Claims
- 1. A control system for an internal combustion engine, comprising:air-fuel ratio control means for normally controlling an air-fuel ratio of air-fuel mixture supplied to the internal combustion engine to a lean side with respect to a stoichiometric ratio for a lean mixture combustion, and temporarily controlling the air-fuel ratio to a rich side with respect to the stoichiometric air-fuel ratio; NOx catalyst means for occluding NOx in an exhaust gas exhausted at the time of the lean mixture combustion and releasing the occluded NOx from the NOx catalyst by temporarily controlling the air-fuel ratio to the rich side for a rich mixture combustion; catalyst state detecting means for detecting an NOx purification state of the NOx catalyst; rich time updating means for updating a rich time for the rich mixture combustion so as to be shortened in a predetermined time period; and update cancelling means for canceling an update of the rich time so as to be shortened when the rich time at that time is discriminated as a limit value from the detected NOx purification state of the catalyst.
- 2. The control system as in claim 1, wherein:the catalyst state detecting means comprises a gas concentration sensor provided on a downstream side of the NOx catalyst, and discriminating means for discriminating a degree of NOx purification of the NOx catalyst on the basis of an output value of the sensor.
- 3. The control system as in claim 1, further comprising:storing means for storing the updated rich time for every operating zone of the internal combustion engine.
Priority Claims (2)
Number |
Date |
Country |
Kind |
9-279133 |
Oct 1997 |
JP |
|
10-74183 |
Mar 1998 |
JP |
|
RELATED APPLICATION
This application is a division of our prior application Ser. No. 09/166,937 filed Oct. 6, 1998 now U.S. Pat. No. 6,148,612.
US Referenced Citations (17)
Foreign Referenced Citations (4)
Number |
Date |
Country |
19607151 |
Jul 1997 |
DE |
0733787 |
Sep 1996 |
EP |
8-261041 |
Oct 1996 |
JP |
8-260948 |
Oct 1996 |
JP |
Non-Patent Literature Citations (3)
Entry |
Patent Abstracts of Japan, vol. 1998, No. 14, Dec. 1998 & JP 10252524 (Fuji Heavy Ind Ltd), Sep. 1998. |
Patent Abstracts of Japan, vol. 1999, No. 01, Jan. 1999 & JP 10266884 (Mitsubishi Motors Corp), Oct. 1998. |
Patent Abstracts of Japan, vol. 1997, No. 03, Mar. 1997 & JP 08296471 (Nissan Motor Co. Ltd), Nov. 1996. |