The Study On The Testing Method Of OBD Function For SCR And DPF Aftertreatment Of Heavy-duty Diesel Vehicles

On-Board diagnostic(OBD) system is an online monitoring and diagnosis system for vehicle emissions.The research and application of OBD technology for heavy-duty diesel vehicles is in a stage of rapid development.In 2008,Chinese Ministry of Environmental Protection issued HJ437-2008 which details the technical requirements of OBD system for heavy diesel vehicles.There are two paths for the aftertreatment system of heavy-duty diesel vehicles in stage 4 of National emission standard.One of the paths is SCR aftertreatment and the other one is EGR+DPF aftertreatment.They both should meet the OBD regulations.To carry out the OBD function test of SCR and DPF aftertreatment,this subject has established an OBD test platform which can meet the stage 5 of National emission standard.The platform which is able to meet the regulatory requirements of ESC,ETC and OBD test includes dynamometer system,boundary conditions control system,emissions testing system and OBD diagnostic instruments.This subject summarizes main and critical faults and its characterisitics of the heavy-duty diesel vehicles,including various faults of SCR and DPF. This subject details the testing process of OBD function for heavy-duty diesel vehicles,including OBDⅠ/OBDⅡ function testing and NOx control testing.All kinds of fault simulation projects of OBDⅠ/OBDⅡ function testing have similar testing process,but NOx control testing adopts different testing process and methods according to different de-NOx ways.This subject carried out a series of OBD function tests on the basis of testing process and methods,and the results of tests verified the reliability of the platform and the feasibility of the test method.Besides,through the comparison between the test results of gaseous pollutants in NOx control tests and regulatory emissions and OBD limits.The subject draw a conclusion that the OBD system of heavy-duty only alarms when NOx exceeds standard seriously.This subject has developed an virtual instrument which can be used to test the OBD function of SCR electronic control unit.This instrument can communicate with the SCR electronic control unit which is developed on the basis of SAEJ1939.The instrument can simulate some basic sensor signals of diesel and SCR aftertreatment system and several common signals of SCR serious functional faults.The instrument has the OBD diagnostic reading capabilities.The subject verified the reliability of the testing instrument through the OBD function testing of SCR electronic control unit “AERI-DCU”.The testing methods of OBD function of SCR and DPF aftertreatment system can provide guidance to OBD certification test of heavy-duty.The virtual instrument which is used to test OBD function can be applied to help the development of SCR electronic control unit and support the testing work in the type approval agency.