Research On Full Flexible Operation Strategy Of Engine Electromagnetic Valve Train

The self-developed electromagnetic valve train(EMVT)is a new type of fully flexible valve train,and the full flexibility is reflected in the valve motion parameters can be adjusted independently,continuously and real-time.The preliminary study of the research group mainly focused on optimizing the timing and lift of the valve.Studies have shown that the EMVT can effectively reduce pumping losses under part load and improve engine fuel economy.In this paper,the advantage of fully flexible EMVT is applied to study the engine variable displacement technology.By flexibly adjusting the operating parameters of the valve,the distribution of active cycle and inactive cycle can be dynamically controlled,and the effective displacement of the engine can be changed with the change of load.The conventional variable valve train is difficult to realize the frequent conversion between active cycle and inactive cycle,which limits the development of variable displacement technology to some extent.As a fully flexible camless valve train,the EMVT provides a feasible technical approach for the realization of variable displacement technology.However,there are still some problems to be solved in the application of variable displacement technology,such as valve operation strategy when the cylinder converts between active cycle and inactive cycle,the distribution of active cycle and inactive cycle,and engine load control under constant load and variable load conditions.Based on the fully flexible EMVT,further research on the variable displacement technology is carried out in the thesis.Firstly,the valve operation strategies of variable displacement are explored.Then,the effects of firing cycle load,the distribution of active cycle and inactive cycle on engine speed and fuel economy are analyzed.Finally,the load control method of variable displacement technology is studied under the condition of constant load and variable engine load.The main contents and results of this thesis are summarized as following:(1)The establishment of simulation model and test platform.Firstly,a numerical model of the engine working process is established based on the parameters of the prototype engine,and its accuracy is verified by experiments.Then,considering the frequent conversion between active cycle and inactive cycle of the cylinder in the variable displacement mode,the variable displacement engine model is established to control the valve operation parameters of the EMVT stroke by stroke.Lastly,the prototype engine is modified to complete the installation of the EMVT on the cylinder head of the four-cylinder engine,and the test platform of the EMVT engine is built.(2)By summarizing the valve operation strategy of fixed mode variable displacement,three feasible valve operation strategies are proposed based on electromagnetic intake and exhaust valves.Then,the influence of different valve timing and lift on the power consumption of the inactive cycle and its conversion process is analyzed,and the minimum power consumption and the corresponding valve timing and lift of each valve operation strategy are obtained.Finally,the strategy of keeping exhaust valve open is identified as the valve operation strategy of variable displacement by comparing the minimum power consumption of three valve operation strategies under different number of inactive cycles.(3)Based on the electromagnet intake valve,a valve operation strategy of exhaust gas trapped is designed for variable displacement.The discrete step size of the one-dimensional model is determined by comparing the simulation results of one-dimensional model and three-dimensional model.Based on the one-dimensional model,the influence of the intake valve parameters on the mass fraction of oxygen in the exhaust pipe,energy loss and the minimum in-cylinder pressure of the active cycle and the indicated mean effective pressure(IMEP)of active cycle are investigated to obtain the maximum value of the total IMEP under this strategy.Finally,the improvement of engine fuel economy with the proposed valve strategy is analyzed.(4)Study on constant load control in variable displacement working mode.Based on the speed variation of active stroke and inactive stroke,a method for predicting the distribution of active stroke and inactive is proposed.Through the rolling optimization cycle by cycle,the distribution with the minimum speed fluctuation variance is determined as the optimal distribution.On this basis,the characteristics of the speed in variable displacement working mode and the influences of IMEP of active cycle on the speed fluctuation and fuel economy are analyzed.By comparing with the fixed mode variable displacement technology,it is obtained that the speed fluctuation is within an acceptable range in variable displacement working mode when the active cycle is performed in optimal economical region.Finally,the improvement of engine economy with variable displacement is analyzed.(5)Study on variable load control under variable displacement working mode.Firstly,through theoretical derivation,the formulas for calculating the speed variation of active stroke and inactive stroke under variable load condition are obtained.Then,the method for overall feedback correction of speed variation of active stroke and inactive stroke under variable load condition is put forward to make the model for predicting the distribution of active stroke and inactive stroke suitable for variable load condition.Finally,the engine load control under two different load conditions is analyzed.Under the condition of variable load torque,the prediction model with overall feedback correction can reduce the difference between the speed and the target speed and shorten the time for engine stability.Under the conditions of variable speed and torque,the distribution of active stroke and inactive stroke is controlled by cycle by cycle to make the engine speed run in accordance with the target speed and realize the control of variable engine speed and torque in the variable displacement working mode...