Study On Work Mechanism And Design Of Axial Flow Differential-speed Threshing-separating-cleaning Unit

Combine harvester is an important equipment of rice mechanization harvesting.The threshing-separating-cleaning unit composed of threshing-separating device and cleaning device is the core component of combine harvester.Its working performance influences rice harvest quality directly.With the popularity of super rice and other high-yielding rice,current combine harvester cannot meet the needs of efficient and low-loss harvest operations.Based on this background,this thesis focuses on the key operations of threshing,separating and cleaning,and the goal of reducing the loss rate,the broken rate and the rate of impurities at the process of threshing,separating and cleaning the grain is set,around the market-leading model of transverse-set axial-flow whole feeding combine harvester,under the support of the National Natural Science Fund and other projects.A new type of transverse-set differential-speed axial-flow threshing-separating-cleaning unit was developed and the working principle and performance of system was studied by adopting of the methods of theoretical analysis,numerical simulation and experimental verification.The main contents of this thesis are as follows:First,the movement law of the mixture in the threshing space was studied.The mathematic models of axial-flow drum threshing and separating device were established according to the probability statistical method.The mathematic models were verified by MATLAB software and the working process of axial-flow threshing and separating device was analyzed.The mathematical model of grain damage during threshing was established,which clarifies the critical state of damage of rice shell and the threshing damage mechanism.The movement model of the stripping drum in the roof area,the separating concave area and the movement of the mixture and the threshing part was established.The parameters relationship between the velocity and direction of each component in the mixture and the structure and speed of the threshing drum was obtained.The movement law of the mixture in the threshing space was analyzed.The movement law of the mixture removed was observed and analyzed by the high-speed camera,and the movement model of the mixture in the threshing space was validated.The research of this part provides the theoretical basis for optimizing the axial-flow threshing and separating device.The principle of coaxial differential-speed threshing was proposed.Based on the determination of the connecting force between grain and grain stalks in four super rice varieties,Yongyou 12,Yongyou 9,Jiayou 2 and Yongyou 11,the distribution spectrum of grain connecting force was plotted.The threshing coefficients of the four varieties of rice were calculated and the mathematic relationship model between the average connection force of grain and the tooth top liner velocity and the rotation speed of threshing roller was established and validated.Based on the distribution spectrum of grain connecting force,the principle of coaxial differential-speed threshing was proposed.Focused the semi-feed combine harvester and full-feed combine harvester,the bow-ear type differential-speed threshing drum and the rod-type difference threshing drum were developed.The experiments of differential-speed threshing and single speed threshing were carried out to verify the performance of coaxial differential-speed threshing and separating device.This thesis presents a coaxial differential-speed threshing technique.The application of low-speed segment of differential-speed threshing roller to reduce grain breakage and the high-speed segment of that to reduce the net loss can solve the problem of the high rate of broken and threshing endless existing at the traditional single-speed threshing drum.The movement rule of the material particles in the wind screen cleaning device was studied.In order to grasp the movement rule of the mixture in the wind screen cleaning device,this thesis firstly used the theory of stationary motion to analyze the movement conditions of material particles on the back slipping,forward slipping and throwing on the screen surface,and deduced the expressions of up-slip index,down-index and take-off index further.Then the chaos dynamics theory was used to analyze the process of turning the particles from stable periodic motion to chaos.The material collision model of two particles and multiple particles was established and the collision process between the material groups during the cleaning process was studied,then the dislocation movement rule of the material group on the screen surface was analyzed.At last,the probabilistic model of material sieving from the vertical direction and from the oblique direction was established.The separation process of the material particles on the sieve surface was analyzed and the main factors influencing the probability of materials penetrating the sieve were discussed.The research in this part lays a theoretical foundation for optimizing the structure and working parameters of the wind-sieve type cleaning device.The principle of non-uniform airflow cleaning was proposed and the conical centrifugal cleaning fan was designed,aiming at the problem that the ejector is easy to accumulate at the corner of the entrance of the vibrating screen at the process of cleaning the traditional cylindrical centrifugal fan from the perspective of optimizing the flow field distribution of air outlet.According to the structure of the wind-sieve type cleaning device,a three-dimensional model of the whole flow passage was established.The CFD software was used to numerically simulate the flow field distribution of the cleaning room under the action of the cylindrical cleaning fan and the conical cleaning fan with different taper blades.The flow field of different types of cleaning fans was experimentally verified by the method of distributing-point method,which implies the action mechanism of applying the transverse wind to optimize the sieve-surface distribution of extraction of conical cleaning fan.Aimed at the rice separation process,the movement process of material in the cleaning room was simulated and the material selection was tested,and the distribution of materials under the action of cylindrical cleaning fan and conical cleaning fan was compared and analyzed.The results show that the conical clean-up fan can apply the transverse wind to blow away the exudate gathered in the inlet of the vibrating screen to some extent,which makes the exudate distribute more evenly the vibrating screen and is conducive to improve the cleaning quality.A new type of transverse-set differential-speed axial-flow threshing-separating-cleaning unit was developed.Based on the new idea that re-threshing small spike heads and short stalks can reduce the impurity rate of selection,a new type of transverse-set differential-speed axial-flow threshing-separating-cleaning unit which consisted of coaxial differential-speed threshing cylinder,conical centrifugal fan was designed to solve the problem of high impurity rate of traditional transverse-set axial-flow threshing-separating-cleaning unit.The performance testing bench of transverse-set differential-speed axial-flow threshing-separating-cleaning unit was developed,according to the actual structure and sizes.The performance test was carried out by applying the quadratic orthogonal rotation combination design method.The regressive mathematical model of loss rate,breakage rate,impurity rate and threshing power was established,and the influence of three factors on the working performance index were analyzed,which were the speed combination of differential-speed roller,the conical fan blade taper and the length ratio of high and low speed of differential-speed roller.The multi-objective optimization calculation of the regression model was carried out,and the optimal parameter combination and the corresponding performance index were obtained.The results of bench test and field test indicate that the working performance of transverse-set differential-speed axial-flow threshing separating cleaning unit is much better than that of the traditional transverse-set axial-flow combine harvester and the industry standard.