Research And Application Of OBD Function For Urea SCR System

With the release of more and more strengint diesel emission regulations, the ureaSelective Catalytic Reduction (SCR) considered as the most suitable deNO_x aftertreatment technology in China has become the focus of the domestic OEMs anddiesel manufactures. The On-board Diagnostics (OBD) of the SCR is one of the keyapplication technical issues of the SCR and has been put on the agenda in the nationalregulation implementation. The major task of the paper is to develop the OBDfunction of the SCR system with a self-owned intellectual property right to meet therequirements of the national regulations.According to the OBD requirements for the SCR system in the nationalregulation HJ437-2008, this paper realized the overall design and the division offunction modules. The failure diagnostic part is divided into the conventionaldiagnosis and the emission related diagnosis. The diagnosis of the basic functions ofthe SCR system including the diagnosis of sensors, the diagnosis of communicationfailures, the diagnosis of reductant supplement failures, and the diagnosis of thecatalyst failure are designed. Two technical routes based on the NO_x control and theAdblue control of the emission related diagnosis are explored. In the fault responsepart, functions such as MIL control, trouble code storage and torque limit control aredeveloped. The basic communication mode is built based on the standard of SAEJ1939OBD CAN protocol.Through the HIL simulation test, the basic functions of the OBD systemincluding the diagnosis of sensors, the basic logic of the NO_x control, some diagnosisof the Adblue control, the diagnosis of reductant supplement failures and thediagnosis of communication failures are verified. On the bench test, the functions ofthe NO_x control and the Adblue control, as well as the diagnosis of the catalyst aredemonstrated, which means the OBD system can fulfill the requirements of thenational OBD regulation.