Patent ID: 8286418

Claim:
An exhaust gas control apparatus for an internal combustion engine, which is applied to an internal combustion engine having a plurality of cylinders and a turbo charger, wherein the internal combustion engine is a spark ignition internal combustion engine, an exhaust passage of the internal combustion engine includes a first branch passage and a second branch passage, the first branch passage connects exhaust sides of cylinders of a first cylinder group composed of a first part of the plurality of cylinders and a turbine of the turbo charger, and is provided with an exhaust gas cleaning catalyst, and the second branch passage connects exhaust sides of cylinders of a second cylinder group composed of a second part of the plurality of cylinders and the turbine, the second branch passage being in communication with the first branch passage upstream of the exhaust gas cleaning catalyst, the exhaust gas control apparatus comprising: a valve switch device, which is an exhaust gas switching valve, disposed at a communication part through which the first branch passage and the second branch passage are in communication, the valve switch device being switchable between an introducing position, at which exhaust gas is introduced into the exhaust gas cleaning catalyst from cylinders of the second cylinder group, and a block position, at which introduction of the exhaust gas is blocked; an air-fuel ratio detecting device, which is an air-fuel ratio sensor, disposed between the communication part and the exhaust gas cleaning catalyst in the first branch passage, the air-fuel ratio detecting device detecting an air-fuel ratio of the exhaust gas; an electronic control unit (ECU) programmed to execute control of the exhaust gas control apparatus, the ECU including valve control programming instructions, which when executed, switch a position of the valve switch device based on an operating condition of the internal combustion engine, ignition timing control programming instructions, which when executed, retard an ignition timing for cylinders of the second cylinder group more than an ignition timing for cylinders of the first cylinder group when the valve switch device is switched to the block position, and feedback correcting programming instructions, which when executed, set an amount of feedback correction in accordance with a difference between the air-fuel ratio detected by the air-fuel ratio detecting device and a target air-fuel ratio, and correct an amount of fuel to be supplied to each cylinder, respectively, in a feedback manner in accordance with the amount of feedback correction, wherein in a case that the feedback correcting programming instructions are executed to correct the amount of fuel to be supplied to each cylinder in a feedback manner, the valve control programming instructions are executed to switch the valve switch device to the introducing position.