Modeling And Simulation Of The Application Layer Software For A Variable Valve Timing Control System Of The Gasoline Engine

To meet the increasingly stringent emission regulations and energy savingrequirements, variable valve timing (VVT) technology is generally used in sparkignition engine to improve the fuel economy, power performance and emission level.The effectiveness of VVT technology largely depends on the VVT control system. Asone of the most important parts in engine management system (EMS), the VVT controlsystem should adjust flexibly intake and exhaust phase and provide best valve timingaccording to the operation conditions and different operating modes, through control forthe charge velocity, charge mass, the residual gas coefficient, to maximize thevolumetric efficiency and optimize the combustion process, thus comprehensivelyimprove the performance of engine. Given that the control targets of engineperformances have strong association with each other, various factors and relatedvariables must be taken into consideration when developing the VVT control system,therefore, studying on the control strategy of VVT system in application layer softwarebecomes critical.In this paper，aimed at the turbocharged gasoline direct injection engine with vanetype double VVT (D-VVT) system, mainly focusing on formation of camshaft phasecontrol target value and generation of the phaser control signal, the control logic andcontrol algorithm in application layer software for the VVT control system were studiedusing the model-based method. The control model was established on the ASCETplatform and simulation study was performed. The main research work is as follows:(1) According to the control principles and control requirements of the VVTsystem, the overall framework model of the VVT control system was constructed on thebasis of modularization.(2) Models of adaptation calculation, valve opening calculation, desired anglescalculation of intake and exhaust camshaft, overlapping angle calculation wereestablished. According to the operation conditions of the engine, the adaptive requestwas judged to determine whether or not an adaptation adjustment of the relative positionbetween camshaft and crankshaft was conducted. The actual angles of intake andexhaust camshaft was filtered for removing jitter and the angle at1mm valve lift wasconverted to the angle at0.5mm valve lift so that the requirements of intake chargingcalculation and control accuracy were met. According to the operating conditions of theengine, the control models of the camshaft phase target values for homogeneous combustion mode, catalyst-heating mode and scavenge mode were built, and desiredangles of intake and exhaust camshaft as well as overlapping angles were calculated,respectively. Simulation results of the control logic for different operation modes showthat, under given conditions, the expected angles of intake and exhaust camshaft arechanged with engine speed and air charge mass, so the working requirements of theengine are satisfied.(3) Models of camshaft angle control, the controller and the auxiliary moduleswere established. When meeting the camshaft control conditions, according to thedifference between desire dangle and actual angle, the closed-loop control for thecamshaft angles were implemented using the PID control algorithm. Considering thenonlinear characteristics of the VVT mechanism, maps of P, I, D parameters wereseparately set up, to allow calibration of the PID parameters according to differentoperation conditions, so ensure that the VVT mechanism could have good dynamicresponse and static stability. The simulation results of control effect on fault mode andnormal mode show that, the intake and exhaust camshaft can track the change of desiredangle well.