| With the continuous expansion of cities in various countries,metro,as a comfortable and convenient public transport,has become an important direction of urban traffic development.Air-conditioning units for metro vehicles have the characteristics of harsh working environment,complex frame structure and high requirements of manufacturing technology.If the frame fails in strength after being subjected to static or vibration loads generated during the operation of metro vehicles,the reliability of air-conditioning units will be seriously destroyed and the driving safety and stability of vehicles will be affected.Therefore,it is necessary to analyze the static strength,dynamic characteristics and fatigue life of the air-conditioning unit.With the continuous improvement of air-conditioning unit structure design and development mode and production process level,the structure of air-conditioning unit is improved to achieve the coordination and unification of lightweight and manufacturability on the premise of meeting the requirements of strength and rigidity.Firstly,taking the frame of air-conditioning unit in metro vehicles as the research object,the finite element model of air-conditioning unit is established by using Hypermesh and Ansys Workbench finite element analysis software.According to the standard EN12663-2010,the static characteristics of air-conditioning unit under inertial load are checked.The maximum stress and displacement of the structure under different load conditions are 167.08 MPa and 1.1 mm respectively,and the strength coefficients under different conditions are calculated.The strength of air-conditioning unit under lifting condition is calculated and the strength coefficient is obtained.The result meets the standard requirements.Then,in order to obtain the dynamic characteristics of the air-conditioning unit,the modal analysis is carried out on the structure of the air-conditioning unit to obtain its natural frequency and vibration type.The first six-order frequency range of the structure has exceeded 20 Hz from 34.58 Hz to 54.33 Hz,which will not resonate with the body.By applying random vibration load excitation,the random vibration analysis of the air-conditioning unit box structure is carried out.According to the three-interval method of Gauss distribution and Miner linear cumulative damage theory,combined with the standard X III-1539-96/X V-845-96,the fatigue cumulative damage coefficient of the frame under random vibration is 0.27,which is less than the fatigue failure critical value 1 and meets the fatigue life requirements.Finally,based on the analysis results of static and dynamic characteristics of the air-conditioning unit frame,the structure was improved and optimized according to the actual manufacturing process level,and the results before and after optimization were compared: the stress values at the connection between the two side panels and the bulkhead of the box were reduced from 88.75 MPa to 18.28 MPa,88.58 MPa to18.06 MPa,respectively.The strength increase effect was obvious and the purpose of optimization was achieved.According to the force and deformation of the cover plate under the trampling condition,the cover plate is improved and optimized.The results show that the optimized cover plate structure can not only meet the requirements of the trampling condition,but also meet the load intensity requirements of the vehicle during the operation.Vibration impact test of air-conditioning unit with optimized structure is carried out according to the requirements of vibration impact standard of rail vehicle equipment.The result shows that the air-conditioning unit with optimized structure can meet the test requirements and verify the reliability and stability of air-conditioning unit structure. |
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