System and method for controlling airflow through a ventilation system of an engine when cylinders of the engine are deactivated

1. A system comprising:

an airflow determination module that determines an amount of airflow through a ventilation system for a crankcase of an engine; and

a cylinder activation module that compares the amount of airflow through the ventilation system to a first amount of airflow and, when a cylinder of the engine is deactivated while the engine is running, selectively activates the cylinder when the amount of airflow through the ventilation system is less than the first amount of airflow.

2. The system of claim 1 further comprising a nitrogen oxide (NOx) estimation module that estimates a level of nitrogen oxide within the crankcase of the engine based on the amount of airflow through the ventilation system, wherein the cylinder activation module selectively activates the cylinder based on the nitrogen oxide level.

3. The system of claim 1 wherein the cylinder activation module activates the cylinder when the amount of airflow through the ventilation system is less than the first amount of airflow for a first period.

4. The system of claim 3 further comprising a desired airflow module that determines a desired amount of airflow through the ventilation system, wherein the cylinder activation module selectively activates the cylinder when the amount of airflow through the ventilation system during the first period is less than the desired amount of airflow.

5. The system of claim 4 wherein the desired airflow module determines the desired amount of airflow through the ventilation system based on ambient temperature, ambient humidity, and engine wear.

6. The system of claim 4 wherein the desired airflow module determines the desired amount of airflow through the ventilation system based on a level of nitrogen oxide within the crankcase of the engine.

7. The system of claim 6 further comprising a nitrogen oxide (NOx) estimation module that estimates the nitrogen oxide level based on an amount of nitrogen oxide that enters the crankcase due to blowby and an amount of nitrogen oxide that exits the crankcase through the ventilation system.

8. The system of claim 7 wherein the NOx estimation module estimates the amount of nitrogen oxide that enters the crankcase due to blowby based on engine load.

9. A system comprising:

an airflow determination module that determines an amount of airflow through a ventilation system for a crankcase of an engine; and

a cylinder activation module that, when a cylinder of the engine is deactivated while the engine is running, selectively activates the cylinder when the amount of airflow through the ventilation system is less than a first amount of airflow for a first period, wherein:

the airflow determination module predicts the amount of airflow through the ventilation system when the cylinder is activated; and

the cylinder activation module activates the cylinder when the predicted amount of airflow through the ventilation system is greater than a second amount of airflow.

10. The system of claim 9 wherein the airflow determination module determines the predicted amount of airflow through the ventilation system based on engine load.

11. A method comprising:

determining an amount of airflow through a ventilation system for a crankcase of an engine;

comparing the amount of airflow through the ventilation system to a first amount of airflow; and

when a cylinder of the engine is deactivated while the engine is running, selectively activating the cylinder when the amount of airflow through the ventilation system is less than the first amount of airflow.

12. The method of claim 11 further comprising:

estimating a level of nitrogen oxide within the crankcase of the engine based on the amount of airflow through the ventilation system; and

selectively activating the cylinder based on the nitrogen oxide level.

13. The method of claim 11 further comprising activating the cylinder when the amount of airflow through the ventilation system is less than the first amount of airflow for a first period.

14. The method of claim 13 further comprising:

determining a desired amount of airflow through the ventilation system; and

selectively activating the cylinder when the amount of airflow through the ventilation system during the first period is less than the desired amount of airflow.

15. The method of claim 14 further comprising determining the desired amount of airflow through the ventilation system based on ambient temperature, ambient humidity, and engine wear.

16. The method of claim 14 further comprising determining the desired amount of airflow through the ventilation system based on a level of nitrogen oxide within the crankcase of the engine.

17. The method of claim 16 further comprising estimating the nitrogen oxide level based on an amount of nitrogen oxide that enters the crankcase due to blowby and an amount of nitrogen oxide that exits the crankcase through the ventilation system.

18. The method of claim 17 further comprising estimating the amount of nitrogen oxide that enters the crankcase due to blowby based on engine load.

19. A method comprising:

determining an amount of airflow through a ventilation system for a crankcase of an engine;

when a cylinder of the engine is deactivated while the engine is running, selectively activating the cylinder when the amount of airflow through the ventilation system is less than a first amount of airflow for a first period;

predicting the amount of airflow through the ventilation system when the cylinder is activated; and

activating the cylinder when the predicted amount of airflow through the ventilation system is greater than a second amount of airflow.

20. The method of claim 19 further comprising determining the predicted amount of airflow through the ventilation system based on engine load.