Exhaust gas recirculation control in a dynamic skip fire engine

1. A method of selecting a firing pattern in a skip fire controlled 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;

selecting the firing pattern based at least in part on the desired exhaust gas recirculation flow rate and the position of the exhaust gas recirculation valve;

determining an engine speed;

determining a firing fraction;

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, the firing fraction, and the boost pressure.

2. 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.

3. The method as recited in claim 2 , further comprising:

selecting a new firing pattern if the desired exhaust gas recirculation flow rate exceeds the maximum gas recirculation flow rate.

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

determining a valve timing; and

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

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

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

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

selecting a new firing pattern if the desired exhaust gas recirculation flow rate exceeds the maximum gas recirculation flow rate.

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

determining an oxygen level in the intake manifold;

adjusting the firing pattern 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.

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

determining a level of nitrogen oxides in the exhaust system;

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

9. The method as recited in claim 1 , wherein the firing pattern does not result in firings being as evenly distributed as possible.

10. The method as recited in claim 1 , wherein the selected firing pattern fires more cylinders that directly vent into a first exhaust manifold than cylinders that do not directly vent into the first exhaust manifold.

11. The method as recited in claim 1 , wherein at least one skipped working cycle in the firing pattern is a pumping working cycle.

12. The method as recited in claim 1 , wherein the selected firing pattern reduces engine-cycle-to-engine-cycle fluctuations in a number of cylinder firings venting into a first exhaust manifold.

13. A method of selecting a firing pattern in a skip fire controlled 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; and

selecting a firing pattern based at least in part on the desired exhaust gas recirculation flow rate and the position of the exhaust gas recirculation valve, wherein the selected firing pattern has more engine-cycle-to-engine-cycle fluctuations in a number of cylinder firings venting into a second exhaust manifold than a number of cylinder firings venting into a first exhaust manifold.

14. A skip fire controlled, turbocharged, 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 that includes non-transitory executable instructions stored in a memory to;

determine a firing pattern based at least in part on a desired exhaust gas recirculation flow rate;

determine an engine speed;

determine a firing fraction;

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, the firing fraction, and the boost pressure.

15. The engine as recited in claim 14 , 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.

16. The engine as recited in claim 14 , further comprising:

a sensor to measure the 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.

17. A skip fire controlled, turbocharged, 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 that determines a firing pattern based at least in part on a desired exhaust gas recirculation flow rate, wherein the engine control system uses a first control algorithm to control a first firing pattern for cylinders that vent into the first exhaust manifold and a second control algorithm to control a second firing pattern for cylinders that vent into the second exhaust manifold.

18. The engine as recited in claim 17 wherein the firing pattern does not result in firings being as evenly distributed as possible.

19. The engine as recited in claim 17 wherein the engine has a plurality of cylinders and the firing pattern has a repeating pattern length that is at least twice a number of cylinders in the engine.