Study On Control Strategy Of Cam-driven Hydraulic Variable Valve Actuation Engine

In recent years,the rapid development of automotive industry and the extraordinary growth of the vehicle population had brought about serious problems between automotive,energy and environment.Energy saving and emission reduction is the development direction of automotive engines.The existence of throttle and the limitation of compression ratio are two main reasons for the low thermal efficiency of gasoline engine.Variable valve actuation technology is an effective way to significantly improve the engine fuel economy.Combining the advantages of the cam driven and the non cam driven variable valve actuation technology,a Cam-driven Hydraulic Variable Valve Actuation Mechanism is developed,which can realize the valve close timing and the lift of valve continuous variable with relatively simple mechanism configuration.Variable valve technology has many control strategies for adjusting the valve movement parameters,In order to further enhance the energy-saving potential of variable valve actuation gasoline engine,it is necessary to study various control strategies and select the appropriate control strategies under different working conditions.To solve the above problem,at the beginning,a one-dimensional simulation model of gasoline direct engine is established by GT-Power simulation platform and a variable valve mechanism model is built based on AMESim software.In this study,the intake valve movement process is based on the calculation results of AMESim simulation model.Combining the control of throttle module in GT-Power engine simulation model can realize the TH load control strategy,the EIVC load control strategy and the TE load control strategy.The research studies the effects of three load control strategies on engine performance at different speed and load conditions.And the research reaches the following conclusion.1.Different load control strategies make the difference in in-cylinder pressure,temperature and average turbulent kinetic energy,which have significant influence on combustion process.The in-cylinder temperature,pressure,maximum explosive pressure,maximum combustion temperature and average turbulent kinetic energy reduced under the early intake valve close conditions.And which increase the ignition delay and combustion duration.The ignition delay and combustion duration are the highest under EIVC load control strategy,and the difference decreases with the increase of engine load.2.Different load control strategies make the difference in energy transfer processing.The total fuel combustion energy converse into indicated work is affected by the changes of heat transfer loss and exhaust loss.Early intake valve close conditions are beneficial to reduce heat transfer loss,but increase the exhaust loss.For the indicated thermal efficiency,EIVC load control strategy can make the best comprehensive benefit ratio for the reducing of heat transfer loss and the increasing of exhaust loss under all load conditions at low speed.With the increase of speed,the indicated thermal efficiency of EIVC load control strategy is worse than that of TH load control strategy under low load conditions.Under medium and high speed and low load conditions,when TE load control strategy is used,the engine indicated thermal efficiency is the highest.3.Different load control strategies make the difference in the efficiency of indicated work converting to effective work.The change of mechanical efficiency under different load control strategies is affected by the combined effect of pumping loss and friction loss.Early intake valve close conditions are beneficial to reduce pumping loss and friction loss.EIVC load control strategy has the most obvious improvement effect and the engine mechanical efficiency is the highest at all speed and load conditions.4.The change of effective thermal efficiency under different load control strategies is affected by the combined effect of indicated thermal efficiency and mechanical efficiency.Under low speed conditions,the engine indicated thermal efficiency and mechanical efficiency are the highest when EIVC load control strategy is used.So the effective thermal efficiency becomes the highest under EIVC load control strategy.With the increase of speed,the suitable application load range of EIVC load control strategy decreases gradually.Under medium and high speed and low load conditions,the energy distribution of TE load control strategy is more reasonable,which makes the effective thermal efficiency become the highest and the fuel economy achieve the best level.Multi-parameter coordinated adjustment is required for different load control strategies which can be realized by using cam-driven hydraulic variable valve mechanism.The parameters include intake valve lift,intake valve opening duration and throttle opening.In order to further explore the optimal results in the design space,the DOE(Design Of Experiment)method was applied to optimize the load control parameters with multiple objectives.And the research reaches the following conclusion.1.At low and medium speed(1000-3000r/min),the optimal load control strategy in all load conditions is EIVC load control strategy.In the range of medium and high speed(3000-5000 r/min),the optimal load control strategies in medium and low load conditions are TE load control strategies and for medium and high load conditions is still EIVC load control strategy.2.The economic level of the engine can be improved obviously by using the optimal load control strategy.At low and medium speed(1000-3500r/min),the brake specific fuel consumption under medium and small load conditions is reduced by 4%-6% and reduced by 2.5%-3.5% under high load conditions.In the range of medium and high speed(3500-5000 r/min),the brake specific fuel consumption under medium and small load conditions is reduced by 3%-5% and reduced by 1%-3% under high load conditions.