Research On The Core Technology Of On Board Diagnostic System For Emission Control Of Light Gasoline Vehicle

As an effective method for emission monitoring, On-Board Diagnostic (OBD)system has been generally brought into the emission standards in mostautomobile-producing countries and regions. In this paper the core technologies of OBDsystem are researched by data analysis, mathematical modeling, numerical simulationand experimental investigation.Engine misfire detection is studied based on the crankshaft speed fluctuation.Through engine misfire bench test, the influence of58X wheel tolerances onrecognizing misfire is studied, and the remedy strategies for58X wheel tooth learningin misfire detection are studied and optimized. The time domain moving averagemethod is adopted to eliminate the noise in the reference period measurement processand a gasoline engine misfire detection method based on crankshaft speed multiplefiltering is presented. The test verifys that the method can recognize multi-cylindersrandom misfires accurately without fuel-cut self-earning and fuel-on self-learningmodifications.Three-way converter (TWC) deterioration diagnosis is studied based on the oxygenstorage capability of TWC. The paper focuses on switching lambda sensors which arewidely installed on automobiles. Based on chemical reaction kinetics, the oxygenstorage rate model of TWC is established. The established oxygen storage rate model issimulated in Matlab/Simulink. The diagnostic algorithm for TWC degradation isdesigned based on the oxygen storage rate model. The degradation factors of the oxygenstorage rate model of TWC are studied by online feedback correction method. The testdata on engine bench indicates that the oxygen storage rate model has a high accuracy,and the diagnostic algorithm for TWC degradation is validated.Exhaust gas oxygen sensor (EGOS) aging is studied based on the signal fault ofEGOS. The EGOS aging test bench is set up by using the oxygen signal generator. Thediagnosis strategy for EGOS degradation and the relevant test verification on enginebench are presented. The impact of EGOS aging on air-fuel ratio and emissions isstudied. During oxygen sensor response slowing to gas mixture from lean to rich thenormalized air fuel ratio decreases gradually and the emission concentrations of HCand CO increase; during oxygen sensor response slowing to gas mixture from rich to lean the normalized air fuel ratio increases gradually and the emission concentrationsof NOx increase. An adaptive correction PI air-fuel ratio control algorithm for oxygensensor slow response is presented based on the original air-fuel ratio PI controller in SIengines with a switching oxygen sensor. The adaptive correction PI control system isthen simulated in Matlab/Simulink, and the results show that the slow response ofswitching oxygen sensor has less effect on air-fuel ratio and the adaptive PI controller isvalid.