Thermal Analysis Of Two Speed Automatic Transmission Drive System For Pure Electric Automobile

At present, due to the shortage of petroleum and accompanied with the greenhouse effect, toxic gas emissions increasing and other environmental issues, countries all over the world have been gradually carring out research and development of pure electric vehicles.Currently the electric drive of the electric vehicle is usually composed of a motor, reducer,and differential. But the dynamic performance is greatly restricted due to the low degree of integration of the structure. So using two speed transmission mechanism gradually attracted the attention of the people. Because of the small volume and high degree of integration structural characteristics of it, this will lead to reducing the area of heat radiating, worsing the heat transfer condition and the system temperature sudden increasing.The high temperature will bring adverse effects to the normal work of the system, such as the agglutination of gears,bearings and other important parts;the decomposition and metamorphism of the lubricating oil and so on.So the overall thermal analysis for the drive system of electric vehicle, studying the rule of heat transfer of the transmission system and the distribution of temperature field has very important theoretical significance and practical value.Based on the mechanical theory and related design Requirements, the stress analysis of the gear,bearing and other key parts of the system are carried out. The calculation model of friction power loss of the gear,bearing and Synchronizer are builded according to the principle of friction loss.For helical gear, the thermal power loss calculation model is builted from three aspects like the sliding friction loss, the stir oil loss and windage loss.For rolling bearings, the friction power loss calculation model were established respectively for ball bearing, tapered roller bearings and needle roller bearings through the analysis of the size and working conditions of various types of the bearings. For the synchronizer, the friction power loss calculation model is builted based on the analysis of its structure and heat generation mechanism.The convection coefficient of the contact surface between the gear, bearing, box and lubricating oil,air are calculated according to the principle of heat transfer and resistance calculation theory.Then heat resistance are gained between each node.And with the application of the thermal network method,the thermal network diagrams and heat balance equations of all radios are set up.Finally the temperature response data and distribution of all the nodes in the first radio are obtained through programming with the Matlab software.By carrying the temperature measuring experiment platform, the temperature data of some key nodes are acquisited in the steady working state acquisition and compared the result with the theoretical analysis result, to prove the accurate of theory analysis method.