| 摘要 |
PURPOSE:To prevent after-burning by opening and closing a solenoid valve for supplying secondary air to the upper stream of a ternary catalyst at the frequency of 1-2Hz, periodically varying an air-fuel ratio within the range of + or -0.2- + or -1.0, and fully opening the solenoid valve after temporarily fully closing said valve at engine deceleration. CONSTITUTION:A secondary air supplying hole 60 is provided on an exhaust manifold 3, and secondary air is supplied to the upper stream of a ternary catalyst 5 via a control valve 50 and a check valve 59. Negative pressure is introduced into the negative pressure chamber 53 of the control valve 50 via a solenoid valve 51, and this solenoid valve 51 is opened and closed at the frequency of 1-2Hz by means of a solenoid driving circuit 70, and an air-fuel ratio is periodically varied within the range of + or -0.2-+ or -0.1 via the control valve 50 taking a theoretical air-fuel ratio as a center. An idle switch 71 and a number-of- revolutions switch 72 are connected to the driving circuit 70, and the solenoid valve 51 is fully opened after temporarily fully closing said valve at deceleration, so as to allow after-buring to be prevented as well as an exhaust gas purifying characteristic to be improved. |
