Use of Ragazzini method to design idle speed control algorithms

Spark advance and throttle angle are used together to implement the control action on a 2.9l EFI engine. The throttle angle is controlled by an electronic throttle control system which tracks a requested throttle angle sent from an idle speed controller. A computer-aided control system design package was used for the design. The engine model is linearized about an idle speed operating point and includes the effects of bank-to-bank fuel injection and intake-to-power delay. The model has two control inputs, spark advance and throttle angle; one disturbance input, load torque; and one output, engine speed. The controller was designed using a modification of the direct design method of Ragazzini. This method is an algebraic method of controller design in the discrete domain which provides significantly better control and disturbance rejection than the more conventional PID algorithms for this application. The effect of spark advance on engine speed is significantly faster than the effect of throttle and therefore the intention is to use spark advance for transient control and initial rejection of load disturbances