| Nowadays,the number of motor vehicles is increasing year by year,and the urban traffic is becoming more and more congested,resulting in more and more cars working under idle or medium and small load conditions.It is urgent to improve fuel economy and promote the development of new power system technology.Variable displacement technology(Intelligent Cylinder Deactivation Technology)can stop part of the cylinder under partial load,reduce pumping loss and heat loss,which can improve fuel economy and improve the effective thermal efficiency of the engine.It has gradually become a hot field in the new technology of efficient and clean internal combustion engine.Compared with the traditional static cylinder deactivation technology,the dynamic cylinder deactivation technology solves the problems of uneven heating and inconsistent wear of each cylinder.Therefore,the dynamic skip cylinder deactivation in a certain mode is the development trend of variable displacement technology in the future.However,the problem of torque fluctuation and intake pressure fluctuation caused by cycle cylinder deactivation has always been a difficulty in variable displacement technology.In addition,a simple and reliable actuator is a key and important prerequisite for the application and test of variable displacement technology.Therefore,based on the self-developed hydraulic variable valve mechanism,this paper takes the cylinder deactivation control strategy as the research object,and aims at reducing torque fluctuation and improving fuel economy.The main research work and conclusions are as follows :(1)The hydraulic variable valve mechanism of four-cylinder gasoline engine is designed and developed,which can realize continuous variable valve lift and closing time.Aiming at the problem that the valve needs to be seated smoothly,a seating buffer mechanism is designed.According to the principle of hydraulic system of variable valve mechanism and the working principle of variable-displacement engine,the transfer function of the system is deduced and the numerical model of the engine is established.The AMESim simulation platform of hydraulic variable valve mechanism of four-cylinder engine and the joint simulation platform of engine GTPower and Simulink are built.The experimental platform of flexible variable valve motion characteristics and engine performance are built and tested from the aspects of structural design,functional design and control software module design.It lays a platform foundation for the subsequent research of variable displacement technology.(2)Aiming at the problem of pressure fluctuation in hydraulic system,experimental research and simulation analysis were carried out.Based on the Taguchi method,an orthogonal test with interaction was designed to explore the influence of multi-factor coupling effects such as tappet piston diameter,valve piston diameter and valve spring preload on valve lift,seating speed and pressure fluctuation in valve piston chamber.The influence of key parameters such as valve spring stiffness,valve piston mass and orifice diameter on system pressure fluctuation is further analyzed.By optimizing the design parameters of key components,the pressure fluctuation in the system is reduced and the reliability of the hydraulic variable valve mechanism is improved.(3)Aiming at the problem of low in-cylinder pressure after cylinder deactivation and negative compression power during cylinder deactivation,a variable displacement valve control strategy based on electro-hydraulic drive intake and exhaust valve opening and closing mode is proposed.The variation rules of in-cylinder pressure,oxygen mass fraction in exhaust gas and torque fluctuation during cylinder deactivation and working mode conversion are analyzed,and the control parameters of intake and exhaust valves at the best cylinder deactivation time are optimized.The energy saving mechanism of variable displacement technology is analyzed from the aspects of indicated thermal efficiency,mechanical efficiency and effective thermal efficiency.Based on the optimal intake and exhaust valve closing time,the engine can improve the fuel economy by8.7 % at medium and small loads.It provides a certain design reference for the development of variable displacement engine based on hydraulic variable valve mechanism.(4)Aiming at the problem of torque fluctuation and intake pressure fluctuation caused by cycle cylinder deactivation,a cycle mode cylinder deactivation control strategy with constant cycle frequency constant cylinder deactivation frequency,variable cycle frequency constant cylinder deactivation frequency and variable cycle frequency variable cylinder deactivation frequency is proposed.The cycle cylinder deactivation rate is determined by controlling the cycle frequency and the cylinder deactivation frequency,which provides a new method for exploring the torque fluctuation of the cycle cylinder deactivation.The intake compensation method based on the cylinder deactivation compensation coordinate system is proposed,which improves the nonuniformity of the intake air of each cylinder of the cycle cylinder deactivation.After compensation,the non-uniformity of the intake air volume and the mean indicated pressure of each cylinder are within 2 %,and the maximum torque fluctuation is reduced by 52 %.It provides a useful reference for improving the smoothness of engine dynamic cylinder stopping.In addition,from the perspective of the average turbulent kinetic energy in the cylinder,the pressure in the cylinder,the ignition delay period and the combustion duration,the fuel economy of the throttle control strategy(TH),the early intake valve closed control strategy(EIVC)and the intake valve and throttle synergy control strategy(IVTS)are analyzed,and further compared with the control strategy of different cylinder deactivation rates,so as to select the best fuel saving control strategy in different engine operating ranges.(5)Aiming at the problem of uneven operation of each cylinder caused by different cylinder deactivation ratios between adjacent working cycles,a random dynamic cylinder deactivation control strategy based on nonlinear model prediction is proposed.Firstly,the RBF neural network model of the engine random dynamic cylinder deactivation system is built.The K-means algorithm and the P-nearest algorithm are used to train the center position c and the width σ of the hidden layer nodes offline,respectively.The recursive least squares(RLS)algorithm is used to train the output layer weight vector w online.Then,the nonlinear model predictive control system structures with the minimum torque fluctuation and the minimum BSFC are built respectively.The results show that the average torque fluctuation per cycle is improved by 9 %-18.75 % and the BSFC is improved by about 2 % under different working conditions,which verifies the effectiveness of this strategy in reducing the dynamic fluctuation of random dynamic cylinder stopping torque and improving fuel economy. |
PDF Full Text Request