Abstract: In a system for detecting deterioration of an exhaust catalyst, when a catalyst temperature exceeds 150° C., the changing widths of the output voltage of an oxygen sensor downstream of the catalyst are integrated for a predetermined sampling period to determine data &Sgr;V reflecting the amount of purified gas component, and the deviation of the air/fuel ratio detected by an air/fuel ratio sensor upstream of the catalyst, and a target A/F and an exhaust gas flow rate or an intake flow rate are multiplied so that data &Sgr;A/F&Circlesolid;Q of the fluctuation of the gas component flowing into the catalyst are determined by integrating the multiplied values. At the instant when the catalyst temperature reaches 550° C., the data &Sgr;V, as integrated till then, are compared with a deterioration determining value, as set according to the data &Sgr;A/F&Circlesolid;Q, to determine whether the catalyst is deteriorated.

Abstract: In a system for detecting deterioration of an exhaust catalyst, when a catalyst temperature exceeds 150.degree. C., the changing widths of the output voltage of an oxygen sensor downstream of the catalyst are integrated for a predetermined sampling period to determine data .SIGMA.V reflecting the amount of purified gas component, and the deviation of the air/fuel ratio detected by an air/fuel ratio sensor upstream of the catalyst, and a target A/F and an exhaust gas flow rate or an intake flow rate are multiplied so that data .SIGMA.A/F .cndot.Q of the fluctuation of the gas component flowing into the catalyst are determined by integrating the multiplied values. At the instant when the catalyst temperature reaches 550.degree. C., the data .SIGMA.V, as integrated till then, are compared with a deterioration determining value, as set according to the data .SIGMA.A/F.cndot.Q, to determine whether the catalyst is deteriorated.

Abstract: In order to optimally suppress effects of error exerted upon control results by any modeling error which may arise from load fluctuations or the like of the internal combustion engine approximated as a dynamic model under an advanced control theory, present and past values of an operating quantity and control quantity which correspond respectively to a control input and control output of an internal combustion engine are utilized as state variable quantities representing the internal state of the dynamic model of an internal combustion engine. Furthermore, the target value and difference are accumulated for the foregoing control quantity. Modeling of the internal combustion engine is performed in realtime, and optimal feedback gain is calculated periodically or under certain specified conditions for a regulator constructed on the basis of these model constants calculated in realtime.

Abstract: An air-fuel ratio control system for an internal combustion engine utilizes a pre-stored standard relation between an air-fuel ratio sensor signal and a standard air-fuel ratio indicative value for deriving the standard air-fuel ratio indicative value based on the sensor signal. The system further utilizes a pre-stored modified relationship between the standard air-fuel ratio indicative value and a for-control air-fuel ratio indicative value for deriving a for-control air-fuel ratio indicative value based on the derived standard air-fuel ratio indicative value. In the modified relationship, the for-control air-fuel ratio indicative value varies with respect to a corresponding variation of the standard air-fuel ratio indicative value within a given range across the standard air-fuel ratio indicative value representing a stoichiometric air-fuel ratio.

Abstract: An air-fuel ratio control system for an internal combustion engine uses a dynamic model which is set as an approximation to a controlled object. The controlled object covers an operation sequence from a fuel injection valve to an air-fuel ratio sensor which is provided downstream of a catalytic converter for detecting an actual air-fuel ratio based on the exhaust gas downstream of the catalytic converter. The system derives a fuel injection amount to be fed to the engine by performing a state-feedback control in such a manner as to control the actual air-fuel ratio to a target air-fuel ratio. The system performs the state-feedback control using, as state variables, current and past input and output data relative to the dynamic model. Accordingly, the actual air-fuel ratio monitored on the downstream-side of the catalytic converter is controlled to the target air-fuel ratio without delay by directly deriving the fuel injection amount using the state-feedback control.

Abstract: An air-fuel ratio control system for an internal combustion engine utilizes a pre-stored standard relation between an air-fuel ratio sensor signal and a standard air-fuel ratio indicative value for deriving the standard air-fuel ratio indicative value based on the sensor signal. The system further utilizes a pre-stored modified relationship between the standard air-fuel ratio indicative value and a for-control air-fuel ratio indicative value for deriving a for-control air-fuel ratio indicative value based on the derived standard air-fuel ratio indicative value. In the modified relationship, the for-control air-fuel ratio indicative value varies with respect to a corresponding variation of the standard air-fuel ratio indicative value within a given range across the standard air-fuel ratio indicative value representing a stoichiometric air-fuel ratio.

Abstract: An engine speed control apparatus having an auxiliary air amount controller is disclosed. The apparatus has an actuator which is attached to an engine intake manifold so as to bypass a throttle valve and controls a flow rate of an auxiliary air and a control unit for driving the actuator. The control unit detects whether an engine is in an idling state or not on the basis of a combination of an engine rotational speed and other information. When the idling state is detected, a target value of an intake pressure on the downstream side of the throttle valve is set in accordance with the engine speed at that time. The control unit drives and controls the actuator so that the actual intake pressure coincides with the target value. Thus, when the operating mode of the engine is shifted from the non-idling state to the idling state, an air amount which is required by the engine can be accurately supplied and the engine speed can be rapidly converged to the target value.