| 摘要 |
<p>PURPOSE: To restrain deterioration of a catalyst by providing a by-pass passage to by-pass a first catalyst converter, interposing a second catalyst converter in the downstream of this by-pass passage and opening and closing a by-pass valve to selectively open the first catalyst converter and the by-pass passage by exhaust temperature deviation. CONSTITUTION: A first catalyst converter 1 and a second catalyst converter 6 are set in parallel in an exhaust passage 9 of an engine for an automobile. Additionally, a by-pass passage 8 to by-pass the first catalyst converter 1 is arranged in the exhaust passage 9, and a by-pass valve 10 is interposed at a branching part of both of the passage 9 and the passage 8. The by-pass valve 10 is controlled so as to open the first catalyst converter 1 under a driving condition that exhaust temperature is lower than a standard value and to open the by-pass passage 28 under a condition that exhaust temperature is higher than the standard value. Additionally, at this time, degrees of deterioration of the catalyst converters 1, 2 are detected from outputs of oxygen sensors 11, 12 provided on the upstream and downstream sides of the first catalyst converter, and the aforementioned standard value is corrected low as the degree of deterioration rises.</p> |
