| 摘要 |
PURPOSE:To improve an exhaust gas purification characteristic without yielding any fluctuation of combustion by opening and closing a solenoid valve for supplying secondary air to the upper stream of a ternary catalyst within the frequency range of 1-2Hz, and periodically varying an air-fuel ratio within the range of + or -0.2-+ or -1.0 taking a theoretical air-fuel ratio as a center. CONSTITUTION:A secondary air supplying hole 60 is provided on an exhaust manifold 3, and secondary air is supplyed 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 within the frequendy range of 1-2Hz by means of a solenoid driving circuit 70. The flow passage area of the secondary air supplying hole 60 set such that an air-fuel ratio upstream from the ternary catalyst is periodically varied within the range of + or -0.2-+ or -1.0 taking a theoretical air-fuel ratio as a center by opening and closing the control valve 50 caused by the periodically opening and closing of the solenoid valve 51, enabling the purification characteristic of the ternary catalyst to be improved by making use of the oxygen storing capability of the ternary catalyst. |
