Optimization Of Cam-driven Hydraulic Variable Valve Actuation Mechanism

As a new type technology of engine,variable valve actuation can be used to improve combustion,emission and fuel consumption.Nowadays variable valve technology is mainly divided into two kinds: cam driven and non cam driven.Combining the advantages of the cam driven and the non cam driven,and avoiding the disadvantages,Cam-driven Hydraulic Variable Valve Actuation Mechanism is proposed and developed,which can realize the valve close timing and the lift of valve continuous variable with relatively simple mechanism configuration.However,in the process of engine reverse test,the problem of valve seating speed control is exposed.At the same time,in the follow-up study,it was found that when the old mechanism is in operation,the relief valve as the system’s internal key control components,each cycle must be open and close once,and valve opening and closing is a certain response time and duration,which will enhance the cylinder hydraulic fluctuation,affecting valve control.Therefore,it is necessary to optimize the way of seating speed control and realization.Firstly,based on the deficiency of the seating speed control and the realization of the cam-driven hydraulic variable valve actuation mechanism designed and developed by the group,this paper puts forward the optimized improvement scheme for the original mechanism: The realization mode,in addition to the application of the relief valve to control the pressure of the high-pressure system and realize the valve variably.The valve can be used to control the pressure of the high-pressure system by using the throttle valve,and the valve seat speed control mode,use the uniform four hole gradually shut down throttling control and thin-walled small orifice throttling control.And the system structure,working principle and working process of the new optimized mechanism are introduced in detail.Then,the simulation research platform and the establishment of the experimental research platform are mainly introduced.It’s a new scheme(a)uniform four hole gradually turn off buffer throttling,electro-hydraulic proportional relief valve to realize valve variable continuously AMESim simulation model,and scheme(b)thin-walled small hole throttle buffering,throttle valve control of oil discharge AMESim simulation model.And,The main updated modules,such as the cam module,seating buffer module,are introduced in parameter setting.In the establishment of the experimental research platform,based on the original test-bed design,the related parts are redesigned according to the optimization scheme(a)and(b),and the temperature control system and the pressure collection system are installed on the new reverse test platform.Finally,the simulation results and the results of the reverse test of the valve seating cushion mode are analyzed and chosen,and the influence factors of valve movement law are studied.Comparing the valve seating velocity under each buffering scheme in the reverse test,and combining the valve lift curve,the bufferring scheme of the thin-wall orifice throttling is obtained,which is a better buffer for controlling the valve seating speed.And the larger setting pressure of the relief valve,the smaller the throttle opening and the higher the engine speed,the greater the maximum lift range,the larger the maximum lift and the later the closing time.The higher pressure of the oil,the earlier the opening time of valve,but the maximum lift and closing time of the valve is not effected critically.And there is a phenomenon of hydraulic fluctuation in the Cam-driven Hydraulic Variable Valve Actuation Mechanism,this paper probes into the influence of the control parameters on the hydraulic fluctuation phenomenon.The higher the speed,the smaller the throttle opening,the more violent the hydraulic fluctuation phenomenon,and theoretically proposed that the hydraulic fluctuation can be improved by increasing the piston area of the valve and reducing the mass of the moving parts.