Exhaust gas recirculation control in an internal combustion engine

1. A method of selecting cylinders to deactivate in an internal combustion engine, the engine having an intake manifold and an exhaust system, comprising:

determining a desired exhaust gas recirculation flow rate;

determining a position of an exhaust gas recirculation valve;

deactivating selected cylinders based at least in part on the desired exhaust gas recirculation flow rate and the position of the exhaust gas recirculation valve; and

determining an engine speed;

determining a boost pressure in the intake manifold; and

regulating a maximum exhaust gas recirculation rate based at least in part on the engine speed and the boost pressure.

2. The method as recited in claim 1 , wherein a pattern of firings and deactivation is fixed for certain cylinders over an extended number of engine cycles.

3. The method as recited in claim 1 , further comprising:

comparing the desired exhaust gas recirculation flow rate with the maximum exhaust gas recirculation flow rate.

4. The method as recited in claim 3 , further comprising:

selecting different cylinders to deactivate if the desired exhaust gas recirculation flow rate exceeds the maximum gas recirculation flow rate.

5. The method as recited in claim 1 , further comprising:

determining a valve timing; and

calculating the maximum exhaust gas recirculation rate based at least in part on the valve timing.

6. The method as recited in claim 5 , further comprising:

comparing the desired exhaust gas recirculation flow rate with the maximum exhaust gas recirculation flow rate.

7. The method as recited in claim 6 , further comprising:

selecting different cylinders to deactivate if the desired exhaust gas recirculation flow rate exceeds the maximum gas recirculation flow rate.

8. The method as recited in claim 1 , further comprising:

determining an oxygen level in the intake manifold;

adjusting cylinders to deactivate or the exhaust gas recirculation valve position if the oxygen level deviates from a desired oxygen level by more than a pre-defined threshold amount.

9. The method as recited in claim 1 , further comprising:

determining a level of nitrogen oxides in the exhaust system;

adjusting cylinders to deactivate or the exhaust gas recirculation valve position if the level of nitrogen oxides exceeds a pre-defined threshold.

10. The method as recited in claim 1 , wherein the selection of cylinders to deactivate does not result in firings being as evenly distributed as possible.

11. The method as recited in claim 1 , wherein among cylinders not selected to be deactivated fire, more cylinders that directly vent into a first exhaust manifold are fired than cylinders that do not directly vent into the first exhaust manifold.

12. The method as recited in claim 1 , wherein at least one working cycle having a deactivated cylinder is a pumping working cycle.

13. The method as recited in claim 1 , wherein selecting cylinders to deactivate reduces engine-cycle-to-engine-cycle fluctuations in a number of cylinder firings venting into the first exhaust manifold.

14. The method as recited in claim 1 , wherein selecting cylinders to deactivate has more engine-cycle-to-engine-cycle fluctuations in a number of cylinder firings venting into the second exhaust manifold than a number of cylinder firings venting into the first exhaust manifold.

15. An internal combustion engine, the engine having an intake manifold, an exhaust gas recirculation system, and an exhaust system having at least two exhaust manifolds, the engine comprising:

an exhaust gas recirculation feed line connected to the exhaust system, wherein the exhaust gas circulation feed line has a more direct fluid connection to a first exhaust manifold than to a second exhaust manifold; and

an engine control system configured to:

deactivate at least one cylinder based at least in part on a desired exhaust gas recirculation flow rate;

determine an engine speed;

determine a boost pressure in the intake manifold; and

regulate a maximum exhaust gas recirculation rate based at least in part on the engine speed and the boost pressure.

16. The engine as recited in claim 15 , further comprising:

an oxygen sensor located in the intake manifold, wherein a signal from the oxygen sensor is used as part of a feedback loop to determine the desired exhaust gas recirculation flow rate.

17. The engine as recited in claim 15 , further comprising:

a nitrogen oxides sensor to measure a level of nitrogen oxides located in the exhaust, wherein a signal from the nitrogen oxides sensor is used as part of a feedback loop to determine the desired exhaust gas recirculation flow rate.

18. An internal combustion engine, the engine having an intake manifold, an exhaust gas recirculation system, and an exhaust system having at least two exhaust manifolds, comprising:

an exhaust gas recirculation feed line connected to the exhaust system, wherein the exhaust gas circulation feed line has a more direct fluid connection to a first exhaust manifold than to a second exhaust manifold; and

an engine control system for selecting cylinders to deactivate based at least in part on a desired exhaust gas recirculation flow rate, wherein the engine control system uses a first control algorithm to select a first set of cylinders to deactivate for cylinders that vent into the first exhaust manifold and a second control algorithm to select a second set of cylinders to deactivate for cylinders that vent into the second exhaust manifold.

19. The engine as recited in claim 18 , wherein selecting cylinders to deactivate does not result in firings being as evenly distributed as possible.

20. The engine as recited in claim 18 , wherein the engine has a plurality of cylinders and a selected firing pattern has a repeating pattern length that is at least twice a number of cylinders in the engine.