| Rapeseed is an important oil crop in China,its acreage and total output ranked first in the world.Traditional rapeseed planting is mainly based on artificial planting method,which has the disadvantage of high labor intensity and high production cost.Therefore,mechanized rapeseed planting has become an inevitable trend.The middle and lower reaches of Yangtze River is the main producing area of winter rapeseed in our country.The soil in this area is sticky and its moisture content fluctuates greatly,which leads the stability of ditching and tilling difficult to be guaranteed at the time of planting.In this doctoral dissertation,study on design and mechanism of ditching and tilling components for rape planter was conducted and the main research conclusions are as following:?1?The physical and mechanical parameters of soil and rice straw in rice-rapeseed rotation area were tested.The test results showed that the average depth of plough layer was within 15 cm,the thickness of plough pan was about 10 cm,and the average soil compactness were 238.61627.2kPa.The soil texture were clay and heavy,the plastic limit and liquid limit moisture contents were 25.1%28.7%and34.2%39.1%respectively.The amount of rice straw in tested fields were 0.981.24g/m2,the average stubble heights were 20.745.7 cm,and the moisture contents of rice straws were 29.6%66.8%.The analysis results showed that the perennial rotary tillage makes the soil layer shallow,the thickness of plough pan and soil compactness became large.When the soil moisture was higher than 25%,the working capacity of direct seeder would reduce.And the moisture content of rice straws were high which caused the rice straws were difficult to be cut off.The influence of working conditions on the performance of traditional ditching and tillage components was analyzed.The factors and basic data which affecting the design of ditching and tillage components were defined.?2?The design and analysis of ditching and tillage components for rapeseed direct seeder were carried out.Considering the soil of in Mid-lower Yangtze River is sticky and the amount of straw is large,and the furrow should be ditched while planting rapeseed,a combined ditching and tillage scheme which working by active plowing and passive crushing,ditching was put forward.A front ditching plow,a combined ship type opener,and a toothed harrow type furrow opener were designed to be ditching components.The driven disc plows and passive crushing roller were designed to be tillage components.The research conclusions are as follows:?1?According to the principle that the plow has better cutting and drag reduction characteristics when its guide curve of plow surface is a smooth circular arc curve,the main structural parameters of front ditching plow were determined as the maximum element line angle was 45°,the minimum element line angle is 40°,and the starting angle was 60°;?2?The cutting soil mechanics model of ship cutting edge and the extrusion soil mechanics model of plow surface were established respectively.The study results showed that when the starting angle of shaping surface was small,it had better drag reduction characteristics.The main structural parameters of the combined ship-type opener ere determined as the initial slip angle of the cutting edge curve was23°,the termination slip angle was 45°,the cutting edge opening was 255mm,the maximum element angle of the shaping surface was 67°,the minimum element angle was 64.98°,the width and length of shaping surface were 72 mm and 216mm;?3?According to analyze the motion process of the rake-type mechanism and the cutting mechanism of skating opener,the main structural parameters of toothed harrow type furrow opener were determined;?4?The kinematics and dynamics models of the interaction between the driven disc plows and soil were established,and the effects of the main working and structural parameters on the working performance were analyzed.The main structural parameters of driven disc plows were determined as the working depth was 130180 mm,the working deflection angle is 27°,the rotation speed was 65188 r/min,and the speed ratio coefficient was 1.123.24;?5?The interaction mechanism between ship typed soil-contact surface and soil extrusion was analyzed.It was concluded when the width of ditching area was 350mm,the quality of furrow and seedbed can be ensured.?3?Under the three working conditions whose soil moisture content were 24.67%,30.40%and 37.61%respectively,and the corresponding average soil compactness were 848.44kPa,647.58kPa and 506.84kPa.The performance test and analysis of rapeseed direct seeder for ditching and tillage components were carried out.The surface section witch operated by ditching and tillage component were surveyed and measured by using laser orthogonal test method and modern power consumption test system.The testing results were as follows:?1?The average furrow depth witch ditched by ditching components was 241.6308.4mm,and the average furrow width was 328.6386.8mm.The stability coefficient of furrow width and furrow depth was above 85%,which meets the agronomic requirements of rape sowing furrow;?2?The actual working depth of the driven disc plows were consistent with the control depth,and tillage stability coefficients were more than 85%;?3?The comparison results showed that the passive crushing roller had bad effect to crush soil,it can not realize the crushing function on the clay and sticky fields,and the toothed harrow type furrow opener can not work stably on the clay fields after the passive crushing roller works;?4?The test results of traction resistance of furrow opener showed that the combined ship type furrow opener was the main load-bearing component,and its traction power consumption accounts for 66.1%72.1%of the total traction power consumption;?5?The orthogonal test indicated that the optimum operation condition was:the tillage depth was 180mm,the speed of machine was 3.5km/h,operating speed of driven disc plows was 160r/min.Under this condition,the power consumption was 24.37kW,straw coverage rate was 92.78%,soil crushing rate was66.74%,seedbed roughness was 24.18mm,landfill rate was 92.30%.?4?Considering the lack of theoretical basis for the design of resistance reduction of plow surface,the research on the relationship between resistance and the internal geometry properties of ship type plows with different curves were carried out by using the method of differential geometry analysis and EDEM simulation.In order to obtain the better shape of plastic surface with well resistance reduction characteristics,and to explore the relationship between traction resistance and the inherent geometric properties of plastic surface,the macroscopic parametric equation of plastic surface was established.The first and second basic forms and the corresponding intrinsic geometric quantities of plastic surface with the guide curve as the linear,parabolic and exponential linear type are calculated based on differential geometry theory.The intrinsic geometric quantities E,L,M are determined to be the main factors affecting the inherent geometric properties of ship type plow with different guide curves.The simulation results of traction resistance characteristics indicated that the traction resistance of three types of ship type plows increases with the add of operating speed.The intrinsic geometrical quantities E,L,M of the plastic surface are the inherent geometric factors which affect the traction resistance characteristics of ship type plows with different curve type.The parabolic type plow has better resistance reduction characteristics when the operating velocity was 0.6?1.4m/s and the maximum variation of element angle was 0°,5°,10°.And its resistance were reduced by 11.54%,13.82%,14.77%and 26.32%,22.09%,30.76%respectively compared with the linear type plow and exponential type plow.The changing rate of E-value reflects the degree of traction resistance changes with velocity change.The scale of traction resistance of ship type plow is reflected by the scale of L-value,the smaller the traction resistance is,the smaller the traction resistance of ship type plow.The function form of M-value is simple and it has lower fluctuation range,the ship type plow has better drag reduction characteristics.The parameter optimization results indicated that when the operating velocity was 1.4m/s,the maximum element angle was 66.4°and the variation of element angle umaxax was 3.8°,the minimum traction resistance was 403.52N.?5?Combining with the characteristics that reverse rotary tillage can increase the cutting speed,improve the crushing and landfill quality compared with traditional forward rotary and passive crushing parts,a combined ditching and tillage scheme which tillage by active plowing and reverse rotary,ditching by passive components was put forward.The improved design and analysis for tillage components of rapeseed direct seeder were carried out.The main study conclusions were as follows:?1?The kinematics and dynamics mathematical models of reverse rotary tillage device were established.According to analyzed the influencing factors of soil thickness and throwing track,The main working parameters of reverse rotary were determined as rotation speed was 220270r/min,the working speed was 1.21.7m/s,and the distance between the top of rotary tillage roller and main frame was 120mm;?2?The EDEM discrete element simulation model of the interaction between the driven disc plows and the reverse rotary tillage device and soil was established.The simulation results showed when the tillage depth of driven disc plows were fixed,the soil volume on both sides of the reverse rotary device can be ensured to be relatively uniform.The soil volume and drag resistance of the machine would increased as the add of tillage depth.But adding the tillage depth can significantly improve the landfill quality of the seedbed after the machine operated.When the tillage depth of the reverse rotary tillage device is fixed,increasing the working speed of the reverse rotary tillage device and reducing the working speed of the machine can effectively reduce the soil volume and the drag resistance,it can improve the stability of the tillage components.The optimum working parameters of the machine are as follows:the tillage depth and rotate speed of driven disc plows were 180mm and 180r/min,the tillage depth and rotate speed of reverse rotary tillage device was 120mm and 270r/min,the working speed was 1.2 m/s;?3?Field tests showed that under the optimum working parameters,the machine had stable working performance.The stability coefficients of tillage depth and ditching were above 90%,the straw covering rate was 92.36%,the average landfill was 20.3 mm,and the average soil crushing rate was 86.5%.The working quality of ditching and tillage components met the requirements of rapeseed sowing agronomic.Innovation point 1:A combined ship type opener was designed to ditching furrows,according the differential geometry theory and EDEM simulation,the relationship of between main contact surface and traction resistance of ship type plow was explored;Innovation point 2:The driven disc plows and reverse rotary combine tillage components were designed,which suit for working in rice-rapeseed rotation area. |
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