Study On Intake Performance Of SI Engine With Fully Variable Valve Hydraulic Actuation System And Control Strategy

The traditional gasoline engine regulates inflow gas by throttle. At low load condition large pumping loss leads to high rate of fuel consumption. Furthermore, fixed valve train can't take into account all the operating conditions. Therefore, studying on both valve lift and opening duration variable at any time to replace the throttle body to control inflow mass is very important. A system supplies demanding inflow gas all the time to improve engine's performance of power, economy and emissions is of great practical significance.Based on the K157FMI engine, its intake cam profile and actuator are re-designed. The movement of the valve is controlled by cam profile and hydraulic system. When valve opening, the lift motion is related to the cam. At appropriate time, the hydraulic system controls valve to drop down. The valve opening duration is determined by the time when the liquid goes out of the controller. The main contents as follows:First of all, we simplify the hydraulic system to a tappet chamber and a piston chamber and the valve movement is treated as a single quality system droved by hydraulic force. The mathematical modal is established and verified by experiment using LVDT sensor. The results show that the calculation modal is accurate. The lift varies continually from 0 to 7.4mm and the closing angle can be changed 260°CA after the TDC of intake course. Therefore the throttle-free load control of engine can be realized by control the lift and closing time of intake valve.Secondly, establish engine simulation model by AVL BOOST software. We measure flow coefficient of the valve port, intake mass flow, intake manifold pressure, cylinder pressure via experiment and refine the simulation model according to the test results. Intake mass flow experiments indicate that FVVT can control the volume coefficient changing from 0～1 so that it can take place of throttle to regulate intake mass precisely. The manifold pressure signifies press fluctuation is in a relationship with the tube length. The cylinder pressure results show that pumping loss can be reduced significantly with throttle-free load control.Finally, we propose the control strategy of valve motion for idling, partial load and full load operating conditions.In order to achieve the demanding valve motion, the corresponding phase angel that oil vents from controller is drew up. We simulate engine performance in various operating conditions:in idle condition, it reduces the residual gas coefficient and increases airflow velocity, so that idle stability is improved. Fuel consumption is dropped in partial load condition due to decreasing pumping loss. Torque and power are enhanced in full load resulting from increasing intake gas mass.