Study On Improving The Control Precision Of The Transient AFR Of Electronic Controlled Gasoline Engine

With the highlight of environmental problems,motor vehicle emission regulations become more stringent,gasoline engine air-fuel ratio directly affect the efficiency of three-way catalytic converter,so the gasoline engine air-fuel ratio control accuracy is very important.In the steady working condition,PID control can be used to control the air-fuel ratio in the vicinity of the theoretical air-fuel ratio.For the transient working condition,although a large number of experiments have been used to calibrate the transient fuel injection pulse pattern to correct the air-fuel ratio of the engine some results have been obtained,but the control precision is not high and the consistency is poor.To solve the above problems,this paper has conducted the following research.First of all,based on the theory of engine average model,the engine simulation model was established with the experimental data,and the simulation model was debugged and verified.The accuracy of the simulation model is within ± 3%,which meets the requirement of transient working condition control strategy development.Then,the fuel film model compensation controller was established based on feedforward control.The fuzzy inference controller was established based on fuzzy inference system.Combining fuzzy inference system with PID control,the FIS-PID controller was founded.The fuzzy inference system and neural network were combined to form an adaptive network-based fuzzy inference system controller.The above four kinds of controllers were simulated and analyzed respectively.(1)The fuel film model compensation strategy can compensate for the dynamic effect of fuel film caused by air-fuel ratio fluctuations,to achieve the ideal effect,but the anti-interference ability of the feedforward control is poor in the engieering practice.It is difficult to completely eliminate the air-fuel ratio deviation by the fuel film model compensation strategy,and the fuel film compensation controller rely on the accuracy of the fuel film deposition ratio coefficient and the fuel film evaporation time constant.(2)The fuzzy inference system is satisfied the control requirement when the mutation amplitude is not too large.When the amplitude is large,there is a short time part beyond the control design requirement.The accuracy of this program needs to be further improved.(3)Based on the fuzzy inference system,PID control was introduced.When the adjustment request is large,the fuzzy reasoning system is adopted.When the adjustment is not large,the local adjustment is carried out by PID.From the results in the throttle opening degree of change in the larger range of slowdown,air-fuel ratio deviation is only 1.23%,which is met the control requirements of ±3%.Transient air-fuel ratio has been significantly improved,the worst also reached 742.65% of the control effect.(4)On the basis of the fuzzy inference system,the neural network was combined,and the fuzzy control system based on expert experience was added to the adaptive function to form an adaptive network-based fuzzy inference system.Focusing on the simulation analysis for the accelerated conditions,the air-fuel ratio deviation is about 2.5%,which was met the control requirements.In summary,the fuel film model compensation strategy is the highest accuracy,but the high precision fuel film model parameters is difficult to obtain,and the parameters based on the feedforward control anti-jamming performance is poor,the scheme is not ideal.The accuracy of the fuzzy inference system is slightly worse than that of FIS-PID control and adaptive network-based fuzzy inference system.Adaptive network-based fuzzy inference system meet the current demand,but its dynamic response speed is obviously solwer than the FIS-PID control.If the transient air-fuel ratio is slow,it has a negative effect on driving and emission.Meanwhile the control operation is more complicated and the hardware requirements are high,and it is difficult to implement in some cost control demanding products.The precision of FIS-PID control is the highest among several kinds of feedback control,and its response speed is also the best.So the FIS-PID control is a high precision and consistent with the control method of engineering application in the control strategy of air-fuel ratio in gasoline engine transient working condition.