Study Of On-board Diagnostics System For Heavy Duty CNG Engine

With emission regulations becoming more and more strict ,the Light-duty vehicles need to install on-board diagnostics (OBD) system that have been required by emission standard .By July 1 st,2010,all light-duty vehicles must install OBD system .At the same time ,the technology of OBD for Heavy-duty vehicles have been included in the proposal. At present, the study of OBD system for Heavy-duty vehicles is on the initial stage in china. This paper had a preliminary study of the OBD system for Heavy-duty CNG engine, on the one hand, it would improve the efficiency and accuracy of the engine diagnosis for heavy-duty CNG engine, on the other hand, it would provide a theoretical reference for OBD system regulations of heavy-duty CNG engine, which would promote the development of OBD system for domestic Heavy-duty vehicles.This paper designed the OBD system of WT615Z280CNG engine ,according to regulations of OBD system . Also designed the strategy of diagnosis for the module of engine components ,misfire and catalytic converter ,developed the diagnostic program of emission-related components, which made this system have the function of detecting the malfunction of engine components ,misfire and catalytic converter and so on .This paper had an experimental study of fault diagnosis which based on the test bench of WT615Z280CNG engine. The diagnosis of misfire was studied in this paper which mainly discussed the method of crankshaft speed fluctuations and wide-domain oxygen sensor .Also studied the algorithm of engine roughness ,the difference of signal for wide-domain oxygen sensor before and after misfire, as well as the impact of misfire on engine emission and so on. In the mean time also studied the Characteristics and efficiency diagnosis of special catalytic converter for CNG engine,using upstream/downstream dual oxygen sensor to measure deterioration of catalytic converter.