Modeling And Simulation Of The Control Software For A Variable Vavle Timg Special Adjustment Of The Gasoline Engine

Varible valve timing (VVT) technology used in gasoline engine can effectively increase the volumetric efficiency and improve the fuel economy,power and emissions. In addition to the phaser itself and the control system hardware,the accuracy and rapidity of phase control is largely dependent on the VVT control software located in the application layer of EMS.therefore,the control algorithm and the control strategies have always been the key research of VVT control system. According to different engine conditions, the optimum valve timing is detemined in VVT control strategy. The duty cycle signal sent to the oil control valve is calculated in WT control algorithm which is based on the target cam phase and actual phase. Except for considering the control strategy in normal mode,the VVT control system should also take into account the control objectives and measures in some special modes.In this paper, aimed at vane type VVT mechanism in a1.5TGDI gasoline engine, focus on three aspects of close loop control algorithem, the formation of target phase in special camshaft adjustment and the duty cycle switch at low speed and low oil pressure. With the model-based approach,the corresponding control models are established in ASCET and some simulations are peformed.The main work is as follows:(1)According to more comprehensive consideration of adjustment mode in VVT system,depending on different purpose of WT adjustment,the calculation of target phase is divided into normal mode and special mode,then a complete framework of VVT control software is established.(2)The significant dynamic non-linear characteristic of phaser is exhibited due to the different adjustment load in the direction of advance and retard which is caused by the return spring in the phaser and the camshaft load torque.The problem is solved by using segment PID algorithm which means establishing different parameter MAP in two dirctions.The integral separation algorithm is adopted to prevent the saturation of integral part during a large range adjustment, the deadzone in algorithm avoid frequently jitter of the spool in oil control valve. In order to verify the control effect,a simplified phaser model is established to simulate the close loop control.The results show that the adjustment period is remained at1s and the simulation results keep a good consistency with the experiment results. (3) The control methods of several special adjustment are considered in control strategy.The preventive cleaning module is developed to prevent the impurities from blocking the oil control vavle and the oil channel.The stopping adjustment module of exhaust camshaft is designed to increase the adjustmet speed of intake camshaft under low oil pressure. According to the speed gradient and the extent of target and actual phase,the enable moudle of increasing idle speed is established to increase oil pressure and ensure the exhaust camshaft moving to the advance direction when the speed gradient decent too fast.In order to improve the vane speed of leaving the locking positon when the phaser starts to work,the camshaft unlocked moudle is established to use the fast switching of duty cycle to accelerate the oil flow in phaser. Above adjustment requirements are prioritizated to dispatch execution order resonably and avoid adjustment disorder.(4)According to the stress analysis of vavle mechanism and the use of measured data of the cam profile,the function of cam profile is fitted by the principle of least squares and the camshaft torque based on cam angle is derived and calculated. According to the impact of load torque on the phase adjustment,the virtual check valve strategy is proposed to use the fast response of oil control valve and the alternating characteristics of camshaft torque to reduce the inhibition of positive camshaft torque in adjustment.