| Coal is the most stable,economic and independent energy resource in China,and its main energy status will last for quit a long time.With the decrease of shallow coal resources and the transformation of China’s economy to the high-quality growth,coal mining is developing in the direction of deep mining and intelligentized mining.The geological characteristics of high in-situ stress and strong mining disturbance in deep coal seam make the working environment and task of shearer more complex.Cutting unit is a multistage gear transmission system supported by ranging arm housing.It has complex structure,numerous parts and frequent faults.Thus,it is the weakest part of a shearer.Once the shearer shuts down due to malfunction in underground mine it often needs to be transported to the ground for maintenance,which causes paralysis of the whole working face,and reduces the production efficiency and economic benefits of enterprises.At present,there is still a gap between the reliability of domestic shearers and that of imported shearers.The reason is the lack of design theory and key technology.This thesis is supported by the National Basic Research Program of China(973 Program,Grant No.2014CB046304).Considering the heavy and impact load conditions and configuration characteristics of the cutting unit of drum shearer,the dynamic coupling mechanism between multi-stage gear transmission and cantilevered housing is investigated.The dynamic characteristics of the cutting unit under typical load conditions is revealed.The method to improve the dynamic performance of cutting unit is proposed.The main contents of this thesis are as follows:(1)Coupling dynamic modeling of multistage gear transmission-housing of cutting unitThe coupling dynamic modeling of multistage gear transmission-housing of cutting unit is summarized as the modeling problem of multistage gear system under large deformation condition.Aiming at this problem,a large-deforming gear dynamic model and an efficient modeling method for multistage gear system are proposed.In the large-deforming gear dynamic model,each gear is treated as a concentrated mass with six degrees of freedom.Considering the influence of system deformation on engagement angle and actual meshing zone,the thin slice method for meshing excitation is improved,and the meshing state of gear pair under large deformation condition is simulated accurately.The efficient modeling method for multistage gear system is based on dynamic substructure method.Based on the key steps such as substructure decomposition,substructure combination and local/global degree of freedom conversion,the normalized matrix operation form of substructure combination is deduced.The efficient modeling method can quickly establish the dynamic model of gear systems with different transmission configurations(2)Coupling dynamic characteristics of multistage gear transmission-housing of cutting unitThe natural vibration characteristics of the housing and multistage gear transmission are analyzed separately,and four vibration modes are classified according to the modal shape of the multistage gear transmission.Then the natural frequency,vibration mode and modal energy are synthetically used to analyze the natural vibration characteristics of the multistage gear transmission-housing coupling system.The dynamic deformation,dynamic load and acceleration of the cutting unit at different rotational speeds are simulated,and influences of the housing on the dynamic simulation results are analyzed.(3)Dynamic characteristics of cutting unit under variable load conditionsThe dynamic responses of cutting unit under stable and impact loads are studied.The effects of load factor and load fluctuation coefficient on gear meshing state,dynamic bearing force and housing vibration characteristics are analyzed,and some conclusions are verified by experiments.The effects of different gear dynamic models on simulation results are analysed.The transient responses of the cutting unit under impact load are studied,and the weak parts of the system are identified by modal analysis.(4)Improvement of dynamic performance of cutting unitThe dynamic performance of the cutting unit is improved from two aspects: the topological optimization of the housing and the tooth modification of the multistage gear transmission.Housing deformation is an important reason for unbalance load of internal gear transmission.By topological optimization of the housing,the housing deformation and the unbalance load for tooth surface under stable random load and step load are reduced.The impact load due to gear meshing and unbalance load for tooth surface are the key causes of system vibration and premature damage.A new tooth modification method for multistage gear transmission considering housing deformation is proposed,which reduces the peak contact stress of each gear pair by 21.1% and the dynamic factor by 25.5% on average under rated load condition. |
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