Intake air oxygen compensation for EGR

1. A method, comprising:

measuring intake oxygen concentration with an intake oxygen sensor located in an intake between a compressor outlet and a throttle inlet; and

during boosted conditions only,

correcting the measured intake oxygen concentration based on a fuel canister vapor purge into the intake upstream of the compressor; and

adjusting recirculation of exhaust gas into the intake passage upstream of the compressor responsive to the corrected intake oxygen concentration.

2. The method of claim 1 , wherein correcting the measured intake oxygen concentration only during boosted conditions comprises correcting the measured intake oxygen concentration when a boost pressure is greater than a barometric pressure and a manifold absolute pressure is greater than the barometric pressure.

3. The method of claim 2 , wherein correcting the measured intake oxygen concentration is performed using a purge correction factor.

4. The method of claim 3 , further comprising determining the purge correction factor based on the fuel canister vapor purge when the exhaust gas recirculation is off.

5. The method of claim 4 , further comprising estimating the fuel canister vapor purge from a change in the measured intake oxygen concentration.

6. The method of claim 1 wherein measuring intake oxygen concentration comprises measuring the intake oxygen concentration with the intake oxygen sensor during boosted and unboosted conditions.

7. A method, comprising:

measuring intake oxygen concentration with an intake oxygen sensor located in an intake between a compressor outlet and a throttle inlet;

determining a purge correction factor based on the measured intake oxygen concentration only while low-pressure exhaust gas recirculation is off and fuel vapor canister purging into an engine intake is on;

correcting the measured intake oxygen concentration based on the purge correction factor; and

adjusting the exhaust gas recirculation responsive to the corrected intake oxygen concentration.

8. The method of claim 7 , further comprising determining the purge correction factor and correcting the intake oxygen concentration only during boost conditions.

9. The method of claim 7 , wherein correcting the measured intake oxygen concentration comprises:

correcting the measured intake oxygen concentration by a first amount when fuel vapor is purged along a first path upstream of the intake oxygen sensor; and

correcting the measured intake oxygen concentration by a second amount when fuel vapor is purged along a second path downstream of the intake oxygen sensor.

10. The method of claim 9 , wherein the fuel vapor purged along the first path passes through an ejector before continuing on to the intake upstream of the intake oxygen sensor and the compressor.

11. The method of claim 9 , wherein the fuel vapor purged along the second path enters the intake downstream of a throttle outlet.

12. The method of claim 9 , wherein the first path comprises a boosted path.

13. The method of claim 12 , wherein the second path comprises a vacuum path.

14. A method comprising,

measuring intake oxygen concentration with an intake oxygen sensor located in an intake between a compressor outlet and a throttle inlet;

only during a first condition when exhaust gas recirculation is off, and canister purge is on, estimating a purge fuel concentration based on the measured intake oxygen concentration; and then

during a second condition when exhaust gas recirculation is on, and canister purge is on, correcting the measured intake oxygen concentration based on the estimated purge fuel concentration.

15. The method of claim 14 , wherein the first condition further comprises a boost pressure greater than a barometric pressure and a manifold absolute pressure greater than the barometric pressure.

16. The method of claim 14 , wherein the second condition further comprises a boost pressure greater than a barometric pressure and a manifold absolute pressure greater than the barometric pressure.

17. The method of claim 14 , wherein correcting the measured intake oxygen concentration based on the estimated purge fuel concentration during the second condition comprises determining a purge correction factor from the estimated purge fuel concentration, and correcting the measured intake oxygen concentration using the purge correction factor.