A system for detecting and controlling air-fuel ratio imbalance conditions between cylinders of an internal combustion engine having a plurality of cylinders is disclosed.

A method in a combustion engine 100 for determining a desired fuel setting λ+. The method comprises configuring a fuel setting λ, determining a combustion engine parameter β in dependence of the configured fuel setting λ, wherein the combustion engine parameter is related to the fuel setting by a convex function relationship, and updating the fuel setting λ towards the desired fuel setting λ+, based on the determined combustion engine parameter β and on the convex function relationship between the fuel setting λ and the combustion engine parameter β.

A method in a combustion engine 100 for determining a desired fuel setting λ+. The method comprises configuring a fuel setting λ, determining a combustion engine parameter β in dependence of the configured fuel setting λ, wherein the combustion engine parameter is related to the fuel setting by a convex function relationship, and updating the fuel setting λ towards the desired fuel setting λ+, based on the determined combustion engine parameter β and on the convex function relationship between the fuel setting λ and the combustion engine parameter β.

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.

A system for detecting and controlling air-fuel ratio imbalance conditions between cylinders of an internal combustion engine having a plurality of cylinders is disclosed.

A system for detecting and controlling air-fuel ratio imbalance conditions between cylinders of an internal combustion engine having a plurality of cylinders is disclosed.

When a purge valve opens, a CPU calculates a purge concentration learning value based on an air-fuel ratio detected by an air-fuel ratio sensor. Additionally, under the condition that a temperature increase request of a three-way catalyst is generated, the CPU performs dither control that sets one of a plurality of cylinders as a rich combustion cylinder, which is richer than a theoretical air-fuel ratio, and the remaining cylinders as lean combustion cylinders, which are leaner than the theoretical air-fuel ratio. When the dither control is performed, the CPU forbids the update of the purge concentration learning value.

A first limit requesting process limits a dither control process of fuel injection valves in such a manner that the absolute value of the difference between the air-fuel ratios of the cylinders becomes smaller when the degree of variation of the injection amounts of the fuel injection valves provided for respective cylinders is great than when the degree of variation is small. A second limit requesting process limits the dither control process in such a manner that the absolute value is smaller when the torque fluctuation amount of the internal combustion engine is great than when the torque fluctuation amount is small. The limiting process limits the dither control process in accordance with one of requests generated by the first limit requesting process and the second limit requesting process that causes the absolute value to be smaller than the other.

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.

A fuel injection controller updates an air-fuel ratio learning value such that the amount of correction of a fuel injection amount according to an air-fuel ratio feedback correction value approaches zero. Further, the fuel injection controller makes an update rate of the air-fuel ratio learning value lower when the variation among respective-cylinder correction values, which are set for the respective cylinders in order to differentiate air-fuel ratios of a plurality of cylinders, is great than when the variation among the respective-cylinder correction values of the cylinders is small.