Research On Continuously Variable Valve Actuation For Miller Cycle Engine

Miller cycle is an effective measure to reduce the NOx emission of internal combustion engine.The performance of Miller cycle engine is affected by the depth of Miller cycle.Flexible valve closing timing will widen the optimal working area of Miller cycle engine.At present,most Continuously Variable Valve Lift(CVVL)need to cooperate with Variable Valve Timing(VVT)in order to achieve Miller cycle by adjusting the timing of intake valve closing under the premise of the timing of intake valve opening required.Moreover,in order to ensure that the exhaust valve operation is not affected,this kind of scheme can only be applied to the intake/exhaust camshaft misalignment engine.In this paper,a continuously variable valve actuation for Miller cycle engine is designed for the base engine with intake/exhaust cam coaxial.By adjusting the phase of eccentric wheel,the intake valve opening timing is basically unchanged,the intake valve closing timing is substantially continuously variable,and the exhaust valve operation is unchanged,which meets the requirements of Miller cycle for the intake/exhaust valve operation.The research of the actuation is of great significance to Miller cycle engine.In this paper,a series of simulation analysis of CVVAM actuation is carried out.The multi-rigid-body kinematics and dynamics simulation of CVVAM actuation is carried out based on ADAMS software.The simulation results show that the phase of eccentric wheel is from 0 to 30 degrees,the valve opening timing is basically unchanged,the valve closing timing is continuously adjustable in the 48°CA range,the valve lift is continuously variable from 13.7 mm to 11.8 mm,and the valve fullness coefficient increases monotonously with the increase of the regulating phase.Under different engine speeds and eccentric wheel phases,the valve seating speeds are lower than 0.40m/s,and the valve seating condition is good.In addition,the kinematics and dynamics of the variable valve actuation with different valve clearances are calculated,and the simulation results meet the design requirements of the valve mechanism.The finite element analysis of the actuation is carried out by using ANSYS software,and the vibration characteristics and strength of the mechanism are evaluated and checked.The natural frequencies of the actuation are calculated by modal analysis,and the structure of the actuation is optimized so that the natural frequencies of the actuation are far away from the main vibration frequencies of the engine and do not resonate with the engine.The simulation results of transient dynamics of flexible body show that the maximum stress of cam,roller,rocker arm,valve bridge,push rod and other components meet the allowable stress requirements of the designed material.Through a series of simulation calculations,it is considered that CVVAM actuation can meet the working needs of Miller cycle engine.