Design And Performance Analysis Of A New Type Of Variable Valve Lift And Timing Mechanism

In the era of global energy crisis and environmental pollution,engine energy saving and emission reduction technologies are of great significance to alleviate the energy crisis,improve the environment and promote the realization of "dual carbon" goal in China.Different from other energy saving and emission reduction technologies,the variable valve lift technology can optimi ze the intake strategy,change the valve lift,and reduce the pumping loss according to the requirement of different engine operating conditions.Especially under partial load conditions.which is of great significance to improve the fuel economy of the en gine.In this dissertation,a new type of variable valve lift and timing mechanism(EVVTL)is designed and studied,and described its structural composition and working principle in detail,and analyzed the valve lift adjustment and control strategies under different adjustment angles.Combined with the expected motion characteristics of the mechanism,and taking the 0deg adjustment angle as the design benchmark,the design boundary parameters of the cam profile with different valve lifts are determined,and the discrete points are fitted by the cam profile equation.Based on the established kinematics numerical model of the mechanism,the lift adjustment characteristics of the mechanism are calculated and analyzed.The results show that: the maximum valve lift value under different working conditions decreases,the valve opening duration shortens,and the valve closing time advances : with the increase of the camshaft adjustment angle.The change of valve lift value is smaller when the load is heavy,and the opposite is true when the load is medium and small.The multi-rigid body dynamics model of EVVTL mechanism is established by Adams software,and the changes of valve dynamics parameters and the load of key components are analyzed by simulating different wo rking conditions.The results indicate that in the range of 0 to 65 deg adjustment angle,in addition to the small deviation of each curve caused by the inertia force of each part of the mechanism and the overall stiffness,the valve lift,speed and acceler ation curve and the design curve are in the shape and change law.The above is basically the same,the curve is smooth and gentle,the valve has no abnormal opening and rebound phenomenon,and shows good dynamic characteristics.Within the full range of operating conditions,the two cams are in good contact with the corresponding rollers,and there is no fly-off phenomenon,and the valve sits smoothly without secondary opening and "rebound".Through the flexible processing of some components,the maximum lo ad boundary condition of the key components is obtained,and the intermediate lever finite element model is established based on this as the input load boundary.The simulation analysis shows that the maximum stress of the intermediate lever is 273.42 MPa a nd the safety factor reaches 2.63 due to the influence of the tension at the transition part of each shaft-hole connection.Obviously,the structural strength meets the expected safety range,and its first-order natural frequency is much larger than the vi bration frequency range of the whole machine,which will not cause resonance during high-speed operation.Based on the bench test of the EVVTL principle prototype and the original machine,the pumping loss and the common law of the EVVTL principle prototyp e and the original machine under different working conditions are compared and analyzed.The results show that: Due to the higher intake pressure of the EVVTL principle prototype,its pumping loss is smaller than that of the original machine in most working conditions,especially in small and medium loads,the gap between the two is particularly significant.In addition,under different speed and load conditions,the EVVTL principle prototype runs smoothly and shows good lift adjustment characteristics;Under common working conditions,the pumping loss is reduced by 4%to 15% compared with the original machine,and in some working conditions,the single-cylinder fuel consumption rate is reduced by more than 10%,showing good fuel economy.