Control apparatus for operating a fuel metering valve

1. A control apparatus for operating a fuel metering valve associated to a fuel pump arranged to supply fuel into a fuel rail, the fuel metering valve having a valve member and an electric actuator arranged to move the valve member for regulating a fuel flow-rate supplied by the fuel pump into the fuel rail, the control apparatus comprising an electronic control unit connected to the fuel metering valve and configured to:

determine a target value (q* tot ) for the fuel flow-rate;

use a nominal function (F n ), correlating values of the fuel flow-rate to corresponding values of an adjustable parameter of an electric signal driving the actuator of the fuel metering valve, to determine a nominal value (r n ) of the adjustable parameter that corresponds to the target value (q* tot ) of the fuel flow-rate;

use the determined nominal value (r n ) to calculate a corrected value (r*) of the adjustable parameter; and

set the adjustable parameter of the electric signal at the corrected value (r*);

wherein the electronic control unit is configured to calculate the corrected value (r*) of the adjustable parameter by:

estimating a value (q^ tot ) of the fuel flow-rate that approximates a real value (q tot ) thereof;

calculating a difference between the target value (q* tot ) and the estimated value (q^ tot ) of the fuel flow-rate;

using said difference to determine a value (Δr*) of a correction term indicative of a deviation of the nominal function (F n ); and

calculating the corrected value (r*) of the adjustable parameter as a function of the nominal value (r n ) thereof and of the calculated value (Δr*) of the correction term.

2. A control apparatus according to claim 1 , wherein the electronic control unit is configured to determine the value (Δr*) of the correction term by:

calculating a derivative of the nominal function (F n ) at the point corresponding to the target value (q* tot ) of the fuel flow-rate;

calculating a derivative of the nominal function (F n ) at the point corresponding to the estimated value (q* tot ) of the fuel flow-rate; and

calculating the correction term value (Δr*) as a function of said derivatives and of the difference between the target value (q* tot ) and the estimated value (q^ tot ) of the fuel flow-rate.

3. The control apparatus according to claim 2 , wherein the electronic control unit is configured to calculate the value (Δr*) of the correction term by:

calculating an average between the derivatives of the nominal function (F n ) calculated at the points corresponding to the target value (q* tot ) and to the estimated value (q^ tot ) of the fuel flow-rate; and

multiplying the calculated average for the difference between the target value (q* tot ) and the estimated value (q^ tot ) of the fuel flow-rate.

4. The control apparatus according to claim 3 , wherein the electronic control unit is configured to calculate the average between the derivatives of the nominal function (F n ) as an harmonic mean thereof.

5. The control apparatus according to claim 1 , wherein the electronic control unit is configured to estimate the value (q^ tot ) of the fuel flow-rate by:

measuring a value (Y) of a fuel rail pressure; and

determining the estimated value (q^ tot ) of the fuel flow-rate on the basis of the measured value (Y) of the fuel rail pressure.

6. The control apparatus according to claim 5 , wherein the electronic control unit is configured to determine the estimated value (q^ tot ) of the fuel flow-rate using the measured value (Y) of the fuel rail pressure as input of a mathematical model that yields as output the estimated value (q^ tot ) of the fuel flow-rate.

7. The control apparatus according to claim 5 , wherein the electronic control unit is configured to determine the target value (q* tot ) of the fuel flow-rate by:

setting a target value (Y*) for the fuel rail pressure;

calculating a difference between the target value (Y*) and the measured value (Y) of the fuel rail pressure; and

calculating a feedback contribution (q PI ) to the target value (q* tot ) of the fuel flow-rate as a function of the calculated difference.

8. The control apparatus according to claim 7 , wherein the electronic control unit is configured to calculate the feed-back contribution (q PI ) using the difference between the target value (Y*) and the measured value (Y) of the fuel rail pressure as input of a proportional-integrative controller ( 535 ) that yields as output the feed-back contribution (q PI ).

9. The control apparatus according to claim 7 , wherein the electronic control unit is configured to determine the target value (q* tot ) of the fuel flow-rate by:

calculating a feed-forward contribution (q* L ) to the target value (q* tot ) of the fuel flow-rate on the basis of the target value (Y*) of the fuel rail pressure; and

adding the feed-forward contribution (q* L ) to the feedback contribution (q PI ) of the fuel flow-rate.

10. The control apparatus according to claim 9 , wherein the electronic control unit is configured to calculate the feed-forward contribution (q* L ) using the target value (Y*) of the fuel rail pressure as input of a mathematical model that yields as output the feed-forward contribution (q* L ).

11. The control apparatus according to claim 1 , wherein the adjustable parameter of the electric signal driving the actuator of the fuel metering valve is an electrical current.

12. The control apparatus according to any of the claims from 1 , wherein the adjustable parameter of the electric signal driving the actuator of the fuel metering valve is a timing of a sequence of electrical current pulses forming the signal.

13. A method for operating a fuel metering valve associated to a fuel pump arranged to supply fuel into a fuel rail, the fuel metering valve having a valve member and an electric actuator arranged to move the valve member for regulating a fuel flow-rate supplied by the fuel pump into the fuel rail, the method comprising:

determining a target value (q* tot ) for the fuel flow-rate;

using a nominal function (F n ) correlating values of the fuel flow-rate to corresponding values of an adjustable parameter of an electric signal driving the actuator of the fuel metering valve, to determine a nominal value (r n ) of the adjustable parameter that corresponds to the target value (q* tot ) of the fuel flow-rate;

using the determined nominal value (r n ) to calculate a corrected value (r*) of the adjustable parameter; and

setting the adjustable parameter of the electric signal at the corrected value (r*),

wherein the corrected value (r*) of the adjustable parameter is calculated by:

estimating a value (q^ tot ) of the fuel flow-rate that approximates a real value (q tot ) thereof;

calculating a difference between the target value (q* tot ) and the estimated value (q^ tot ) of the fuel flow-rate;

using said difference to determine a value (Δr*) of a correction term indicative of a deviation of the nominal function (F n ); and

calculating the corrected value (r*) of the adjustable parameter as a function of the nominal value (r n ) thereof and of the calculated value (Δr*) of the correction term.