Patent ID: 7247190

Claim:
An exhaust gas cleaning apparatus for an engine comprising: a fuel delivery device configured to deliver a fuel delivery quantity of fuel to the engine to produce an excess air ratio that is lean during normal operation of the engine; an exhaust gas cleaning device arranged in an exhaust system and configured to clean exhaust gas during a lean operation; and a control unit configured to control the fuel delivery device, the control unit including a regeneration timing determining section configured to determine a regeneration operation timing to regenerate the exhaust gas cleaning device; a regeneration control section configured to adjust the excess air ratio toward a rich target value to regenerate the exhaust gas cleaning device by controlling an intake air throttle valve in an intake passage of the engine; a feedback control section configured to feedback-control the fuel delivery quantity such that the excess air ratio is substantially maintained at the rich target value during regeneration; and a feedback control restricting section configured to restrict the feedback control during regeneration until a difference between the rich target value and an actual excess air ratio is less than a prescribed value, the regeneration control section being further configured to reduce an opening degree of the intake air throttle valve to a prescribed opening degree before the difference between the rich target value and the actual excess air ratio is less than the prescribed value, and maintain the fuel delivery quantity during regeneration before the difference between the rich target value and the actual excess air ratio is less than the prescribed value to a fuel delivery quantity being delivered before the regeneration starts.