Method and system for cylinder imbalance estimation

Patent metadata

Field	Value
Publication number	US-10801431-B2
Application number	US-201916271491-A
Country	US
Kind code	B2
Filing date	Feb 8, 2019
Priority date	Oct 6, 2017
Publication date	Oct 13, 2020
Grant date	Oct 13, 2020

Abstract

Methods and systems are provided for learning a cylinder-to-cylinder air variation. During conditions when a PFDI engine is operated in a port-injection only mode, prior to port fuel injection, a direct-injection fuel rail pressure may be lowered via direct-injection. Then, prior to a spark event in a port-injected cylinder, the direct-injector may be transiently opened to use the rail pressure sensor for estimating a cylinder compression pressure, and inferring cylinder air charge therefrom.

First claim

The invention claimed is:

1. A method, comprising:
injecting fuel from a direct injector, with output of a high-pressure pump reduced, to lower direct injection fuel rail pressure below a threshold pressure;
then, port injecting fuel into a cylinder and commanding the direct injector to selectively open a threshold duration before a spark event in the cylinder, without injecting any fuel from the direct injector; and
learning a cylinder air-charge estimate based on a rise in the fuel rail pressure.

2. The method of claim 1 , wherein injecting fuel from the direct injector with the output of the high-pressure pump reduced includes injecting fuel from the direct injector with the high-pressure pump disabled.

3. The method of claim 1 , further comprising, learning an air-fuel ratio error for the cylinder based on the learned air-charge estimate.

4. The method of claim 3 , further comprising adjusting cylinder fueling responsive to the learned air-charge estimate for the cylinder, the cylinder fueling increased as the learned air-charge estimate exceeds an expected air-charge estimate, the cylinder fueling decreased as the learned air-charge estimate exceeds the expected air-charge estimate.

5. The method of claim 1 , wherein the threshold pressure is determined as a function of one or more of barometric pressure, engine speed, and load.

6. The method of claim 1 , wherein the threshold pressure is a pressure below which opening of the direct injector results in no fuel flowing out of the direct injector into the cylinder.

7. The method of claim 1 , wherein the threshold pressure is lower than a compression pressure expected in the cylinder during a combustion event immediately following the spark event in the cylinder.

8. The method of claim 1 , wherein the threshold duration is based on engine speed and load.

9. The method of claim 1 , wherein port injecting fuel into the cylinder includes port injecting during an exhaust stroke or an intake stroke of the cylinder, and wherein the direct injector is commanded to open during a compression stroke of the cylinder.

10. The method of claim 1 , wherein the rise in the fuel rail pressure is sensed via a direct injection fuel rail pressure sensor, and wherein commanding the direct injector to selectively open includes commanding a pulse-width to the direct injector based on a range and sensitivity of the fuel rail pressure sensor.

11. The method of claim 3 , wherein the cylinder is one of a plurality of engine cylinders, the method further comprising learning the air-charge estimate for each of the plurality of engine cylinders over a number of consecutive cylinder events.

12. The method of claim 11 , wherein learning the cylinder air-fuel ratio error further includes learning the cylinder air-fuel ratio error based on a deviation between the air-charge estimate of the plurality of engine cylinders.

13. The method of claim 11 , wherein the threshold pressure is a lower threshold pressure, the method further comprising learning the air-charge estimate for each of the plurality of engine cylinders over the number of consecutive cylinder events until the fuel rail pressure is above an upper threshold pressure, higher than the lower threshold pressure, then injecting fuel from the direct injector with the output of the high-pressure pump reduced, to lower the fuel rail pressure to the lower threshold pressure, and then resuming the learning.

14. A method for an engine, comprising:
injecting fuel from a direct injector, with a high-pressure pump disabled, to lower direct injection fuel rail pressure below a threshold pressure;
then, injecting fuel into a cylinder from a port injector on an intake stroke of the cylinder and commanding the direct injector to selectively open on a compression stroke of the cylinder, before a spark event in the cylinder; and
learning an air-fuel ratio error for the cylinder based on a sensed rise in the fuel rail pressure.

15. The method of claim 14 , wherein the threshold pressure is a pressure below which the selectively opening of the direct injector results in no fuel flowing out of the direct injector into the cylinder.

16. The method of claim 15 , wherein the cylinder is one of a plurality of engine cylinders, and the threshold pressure is a lower threshold pressure, the method further comprising:
learning the air-fuel ratio error for each of the plurality of engine cylinders over a number of consecutive cylinder events until the fuel rail pressure exceeds an upper threshold pressure, above which fuel flows into the cylinder when the direct injector is commanded open, the upper threshold pressure higher than the lower threshold pressure;
then, injecting fuel from the direct injector, with the high-pressure pump disabled, to lower the fuel rail pressure to the lower threshold pressure; and
then, resuming the learning.

17. The method of claim 14 , wherein learning the cylinder air-fuel ratio error includes learning an air-charge estimate for the cylinder based on the sensed rise in the fuel rail pressure.

18. The method of claim 14 , wherein commanding the direct injector to selectively open on the compression stroke of the cylinder includes commanding the direct injector to open at a timing based on engine speed, the direct injector commanded open for a duration based on the engine speed.

19. The method of claim 14 , further comprising, adjusting subsequent fueling of the cylinder based on the estimated cylinder air-charge.

20. The method of claim 14 , wherein the injecting and learning is performed during a deceleration fuel shut-off event.

21. An engine system, comprising:
an engine including a cylinder;
each of a port fuel injector and a direct fuel injector coupled to the cylinder;
a high pressure fuel pump delivering fuel to the direct injector via a direct injection fuel rail;
a pressure sensor for estimating a direct injection fuel rail pressure; and
a controller with computer readable instructions stored on non-transitory memory for:
operating the direct injector with the fuel pump disabled until the fuel rail pressure falls below a threshold pressure, and then disabling the direct injector, wherein below the first threshold pressure, operating the direct injector results in no fuel flowing out of the direct injector;
while port fueling the cylinder, transiently opening the direct injector before a spark event of the cylinder, without delivering any fuel via the direct injector, a timing and duration of opening the direct injector based on engine speed;
estimating cylinder air-charge based on a change in fuel rail pressure during the transient opening; and
adjusting subsequent cylinder fueling based on the estimated cylinder air-charge.

22. The system of claim 21 , wherein the threshold pressure is adjusted as a function of barometric pressure.

Assignees

• Ford Global Tech Llc

Inventors

• Thomas Joseph Lyle
• Sanborn Ethan D
• Hollar Paul
• Dusa Daniel

Classifications

• F02D2200/0616

  determined by estimation · CPC title

• F02D35/024

  using an estimation · CPC title

• F02D41/3836

  Controlling the fuel pressure · CPC title

• F02D41/18

  by measuring intake air flow · CPC title

• F02D41/3094 Primary

  the fuel injection being effected by at least two different injectors, e.g. one in the intake manifold and one in the cylinder · CPC title