| 摘要 |
<P>PROBLEM TO BE SOLVED: To quickly activate NO<SB>X</SB>catalyst or keep the activity of the NO<SB>X</SB>catalyst high. <P>SOLUTION: The NO<SB>X</SB>catalyst is arranged in an engine exhaust passage, and a reducing agent is temporarily supplied to the NO<SB>X</SB>catalyst in order to reduce NO<SB>X</SB>in the NO<SB>X</SB>catalyst to reduce the quantity of NO<SB>X</SB>stored in the NO<SB>X</SB>catalyst. This device has a selector valve 61 for controlling the quantity of exhaust gas carried into the NO<SB>X</SB>catalyst by controlling the quantity of exhaust gas bypassing the NO<SB>X</SB>catalyst. When the temperature of the NO<SB>X</SB>catalyst is low, the reducing agent is supplied into the NO<SB>X</SB>catalyst (arrow RF) when the selector valve is held in a normal flow position, and the quantity of exhaust gas GE carried into the NO<SB>X</SB>catalyst is thus high. When the temperature of NO<SB>X</SB>catalyst is high, the reducing agent is supplied into the NO<SB>X</SB>catalyst (arrow RT) in the transition of switching the selector valve from the normal flow position to a counter flow position or reversely, or when the quantity of exhaust gas carried into the NO<SB>X</SB>catalyst is reduced. <P>COPYRIGHT: (C)2004,JPO |
