Simulation And Experiment Research Of A Fully Variable Hydraulic Valve System

Fully Hydraulic Variable Valve System(FHVVS)is a hydraulic variable valve train,which can realize three successive changes of intake valve lift,opening duration and valve timing.FHVVS can control the fresh air volume coming into the cylinder by changing the closing time of intake valve,and thereby throttle can be removed to achieve unthrottled control strategy.Variable valve technology plays an important role in solving the problems of energy saving and environmental pollution reduction,so variable valve technology is one of the important research directions of engines nowadays.A new type of fully variable hydraulic valve system is introduced in this paper.The main work is as follows:(1)The structures and working principles of FHVVS are introduced,including the valve driving mechanism,controlling mechanism,valve seating mechanism.Valve driving mechanism makes the valve open and close through high pressure oil;valve seating mechanism can control the valve seating velocity;controlling mechanism is used to control the oil relieving angle,so as to achieve the full variable valve timing.(2)The four cylinders gasoline engine BJ4486EQ is selected to be the prototype,which is equipped with the FHVVS.Characters of valve movement and hydraulic fluctuation of FHVVS are studied on the test bench.Laser displacement sensors and piezoelectric pressure sensors are installed on test platform.The original signals are collected and transmitted to the computer through the acquisition card,and then programmed and processed by Matlab.(3)Software AMESim is used for modeling and simulation,and simulation model of the FHVVS is established.The simulation model is divided into four parts:cam driving model,hydraulic transmission model,valve component model and controlling system model.Through simulation,valve seating mechanism is optimized to achieve a soft valve landing,while there is no abnormal phenomenon.Cam profile is optimized,so that the intake valve has better acceleration performance.Stiffness parameters of FHVVS are optimized,which makes better dynamic performance of FHVVS at high speed.It has more stable and reliable operation.(4)The performance parameters of FHVVS are studied.The intake valve has good high-speed dynamic performance when the engine is running at high speed.The relationship between the angle of the stepper motor and the valve lift is studied when the step motor controls the oil relieving angle.At different speeds,the relationship between the time value and the speed is studied through linear fitting.The consistency between the simulated data and the measured data is studied,and the simulation error is allowable.The fluctuation of the multiple cycles of the intake valve lift is analyzed,and the reasons for this inhomogeneity are studied.(5)Hydraulic transmission is used by FHVVS to drive the valve open and close.Hydraulic oil fluctuates,and as the speed increases,the fluctuation phenomenon turns to be more serious,which limits the engine maximum speed.Therefore,influence on FHVVS of the pressure fluctuation needs to be explored.With the increase of speed,hydraulic fluctuation is more and more intense.The peak value of the corresponding valve acceleration is bigger and bigger,but it doesn't exceed the theoretical acceleration value.Therefore,FHVVS can work at the maximum speed 5000r/min.