| Construction machinery as an off-road vehicle plays an important role in China's economic and social development.In recent years,the national energy conservation and emissions reduction work is becoming more and more strict,especially our country has enforced the national ? emission standards for off-road mobile machinery mobile machinery.The problems of high energy consumption,high heat production and low efficiency of domestic loader have become an urgent problem for the industry and researchers.Moreover,because of the special structure and operation mode of engineering machinery,these problems are more complicated and severe.Combined with the project in the National Science & Technology Pillar Program during the Twelfth Five-year Plan Period,"Research and development of integrated intelligent engineering equipment for energy conservation and security",the key technology of thermal management for stage ? loader transmission system is studied by using the combination of theoretical calculation,numerical simulation and experiment.(1)Based on the test data of loader performance test,the energy flow and energy loss of each system under the V-type shovel loading operation and high-speed running condition are analyzed.Through the study of the law of torque distribution of engine,the actual dynamic characteristics of hydraulic torque converter on loader are analyzed.On this basis,the dynamic simulation model of loader transmission system is established.The accuracy of this mathematical model can meet the requirements of engineering calculation,which can effectively simulate the operation of powertrain.In order to improve the performance of wheel loader transmission system and reduce heat generation,the main parameters of loader transmission system are optimized by genetic algorithm.After optimization,the engine fuel consumption decreased by 3.0%,and the heat output of the transmission system decreased by 3.8%,so that the "overheat" problem of wheel loader was alleviated to a certain extent.(2)According to the heat dissipation requirements of loader transmission system,the plate-fin oil radiator needed for the two-loops cooling system of loader was designed by using the combination of Log-Mean Temperature Difference method and CFD numerical simulation.The performance test and design method of the oil radiators were verified by the radiator bench test.The effects of different flow patterns on the internal flow field of four kinds of oil radiators in H type,X-1 type,X-2 type and Z type were studied.The relationship between nonuniformity of flow field and the heat dissipation performance of oil radiator is analyzed by extracting the specific state characteristic parameters of each microchannel,and the suitable flow mode of different fins is obtained.The flow pattern of oblique flow in the flow field is studied by using CFD simulation,and the comparison shows that the influence of fin wavelength was most significant in four structural parameters of offset strip fin.The comprehensive performance of the three main flow patterns under the same fin structure parameters was evaluated by introducing j/f factor.The results show that the parallel flow performance is the best,followed by the oblique flow,the vertical flow the worst.These studies provide a theoretical basis for better performance of heat transfer performance of oil radiator.(3)Based on the theory of effectiveness-NTU method,the relationship between distribution of surface air velocity and the resistance performance of radiator is derived.In order to reduce the pressure loss,the air distribution state in heat dissipation module is predicted and characterized by defining the nonuniform coefficient of cooling fan outlet section.The variable circulation design of loader cooling fan was carried out by the isolated airfoil method.On the basis of verifying the accuracy of simulation,the influence of different structural parameters on the nonuniform coefficient is analyzed emphatically.At the same time,it provides a reference for fan matching selection and optimization design.The resistance performance of the combination characteristics of heat dissipation module is further studied by using the established wind chamber model.It was found that the variable circulation fan can make full use of the high speed area of tip,but also causes the nonuniformity of the air velocity distribution.With the increase of variable circulation coefficient,the airflow uniformity is improved.The small hub ratio and circumferential forward skew are both conducive to the improvement of airflow state,but the latter need to choose the appropriate forward skew angle.(4)Taken the underhood of wheel loader as the research object,CFD method is used to simulate the internal flow field state of original engine cabin structure under the condition of V-type shovel loading operation.After verifying the accuracy of the simulation model,the underhood with two-loops cooling system was analyzed.In order to ensure the cooling air flow constant,the engine and fan transmission ratio was reduced to 0.9 based on the relationship between the fan speed and volume flow of underhood.Combined with the analysis results,the vehicle thermal balance test was carried out for the physical prototype with the two-loops cooling system.Through the analysis of test data,the results show that the two-loops cooling system can meet the heat dissipation demand of wheel loader,and its energy consumption is 21.4% lower than that of the original cooling system. |
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