Air System Modeling And Control Of Electrically Assisted Turbocharged Diesel Engine

Exhaust turbocharging technology has become one of the key technologies of energy saving and emission reduction for diesel engines by its "making waste profitable" advantage,which has been more mature and widely used wordwide.Due to the structural characteristics of the traditional turbocharged diesel engine,there exist some typical matching problems that the engine torque is insufficient in low speed zone and the transient response characteristic is poor.The Electrically-Assisted turbocharging technology came into being as an effective measure to solve these problems.It is able to effectively eliminate the detrimental effect of "Turbo Lag",realize the rapid adjustment of the intake air mass flow,and turn the excess energy into electricity to improve exhaust gas utilization rate.In fact,the structure characteristic of Electrically-Assisted turbocharged diesel engine is that the high-speed motor parts is integrated into traditional turbocharger,which increases the complexity and coupling degree of diesel engine air system,and puts forward a new challenge to the air system control of the Electrically-Assisted turbocharged diesel engine.In this paper,the research on the modeling and control of ElectricallyAssisted turbocharged diesel engine system is developed,aiming for meeting the diesel engine torque demand through the coordinate control of gas and oil,and improving the performance of diesel emissions.First of all,according to the structural characteristics and working mechanism of the Electrically-Assisted turbocharged diesel engine,the variable geometry turbocharged diesel engine system module and high-speed motor system module are set up respectively in the AMESim simulation software.And then based on the modular modeling thought,an Electrically-Assisted turbocharged diesel engine simulation model is constructed by combination of the above two modules.By the dynamical property analysis of the model under transient and steady state conditions and comparison with response effect of the traditional turbocharged diesel engine,the functional rationality of the model can be validated.Based on this,a control oriented mean value air system model is developed with mechanism/map mixed described,which build the foundation for the design of the later air control system.Secondly,the rapid response for torque demand of Electrically-Assisted turbocharged diesel engine can be achieved while ensuring the target that the air-fuel ratio is in the right values to improve emissions through the coordinated control of diesel engine oil and air parts.According to the expected torque demand,the oil control part obtains the fuel injection quantity currently required by the fuel injection MAP.The main focus in this paper is the control of air part,and it mainly consists of two control sections including the assisted motor and variable geometry turbocharger(VGT).The control scheme is divided into the following two steps: The first step according to the expected torque and speed of diesel engine,the expected motor working state is planned under the current engine working condition.And the open or close signal and the duty cycle signal of the motor is output by the logic control rules that control voltage to regulate the motor working in the motor,generator or off state.At the same time according to the current torque demand and engine conditions,the desired exhaust manifold pressure value is obtained through the calibration of exhaust manifold pressure planning MAP;In the second step,in order to achieve the desired exhaust manifold pressure,the VGT controller is utilized to complete the exhaust manifold pressure tracking.Aiming at ensuring the safe operation of the engine system and considering the physical saturation characteristics of the nozzle vane,nonlinear model predictive control method is applied to the VGT controller design,So that the actual exhaust manifold pressure quickly and accurately track the expected value,and the amount of intake air can reach the desired level.Therefore,the control of the air system is fulfilled by the nozzle vane opening of VGT and the motor control signal,to reach the goals that the amount of fresh air can be in accord with the fuel injection quantity to meet the engine performance requirements,and the diesel engine can have good power,fuel economy and emissions performance.At last,the validity of the designed air control system of the Electrically-Assisted turbocharged diesel engine is verified in AMESim.The comparison with the traditional turbocharged structure shows that the Electrically-Assisted turbocharged structure can meet the requirements of air system control better and improve the diesel engine performance.