Research On Valve Motion Law Of Hydraulic Variable Valve System

The valve system is an important part of the engine,its performance would directly affect the engine power,fuel economy and emission level.Variable valve technology could reasonably adjust the valve timing and lift according to the variant operating condition of the engine,which could increase volumetric efficiency of the engine and reduce pumping loss,in order to accomplish the aim of improving the engine power,reducing emissions and fuel consumption.The valve movement rules of a new continuous hydraulic variable valve timing and lift technology and system proposed by our research team has been studied in this paper by the method of combining theoretical research and experiment.The purpose is to meet the engine valve demand to the greatest extent and make the valve movement with good kinematics and dynamics characteristics.The paper focuses on two parts.One is the adaptability between the adjustment method and parameters of the hydraulic variable valve timing and lift system,and the optimal valve parameters of the engine.The other is the optimization of the valve movement parameters.The main contents of this paper include the following aspects:The demand of valve parameters under different engine working conditions is studied.The simulation model of engine working process is established,and the valve parameters of the engine are optimized.The variation trends and the general law between valve parameters and engine operating conditions are studied,which can lay the foundation for valve adjustment scheme development and valve parameters determination.The valve adjustment scheme of hydraulic variable valve timing and lift system is studied.For a variable valve system,the adjustment of valve parameters is limited by the method,technology,structure and parameters of the system,therefore,it can not fully the optimal valve parameters of the engine.The valve adjustment scheme of hydraulic variable valve timing and lift system is proposed on the basis of considering the engine valve demand,system regulation and control,the design of valve cam and the integration of system structure.Compared with the valve adjustment scheme based on the variable camshaft phase,the valve adjustment scheme of hydraulic variable valve timing and lift system is more suitable for the optimal valve parameters of the engine.The mathematical theory model and the numerical simulation model of hydraulic variable valve timing and lift system are established.The movement rules and parameters of system are simulated on the basis of fully considering the hydraulic parameters and structural parameters which have great influence on system movement rules.By comparing with the corresponding experimental results,the simulation fits well with experimental results.The numerical simulation model,the setting of parameters and the output results are reliable.Therefore,the numerical simulation model can be used as a basis for the valve movement parameters analysis and optimization.According to the demand of the optimal valve parameters and the problems existing in the previous study,the valve movement parameters are optimized.The optimal design method of the valve cam in the hydraulic variable valve timing and lift system is studied.The optimized valve cam can meet demands like contact stress,lubricating properties mechanism dimensions as well as the oil compression compensation,pressure control and valve adjustment.The influence of valve spring parameters on the valve adjustment performance is analyzed and the valve spring parameters are optimized by the numerical simulation model.The valve spring with optimized parameters can effectively improve the valve dynamic characteristics,the hydraulic parameter characteristics and the valve adjustment performance.The contributory factors of valve seating velocity and timing are studied and the buffer mechanism parameters are optimized by the numerical simulation model.The buffer mechanism with optimized parameters can improve the valve characteristics,which could make the valve have lower seating velocity and less timing delay simultaneously.The valve cam,the valve spring parameters and the seating buffer mechanism parameters of the original system are modified according to the optimization results.The experimental study and performance evaluation of the valve movement rules are carried out.The experimental results show that,the pressure fluctuation has been reduced efficiently by decreasing the peak cam acceleration,which improve the system suitable speed to above 5000r/min.After the optimization of valve spring parameters,the valve can be adjusted at a higher speed,and the system can effectively adjust the valve within the range of 4500r/min.In the premise of ensuring the valve with a smaller timing delay,the buffer mechanism with optimized parameters make the valve seating velocity and rebound heigh to reach the requirements of stable valve seating.The actual valve parameters of the hydraulic variable valve timing and lift system is close to the optimal valve parameters of engine.The results of engine performance prediction show that,compared with the conventional fixed valve system and other commonly used variable valve system,the hydraulic variable valve timing and lift system has obvious advantages.