| With the increase of car ownership and the crowding in urban roads,the cars would be in transient conditions frequently while driving,which include starting,fast acceleration and sharp deceleration.The transient condition on automotive engine is different from steady condition,for that the combustion state and emission performance tend to be worse.In addition,the stringent emission regulations increase the proportion of transient testing cycles on engine,as well as tightening the emissions limits.So how to improve the engine performance under transient condition has become the focus among many researchers.This research has made control strategies that are based on HT5 ECU and 2.8TC diesel engine on transient condition of high-pressure common rail system,further improving the functions of ECU control system.Firstly,the signals of important sensors on common rail system are filtrated so that the reasonable signals could provide basis for identification and control of the transient condition.Except for the stop condition,start condition,idle condition,steady condition and over-speed condition,the fast acceleration condition and sharp deceleration condition are added.And the transformation model among these conditions is set up on the basis of the principle of state machine.Then the Stateflow software and the experiment bench are used to simulate and test respectively to verify the feasibility of conversion strategy.Secondly,the common rail diesel engine uses control strategy of fuel injection based on the target torque by analyzing the dynamics and torque structure of whole vehicle.And the torque is set as the connection between the power and fuel quantity.The concept of target torque is the same as the indicated torque in this study,which contains the brake torque that is converted from the driver demand torque,the torque of driving the attachments,the torque of driving the fuel pump and friction torque.The fuel quantity is converted from the target torque through a model.Besides,the calculation models of injection times,injection timing and injection pulse width are set up to control the fuel rate.Also the control of rail pressure is realized by using open-loop strategy combining with feedforward PID strategy.All of these models provide security for the flexible control of high-pressure common rail diesel engine.As to fast acceleration condition,by simulating the acceleration process when vehicle is under common gear with the GT-SUITE and Simulink software platform,the simulation results between two models of torque to fuel are compared.The one is based on real-time pedal position.The other one is based on increasing pedal position.The results show that the latter sacrificing a small part of power performance,but reduce the decreasing degree of excess air coefficient and improve the indicated thermal efficiency.Then the model of torque to fuel that is based on increasing pedal position is converted into ECU code.Through the bench experiments,the conversion of fast acceleration mode,the model of torque to fuel and the control of rail pressure are verified.And the experiment results meet the control demand.Finally,sharp deceleration process is divided into fuel-cut process and fuel-recover process through setting the fuel-cut speed and fuel-recover speed respectively in the research.By building the calculation model of torque to fuel quantity and taking some experiment tests,as well as preliminary calibration,the diesel engine converts to idle mode smoothly from sharp deceleration mode with low fuel consumption,fast speed and high following accuracy of rail pressure.The control strategies based on target torque on transient condition have been realized successfully by experiment tests on the condition of fast acceleration and sharp deceleration,making the self-developed software control system more complete,and also providing reliable supports for subsequent performance calibration and optimization. |
