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To solve the problems of low removal rate and incomplete separation for the current longitudinal-axial-flow combined harvester in the case of harvesting rice and wheat, a segmented longitudinal-axial-flow threshing device was designed in this paper. The threshing device mainly comprised a tapered threshing roller, a concave sieve with adjustable threshing strength, a 360° separation device and an electric control system for operating parameters. Through the single factor tests, the optimal switching states of the concave sieve with adjustable threshing strength for rice and wheat threshing was obtained respectively. In order to find out the influence rule of the working parameters of the device on the threshing effects and the optimal parameter combination, the multi-objective optimization tests were carried out. The rotational speed of roller, the angle of deflector, the threshing gap of concave sieve, the separation gap of concave sieve and the feeding rate were selected as the influence factors and the crushing rate, impurity rate and loss rate were selected as the test indexes. The test results showed that the significant sequence of influence of threshing parameters on the crushing rate was the rotational speed of roller, the threshing gap of concave sieve, the angle of deflector, the feeding rate, the separation gap of concave sieve. The significant sequence of influence of threshing parameters on impurity rate was the rotational speed of roller, the angle of deflector, the threshing gap of concave sieve, the feeding rate, the separation gap of concave sieve. The significant sequence of influence of threshing parameters on loss rate was the rotational speed of roller, the angle of deflector, the threshing gap of concave sieve, the feeding rate, the separation gap of concave sieve. Through multi-objective parameter optimization analysis, the optimal working parameters combination for wheat threshing were determined that the rotational speed of roller was 905 r/min, the angle of deflector was 69°, the threshing gap of concave sieve was 18 mm, the separation gap of concave sieve was 19 mm and the feeding rate was 4 kg/s. The field verification tests were carried out using the optimal working parameters combination. The results indicated that the crushing rate was reduced from 1.46% to 1.00%, the impurity rate was reduced from 1.85% to 1.43% and the loss rate was reduced from 1.72% to 1.20% compared with the conventional longitudinal-axial-flow threshing device. All the relative errors between the measured values and the optimized values were less than 5%, the working indicators met the requirements of relevant national standards. The device effectively solved the problems of high crushing rate, unclean threshing and incomplete separation, the research results can provide reference for the structural improvement and operation parameters optimization of the threshing device of longitudinal-axial-flow combined harvester. [ABSTRACT FROM AUTHOR]

Aimed at the problem of high cleaning loss rate, impurity rate and secondary impurity rate due to improper adjustment of main operating parameters of wheat combine harvester double-outlet multi-dults cleaning device, single factor and multi-factor optimization tests that took feed amount, wind door opening, fan speed, upper and lower wind deflector angles as main test factors were conducted. The influences of each test factor on the cleaning loss rate, impurity rate, and secondary impurity rate were studied to find the optimal parameter combination. Firstly, referring to the relevant parameters of Kubota 988 model, which has a large amount of wheat harvester in the market, a test-bed with double air outlet multi-ducts for combine harvesters was built. When there were four ducts, the wheat cleaning loss rate 0.78% and impurity rate 0.48% were the lowest compared to the two or three ducts. Moreover, through single factor test of double air outlet four ducts cleaning device, the optimal range of feed amount was determined from 4.5 to 5.8 kg/s, wind door opening was 0°-20°, fan speed was 1 200-1 600 r/min, upper and lower wind deflector angles were 0°-20°. The results of single factor test showed that the cleaning loss rate increased with the increase of the feed amount and fan speed, and decreased with the increase of the upper and lower wind deflector angles; the impurity rate decreased with the increase of fan speed, and increased with the increase of the feed amount and upper and lower wind deflector angles; the secondary impurity rate increased with the increase of feed amount, and decreased with the increase of the wind door opening, fan speed and upper and lower wind deflector angles. The multi factor bench test and the orthogonal test with five factors and three levels were carried out by using the Box Behnken center combination test design theory. The regression equations about the cleaning loss rate, impurity rate and secondary impurity rate were obtained. The results showed that the factors of fan speed, feed amount, upper wind deflector angle had significant impact on the cleaning loss rate, the factors of fan speed, upper and lower wind deflector angles have impact on the impurity rate, and the factors of upper wind deflector angle, the fan speed and the feeding amount have significant influence on the secondary impurity rate. Through optimization of the target parameters, the optimal parameters combination were the feeding amount 4.5 kg/s, the wind door opening 10.2°, the fan speed 1 548 r/min, the upper and lower wind deflector angles 20° and 0°, at this time, the cleaning loss rate, impurity rate and secondary impurity rate were 0.79%, 0.40% and 0.82% respectively. Furthermore, the bench test under the optimal parameter combination condition was carried out to verify the accuracy of the optimal results. The results of bench test showed that the cleaning loss rate, impurity rate and secondary impurity rate were 0.75%, 0.38% and 0.76% respectively, and the error between test results and optimization results were 5.1%, 5.0% and 7.3% respectively. The results of this study can provide the references for the adjustment operating parameters and technical support for improving the performance of the multi-ducts cleaning device of the combine harvester. [ABSTRACT FROM AUTHOR]