Injector valve force control

1 . A method for controlling a fuel injector, the method comprising: applying a first current to a control valve having an actuated state and a resting state, the first current causing the control valve to move from the resting state to the actuated state; applying a second current that causes the control valve to remain in the actuated state, the second current having an amplitude that is lower than an amplitude of the first current; maintaining the second current for a duration; stopping the second current at an end of the duration to allow the control valve to return to the resting state; measuring a control valve return time based on an induced current; comparing the measured control valve return time to an expected control valve return time and setting the amplitude of current for a fuel injection event based on the comparison; and increasing the second current when the control valve return time is shorter than the expected control valve return time.

2 . The method of claim 1 , further including decreasing the amplitude of the current of an additional fuel injection event.

3 . The method of claim 1 , wherein the method further includes determining a minimum current that reduces variability of the control valve return time and setting the amplitude of current for the fuel injection event to the minimum current.

4 . The method of claim 1 , wherein the first current has a first amplitude and the second current has a second amplitude, the second amplitude being lower than the first amplitude.

5 . The method of claim 1 , wherein the method is repeated on all fuel injectors in an internal combustion engine.

6 . A method for controlling a fuel injector, the method comprising: determining an expected valve return time for a control valve of the fuel injector, the expected valve return time being associated with an amplitude of current; applying a current to the control valve, the control valve having an actuated state and a resting state, the current causing the control valve to be in the actuated state; stopping supply of the current to the control valve; measuring a valve return time, after stopping supply of the current, based on induced current; comparing the measured valve return time to the expected valve return time; setting a current amplitude for a fuel injection event based on the comparison; increasing the current amplitude when the measured valve return time is sooner than the expected valve return time; and decreasing the current amplitude when the measured valve return time exceeds the expected valve return time.

7 . The method of claim 6 , further including increasing the current amplitude until the measured valve return time does not deviate from the expected valve return time.

8 . The method of claim 6 , wherein the method further includes using the current amplitude for a fuel injection event that is controlled with the control valve.

9 . The method of claim 6 , wherein the method is repeated on every fuel injector in an internal combustion engine.

10 . A system for controlling a fuel injector, the system comprising: a control valve having an actuated state and a resting state; a control valve solenoid capable of causing the control valve to move between the actuated state and the resting state; and a controller, the controller configured to: determine an expected control valve return time at which the control valve returns to the resting state from the actuated state, apply current to the control valve for a duration, measure the control valve return time based on induced current, compare the measured control valve return time to the expected control valve return time, determine an amplitude of current for a fuel injection event based on the comparison, increase the amplitude to cause the measured control valve return time to be approximately equal to the expected control valve return time, and decrease the current when the measured control valve return time is not sooner than the expected control valve return time for a plurality of fuel injection events.

11 . The system of claim 10 , wherein the controller is further configured to increase the amplitude when the measured control valve is lower than the expected control valve return time.

12 . The system of claim 10 , wherein the controller is further configured to increase the amplitude across a plurality of amplitude levels based on a plurality of measured control valve return times for the fuel injector.

13 . The system of claim 10 , wherein the system includes a plurality of fuel injectors, the controller being further configured to determine different current amplitudes for respective fuel injectors.