Study Of Transient Air Fuel Ratio Control In Automobile Engine

For recent forty years, because both energy source shortages and environment pollution are becoming serious day by day, all of the world come to set down more and more rigorous code on economical fuel consumption in gasoline engine and exhaust. As the promotion of a series of national criterion that is force to carry out in autos and engines, the engine control system has a dramatic change, which pushes the auto-tech to a development at a very fast speed at the same time. At present, there are more ways and technologies to improve the economical consumption and low nocuous exhaust in vehicle engine, and the one used widely is the combination of electrical control on fuel injection system and three ways catalytic converter which can transform the pollutions in the exhaust in the largest number while the air fuel ratio is near its theory value.The present electrical control fuel injection technologies can keep the air fuel ratio near its theory value at static working conditions, which can keep the three ways catalytic converter working in the maximum efficiency, so the engine can get a good condition in both fuel consumption and exhaust. However, under the transient conditions, it is difficult to control the air fuel ratio that is far from theory value. As a result, it is no way to actualize the three ways catalytic converter, then, the result is not in expected anyway. So both controlling of the transient air fuel ratio and improving the transform efficiency have become a key technique, which can reduce the exhaust and protect the environment. In this paper, the transient air fuel ratio control model based on an average value model is established aiming at the controlling of transient air fuel ratio. According to the simulation, the transient air fuel ratio strategy is analyzed and studied thoroughly, which provides a new way to control the transient air fuel ratio, and a new way to improve the engine capability under the transient working condition.At the beginning of this paper, the development and actuality of engine are introduced, then it is discussed that what is the advantages of electrical control fuel injection and the disadvantages and its inducement of transient air fuel ratio under the transient working condition. The new direction of electrical fuel injection technique is also discussed. After the advantages and disadvantages in various techniques are compared and analyzed, the control scheme is raised which is used for transient air fuel ratio control, and which is based on average value model. In this paper, the sub models which include the fuel evaporation model, intake air bypass model, and power output model are analyzed and ascertained thoroughly. The models are improved through waterish wall affection compensation. Under the precondition that the control precision is guaranteed, the control model for transient air fuel ratio is established and perfected.In the process of air fuel ratio being realized, in order to confirm the unknown parameters in the model, and to get the 3-dimension map of the model parameters, the demarcated working condition experiments should be as more as possible. So as to increase the precision, the MATLAB function named Polyfit and neutral net are used for dealing with the dates. After the parameters under the working conditions except demarcated working condition are got, the model's 3-dimension maps will be detailed.In the following, the air fuel ratio control strategy which is used in transient transitional working condition is analyzed. Based on the original engine air fuel ratio control, two new control strategies of transient air fuel ratio are designed. One side, in hardware, behind the throttle, the sub throttle is added to the engine. The additional sub throttle is aim at enhancing inlet air so that the engine can work in a good condition, when the inlet fuel is less than the value that ECU computes and outputs because of the formation of fuel film under the acceleration working condition. Another side, in software, the predicted control of inlet air and fuel provided are added to the engine. Under the transient working condition, based on present working circle, constant plus Kuerman filter computation which is in the modern control theory, is used to predict the inlet air in the next working circle. The ECU can check the map and then gets the corresponding fuel injected into the cylinder according to the inlet air, at the same time, it outputs the throttle position and injection signal to the engine, so that the air fuel ratio can control exactly.Finally, 3 control strategies including the original engine are computed and simulated with models that are transient air fuel control models. It indicates that: compared with original control model, controlling of assistant throttle and predict control are superior, and both of them are based on transient air fuel ratio original control. The two control schemes have their own characters. On the aspect of transient air fuel ratio the predict control model has a strong power in competition. On the aspect of integrative capability optimized, the additional throttle control has a perfect result.As mentioned above, the research of vehicle engine transient air fuel ratio control is the future trend, which is that the engine is fuel-saving and environment-protecting. The research result of this paper will be technique-supporting and very helpful to exploitation and development of new products and parts. The control of additional throttle will provide academic gist for the studies that is variable timing cam and electrical inlet and exhaust valves without cams. Predictable control can serve academic gist for electrical throttle with transient air fuel ratio control. In all, the research of vehicle engine transient air fuel ratio control is very valuable in applications and it is far-reaching significance.