Air-fuel ratio control apparatus and method of internal combustion engine

• US 6,250,074 B1
• Filed: 05/01/2000
• Issued: 06/26/2001
• Est. Priority Date: 05/10/1999
• Status: Expired due to Term

• Current Assignee: Toyota Jidosha Kabushiki Kaisha (Toyota Motor Corporation)
• Original Assignee: Toyota Jidosha Kabushiki Kaisha (Toyota Motor Corporation)
• Inventors: Tanaka, Hiroshi, Suzuki, Naoto
• Primary Examiner(s): Denion, Thomas
• Assistant Examiner(s): TRAN, BINH Q
• Application Number:
  US09/561,799
• Time in Patent Office: 421 Days
• Field of Search: 602/85, 602/86, 602/76, 602/95, 602/97, 603/00, 602/74, 603/01, 123/443, 123/691
• US Class Current: 60/285
• CPC Class Codes: F01N 13/009 having two or more separate purifying devices arranged in series
• CPC Class Codes: F01N 13/011 having two or more purifying devices arranged in parallel
• CPC Class Codes: F01N 2570/04 Sulfur or sulfur oxides
• CPC Class Codes: F01N 3/0842 Nitrogen oxides
• CPC Class Codes: F02D 41/028 Desulfurisation of NOx traps or adsorbent
• CPC Class Codes: F02D 41/1439 characterised by the position of the sensor
• CPC Class Codes: F02D 41/1443 with one sensor per cylinder or group of cylinders

Abstract

First and second cylinder groups are connected to a NOx absorbent via a confluent exhaust pipe. The target values of the air-fuel ratio of exhaust gas from the first cylinder group and the second cylinder group are set to a relatively rich value and a relatively lean value, respectively. The target values of the air-fuel ratio of exhaust gas from the first and second cylinder groups are set so that the influent exhaust gas average air-fuel ratio entering the NOx absorbent becomes equal to a relatively slightly rich value. HC in exhaust gas from the first cylinder group and oxygen in exhaust gas from the second cylinder group react in the NOx absorbent to heat the NOx absorbent and cause the NOx absorbent to release SOx. Based on an output signal of an air-fuel ratio sensor disposed downstream of the NOx absorbent, the amounts of fuel to be injected to the first and second cylinder groups are controlled so that the influent exhaust gas average air-fuel ratio becomes equal to its target value.

Claims

1. An air-fuel ratio control apparatus for an internal combustion engine including a plurality of cylinders divided into a first cylinder group and a second cylinder group, the first and second cylinder groups being connected to a common confluent exhaust passage with an emission control catalyst device disposed therein, the air-fuel ratio control apparatus comprising:

first means for setting an influent target value of an average influent air-fuel ratio of exhaust gas flowing into the emission control catalyst device;

second means for setting a first group target value of a first group air-fuel ratio of exhaust gas from the first cylinder group to a value richer than the influent target value, and setting a second group target value of a second group air-fuel ratio of exhaust gas from the second cylinder group to a value leaner than the influent target value, and the second means setting the first group target value and the second group target value so that, when the first group air-fuel ratio and the second group air-fuel ratio are equal to the first group target value and the second group target value, respectivly, the average influent air-fuel ratio becomes equal to the influent target value;

third means for calculating a first amount of fuel to be injected to cylinders of the first cylinder group and a second amount of fuel to be injected to the cylinders of the second cylinder group so that the first group air-fuel ratio and the second group air-fuel ratio become equal to the first group target value and the second group target value, respectively;

an air-fuel ratio sensor disposed in a portion of the confluent exhaust passage extending downstream of the emission control catalyst device; and

fourth means for correcting, based on an air-fuel ratio detected by the air-fuel ratio sensor, the first amount of fuel and the second amount of fuel so that the average influent air-fuel ratio becomes equal to the influent target value.

2. An air-fuel ratio control apparatus of an internal combustion engine according to claim 1, wherein the emission control catalyst device is formed by a NOx absorbent that absorbs NOx when the air-fuel ratio of exhaust gas flowing into the emission control catalyst device is leaner than a theoretical air-fuel ratio, and releases absorbed NOx when an oxygen concentration in exhaust gas flowing into the emission control catalyst device decreases, and wherein the influent target value is set to a value slightly richer than the theoretical air-fuel ratio.

3. An air-fuel ratio control apparatus of an internal combustion engine according to claim 2, further comprising:

fifth means for setting the first group target value and the second group target value to the theoretical air-fuel ratio; and

sixth means for correcting, based on the air-fuel ratio detected by the air-fuel ratio sensor, the first amount of fuel and the second amount of through a feedback correction operation so that the first group air-fuel ratio and the second group air-fuel ratio become equal to the theoretical air-fuel ratio.

4. An air-fuel ratio control apparatus of an internal combustion engine according to claim 3, wherein the fourth means corrects the first amount of and the second amount of fuel through a feedback correction operation, and wherein an absolute value of a feedback gain of the fourth means is smaller than an absolute value of a feedback gain of the sixth means.

5. An air-fuel ratio control apparatus of an internal combustion engine according to claim 3, wherein the air-fuel ratio sensor detects whether the air-fuel ratio is richer or leaner than a predetermined reference air-fuel ratio, and wherein when a detected exhaust gas air-fuel ratio is leaner than the predetermined reference air-fuel ratio, the first amount of fuel and the second amount of fuel are subjected to an increasing correction, and when the detected exhaust gas air-fuel ratio is richer than the predetermined reference air-fuel ratio, the first amount of fuel and the second amount of fuel are subjected to a decreasing correction.

6. An air-fuel ratio control apparatus of an internal combustion engine according to claim 2, wherein the air-fuel ratio sensor detects whether the air-fuel ratio of exhaust gas is richer or leaner than a predetermined reference air-fuel ratio, and wherein when a detected exhaust gas air-fuel ratio is leaner than the predetermined reference air-fuel ratio, the first and second amounts of fuel are subjected to an increasing correction, and when the detected exhaust gas air-fuel ratio is richer than the predetermined reference air-fuel ratio, the increasing correction of the first and second amounts of fuel is prevented.

7. An air-fuel ratio control apparatus of an internal combustion engine according to claim 6, wherein the increasing correction of the first and second amounts of fuel is started after a predetermined first set time elapses following a switch of the detected exhaust gas air-fuel ratio from a richer side to a leaner side of the predetermined reference air-fuel ratio.

8. An air-fuel ratio control apparatus of an internal combustion engine according to claim 7, wherein the increasing correction of the first and second amounts of fuel is prevented after a predetermined second set time longer than the first set time elapses following a switch of the detected exhaust gas air-fuel ratio from the leaner side to the richer side of the predetermined reference air-fuel ratio.

9. An air-fuel ratio control apparatus of an internal combustion engine according to claim 6, wherein a correcting operation of the first and second amounts of fuel is stopped when the detected exhaust gas air-fuel ratio is on the richer side of the predetermined reference air-fuel ratio.

10. An air-fuel ratio control method for an internal combustion engine in which a plurality of cylinders are divided into first and second cylinder groups connected to a common confluent exhaust passage with an emission control catalyst device disposed therein, the control method comprising:

setting an influent target value of an average influent air-fuel ratio exhaust gas flowing into the emission control catalyst device;

setting a first group target value of a first group air-fuel ratio of exhaust gas from the first cylinder group to a value richer than the influent target value, and setting a second group target value of a second group air-fuel ratio of exhaust gas from the second cylinder group to a value leaner than the influent target value, and setting the first group and second group target so that when the first group and second group air-fuel ratios are equal to the first group and second group target values, respectivly, the average influent air-fuel ratio becomes equal to the influent target value;

calculating a first group amount of fuel to be injected to the first cylinder group and a second group amount of fuel to be injected to the second cylinder group so that the first group air-fuel ratio and the second group air-fuel ratio become equal to the first group and second group target values, respectively;

correcting the first group and second group amounts of fuel so that the average influent air-fuel ratio becomes equal to the influent target value, based on an air-fuel ratio detected by an air-fuel ratio sensor disposed in a portion of the confluent exhaust passage downstream of the emission control catalyst device.

11. An air-fuel ratio control method of an internal combustion engine according to claim 10,

wherein the emission control catalyst device is formed by a NOx absorbent that absorbs NOx when the air-fuel ratio of exhaust gas flowing into the emission control catalyst device is leaner than a theoretical air-fuel ratio, and releases absorbed NOx when an oxygen concentration in exhaust gas flowing into the emission control catalyst device decreases,

wherein the influent target value is set to a value slightly richer than the theoretical air-fuel ratio.

12. An air-fuel ratio control method of an internal combustion engine according to claim 11, further comprising:

setting the first group target value and the second group target value to the theoretical air-fuel ratio; and

correcting, based on the air-fuel ratio detected by the air-fuel ratio sensor, the first amount of fuel and the second amount of through a first feedback correction operation so that the first group air-fuel ratio and the second group air-fuel ratio become equal to the theoretical air-fuel ratio.

13. An air-fuel ratio control method of an internal combustion engine according to claim 12, wherein the correction of the first group and second group amounts of fuel that the average influent air-fuel ratio becomes equal to the influent target value is performed through a second feedback correction operation, and wherein an absolute value of a feedback gain of the first feedback correction operation is smaller than an absolute value of a feedback gain of the second feedback correction operation.

14. An air-fuel ratio control method of an internal combustion engine according to claim 12, wherein the air-fuel ratio sensor detects whether the air-fuel ratio is richer or leaner than a predetermined reference air-fuel ratio, and wherein when a detected exhaust gas air-fuel ratio is leaner than the predetermined reference air-fuel ratio, the first amount of fuel and the second amount of fuel are subjected to an increasing correction, and when the detected exhaust gas air-fuel ratio is richer than the predetermined reference air-fuel ratio, the first amount of fuel and the second amount of fuel are subjected to a decreasing correction.

15. An air-fuel ratio control method of an internal combustion engine according to claim 11, wherein the air-fuel ratio sensor detects whether the air-fuel ratio of exhaust gas is richer or leaner than a predetermined reference air-fuel ratio, and wherein when a detected exhaust gas air-fuel ratio is leaner than the predetermined reference air-fuel ratio, the first and second amounts of fuel are subjected to an increasing correction, and when the detected exhaust gas air-fuel ratio is richer than the predetermined reference air-fuel ratio, the increasing correction of the first and second amounts of fuel is prevented.

16. An air-fuel ratio control method of an internal combustion engine according to claim 15, wherein the increasing correction of the first and second amounts of fuel is started after a predetermined first set time elapses following a switch of the detected exhaust gas air-fuel ratio from a richer side to a leaner side of the predetermined reference air-fuel ratio.

17. An air-fuel ratio control method of an internal combustion engine according to claim 16, wherein the increasing correction of the first and second amounts of fuel is prevented after a predetermined second set time longer than the first set time elapses following a switch of the detected exhaust gas air-fuel ratio from the leaner side to the richer side of the predetermined reference air-fuel ratio.

18. An air-fuel ratio control apparatus of an internal combustion engine according to claim 15, wherein a correcting operation of the first and second amounts of fuel is stopped when the detected exhaust gas air-fuel ratio is on the richer side of the predetermined reference air-fuel ratio.

19. An air-fuel ratio control apparatus for an internal combustion engine including a plurality of cylinders divided into a first cylinder group and a second cylinder group, the first and second cylinder groups being connected to a common confluent exhaust passage with an emission control catalyst device disposed therein, the air-fuel ratio control apparatus comprising:

an air-fuel ratio sensor disposed in a portion of the confluent exhaust passage extending downstream of the emission control catalyst device; and

a control system that sets an influent target value of an average influent air-fuel ratio of exhaust gas flowing into the emission control catalyst device,

sets a first group target value of a first group air-fuel ratio of exhaust gas from the first cylinder group to a value richer than the influent target value, and sets a second group target value of a second group air-fuel ratio of exhaust gas from the second cylinder group to a value leaner than the influent target value, and the second means setting the first group target value and the second group target value so that, when the first group air-fuel ratio and the second group air-fuel ratio are equal to the first group target value and the second group target value, respectivly, the average influent air-fuel ratio becomes equal to the influent target value,

calculates a first amount of fuel to be injected to cylinders of the first cylinder group and a second amount of fuel to be injected to the cylinders of the second cylinder group so that the first group air-fuel ratio and the second group air-fuel ratio become equal to the first group target value and the second group target value, respectively, and

corrects, based on an air-fuel ratio detected by the air-fuel ratio sensor, the first amount of fuel and the second amount of fuel so that the average influent air-fuel ratio becomes equal to the influent target value.

20. An air-fuel ratio control apparatus of an internal combustion engine according to claim 19, wherein the emission control catalyst device is formed by a NOx absorbent that absorbs NOx when the air-fuel ratio of exhaust gas flowing into the emission control catalyst device is leaner than a theoretical air-fuel ratio, and releases absorbed NOx when an oxygen concentration in exhaust gas flowing into the emission control catalyst device decreases, and wherein the influent target value is set to a value slightly richer than the theoretical air-fuel ratio.