Thermal Balance Analysis Of High Speed Gearbox Of Electric Vehicle Based On Thermal Network Structure

The high speed differential gear box transmission system of electric vehicle studied in this paper is the motor that drives the power output,the reducer and the differential gear box combined with the gear box to reduce and twist,and drive the car to drive normally.Due to the small volume,high integration,12000r/min speed,small heat dissipation area,poor heat transfer,heat conduction,and severe temperature rise,the differential gear box of electric vehicle is very easy to cause a series of serious consequences such as the failure of the core parts such as gears and bearings and the breakdown of the lubricating oil.Therefore,it is necessary for the high speed difference of electric vehicles.The thermal characteristics of the gearbox transmission system are analyzed and the distribution of temperature field of each component in the system is studied.It is of great guiding significance and engineering value for the heat analysis and design of the gear box in the future.The main contents of the paper include:(1)By analyzing the structural characteristics and transmission principle of the transmission system of electric vehicle differential gear box,according to the relevant design methods and theoretical knowledge of the mechanical design,the corresponding stress analysis and calculation of the core parts of the gear box of the differential gear box of the electric vehicle,such as bearings and gears,are analyzed and calculated.(2)Based on the principle of friction loss correlation,a calculation model of heat transfer and heat transfer resistance between the main heat source meshing gear and the bearing friction power loss model of the transmission system of electric vehicle is established.For the calculation model of gear meshing power loss,the corresponding mathematical model is set up from four forms of sliding friction power loss,rolling friction power loss,agitation power loss and wind resistance power loss.For bearing friction power loss model,ball bearing and cone roll are studied according to the different bearing types.The friction torque calculation method of sub bearing and roller bearing is established,and the corresponding friction loss model of bearing is established.According to the theory of heat transfer,thermal conductivity and thermal resistance,the heat transfer and convection heat transfer coefficient of the core parts of the gear,bearing,box and other parts of the lubricating oil and air lubricants are obtained,and the thermal resistance calculation model of the parts of the differential gear box transmission system of the electric vehicle is established.(3)The heat transfer path in the gear box of the electric vehicle is analyzed and analyzed.According to the structure characteristics of the gear box,the node is divided and the thermal network model of the gear box is set up.The thermal network model of the differential gear box of the electric vehicle is set up,the heat balance equation of the corresponding temperature node is listed.The steady-state temperature value and distribution rule of all the temperature nodes in the gear box transmission system of the electric vehicle are obtained by MATLAB programming.When the gear box runs for a certain time,the gear box is operated for a certain time.After that,the heat exchange of the gear box is balanced with the outside,and the temperature values of each temperature node are all stable.The time and temperature of the stable state are closely related to the input speed and torque.(4)Through the analysis of the heat balance of the gear box with different depth of the oil,the high oil immersion depth will increase the loss of the power of the gear,increase the loss of the heat power,lower the depth of the soaked oil,and lack the lubrication between the gear pair and the bearing,which can not get the heat in time,which leads to the increase of the temperature of the gear box.The influence of the lubricating oil with different kinematic viscosity on the heat balance temperature and balance time of the electric vehicle's differential gear box is analyzed.The steady-state temperature field of the key nodes,such as gear and bearing,is calculated respectively,which provides theoretical guidance for the heat balance design of the electric vehicle's differential gear box.