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.

An engine comprising: a fuel injection device including a rack and an actuator, the rack being configured to regulate the amount of fuel injected to a combustion chamber, the actuator being configured to control the position of the rack; and a control device that controls fuel injection performed by the fuel injection device based on an instructed revolution number, and that performs a dither control on the actuator, wherein the control device has information of a revolution number variation region that is based on the relationship between a dither frequency in the dither control and an engine revolution number, and upon determining that the instructed revolution number is within the revolution number variation region, changes at least one of the dither frequency and the instructed revolution number. Thus, an engine capable of reducing a periodic variation in engine speed which may be caused by a dither control is provided.

A control device for an internal combustion engine includes an electronic control unit configured to perform dither control processing for controlling the fuel injection valve based on a requested injection amount such that a part of cylinders among a plurality of cylinders becomes a lean combustion cylinder and cylinders different from the part of cylinders among the cylinders become a rich combustion cylinder, and restriction processing for, in a case where the requested injection amount is equal to or greater than a first injection amount, making no restriction on the dither control processing, and in a case where the requested injection amount is within a second injection amount range of an injection amount smaller than the first injection amount, restricting the dither control processing to a side where a leaning degree of an air-fuel ratio of a cylinder having a leanest air-fuel ratio among the cylinders decreases.

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 gas engine is provided to control an air-fuel ratio in response to changes in composition of fuel gas. A gas engine 1 includes: an A/F valve 22; a solenoid valve 21; and a control unit 10 configured to perform perturbation using the solenoid valve 21 and set a relationship between an air-fuel ratio and respective opening degrees of the solenoid valve 21 and the A/F valve 22 under a specific engine operation condition using standard fuel gas. During an actual operation in a period in which the engine operation condition is deemed to be stable, when an opening-degree average value b of the solenoid valve 21 deviates from an opening-degree target value a of the solenoid valve 21 set in the control unit 10 under the above operation condition, the control unit 10 adjusts the opening degree of the A/F valve 22 so that the opening-degree average value b equals the opening-degree target value a.

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.

A controller for an internal combustion engine includes processing circuitry. The processing circuitry performs a dither control process and a multi-injection process. Multiple injections in the multi-injection process includes a first injection and a second injection performed at a timing retarded from the first injection. The dither control process includes at least one of a process performed on a cylinder changed to a lean combustion cylinder so that a reduction amount of fuel injected through the first injection is greater than a reduction amount of fuel injected through the second injection and a process performed on a cylinder changed to a rich combustion cylinder so that an increase amount of fuel injected through the first injection is greater than an increase amount of fuel injected through the second injection.

Methods and systems are provided for a single heat exchanger coupled to a main exhaust passage upstream of one or more exhaust catalysts or in between two exhaust catalysts for exhaust heat recovery and exhaust gas recirculation (EGR) cooling. In one example, in the pre-catalyst configuration of the heat exchanger, during exhaust heat recovery, a portion of exhaust may be routed via the heat exchanger while the remaining portion of exhaust may be routed directly to the exhaust catalysts, and fueling may be adjusted on a per-cylinder basis to maintain a target exhaust air-fuel-ratio at the exhaust catalysts.

Systems and methods for monitoring cylinder air/fuel imbalances are provided. In one example approach, a method comprises, identifying a cylinder with a potential air/fuel imbalance based on crankshaft accelerations generated by a series of rich, lean, and stoichiometric conditions in the cylinder while keeping the engine at stoichiometry.