1996-02-01

Controlling the Load and the Boost Pressure of a Turbocharged SI Engine by Means of Early Intake-Valve Closing 960588

Early Intake-Valve Closing (EIVC), which has been suggested to control the load of SI engines for a long time, is applied in this paper to control the load and the boost pressure of a turbocharged SI engine.Load control by means of EIVC reduces the pumping loss at the part load, and boost pressure control by means of EIVC eliminates the disadvantages of the conventional boost control system with wastegate and reduces the pumping loss at high speeds and loads. Another advantage of this control concept is the possibility to utilize the internal cooling effect of the charge when the intake-valve is closed before BDC. The lower compression temperature of the EIVC engine in comparison with the conventional engine is very helpful to reduce the tendency to knock and can be effectively utilized to improve the thermal efficiency.The performance of such an EIVC engine is compared on the basis of engine simulation with that of a conventional throttled engine of which the boost pressure is controlled by means of wastegate. The results show the EIVC engine to have lower specific fuel consumption not only at the part load but also at the full load. This control concept also makes it possible to improve the torque performance of a turbocharged SI engine at low speeds.

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