The Urea-SCR System Control Strategy For Vehicles Based On ADRC

The urea-SCR technology is acting as the major after-treatment scheme for NO_X from truck diesel engines to meet National?or National?emission regualtions in China.However,a common problem emerged on the vehicles passed through type approvals on emissions and on on board dignostics?OBD?systems.The real NO_X quantities emitted into the air were much higher sometimes for the above vehicles as compared to the thresholds of the related emission legislations.As a result,the engine torque limiters were activated via the OBD systems,which affected the normal operation of the related vehicles.In addition,the requirement of NO_X conversion efficiency will up to 90%for a truck diesel engine to meet National?,which means matching a urea-SCR system for the engine will remain the promising option.According to the actuality of the urea-SCR technology,a significant innovation on the control system is necessary to solve the application problems at present and in the future.At the present stage,the excessive NO_X emission from a truck diesel engine with a urea-SCR system is attributable to the lack of disturbance rejection ability of the SCR controller.With the thresholds of NO_X specific emission and OBD system alarm adjusting downwords at National?stage,the NO_X over-discharged problem will become more prominent for truck diesel engines,if no disturbance restraint performance improvement is made for SCR controllers.It's imperative to develop the novel SCR controllers with excellent performances on disturbances rejection and dynamics response,to obtain quite high conversion efficiencies and accurate emission quantities for NO_X from diesel engines with urea-SCR devices.In this paper,a nolinear active disturbance rejection controller?NADRC?for a set of SCR system will be designed and applied on truck engines,to solve the NO_X over-discharged problem via the improvement on the accuracy of NO_X controlling,the performance of disturbances rejection,and the conversion efficiency of NO_X.Firstly,a reduced mathematical model was extracted based on the properties analysis for a urea-SCR system,and then the whole system framework of the NADRC controller was build.The contradiction between the fast response and the small overshot was reconciled via the transistion process arrangement of NO_X targets,the nonlinear combination of error feedback gains,and so on.The internal and the external disturbances,the SCR system suffered from,were regarded as a generalized disturbance for the improved controller.An extended state observer?ESO?was established to evaluate the disturbance action,and a special feedback control law was adopted to deal with the diversity of disturbances on vehicles.Secondly,a controller simulation model was build and the related controller parameters were calibrated via the combination of experiences and index optimization.Some simulations were conducted based on data from engine benches and vehicle tests successively.The initial values of the controller state variables were found to be the major parameters at engine bench calibration stage according to the simulation outcomes.Lastly,the dynamics performance and the disturbances rejection ability of the NADRC strategy were evaluated via engine bench tests and field tests successively.Research results indicated that the novel controller did well in the diesel engine emission type approval for National?,had potential to make further NO_X reduction through detailed calibration,and could be treated as the core technology of the diesel engine aimed on National?.The novel controller based on the NADRC was a success on disturbances rejection and accuracies of NO_X emission.The truck diesel engine with the SCR controller could run with low NO_X emitted into the air always.The NO_X over-shoot problem as the result was solved.This research realized the application of the nonlinear active disturbance rejection control technology on the urea-SCR control system for the first time.As the results,the performances of dynamics response and disturbances rejection were improved,and the NO_X over-shoot problem for the truck diesel engine was solved.In this paper,a clear and simple calibration regulation for the SCR controller based on the NADRC technology was proposed and applied.According to the new calibration regulation,the parameters of the SCR controller were confirmed via simulations,and the initial values of the state variables were calibrated based on engine bench tests.A simplified controller parameters tuning method with the combination of experiences and index optimization was provided and applied for the first time also.The reduced mathematical model of the controlled object with the fixed time lag and time constant was proposed and build,with the working process of the object was characterized as a first-order process with a time delay.So the development of the SCR controller was independent on the accurated controlled object mathematical model,the difficulties involved during the control system design were reduced significantly.