Abstract:
An electromagnetic actuation system includes an actuator having an electrical coil, a magnetic core, and an armature. The system further includes a controllable drive circuit for selectively driving current through the electrical coil. A control module provides an actuator command to the drive circuit effective to drive current through the electrical coil to actuate the armature. The control module includes a magnetic force control module configured to adapt the actuator command to converge magnetic force within the actuator to a preferred force level.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 61/968,007, filed on Mar. 20, 2014, and U.S. Provisional Application No. 61/955,942, filed on Mar. 20, 2014, both of which are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     This disclosure is related to solenoid-activated actuators. 
     BACKGROUND 
     The statements in this section merely provide background information related to the present disclosure. Accordingly, such statements are not intended to constitute an admission of prior art. 
     Solenoid actuators can be used to control fluids (liquids and gases), or for positioning or for control functions. A typical example of a solenoid actuator is the fuel injector. Fuel injectors are used to inject pressurized fuel into a manifold, an intake port, or directly into a combustion chamber of internal combustion engines. Known fuel injectors include electromagnetically-activated solenoid devices that overcome mechanical springs to open a valve located at a tip of the injector to permit fuel flow therethrough. Injector driver circuits control flow of electric current to the electromagnetically-activated solenoid devices to open and close the injectors. Injector driver circuits may operate in a peak-and-hold control configuration or a saturated switch configuration. 
     Fuel injectors are calibrated, with a calibration including an injector activation signal including an injector open-time, or injection duration, and a corresponding metered or delivered injected fuel mass operating at a predetermined or known fuel pressure. Injector operation may be characterized in terms of injected fuel mass per fuel injection event in relation to injection duration. Injector characterization includes metered fuel flow over a range between high flow rate associated with high-speed, high-load engine operation and low flow rate associated with engine idle conditions. 
     It is known for engine control to benefit from injecting a plurality of small injected fuel masses in rapid succession. Generally, when a dwell time between consecutive injection events is less than a dwell time threshold, injected fuel masses of subsequent fuel injection events often result in a larger delivered magnitude than what is desired even through equal injection durations are utilized. Accordingly, such subsequent fuel injection events can become unstable resulting in unacceptable repeatability. This undesirable occurrence is attributed to the existence of residual magnetic flux within the fuel injector that is produced by the preceding fuel injection event that offers some assistance to the immediately subsequent fuel injection event. The residual magnetic flux is produced in response to persistent eddy currents and magnetic hysteresis within the fuel injector as a result of shifting injected fuel mass rates that require different initial magnetic flux values. Generally, the fuel flow rate for each of the closely spaced multiple injection events is based upon controlling electrical current to the fuel injector independent of residual magnetic flux that may be present within the fuel injector. 
     SUMMARY 
     An electromagnetic actuation system includes an actuator having an electrical coil, a magnetic core, and an armature. The system further includes a controllable drive circuit for selectively driving current through the electrical coil. A control module provides an actuator command to the drive circuit effective to drive current through the electrical coil to actuate the armature. The control module includes a magnetic force control module configured to adapt the actuator command to converge magnetic force within the actuator to a preferred force level 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       One or more embodiments will now be described, by way of example, with reference to the accompanying drawings, in which: 
         FIG. 1-1  illustrates a schematic sectional view of a fuel injector and an activation controller, in accordance with the present disclosure; 
         FIG. 1-2  illustrates a schematic sectional view of the activation controller of  FIG. 1-1 , in accordance of the present disclosure; 
         FIG. 1-3  illustrates a schematic sectional view of an injector driver of  FIGS. 1-1 and 1-2 , in accordance to the present disclosure; 
         FIG. 2  illustrates a non-limiting exemplary first plot  1000  of measured current and fuel flow rate and a non-limiting exemplary second plot  1010  of measured main excitation coil and search coil voltages for two successive fuel injection events having identical current pulses that are separated by a dwell time that is not indicative of being closely spaced, in accordance with the present disclosure; 
         FIG. 3  illustrates a non-limiting exemplary first plot  1020  of measured current and fuel flow rate and a non-limiting exemplary second plot  1030  of measured main excitation coil and search coil voltages for two successive fuel injection events having identical current pulses that are separated by a dwell time that is indicative of being closely spaced, in accordance with the present disclosure; 
         FIG. 4  illustrates an exemplary embodiment of a magnetic force control module using magnetic flux feedback and current feedback to control current applied to an electrical coil of a fuel injector for controlling activation thereof, in accordance with the present disclosure; and 
         FIG. 5  illustrates an exemplary embodiment of a magnetic force control module using magnetic flux feedback to control current applied to an electrical coil of a fuel injector for controlling activation thereof, in accordance with the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     This disclosure describes the concepts of the presently claimed subject matter with respect to an exemplary application to linear motion fuel injectors. However, the claimed subject matter is more broadly applicable to any linear or non-linear electromagnetic actuator that employs an electrical coil for inducing a magnetic field within a magnetic core resulting in an attractive force acting upon a movable armature. Typical examples include fluid control solenoids, gasoline or diesel or CNG fuel injectors employed on internal combustion engines and non-fluid solenoid actuators for positioning and control. 
     Referring now to the drawings, wherein the showings are for the purpose of illustrating certain exemplary embodiments only and not for the purpose of limiting the same,  FIG. 1  schematically illustrates a non-limiting exemplary embodiment of an electromagnetically-activated direct-injection fuel injector  10 . While an electromagnetically-activated direct-injection fuel injector is depicted in the illustrated embodiment, a port-injection fuel injector is equally applicable. The fuel injector  10  is configured to inject fuel directly into a combustion chamber  100  of an internal combustion engine. An activation controller  80  electrically operatively connects to the fuel injector  10  to control activation thereof. The activation controller  80  corresponds to only the fuel injector  10 . In the illustrated embodiment, the activation controller  80  includes a control module  60  and an injector driver  50 . The control module  60  electrically operatively connects to the injector driver  50  that electrically operatively connects to the fuel injector  10  to control activation thereof. Feedback signal(s)  42  may be provided from the fuel injector to the actuation controller  80 . The fuel injector  10 , control module  60  and injector driver  50  may be any suitable devices that are configured to operate as described herein. In the illustrated embodiment, the control module  60  includes a processing device. In one embodiment, one or more components of the activation controller  80  are integrated within a connection assembly  36  of the fuel injector  36 . In another embodiment, one or more components of the activation controller  80  are integrated within a body  12  of the fuel injector  10 . In even yet another embodiment, one or more components of the activation controller  80  are external to—and in close proximity with—the fuel injector  10  and electrically operatively connected to the connection assembly  36  via one or more cables and/or wires. The terms “cable” and “wire” will be used interchangeably herein to provide transmission of electrical power and/or transmission of electrical signals. 
     Control module, module, control, controller, control unit, processor and similar terms mean any one or various combinations of one or more of Application Specific Integrated Circuit(s) (ASIC), electronic circuit(s), central processing unit(s) (preferably microprocessor(s)) and associated memory and storage (read only, programmable read only, random access, hard drive, etc.) executing one or more software or firmware programs or routines, combinational logic circuit(s), input/output circuit(s) and devices, appropriate signal conditioning and buffer circuitry, and other components to provide the described functionality. Software, firmware, programs, instructions, routines, code, algorithms and similar terms mean any instruction sets including calibrations and look-up tables. The control module has a set of control routines executed to provide the desired functions. Routines are executed, such as by a central processing unit, and are operable to monitor inputs from sensing devices and other networked control modules, and execute control and diagnostic routines to control operation of actuators. Routines may be executed at regular intervals, for example each 3.125, 6.25, 12.5, 25 and 100 milliseconds during ongoing engine and vehicle operation. Alternatively, routines may be executed in response to occurrence of an event. 
     In general, an armature is controllable to one of an actuated position and a static or rest position. The fuel injector  10  may be any suitable discrete fuel injection device that is controllable to one of an open (actuated) position and a closed (static or rest) position. In one embodiment, the fuel injector  10  includes a cylindrically-shaped hollow body  12  defining a longitudinal axis  101 . A fuel inlet  15  is located at a first end  14  of the body  12  and a fuel nozzle  28  is located at a second end  16  of the body  12 . The fuel inlet  15  is fluidly coupled to a high-pressure fuel line  30  that fluidly couples to a high-pressure injection pump. A valve assembly  18  is contained in the body  12 , and includes a needle valve  20 , a spring-activated pintle  22  and an armature portion  21 . The needle valve  20  interferingly seats in the fuel nozzle  28  to control fuel flow therethrough. While the illustrated embodiment depicts a triangularly-shaped needle valve  20 , other embodiments may utilize a ball. In one embodiment, the armature portion  21  is fixedly coupled to the pintle  22  and configured to linear translate as a unit with the pintle  22  and the needle valve  20  in first and second directions  81 ,  82 , respectively. In another embodiment, the armature portion  21  may be slidably coupled to the pintle  22 . For instance, the armature portion  21  may slide in the first direction  81  until being stopped by a pintle stop fixedly attached to the pintle  22 . Likewise, the armature portion  21  may slide in the second direction  82  independent of the pintle  22  until contacting a pintle stop fixedly attached to the pintle  22 . Upon contact with the pintle stop fixedly attached to the pintle  22 , the force of the armature portion  21  causes the pintle  22  to be urged in the second direction  82  with the armature portion  21 . The armature portion  21  may include protuberances to engage with various stops within the fuel injector  10 . 
     An annular electromagnet assembly  24 , including an electrical coil and magnetic core, is configured to magnetically engage the armature portion  21  of the valve assembly. The electrical coil and magnetic core assembly  24  is depicted for illustration purposes to be outside of the body of the fuel injector; however, embodiments herein are directed toward the electrical coil and magnetic core assembly  24  to be either integral to, or integrated within, the fuel injector  10 . The electrical coil is wound onto the magnetic core, and includes terminals for receiving electrical current from the injector driver  50 . Hereinafter, the “electrical coil and magnetic core assembly” will simply be referred to as an “electrical coil  24 ”. When the electrical coil  24  is deactivated and de-energized, the spring  26  urges the valve assembly  18  including the needle valve  20  toward the fuel nozzle  28  in the first direction  81  to close the needle valve  20  and prevent fuel flow therethrough. When the electrical coil  24  is activated and energized, electromagnetic force (herein after “magnetic force”) acts on the armature portion  21  to overcome the spring force exerted by the spring  26  and urges the valve assembly  18  in the second direction  82 , moving the needle valve  20  away from the fuel nozzle  28  and permitting flow of pressurized fuel within the valve assembly  18  to flow through the fuel nozzle  28 . A search coil  25  is mutually magnetically coupled to the electrical coil  24  and is preferably wound axially or radially adjacent coil  24 . Search coil  25  is utilized as a sensing coil. 
     The fuel injector  10  may include a stopper  29  that interacts with the valve assembly  18  to stop translation of the valve assembly  18  when it is urged to open. In one embodiment, a pressure sensor  32  is configured to obtain fuel pressure  34  in the high-pressure fuel line  30  proximal to the fuel injector  10 , preferably upstream of the fuel injector  10 . In another embodiment, a pressure sensor may be integrated within the inlet  15  of the fuel injector in lieu of the pressure sensor  32  in the fuel rail  30  or in combination with the pressure sensor. The fuel injector  10  in the illustrated embodiment of  FIG. 1-1  is not limited to the spatial and geometric arrangement of the features described herein, and may include additional features and/or other spatial and geometric arrangements known in the art for operating the fuel injector  10  between open and closed positions for controlling the delivery of fuel to the engine  100 . 
     The control module  60  generates an injector command (actuator command) signal  52  that controls the injector driver  50 , which activates the fuel injector  10  to the open position for affecting a fuel injection event. In the illustrated embodiment, the control module  60  communicates with one or more external control modules such as an engine control module (ECM)  5 ; however, the control module  60  may be integral to the ECM in other embodiments. The injector command signal  52  correlates to a desired mass of fuel to be delivered by the fuel injector  10  during the fuel injection event. Similarly, the injector command signal  52  may correlate to a desired fuel flow rate to be delivered by the fuel injector  10  during the fuel injection event. As used herein, the term “desired injected fuel mass” refers to the desired mass of fuel to be delivered to the engine by the fuel injector  10 . As used herein, the term “desired fuel flow rate” refers to the rate at which fuel is to be delivered to the engine by the fuel injector  10  for achieving the desired mass of fuel. The desired injected fuel mass can be based upon one or more monitored input parameters  51  input to the control module  60  or ECM  5 . The one or more monitored input parameters  51  may include, but are not limited to, an operator torque request, manifold absolute pressure (MAP), engine speed, engine temperature, fuel temperature, and ambient temperature obtained by known methods. The injector driver  50  generates an injector activation (actuator activation) signal  75  in response to the injector command signal  52  to activate the fuel injector  10 . The injector activation signal  75  controls current flow to the electrical coil  24  to generate electromagnetic force in response to the injector command signal  52 . An electric power source  40  provides a source of DC electric power for the injector driver  50 . In some embodiments, the DC electric power source provides low voltage, e.g., 12 V, and a boost converter may be utilized to output a high voltage, e.g., 24V to 200 V, that is supplied to the injector driver  50 . When activated using the injector activation signal  75 , the electromagnetic force generated by the electrical coil  24  urges the armature portion  21  in the second direction  82 . When the armature portion  21  is urged in the second direction  82 , the valve assembly  18  in consequently caused to urge or translate in the second direction  82  to an open position, allowing pressurized fuel to flow therethrough. The injector driver  50  controls the injector activation signal  75  to the electrical coil  24  by any suitable method, including, e.g., pulsewidth-modulate (PWM) electric power flow. The injector driver  50  is configured to control activation of the fuel injector  10  by generating suitable injector activation signals  75 . In embodiments that employ a plurality of successive fuel injection events for a given engine cycle, an injector activation signal  75  that is fixed for each of the fuel injection events within the engine cycle may be generated. 
     The injector activation signal  75  is characterized by an injection duration and a current waveform that includes an initial peak pull-in current and a secondary hold current. The initial peak pull-in current is characterized by a steady-state ramp up to achieve a peak current, which may be selected as described herein. The initial peak pull-in current generates electromagnetic force that acts on the armature portion  21  of the valve assembly  18  to overcome the spring force and urge the valve assembly  18  in the second direction  82  to the open position, initiating flow of pressurized fuel through the fuel nozzle  28 . When the initial peak pull-in current is achieved, the injector driver  50  reduces the current in the electrical coil  24  to the secondary hold current. The secondary hold current is characterized by a somewhat steady-state current that is less than the initial peak pull-in current. The secondary hold current is a current level controlled by the injector driver  50  to maintain the valve assembly  18  in the open position to continue the flow of pressurized fuel through the fuel nozzle  28 . The secondary hold current is preferably indicated by a minimum current level. The injector driver  50  is configured as a bi-directional current driver capable of providing a negative current flow for drawing current from the electrical coil  24 . As used herein, the term “negative current flow” refers to the direction of the current flow for energizing the electrical coil to be reversed. Accordingly, the terms “negative current flow” and “reverse current flow” are used interchangeably herein. 
     Embodiments herein are directed toward controlling the fuel injector for a plurality of fuel injection events that are closely-spaced during an engine cycle. As used herein, the term “closely-spaced” refers to a dwell time between each consecutive fuel injection event being less than a predetermined dwell time threshold. As used herein, the term “dwell time” refers to a period of time between an end of injection for the first fuel injection event (actuator event) and a start of injection for a corresponding second fuel injection event (actuator event) of each consecutive pair of fuel injection events. The dwell time threshold can be selected to define a period of time such that dwell times less than the dwell time threshold are indicative of producing instability and/or deviations in the magnitude of injected fuel mass delivered for each of the fuel injection events. The instability and/or deviations in the magnitude of injected fuel mass may be responsive to a presence of secondary magnetic effects. The secondary magnetic effects include persistent eddy currents and magnetic hysteresis within the fuel injector and a residual flux based thereon. The persistent eddy currents and magnetic hysteresis are present due to transitions in initial flux values between the closely-spaced fuel injection events. Accordingly, the dwell time threshold is not defined by any fixed value, and selection thereof may be based upon, but not limited to, fuel temperature, fuel injector temperature, fuel injector type, fuel pressure and fuel properties such as fuel types and fuel blends. As used herein, the term “flux” refers to magnetic flux indicating the total magnetic field generated by the electrical coil  24  and passing through the armature portion. Since the turns of the electrical coil  24  link the magnetic flux in the magnetic core, this flux can therefore be equated from the flux linkage. The flux linkage is based upon the flux density passing through the armature portion, the surface area of the armature portion adjacent to the air gap and the number of turns of the coil  24 . Accordingly, the terms “flux”, “magnetic flux” and “flux linkage” will be used interchangeably herein unless otherwise stated. 
     For fuel injection events that are not closely spaced, a fixed current waveform independent of dwell time may be utilized for each fuel injection event because the first fuel injection event of a consecutive pair has little influence on the delivered injected fuel mass of the second fuel injection event of the consecutive pair. However, the first fuel injection event may be prone to influence the delivered injected fuel mass of the second fuel injection event, and/or further subsequent fuel injection events, when the first and second fuel injection events are closely-spaced and a fixed current wave form is utilized. Any time a fuel injection event is influenced by one or more preceding fuel injection events of an engine cycle, the respective delivered injected fuel mass of the corresponding fuel injection event can result in an unacceptable repeatability over the course of a plurality of engine cycles and the consecutive fuel injection events are considered closely-spaced. More generally, any consecutive actuator events wherein residual flux from the preceding actuator event affects performance of the subsequent actuator event relative to a standard, for example relative to performance in the absence of residual flux, are considered closely-spaced. 
       FIG. 1-2  illustrates the activation controller  80  of  FIG. 1-1 , in accordance with the present disclosure. Signal flow path  362  provides communication between the control module  60  and the injector driver  50 . For instance, signal flow path  362  provides the injector command signal (e.g., command signal  52  of  FIG. 1-1 ) that controls the injector driver  50 . The control module  60  further communicates with the external ECM  5  via signal flow path  364  within the activation controller  380  that is in electrical communication with a power transmission cable. For instance, signal flow path  364  may provide monitored input parameters (e.g., monitored input parameters  51  of  FIG. 1-1 ) from the ECM  5  to the control module  60  for generating the injector command signal  52 . In some embodiments, the signal flow path  364  may provide feedback fuel injector parameters (e.g., feedback signal(s)  42  of  FIG. 1-1 ) to the ECM  5 . 
     The injector driver  50  receives DC electric power from the power source  40  of  FIG. 1-1  via a power supply flow path  366 . The signal flow path  364  can be eliminated by use of a small modulation signal added to the power supply flow path  366 . Using the received DC electric power, the injector driver  50  may generate injector activation signals (e.g., injector activation signals  75  of  FIG. 1-1 ) based on the injector command signal from the control module  60 . 
     The injector driver  50  is configured to control activation of the fuel injector  10  by generating suitable injector activation signals  75 . The injector driver  50  is a bi-directional current driver providing positive current flow via a first current flow path  352  and negative current flow via a second current flow path  354  to the electrical coil  24  in response to respective injector activation signals  75 . The positive current via the first current flow path  352  is provided to energize an electrical coil  24  and the negative current via the second current flow path  354  reverses current flow to draw current from the electrical coil  24 . Current flow paths  352  and  354  form a closed loop; that is, a positive current into  352  results in an equal and opposite (negative) current in flow path  354 , and vice versa. Signal flow path  371  can provide a voltage of the first current flow path  352  to the control module  60  and signal flow path  373  can provide a voltage of the second current flow path  354  to the control module  60 . The voltage and current applied to the electrical coil  24  is based on a difference between the voltages at the signal flow paths  371  and  373 . In one embodiment, the injector driver  50  utilizes open loop operation to control activation of the fuel injector  10 , wherein the injector activation signals are characterized by precise predetermined current waveforms. In another embodiment, the injector driver  50  utilizes closed loop operation to control activation of the fuel injector  10 , wherein the injector activation signals are based upon fuel injector parameters provided as feedback to the control module, via the signal flow paths  371  and  373 . A measured current flow to the coil  24  can be provided to the control module  60 , via signal flow path  356 . In the illustrated embodiment, the current flow is measured by a current sensor on the second current flow path  354 . The fuel injector parameters may include flux linkage, voltage and current values within the fuel injector  10  or the fuel injector parameters may include proxies used by the control module  60  to estimate flux linkage, voltage and current within the fuel injector  10 . 
     In some embodiments, the injector driver  50  is configured for full four quadrant operation.  FIG. 1-3  illustrates an exemplary embodiment of the injector driver  50  of  FIGS. 1-2  utilizing two switch sets  370  and  372  to control the current flow provided between the injector driver  50  and the electrical coil  24 . In the illustrated embodiment, the first switch set  370  includes switch devices  370 - 1  and  370 - 2  and the second switch set  372  includes switch devices  372 - 1  and  372 - 2 . The switch devices  370 - 1 ,  370 - 2 ,  372 - 1 ,  372 - 2  can be solid state switches and may include Silicon (Si) or wide band gap (WBG) semiconductor switches enabling high speed switching at high temperatures. The four quadrant operation of the injector driver  50  controls the direction of current flow into and out of the electrical coil  24  based upon a corresponding switch state determined by the control module  60 . The control module  60  may determine a positive switch state, a negative switch state and a zero switch state and command the first and second switch sets  370  and  372  between open and closed positions based on the determined switch state. In the positive switch state, the switch devices  370 - 1  and  370 - 2  of the first switch set  370  are commanded to the closed position and the switch devices  372 - 1  and  372 - 2  of the second switch set  372  are commanded to the open position to control positive current into the first current flow path  352  and out of the second current flow path  354 . These switch devices may be further modulated using pulse width modulation to control the amplitude of the current. In the negative switch state, the switch devices  370 - 1  and  370 - 2  of the first switch set  370  are commanded to the open position and the switch devices  372 - 1  and  372 - 2  of the second switch leg  372  are commanded to the closed position to control negative current into the second current flow path  354  and out of the first current flow path  352 . These switch devices may be further modulated using pulse width modulation to control the amplitude of the current. In the zero switch state, all the switch devices  370 - 1 ,  370 - 2 ,  372 - 1 ,  372 - 2  are commanded to the open position to control no current into or out of the electromagnetic assembly. Thus, bi-directional control of current through the coil  24  may be effected. 
     In some embodiments, the negative current for drawing current from the electrical coil  24  is applied for a sufficient duration for reducing residual flux within the fuel injector  10  after a secondary hold current is released. In other embodiments, the negative current is applied subsequent to release of the secondary hold current but additionally only after the fuel injector has closed or actuator has returned to its static or rest position. Moreover, additional embodiments can include the switch sets  370  and  372  to be alternately switched between open and closed positions to alternate the direction of the current flow to the coil  24 , including pulse width modulation control to effect current flow profiles. The utilization of two switch sets  370  and  372  allows for precise control of current flow direction and amplitude applied to the current flow paths  352  and  354  of the electrical coil  24  for multiple consecutive fuel injection events during an engine event by reducing the presence of eddy currents and magnetic hysteresis within the electrical coil  24 . 
       FIG. 2  illustrates a non-limiting exemplary first plot  1000  of measured current and fuel flow rate and a non-limiting exemplary second plot  1010  of measured main excitation coil and search coil voltages for two successive fuel injection events having identical current pulses that are separated by a dwell time that is not indicative of being closely spaced. Dashed vertical line  1001  extending through each of plots  1000  and  1010  represents a first time whereat an end of injection for the first fuel injection event occurs and dashed vertical line  1002  represents a second time whereat a start of injection for the second fuel injection event occurs. The dwell time  1003  represents a period of time between dashed vertical lines  1001  and  1002  separating the first and second fuel injection events. In the illustrated embodiment, the dwell time exceeds a dwell time threshold. Thus, the first and second fuel injection events are not indicative of being closely-spaced. 
     Referring to the first plot  1000 , measured current and flow rate profiles  1011 ,  1012 , respectively, are illustrated for the two fuel injection events. The vertical y-axis along the left side of plot  1000  denotes electrical current in Amperage (A) and the vertical y-axis along the right side of plot  1000  denotes fuel flow rate in milligrams (mg) per milliseconds (ms). The measured current profile  1011  is substantially identical for each of the fuel injection events. Likewise, the measured fuel flow rate profile  1012  is substantially identical for each of the fuel injection events due to the fuel injection events not indicative of being closely-spaced. 
     Referring to the second plot  1010 , measured main excitation coil and search coil voltage profiles  1013 ,  1014 , respectively, are illustrated for the two fuel injection events. The measured main coil voltage may represent a measured voltage of the electrical coil  24  of  FIG. 1-1  and the measured search coil voltage may represent a measured voltage of a search coil mutually magnetically coupled to the electrical coil  24  of  FIG. 1-1 . The vertical y-axis of plot  1010  denotes voltage (V). Accordingly, when the main excitation coil is energized, magnetic flux generated by the main excitation coil may be linked to the search coil due to the mutual magnetic coupling. The measured search coil voltage profile  1014  indicates the voltage induced in the search coil which is proportional to the rate of change of the mutual flux-linkage. The measured main excitation coil and search coil voltage profiles  1013 ,  1014 , respectively, of plot  1010  are substantially identical for each of the first and second fuel injection events that are not indicative of being closely-spaced. 
       FIG. 3  illustrates a non-limiting exemplary first plot  1020  of measured current and fuel flow rate and a non-limiting exemplary second plot  1030  of measured main excitation coil and search coil voltages for two successive fuel injection events having identical current pulses that are separated by a dwell time that is indicative of being closely spaced. The horizontal x-axis in each of plots  1020  and  1030  denotes time in seconds (s). Dashed vertical line  1004  extending through each of plots  1020  and  1030  represents a first time whereat an end of injection for the first fuel injection event occurs and dashed vertical line  1005  represents a second time whereat a start of injection for the second fuel injection event occurs. The dwell time  1006  represents a period of time between dashed vertical lines  1004  and  1005  separating the first and second fuel injection events. In the illustrated embodiment, the dwell time is less than a dwell time threshold. Thus, the first and second fuel injection events are indicative of being closely-spaced. 
     Referring to the first plot  1020 , measured current and flow rate profiles  1021 ,  1022 , respectively, are illustrated for the two fuel injection events. The vertical y-axis along the left side of plot  1020  denotes electrical current in Amperage (A) and the vertical y-axis along the right side of plot  1020  denotes fuel flow rate in milligrams (mg) per second (s). The measured current profile  1021  is substantially identical for each of the fuel injection events. However, the measured flow rate profile  1022  illustrates a variation in the measured fuel flow rate between each of the first and second fuel injection events even though the measured current profiles are substantially identical. This variance in the measured fuel flow rate is inherent in closely-spaced fuel injection events and undesirably results in an injected fuel mass delivered at the second fuel injection event that is different than an injected fuel mass delivered at the first fuel injection event. 
     Referring to the second plot  1030 , measured main excitation coil and search coil voltage profiles  1023 ,  1024 , respectively, are illustrated for the two fuel injection events. The measured main coil voltage may represent a measured voltage of the electrical coil  24  of  FIG. 1-1  and the measured search coil voltage may represent a measured voltage of a search coil mutually magnetically coupled to the electrical coil  24  of  FIG. 1-1 . The vertical y-axis of plot  1030  denotes voltage (V). Accordingly, when the main excitation coil is energized, magnetic flux generated by the main excitation coil may be linked to the search coil due to the mutual magnetic coupling. The measured search coil voltage profile  1024  indicates the voltage induced in the search coil which is proportional to the rate of change of the mutual flux-linkage. The measured main excitation coil and search coil voltage profiles  1023 ,  1024 , respectively, of plot  1030  differ during the second injection event in comparison to the first fuel injection event. This difference is indicative of the presence of residual flux or magnetic flux when the injection events are closely-spaced. Referring to plot  1010  of  FIG. 2  the measured main excitation coil and search coil voltage profiles  1013 ,  1014 , respectively do not differ during the second injection event in comparison to the first fuel injection event when the first and second fuel injection events are not closely-spaced. 
     Referring back to  FIG. 1-1 , exemplary embodiments are further directed toward providing feedback signal(s)  42  from the fuel injector  10  back to the control module  60  and/or the injector driver  50 . Discussed in greater detail below, sensor devices may be integrated within the fuel injector  10  for measuring various fuel injector parameters for obtaining the flux linkage of the electrical coil  24 , voltage of the electrical coil  24  and current provided to the electrical coil  24 . A current sensor may be provided on a current flow path between the activation controller  80  and the fuel injector to measure the current provided to the electrical coil or the current sensor can be integrated within the fuel injector  10  on the current flow path. The fuel injector parameters provided via feedback signal(s)  42  may include the flux linkage, voltage and current directly measured by corresponding sensor devices integrated within the fuel injector  10 . Additionally or alternatively, the fuel injector parameters may include proxies provided via feedback signal(s)  42  to—and used by—the control module  60  to estimate the flux linkage, magnetic flux, the voltage, and the current within the fuel injector  10 . Having feedback of the flux linkage of the electrical coil  24 , the voltage of the electrical coil  24  and current provided to the electrical coil  24 , the control module  60  may advantageously modify the activation signal  75  to the fuel injector  10  for multiple consecutive injection events. It will be understood that conventional fuel injectors are controlled by open loop operation based solely upon a desired current waveform obtained from look-up tables without any information related to the force producing component of the flux linkage (e.g., magnetic flux) affecting movement of the armature portion  21 . As a result, conventional feed-forward fuel injectors that only account for current flow for controlling the fuel injector, and are prone to instability in consecutive fuel injection events that are closely-spaced. 
     Embodiments herein are directed toward controlling the active magnetic flux within the fuel injector to directly control the electromagnetic force that urges the armature portion  21  in the second direction  82 . Controlling the electromagnetic force directly through controlling the active magnetic flux is operative to overcome undesirable delays and instabilities caused by secondary magnetic effects like eddy currents and magnetic hysteresis within the fuel injector. As aforementioned, the electromagnetic force is generated when the electrical coil  24  is energized. This electromagnetic force is produced by the active magnetic flux passing through the armature portion  21  within the fuel injector  10 . It will be understood that the active magnetic flux is equivalent to the flux linkage divided by the number of turns of the coil  24  in the embodiments described herein because the electrical coil  24  is energized through typical induction. Accordingly, implementation of active magnetic flux control to directly control the magnetic force requires that the flux linkage of the electrical coil  24  be obtained. 
     Embodiments herein are not concerned with any one technique for obtaining the active magnetic flux or the equivalent flux linkage. In some embodiments, a search coil may be utilized around the electrical coil, wherein magnetic flux created by the main coil links the search coil due to mutual magnetic coupling. Voltage induced in the search coil is proportional to the rate of change of the mutual flux linkage. Accordingly, the voltage of the search coil can be provided via feedback signal(s)  42  to the control module  60  for estimating the flux linkage. Thus, the search coil is indicative of sensing devices integrated within the fuel injector  10  for obtaining the flux linkage. In other embodiments, a magnetic field sensor such as a hall sensor may be positioned within a magnetic flux path within the fuel injector for measuring the active magnetic flux. Similarly, other magnetic field sensors can be utilized to measure the active magnetic flux such as, but not limited to, analog hall sensors and Magnetoresistive (MR) type sensors. The active magnetic flux measured by such magnetic field sensors can be provided via feedback signal(s)  42  to the control module  60 . It is understood that these magnetic field sensors are indicative of sensing devices integrated within the fuel injector for obtaining the active magnetic flux. 
       FIG. 4  illustrates an exemplary embodiment of a magnetic force control module using magnetic flux feedback and current feedback to control current applied to an electrical coil of a fuel injector for controlling activation thereof. The magnetic force control module  300  may be implemented within—and executed by a processing device of—the control module  60  of the activation controller  80  of  FIG. 1-1 . Accordingly, the magnetic force control module  300  will be described with reference to  FIG. 1-1 . The magnetic force control module  300  includes a force command generation (FCG) module  310 , a first difference unit  312 , a proportional integral (PI) force control module  314 , a second difference unit  316 , a PI current control module  318 , an injector driver  320 , a current sensor  322  and a force mapping module  324 . The control module  60  of the activation controller  80  of  FIG. 1-1  may encompass the FCG module  310 , the first and second difference units  312 ,  316 , respectively, the PI force control module  314  and the force mapping module  324 . The injector driver  50  of the force activation controller  80  of  FIG. 1-1  may encompass the PI current control module  318  and the injector driver  320 . However, the control module  60  and injector driver  50  may encompass different combinations of those features listed above. 
     In the illustrated embodiment, a desired fuel flow rate  309  is input to the FCG module  310 . The desired fuel flow rate  309  may be provided from an external module, e.g., the ECM  5 , based on the aforementioned input parameters  51  for achieving a desired injected fuel mass, as described above with reference to  FIG. 1-1 . The FCG module  310  outputs a magnetic force command  311  based on the desired fuel flow rate  309 . The magnetic force command  311  is indicative of a command to generate a magnetic force required to move the armature portion  21  in the second direction  82  to activate the fuel injector  10  in the open position to deliver the desired fuel flow rate  309  to the combustion chamber  100 . However, it will be appreciated that the magnetic force command  311  does not account for the presence of residual flux, e.g., magnetic flux, present within the fuel injector due to hysteretic and eddy current effect. The presence of residual flux may cause instability within the fuel injector that may impact fuel flow rates and injected fuel masses being delivered to the combustion chamber. Accordingly, moving the armature portion  21  based solely upon the magnetic force command may result in a fuel flow rate actually delivered to the combustion chamber that deviates from the desired fuel flow rate  309  thereby resulting in an inaccurate injected fuel mass being delivered to the fuel injector  10 . 
     The magnetic force command  311  is input to the first difference unit  312 . The first difference unit  312  compares magnetic force feedback  325  within the fuel injector  10  to the magnetic force command  311 . The magnetic force feedback  325  is output from the force mapping module  324  based upon magnetic flux feedback  323  provided from the fuel injector  10 . The magnetic flux feedback  323  indicates the active magnetic flux present within the fuel injector  10 . The active magnetic flux, or equivalent flux linkage, present within the fuel injector  10  can be obtained by any of the methods as described above with reference to the illustrated embodiment of  FIG. 1-1  using one or more sensing devices integrated into the fuel injector  10 . Thus, active magnetic flux feedback  323  may be transmitted from the fuel injector  10  via the feedback signal(s)  42  as described above with reference to the illustrated embodiment of  FIG. 1-1 . Based upon known relationships, the force mapping module  324  can utilize look-up tables or analytical functions to output the magnetic force within the fuel injector  10  (magnetic force feedback  325 ). Thus, the magnetic force feedback  325  indicates the magnetic force of the armature portion  21  including force attributable to residual flux in the presence of the active magnetic flux within the fuel injector  10 . 
     Based upon the comparison between the magnetic force feedback  325  and the magnetic force command  311 , the first difference unit  312  outputs an adjusted magnetic force command  313  that takes into account the presence of magnetic flux  323  within the fuel injector  10 . The adjusted magnetic force command  313  is input to the PI force control module  314  whereby a current command  315  is generated. The current command  315  is indicative of a commanded pull-in current and hold-current over a duration to activate the fuel injector  10  for delivering the desired fuel flow rate  309 . However, while the current command  315  does account for the magnetic force feedback  325  within the fuel injector, the current command  315  does not account for current present within the fuel injector, e.g., flowing through the electrical coil  24 . 
     Accordingly, current feedback  327  indicates current measured by the current sensor  322  positioned on a current flow path between the fuel injector  10  and the injection driver  320 . The second difference unit  316  outputs an adjusted current command  317  based on a comparison between the current command  315  and the current feedback  327  measured by the current sensor  322 . The adjusted current command  317 , which accounts for magnetic flux and current feedback from the fuel injector  10 , is input to the PI current control module  318  whereby a commanded PWM electric power flow signal  319  is generated and input to the injector driver  320 . Based upon the commanded PWM electric power flow signal  319 , which accounts for the current feedback  327  and magnetic force feedback  325  within the fuel injector  10 , the injector driver  320  may provide current in a first direction  321  for energizing the electrical coil  24  for activating the fuel injector  10  to deliver the desired injected fuel mass to the combustion chamber  100  of the engine. It will be understood that the injection driver  320  can include a bi-directional current driver capable of providing positive current (e.g., first direction  321 ) for energizing the electrical coil and negative or reverse current for drawing current from the electrical coil for purposes such as reducing residual flux. Therefore, the magnetic force control module  300  enables the desired fuel flow rate  309  to be achieved for each one of a plurality of fuel injection events in rapid succession using closed loop operation based upon the magnetic force feedback  325  and the current feedback  327  within the fuel injector  10 . 
       FIG. 5  illustrates an exemplary embodiment of a magnetic force control module using magnetic flux feedback to control current applied to an electrical coil of a fuel injector for controlling activation thereof. The magnetic force control module  400  may be implemented within—and executed by a processing device of—the control module  60  of the activation controller  80  of  FIG. 1-1 . 
     Accordingly, the magnetic force control module  400  will be described with reference to  FIG. 1-1 . The magnetic force control module  400  includes a force command generation (FCG) module  410 , a first difference unit  412 , a proportional integral (PI) force control module  414 , an injector driver  420 , and a force mapping module  424 . The control module  60  of the activation controller  80  of  FIG. 1-1  may encompass the FCG module  410 , the difference units  412 , the PI force control module  414  and the force mapping module  424 . The injector driver  50  of the force activation controller  80  of  FIG. 1-1  may encompass the injector driver  320 . However, the control module  60  and injector driver  50  may encompass different combinations of those features listed above. 
     In the illustrated embodiment, a desired fuel flow rate  409  is input to the FCG module  410 . The desired fuel flow rate  409  may be provided from an external module, e.g., the ECM  5 , based on the aforementioned input parameters  51  for achieving a desired injected fuel mass, as described above with reference to  FIG. 1-1 . The FCG module  410  outputs a magnetic force command  411  based on the desired fuel flow rate  409 . The magnetic force command  411  is indicative of a command to generate a magnetic force required to move the armature portion  21  in the second direction  82  to activate the fuel injector  10  in the open position to deliver the desired fuel flow rate  409  to the combustion chamber  100 . However, it will be appreciated that the magnetic force command  411  does not account for the presence of residual flux, e.g., magnetic flux, present within the fuel injector due to hysteretic and eddy current effect. The presence of residual flux may cause instability within the fuel injector that may impact fuel flow rates and injected fuel masses being delivered to the combustion chamber. Accordingly, moving the armature portion  21  based solely upon the magnetic force command may result in a fuel flow rate actually delivered to the combustion chamber that deviates from the desired fuel flow rate  409  thereby resulting in an inaccurate injected fuel mass being delivered to the fuel injector  10 . 
     The magnetic force command  411  is input to the difference unit  412 . The first difference unit  412  compares magnetic force feedback  425  within the fuel injector  10  to the magnetic force command  411 . The magnetic force feedback  425  is output from the force mapping module  424  based upon magnetic flux feedback  423  provided from the fuel injector  10 . The magnetic flux feedback  423  indicates the active magnetic flux present within the fuel injector  10 . The active magnetic flux, or equivalent flux linkage, present within the fuel injector  10  can be obtained by any of the methods as described above with reference to the illustrated embodiment of  FIG. 1-1  using one or more sensing devices integrated into the fuel injector  10 . Thus, active magnetic flux feedback  423  may be transmitted from the fuel injector  10  via the feedback signal(s)  42  as described above with reference to the illustrated embodiment of  FIG. 1-1 . Based upon known relationships, the force mapping module  424  can utilize look-up tables or analytical functions to output the magnetic force within the fuel injector  10  (magnetic force feedback  425 ). Thus, the magnetic force feedback  425  indicates the magnetic force of the armature portion  21  including force attributable to residual flux in the presence of the active magnetic flux within the fuel injector  10 . 
     Based upon the comparison between the magnetic force feedback  425  and the magnetic force command  411 , the difference unit  412  outputs an adjusted magnetic force command  413  that takes into account the presence of magnetic flux  423  within the fuel injector  10 . The adjusted magnetic force command  413  is input to the PI force control module  414  whereby PWM electric power flow signal  429  is generated and input to the injector driver  420 . Thus, the commanded PWM electric power flow signal  429  accounts for magnetic force feedback  425  within the fuel injector, whereas the commanded PWM electric power flow signal  319  of the magnetic force control module  300  of  FIG. 4  accounts for both magnetic force feedback  325  and current feedback  327 . Therefore, the magnetic force control module  400  enables a desired fuel flow rate  409  to be achieved for each one of a plurality fuel injection events in rapid succession using closed loop operation based upon the magnetic force feedback  425  within the fuel injector  10 . 
     The disclosure has described certain preferred embodiments and modifications thereto. Further modifications and alterations may occur to others upon reading and understanding the specification. Therefore, it is intended that the disclosure not be limited to the particular embodiment(s) disclosed as the best mode contemplated for carrying out this disclosure, but that the disclosure will include all embodiments falling within the scope of the appended claims.