Software Development Of Automobile Exhaust Aftertreatment Diagnosis System Based On CAN Protocol

With the rapid development of automobile industry,automobile exhaust emissions brought serious environmental pollution.Major automobile manufacturers began to adopt selective catalytic reduction(SCR)after-treatment technology to reduce the emission of polluted gases.However,under the condition of long-term urea injection in SCR system,there are some problems such as the failure of heating solenoid valve in urea box,blockage of urea injection system and the failure of urea injection.Therefore,aiming at testing and fault diagnosis of automobile exhaust aftertreatment system,this paper developed a fault diagnosis software with special functions such as reading fault code,clearing fault code,reading data stream,action test and SCR urea injection test.The main research and work of this paper are as follows:Firstly,the function of message and frame structure of controller local area network(CAN)bus in automobile fault diagnosis system was described,and then the theoretical structure of IS015765 protocol was analyzed in detail.The communication data and parameters of CAN protocol were analyzed and applied through the communication protocol between upper and lower computer.Secondly,the development scheme of exhaust aftertreatment diagnosis system was designed.The internal relationship and function of the structure of the diagnostic system for exhaust gas post-processing were analyzed,and the development tools of the diagnostic system software were selected.Thirdly,in the process of developing diagnostic software,the simulation file was designed,which recorded the data of exhaust gas post-processing stored in the electronic control system(ECU).Then,through the communication between diagnostic instrument and analog ECU,the data information of exhaust gas post-processing was parsed into parsing files,and the database of diagnostic function module was developed according to the rules of XML.The diagnostic program was developed by Visual Studio2012 software.The fault information of the exhaust gas post-processing system was read by calling the function modules of the diagnostic database,and the automobile exhaust post-processing fault diagnosis function was realized.Finally,aiming at the effect evaluation of the diagnostic software for exhaust gas post-processing,the reliability simulation and vehicle verification of the diagnostic software were designed.Based on automobile diagnostic instrument and analog ECU,a simulation verification platform for exhaust gas post-processing was built,and the functional modules of the diagnostic software were preliminarily verified.The vehicle diagnostic instrument was used to communicate with the real vehicle ECU,and a vehicle verification platform for vehicle exhaust aftertreatment was built for vehicle verification.The validation results showed that the diagnostic software can effectively test and diagnose the automobile exhaust aftertreatment system.