Method and system for operating dual-exhaust engine
First Claim
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 Assignments
0 Petitions
Accused Products
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.
228 Citations
13 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. - View Dependent Claims (2, 3, 4, 5)
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 NOx is stored in the trap, and wherein the controller is further arranged to determine a need for releasing previously stored NOx from the trap and, in response to determining a need for releasing previously stored NOx, 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. - View Dependent Claims (7, 8, 9)
-
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. - View Dependent Claims (11, 12, 13)
-
Specification