This paper describes a simple engine model at idling and it applies particularly to idle speed control.
Through linearization in the neighborhood of the nominal operating points (650 rpm), the engine is expressed as a reduced-order constant coefficient state variable (2 state) model. It was produced through the system order-reduction method.
The strategy for controlling idle speed uses the Linear Quadratic and Integral (LQI) optimal control theory. The tracking controller was designed using a state variable engine model, and the performance index was minimized. Since state variables are artificially introduced, they are not directly accessible. Therefore, they must be estimated in accordance with a stored dynamic model (i.e. observer), in which the engine dynamic behavior is estimated on the basis of a state variable model which represents the engine's internal states, in determining controlling values.
Since the simple model - oriented LQI controlling method with state observer neither requires exact engine models nor any of the various sensors, the resulting controlling calculations are not particularly complicated. Therefore, it can be easily implemented in an onboard 8 bit microprocessor based system.
From the experimental results, it was found that the controller can perform tracking with a higher response speed, even in the transient state where the engine is subjected to various torque disturbances.