| In the rice-rape rotation area,the residue of straw is large,the stubble is high,the soil is thick and sticky,so it is difficult to incorporation straw into the soil.To solve the above problems,based on the previous research of the research group,this paper designed a combined tillage machine for deep rotary burying of straw incorporation into soil with the main purpose of reducing the power of rotary burying roll,increaseing the depth of straw burying and the degree of straw-soil mixing.Based on the study of the sliding cutting characteristics of rice and rape straw,a sliding cutting self-excited vibration subsoiling device was designed.The working process and effect are analyzed by means of discrete element simulation,soil bin test and field test.Based on the experiment of deep rotary burying combined tillage,the reasonable design and optimization of rotary burying roll for straw incorporation into soil were carried out.Finally,the working effect of combined tillage machine for deep rotary burying of straw incorporation into soil was tested through the research of straw spatial distribution after field experiment.The main conclusions are as follows:（1）The experiments of slow cutting and fast cutting were carried out on rice straw and rape straw respectively,and the better range of sliding cutting angle was obtained.The slow cutting of rice straw and the fast cutting of rape straw have different characteristics on the different sliding cutting angles of cutting tools.In the slow cutting,when the sliding cutting angle is 60°,the cutting force per unit diameter was the smallest,and when the sliding cutting angle is 45°,the power consumption per unit diameter was the smallest.In the fast cutting,when the angle is 30°,the cutting force and power per unit diameter were the smallest.Therefore,when considering the design of subsoiling and straw returning tools,the range of sliding cutting angle that can be selected first is 30°～60°.（2）A sliding cutting self-excited vibration drag reduction subsoiling device was designed,which mainly includes the sliding cutting type shank by using the sliding cutting principle and the corresponding self-excited vibration device.Through the establishment of the dynamic equation,the theoretical analysis and parameter design of the important parameters of the sliding cutting shank were carried out,and the actual cutting edge angle of the shank was analyzed and calculated by the establishment of the geometric equation.Taking the draught force as the test index,the soil bin comparison test was carried out on the subsoilers,in which the fixed connection sliding type subsoiler reduced the force by 7.79%～8.81%compared with the arc subsoiler at each speeds,and the self-excited vibration connection sliding type subsoiler reduced the force by 15.45%～20.05%compared with the arc subsoiler at each speeds.According to the bond characteristics of clayey loam,a layered soil model suitable for bond characteristics of clay loam was established based on DEM simulation software.The important parameter of the JKR soil contact model was calibrated with draught force as a check index through field comparative experiments.The results showed that when the surface energy of plow layer soil was 42 J?m-2and the surface energy of the bottom layer soil was 48 J?m-2,the error between values of simulation and experimental of draught force was the smallest,which was 0.89%.The results of the DEM simulation showed that the errors of parameters such as disturbance width,disturbance height,disturbance angle and center width of subsoiling were less than 10%compared with the measured values in the field,which indicated that the DEM was in close agreement with the actual soil conditions in the field.Microscopic movement analysis of soil particles showed that the movement of soil particles first goes forward and upward and then downward and backward in the process of subsoiling.After subsoiling,the gaps of soil particles increased significantly,which effectively achieved soil loosening.At the bottom of the groove,a rat path was formed,which played an important role in soil water storage and moisture conservation.The parameter optimization test of sliding cutting self-excited vibration subsoiling device was carried out,the order of significant influence on draught force and soil swelling from large to small was the forward velocity,pretightening force of the spring and the slide-cutting angle of shank.The analysis of the response surface showed that when the pretightening force of the spring,the slide-cutting angle of the shank,and the forward velocity were 6.67 k N,44.21°,and 0.44 m?s-1,respectively,the draught force was3.77 k N,the soil disturbance coefficient was 60.21%,and the soil swelling was 7.70%.The field validation test showed that under the optimal working parameters,the draught force of subsoiling was 3.84 k N,the soil disturbance coefficient was 57.00%,and the soil swelling was 8.33%.The errors with the software analysis were 1.82%,5.63%and 7.56%,respectively.The reliability of the response surface analysis was verified.（3）Combined with the rotary burying roll developed by the research group,a combined tillage machine for deep rotary burying of straw incorporation into soil was designed.The force and power consumption model of it was analyzed.The influence of the operation parameters of the rotary burying roll on the forward speed was calculated.The mechanism of the sliding cutting and burying of straw with the spiral horizontal blade was analyzed.The operation performance test showed that the power consumption of combined deep rotary burying operation is less than the sum of the two operations,which indicated that the operation condition of rotary burying is improved and the power consumption of rotary burying is reduced.Under 1st and 2nd gear speeds of the tractor,the total power of the combined operation of deep rotary burying were accounted for 85.0%and 82.2%of the total sum of individual deep rotary burying operations respectively.The straw burying rate was 92.0%,and the surface evenness after tillage was 1.0 cm,which was greater than the quality evaluation index and met the agronomic requirements.In the mean value comparison of working quality of the high stubble rape straw returning experiment,under the mode of SSR,the pass rate of straw chopping was 89.1%,the straw coverage rate was 93.0%,and the straw proportion of the lower half burying layer was 52.8%,these values were better than SR.The straw proportion of the lower half burying layer of SSR compared with SR increased by 10.5%.The PTO speed and forward speed all had a significant effect on straw proportion of the lower half burying layer of SSR and SR.Subsoiling first can significantly reduce the PTO torque.Under various working conditions,the PTO torque of SSR range was maintained at 381～412 N?m,the PTO torque of SSR decreased by 22.39%～34.04%compared with SR under corresponding working conditions.The PTO speed and the forward speed all had a significant effect on total power consumption of SSR and SR.（4）In view of the problems in the structure of the rotary burying roll,the structure of the cutter head and the machete were optimized.The optimized cutter head cancelled the radial through groove,and used two bolt holes to locate the machete position,which not only realized the free disassembly of the cutter head and the spiral horizontal blade,but also greatly reduced the machining difficulty of the cutter head,correspondingly reduced the thickness of the cutter head,and reduced the installation quality.The optimized machete was equipped with bolt holes matching with the cutter head.At the same time,the cutting edge of the machete was changed from single-sided to double-sided in order to reduce the resistance of soil penetration.The corresponding groove was designed at the end of the machete to directly locate the position of the spiral horizontal blade,which not only realized the quick and accurate positioning of the spiral horizontal blade,but also significantly reduced the processing error.In view of the working quality problems of rotary burying roll,the arrangement of rotary blade was optimized.Based on the amount of axial soil pushing,it was calculated that 2.33 rotary blades are needed to balance the effect of axial lateral pushing under the condition of common tillage depth.Therefore,on the basis of three spiral horizontal blades corresponding to seven rotary blades in a section of rotary burying roll,two rotary blades in one left direction and one right direction were added,which was equivalent to not increasing the amount of axial soil pushing,but also increasing the number of rotary blades,and making three rotary blades distributed between each two spiral horizontal blades.The comparative test of rape straw incorporation into soil showed that,compared with the original rotary burying roll,the optimized rotary burying roll can improve the straw burying rate and straw crushing rate,while the power consumption slightly increases.The test of rice straw incorporation into soil showed that the optimized rotary burying roll can effectively realize the burying of rice straw,and the bottom of the tillage layer is flat after operation.（5）The spatial distribution effect of straw was tested for three kinds of tillage tools:a traditional rotary tiller（TR）,a straw rotary burying and returning machine（SR）,and a subsoiling+straw rotary burying and returning machine（SSR）.The three-dimensional coordinate measuring device was designed to measure the spatial coordinates of straw in the soil after straw incorporation.The measured spatial coordinates were imported into the three-dimensional drawing software to restore the spatial distribution of straw in the soil,and it was quantified and visualized in the three-dimensional drawing.Different tillage tools had great influence on the effect of straw incorporation.Relatively speaking,the cutting effect of straw after TR operation was poor,more straw was left on the surface,less straw was buried in the lower layer of the tillage depth,the straw average length in the divided cells was small,and there were many cells without straw.Compared with TR,the straw average lengths of SR and SSR decreased by 48.2%and 52.7%,respectively.Only a small amount of straw remained on the surface.The layer proportion of straw in the lower layer of tillage depth increased by 154.9%and 214.1%,the average straw length in the cells increased by 114.9%and 98.6%,and the number of cells without straw decreased by 40.2%and 36.0%,respectively.The corresponding simulation model was established by using the discrete element method,and the same operation parameters were set up with the field test.In the layered treatment,the results of simulation and measurement showed that the amount of straw buried in SR and SSR is significantly greater than TR,especially in the lower layer of soil is several times of TR.After TR,SR and SSR operation,the variation coefficients of simulated and measured values of layer proportion of straw showed a decreasing trend.Among them,the variation coefficients of simulated and measured values of TR were the largest,55.8%and 68.2%respectively,and the variation coefficients of SSR were the smallest,28.8%and 28.7%respectively.The results of discrete element simulation and field experiment showed that,after the SSR straw incorporation,the uniformity of vertical and horizontal distribution of straw in the soil was the best.The discrete element simulation fitted the spatial distribution of straw well,and the relative error was within the acceptable range. |
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