| 摘要 |
PURPOSE:To cause an emission control device to exhibit its optimum emission control performance in proportion to air-fuel ratio which is varied over a wide range by treating exhaust gas with oxidizing catalysts during lean combustion, and treating the exhaust gas with three-way catalysts during combustion at theoritical air-fuel ratio. CONSTITUTION:Exhaust pipes are provided with a first catalytic converter 84 including three-way catalysts and a second catalytic converter 86 including oxidizing catalysts and a change valve 92 for changing catalytic converters is provided at the junction portion of exhaust pipes 88 and 90. A control circuit 72 determines whether or not air-fuel ratio is lean-controlled, and during lean control a solenoid valve 96 is turned off and a diaphragm 94a is driven and lowered to a continuous line and the change valve 92 introduces exhaust gas from the upper side into the second catalytic converter 86 as indicated by the arrow X. While lean control is not performed, the solenoid valve 96 is turned on and inlet pipe pressure is applied to the diaphragm 94a and the change valve 92 is driven and exhaust gas from the upper side is introduced into the first catalytic converter 84 including three-way catalysts as indicated by the arrow Y. |
