Research And Development Of Vehicle Misfire Generator For OBD System

On-Board diagnostic (OBD) system test is the key content and difficulty of the implement of Stage III and Stage IV. OBD system monitors the emission-related components from the performance of the engine at any moment. Once the malfunctions of some components may results in emissions exceeding the threshold limits, Malfunction Indicator will be activate. When malfunctions are found, the malfunction indicator light or check engine light will illumine, and Power Control Module (PCM) will store the malfunction information in memorizer simultaneously. Through certain procedures, fault codes can be read from PCM. According to the indication of fault codes, repairman could judge the character and position of malfunction rapidly and precisely, which could prevent in-use vehicles from exceeding emission standard because of the malfunction of some emission-related components.Engine misfire is one of the most important functions. As the OBD monitor of engine misfire, drivers could find the misfire fault and solve the problem immediately and ensure the usage time of catalytic converter and the in-use vehicles will not exceed the emission standard. This project develops a suit of misfire generator for the functional approval test of OBD system. This device could set misfire rate, and make the engine misfire deliberately in order to judge if the OBD system of the vehicles meeting Stage III emission standard is functional. Therefore, this development is significant for the OBD functional approval test and the implement of Stage III nationwide.This paper analyzes the OBD system diagnostic strategies; introduce the monitor principles of engine misfire, oxygen sensor and catalytic converter. The engine misfire types are focused on, and several misfire judging methods are introduced. OBD diagnostic strategies of crankshaft speed fluctuation are elaborated, which offer the theoretical foundation for the development of misfire generator.The design of misfire generator bases on the ignition control signals from ECU...