Method and system for operating dual-exhaust engine

• US 6,467,259 B1
• Filed: 06/19/2001
• Issued: 10/22/2002
• Est. Priority Date: 06/19/2001
• Status: Expired due to Term

• Current Assignee: Ford Global Technologies, LLC (Ford Motor Company)
• Original Assignee: Ford Global Technologies, LLC (Ford Motor Company)
• Inventors: Farmer, David George, Surnilla, Gopichandra
• Primary Examiner(s): Denion, Thomas
• Assistant Examiner(s): TRAN, BINH Q
• Application Number:
  US09/884,563
• Time in Patent Office: 490 Days
• Field of Search: 602/74, 602/76, 602/85, 602/86, 602/95, 602/97, 123/443
• 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 13/0097 the purifying devices are arranged in a single housing
• CPC Class Codes: F01N 13/011 having two or more purifying devices arranged in parallel
• CPC Class Codes: F01N 3/0842 Nitrogen oxides
• CPC Class Codes: F02D 2041/389 for injecting directly into the cylinder
• CPC Class Codes: F02D 41/0082 per groups or banks F02D41/0087 takes precedence
• CPC Class Codes: F02D 41/0275 the exhaust gas treating apparatus being a NOx trap or adsorbent
• CPC Class Codes: F02D 41/1443 with one sensor per cylinder or group of cylinders

Abstract

An exhaust gas treatment system for an internal combustion engine includes a pair of upstream emission control devices which respectively receive the exhaust gas generated by a respective group of cylinders, and a single, shared downstream emission control device receiving catalyzed exhaust gas from each of the upstream emission control devices. After the downstream device stores a selected constituent gas generated when each cylinder group is operating “lean,” the downstream device is purged by operating the first cylinder group with a stoichiometric air-fuel mixture while operating the second cylinder group with a rich air-fuel mixture, such that the combined catalyzed exhaust gas flowing through the downstream device during the purge event has an air-fuel ratio slightly rich of stoichiometry. As a result, the invention improves overall vehicle fuel economy because only one of the upstream devices is purged of stored oxygen when purging the downstream device of previously-stored constituent gas.

Claims

1. A method of controlling the operation of an internal combustion engine having a plurality of cylinders respectively burning an air-fuel mixture to generate exhaust gas, each cylinder being associated with a selected one of exactly two cylinder groups, the exhaust gas from each cylinder group flowing through a respective one of a pair of upstream emission control devices and a common downstream emission control device, the downstream device storing a selected constituent gas of the exhaust gas when the exhaust gas flowing through the second device is lean of a stoichiometric air-fuel ratio and releasing previously-stored constituent gas when the exhaust gas flowing through the trap is rich of the stoichiometric air-fuel ratio, the method comprising:

supplying a first air-fuel mixture to each cylinder group, wherein the first air-fuel mixture is characterized by a first air-fuel ratio lean of the stoichiometric air-fuel ratio, whereby an amount of the selected constituent gas is stored in the trap;

determining a need for releasing previously stored constituent gas from the downstream device; and

in response to determining a need for releasing previously stored constituent gas from the downstream device, supplying a second air-fuel mixture to the cylinders of the first cylinder group while simultaneously supplying a third air-fuel mixture to the cylinders of the second cylinder group, wherein the second air-fuel mixture is characterized by a stoichiometric second air-fuel ratio and the third air-fuel mixture is characterized by a third air-fuel ratio rich of the stoichiometric air-fuel ratio, and wherein the second and third air-fuel mixtures combine to form a fourth air-fuel mixture flowing through the trap, the fourth air-fuel mixture being characterized by a fourth air-fuel ratio rich of the stoichiometric air-fuel ratio.

2. The method of claim 1, wherein determining the need for releasing previously-stored constituent gas from the downstream device includes:

calculating a first measure representing a cumulative amount of the selected constituent gas stored in the device when supplying the first air-fuel mixture;

determining a reference value representing an instantaneous capacity of the downstream device to store the selected constituent gas; and

comparing the first measure to the reference value.

3. The method of claim 1, wherein the fourth air-fuel ratio, when normalized by the stoichiometric air-fuel ratio, is no greater than about 0.75.

4. The method of claim 1, including retarding spark to the second cylinder group when supplying the third air-fuel mixture to the second cylinder group.

5. The method of claim 1, including selecting the second and third air-fuel ratios, respectively, such that a first torque generated upon operation of the cylinders of the first cylinder group using the second air-fuel mixture is approximately equal to a second torque generated upon operation of the cylinders of the second cylinder group using the third air-fuel mixture.

6. A system for controlling the operation of an internal combustion engine, wherein the engine includes a plurality of cylinders respectively burning an air-fuel mixture to generate exhaust gas, each cylinder being associated with a selected one of exactly two cylinder groups, the exhaust gas from each cylinder group flowing through a respective one of a plurality of upstream emission control devices and a common downstream emission control device, the downstream device storing an amount of a selected constituent gas of the exhaust gas when the exhaust gas flowing through the downstream device is lean of a stoichiometric air-fuel ratio and releasing previously-stored constituent gas when the exhaust gas flowing through the downstream device is rich of the stoichiometric air-fuel ratio, the system comprising:

a controller including a microprocessor arranged to supply a first air-fuel mixture to each cylinder group, the first air-fuel mixture being characterized by a first air-fuel ratio lean of the stoichiometric air-fuel ratio, whereby an amount of NO_x is stored in the trap, and wherein the controller is further arranged to determine a need for releasing previously stored NO_x from the trap and, in response to determining a need for releasing previously stored NO_x, to supply a second air-fuel mixture to the cylinders of the first cylinder group while simultaneously supplying a third air-fuel mixture to the cylinders of the second cylinder group, the second air-fuel mixture being characterized by a stoichiometric second air-fuel ratio and the third air-fuel mixture being characterized by a third air-fuel ratio rich of the stoichiometric air-fuel ratio, the second and third air-fuel mixtures combining to form a fourth air-fuel mixture flowing through the trap, and the fourth air-fuel mixture being characterized by a fourth air-fuel ratio rich of the stoichiometric air-fuel ratio.

7. The system of claim 6, wherein the controller is further arranged to calculate a first measure representing a cumulative amount of NO_x stored in the device when supplying the first air-fuel mixture, to determine a reference value representing an instantaneous NO_x-storage capacity for the device, and to compare the first measure to the reference value.

8. The system of claim 6, wherein the controller is further arranged to retard spark to the second cylinder group when operating the second cylinder group with the third air-fuel mixture.

9. The system of claim 8, wherein the controller is further arranged to select the second and third air-fuel ratios, respectively, such that a first torque generated upon operation of the cylinders of the first cylinder group using the second air-fuel mixture is approximately equal to a second torque generated upon operation of the cylinders of the second cylinder group using the third air-fuel mixture.

10. A method of controlling the operation of an internal combustion engine having a plurality of cylinders respectively burning an air-fuel mixture to generate exhaust gas, each cylinder being associated with a selected one of exactly two cylinder groups, the exhaust gas from each cylinder flowing through a selected one of a plurality of upstream emission control device before flowing as a combined exhaust gas through a common downstream emission control device, the downstream device storing an amount of a selected constituent gas of the exhaust gas when the exhaust gas flowing through the downstream device is lean of a stoichiometric air-fuel ratio and releasing previously-stored constituent gas when the exhaust gas flowing through the device is rich of the stoichiometric air-fuel ratio, the method comprising:

determining a need for releasing previously-stored constituent gas from the downstream device; and

in response to determining a need for releasing previously-stored constituent gas, operating the cylinders of the first cylinder group with a stoichiometric air-fuel mixture while simultaneously operating the cylinders of the second cylinder group with a first rich air-fuel mixture to thereby release previously-stored constituent gas from the downstream device.

11. The method of claim 10, wherein the combined exhaust gas from the cylinders of the first and second cylinder groups when operating with the stoichiometric air-fuel mixture and the first rich air-fuel mixture, respectively, is characterized by an air-fuel ratio of no greater than about 0.75.

12. The method of claim 10, including retarding spark to the second cylinder group when supplying the first rich air-fuel mixture to the cylinders of the second cylinder group.

13. The method of claim 10, including balancing the torque output of the first and second cylinder groups when respectively operating the first and second cylinder groups with the stoichiometric air-fuel mixture and the first rich air-fuel mixture.