Research On Diagnostic Strategy And Calibration For On-board Diagnostic System Of Gasoline Engine

It is believed that the automobile exhaust is the primary factor of the air pollution. It has become seriously affecting the human life. More strict requirements had been put forward to control the environment problem around the world."Limits and measurement methods for emissions from light-duty vehicles (China Ⅲ, Ⅳ) GB18352.3-2005" was promulgated in2005in China to monitor emission states in the car of the whole life. Promulgated in2013"Limits and measurement methods for emissions from light-duty vehicles (China Ⅴ)GB18352.5-2013" has taken higher requirements for on-board diagnosis system.Based on the main research of on-board diagnosis system, this thesis expounds the composition, principle, main features of the system. The oxygen sensor fault diagnosis, misfire fault diagnosis, coolant temperature sensor fault diagnosis and the diagnosis of intake manifold absolute pressure sensor was discussed in this thesis.In terms of misfire fault diagnosis, the principle of misfire based on crankshaft speed fluctuation was analyzed in Section3. The method of the roughness of R and the deformation of Q had been taken to ensure the effectiveness of misfire detection. The map of limits caused by emissions exceeding the standard and by catalytic converter damaged was obtained through the calibration procedure.In terms of oxygen sensor diagnosis, the characteristics and principle of the oxygen sensor and the role in fuel closed-loop control was analyzed in Section4. For the oxygen sensor circuit malfunction, the method of test the range of voltage value was raised. For the oxygen sensor aging failure, the method of comparing theory and practical cycle value was adopted. The cycle map of the oxygen sensor under the theoretical condition was obtained through the calibration procedure.In terms of the coolant temperature sensor fault diagnosis and the intake manifold absolute pressure sensor fault diagnosis, the principles and common faults of these two kinds of sensors was discussed in section5. The method of detecting the voltage signal to determine whether to malfunction was adopted. Against the unreasonable malfunctions, the important map of limit was calibrated.With the failure simulator, The type I emission test base on the various fault to confirm the rationality of the limit of the calibration and the reliability of fault diagnosis strategy were carried out. At the same time it is proved that the fault diagnosis of strategy and calibration approach can pass through the certification test.