The Development Of OBD For SCR System Of Diesel Engine

Compared with gasoline vehicles, because of the outstanding advantages in power and economy, diesel vehicles have been more widely used. Only using the purification technology inside the engine, it is hard to meet the increasingly stringent emissions regulations. Purification technology inside the engine combined with post-processing technology is very necessary. Selective Catalytic Reduction (SCR) technology as one of the post-processing techniques will be mainly used in ChinaⅣ. Clearly defined in national regulations HJ437, vehicles meeting the requirements of ChinaⅣmust be equipped with OBD systems. For SCR system, this paper designed the OBD for SCR system.Three kinds of overall OBD implementations for SCR system are proposed to compare to the optimal selection, according to the present situation that diesel engine fuel system and post-processing systems are often from different vendors. CAN bus protocol has been deeply studied and CAN bus communication has been basically achieved. Research has been done on SAE J1939 which is based on CAN 2.0B and the communication between the ECU in the engine side and DCU, the SCR controller, has been achieved. The main detection components in OBD system of post-processing system are given and the fault diagnosis strategy of OBD system is anaylized. According to the main detection components of OBD system, this paper details the monitoring methods of the specific failure, diagnostic strategies, fault recognition and fault storage, using the Freescale S12X family of chips and Code Warrior, the development environment, to achieve the basic functions of SCR OBD system.BootLoader based on CAN bus is developed, achieving the DCU's online update feature and solving the problem frequently removing the DCU shell and BDM programming hassles when DCU need to be upgraded. And PC program matched with the BootLoader is developed with VC 6.0. Finally, the OBD system calibration and validation experiments are done through simulation and engine bench test, proving the feasibility of the development of the OBD system.