| At present,improving the economy and emission performance of the engine can be critical for solving the energy and environment problems. The feedback system of air-fuel ratio is the core technology of modern control technology for engines.Three way catalytic converter is widely used as the after treatment system.The built-in catalyst changes the CO、HC and NOx to the products efficiently which are healthy for human beings only when lambda near to1. With the aging of the oxygen sensor,the maximum voltage and the median voltage signals declined which leads to a shift in the window of air-fuel ratio.Three way catalytic converter works out of the optimal range In view of the above problems, a new method based on delay time by coupled simulation was put forward in this paper.In this paper,the air fuel ratio closed loop control system of a four cylinder gasoline engine was built by coupling simulation with GT-POWER and Simulink.The influence which the PI controller parameters have to the closed loop system was discussed.After that,a time delay was added to the system based on the traditional PI controller to deal with the offset of air-fuel ratio caused by the aging of the oxygen sensor.The time for enriching or diluting the mixture increased with the addition of the delay time,this could amend the offset of air-fuel ratio effectively.So that the three way catalytic converter works out of the optimal range which results in a efficiency decline for the conversion of CO、HC and NOx.The voltage of the oxygen sensor occurs downward shift due to aging,or upward shift results from the NO which cannot be detected when it works in the high temperature zone.The two kinds of situations were simulated.The outputs of the air-fuel ratio were compared between the two cases. The result was verified from the quantity of emissions.The results shows that the air-fuel offset could be compensated by the PI controller strategy based on the delay time. |
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