Research On Rail Pressure Control Of GDI Engine

As an important technology to improve the fuel economy of gasoline engines, Gaso-line Direct Injection(GDI) has aroused common concern. Compared with traditional ProtFuel Injection engine, the GDI engine can ensure more output torque and better emis-sions under the same fuel consumption conditions. The rail fuel system in this typeengine can supply the high pressure fuel to realize gasoline direct injection process. Theinjection mass is determined by pressure in the common rail, and the unstable rail pres-sure makes the injection quantity can not be controlled precisely, which makes the engineperformance deteriorated. In this paper, a GDI engine rail pressure control algorithm isdesigned with model-based controller development method and the simulation tests verifythe efectiveness of the algorithm.The thesis mainly includes the following three parts:(1)The pressure diferential equations of high pressure pump, common rail and in-jectors are established according to the physical structure and features of the GDI enginecommon rail system. Because the form of the model is complex, the model is simplifiedand reduced order, e.g. the injectors dynamic are ignored and a injection rate parameteris introduced here.(2)Because the rail system contains a strong non-linear structure and the form of themathematical model is complex, the backstepping technique is used to derive a nonlin-ear rail pressure controller. Backstepping technique is based on the Lyapunov stabilitytheory and the controller for the whole system is designed through designing the virtualcontrol input for each state in the system. The stability of system is guaranteed by thismethod. There is a strong coupling between the fuel pressure of high pressure pump andrail pressure in the system model. In order to apply the backstepping method, some in-termediate variable is needed here. In the process of controller development, the integralterm is used for engineering application. The form of the final controller can be rewrittenas a feed-forward part and a PID feed-back part. The dynamic fuel characteristics of thehigh-pressure pump and the rail are included in the feed-forward. The pressure controlalgorithm is realizable.(3)The efectiveness of the controller is verified by the simulation test in Simulink and AMESim. The Simulink model of GDI engine fuel system is established accordingto the modeling principle. The results of the constant value tracking and sine trackingsimulations show that the closed-loop system is stable and the rail pressure controller hasa good efect. To further validate the controller performance, the same simulations havebeen done. The output error is within the allowable range for rail pressure control.This paper makes some progress on the issue of the rail pressure control and providesa new approach for GDI engine rail pressure control. Further research work needs to bedone. For example, the ofine simulations are finished in this paper, and some onlinesimulations are needed for verifying the real-time response of the controller. In orderto realize the control algorithm in C language, some characteristic map data need bemeasured, such as the pump fuel characteristics map of high pressure pump and the fuelreservoir characteristics map of rail, which will make the controller more practical.