Claims
- 1. An exhaust gas purification system for an internal combustion engine comprising:
- an internal combustion engine capable of fuel combustion at lean air-fuel ratios and having an exhaust manifold and an exhaust conduit connected to the exhaust manifold, wherein the engine operates at one of a stoichiometric air-fuel ratio and a rich air-fuel ratio while it is being warmed-up and wherein the engine operates at a lean air-fuel ratio after it has been warmed-up;
- a dual passage portion provided in the exhaust conduit and located downstream of and close to the exhaust manifold of the engine, the dual passage portion including a first passage and a second passage which are connected in parallel to each other;
- a first NO.sub.x reducing catalyst installed in the first passage and constructed of zeolite carrying Copper to reduce nitrogen oxides included in exhaust gas from the engine under oxidizing gas conditions and in the presence of hydrocarbons;
- a second catalyst installed in the first passage downstream of the first catalyst and constructed of one of a three-way catalyst and an oxidizing catalyst;
- a third catalyst installed in the second passage and constructed of one of a three-way catalyst and an oxidizing catalyst, wherein said third catalyst is located within the second passage such that the temperature of the exhaust gas passing through the second passage is not affected by prior catalytic contact;
- a flow switching valve for switching flow of exhaust gas from the engine between the first passage and the second passage; and
- valve control means for switching the flow switching valve so as to cause exhaust gas to flow through the second passage while the engine is being warmed-up and while the engine is operating at one of a stoichiometric air-fuel ratio and a rich air-fuel ratio and to cause exhaust gas to flow through the first passage after the engine has been warmed-up and when the engine is operating at a lean air-fuel ratio.
- 2. A system according to claim 1, wherein the first passage and the second passage of the dual passage portion are spaced apart at longitudinally intermediate portions of the first passage and the second passage.
- 3. A system according to claim 1, wherein the second passage surrounds the first passage so that the third catalyst surrounds the first catalyst and the second catalyst.
- 4. A system according to claim 1, wherein the first passage surrounds the second passage so that the first catalyst and the second catalyst surround the third catalyst.
- 5. A system according to claim 1 and further comprising a fourth, three-way, catalyst installed downstream of the dual passage portion.
- 6. A system according to claim 1 and further comprising an exhaust gas recirculation system and an EGR control routine, wherein EGR is set to "ON" at high exhaust gas temperature and at medium engine loads.
- 7. A system according to claim 6 and further comprising a fuel injection control routine, wherein a fuel injection amount modification factor KLEAN is selected to be larger when EGR is set at "ON" than when EGR is set at "OFF".
- 8. A system according to claim 7, wherein the valve control means includes a flow switching valve control routine wherein
- (a) when a current engine cooling water temperature is equal to or higher than a predetermined temperature and the fuel injection amount modification factor is smaller than 1.0, the flow switching valve is switched to cause exhaust gas to flow through the first catalyst and the second catalyst, and
- (b) when the current engine cooling water temperature is lower than the predetermined temperature and when the current engine cooling water temperature is equal to or higher than the predetermined temperature and the fuel injection amount modification factor is equal to or larger than 1.0, the flow switching valve is switched to cause exhaust gas to flow through the third catalyst.
Priority Claims (1)
Number |
Date |
Country |
Kind |
2-135233 |
May 1990 |
JPX |
|
Parent Case Info
This application is a continuation of application Ser. No. 07/709,000, filed on May 25, 1991, now U.S. Pat. No. 5,233,830.
US Referenced Citations (1)
Number |
Name |
Date |
Kind |
4297328 |
Ritscher |
Oct 1981 |
|
Foreign Referenced Citations (4)
Number |
Date |
Country |
2259946 |
Jun 1974 |
DEX |
139145 |
May 1989 |
JPX |
1334797 |
Oct 1973 |
GBX |
1347542 |
Feb 1974 |
GBX |
Continuations (1)
|
Number |
Date |
Country |
Parent |
709000 |
May 1991 |
|