| 摘要 |
PURPOSE:To improve characteristics of exhaust gas of a 'lean-burn' engine by arranging and installing an oxygen concentration detecting means in an exhaust gas passage between a first catalytic converter and a second catalytic converter. CONSTITUTION:A lean NOx catalytic converter 14 and a three-way catalytic converter 16 are arranged and installed in an exhaust pipe 12 connected through an exhaust manifold 11 on the exhaust side of an engine 10, from the upstream in that order. In this case, an oxygen concentration detecting means 22 for detecting the oxygen concentration in exhaust gas, is installed to the exhaust pipe 12 between the lean NOx catalytic converter 14 and the three-way catalytic converter 16. The oxygen concentration in exhaust gas flowing into the three- way catalytic converter 16 immediately after the operation of the engine is switched from a lean air-fuel ratio operation to a stoichiometric air-fuel operation, can be thus exactly detected, and thereby the characteristics of exhaust gas can be improved. |
