Methods and systems for fuel canister purge flow estimation with an intake oxygen sensor

Patent metadata

Field	Value
Publication number	US-9322367-B2
Application number	US-201414155261-A
Country	US
Kind code	B2
Filing date	Jan 14, 2014
Priority date	Jan 14, 2014
Publication date	Apr 26, 2016
Grant date	Apr 26, 2016

Abstract

Methods and systems are provided for estimating a fuel canister purge flow based on outputs of an intake manifold oxygen sensor. For example, during boosted engine operation when exhaust gas recirculation (EGR) is flowing below a threshold and purge is enabled, purge flow may be estimated based on changes in the sensor output while modulating a canister purge valve between an open and closed position. Then, during subsequent operation wherein EGR and purge flow are enabled, the output of the sensor may be adjusted based on the estimated purge flow.

First claim

The invention claimed is:

1. An engine method, comprising:
during boosted engine operation with exhaust gas recirculation (EGR) flowing below a first threshold,
modulating a canister purge valve (CPV); and
estimating a purge flow rate based on an output of an intake oxygen sensor responsive to the modulating, the first threshold based on a response time of the CPV.

2. The method of claim 1 , wherein the modulating includes opening and closing the CPV at a frequency, the frequency based on a canister load and a sensitivity of the intake oxygen sensor.

3. The method of claim 2 , further comprising decreasing EGR to below the first threshold and modulating the CPV in response to one or more of a duration since a previous purge flow estimation or EGR flow below a second threshold, the first threshold further based on the frequency of modulating the CPV.

4. The method of claim 2 , further comprising decreasing EGR from a first level above the first threshold to a second level below the first threshold prior to modulating the CPV.

5. The method of claim 1 , wherein estimating the purge flow rate includes comparing a first output of the intake oxygen sensor with the CPV open and a second output of the intake oxygen sensor with the CPV closed and wherein the estimating is further based on a transport delay of purge flow between the CPV and the intake oxygen sensor.

6. The method of claim 1 , wherein the estimating the purge flow rate includes determining a change in intake oxygen measured by the intake oxygen sensor during the modulating and converting the change in intake oxygen to equivalent hydrocarbons to determine the purge flow rate.

7. The method of claim 1 , wherein EGR flowing includes flowing exhaust gas through a low pressure EGR system, the low pressure EGR system coupled between an exhaust passage downstream of a turbine and an intake passage upstream of a compressor.

8. The method of claim 1 , wherein EGR flowing includes EGR flowing at a flat EGR schedule wherein an EGR fraction is relatively constant.

9. The method of claim 1 , further comprising, adjusting engine fueling based on the estimated PCV flow, the engine fueling decreased as the estimated PCV flow increases.

10. The method of claim 1 , further comprising adjusting an EGR valve based on the output of the intake oxygen sensor during the modulating.

11. The method of claim 1 , further comprising storing the estimated purge flow rate as a function of one or more of boost pressure or canister load in a look-up table in a memory of a controller.

12. The method of claim 11 , further comprising during subsequent boosted engine operation with EGR flowing above the first threshold, adjusting an EGR valve based on an output of the intake oxygen sensor and a previously stored purge flow rate.

13. An engine method, comprising:
during a first condition when an engine is boosted, fuel canister purge is enabled, and exhaust gas recirculation (EGR) is flowing below a first threshold,
modulating a canister purge valve (CPV); and
adjusting an EGR valve based on an output of an intake oxygen sensor during the modulating; and
during a second condition when the engine is boosted, fuel canister purge is enabled, and EGR is flowing at or above the first threshold,
not modulating the CPV; and
adjusting the EGR valve based on an output of the intake oxygen sensor and a stored purge flow estimate.

14. The method of claim 13 , wherein modulating the CPV includes pulse width modulating the CPV to open and close the CPV at a pulse width, the pulse width based on a fuel canister load and a sensitivity of the intake oxygen sensor, the pulse width increasing with increasing fuel canister load.

15. The method of claim 14 , further comprising during the first condition, decreasing EGR below a second threshold, the second threshold below the first threshold and the second threshold based on the pulse width.

16. The method of claim 13 , wherein adjusting the EGR valve based on the stored purge flow estimate includes adjusting the EGR valve based on a purge flow estimate determined during previous engine operation during the first condition, the stored purge flow estimate stored in a memory of a controller.

17. The method of claim 13 , further comprising during a third condition when the engine is not boosted, adjusting the EGR valve based on the output of the intake oxygen sensor and not adjusting the output based on purge flow.

18. An engine system, comprising:
an engine including an intake manifold
a crankcase coupled to the intake manifold via a PCV valve;
a turbocharger with an intake compressor, an exhaust turbine, and a charge air cooler;
an intake throttle coupled to the intake manifold downstream of the charge air cooler;
a canister configured to receive fuel vapors from a fuel tank, the canister coupled to the intake manifold via a purge valve;
an EGR system including a passage for recirculating exhaust residuals from downstream of the turbine to upstream of the compressor via an EGR valve;
an intake oxygen sensor coupled to the intake manifold, downstream of the charge air cooler and upstream of the intake throttle; and
a controller with computer readable instructions for:
learning a correction factor for the intake oxygen sensor based on purge flow from the canister; and
adjusting a position of the EGR valve based on an output of the intake oxygen sensor relative to the correction factor.

19. The system of claim 18 , wherein learning the correction factor includes determining a change in intake oxygen at the intake oxygen sensor during modulating a position of the purge valve, the modulating occurring when the engine is boosted, purge is enabled, and EGR is flowing below a threshold, and the modulating including modulating the purge valve between an open and closed position at a set rate.

20. The system of claim 19 , wherein the computer readable instructions further include instructions for estimating purge flow based on the change in intake oxygen during modulating the position of the purge valve, the change in intake oxygen being a change in measured intake oxygen between a first output of the intake oxygen sensor when the purge valve is open and a second output of the intake oxygen sensor when the purge valve is closed.

Assignees

• Ford Global Tech Llc

Inventors

• Vigild Christian Winge
• Buckland Julia Helen

Classifications

• F02M25/0836 Primary

  Arrangement of valves controlling the admission of fuel vapour to an engine, e.g. valve being disposed between fuel tank or absorption canister and intake manifold · CPC title

• F02M26/40

  with timing means in the recirculation passage, e.g. cyclically operating valves or regenerators; with arrangements involving pressure pulsations · CPC title