Integrated Design And Pressure Fluctuation Simulation Of Hydraulic Variable Valve System For Four Cylinder Engine

With the rapid growth of the world’s car ownership and the increasingly stringent emission regulations,the energy-saving and emission reduction technology of engine has become a research hotspot at home and abroad in recent years,in which the fully variable valve system,as an important means to achieve energy-saving and emission reduction,is favored by various research institutions and automobile companies.According to the characteristics of cam driven and non cam driven variable valve mechanism,this paper combines the advantages of cam driven and electro-hydraulic variable valve mechanism,and designs the hydraulic full variable valve system of four cylinder machine driven by cam.According to the operation principle of the system and the selected parameters of the four cylinder gasoline engine,the simulation model of the four cylinder hydraulic variable valve system is built in Matlab / Simulink software.The cam profile of the original engine is transformed into Gauss function as the initial driving force input.Then according to the rocker ratio of the original engine,the tappet piston diameter and valve piston diameter are determined to be 18.0mm and 16.0mm respectively,and the pipeline diameter is 7.0m by simulation calculation m.The bending angle of the pipeline is 70 °.Two kinds of valve seating buffer mechanisms,plunger throttle type and orifice throttle type,are designed.By comprehensive comparison,the orifice throttle type valve seating buffer mechanism with short hole as the buffer hole is selected.When the buffer hole diameter is less than 1.5mm,the valve seating speed is guaranteed to be within the excellent range(less than 0.5m / s).Hydraforce is selected to realize continuous variable valve lift and closing time by controlling oil discharge of the system Nv08-21 adjustable needle throttle valve is the key part of regulating the oil discharge.According to its flow performance curve,the relationship between the regulating angle(0 °-360 °)and the throttling crosssectional area is determined,and the oil discharge regulation is transformed into needle valve angle regulation.The simulation results also prove the feasibility of this scheme.In order to realize the practical application of the variable valve system,the influences of the factors such as the fuel supply pressure,temperature,speed,needle valve adjusting angle on the system motion characteristics such as valve lift,speed,acceleration and system pressure fluctuation are explored respectively,and the engine is stopped under medium and small load.Finally,according to the actual size of the prototype,the preliminary structural design of the whole mechanism,tappet piston,valve piston,etc.