Development Of China 6 Aftertreatment OBD System For Light Duty Gasoline Vehicles

With the implementation of the China 6 emission regulations for light duty gasoline vehicles,the use of Three-Way Catalytic Converter(TWC)and Gasoline Particulate Filter(GPF)integrated aftertreatment system to reduce harmful emissions has become a mainstream trend.On-Board Diagnostics(OBD)is an essential component of the engine management system.Its basic functions include monitoring and diagnosing emissionsrelated components;indicating faults through Malfunction Indicator Lamp;storing faultrelated information;communicating with diagnostic software.The increased complexity of the aftertreatment system brings new challenges to OBD development work.Combining the domestic and international OBD research experience,this thesis analyzed the requirements of OBD software and hardware,and developed a set of aftertreatment OBD system for light duty gasoline vehicles meeting China 6 based on the idea of Rapid Control Prototyping.The system hardware was customized by the NI PXI platform.The hardware was selected according to the measurement requirements of the aftertreatment components,and the acquisition and communication of the sensor signals and engine operating parameters were realized.The system defined four fault types of GPF: removal,leakage,overload and blockage,as well as two state of TWC: aging and criticality.Fault samples were prepared and standard data sets were established based on emission results.The thesis researched fault diagnosis algorithms based on neural network in MATLAB,selecting Backpropagation Neural Network(BPNN)and Deep Belief Network(DBN)as the model structure of GPF and TWC respectively,and selecting reasonable training parameters.After a large number of offline tests,it was proved that the algorithm had good diagnostic accuracy and generalization performance.The overall construction of the OBD system model was completed in Simulink based on the offline algorithm,including three sub-models: diagnostic condition judgment,neural network diagnosis and fault decision.Various system interfaces and variables were defined to form complete diagnostic logic and the overall function of the OBD system were improved.Based on Veri Stand,the development platform of OBD system was developed,realizing functions including hardware configuration,model code generation and downloading,and ECU communication.The designed interactive interface enabled real-time status monitoring and parameter calibration of the system.The basic diagnostic function of the aftertreatment OBD system was verified by bench test.The test results showed that the OBD system could correctly diagnose the corresponding faults of the aftertreament components under unknown steady-state conditions,and the discrimination of various fault modes was good.The diagnostic condition judgment module and the fault decision module of the aftertreatment OBD system were verified by drum test.The test results showed that the OBD system could correctly identify the diagnostic conditions,calculate the real time probability of failure and make reasonable fault decisions in the actual driving cycle,which meets the design requirements.