Research On Control Strategy And Matching Of Amino SCR System Of Diesel Engine

There are two technical routes that we can choose for National IV/V stage, among them selective catalytic reduction (SCR) can significantly reduce the NOx emission of diesel engine. Around the key technologies that need to be solved of industrialization of SCR system, this paper focuses on the research of SCR ECU Hardware reliability design, AdBlue injection control strategy, fault diagnosis system and SCR ECU calibration system, we also install the developed SCR ECU to the6.6L diesel of a host plant to matching application.Firstly, this paper completed the hardware design of SCR electronic control unit according to functional requirements, considering the vibration, heat dissipation, reliability, cost, installation, debugging, version upgrades, et al. Electromagnetic compatibility design was taken based on two aspects:circuit schematic and PCB, and reliability of designed electronic control unit was tested.Then this paper apply ATI’s calibration software Vision to establish the SCR ECU calibration platform, which can realize monitoring variable, online calibration, write calibration data to ECU Flash, et al. Based on Polling and DAQ mode of CCP protocol, introduced the MCD three layer model of ASAM, we develop a calibration system for electronic control unit using VB environment. A diagnostic software was developed based on ISO15765protocol and was integrated into the calibration system.Secondly, through theoretical analysis and experimental research results we established the raw emissions NOx prediction model and calculation model of accelerated NOx sensor signal. Based on the research on the performance of SCR catalyst we determined using the catalyst bed temperature and exhaust mass flow instead of speed and load as input of basic pulse spectrum of optimal AdBlue supply coefficient KoP and NOx target conversion efficiency, which can reduce environmental impact. we design the feedforward control strategy of AdBlue injection control based on the model. ESC and ETC cycle test verified emissions prediction accuracy and robustness of the feedforward control algorithm.The paper also studied on NH3storage characteristics of catalytic converter during work, the results show NH3coverage ratio has a great influence on NH3leakage in the transient process. Each operation point has a NH3coverage ratio threshold which can ensure NH3leakage volume ratio is less than1.0×10-5during the rapid heating process and try to improve the NOx conversion efficiency. According to the research results of the NH3coverage ratio and storage capacity on the catalyst surface, we established estimation model, put forward the leakage control strategy.According to the OBDI+NOx stage monitoring requirements for SCR system, this paper apply threshold diagnosis method, logical diagnosis method and the synthetical diagnosis method to make diagnosis of electrical circuit, system state abnormity and sensor signal rationality. In order to prevent further emission deterioration, NOx emission excess diagnosis algorithm was developed. Finally, each type of diagnostic algorithm was validated.