Numerical Calibration Of Variable Valve Timing For Turbocharged Direct Injection Engine

Variable valve timing is widely used in engines for improving engine power and satisfying fuel economy and emission.However,the traditional test method for the intake and exhaust phase of all-round scan to determine the optimal intake and exhaust valve timing engine under different operating conditions,due to the huge amount of work and consume a large amount of manpower and material resources,is not conducive to engine products.Therefore,in order to reduce the workload of the test calibration of the variable valve timing test for a supercharged direct injection engine,the numerical cycle simulation method,based on the principle of thermodynamics,is applied to study the influence of the intake and exhaust valve timing under different working conditions;determine the control strategy of variable valve timing of turbocharged direct injection engine,and acquire optimal value of intake and exhaust valve timing under different conditions,The main research contents are as follows:Based on the principle and method of engine thermodynamic cycle simulation,structure,working principle and related test data of a supercharged direct injection engine,this paper establish the simulation model of the turbocharged direct injection engine,which is corrected and verified through the test of the engine external characteristic bench subsequently.The simulation results of the pressure,torque,fuel consumption and other parameters in the cylinder have proved that the simulation model of the turbocharged direct injection engine has high calculation precision.Based on the simulation model of the turbocharged direct injection engine,according to the sweep gas coefficient and air sweeping mass at the maximum valve overlap angle at different speeds,this paper divided the full load conditions into air sweep area and non-sweep area,and analyzed the influence of the intake and exhaust valve at full load condition on the performance of each region,to form the overall control strategy of the variable valve timing of each region under the full load condition of the turbocharged direct injection engine.The results show that: In the scavenging area of the 1200~2400r/min speed,the valve overlap angle should be increased to use the scavenging effect to increase the in-cylinder intake air amount and reduce the knocking tendency;In the medium speed condition,under the combined control of wastegate,the most advanced exhaust valve timing is adopted and the maximum power optimization is used to optimize the intake valve at the same time,so as to improve the engine power greatly,and pay the smaller fuel economy and added the smaller turbine mechanical load and heat load;when the engine speed enters the high speed range,in order to utilize the gas inertial flow effect,a more delayed intake cam timing angle should be used,and the exhaust cam timing angle from 263°CA’s initial phase is appropriately advanced to reduce exhaust backflow and negative-pumping-power;The variable valve timing control strategy of the supercharged direct-injection engine under full load conditions,which is formed by the numerical cycle simulation method,can significantly improve the dynamic performance under high load conditions.In addition,the comparison of the test calibration results and numerical calibration results shows that the numerical calibration can provide a simple and feasible method for the study of variable valve timing control strategies,and can provide the correct direction for the test calibration,and reduce the test calibration time and cost.Firstly,analyzed the change rule of the fuel economy of the supercharged direct injection engine with the intake and exhaust valve timing under medium and low load conditions,and completed the numerical calibration of the variable timing of the best intake and exhaust in medium and low load conditions.Secondly,based on the residual exhaust gas coefficient,studied the influence of the intake and exhaust valve timing on the idle conditions.the results show that: In the low-load and low-speed range,the intake and exhaust cam timing angles are relatively late;as the speed and load increase,the intake and exhaust cam timing is relatively advanced,and in the medium and high speed,medium and low load operating conditions,The timing of the intake and exhaust cam angles is the most advanced;in the idle conditions,the minimum valve overlap angle should be used in order to reduce the residual exhaust gas coefficient in the cylinder,ensure the combustion stability and improve the fuel economy of the engine.The low-load,idle-speed variable valve timing phase strategy for turbocharged direct injection engine formed by numerical cyclic simulation method can improve the fuel economy of supercharged direct injection engine to a certain extent.In addition,The comparison between the experimental calibration results and the numerical calibration results again shows that the numerical simulation can be effectively applied to the calibration of intake and exhaust valve timing.