The Research Of Scavenging Control Strategy And Modeling And Simulation For Direct Injection Gasoline

Strict restrictions on fuel consumption and pollutant emissions promote the extensive use of new engine technology,Turbocharged Direct Injection Gasoline Engine(TGDI),combined with continuous variable valve timing(CVVT)system,has become the mainstream.In order to further enhance the torque response of the TGDI engine at low speed and heavy load conditions,matching those engine systems to make part of fresh air flow from intake manifold directly into exhaust manifold during valve overlapping,this phenomenon is called scavenging.Scavenging technology can be used to improve the response delay phenomenon of turbocharger without increasing hardware costs.However,too high exhaust temperature caused by scavenging restricts the application of scavenging technology.Therefore,it is necessary to precisely control the air-fuel ratio and exhaust temperature in the scavenging mode,the control strategy becomes the key of achieving scavenging technology.Based on the previous study,the scavenging control model is constructed,and the scavenging control strategy based on the model is improved,The camshaft phase,the scavenging feedback and the lambda control strategy are designed.The modular and graphical control model is constructed by ASCET software,and the model was tested by means of gasoline engine bench test data.The main research contents are as follows:(1)The camshaft phase control strategy was established,including scavenging condition determination,intake camshaft target phase calculation and exhaust camshaft target phase calculation.The results showed that the scavenging condition was satisfied when the boost condition,speed condition and load condition were satisfied,and the transition of scavenging mode to the homogeneous was smooth by introducing the filtering function so that the engine could run stably.During the scavenging process,the intake camshaft phase was reduced and the exhaust camshaft phase was increased,the open time of intake valve was advanced and the close time of exhaust valve was delayed,which was conducive to the occurrence of scavenging phenomenon.The model validation results met the control requirements.(2)Scavenging feedback control was induced to achieve the purpose of component protection.Maximum allowable scavenging air mass is calculated based on the temperature requirements of the catalyst,thereby to calculate the maximum valve overlap angle.And then adjust the target camshaft phase by using the maximum valve overlap angle to ensure that the valve overlap angle is within the specified range.The results showed that with the increase of the temperature upstream the catalyst,the maximum allowable scavenging air mass and the maximum valve overlap angle was reduced.When the target valve overlap angle was greater than the scavenging maximum valve overlap angle,the exhaust camshaft phase was decreased firstly.If the valve overlap angle could not be reduced to the threshold,then the intake camshaft phase was increased.The validation results met the requirements of the control strategy.(3)The cylinder lambda in the scavenging mode was calculated to control fuel injection.In addition,according to the value of the cylinder lambda,the degree of cylinder enrichment could be determined to judge whether to activate scavenging feedback control or not.The results showed that during the scavenging period,the lambda in cylinder decreased and the mixture in cylinder was enriched,the exhaust air-fuel ratio is close to stoichiometric air-fuel ratio.