Design And Simulation Of Variable Valve System For Diesel Engine

Energy shortage and environmental pollution are two practical problems in the automotiveindustry. To develop low-power and environmentally friendly vehicle engine is the maindirection in today’s car industry. The valve in traditional engine is driven by the camshaft,and its movement is determined by the cam profile, which will just guarantee the performancein a certain condition of the engine, thus increasing the difficulty factor to ensure the engineperformance always in the best states. Variable Valve Actuation (VVA) is an effective way toimprove performance and reduce harmful emissions of the engine which can be controlled byvariable valve lift (VVL) and variable valve timing (VVT) at any time under differentoperating condition.This study focused on realizing the variable valve system on a diesel engine. Combinedwith the characteristics of the test engine’s structure, an Electro-Hydraulic Variable ValveSystem (EHVVS) has been invented after a detailed analysis of the structure and workingprinciple of VVA in domestic and foreign.The author established the Simulation model of the EHVVS by MATLAB in order to studythe influence of the parameters of the Electro-Hydraulic Variable Valve System on themovement of the valve. Some simulations on different oil pressure and structural parameters,including the diameter of driven piston, flow area of solenoid, diameter of inflow hole, valvespring stiffness, preload of valve spring have been done to achieve the movement of the valve,especially the process of the opening and closing of the additional lift. The results show thatthe diameter of driven piston, flow area of solenoid, diameter of inflow hole have impacts onthe opening and closing process of the additional lift, valve spring stiffness and preload ofvalve spring mainly effect the closing time of the additional lift, but the oil pressure just effectthe opening speed of the additional lift. Moreover, the working scope of the variable valvesystem is determined by the movement of the piston and valve. On the basic of the aboveresults, a set of best optimal structural parameters of the EHVVS were determined, and thedelayed intake valve closing (IVC) in each engine speed could be flexibly adjusted with theseparameters. At last, a control MAP is determined according to the simulation.The engine model is built by GT-Power, and its accuracy is verified according to theexperimental data. Then a set of simulations are undertaking on this engine model in order toget the engine intake performance in different intake valve lift and different intake valveclosing time. The results show when the additional lift increase to1.7mm,2.2mm and3.0mmon the basis of the origin valve lift, the amount of the intake air doesn’t change; as the intakevalve closing delayed from0°CA to80°CA, the effective compression ratio reduces from 17.0to6.4, the amount of intake air reduced because of the air mass flow back into the intakemanifold, and the amount of intake air is approximate in these three different additional liftunder the same intake valve closing time. So, the intake valve closing time is the mainreason to affect the gas backflow.Finally, the EHVVS’s experimental system is constructed and divided to four subsystems,including the drive system, hydraulic system, electronic control system and data acquisitionsystem, then give a detail describe of the working principle of the main components and itsselecting principle, making a solid foundation for the following research.