| 摘要 |
<p>PURPOSE:To effectively purify NOx and HC without any interference with air-fuel ratio control by switching and controlling the condition of air supply to a catalyst portion according to the operating condition of an engine and the exhaust gas temperature. CONSTITUTION:A control unit 70 judges the operating condition of an engine according to an opening degree of a throttle valve 42 from an opening sensor 16 and the engine speed from an engine speed sensor 62. During high load operating condition of the engine, a driving signal is sent to a solenoid valve 58 of a switching valve unit 46 to stop the supply of air to a three way catalytic converter 20. During low load operating condition, a driving signal is selectively sent to solenoid valves 59, 60 according to an operating region and the exhaust gas temperature from an exhaust gas temperature from an exhaust gas temperature sensor 28 to supply air to the three way catalytic converter 20 through one of air supply branch passages 51 - 53. Thus, both NOx and HC contained in the exhaust gas can be properly purified without any interference with air-fuel ratio control in the transient state.</p> |
