Research On Continuously Variable Valve Mechanism For Miller Cycle Diesel Engine

According to the research,The Miller cycle reduces emissions significantly.It requires the combination of CVVL and VVT in traditional engines and it is only applicable to the condition with different shaft of the intake/exhaust CAM.Based on the above conclusions,this paper designs two sets of bottom coaxial valve mechanisms with different port arrangement for diesel engine with cylinder diameter of 180 mm and maximum speed of2000r/min.The mechanisms are called CVVM(Continuous Variable Valve for Miller Cycle Diesel Engine).By adjusting the angle of eccentric wheel,the intake side of mechanisms can achieve Miller cycle and the exhaust side can maintain normal operation without VVT.After the design scheme of CVVM is determined,two sets of three-dimensional models are built by Creo and then the dynamic characteristics are simulated and analyzed by ADAMS.The results show that when the maximum speed of the diesel engine is 2000r/min,the opening time of CVVM’s intake side is basically unchanged,while the closing time’s adjustment range is large and continuously variable with the change of eccentric angle.The intake side of mechanisms achieve Miller cycle and the ventilation effect is gerat.The exhaust side of mechanisms run stably.The valve seating speed on the intake/exhaust side of mechanisms is less than 0.35 m /s and the seating force is less than 6 times of the valve spring preloading force within the adjustment range of the eccentric angle.The seating condition is great.The contact force curves of components are stable,and there is no flying off phenomenon during operation which meets the design requirements of valve mechanism.After the completion of ADAMS simulation,ANSYS is used to conduct modal analysis and transient dynamics analysis on the two sets of mechanisms.Vibration is evaluated through modal analysis and intensity is checked through transient dynamics analysis.According to the results,The natural frequencies of mechanisms effectively avoid the vibration excitation source generated by the target diesel engine and this condition avoids the occurrence of resonance phenomenon.The maximum stress of components is less than the allowable stress of the parts and the distribution is uniform.The mechanisms meets the requirements of intensity check.Finally,the CVVM parallel mechanism is optimized by adding hydraulic clearance regulator and the simulation is carried out in AMESim.By comparing the simulation results with the original results,it is found that the addition of hydraulic clearance regulator improves the operation effect of CVVM parallel mechanism’s intake side.Therefore,CVVM parallel mechanism can obtain better effect and a wider application prospect by adding hydraulic clearance regulator.