Exhaust gas cleaning apparatus and method thereof

An exhaust gas cleaning control method for an exhaust system including a main exhaust passage with a main catalytic converter disposed in the main exhaust passage, a bypass exhaust passage with a bypass catalytic converter disposed in the bypass exhaust passage, and a selector valve disposed between a branching point of the bypass exhaust passage and a merging point of the bypass exhaust passage on an upstream side of the main catalytic converter to selectively open and close the main exhaust passage to switch a pathway for the exhaust gas between the main exhaust passage and the bypass exhaust passage, the method comprising:

• detecting an operating condition of at least one of the internal combustion engine and the main catalytic converter;
• conducting exhaust gas from an internal combustion engine through one of the main exhaust passage and the bypass exhaust passage to the main catalytic;
• selectively controlling the selector valve to block or open the flow of the exhaust gas through the main exhaust passage to the main catalytic converter based on the operating condition that was detected;
• and
• controlling a combustion state of the internal combustion engine to a rich combustion state with a rich air fuel ratio while the controlling the selector valve to block the flow of the exhaust gas through the main exhaust passage, and then, afterwards, controlling the selector valve to direct the flow of the exhaust gas through the main exhaust passage such that residual air remaining in the main exhaust passage mixes with rich exhaust gas from the bypass exhaust passage.