A method for controlling an internal combustion engine is disclosed. The method may include receiving knock data corresponding to knock levels over a time period. The method may also include determining from the knock data whether the knock levels change over the time period. Further, the method may include determining that a variation in the gas composition of the gaseous fuel supplied to the internal combustion engine has occurred when the knock levels change over the time period. In addition, the method may include adjusting an operating condition of the internal combustion engine to adapt a knock susceptibility of the internal combustion engine to the varying gas composition.

A method for operating an internal-combustion engine having an exhaust gas catalyst, a first exhaust gas sensor upstream of the exhaust gas catalyst and a second exhaust gas sensor downstream of the exhaust gas catalyst. A fill level of an exhaust gas component that can be stored in the exhaust gas catalyst is determined using a theoretical catalyst model, into which, as the input value, a signal of the first exhaust gas sensor (a first signal); a signal of the second exhaust gas sensor (a second signal); and a target signal are provided. The target signal corresponds to the signal that would be expected at the determined fill level in the exhaust gas catalyst. The catalyst model is reinitiated when the deviation of the second signal from the target signal exceeds a predetermined threshold value. The fill level is also regulated, and an air-fuel mixture is adjusted.

An air-fuel ratio detection device 1, 1 comprises: a sensor element 2, 2 including a sensor cell 10; a voltage application circuit 40, 40 applying voltage to the sensor cell; a current detector 42, 42 detecting an output current of the sensor cell; an air-fuel ratio calculating part 61 configured to calculate an air-fuel ratio of an exhaust gas; and a parameter detecting part 62 configured to detect or calculate a temperature correlation parameter correlated with a temperature of the sensor element. The air-fuel ratio calculating part is configured to calculate the air-fuel ratio of the exhaust gas based on the temperature correlation parameter and the output current detected when a predetermined voltage is applied to the sensor cell.

Provided is a method for diagnosing exhaust sensors, where at least one substance resulting from combustion is reduced by an additive. A first sensor intended to measure an occurrence of said substance upstream said supply of additive, and a second sensor intended to measure an occurrence of said substance downstream said supply of additive. The method comprises: determining whether the locations of said first and second sensors are reversed by: determining if a second measurement value of said second sensor exceeds a corresponding first measurement value of said first sensor at least to a first extent, and when this condition occurs, determining that the locations of said first and second sensors sensor are reversed, said measurement values are determined when a supply of additive is set to obtain at least a first reduction of said at least one substance to be reduced.

A plant control system comprises a target value calculating part calculating a target value r of a control output x of a plant, a target value correcting part correcting the target value so as to calculate a corrected target value w, and a feedback controller determining a control input. The target value correcting part, if making the control output change to the target value, sets the corrected target value so that an amount of correction of the target value becomes equal to or less than a predetermined value, then changes the corrected target value so that the amount of correction of the target value becomes larger than the predetermined value, then changes the corrected target value so that the amount of correction of the target value becomes equal to or less than the predetermined value before the control output reaches the target value.

An exhaust gas recirculation (EGR) control method includes a valve duty differentiated control including: detecting, by a controller, an engine operation region, a mixer region, and an external factor region as a valve control condition for an EGR valve duty correction variable for controlling an EGR system; applying, by the controller, the EGR valve duty correction variable to an EGR valve duty, which is set by a target air amount to an intake air amount, to calculate a minimum EGR valve duty; and outputting, by the controller, the calculated minimum EGR valve duty to an EGR valve as the EGR valve duty.

A method for operating an internal-combustion engine having an exhaust gas catalyst, a first exhaust gas sensor upstream of the exhaust gas catalyst and a second exhaust gas sensor downstream of the exhaust gas catalyst. A fill level of an exhaust gas component that can be stored in the exhaust gas catalyst is determined using a theoretical catalyst model, into which, as the input value, a signal of the first exhaust gas sensor (a first signal); a signal of the second exhaust gas sensor (a second signal); and a target signal are provided. The target signal corresponds to the signal that would be expected at the determined fill level in the exhaust gas catalyst. The catalyst model is reinitiated when the deviation of the second signal from the target signal exceeds a predetermined threshold value. The fill level is also regulated, and an air-fuel mixture is adjusted.

An exhaust gas recirculation (EGR) control method includes a valve duty differentiated control including: detecting, by a controller, an engine operation region, a mixer region, and an external factor region as a valve control condition for an EGR valve duty correction variable for controlling an EGR system; applying, by the controller, the EGR valve duty correction variable to an EGR valve duty, which is set by a target air amount to an intake air amount, to calculate a minimum EGR valve duty; and outputting, by the controller, the calculated minimum EGR valve duty to an EGR valve as the EGR valve duty.

An air-fuel ratio detection device 1, 1 comprises: a sensor element 2, 2 including a sensor cell 10; a voltage application circuit 40, 40 applying voltage to the sensor cell; a current detector 42, 42 detecting an output current of the sensor cell; an air-fuel ratio calculating part 61 configured to calculate an air-fuel ratio of an exhaust gas; and a parameter detecting part 62 configured to detect or calculate a temperature correlation parameter correlated with a temperature of the sensor element. The air-fuel ratio calculating part is configured to calculate the air-fuel ratio of the exhaust gas based on the temperature correlation parameter and the output current detected when a predetermined voltage is applied to the sensor cell.

A basic opening (A0) of an EGR control valve (22) is set, based on a current engine operation state. A differential pressure (P1) across the EGR control valve (22) is calculated, based on an actual exhaust system temperature (T1) sensed by an exhaust temperature sensor (33). A reference differential pressure (P0) is calculated, which is a differential pressure across the EGR control valve (22) in a steady state corresponding to the current engine operation state. A reference pulsation amplitude (D) is calculated, which is an amplitude of pulsation of the reference differential pressure (P0). The basic opening (A0) is corrected, based on the differential pressure (P1), the reference differential pressure (P0), and the reference pulsation amplitude (D).