Investigation Of Misfire Diagnosis Block From Jetta OBD System

With the growing number of automotive and the strengthening of global environmental awareness, vehicle emissions are facing unprecedented attention. And emissions regulations have become increasingly harsh. Beijing government plans to execute Eu3 emission regulations in 2005.07.01.And one year after execute EU3+EOBD (now change to 2007.07.01).Using electronic control unit (ECU) to precisely control supplying fuel and ignition will significantly reduce emissions. However, to meet the increasingly stringent emissions regulations, apart from the electronic control system, OBD diagnostic system must also be adding. because after the new vehicles used some time, as the damage of the engine management system (EMS)'s control components and the impact of the aging of catalyst, automobile emissions have varying degrees of deterioration, or even much higher than the statutory requirements. United States Environmental Protection (EPA)'s survey found that 60% of HC comes from 20% vehicles which emission control system have malfunction or performance reduced in light vehicles. These problems will not significantly affect the others performance of vehicle, so the driver was not aware of the problem. When the engine works, the on-board Diagnosis can detect some parts of EMS which related to emissions. If the on-board Diagnosis finds fault, it will promptly notify drivers.Based on the Jetta 1.6L gasoline, we researched the OBDII system misfire diagnostic module's theory algorithm and the determination process, and calibrated the necessary information.1.This paper analyzed the ignition process of the SI engine, and the reason of misfire. The malfunction of the fuel injection, ignition, intake and exhaust systems can cause a misfire, but the malfunction of the ignition, intake exhaust systems can be easily detected. Sometimes the misfire caused by the ignition system's fault. Because the turbulence after the ignition made the flame can't continue. This kind of misfire also created the pressure to push the piston, but the pressure was so small, that was harm for the converter, and increased the emissions. So the reliable misfire detection method was particularly important.Several misfire detection methods were put by some researchers, by analyzing these methods, we found their advantages and disadvantages:The temperature of the converter can't be used for the misfire detection, because the temperature hardly changed if the low ratio of misfire, and the number of misfire cylinders can't be counted at the same time.The signal of the oxygen sensor can't be used for the misfire detection, because the individual misfire can't cause the voltage changed. Even we installed oxygen sensor in each cylinder.The method which measures the cylinder pressure depends on the sensor'cost. Evaluated the fluctuation of Crank speed can detect the misfire. The engine administrating system added the information of crank position can satisfy this requirement, and don't need to instill sensors additional.We adopted the method that evaluated the fluctuation of Crank speed to detect the misfire of Jetta 1.6L OBD system. And detailed analyzed the mathematical model of this method.2.Achieve building platform of experiment structures. The most important tasks are main misfire generator installation and testing. In the past, many misfire tests were simulated by software. Software simulation might not be reliable. If you want to judge whether the misfire occurred by software, that would increase the complexity of system .And it is not very accurate. The misfire by misfire generator is credible. And the rate of misfire can be artificially set to evaluate the reliability of diagnosis.3.Explain the details of the misfire detection algorithm. Most Conditions can be detected by Evaluating Crankshaft Speed means. Since the engine is always operating in dynamic condition, so it's very difficult to detect some condition. And this is very easy to make mistakes. Therefore, some of parameters, static component, dynamic component and curvature component were added into the algorithm. This makes the algorithms more reliable and the results of misfire detecting more credible. Achieve calibration of engine roughness threshold, engine roughness threshold of multiple misfiring and the factor of coolant. Achieve misfire periodicity adaptation.4.Achieve calibration the rate of misfire which caused by the damage of the converter. Including determine the algorithm of the rate of misfire caused damage to the converter. As it is not possible to create real-time misfire surveillance which caused by the damage of the converters, it requires more scientific evaluationmethod to calibration, so the introduction of elements of a misfire make the rate of misfire is determined under a more directly and reliable significance. In addition, successful completion rate of misfire caused by the damage to the converter calibration work.5.Accomplish demarcating of unlimited value of 1.5 times rate of the misfire. The major task is selecting the proper aging converters. Calibration experiments in emissions caused by the fire exceeded the limit of 1.5 times the rate of demarcation. The experimental results can be seen only from the 2% rate could cause a misfire assay cycle emissions exceeded the standard 1.5 times. It is more possible to see the need for better diagnosis of this misfire.6.Achieved the demarcation diagnosis of the fade out conditions. Since the restrictions of detection method, testify every engine operating point is impossible .Then detailed calibration of diminished conditions is needed.