| China four emission regulations for commercial vehicle will be carried out soon. Compared with China three emission regulation, PM and NO_x are more stringent. NO_x is decreased by 30 percent and PM is decreased by 80 percent.FAW began the research about the emission regulations policy and technical route, control strategy from 2006 year. Under this background, we research the SCR urea dosing control strategy deeply by a project. Based on this project, SCR urea dosing control strategy for China five is reseaeched.One of the technical route for FAW is combustion optimization inside engine with SCR aftertreatment. Engine is based on the diesel engine of China three. By the optimization of engine performance, the nozzle, combustion chamber, turbocharger matched are fit for the engine of China four. Engine is calibrated by DOE method at universal working condition. The result of the test is that the BSFC is 199g/kW.h, PM is 0.018 g/kW.h which meets the emission regulations of China four, NO_x is 9 g/kW.h.The work flow of urea dosing control strategy of SCR is according to the V flow which is used internationally. According to the V flow, we finish requirement definition, reqirement decomposition, plant model establishing, offline simulation and rapid control prototype verification for control strategy.In the urea dosing control strategy for China four, we establish the urea dosing map. Based on this map, urea dosing is corrected. To prevent much dosing, the urea dosing quantity is limited. To ensure that the air mass flow is accurate at the transient condition, we construct the exhaust mass flow model. AT the same time, slow dosing strategy is constructed for ammonia slip at the transient condition.The urea dosing map is dependent on several factors: the efficiency of SCR catalyst, the temperature in the steady condition and transient condition. By researching the ETC, we establish the sensitive area and find the intersection between the steady condition and the transient condition. To fit for catalyst deterioration or the other changes, the urea dosing map is corrected which make the control strategy is more stability. The exhaust mass folw model can predict the exhaust mass flow, and can improve the urea dosing accuracy which can decrease the adverse factors that influence the urea dosing quantity. At the transient condition, ammonia asorpted on the catalyst is influenced by the temperature and emission, and it is very easy to produce the ammonia slip, so we establish the slow dosing model to decrease the ammonia slip.SCR catalyst model based on AMESim software is established. The accuracy model is got by the model parameterization and adjusting. To verificate the transient urea dosing control strategy, the urea dosing control model based on simulink simulation with SCR model. We verificate the control strategy and adjust it ,then experience many repetitions. By simulation, we got the optimization results and verificate these results by RCP. The results by RCP are near to the simulation result. The result of NO_x ETC is 3g/kW.h, and the result of NO_x ESC is 3.03g/kW.h. The emission fulfils the China four emission regulations. Ammonia slip is little and the peak slip quantity of ETC is 6 ppm.Urea dosing control strategy is SCR model based on the closed loop control. By the ammonia loading closed loop control, ammonia slip is decreased and the emission satisfies the China five emission regulations. The ammonia slip selection is according to the strategy of China four. The SCR model for the control is based on the Eley-Rideal mechanism and combined with the chemistry reaction dynamic and material balance principle. Compared with open loop and closed loop control, the model based closed loop control is better than the open loop control, which can control ammonia slip. For the verification of RCP, the result is fit to the simulation.
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