| 摘要 |
An emission control system for an engine includes a catalyst and an exhaust-gas sensor provided downstream of the catalyst in a flow direction of exhaust gas. The exhaust-gas sensor includes a sensor element that includes a pair of electrodes and a solid electrolyte body located between the electrodes. The emission control system further includes a constant current supply portion that changes an output characteristic of the exhaust-gas sensor by applying a constant current between the electrodes, a catalytic-state determination portion which determines a rich/lean state of the catalyst, a rich direction control portion which performs and terminates a rich direction control depending on the rich/lean state of the catalyst, a lean direction control portion which performs a lean direction control after the rich direction control, and a characteristic control portion which performs a lean responsiveness control at least during the lean direction control.
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