Basic Study On OBD Technology Of Low Emission Vehicles

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, OBD 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 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 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.OBD authentication is one of the items of national type-approval period. OBD authentication procedure is processing function demonstration test. The devices of engine misfire, oxygen sensor deterioration simulation and threshold catalytic converter can be taken by the vehicles manufactures. The requirement to OBD systems is not more stringent during new vehicles admittance period, the important difficulty is how to assure the OBD function during production consistency and in-use periods. In the developed auto manufactured areas, the management trend is not more and more important in new products admittance period, however how to insure the vehicles under low emissions state become important. The requirements of OBD and in-use compliance in Europe emission regulations give an attestation to this kind of trend.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. A set of gasoline-fuelled engine misfire generator and a set of oxygen sensor deterioration simulator were designed in this thesis, which can cause the engine misfire and control the misfire rate; oxygen sensor voltage excursion, response time delay etc., so with the two devices, we can estimate if the OBD functions work well, especially during the new vehicles production consistency period. 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.The design of misfire generator is based on the ignition controlling signals from ECU to calculate ignition times. Misfire order to shield some ignition signals is sent by control single-chip, which will cause misfire. Simultaneously a suit of control software is designed to control the misfire rate, misfire style, and could observe misfire cylinder number real-timely, which supply a convenient operation environment.A set of oxygen sensor deterioration simulator was designed. The device includes signal collection system and signal disposal system, which can adjust the oxygen output wave upper limit and lower limit, and response time delay values. Communication faucet can import oxygen sensor voltage signal to the computer through USB line, the software can display oxygen sensor signal and control the output wave under different deterioration modes, so it can control the signals from oxygen sensor to ECU real-timely.With the misfire generator and oxygen deterioration simulator, emission validation tests on chassis dynamometer were carried out, primary test results indicated that these devices can all meet the design targets, and acquired prospective effect.