, damage rate, threshing efficiency, and threshing power consumption) by both methods for threshing gap adjustment. The experiment result shows that the drum adjustment method with variable-diameter drum features higher grain-entrainment loss rate, threshing efficiency, and threshing power consumption, yet stable in terms of consumption fluctuation, but a lower damage rate than their counterparts with concave adjustment method.
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