Method for improving closely-spaced multiple-injection performance from solenoid actuated fuel injectors

1. Method for controlling an electromagnetically-activated fuel injector in an internal combustion engine, comprising:

monitoring operation of the engine, the operation comprising a plurality of fuel injection events per cylinder per combustion cycle;

when the monitored operation indicates a dwell time between two consecutive fuel injection events being less than a dwell time threshold,

monitoring a respective desired injected fuel mass for each of the plurality of fuel injection events;

selecting a desired current waveform from a plurality of current waveforms whereat each respective desired injected fuel mass is achieved based on at least one of the fuel injection events; and

controlling the fuel injector using the desired current waveform;

wherein the dwell time threshold is selected based upon calibrated short dwell times that cause instability in fuel injection mass.

2. The method of claim 1 , wherein selecting the desired current waveform comprises:

for each of the plurality of current waveforms:

mapping injection duration versus delivered injected fuel mass for each fuel injection event;

selecting a respective injection duration for each of the fuel injection events whereat a respective delivered injected fuel mass achieves the respective desired injected fuel mass based on the mapping; and

selecting the desired current waveform whereat the respective delivered injected fuel mass repeatedly achieves the respective desired injected fuel mass for each fuel injection event.

3. The method of claim 2 , wherein selecting the desired current waveform further comprises:

for each fuel injection event that is subsequent to a first fuel injection event, selecting the desired current waveform whereat the respective delivered injected fuel mass repeatedly achieves the respective desired injected fuel mass using the respective injection duration for an immediately preceding fuel injection event.

4. The method of claim 2 , wherein selecting the desired current waveform further comprises:

for each fuel injection event that is subsequent to a first fuel injection event, selecting the desired current waveform whereat the respective delivered injected fuel mass repeatedly achieves the respective desired injected fuel mass using at least the respective injection duration for the first fuel injection event of the plurality of fuel injection events.

5. The method of claim 2 , wherein the respective delivered injected fuel mass repeatedly achieves the respective desired injected fuel mass for each fuel injection event when the respective delivered injected fuel mass comprises an actual deviation from the respective desired injected fuel mass that violates a deviation threshold.

6. The method of claim 5 , wherein the actual deviation from the respective desired injected fuel mass is determined by:

mapping injection duration versus deviation from the respective desired injected fuel mass for each of the fuel injection events;

determining the actual deviation from the respective desired injected fuel mass for a first fuel injection event using the respective injection duration selected for the first fuel injection event; and

determining the actual deviation from the respective desired injected fuel mass for each fuel injection event that is subsequent to the first fuel injection event using the respective injection duration selected for at least one of the one or more preceding fuel injection events and the respective injection duration for the corresponding fuel injection event.

7. The method of claim 1 , wherein the dwell time between consecutive fuel injection events defines a period of time between an end of injection for the first of the consecutive fuel injection events and a start of injection for the subsequent of the consecutive fuel injection events.

8. The method of claim 1 , wherein the dwell time threshold is selected such that dwell times less than the dwell time threshold are indicative of producing instability in the fuel injection events.

9. The method of claim 1 , wherein the plurality of fuel injection events comprise a first fuel injection event and two or more fuel injection events subsequent to the first fuel injection event.

10. Method for controlling an electromagnetically-activated fuel injector in an internal combustion engine, comprising:

monitoring operation of the engine, the operation comprising a plurality of fuel injection events per cylinder per combustion cycle;

for each fuel injection event of one or more consecutive fuel injection events having respective dwell times less than a dwell time threshold:

monitoring a respective desired injected fuel mass to be delivered by the fuel injector;

selecting a respective desired current waveform from a plurality of current waveforms, comprising

for each of the plurality of current waveforms, mapping injection duration versus delivered injected fuel mass and selecting a respective injection duration whereat a respective delivered injected fuel mass achieves the respective desired injected fuel mass, and

selecting the respective desired current waveform whereat the respective delivered injected fuel mass repeatedly achieves the respective desired injected fuel mass; and

controlling the fuel injector using the respective desired current waveform selected for each fuel injection event of the one or more consecutive fuel injection events having respective dwell times less than the dwell time threshold;

wherein the dwell time threshold is selected based upon calibrated short dwell times that cause instability in fuel injection mass.

11. The method of claim 10 , wherein the respective desired current waveforms selected for the fuel injection event are identical.

12. The method of claim 10 , wherein the respective desired current waveforms selected for the fuel injection events comprise at least one of the fuel injection events having a respective desired current waveform that is different from each respective desired current waveform of the one or more other fuel injection events.

13. The method of claim 10 , wherein selecting the respective desired current waveform whereat the respective delivered injected fuel mass repeatedly achieves the respective desired injected fuel mass comprises:

for each second fuel injection event of one or more consecutive pairs of fuel injection events, selecting the respective desired current waveform whereat the respective delivered injected fuel mass repeatedly achieves the respective desired injected fuel mass using the respective injection duration for the corresponding first fuel injection event of each consecutive pair.

14. The method of claim 10 , wherein each of the plurality of current waveforms is characterized by an initial peak pull-in current and a secondary hold current.

15. The method of claim 10 , wherein the respective delivered injected fuel mass repeatedly achieves the respective desired injected fuel mass for each fuel injection event when the respective delivered injected fuel mass comprises an actual deviation from the respective desired injected fuel mass that is less than a deviation threshold.

16. The method of claim 15 , wherein the actual deviation from the respective desired injected fuel mass is determined by:

mapping injection duration versus deviation from the respective desired injected fuel mass for each of the fuel injection events;

determining the actual deviation from the respective desired injected fuel mass for a first fuel injection event using the respective injection duration for the first fuel injection event; and

determining the actual deviation from the respective desired injected fuel mass for each fuel injection event that is subsequent to the first fuel injection event using the respective injection duration for the one or more preceding fuel injection events and the respective injection duration for the corresponding fuel injection event.

17. The method of claim 10 , further comprising:

selecting a fixed current waveform when the respective dwell times are at least the predetermined dwell time threshold.