Study On Robust Control For Engine Idle Speed Based On Mixed Uncertainties Modeling

Idle speed condition which has close relation to the engine emissions and energy consumption, is one of the important working condition of engine, and engines operate under this condition lots of the time. During the process of idle speed, air-conditioning compressor, power steering gear and automatic transmission changed suddenly, and these disturbance factors make the working-engine speed fluctuating, instability or even flame-out. So in order to meet the demand of the auto emission regulations which become more and more strict today, it is especially important to control the idle speed and keep it stable as far as possible.A lot of factors should take into consideration when controlling the idle speed of the engine, such as the uncertain lagging time of the system, the disturbance and the noise of sensors signal measurement, the effect of environment and the parametric variation with aging and frication etc. All these factors increase the instability of engine-control, and the regular control method needs accurate engine model. Could not satisify the demand of idle speed. Considering the advantages of Robust control theory on uncertainty control and the stability requirement of the idle speed, this paper applying the Robust control to the idle speed on the basis of the creation of the engine model. The dissertation mainly consists of three parts:Firstly, Building a mean value model of engine.the study focuses on the four-cylinder engine model which is devided into several parts according to whose actual course of work: Throttle, Intake manifold, Mass flow rate, Compression stroke.Then builds respectively a model, and the reliability ofthe model verificated and debug. and carries out the simulated analysis. Based on the engine model, uncertainty analysis is done on the influencing factors when the engine is working in idle speed condition.Secondly, H - infinity robust control theory was Applicated based on a simplified nominal model of engine in idle speed condition, the frequency weighting function method was used to designed H∞controller. In order to test the performance of H∞controller, Another PI controller which is regular used in idle speed control, was designed based on the simplified model of engine, The simulating result indicates that the H∞controller obviously performs much batter than the PI controller does.Thirdly, adapted theμsynthesis to analyze parametric uncertainties and unmodelled dynamic characteristics, then usingμsynthesis,H∞control and LMI functions in robust control toolbox to analyzed the nominal model of engine respectively, comparatived the analysis of all these results. Finally, apply D-K interation process to generalized mixed engine model with uncertainties, design out theμsynthesis controller by programed. Comparing with the results show that once the premise of generalized uncertainties exists, the function ofμsynthesis controller is better than H∞controller's in robust control.Based on the current review of the existing engine idle speed control methods, Two new methods was introduced: H - infinity robust control theory andμsynthesis to control idle speed of engine. The study shows that two new control methods is good than the original control method in response to the transitional period, The overshooting number, resisting interference capabilities. H∞controller is good at robust of the system. Andμsynthesis can balanced the stability and performance of the system.