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The engine load rate is an important factor of vehicle fuel economy. The load Characteristics of petrol engine indicate that when the load rate is lower, the fuel consumption rate is higher; on the contray, when the load rate is higher, the fuel consumption is lower. In generally, the engine power is desigened by the maximum load of vehicle, so the engine load rate is lower at most conditions.In this paper, the engine’s work displacement is changed by stopping the injector’s work alternately, circulated and regularly. This makes that using high displacement when the load is big, low displacement when the load is small,so it can not only guarantees the power requirement, but also improves fuel economy.Firstly, this paper introduces the basic theory and method of variable power displacement in circuitation(VPDC), analyzes fuzzy reasoning and control theory and its application on the VPDC. Also, it gives several work modes of VPDC and improves some small displacement’s work modes. Secondly, it puts emphasis on control stategy of VPDC, gives the fuzzy levels of input parameters, and designs the control strategies of VPDC under all kinds of driving conditions. In the meanwhile, the model of more inputs and one output has been given, also the engine power has been indentified fuzzily. Finally, the controller of VPDC based on PIC16F886 has been desigened, and the program which included control strategies has been writed. What’s more, the road tests have been done. The results prove that the controller which is fixed on the Jetta vehicle can choose the engine power according to the driving conditions automatically. Also the fuel consumption and discharge can be reduced.
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