Research On On-board Diagnosis Algorithm For SCR System Efficiency Of Heavy Diesel Engine

With the increase pollution in motor vehicle,emissions regulations for motor vehicle pollution escalation,in addition to requiring the new production engines to meet the production certification,but also need the On-board Diagnostic system to monitor the emissions.The OBD system is an on-line monitoring system for controlling vehicle emissions.The research on OBD technology of heavy duty diesel vehicles is in the stage of rapid research and development.At present,OBD 2 stage is necessary for the transition of SCR system from serious functional failure to SCR efficiency reduction failure.The SCR system efficiency diagnosis will become the heavy duty diesel OBD technology core demands.In order to determine the core key problem of SCR system efficiency diagnosis,we compares several research directions of emission problems and analyzes the current OBD regulations HJ437-2008.The regulations of the SCR system efficiency diagnosis are clarified.In addition,the similarities and differences between OBD regulations and actual road emission test regulations are compared in detail,and the concept of window method is borrowed from the PEMS,and the core architecture of SCR system efficiency diagnosis algorithm is determined.In this paper,the whole framework of SCR system efficiency diagnosis algorithm is established for OBD regulation.The efficiency diagnosis algorithm considers how to extract the characteristics from raw data more effectively.We used the linear algorithm and the nonlinear algorithm these two different research techniques to realize the diagnosis algorithm.In this paper,we used three main steps to extract the most useful information from the raw data,original feature extraction,principal component analysis and feature selection.In the feature selection,this paper creates the concept of steady-state condition coefficient to distinguish the steady-state and transient conditions from the operating conditions.Linear algorithm based on linear regression diagnosis algorithm,nonlinear algorithm using neural network to achieve,by comparing the difference between the two algorithms to achieve the effect of the nature of the efficiency of the diagnosis were discussed.In order to solve the problem of data source,this paper established the model of SCR system based on Matlab/Simulink.The research of this paper is mainly based on the data to carry out the development of the efficiency diagnosis algorithm.The data acquisition is very important.The traditional test bench is used to obtain the test data,which is expensive,time-consuming and too many influencing factors.Therefore,this paper proposes the establishment of SCR system model as a data source,SCR system model can reflect the SCR system internal physical and chemical nature better,and low cost,time-consuming short.After the parameters are calibrated,the SCR model can approximate the working state of the SCR system and meet the research requirements of this topic.In this paper,from the perspective of OBD regulations,the main method of SCR system efficiency diagnosis is clarified,which provides a guiding for the development of SCR system efficiency diagnosis algorithm of heavy duty diesel engine.In this paper,a data-based SCR system efficiency diagnosis algorithm is proposed,and the SCR model is used as the data source to reduce the cost and test error.This paper completes the linear algorithm and the nonlinear algorithm,and uses the linear regression and neural network to complete the SCR system efficiency diagnosis algorithm design respectively.