The Research Of Scavenging Function Strategy For Direct Injection Gasoline Based On Ascet

With increasing oil energy crisis and human concern for environmental problems,engine downsizing has been an effective means to save energy and decrease emission,while the gasoline direct injection with turbocharger (TGDI) is an importantdevelopment direction of gasoline engine miniaturization. Nowadays scavengingfunction is an effective way to decrease turbo response delay and improve superchargedengine dynamic performance at low speed, based on improving power performance withreducing fuel consumption and emission.Scavenging conditions, function principle under the low speed and full loadoperation condition, influences on engine performance, application for four-strokedirect-injection gasoline engine and control problems were analyzed in detail. Differentscavenging evaluation coefficients were summarized in this paper, and scavenging ratiowas proposed for this scavenging control strategy study. A scavenging strategy based ontorque control was put forward in this paper, using a TGDI with dual variable valvetiming technology as the research object. A simplified scavenging control model wasbuilt on ETAS ASCET-MD software Platform through the combination ofmodularization and structured programming method, including scavenging logic control,turbocharger operating conditions and scavenging feedback based on catalyticconverters temperature change.The current operating conditions of the exhaust gas turbocharger was considered insetting the activation condition of scavenging control, in order to avoid that thescavenging might cause excessive supercharged pressure which once increased beyondthe limit pressure, causing detonation. A scavenging gas mass calculation model and theair-fuel ratio setting model scavenging were built to meet the stringent emissionregulations, as the scavenging gas mass was subtracted from total intake air mass inin-cylinder injection calculation precisely. In addition, to avoid scavenging to causecatalytic converter overheating, a feedback control model based on catalytic converterstemperature change was built from the in-cylinder fuel injection and valve overlap twoaspects to restrict scavenging.The scavenging logic control strategy was integrated to be a project throughoff-line simulation to verify its correctness, on the basis of modeling and simulation ofthe condition determination, scavenging mode control and scavenging camshaft angle. At last, scavenging logic control model was improved by adding the failure factors,including hardware faults, software control faults and continuous scavenging factorswhich may introduce catalytic converter overheating. The optimized simulation resultsshowed that, scavenging strategy can controlled in accordance with the requirements toopen and exit accurately at closing actual engine operating. While the scavenginginterval to activate is not less than the set value, and cumulative scavenging in thepredetermined time is not exceeding the permit value.The scavenging activation conditions used in this paper can be applied to anyTGDI engines with variable valve timing control, and the scavenging control strategiesbefore and after optimization can be transplanted completely, providing reference forthe scavenging research.