Abstract:
A method for detecting and controlling the position of a valve actuator is provided. The method includes applying a plurality of signals of different duration and/or magnitude to the valve actuator and measuring a signal from the valve actuator. This signal from the valve actuator is indicative of valve movement for each of the plurality of applied signals. The method further includes adjusting an injection signal to the valve actuator based at least from the measured signals from the valve actuator. This disclosure also applies this method to a solenoid actuator of a fuel injector.

Description:
TECHNICAL FIELD 
   The present disclosure relates generally to a method for detecting and controlling the movement of a component of an actuator for use in a work machine, and more particularly to a valve component of a solenoid-operated actuator for use in a work machine. 
   BACKGROUND 
   Work machines utilize actuators for a number of applications. For example, fuel injectors, commonly used to deliver fuel to a combustion chamber in an internal combustion engine, utilize actuators. A fuel injector may deliver a certain quantity of fuel, which may be, for example, diesel fuel, to the combustion chamber in the engine at a certain time in the operating cycle of the engine. The amount of fuel delivered to the combustion chamber may depend on the operating conditions of the engine such as, for example, the engine speed and the engine load. 
   Precisely controlling the quantity and timing of the fuel delivered to each combustion chamber in the engine may lead to an increase in engine efficiency and/or a reduction in the generation of undesirable emissions. To improve control over the quantity and timing of fuel delivery, a typical fuel injection system includes an electronic control module that controls the timing and quantity of fuel delivered by a fuel injector. The electronic control module transmits a control signal to the fuel injector in the engine to deliver a certain quantity of fuel to the combustion chamber at a certain point in the operating cycle. The control module sends a signal to an actuator, typically a solenoid, of the fuel injector to control the quantity and timing of fuel injected. The control module can vary this signal in order to control the duration of solenoid activation and the control module can vary the magnetic force, or magnitude, created by the solenoid. 
   The solenoid controls the flow of high pressure activation fluid to the injector by opening and closing a high pressure inlet. The high pressure inlet receives a high pressure activation fluid from a high pressure supply, such as a high pressure rail, of the work machine. Typically, the solenoid controls the movement of a valve member controlling a high pressure inlet of the fuel injector. The valve member, in its first or closed position, prevents the flow of the high pressure activation fluid. When moved to a second or open position, the valve member allows the high pressure activation fluid to enter the injector. Activating the solenoid urges the valve member towards its open position, starting the injection cycle. The high pressure fluid acts within the fuel injector, causing injection of fuel to occur. Deactivating the solenoid ends the injection cycle and releases pressure caused by the high pressure fluid within the injector. 
   Most work machines utilize more than one combustion chamber and therefore require more than one fuel injector. The work machine typically operates most efficiently when the fuel injectors for each combustion chamber inject fuel for the same duration. Otherwise, the work machine may experience excessive power growth, greater emissions, and/or oil dilution problems. In addition, operating the fuel injectors in this manner may minimize engine noise, vibrations and harshness. To synchronize the fuel injectors within an engine, the control module has a preset profile for the fuel injectors correlating fuel quantity injected with solenoid activation duration. The amount of fuel delivered by the fuel injector depends on the movement of the valve member controlling the supply of the high pressure activation fluid. The faster or slower the valve member moves from its closed position to its open position varies the timing and amount of fuel delivered. Similarly, the amount of time the valve member takes to return to its closed position from its open position varies the timing and amount of fuel delivered. 
   However, no two fuel injectors perform in the same manner due to slight variations in mechanical tolerances during manufacture and the wear of components through use. This means that the same signal sent to different fuel injectors may result in a different quantity of fuel injected by each fuel injector. In addition, the timing and duration of injection may vary from injector to injector. Adjusting for these variations may improve fuel efficiency and/or reduce unwanted emissions. Typical solutions to these variations focus on understanding the valve member&#39;s motion. 
   U.S. Pat. No. 5,995,356 (“the &#39;356 patent”) discloses a method to detect the movement of a solenoid-operated valve element. The &#39;356 patent discloses activating a solenoid by sending current to the solenoid to urge a valve to its open position; then deactivating the solenoid so that the valve is urged towards its closed position. At a predetermined time after deactivating the solenoid, the current in the solenoid is measured to detect a predetermined characteristic change. This predetermined characteristic change corresponds to the valve having returned to its closed position. The &#39;356 patent also discloses a circuit solution for measuring the current in the solenoid. This circuit is an example of a free-wheel circuit, where free wheeling means the circuit has a predetermined resistance so that when the energy which is stored in the solenoid is provide to the circuit, the current can be measured. The &#39;356 patent, however, does not disclose how to use the information collected through the disclosed method. 
   Another characteristic of the movement of the valve member may also cause fuel injector inefficiencies. In some instances, the differences in the motion of the valve member as it moves from its closed position to its open position influences the timing and the amount of fuel injected into the combustion chamber. Eliminating or minimizing the variation in this opening motion from fuel injector to fuel injector may decrease differences in the fuel injection rate leading to an increase in fuel efficiency and/or reduction in unwanted emissions. 
   The method of the present disclosure solves one or more of the problems set forth above. 
   SUMMARY OF THE DISCLOSURE 
   In accordance with one exemplary embodiment, a method for adjusting a signal delivered to a valve actuator of a fuel injector includes applying a plurality of signals of different duration or magnitude to the valve actuator. The method also provides for measuring a signal from the valve actuator indicative of a valve movement for each of the plurality of applied signals and adjusting an injection signal to the valve actuator based at least in pail on the measured signals from the valve actuator. 
   According to yet another embodiment, a method is provided for adjusting a signal delivered to a valve actuator of a fuel injector by periodically applying a plurality of signals of different duration or magnitude to the valve actuator and measuring a signal from the valve actuator indicative of a valve movement for each of the plurality of applied signals. The method further provides for determining a valve movement time from at least the durations or magnitudes of the plurality of applied signals and the measured signals from the valve actuator and further determining at least one offset value by comparing the valve movement to a reference valve movement profile. The method also provides for adjusting the initiation or duration of an injection signal to the valve actuator based on the at least one offset value. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a partial diagrammatic cross-sectional side view of an actuator assembly of an exemplary fuel injector in accordance with the present disclosure; 
       FIG. 2  is a graphic illustration of fuel quantity injected as a function of solenoid activation duration in accordance with the present disclosure; 
       FIG. 3   a  is a graphic illustration of applied current as a function of solenoid activation duration in accordance with the present disclosure; 
       FIG. 3   b  is a graphic illustration of measured voltage indicative of the motion of a valve element as a function of solenoid activation duration in accordance with the present disclosure; 
       FIG. 4  is a graphic illustration of measured time as a function of solenoid activation duration in accordance with the present disclosure; 
       FIG. 5   a  is a graphic illustration of current as a function of solenoid activation duration in accordance with the present disclosure; 
       FIG. 5   b  is a graphic illustration of measured motion of a valve element as a function of solenoid activation duration in accordance with the present disclosure; and 
       FIG. 6  is a flowchart illustrating an exemplary method for performing an adaptive trim sweep and creating an adaptive trim profile for an actuator assembly of a fuel injector in accordance with the present disclosure. 
   

   DETAILED DESCRIPTION 
   Reference will now be made in detail to exemplary embodiments of the disclosure, illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. 
   Referring to the figures, an actuator assembly  10  of a common rail fuel injector is shown generally in  FIG. 1 . Actuator assembly  10  may include a solenoid  12 , a bias spring  14 , a valve member  16 , an armature  18 , a control wire  11  connected to an actuator assembly control unit  13 , a low pressure drain passage  20 , an internal injector passage  22 , and a high pressure activation fluid inlet  24 . Internal injector passage  22  may communicate with a nozzle tip (not shown) of the fuel injector for injecting activation fluid into a combustion chamber of an engine. It should be understood, however, that the method disclosed here is not limited for use with this particular actuator assembly. It should be understood that the method of this disclosure may be performed with any electronically controlled valve for communicating a fluid to, or within, a fuel injector, including but not limited to admission valves, spill valves, check control valves, such as those used in but not limited to hydraulically actuated fuel injectors, mechanically activated fuel injectors, and common rail fuel injectors. 
   The bias spring  14  may bias armature  18 , connected to valve member  16 , downward, biasing valve member  16  towards a first or closed position. When activated, the solenoid  12  urges armature  18  and valve member  16  upwards, urging valve member  16  towards a second or open position. 
   In its closed position, valve member  16  prevents the high pressure activation fluid in high pressure activation fluid inlet  24  from communicating with internal injector passage  22  or low pressure drain passage  20  of actuator assembly  10 . Also, when valve member  16  is in its closed position, internal injector passage  22  fluidly communicates with low pressure drain passage  20 . When valve member  16  is in its open position, high pressure activation fluid from high pressure activation fluid inlet  24  can communicate with internal injector passage  22 . 
   The control unit  13  may contain a reference profile for actuator assembly  10  that is programmed into the control unit  13  when the actuator assembly  10  is installed. The manufacturer may create this reference profile by testing a nominal fuel injector and determining at least its injection, timing, and duration characteristics. An exemplary reference profile is illustrated in  FIG. 2  at  100 , where fuel quantity injected versus solenoid activation duration is shown. Reference profile  100  corresponds to the expected quantity of fuel injected by actuator assembly  10  for a given solenoid activation duration at a certain rail pressure when activated by the control unit  13 . The control unit  13  may contain a reference profile  100  for each actuator assembly  10  of the work machine and may include profiles for various possible rail pressures. In addition, the control unit  13  may extrapolate fuel quantity as a function of solenoid activation duration for other rail pressures not profiled. Using reference profile  100  or another profile, the control unit  13  may determine an appropriate signal duration to be sent to solenoid  12  to obtain a desired quantity of fuel injected at the measured rail pressure. The control unit  13  also receives signals from solenoid  12  and performs any necessary calculations for adjusting the current signal sent to the solenoid  12 , as will be described in more detail below. It should be understood that more than one control unit  13  may be used to control activation of solenoid  12 , for receiving current from solenoid  12 , and for performing any necessary calculations for adjusting the current signal sent to solenoid  12 . 
   After determining the desired solenoid activation duration from reference profile  100  or another profile based on rail pressure and desired fuel quantity, the control unit  13  for actuator assembly  10  initiates injection by sending a current signal to solenoid  12 . Referring to  FIG. 1 , activating solenoid  12  generates an electromagnetic field urging armature  18 , connected to valve member  16 , upwards and moves valve member  16  towards its open position. When valve member  16  starts moving towards its open position, the high pressure activation fluid in high pressure activation fluid inlet  24  can communicate with internal injector passage  22 . As noted above, internal injector passage  22  may be configured to supply the high pressure activation fluid to the nozzle tip of the injector (not shown) for injecting into a combustion chamber of the engine of the work machine. To end injection, the control unit  13  deactivates solenoid  12  by stopping the current signal to the solenoid  12 , with the duration of the signal being determined by the reference profile  100 . Without the electromagnetic force of solenoid  12  acting on armature  18 , bias spring  14  urges armature  18  downward, moving valve member  16  towards its closed position. In its closed position, valve member  16  prevents the high pressure activation fluid in high pressure activation fluid inlet  24  from communicating with internal injector passage  22 . In its closed position, valve member  16  allows communication between internal injector passage  22  and low pressure drain passage  20 . This results in a lowering of the pressure in the internal injector passage  22  and in the nozzle of the injector. 
   Due to manufacturing tolerances and the wear of mechanical parts through continued use, the quantity of fuel injected may vary from fuel injector to fuel injector. For example, two fuel injectors having actuator assemblies that are energized for the same duration may supply two significantly different quantities of fuel. Furthermore, these variations may cause both the start and the end of injection to occur at different times because the movement of the valve member  16  may deviate from the reference profile  100  due to the differences in manufacturing tolerances and the wear of parts through use. As will be discussed in more detail below, an adaptive trim sweep may help to determine deviations from the reference profile  100 . In addition, the adaptive trim sweep may assist in creating an adaptive trim profile that can be used to adjust the duration and timing of solenoid activation in order to compensate for actuator variations and more particularly, control the timing and quantity of fuel injected. 
   First, the control unit  13  determines whether the conditions to run the adaptive trim sweep are met. These conditions may include, but are not limited to, whether an actuator assembly  10  has reached a predetermined age and/or whether an actuator assembly  10  was replaced. The adaptive trim sweep may be designed to only run if these or other conditions are satisfied. Other conditions, such as engine load or engine run-time may also be used to determine when to run the adaptive trim sweep. In the exemplary method, the pressure of the high pressure activation fluid is held near constant during the adaptive trim sweep. If the rail pressure deviates outside a predetermined range during the adaptive trim sweep, the control unit  13  will terminate the adaptive trim sweep. 
     FIG. 3   a  graphically illustrates current as a function of solenoid activation duration where current is shown on the vertical axis and solenoid activation duration is shown on the horizontal axis. To run the adaptive trim sweep of actuator assembly  10 , the control unit  13  sends a current signal to solenoid  12  for a first duration (D 1 ), shown at  200  in  FIG. 3   a,  to urge the valve member  16  towards its open position. The magnitude of the current signal sent to solenoid  12  is initially high, as seen at  201  in  FIG. 3   a,  in order to quickly create a solenoid electromagnetic force strong enough to overcome the bias force from bias spring  14  acting upon armature  18  and valve member  16 . After a predetermined time corresponding to an initial movement of valve member  16  towards its open position, the magnitude of the current signal to solenoid  12  is decreased to a level that will continue to urge valve member  16  towards its open position as seen at  203 . When duration (D 1 ) ends, shown at  200 , the control unit  13  ends the current signal to solenoid  12 . This allows the electromagnetic force created by solenoid  12  to dissipate, allowing bias spring  14  to bias armature  18  and valve member  16  towards its closed position. 
   Upon ending the signal duration (D 1 )  200 , the current in solenoid  12  is then routed into a free-wheel circuit (not shown) after a pre-determined delay and a first induced voltage (V 1 ), shown at  202  in  FIG. 3   b,  is measured. The first induced voltage (V 1 )  202  is indicative of valve member  16  movement from its partially open position to its fully closed position for the current signal applied for duration (D 1 ). Using the first induced voltage (V 1 )  202 , the control unit  13  can extrapolate valve member  16  motion as a function of solenoid activation duration (D 1 ), as graphically illustrated in  FIG. 3   b,  where valve member  16  motion is shown on the vertical axis and solenoid activation duration is shown on the horizontal axis. A first time (T 1 ), shown at  204  in  FIG. 3   b,  is computed from the end of duration (D 1 ), shown at  200 , to the end of valve member  16  motion shown at  205 . 
   Next, the control unit  13  sends a second current signal to the solenoid  12  for a second duration (D 2 ), shown at  206  in  FIG. 3   a,  such that the second duration (D 2 )  206  is longer than the first duration (D 1 )  200 . Upon ending the second current signal at the end of second duration (D 2 )  206 , the remaining current in the solenoid  12  is again routed into the free-wheel circuit and a second induced voltage (V 2 ) is measured. The second induced voltage (V 2 ) is indicative of valve member  16  movement from its partially open position to its fully closed position for the current signal applied for duration (D 2 ). From this voltage (V 2 ), the control unit  13  extrapolates valve member  16  motion as a function of solenoid activation duration (D 2 ) as seen in  FIG. 3   b  at  208 . A second time (T 2 ), shown at  210  in  FIG. 3   b,  is computed from the end of duration (D 2 ) to the end of valve member  16  motion shown at  209  . 
   The control unit  13  then compares the time values (T 1 ) and (T 2 ) for each duration (D 1 ) and (D 2 ). If the time value (T 2 ) is greater than the time value (T 1 ), the control unit  13  continues running the adaptive trim sweep with additional current signals with increasing solenoid activation durations. The control unit  13  continues this adaptive trim sweep until an initial peak duration  302  in  FIG. 4  is identified. 
     FIG. 4  graphically illustrates the identification of an initial peak duration by plotting the time from end of current to end of valve member  16  motion as a function of solenoid activation duration. Time is plotted on the vertical axis and solenoid activation duration is plotted on the horizontal axis. Initial peak duration  302  occurs the first time value (Tn), shown at  300  in  FIG. 4 , from duration (Dn), shown at  302  in  FIG. 4 , is greater than the time value (Tn+1), shown at  304  in  FIG. 4 , from duration (Dn+1), shown at  306  in  FIG. 4 , where (n) represents an iteration and (n+1) represents one iteration occurring directly after iteration (n). This peak duration  302  corresponds to the first time the applied current is sufficient to move valve member  16  to its fully open position. The reduction in time (Tn+1)  304  compared to time (Tn)  300  corresponds to valve member bounce. Valve member bounce occurs when the valve member  16  is urged towards its open position by solenoid  12  at such a velocity that the valve member  16  hits its fully open position and bounces away from its fully open position. As it bounces away toward its closed position, the velocity of the return motion is higher causing a reduction in return time. To locate the peak duration (Dn)  302  corresponding to valve member  16  reaching its fully open position, the control unit  13  performs the adaptive trim sweep until time (Tn+1)  304  and time (Tn)  300  are found. 
   During installation of the actuator assembly  10 , a reference minimum duration, shown at  100   a  in  FIG. 4 , and a reference return time, shown at  100   b  in  FIG. 4 , are also programmed into the control unit. The manufacturer may determine these values by testing a representative fuel injector. The reference minimum duration  100   a  indicates a predetermined minimum solenoid activation duration required to urge valve member  16  from its fully closed position to its fully open position at a certain rail pressure. The reference return time  100   b  corresponds to a predetermined return time required for bias spring  14  to bias valve member  16  from its fully open position to its fully closed position for a given rail pressure. This reference return time  100   b,  therefore, corresponds to difference between the end of the current signal and the end of valve member  16  motion. 
   Once the peak duration (Dn)  302  is found, the control unit  13  determines how the actuator assembly  10  deviates from the reference profile  100 . The control unit  13  determines a start trim offset value  308  from the difference between solenoid activation duration corresponding to the peak duration  302  and the reference minimum duration  100   a.  The start trim offset value  308  is indicative of how the movement of valve member  16  from its fully closed position to its fully open position deviates from reference minimum duration  100   a.  The control unit  13  also determines an end trim offset value  310  from the difference between the end of current to end of valve member  16  motion and reference return time  100   b  as shown at  310 . The end trim offset value  310  is indicative of how movement of valve member  16  from its fully open position to its fully closed position deviates from reference return time  100   b.  Alternatively, end trim offset value  310  may be determined as the difference between reference time  100   b  and a duration (Ds) at a time (Ts), shown at  312  in  FIG. 4 , after peak duration (Dn)  302 . Time (Ts)  312  is indicative of the time required for bias spring  14  to bias valve member  16  from its fully open position to its fully closed position after valve member  16  has reached and remained in its fully open position. Time (Ts)  312  can be found when time (Ts)  312  at duration (Ds) is greater than time (Tn+1)  304  at duration (Dn+1)  306 , where duration (Ds) is greater than duration (Dn+1)  306 . This time (Ts)  312  deviates from the reference return time  100   b  in part because of the wear of mechanical parts through use and because of the limitations of manufacturing tolerances. The faster valve member  16  returns to its fully closed position, the less fuel will be injected into the combustion chamber. The longer valve member  16  takes to travel from its fully open to its fully closed position increases the amount of fuel injected into the combustion chamber. 
   Referring back to  FIG. 2 , the control unit  13  adds the trim values  308 ,  310 , together to get a final trim value  104  to correct differences between reference profile  100  and an adaptive trim profile  102 . This calculated trim  104  when applied will cause the injector profile  102  to overlay the reference profile  100 . The calculated trim values  308 ,  310  enable the control unit  13  to adjust the duration of solenoid activation in order to obtain injection of a desired quantity of fuel at a particular rail pressure. The control unit  13  can extrapolate an adaptive trim profile for other rail pressures in order to adjust solenoid activation duration and more accurately inject a determined quantity of fuel over an entire range of rail pressures. This is graphically illustrated in  FIG. 5   a  showing current as a function of solenoid activation duration. A reference current as a function of solenoid activation duration is shown at  400  and the adaptive trim profile is shown at  402 . As illustrated in  FIG. 5   a,  adaptive trim profile  402  has a shorter duration than the reference duration  400  and therefore the valve member  16  associated with the adaptive trim profile  402  has a faster opening and closing time than the reference opening and closing time. In this example, a faster valve member  16  would be activated for a shorter duration than the reference duration in order to injected the same fuel quantity. 
   This adaptive trim profile  402  enables the control unit  13  to more accurately control the start and the end of injection. This is graphically illustrated in  FIG. 5   b  showing valve member  16  motion as a function of solenoid activation duration. A reference valve member motion is shown at  404  and the adaptive trim profile is shown at  406 . By adjusting the timing and the solenoid activation duration based on the adaptive trim profile  402  in  FIG. 5   a,  the control unit  13  can end valve motion at the same time as the reference profile  404 , as illustrated at point  408  in  FIG. 5   b.  Similarly, the control unit  13  can adjust the timing and solenoid activation duration to end valve motion in its fully open position at the same time as the reference profile  404 , as illustrated at point  410  in  FIG. 5   b.  To do this, the control unit  13  utilizes adaptive trim profile  406 , to synchronize the time when valve member  16  reaches its closed position  408  with the time value from the reference profile  404 . This may require the control unit  13  to deactivate solenoid  12  before the reference profile  404  would normally require or it may require the control unit  13  to keep solenoid  12  active longer than the reference profile  404  would require depending on whether the valve member  16  travels faster or slower from its open position to its closed position than the reference time. In the example illustrated in  FIG. 4 , the injector takes longer to go from its fully open to its fully closed position than the reference. To end injection at the same point, the control unit  13  would end the current to the injector in  FIG. 4  sooner than the reference in  FIG. 4 . This difference in timing is illustrated in  FIG. 5   a.  Similarly, to start injection at the same point, the control unit  13  alters when the solenoid actuation begins to align the time when the valve member reaches its fully open position  410 . 
   The control unit  13  may perform the adaptive trim sweep profile for each fuel injector within the engine of the work machine. Furthermore, the control unit  13  may create an adaptive trim profile for each injector. Using the adaptive trim profile for each injector, the control unit  13  can synchronize the end of injection for multiple fuel injectors by more accurately controlling the movement of each valve member. 
   INDUSTRIAL APPLICABILITY 
   The flowchart of  FIG. 6  illustrates an exemplary method for an adaptive trim sweep and for creating an adaptive trim profile. First, the control unit  13  determines whether the conditions for running the adaptive trim sweep are met. As noted above, these conditions may include whether actuator assembly  10  has reached a predetermined age and/or whether actuator assembly  10  was replaced. (Step  500 ). The control unit  13  next determines whether rail pressure is near constant. If the rail pressure is not near constant, the adaptive trim sweep will terminate. (Step  502 ). To start the adaptive trim sweep, the control unit  13  sends a current signal for duration (Dn)  302  to solenoid  12  to urge valve member  16  towards its open position. Duration (Dn)  302  is greater than (Dn−1). (Step  504 ). The control unit  13  will end the current signal after duration (Dn)  302  and measure the induced voltage (Vn) from solenoid  12 , indicative of valve member  16  movement, in the free-wheel circuit. (Step  506 ). Using the induced voltage (Vn), the control unit  13  next computes time (Tn) from the end of duration (Dn)  302  to the end of valve member  16  motion. (Step  508 ). Time (Tn) is indicative of the time required for valve member  16  to return to its closed position from its open position after duration (Dn)  302  ends. 
   The control unit  13  sends a second current signal to solenoid  12  for duration (Dn+1)  306 , where duration (Dn+1)  306  is greater than duration (Dn)  302 . (Step  510 ). At the end of duration (Dn+1)  306 , the control unit  13  ends the current signal sent to solenoid  12  and measures an induced voltage (Vn+1) from solenoid  12  in the free wheel circuit. (Step  512 ). Using the induced voltage (Vn+1), the control unit  13  computes a time (Tn+1)  304  from the end of duration (Dn+1)  306  to the end of valve member  16  motion. Time (Tn+1)  304  is indicative of the time required for valve member  16  to return to its closed position from its open position after duration (Dn+1)  306  ends. (Step  514 ). 
   Next, the control unit  13  compares the two time values (Tn)  300  and (Tn+1)  304 . If (Tn+1)  304  is less than (Tn)  300 , a peak duration  302 , corresponding to the first time valve member  16  is in its fully open position, occurs at duration (Dn)  302 . If (Tn+1)  304  is greater than (Tn)  300 , the control unit  13  will repeat the adaptive trim sweep. (Step  516 ). If a peak duration  302  is found at time (Tn)  300 , the control unit  13  next determines a start trim offset value  308  and an end trim offset value  310 . (Step  518 ). The start trim offset value  308  corresponds to the difference between the reference duration and the adaptive trim sweep duration (Dn)  302  for valve member  16  to travel from its fully closed position to its fully open position after the current signal is sent to solenoid  12 . The control unit  13  determines the start trim offset value  308  as the difference between the peak duration (Dn)  302  and a reference minimum duration  100   a  ( FIG. 4 ). The end trim offset value  310  corresponds to the difference between the measured time (Tn) for valve member  16  to travel from its fully open position to its fully closed position after the current signal to solenoid  12  ends and a reference time  100   b  ( FIG. 4 ). The control unit  13  determines end trim offset value  310  as the difference between time (Tn) and reference return time  100   b.  Using the start and end trim offset values  308  and  310 , the control unit  13  determines the final trim valve  104  to correct differences between reference profile  100  and an adaptive trim profile  102 . (Step  520 ). In addition, the control unit  13  can extrapolate fuel quantity injected as a function of solenoid activation duration for other rail pressures. Now the control unit  13  can use the desired quantity of fuel to be delivered and the rail pressure to find a corresponding solenoid activation duration for valve member  16  from the adaptive trim profile  102 . This enables the control unit  13  to more accurately control the timing and quantity of fuel injected. 
   As noted above, the control unit  13  can use the method disclosed here for one actuator assembly at a time, or on multiple actuator assemblies at the same time. The control unit  13  may contain a reference profile for each actuator assembly and can create a reference profile for all of the actuator assemblies based on these individual reference profiles. 
   Other embodiments of the disclosure will be apparent to those skilled in the art from consideration of the specification and practice of the disclosure discussed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the disclosure being indicated by the following claims and their equivalents.