Method and control unit for estimating an injected amount of fuel

Abstract

A method for estimating an amount of fuel injected by a fuel injector (2, fig 7) of an internal combustion engine. Processing circuitry is coupled to one or more pressure sensors (6, fig 7) that output a rail pressure of a fuel rail (1, fig 7) supplying fuel to the fuel injector. The fuel injector injects fuel in response to receiving drive pulses of predetermined duration. The method comprises receiving a plurality of pre-injection rail pressure values and a plurality of post-injection rail pressure values, corresponding, respectively, to rail pressure values prior to and after a drive pulse. By extrapolation from the pre-injection rail pressure values, an upper rail pressure value corresponding to an index value at a predetermined timepoint within the drive pulse is determined. By extrapolation from the post-injection rail pressure values, a lower rail pressure value corresponding to the index value at the predetermined timepoint is determined. The pressure drop is determined as the difference between the upper and lower rail pressure values. The amount of fuel injected by the fuel injector is derived from the determined pressure drop. An engine control unit, a vehicle incorporating it, and a computer program product are also disclosed.

Claims

1. A method carried out by processing circuitry, for estimating an amount of fuel injected by a fuel injector of an internal combustion engine, the processing circuitry being coupled to one or more pressure sensors configured to output a rail pressure of a fuel rail supplying, in use, fuel to the fuel injector, the fuel injector being configured to inject fuel in response to receiving each of one or more drive pulses, the drive pulses being of predetermined duration, the method comprising: receiving a plurality of pre-injection rail pressure values and a plurality of post-injection rail pressure values, corresponding, respectively, to rail pressure values prior to and after a drive pulse;determining, by extrapolation from the pre-injection rail pressure values, an upper rail pressure value corresponding to an index value at a predetermined timepoint within the drive pulse;determining, by extrapolation from the post-injection rail pressure values, a lower rail pressure value corresponding to the index value at the predetermined timepoint;determining a pressure drop as the difference between the upper rail pressure value and the lower rail pressure value; andderiving the amount of fuel injected by the fuel injector from the determined pressure drop.

2. The method of claim 1, wherein each of the pre-injection rail pressure values and the post-injection rail pressure values is associated with a respective index value corresponding to elapsed time since an initial point, and wherein (i) determining the upper rail pressure value comprises calculating the mathematical regression of the received pre-injection rail pressure values so as to estimate a pre-injection regression line by least squares method, and / or (ii) determining the lower rail pressure value comprises calculating the mathematical regression of a plurality of the received post-injection rail pressure values so as to estimate a postinjection regression line by least squares method.

3. The method of claim 1 or 2, wherein the plurality of the received postinjection rail pressure values comprises a set of the rail pressure values received after the elapse of a time margin since the end of the drive pulse.

4. The method of claim 2 or 3, wherein (i) determining the upper rail pressure value comprises extrapolating along the pre-injection regression line, whereby the upper rail pressure value is the pressure value corresponding to the index value at the predetermined timepoint, and (ii) determining the lower rail pressure value comprises extrapolating along the post-injection regression line, whereby the lower rail pressure value is the pressure value corresponding to the index value at the predetermined timepoint.

5. The method of claim 4, wherein extrapolating along the pre-injection regression line comprises extrapolating from the last-received one of the plurality of pre-injection rail pressure values.

6. The method of claim 4 or 5, wherein extrapolating along the post-injection regression line comprises (i) extrapolating from the first-received one of the plurality of post-injection rail pressure values or (ii) extrapolating from the first rail pressure value in the set of the rail pressure values after the elapse of a time margin.

7. The method of claim 4, wherein extrapolating along the pre-injection regression line comprises extrapolating from the lower end thereof, and / or extrapolating along the post-injection regression line comprises extrapolating from the upper end thereof.

8. The method of any of claims 2 to 7, wherein (i) the lower end of the pre-injection regression line or the last-received one of the plurality of pre-injection rail pressure values corresponds to the start of the drive pulse and / or (ii) the upper end of the post-injection regression line or the first-received one of the plurality of post-injection rail pressure values corresponds to the end of the drive pulse or to atime point corresponding to the elapse of a time margin after the end of the drive pulse.

9. The method of any of the preceding claims, wherein the predetermined timepoint comprises the centre of the drive pulse.

10. The method of any of the preceding claims, wherein deriving the amount of fuel injected comprises accessing a pre-stored look-up table using the determined pressure drop to return the amount of fuel injected as an estimate based on at least one of fuel type, temperature, injector type and system pressure.

11. The method of any of the preceding claims, wherein the initial point corresponds to the end of the previous pumping event of a fuel pump or to the beginning of the receipt of the plurality of pre-injection rail pressure values.

12. The method of any of the preceding claims, wherein the lower end of the post-injection regression line corresponds to the beginning of the next pumping event by the fuel pump or to the end of the receipt of the plurality of post-injection rail pressure values.

13. The method of any of the preceding claims, wherein the index value corresponds to engine angular position.

14. A method of operating a fuel injection system of an internal combustion engine comprising at least one fuel injector associated with a combustion chamber and coupled to a fuel rail comprising a pressure sensor, wherein injection events are performed by applying to said injector a drive signal of predetermined length; and wherein the method of any of the preceding claims is operated performed to determine the amount of fuel injected during a respective fuel injection event.

15. An engine control unit, for estimating an amount of fuel injected by a fuel injector of an internal combustion engine, the control unit comprising theprocessing circuitry configured to carry out the method of any of the preceding claims.

16. A vehicle incorporating the engine control unit of claim 15.

17. A computer program product comprising instructions which, when executed by processing circuitry, cause the method of any of claims 1 to 13 to be performed.

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