Research On OBD Method And Strategy Of Electromagnetic Driven Linear Pump Liquid Metering Device

With the strict emission regulations,urea Selective Catalytic Reduction（SCR）technology is considered to be the most efficient method for diesel NOx emission.In the phase of China V emission regulations,SCR technology are widely used in Automotive,and the corresponding on-board diagnostic（OBD）system is also indispensable.Technical specification for on-board diagnostic（OBD）system of compression ignition and gas fuel spark ignition engines of vehicles-HJ437 – issued by the Ministry of Environmental Protection in June,2008,which puts forward a mandatory requirement for OBD on SCR system.There are still many problems in SCR_OBD systems for ensuring accuracy of diagnostic,such as: complex system,high cost,reducing system reliability,even unable to detect a part of the dosing system malfunction.Electromagnetic driving linear pump liquid metering device,name ly Free armature injection（FAI）hydrometer.It uses Electromagnetic pulse intermittent injection technology.Its SCR aftertreatment system（FAI_SCR）has the character of injection volume controlling accurately,simple structure and low cost.FAI_SCR dosing injection system can perform linear injection control relying on T3 metering theory,its feedback parameter T3 appear linear relation with injection volume.This paper based on the relationship between T3 parameter variation and several kinds of typical injection system malfunction.By the simulation experiment on flow test bench to summarizes the experimental results and proves the accuracy of assumes.The results indicate that T3 feedback parameter is sensitive to the change of the actual injection volume of dosing unit.It can accurately reflect the change of actual injection volume in a short time.It is proved that the feasibility of fault detection by own characteristic of dosing unit.Based on the diagnostic method summarized from experiment results,on the promise of assure fault detection accurately,determine the fault threshold of T3 in the condition of variety malfunction,voltage,driving pulse width and the change of air pressure in air assistant SCR system,it is formed that a complete set of mechanical malfunction diagnostic strategy of dosing injection system.Based on Freescale MC9S12G128 microcontroller,building a hardware platform that carrying OBD system to diagnose the malfunction of urea liquid level and urea temperature by urea level temperature sensor and the malfunction of open circuit and short circuit that inject driving and air solenoid valve.C code of diagnostic control strategy are compiled by utilizing CodeWorrior software,use software to diagnose air_pump,blocking_pump,locking_pump,droping_pressure.Finally send a CAN frame to reflect the result of system diagnosing by DATAVIEW software.After hardware platform building,software programming,debugging completed,I based on JAC₂.7L prototype diesel engine,building test bench of OBD function.The experiment demonstrated OBD malfunction diagnosis logic,in the way that artificial simulation fault of common form in the market.A complete diagnosis method,strategy and design of experiment of dosing system OBD belonging to FAI_SCR urea dosing injection system are maked y debugging and optimizing mechanical fault diagnosis strategy.