| Hilly and mountainous area accounts for 63.2%of the total cultivated land area in China.The cultivated land is narrow and scattered,lacking of tractor load.Being small volume,light weight,simple structure and easy transfer in the farm land,the mini-tiller has become the main and indispensable agricultural machinery in hilly and mountainous area.At the same time,due to the long-term and arduous of land renovation and construction task,the mini-tiller will still play an important role in agricultural production of hilly and mountainous areas for a very long period in the future.However,intense vibration of the internal combustion engine mini-tiller acting on the operator′s hand not only affects the operation comfort of the machine,but also may cause damage to the operator′s sensory nerves,muscles,bones and joints.As a countermeasure to the tiller vibration,a new type of battery electric mini-tiller(tillage depth>10 cm)was developed,which can be used in the dry land tillage operation in hilly and mountainous area.Power consumption and vibration characteristics,as two key indicators to measure the operation performance of battery electric mini-tiller,have certain opposites.How to coordinate these two key indicators,reduce power consumption and vibration,and improve the operation performance of electric mini-tiller,has become the key factors for wide application of electric mini-tiller in hil y and mountainous area.The power consumption and vibration characteristics of electric mini-tiller were chosen as the research object.Through theoretical analysis and dynamic simulation of rotary blade cutting soil,the geometric parameters of rotary blade were optimized based on the micro mechanism of rotary blade cutting soil.The vibration transmission characteristics of electric mini-tiller were studied by the method of theoretical analysis,numerical simulation and experimental research.The frame of tiller was optimized to reduced the vibration at the handle of mini-tiller.The effects of reducing power consumption and vibration of optimized rotary blade and frame were verified by field test.The comprehensive performance evaluation parameters o f power consumption and vibration characteristics of the electric mini-tiller were established,and the power consumption and vibration characteristics of the electric mini-tiller were comprehensive analysis.The main research conclusions are as follows:(1)In order to reduce the power consumption of electric mini-tiller,a simulation model of“rotary blade-soil”cutting model was established by using smooth particle hydrodynamics.The cutting soil process and power consumption of the current rotary blade were analyzed,and the simulated power consumption was 0.294 kW.According to the power model and the particle motion during dynamics simulation of rotary blade cutting soil.The bending radius r,the sliding angleτ,and the angle between the tangent plane and the line connecting the cutting edge to the center of the rotary blade rollerδwere chosen as the test factors,and the simulated power consumption of rotary blade cutting soil was chosen as the test index.According to the nonlinear optimization method,when r was 36.7 mm,τwas 47.8°andδwas 60.4°,the power consumption of rotary blade cutting soil was the smallest,and its simulated power consumption was0.258 kW,which was 12.24%lower than that of the current rotary blade.The rotary blade before and after optimization were assembled into rotary blade roller(4 pieces×3groups)before and after optimization.The simulated power consumption of rotary blade roller after optimization was 0.789 kW,compared with the simulated power consumption of current(before optimization)rotary blade roller(0.896 kW),the simulated power consumption was reduced by 11.94%.(2)In order to explore the vibration transmission characteristics of the electric mini-tiller,the vibration characteristics of the rotary blade roller,the connection between the support frame and the handrail,and the left and right hand les were selected as the test indexes for the field test.When the tiller under condition of fast gear(commonly used for tillage,forward speed,0.5 m/s),the vibration acceleration values of X(front and back),Y(left and right),Z(vertical)direction transmitted from rotary blade roller to handrail(take the average vibration acceleration values of the left and right handles)through the connection of support frame and handrail were reduced,and the vibration amplitude values were increased.The vibration acceleration values in X,Y and Z direction reduced from 7.23 m/s~2,6.39 m/s~2 and 10.12 m/s~2 to 3.45 m/s~2,3.64m/s~2 and 8.10 m/s~2.The vibration amplitude values in X,Y and Z direction increased from 1.20 m/s~2,1.06 m/s~2 and 2.29 m/s~2 to 2.66 m/s~2,2.49 m/s~2 and 6.80 m/s~2.The vibration acceleration values and vibration amplitudes in Z direction were the largest among X,Y and Z direction,and the vibration effect on handle wass the largest.(3)In order to reduce the vibration at the handle of electric mini-tiller,the topology optimization of frame was carried out based on computational modal analysis and experimental modal analysis,and the vibration characteristics of frame and the handle of mini-tiller were simulated and verified.The results show that:the first-order natural frequency of optimized frame and the maximum vibration amplitude value obtained from computational modal analysis were 13.42 Hz and 27.12 mm,respectively.Compared with that of the frame before optimization obtained from computational modal analysis,the first-order natural frequency(17.25 Hz)reduced by 22.20%,and deviated from the human forearm resonance frequency range(16~30 Hz).The maximum vibration amplitude(34.41 mm)reduced by 21.18%.The optimized frame was assembled into the improved electric mini-tiller,and the vertical vibration acceleration value at the handle obtained from Simulink simulation was 7.16 m/s~2.Compared with that(7.89 m/s~2)obtained by Simulink simulation of frame before optimization,the vibration acceleration value was reduced by 9.25%.(4)The operation power and the exposure time of“white finger disease”(the probability of disease was 10%)were chosen as the power consumption and vibration characteristics evaluation indexs.According to the actual working gear and working time of the electric mini-tiller,the comprehensive performance evaluation parameters of power consumption and vibration characteristics of the electric mini-tiller was established.Electric mini-tillers under different combinations of rotary blade roller before and after optimization combination frame before and after optimization were evaluated by comprehensive performance evaluation parameters.The results showed that the optimized rotary blade roller combination optimized frame has the best comprehensive performance,compared with the current electric mini-tiller(rotary blade roller before optimization combination frame before optimization),the weight reduced from 50 kg to 46.04 kg,decreased by 7.92%.The operation power reduced from 1.73kW to 1.55 kW,decreased by 9.84%.The exposure time of“white finger disease”(The higher the value,the smaller the vibration)increased from 6.16 years to 7.38 years,increased by 19.81%.The purpose of reducing power consumption and vibration at handle of electric mini-tiller was realized. |
PDF Full Text Request