In this invention, an EMF oxygen sensor is subjected to an activation process applying unidirectional voltage between an atmosphere electrode and an exhaust electrode thereof. A control device controlling the oxygen sensor in which a voltage was applied with the atmosphere electrode being positive, additionally applies unidirectional voltage between the electrodes to make the atmosphere electrode positive, for example, when the oxygen sensor was used under an environment in which the air-fuel ratio of the internal combustion engine was rich relative to the theoretical air-fuel ratio. Conversely, a control device controlling the oxygen sensor in which a voltage was applied to make the atmosphere electrode negative, additionally applies unidirectional voltage between the electrodes to make the atmosphere electrode negative, for example, when the oxygen sensor was used under an environment in which the air-fuel ratio was lean relative to the theoretical air-fuel ratio.

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.

A vehicle includes an internal combustion engine, an exhaust purification catalyst, and an air fuel ratio sensor. The internal combustion engine is structured to be motored by an electric motor generator. The exhaust purification catalyst is structured to purify exhaust gas of the internal combustion engine. The air fuel ratio sensor is located upstream of the exhaust purification catalyst and structured to sense an air fuel ratio. When a quantity of oxygen stored in the exhaust purification catalyst is larger than a reference value, it is determined that inflow of oxygen into the exhaust purification catalyst has an insignificant effect on exhaust performance. Then, fuel injection of the internal combustion engine is stopped, the internal combustion engine is motored, and air fuel ratio learning is performed for learning of a sensed value of the air fuel ratio sensor.

A controller for an internal combustion engine includes processing circuitry. The processing circuitry is configured to execute an inflow process when an oxygen storage amount of the catalyst is greater than or equal to a predetermined amount. The inflow process includes operating the fuel injection valve to cause a fluid containing oxygen and unburned fuel to flow into the catalyst. An amount of the unburned fuel is greater than or equal to an ideal amount of unburned fuel that reacts with all of the oxygen. The processing circuitry is configured to execute, based on a detection value of the air-fuel ratio sensor obtained during an execution of the inflow process, a deviation amount calculation process that calculates a deviation amount indication value that indicates a deviation amount of a detection value of the air-fuel ratio sensor.

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.

A control apparatus comprising an air-fuel ratio sensor disposed between the exhaust gas aggregated portion and the three-way catalyst, and which outputs an output value corresponding to an amount of oxygen and an amount of unburnt substances that has reached the exhaust-gas-side electrode layer via the porous; an actual detected air-fuel ratio obtaining section which obtains an actual detected air-fuel ratio by converting an actual output value of the air-fuel ratio sensor into an air-fuel ratio; and an instructed fuel injection amount calculation section which corrects the amount of the fuel injected from a plurality of the fuel injection valves so that the actual detected air-fuel ratio coincides with a target air-fuel ratio; and an air-fuel ratio imbalance indicating value obtaining section which obtains an air-fuel ratio imbalance indicating value which becomes larger as a degree of a non-uniformity among a plurality of the cylinders of cylinder-by-cylinder air-fuel ratios.

A catalytic conversion characteristic of a catalyst, which indicates a relationship between an air-to-fuel ratio and a catalytic conversion efficiency of the catalyst, includes a second air-to-fuel ratio point, which is a point of starting an outflow of NOx from the catalyst and is located on a rich side of a first air-to-fuel ratio point that forms an equilibrium point for a rich component and oxygen. A constant current circuit, which induces a flow of an electric current from an exhaust side electrode to an atmosphere side electrode through a solid electrolyte layer in a sensor element, is connected to the sensor element. A microcomputer controls a current value of the electric current, which is induced by the constant current circuit, based on a difference between the first air-to-fuel ratio point and the second air-to-fuel ratio point at the catalyst.

A controller for an internal combustion engine may comprise a first assignment unit, an observer, a calibration unit, and a second assignment unit. The first assignment unit may determine cylinder-specific measurement signals as a function of the measurement signal from a lambda probe. The observer may include a sensor model of the lambda probe arranged in a feedback branch of the observer. The calibration unit may impress a predefined interference pattern made of cylinder-specific mixture differences and adapt, in reaction to the respectively predefined interference pattern as a function of the observer output variables related to the respective cylinders, an assignment rule between the measurement signal of the lambda probe and a lambda signal. The second assignment unit may carry out, by means of the assignment rule, an assignment between the measurement signal and the lambda signal.

A method and system for monitoring an exhaust gas sensor coupled in an engine exhaust is provided. In one example, the method determines an estimate of an exhaust gas oxygen sensor time constant according to a comparison of air/fuel ratios and a system time constant.

A catalytic conversion characteristic of a catalyst, which indicates a relationship between an air-to-fuel ratio and a catalytic conversion efficiency of the catalyst, includes a second air-to-fuel ratio point, which is a point of starting an outflow of NOx from the catalyst and is located on a rich side of a first air-to-fuel ratio point that forms an equilibrium point for a rich component and oxygen. A constant current circuit, which induces a flow of an electric current from an exhaust side electrode to an atmosphere side electrode through a solid electrolyte layer in a sensor element, is connected to the sensor element. A microcomputer controls a current value of the electric current, which is induced by the constant current circuit, based on a difference between the first air-to-fuel ratio point and the second air-to-fuel ratio point at the catalyst.