0023-6152

AA00697606

4363552

A threshing unit consumes about 40% of power required by a Japanese head feeding combine. Thus, the unit has a major impact on efficiency and energy consumption during harvest. The threshing capacity can be improved by increasing an engine output, while threshing operations should be studied to lower energy consumption. The objectives of this study were to evaluate threshing operations under different acting speeds, locations, and angles of a rod–shaped threshing tooth (hereafter, threshing tooth), and to investigate an evaluation method for threshing operations, which considered energy efficiency. We evaluated percentage of detached grains, energy efficiency, and the grain number of the largest broken panicle (GNLBP) under different rotational speeds (300 rpm, peripheral velocity: 9.4 m/sec; 500 rpm, peripheral velocity: 15.7 m/sec), acting locations of a threshing tooth on a single rice (upper stem, neck node of a panicle, center of a panicle), and acting angles (10°, 30°). The largest PDG was 80% when the threshing tooth acted on a rice with 10° at the neck node of a panicle under 500 rpm. Percentage of detached grains decreased when GNLBP increased. Energy efficiency ranged from 4–42%, and was the highest when the threshing tooth acted on a rice with 10° at the neck node of a panicle under 300 rpm. The acting locations of upper stem (10° and 30°) and neck node of a panicle (30°) suffered large energy loss, because a stem or a panicle was broken. Moreover, energy loss was assumed to be large due to work required for accelerated motion of a panicle, which increased under 500 rpm. In conclusion, the evaluation method in this study effectively identified threshing operations, which lowered energy efficiency.