| At present, in order to reduce fuel consumption and emissions of automobile so as to satisfy strict automobile regulations, the most effective way for the SI engine is to use three-way catalytic(TWC) converter and the electronic injection system which matches it, according to the trend of automobile and electronic technology. As a result it is required that the engine works in every working condition within the region which makes the TWC most effective so that the exhaust emissions can be the least. Relative information show that the average air fuel ration must maintain within the region of 14.7±3.5% in order to keep the most conversion efficiency of the TWC.To realize the high accurate A/F ratio control requires that the quality of intake air must be precisely measured and the injected fuel must be precisely controlled. In actual driving conditions, the engine usually works at transient states, such as acceleration, deceleration, start, warm up, and etc, in which engine parameters (engine speed, torque, inlet state, the fuel transportation, vapor and deposition) varies greatly, and the response characteristics the engine shows is quite different with the steady state, which is the main reason why the emissions are emitted in the transient state of electronic gasoline engines. Therefore how to precisely control the A/F ratio of the transient state to satisfy the highest request of the TWC has become the most important and the most challengeable mission for the engine management system.There are many factors which influence the A/F control precision in transient state. The measure error of the intake air which is caused by the flow passing in and out in the manifold and fuel film effect caused by the injected fuel in the intake port are the main reasons.In this thesis, studies have been deeply done on the fuel film during transient state according to the project Study and Demonstration of the Key Technology of the Industrialization for Low-emission Vehicles"Development and Resolution of the Key Technology for the Low-emission Electronic Controlled Gasoline Vehicles Whose Weight Are below 3.5 tons", taking the hafei lubao DA468Q engine as the experiment platform. Through differentiating fuel film using LSM(least squares method) and then according to the fuel compensation model, injecting strategy during transient condition is designed, and a intake air pressure estimator taking the dynamic induction and exhaust phenomena into account, in this way the intake air estimation is introduced into the engine transient control strategies. The experiment result has certified that the fuel film compensation strategy can minish the A/F fluctuation and further certified the feasibility and rationality using the least-squares estimation to compute fuel film parameters, which supply powerful theory foundation for reasonable control of A/F ratio.The main content of this paper is as follows:1.The experiment bench of DA468Q has been built to satisfy the need of the research. The original engine bus has been improved which makes switching the engine control unit much more conveniently between the original ECU and self-designed ECU, and meantime is more convenient for data acquisition; and in order to flexibly use this electronic control system in the subsequent experiments on the other SI engine and make sure that it can acquire relevant data besides controlling the engine working in good order, the 80C196KC electronic control system is designed using modularization design method, which can be divided into three parts: signal disposal circuit, ECU control circuit and drive circuit. Data acquisition of the engine working parameters for identifying fuel film parameters, identification on the characteristic parameters which is required by the engine model and control strategies during transient condition and other study work has been completed based on this experiment platform.2.A set of software system used for engine bench experiment and analyzing is designed and developed using modularization design method based on the graphic programming language LabVIEW developed by the NI corporation. This software system can acquire, analyze and save plenty of data which come from multiple channels; can real-time display the acquired data in the form of graphic, as a result display every working parameter of the engine timely and intuitively which makes experimenter acknowledge and grasp the experiment process; can realize real-time communication and data savage with other experiment equipment which has standard communication port; moreover it can realize the identification computation of the model parameters and study on the control strategies by taking advantage of the quick computation capacity of the computer and the comprehensive programming capacity of the software Labview and other engineering software, such as MATLAB.3.The theory of fuel film model and fuel film compensation has been expatiated in detail in this thesis, and the feasibility of identification on the fuel film parameters adopting least-squares method has been studied also, and simulation analysis on the three main factors, that is sampling cycle T, Signal to Noise ratio SNR and number of the sample, which influence the least-squares identification precision are made.4.Data acquisition blue print is designed aiming at the main factors which influence the fuel film model parameters, that is engine water temperature, speed, intake manifold pressure, and fuel film model parameters X andτf are computed and identified using least-squares method according to acquired engine data in various conditions, and their variation discipline and influence factors have been analyzed.5.The Mean-Value model has been built using MATLAB/Simulink, which includes inlet mass in the manifold sub model and fuel film sub model. Simulation analysis has been studied on the intake gas dynamic induction and exhaust phenomena and dynamic fuel film effect based on the model, and then the control strategies have been designed and the intake air pressure estimator and fuel film compensator has been validated using simulation method.6.Correct fuel film parameters, X andτf, have been gained on the basis of mathematical calculation and simulation validation using MATLAB/Simulink,then the fuel film compensator has been built using these two parameters, and is introduced into the transient control program, in this way, the transient control of the engine is realized. The AFR deviation value under the compensator control and the none-compensator control is compared and analyzed through experiment, which validated the feasibility of introducing the self-designed fuel film compensation control strategy, and also validated indirectly that identifying fuel film model parameters using least-squares estimation is feasible.The main innovations are as follows:1.Different from the hardware circuit especially designed for a certain experiment, commonness of the sensors and the actuators of the engine electronic control system and the requirement of the signal disposal to the signal acquisition have been considered in this thesis, the modularization method has been adopted, and the total hardware system can be divided into three parts, that is signal disposal circuit, ECU control circuit and drive circuit. The characteristic of this modularization design method is that it can be assembled conveniently and quickly according to different requirement and be used in different experimental study and even other gasoline electronic system study without designing special hardware circuit, which improved experiment efficiency and saved the cost of the experiment.2.In traditional engine experiment, it takes much time for engineering technicians to compile special programming with programming software, such as VC, to satisfy the requirement of data acquisition, saving and experiment monitoring. This is diseconomy and less efficiency for the engineers who are not majored in programming. A new programming method has been used in this paper, this comprehensive monitor software platform consist of LabVIEW graphic programming language and engineering software MATLAB, which improved veracity and agility of data record and meantime improved efficiency and improved human resource, furthermore, the platform can real-time display the acquired data in the form of graphic made the operator acknowdge every working parameter of the engine timely intuitively and grasp experiment progress, this software system is applied all through the experimental study work, satisfied sufficiently the requirement of the experiment and improved the experiment efficiency.3.In the past, the experiment calibration method is mostly used in the calibration of fuel film model parameters X andτf, which requires many experiments and is not suitable for real-time calibration. The classical parameter identification method, least-squares estimation is used in this paper, and the least-squares estimation method is deduced in detail. And the three main factors, that is sampling cycle T, Signal to Noise ratio SNR and number of the sample, which influence the least-squares identification precision are analyzed through simulation, which supply the study of identification of fuel film model parameters with theory foundation.4.Mean estimation value model(MVEM) of DA468Q engine is built based on MATLAB/Simulink, theoretical analysis on the two main factors, dynamic induction and exhaust phenomena and fuel film flow and evaporation effect, which influence A/F ratio fluctuation in transient condition, and pressure estimation model and fuel film compensation model which can be realized in 80C196KC singlechip programming easily are designed after study on control strategies of transient conditions, and feasibility analysis has been done on the self-designed control strategies through transient experiments. The experiments results show that the control strategies in transient condition this developed in this thesis is simple and easy to use, also validated indirectly that identifying fuel film model parameters using least-squares estimation is feasible.
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