A CPU operates a purge valve to control the amount of fuel vapor that flows into an intake passage from a canister. If there is a requirement for increasing the temperature of a three-way catalyst, the CPU executes dither control in which the air-fuel ratio of one of cylinders #1 to #4 is made richer than the stoichiometric air-fuel ratio, and the air-fuel ratio of the remaining cylinders is made leaner than the stoichiometric air-fuel ratio. The CPU executes the dither control and performs feedforward correction of the distribution variation of the fuel vapor to the cylinders #1 to #4 if the amount of fuel vapor from the canister to the intake passage is greater than zero.

A control device for an internal combustion engine includes an electronic control unit configured to execute dither control processing in a first mode and a second mode. The dither control processing is processing for operating a fuel injection valve such that an air-fuel ratio of at least one cylinder among cylinders becomes lean air-fuel ratio, and an air-fuel ratio of cylinders different from the at least one cylinder becomes rich air-fuel ratio when a condition that a regeneration request of the filter occurs is established. In the second mode, an absolute value of the difference between the air-fuel ratio in the lean combustion cylinder and the air-fuel ratio in the rich combustion cylinder smaller than in the first mode.

A temperature estimation module applied to a control apparatus for an internal combustion engine is configured to execute a virtual temperature estimation process that estimates a virtual temperature, which is a temperature of an exhaust purifying device under an assumption that a dither control process is not executed, based on an operation point of the internal combustion engine during execution of the dither control process. The temperature estimation module is further configured to execute an actual temperature estimation process that estimates an actual temperature of the exhaust purifying device based on a difference between the air-fuel ratio of a rich combustion cylinder and the air-fuel ratio of a lean combustion cylinder and based on the operation point of the internal combustion engine during execution of the dither control process.

A controller for an internal combustion engine includes processing circuitry configured to execute: a dither control process of operating fuel injection valves to designate at least one of cylinders as a lean combustion cylinder, in which an air-fuel ratio is leaner than a stoichiometric air-fuel ratio, and to designate at least another one of the cylinders as a rich combustion cylinder, in which an air-fuel ratio is richer than the stoichiometric air-fuel ratio; and an idle-time limiting process of causing an absolute value of a difference between the air-fuel ratio in the lean combustion cylinder and the air-fuel ratio in the rich combustion cylinder to be smaller when the internal combustion engine is idling than when the internal combustion engine is not idling.

A controller for an internal combustion engine is configured to execute a dither control process and an enlarging process. The enlarging process includes at least one of the following two processes: a process of causing an operation region of the internal combustion engine in which the dither control process is executed to be larger in a case in which an amount of particulate matter trapped by the filter is large than in a case in which the amount is small; and a process of causing a degree of richness of the rich combustion cylinder and a degree of leanness of the lean combustion cylinder to be greater in a case in which the amount of particulate matter trapped by the filter is large than in a case in which the amount of particulate matter trapped by the filter is small.

In a dither control process performed on a fuel injection valve, at least one cylinder is set as a rich combustion cylinder and another cylinder is set as a lean combustion cylinder. A dither control process is executed in a first mode when a vehicle is driven in a normal manner by a user. The dither control process is executed in a second mode on condition that a command signal for performing a temperature raising process on the exhaust gas purifier is input from a device outside the vehicle at a repair shop. The absolute value of the difference between the air-fuel ratio of the lean combustion cylinder and the air-fuel ratio of the rich combustion cylinder obtained by the dither control process is set to be greater in the second mode than in the first mode.

In a dither control process of a fuel injection valve, one of a number of cylinders is set as a rich combustion cylinder and another one of the cylinders is set as a lean combustion cylinder. The temperature raising capability required for the dither control process in the second mode is higher than the temperature raising capability in the first mode. A time integration value is obtained by integrating an absolute value of a difference between an air-fuel ratio of the rich combustion cylinder and an air-fuel ratio of the lean combustion cylinder over a predetermined period. In an enlarging process, a time integration value of the second mode is set to be greater than a time integration value of the first mode.

A method for positive crankcase ventilation diagnosis in an engine system with an engine, an intake duct connected to the engine, a PCV line connecting a crankcase of the engine with the intake duct and a sensor for determining an actual PCV pressure (p.sub.act) in the PCV line. The method comprises the steps of: performing a diagnosis measurement by repeatedly determining at least one input parameter (p.sub.int, n.sub.e, p.sub.atm, Q), which is linked to the operation of the engine system, and the actual PCV pressure (p.sub.act), to obtain a plurality of data samples for a plurality of sample times (t.sub.s); using a prediction model (M) to determine a predicted PCV pressure (p.sub.pre); and comparing the actual PCV pressure (p.sub.act) with the predicted PCV pressure (p.sub.pre) to diagnose the PCV line, wherein a diagnosis of the PCV line is based on a model error (p.sub.err).

A controller for an internal combustion engine includes a processing circuit that performs a dither control process on condition that a temperature increase request of a catalyst is made. The processing circuit operates fuel injection valves so that during the dither control process, one or more cylinders are lean combustion cylinders in a first period and another one or more cylinders are rich combustion cylinders and so that the average value of an exhaust gas-fuel ratio is a target air-fuel ratio in a second period including the first period. The dither control process is restricted in a manner that, on condition that the rich process is performed, the degree of richening of the richest exhaust gas-fuel ratio of exhaust gas-fuel ratios in the cylinders is reduced.

When a request for temperature increase of a three-way catalyst is made, a CPU executes dither control in which one of a plurality of cylinders is set as a rich combustion cylinder with a richer air-fuel ratio than a stoichiometric air-fuel ratio and the remaining cylinders are set as lean combustion cylinders with a leaner air-fuel ratio than the stoichiometric air-fuel ratio. When not executing the dither control, the CPU learns a rich learning value that is a learning value of a degree of a rich imbalance based on an upstream-side air-fuel ratio. When the rich learning value is greater than or equal to a predetermined value, the CPU prohibits the dither control.