Research On On-Board Diagnostic Strategy Of The Gasoline Engine Electronic Control System

By the late1970s and the early 1980s, most of the vehicle manufacturers had begun using electron technology to control engine system and detect malfunction of the engine parts, to satisfy the requirement for emission monitor and malfunction diagnosis of vehicles from the environmental protection department. From 30th December, 2006, all the automobiles sold in Beijing must be equipped with EOBD. It will be executed throughout the country from 1st July, 2008. This dissertation takes OBD system of the electronic control gasoline engine as the research content, dissertates in detail the basic control strategy of the gasoline engine electronic control system and the composing, principle, characteristic, diagnosis objects and malfunction manager of OBD. Based on this, an in-depth research on misfire diagnosis, oxygen sensor diagnosis and catalyst converter diagnosis is made.Based on the fluctuant crankshaft rotate speed, the misfire diagnosis algorithm is developed. If the time when the firing cylinder moves from TDC to BDC is longer than the threshold value, misfire should be taken place. In order to fix the misfire threshold value and validate the misfire diagnosis strategy, we have developed the misfire generator. Experiments such as gasoline-level-low-drive and rough-road-drive are made to determine enabled conditions and delay conditions of misfire diagnosis. Vehicles equipped with the misfire generator can illuminate the MIL in the type I emission test, which proves dependability of the misfire diagnosis strategy in this dissertation.Aiming at invalidations of the oxygen sensor, we have developed the oxygen sensor malfunction simulator. Simulate the invalidation modes of the oxygen sensor to research influence to emission caused by invalidation, then make an in-depth analysis on the causes of the influence. Design the oxygen sensor diagnosis strategy. Divide oxygen sensor diagnosis into voltage diagnosis and response diagnosis. Make experiments in cold, hot and altiplano conditions to validate the rationality of the threshold values in oxygen sensor diagnosis. Vehicles equipped with the oxygen sensor malfunction simulator can illuminate the MIL in the type I emission test, which proves dependability of the oxygen sensor diagnosis strategy in this dissertation.Analyze invalidations of the catalyst converter and the detecting methods. Indicate advantage, disadvantage and applicability of the methods. Measure the OSC times of the new catalyst converter, the aged catalyst converter and the threshold catalyst converter. By analyzing, make conclusion that there is corresponding relation between OSC time and work capacity of the catalyst converter. Then develop the converter diagnosis method based on OSC time. Vehicles equipped with the threshold catalyst converter can illuminate the MIL in the type I emission test, which proves dependability of the misfire diagnosis strategy in this dissertation.Misfire diagnosis, oxygen sensor diagnosis and catalyst converter diagnosis are the key contents of the Stage III. By the emission tests, the diagnosis strategy researched in this dissertation can efficiently diagnose misfire malfunction, oxygen sensor malfunction and catalyst converter malfunction.