Simulation Research On Flow And Heat Transfer Of Tractor Power Shift Transmission Lubrication System

With our country’s agricultural machinery gradually develops from tradition to intelligentization,the requirements for the performance and functions of a gricultural machinery are gradually increasing.As a representative of intelligent machinery,power shift tractors have the characteristics of smooth shifting under uninterrupted power,and can work smoothly in various working environments such as high speeds and heavy loads.Since most of the friction loss in the transmission system is converted into heat loss during the load shift process,in order to prolong the service life of the transmission,it is necessary to optimize the design of the structure of the lubrication system to decrease the main friction heat loss in the transmission system.Based on the power routes of the transmission,the distribution of the main heat sources in the transmission is determined and the heat transfer diagram is drawn.Using the GUI module of Matlab,the programs for the calculation of the thermal boundary conditions of the power shift transmission system is written,which lays the foundation for the subsequent finite element analysis of the temperature field of the main heat source.According to the gear heat transfer theory and the results of the calculation of the thermal boundary conditions from Matlab,the finite element simulation analysis of the gear temperature field is completed with Ansys,and the influence factors of the gear thermal conditions and the gear temperature distribution state under different working conditions are studied.By comparing the curve of speed,torque and thermal conditions,the result that the gear thermal power loss is affected by the conditions of speed and torque is obtained,and the speed and torque effects the gears differently on the gears under different work condition.In the case of low gears,the thermal power loss is mainly affected by the torque when the ratio of speed to torque is greater than 1,the thermal power loss is mainly affected by the speed when the ratio of speed to torque is less than 1.In the case of high gears,the speed and torque jointly affect the thermal power loss.Another reason is that the gear convection heat transfer coefficient is mainly affected by the speed,and the speed is always convective with the gear in each work condition,and the thermal coefficient is directly proportional.According to the bearing heat transfer theory and the results of the calculation of thermal boundary conditions,the temperature distribution state of the bearing and the temperatures of each component of the bearing under different working conditions are studied.The finite element simulation analysis of the bearing temperature field is completed by using Ansys,and it is concluded the temperature of the bearing S6-2 on the output shaft is the highest on the 16 th gear.The temperature below the outer ring of the bearing is higher,and the temperature above the inner ring of the bearing is higher than the temperature below the inner ring of the bearing due to the influence of gravity,and the highest temperature area of the bearing roller is located on the surface of the roller due to the friction and heat generation between the rotation of the roller and the inner ring and the outer ring.At the same time,the influence of bearing working speed and friction torque on bearing temperature is studied.The results show that the changing trend of bearing working speed determines the temperature,and the working speed of bearing is directly proportional to bearing temperature.Another result is that the value of the friction torque on the bearing determines the temperature of the bearing,and it is proportional to the temperature of the whole bearing.In order to obtain a better cooling and lubrication effect for the main heat sources in the transmission,a three-dimensional model of the oil injection pipeline of the transmission lubrication system is established based on the thermal balance analysis results of the temperature field of the gears and bearings,and the oil injection lubrication structure of the gears and bearings is optimized.Based on the method of VOF,the influence of different fuel injection distance,angle and speed on the gear cooling and lubrication effect are studied.According to the results of simulation,the best scheme is obtained based on the volume fraction of lubricating oil on the gear surface and the oil filling effect around the gear teeth.The best fuel injection scheme is:the fuel injection distance is 50 mm,the fuel injection angle is 5°,and the fuel injection speed is 15m/s.For the bearings,the influence of different fuel injection aperture,number of fuel injection holes,and fuel injection angle on the cooling and lubrication effect of each component in the bearing is studied by using the method of VOF.According to the results of simulation the best scheme is obtained based on the volume fraction of lubricating oil in the bearing and the oil filling effect between bearing components.The fuel injection scheme is: the injection aperture is 1.5mm,the number of injection holes is 2,and the injection angle is-5°.