A controller for an internal combustion engine is configured to execute a dither control process and an exhaust gas recirculation (EGR) control process. The dither control process includes, when a request to increase a temperature of a catalyst is made, operating the fuel injection valves corresponding to respective cylinders to control the air-fuel ratio in some of the cylinders to become lean and control the air-fuel ratio in other cylinders to become rich. The EGR control process includes operating an adjustment actuator to control an EGR rate. The EGR control process includes operating the adjustment actuator such that the EGR rate is lower when the dither control process is being executed than when the dither control process is not being executed.

A control apparatus for an internal combustion engine is provided. The control apparatus is equipped with an electronic control unit. A CPU with which this electronic control unit is equipped performs dither control for setting a first cylinder as a rich-burn cylinder whose air-fuel ratio is richer than a theoretical air-fuel ratio and setting each of second to fourth cylinders as a lean-burn cylinder whose air-fuel ratio is leaner than the theoretical air-fuel ratio, when a request to raise the temperature of a three-way catalyst is made. Then, the CPU reduces the degree of richness of the rich-burn cylinder and the degree of leanness of each of the lean-burn cylinders while continuing dither control, on the condition that fluctuations at a level equal to or higher than a predetermined value are caused in time-series data on the rotational speed resulting from the combustion in each of the cylinders.

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.

This disclosure includes engines that are capable of controlling an air-fuel ratio responsive to rapid changes in the calorific value of a fuel gas. Some engines include an A/F valve (22), a solenoid valve (21), and a control unit (10) configured to close the A/F valve when an average opening degree of the solenoid valve is lower than a preset target opening degree, and open the A/F valve when the average opening degree is equal to or higher than the target opening degree. In some engines, when the opening degree of the solenoid valve has been an upper limit opening degree or a lower limit opening degree of the solenoid valve over a predetermined number of times, the control unit is configured to compare with the upper or lower limit opening degree, in lieu of the average opening degree, against the target opening degree to open or close the A/F valve.

The exhaust purification system comprises an exhaust purification catalyst, downstream side air-fuel ratio sensor, and control device. The control device performs average air-fuel ratio control which alternately sets a target average air-fuel ratio between a rich air-fuel ratio and a lean air-fuel ratio and inter-cylinder air-fuel ratio control which controls the target air-fuel ratios of the cylinders so that the target air-fuel ratio becomes the rich air-fuel ratio at least at one cylinder among the plurality of cylinders even if the target average air-fuel ratio is set to the lean air-fuel ratio. The control device uses a cumulative value of a first oxygen amount from when switching the target average air-fuel ratio to the lean air-fuel ratio to when again switching it to the rich air-fuel ratio and a cumulative value of a second oxygen amount from when switching the target average air-fuel ratio to the rich air-fuel ratio to when again switching it to the lean air-fuel ratio as the basis for correcting a parameter relating to the air-fuel ratio so that the difference of these becomes smaller as learning control.

An abnormality diagnosis device is for an exhaust gas sensor that detects an air-fuel ratio, or a rich or lean state of exhaust gas from an internal combustion engine and that includes a sensor element having a catalyst layer. The device includes an abnormality diagnosis unit that makes a sensor abnormality diagnosis whereby to change the air-fuel ratio alternately between a rich side and a lean side and to determine whether the exhaust gas sensor is abnormal or not based on response characteristics of the exhaust gas sensor in response to the change of the air-fuel ratio. When making the sensor abnormality diagnosis, the abnormality diagnosis unit calculates the response characteristics of the exhaust gas sensor with exclusion of a sensor output plateau region, which is a region in which an output of the exhaust gas sensor is stagnant due to the catalyst layer.

A hybrid vehicle includes an engine that has a particulate matter filter, a motor, and an electronic control unit. The electronic control unit is configured to control the engine and the motor such that an intermittent operation of the engine is permitted and the hybrid vehicle travels with required power when a vehicle speed is lower than a first predetermined vehicle speed. The electronic control unit is configured to inhibit the intermittent operation of the engine when a deposition amount of particulate matters is equal to or greater than a first deposition amount and a state in which the vehicle speed is equal to or higher than a second predetermined vehicle speed and is lower than the first predetermined vehicle speed is continued for a first predetermined time.

An exhaust purification system comprises an exhaust purification catalyst, a downstream side air-fuel ratio sensor and a control device. The control device makes the air-fuel ratio of the exhaust gas change to an air-fuel ratio at a rich side from the prior air-fuel ratio as air-fuel ratio rich increasing control when the air-fuel ratio of the exhaust gas is made a rich air-fuel ratio and the output air-fuel ratio of the downstream side air-fuel ratio sensor is maintained at a lean judged air-fuel ratio or more, and judges that the downstream side air-fuel ratio sensor suffers from an abnormality, when, due to the air-fuel ratio rich increasing control, the air-fuel ratio of the exhaust gas is made to change to the rich side air-fuel ratio and the output air-fuel ratio of the downstream side air-fuel ratio sensor changes to the lean side.

A system includes an internal combustion ignition engine with an exhaust gas flow, a particulate filter in the exhaust gas flow, a NO.sub.x reduction catalyst in the exhaust gas flow downstream of the particulate filter, a first oxygen sensor coupled to the exhaust gas flow downstream of the NO.sub.x reduction catalyst, and a second oxygen sensor coupled to the exhaust gas flow between the particulate filter and the NO.sub.x reduction catalyst. A controller includes an exhaust conditions module that interprets a first oxygen signal from the first oxygen sensor and a second oxygen signal from the second oxygen sensor and a combustion control module that commands a high engine-out air-fuel ratio when the first oxygen signal indicates a low oxygen content and commands a low engine-out air-fuel ratio when the first oxygen signal indicates a high oxygen content.

In the dither current power supply control method, in order to prevent occurrence of a difference between the target average current and the detected average current, which is caused when a medium current (I0) between a dither large current (I2) and a dither small current (I1) and a waveform average (Ia) of the dither current are different from each other depending on a response time difference (ab) between a rise time (b) and a fall time (a) of the dither current, negative feedback control is carried out by using a command medium current corresponding to the target average current corrected by a correction parameter based on experimentally measured data, thereby suppressing occurrence of a transient fluctuation error by the negative feedback control, so that a highly precise and stable load current is acquired.