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Vehicles fueled by liquefied petroleum gas (LPG) are also required to provide high levels of engine torque and power, in addition to clean emissions for environmental friendliness, low fuel consumption and energy savings. In response to these demands, it can be expected that engine control performance and exhaust emissions can be substantially improved by controlling the fuel supply system with high accuracy. Energy savings along with higher levels of speed, accuracy and reliability can also be expected. The conventional method of controlling fuel supply systems has been to control the fuel injection pressure to a high level at all times under all engine operating conditions, regardless of the amount of fuel injected.

This paper proposes a new returnless LPG fuel supply system designed to increase the efficiency of current LPG engines. With a conventional engine fuel supply system, the fuel pump is driven at a certain speed to pressurize the fuel to an excessive level, and excess fuel that is discharged from the fuel pump but not injected from the injector is returned to the fuel tank via a pressure regulator and a return line. This arrangement keeps the pressure in the fuel supply line at a constant level. Accordingly, during engine idling, fuel cut-off or other times when very little or no fuel is injected from the injector, nearly all the fuel discharged from the fuel pump is returned to the fuel tank via the pressure regulator and return line. Therefore, the energy (electric power) applied to drive the fuel pump is wastefully consumed. Moreover, returning a large amount of excess fuel to the fuel tank can raise the fuel temperature in the tank, causing the fuel to evaporate.

The purpose of this paper is to show precise and robust control of an automotive LPG engine speed, including a modeling method of an automotive engine system and a model base control technique. The modeling is performed for an electronic throttle servo system, an air intake system and an engine drive system. Since the system is highly nonlinear, the sliding mode controller design method with the VSS (Variable Structure System) observer is applied for the throttle control system where the design parameters are optimized by GA (Genetic Algorithm). In order to verify the effectiveness of the proposed modeling method and controller design, the simulation and experiments are performed. The results show the precise control of engine speed. The simulation results show good agreement with experimental results. Also, the robustness of the controller is confirmed by the precise speed control ability under sudden change of the load of the engine.