Optimization And Experimental Study On Mechanical System Of Alfalfa Mower Conditioner

In order to accomplish the efficient,low-loss and high-quality alfalfa harvesting,from the view of alfalfa mowing and conditioning technology,design parameters of profiling system,mow-condition system were optimized and the airflow field formed in the feeding zone was simulated and measured through the combination of simulations and field experiments,basing on the mechanical properties of connections between alfalfa stems and leaves.The mechanical properties of connections between alfalfa stems and leaves were investigated,which provided theory references for the study of the interaction between the mechanical system and alfalfa plants.For the maximum tensile failure load value of the fresh alfalfa plant,the sequence is along the direction of leaves growth>perpendicular to the direction of stem>against the direction of leaves growth according to the different ways of tensile destruction.Fracture characteristics of connection points between stem and leaves showed differences between the three tensile destruction ways.Profiling system is the key part of the alfalfa mower conditioner.Virtual prototyping model was built and related orthogonal experiments were conducted.Average stubble height,stubble stability coefficient and mowing soil-device contact depth were selected as the optimization indicators.The results indicated the best design and operation parameters of the profiling system were the sliding palm length of 188 mm,the cutter bar tilt angle of 4.06°,the ratio of spring pull force and cutting table gravity of 0.85 and the advance speed of 2 m/s.Basing on the parameters mentioned above,the simulation results were the average stubble height of 69.77 mm and stubble stability coefficient of 46.96%,no soil touch phenomenon was observed.Mow-condition system is the key component to accomplish the low-loss harvesting.Virtual mow-condition system prototype model was built and simulations were conducted with different working parameters.Shredding grass coefficient ? model judging the degree of crushing effect on alfalfa plants was supposed and defined,and the best working parameters with disks speed of 1875 r/min and the condition roll speed of 749 r/min were obtained based on the definition above.Field experiments indicated that linear positive correlation existed between the actual shredding rate and coefficient ?(R2=0.9588),which verified the correctness of shredding grass coefficient model.Airflow field of the cutting and conditioning mechanical system could provide support for the alfalfa harvesting.Air flow intersection point in front of the machine was found by simulated calculation using CFX software.The analysis of airflow velocity showed that,the air flow at the above,rear and front of the interaction point was helpful to avoid re-cutting,assist feeding,and contribute to cutting respectively.Relationship models of key airflow field parameters varied with operation parameters were obtained by response surface analysis.After the optimization of the alfalfa mower conditioner,the stubble height of 55.5 mm,exceeding stubble height loss rate of 0.31%,shredded rate of 2.32%and flattening rate of 98.36%were achieved in the field experiments,which all reached the requirements of the national standard for mower conditioner working quality.Compared to the alfalfa artificial harvesting without conditioning procedure,the drying rate of alfalfa plants showed higher than the artificial groups significantly,which revealed good performance of the optimized alfalfa mower conditioner.