Study On Misfire Diagnosis Strategy Of On-Board Diagnostic System

OBD is shortened form of On-Board Diagnostic Systems. OBD is key and difficult point of the EURO III emission regulations. EURO III is more stringent than EUROⅡ,so challenge on the vehicles emissions control technology was bring forward, which includes cancelling the 40 seconds idle period, -7℃low temperature cold start chamber emission test, and in-use compliance test.OBD function is very important during in-use vehicles emissions control period. OBD system can detect many systems and parts which have relation with the vehicles emissions, such as engine, catalytic converter, PM filter, oxygen sensor, emission control system, fuel system, EGR etc.. When malfunction occurred, OBD system can give an alarm to the driver and memorize the malfunction code, so register the driver to go to the service station and give inspection and maintenance (I/M) to the car immediately. OBD technology in the earlier period, can remind the driver some malfunctions occurred through seemly technical methods. The destination of OBD is finding out the malfunctions as soon as possible before vehicles turning into high emissions, but in Europe, the destination of EOBD is how to find the high emissions vehicles.OBD is the one important means of controlling the in-use vehicles emissions. OBD is not omnipotent, OBD can not measure and obtain the vehicles emissions results directly, OBD can indirectly estimate the vehicles emission deterioration through the change of main parameters of the components which have relation with emissions. So the opinion of"when the emission is over the limits values, the OBD system will give an alarm to the driver immediately"is wrong. OBD systems need to be combined with other assistant methods; thereby it can efficiently control emissions during the vehicles whole use life. Based on the OBD threshold value and the different point between every detect content, there maybe occur two possibility, vehicle emissions exceed the limits, but OBD system can not alarm immediately; another case, OBD systems is already MIL on, but the vehicles emissions also below the limits. But the two cases have different venture during in-use period or after-sale period.The OBD function main includes engine misfire, oxygen sensor deterioration and catalytic converter invalidation diagnostics. OBD system can detect some failures which cause high emissions, and maybe remind the driver to inspect and maintenance the vehicles.The OBD system diagnostic strategies were analyzed; the monitor principles of engine misfire, oxygen sensor and catalytic converter are introduced, the engine misfire type and oxygen sensor deterioration are emphasized on in this thesis.