Study On OBD (On-Board Diagnostic) Type Approval Test For Light-duty Gasoline Vehicle

Light-duty vehicle emission standard GB18352.3-2005 was issued in 2005, it was drawled according to EC regulation. OBD checking test is consistent with EC regulation. When GB18352.3-2005 was issued, light-duty vehicle manufacturer and person of inspection institution both not very understand OBD system and OBD test. Both focused on how to test OBD system. Because of test work, we have much communication to aim at OBD test technology with international manufacturer and to discuss OBD test operation procedure and technology method. We have tested many OBD systems including domestic and foreign system and accumulated a lot of data and practice in OBD system test.With OBD system tested by CATARC emission laboratory for domestic and foreign vehicle, the request of OBD test for GB18352.3-2005 was summed up. Basic structure and principle of light-duty vehicle OBD system, light-duty vehicle OBD system verification procedure, OBD system fault simulation technology was illuminated. According to light-duty vehicle test data, problem in OBD test was analyzed. Some amelioration suggestion was given.The main study works in this thesis are:⒈To introduce the OBD system development. To expound the measurement method and emission regulation of light-duty vehicle exhaust emissions, and the correlation problem about extending the application of light-duty vehicle OBD system in our country. The significance of the research work for light-duty petrol vehicle OBD system approval test was given. The main research content of this project was summarized. ⒉To introduce the OBD system structure and basic principle. OBD is important part of engine management, which measure all system, accessory and controller relation to vehicle emissions through complicated logic. On fault condition, it will illumine MIL to prompt driver. To introduce OBD measurement principle and realization method from main content of OBD measurement including oxygen sensor, catalyst and misfire in this thesis.⒊To aim at OBD system checking content included in GB18352.3-2005. To analyze the requirement of light-duty vehicle OBD test according to standard. to analyze the requirement of light-duty vehicle OBD test from appendix I of GB18352.3-2005 about OBD test requirement and the preparation of light-duty vehicle OBD system approval test. It is useful for light-duty vehicle OBD system approval test.⒋To analyze different fault simulation technology of light-duty vehicle OBD system approval test and to summarize correlative test method. Aiming at main item of light-duty vehicle OBD system approval test, to expound oxygen sensor fault, catalyst fault and misfire fault simulation method and test procedure, and to analyze influence factor of simulation approval test.⒌According to practice, reasonable test and evaluation method of light-duty vehicle OBD system checking was issued.⒍One low exhaust vehicle with stepⅢemission standard limit was tested. OBD monitoring signal was measured before and after test using special equipment. The results were compared and analyzed. CO,HC,NOX and fuel consumption results of different test items was contrasted. Fault simulation effect on emission result was summarized.⒎On the basic of statistics from 30 different light-duty petrol vehicle OBD test data, CO,HC,NOX results of oxygen sensor deterioration simulation, catalyst deterioration simulation, misfire simulation test items were analyzed. Most vehicle results are less than OBD test threshold limits because OBD test threshold limits is easiest. Therefore, the vehicle's emissions maybe exceed the approval limits and high emission limits of in-use vehicle, but MIL not be illumined through analyzing test results.Through studying in this thesis, two important conclusions are gotten:(1) Because OBD threshold limits is easier than approval limits for OBD test, some OBD test results exceed approval limits and high emission limits of in-use vehicle, but not exceed OBD limits, the result is pass. Therefore for vehicle emissions checked in practice, some vehicle's emission exceed approval limits, even exceed high emission limits of in-use vehicle, but OBD system MIL does not illumine, this is allowable. It can be said that OBD system is used to identify vehicle's emission condition to ensure the basic requirement of emission control system.(2) Because only requiring to monitor HC to identify whether catalyst is normal in china stepⅢ/Ⅳand CO,NOX result is not examined, it result in part CO , NOX result maybe exceed OBD threshold. Along with technology development, it will be overcomed by more strict regulation.