H-infinity Control Research For Engine Idle Start And Stop System

Idle speed condition has a great influence on the emission production and the fuelconsumption of the engine. If the engine is working at idle condition for a long time,then it is supposed to be turned down to save oil and reduce emissions, and then restartthe engine when the car needs to move again, which is the basic strategy of the idlestart/stop control. The engine is often exposed to some torque disturbances, which willlead to some variations of the engine speed from the ideal idle speed, causing theemission characteristics and fuel economy to become worse. So it is very necessary tokeep the idle speed stable. What is more, in the stopping process, the driver may changethe mind to require the engine to start instead of stopping.This paper focused on the issue of speed variations caused by disturbances in both thestable idle condition and the stopping process, and studied the robust controllerdesigning, including the model establishment, model linearization and controller design.First, a mean-value engine model was first established. Then its validation wasproved by comparing it with enDYNA. In the model, the air mass flow through thethrottle was chosen as the control input and the engine speed as the output, with themanifold pressure and the engine speed as the system state space variables.Second, the nonlinear model was linearized using the differential geometry theory inorder to design the robust controller. The system model became linear and was validated.Finally, with the linear model above, an H-infinity controller was design to suppressthe disturbances. With respect to both the steady idle condition and the engine restartingprocess before the speed become stable, simulations were done with various disturbanceapplied to the engine. The results have shown that the controller is effective indisturbance suppression in the speed control.