A misfire detection device for an internal combustion engine is configured to execute: a deactivating process that deactivates combustion control for air-fuel mixture in one or some of cylinders; a provisional determination process that uses a detection value of a sensor to output a logical value indicating whether a misfire has occurred; a provisional determination counting process that counts a number of times a specific one of the logical value output by the provisional determination counting process has been output; and an official determination process that makes an official determination of whether the misfire has occurred using, as an input, the number of times counted by the provisional determination counting process during a specific period.

A determination device for an internal combustion engine executes a partial fuel cut-off process. The determination device determines that exhaust gas characteristics have deteriorated when the misfire rate of the internal combustion engine is greater than or equal to a determination threshold. The determination device sets the determination threshold to a first determination threshold when the calculated misfire rate is a misfire rate in a period of non-execution of the partial fuel cut-off process. Also, the determination device sets the determination threshold to a second determination threshold, which is less than the first determination threshold, when the calculated misfire rate is a misfire rate in a period of execution of the partial fuel cut-off process.

When an amount of particulate matter (PM) collected by a gasoline particulate filter (GPF) reaches a predetermined amount, a central processing unit (CPU) executes a regeneration process for regenerating the GPF. That is, the CPU stops supply of fuel to any one of cylinders #1 to #4, while increasing an amount of fuel supplied to remaining cylinders. When a temperature of a three-way catalyst becomes equal to or higher than a first temperature, the CPU increases an injection amount to lower a temperature of exhaust gas. When the temperature of the three-way catalyst becomes equal to or higher than the first temperature during the execution of the regeneration process, the CPU does not increase the injection amount.

In the exhaust gas control system, the electronic control unit is configured to execute first air-fuel ratio control for controlling an air-fuel ratio of an air-fuel mixture in a part of cylinders to a lean air-fuel ratio and controlling an air-fuel ratio of an air-fuel mixture in the other part of the cylinders to a rich air-fuel ratio is executed. The electronic control unit is configured to execute second air-fuel ratio control to perform malfunction diagnosis. The electronic control unit is configured to execute second air-fuel ratio control when the execution of the first air-fuel ratio control is interrupted after the temperature of the three-way catalyst becomes equal to or higher than the diagnosis temperature.

A controller for an internal combustion engine includes a detector and a processor. The detector detects a combustion condition of a gas in a cylinder of the internal combustion engine. The processor is configured to calculate a target combustion condition. The processor is configured to calculate an ignition timing such that the combustion condition detected by the detector becomes equal to the target combustion condition via a feedback control with a gain. The processor is configured to calculate a fuel ratio in the gas in the cylinder. The processor is configured to determine the gain so as to increase as the fuel ratio decreases.

A three-way catalyst and an NO.sub.x adsorption catalyst are disposed in an engine exhaust passage. In a predetermined low-load engine operation area, combustion in a combustion chamber is carried out at a lean base air-fuel ratio and an air-fuel ratio in the combustion chamber is changed to a rich range at the time of discharging NO.sub.x from the NO.sub.x adsorption catalyst. In a predetermined high-load engine operation area, the air-fuel ratio in the combustion chamber is controlled to a theoretical air-fuel ratio in a feedback manner. In a predetermined middle-load engine operation area, the combustion in the combustion chamber is carried out at the base air-fuel ratio lower than the base air-fuel ratio in the low-load engine operation area and the air-fuel ratio in the combustion chamber is changed to the rich range with a period shorter than a rich period of the air-fuel ratio for discharging NO.sub.x in the low-load engine operation area.

A method for controlling an internal combustion engine operating on at least partly gaseous fuel is disclosed. The method may include providing a desired burn rate profile corresponding to a desired operation of the internal combustion engine. The method may further include selecting first operating parameters such that an operation of the internal combustion engine with a first gas composition produces a first burn rate profile that corresponds to the desired burn rate profile. The method may also include operating the internal combustion engine with the first operating parameters using a second gas composition. The method may include determining that the second burn rate profile differs from the desired burn rate profile. In addition, the method may include adjusting an operating parameter from among the first operating parameters of the internal combustion engine to approach the desired burn rate profile.

A controller for an internal combustion engine is configured, when the speed of combustion of a fuel in a cylinder changes as the property of the fuel injected from a fuel injection valve changes, to change a combustion limit excess air ratio that is a target value of a fuel injection amount feedforward control according to a first relationship that the combustion limit excess air ratio increases as the speed of combustion of the fuel in the cylinder increases. The controller is also configured, when the speed of combustion of the fuel in the cylinder changes as the property of the fuel injected from the fuel injection valve changes, to change the value of a combustion limit combustion speed parameter that is the target value of a fuel injection amount feedback control according to a second relationship that the speed of combustion of the fuel in the cylinder corresponding to a combustion limit increases as the speed of combustion of the fuel in the cylinder increases.

Systems and methods for controlling a gasoline urea selective catalytic reductant catalyst are described. In one example, an observer is provided that corrects an estimate of an amount of NH.sub.3 that is stored in a SCR. The amount of NH.sub.3 that is stored in the SCR is a basis for generating additional NH.sub.3 or ceasing generation of NH.sub.3.

The invention relates to a control device for an internal combustion engine that includes a turbocharger, and an actuator that changes a turbocharging pressure by regulating exhaust energy for use in drive of the turbocharger. When a target torque is increased during execution of a lean burn operation, the control device switches an operation mode of the internal combustion engine from the lean burn operation to a stoichiometric operation. When the operation mode switching is performed in a turbocharging state, the control device determines whether a target torque is within a range of a torque realizable under the lean air-fuel ratio. When the target torque is within the range, the control device operates the actuator so as to keep the turbocharging pressure at a magnitude equal to or larger than a magnitude at a time point at which the operation mode is switched.