A control device and a control method for a multi-cylinder internal combustion engine including a post-processing device are provided. The control device includes an electronic control unit executing a temperature raising process of raising the temperature of the post-processing device and a recovery-time process. The temperature raising process includes a stopping process and a rich process. In the stopping process, supply of fuel to several of cylinders is stopped. In the rich process, the air-fuel ratio of an air-fuel mixture for different ones of the cylinders other than the several cylinders is made lower than the stoichiometric air-fuel ratio. In the recovery-time process, the concentration of unburned fuel in exhaust gas discharged to the exhaust passage is made higher than an equivalent concentration, when the temperature raising process is stopped. The equivalent concentration is the concentration of unburned fuel being just enough to react with oxygen in the exhaust gas.

An engine device includes: an engine; and a control device that executes a return rich control that controls the engine so that an air-fuel ratio becomes rich over a predetermined period after the engine returns from the fuel cut. When the engine is intermittently stopped during the execution of the return rich control, the return rich control is executed for a period shorter than the predetermined period after the engine is restarted. Thus, when the engine is intermittently stopped during the execution of the return rich control and the engine is restarted thereafter, it is possible to suppress a total period of the return rich control from becoming long. As a result, it is possible to suppress an increase in the amount of hydrocarbons in the exhaust gas and suppress deterioration of emissions.

An exhaust purification system comprising an exhaust purification catalyst, a downstream side air-fuel ratio sensor, and a control device performing air-fuel ratio control for controlling an air-fuel ratio of exhaust gas and abnormality diagnosis control for diagnosing the downstream side air-fuel ratio sensor. In the air-fuel ratio control, the control device alternately and repeatedly switches the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst between a rich air-fuel ratio and a lean air-fuel ratio. In the abnormality diagnosis control, the control device judges that the downstream side air-fuel ratio sensor has become abnormal when the air-fuel ratio of the exhaust gas is made the rich air-fuel ratio by the air-fuel control and the output air-fuel ratio of the downstream side air-fuel ratio sensor changes from an air-fuel ratio richer than a predetermined lean judged air-fuel ratio to an lean air-fuel ratio.

To keep medium purification efficiency at a high level and prevent deterioration of emission performance. An aspect of the present invention includes: a downstream equivalence ratio calculation unit that calculates a catalyst downstream exhaust gas equivalence ratio by using a catalyst statistical model that receives at least a detection value of an air-fuel ratio sensor on an upstream side of a catalyst and outputs a catalyst downstream exhaust gas equivalence ratio; an oxygen output calculation unit that calculates an output value of an oxygen sensor by using an oxygen sensor statistical model that receives the catalyst downstream exhaust gas equivalence ratio and outputs an output value of the oxygen sensor on the downstream side of the catalyst; a downstream equivalence ratio correction unit that corrects the catalyst downstream exhaust gas equivalence ratio calculated by the downstream equivalence ratio calculation unit based on a calculation result of the oxygen output calculation unit and the detection value of the oxygen sensor; and an air-fuel ratio control unit that controls an air-fuel ratio of an air-fuel mixture of an internal combustion engine based on the corrected catalyst downstream exhaust gas equivalence ratio and air-fuel ratio target value.

A reduction method for a catalytic converter in an exhaust system of an internal combustion engine for reducing the oxygen content in the catalytic converter, in particular after an overrun fuel cutoff mode of the internal combustion engine, the method including first injection of fuel into a first cylinder, the first injection taking place after an ignition point in time of a compression stroke of a first working cycle of the cylinder and including an introduction of the injected fuel from the cylinder into the catalytic converter during an exhaust stroke of the first cylinder.

Methods and systems are provided for continually monitoring a functionality of an exhaust catalyst based on roll-down of a monotonically decreasing catalyst activity parameter representing catalyst storage capacity. Catalyst degradation may be indicated responsive to the estimate of catalyst storage capacity lowering below a threshold. Engine operating parameters may be adjusted based on a current level of catalyst storage capacity.

A method and device for controlling a supercharged internal combustion engine is disclosed. An oxygen charge of a catalytic converter of the internal combustion engine is determined. A valve overlap of the internal combustion engine is increased from a lower valve overlap value to an upper valve overlap value. Increasing the valve overlap and/or for at least one phase of the increase, a control value for increasing an air-fuel ratio in at least one cylinder of the internal combustion engine is reduced as a function of the determined oxygen charge.

A method comprising adjusting a fuel injection amount based on a fractional oxidation state of a catalyst, the fractional oxidation state based on reaction rates of grouped oxidant and reductant exhaust gas species throughout a catalyst and a low-dimensional physics-based model derived from a detailed two-dimensional model to obtain a one-dimensional model averaged over time and space that accounts for diffusion limitations in the washcoat and accurately predicts emissions during cold start.

An internal combustion engine mounted on a vehicle includes an exhaust passage provided with a catalyst. A controller for the internal combustion engine includes a processor. The processor is configured to perform an auto-stopping process on the engine when the engine is idling, perform an auto-restarting process on the engine when the engine is automatically stopped, correct an amount of fuel injected into the engine so that the fuel injection amount of the engine is increased by a correction amount after the auto-restarting process is started, and change the correction amount in accordance with an amount of oxygen stored in the catalyst at a point of time when the auto-stopping process is started.

The control system of an internal combustion engine performs normal operation control including lean control for making the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst a lean air-fuel ratio, and rich control for making the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst a rich air-fuel ratio. The normal operation control includes judgment reference decreasing control decreasing the judgment reference storage amount in the lean control when during the time period of performing the lean control, the air-fuel ratio of the exhaust gas flowing out from the exhaust purification catalyst becomes the lean judged air-fuel ratio or more. The control system judges that the exhaust purification catalyst is abnormal when the judgment reference storage amount becomes less than a deterioration judgment value.