Key Parameters Optimization Of A New Electro-Hydraulic Variable Valve Actuation System

To address the increasing scarcity of oil resources and worsening environmental problems, new automotive technologies have been put forward and applied to reduce harmful emissions and engine fuel consumption. For instance, variable valve timing(VVT) system is one of such technologies. This paper introduces a new electro-hydraulic VVT system, which not only can realize fully flexible adjustment like camless variable valve system, but also has a simple and reliable structure.In this paper, the mathematic models of the hydraulic cylinder piston and rotary valve are developed and the optimization model follows, where the power consumption during one period is used as the objective function, and the valve closed condition, the valve maximum lift, as well as the maximum system pressure are seen as the constraints. The model is built into MATLAB/Simulink and verified by test data. The comparison results show that the simulation results match the ex perimental data well enough to conduct further research. Five key optimization parameters are chosen by doing sensitivity analysis with the verified model, which are spring stiffness, the hydraulic cylinder piston area, the valve spring preload, the diamet er of the pipeline and the initial volume of the accumulator.These key parameters are optimized by using Genetic Algorithm(GA) and Simulated Annealing(SA). In the optimization process, the fitness function under the NEDC working condition is built and the values of the optimization parameters are determined. By theoretically analyzing both GA and SA, a new improved GA is proposed via integrating SA into GA, which is also used to optimize the key parameters of the system.Optimization results show that the improved Genetic Algorithm is superior to two basic algorithms alone both with respect to the convergence speed and degree of approaching the optimal solution. The simulation results also show that the optimized system is able to fully regulate valve timing and lift. In addition, the performance is more stable and the energy consumption is much lower compared to the original system.