FUEL INJECTOR AND METHOD FOR CONTROLLING THE SAME

Abstract

A fuel injector for a combustion engine is disclosed. The fuel injector includes an injector body having a nozzle orifice, a solenoid coil mounted in the injector body, a control chamber filled with high-pressure fuel, an armature moved by electromagnetic force of the solenoid coil to vary fuel pressure in the control chamber, and a needle that moves to open or close the nozzle orifice according to the variation in the fuel pressure in the control chamber. The fuel injector further includes piezoelectric actuator for adjusting a fuel injection rate by adjusting an opening speed of the nozzle orifice based on a load condition of the engine.

Claims

1. A fuel injector comprising: an injector body having one or more nozzle orifices; a solenoid coil mounted in the injector body; a control chamber filled with high-pressure fuel; an armature configured to be moved to vary fuel pressure in the control chamber; a needle configured to move to open or close the one or more nozzle orifices according to the variation in the fuel pressure in the control chamber; and an adjustment unit configured to adjust a fuel injection rate by adjusting an opening speed of the nozzle orifices based on a load condition of an engine.

2. The fuel injector of claim 1, wherein the adjustment unit is configured to adjust the opening speed of the nozzle orifices by varying a variation rate of the fuel pressure in the control chamber based on the load condition of the engine when the needle opens the nozzle orifices.

3. The fuel injector of claim 1, wherein the adjustment unit is configured to adjust the opening speed of the nozzle orifices by adjusting the amount of fuel drained from the control chamber based on the load condition of the engine when the needle opens the nozzle orifices.

4. The fuel injector of claim 1, wherein the adjustment unit includes an actuator interposed between the solenoid coil and the armature.

5. The fuel injector of claim 4, wherein the actuator contracts to a minimum thickness if the actuator is de-energized, wherein the actuator expands if the actuator is energized, and wherein a thickness by which the actuator expands is adjusted depending on the magnitude of applied input voltage.

6. The fuel injector of claim 4, wherein an insulation layer is coated on an outer surface of the actuator.

7. The fuel injector of claim 4, wherein an insulator is interposed between the solenoid coil and the actuator.

8. The fuel injector of claim 4, wherein the injector body has a high-pressure fuel passage communicating with the nozzle orifices, wherein a drain chamber is disposed between the solenoid coil and the control chamber, wherein the control chamber has an inlet passage communicating with the high-pressure fuel passage and an outlet passage communicating with the drain chamber, and wherein the armature has a valve part configured to open or close an opening of the outlet passage.

9. The fuel injector of claim 8, wherein a seat portion is formed around the opening of the outlet passage, and wherein a lower end surface of the valve part and the seat portion are spaced apart from, or brought into contact with, each other to open or close the outlet passage.

10. The fuel injector of claim 9, wherein the lower end surface of the valve part and the seat portion are spaced apart from each other by an opening gap when the armature moves upward, and wherein the opening gap is adjusted according to contraction or expansion of the actuator.

11. The fuel injector of claim 10, wherein the opening gap is adjusted to be greater or smaller than a fixed gap of an outlet orifice according to contraction or expansion of the actuator.

12. A method of controlling a fuel injector that includes an injector body having a nozzle orifice, a solenoid coil mounted in the injector body, a control chamber filled with high-pressure fuel and having an inlet passage through which the high-pressure fuel is introduced and an outlet passage through which the high-pressure fuel is drained and that has an outlet orifice formed inside, an armature configured to be moved to vary fuel pressure in the control chamber, a needle configured to move to open or close the nozzle orifice according to the variation in the fuel pressure in the control chamber, and an actuator interposed between the solenoid coil and the armature, the method comprising: contracting the actuator to a minimum thickness under a full load condition of an engine; and expanding the actuator to a predetermined expansion thickness under a partial load condition of the engine.

13. The method of claim 12, wherein an opening gap becomes larger than a fixed gap of the outlet orifice according to contraction of the actuator under the full load condition of the engine.

14. The method of claim 12, wherein an opening gap becomes smaller than or equal to a fixed gap of the outlet orifice according to expansion of the actuator under the partial load condition of the engine.

15. The method of claim 14, wherein a thickness by which the actuator expands is adjusted depending on the magnitude of applied voltage.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The above and other objects, features and advantages of the present disclosure will be more apparent from the following detailed description taken in conjunction with the accompanying drawings:

[0036] FIG. 1 is a sectional view of a fuel injector according to an embodiment of the present disclosure;

[0037] FIG. 2 is a blowup of an upper portion of FIG. 1, where FIG. 2 illustrates a state in which an outlet passage of a control chamber is closed;

[0038] FIG. 3 illustrates a state in which the outlet passage of the control chamber illustrated in FIG. 2 is closed;

[0039] FIG. 4 is a blowup of detail A in FIG. 3;

[0040] FIG. 5 is a graph depicting a fuel injection rate of the fuel injector according to time; and

[0041] FIG. 6 is a flowchart illustrating a method of controlling a fuel injector according to an embodiment of the present disclosure.

DETAILED DESCRIPTION

[0042] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. In the drawings, the same reference numbers will be used throughout to designate the same or equivalent elements. In addition, a detailed description of well-known features or functions will be ruled out in order not to unnecessarily obscure the gist of the present disclosure.

[0043] Terms, such as first, second, A, B, (a), (b), and the like, may be used herein to describe elements of the present disclosure. Such terms are only used to distinguish one element from another element, and the substance, sequence, order, or number of these elements is not limited by these terms. Unless otherwise defined, all terms used herein, including technical and scientific terms, have the same meaning as those generally understood by those skilled in the art to which the present disclosure pertains. Such terms as those defined in a generally used dictionary are to be interpreted as having meanings equal to the contextual meanings in the relevant field of art, and are not to be interpreted as having ideal or excessively formal meanings unless clearly defined as having such in the present application.

[0044] Referring to FIGS. 1 to 3, a fuel injector 10 according to an embodiment of the present disclosure may include an injector body 11, a solenoid coil 12 mounted in the injector body 11, an armature 13 movable by electromagnetic force of the solenoid coil 12, a control chamber 14 formed below the armature 13, and a needle 15 moving between an open position and a closed position according to a variation in fuel pressure in the control chamber 14.

[0045] The injector body 11 may have one or more nozzle orifices 11a. The nozzle orifices 11a may be formed at a lower end of the injector body 11. The nozzle orifices 11a may be opened or closed by a vertical movement of the needle 15. A control rod 16 may be connected to an upper end of the needle 15. The control rod 16 may move upward or downward according to a variation in fuel pressure in the control chamber 14. The control rod 16 and the needle 15 may move upward or downward together. The needle 15 may move between the closed position at which the needle 15 closes the nozzle orifices 11a and the open position at which the needle 15 opens the nozzle orifices 11a.

[0046] A high-pressure fuel passage 17, a nozzle chamber 18, and a middle chamber 19 may be formed inside the injector body 11.

[0047] The high-pressure fuel passage 17 may be connected to a common rail and may receive high-pressure fuel from the common rail. The high-pressure fuel passage 17 may communicate with the control chamber 14, and therefore the control chamber 14 may be filled with the high-pressure fuel. The high-pressure fuel passage 17 may communicate with the nozzle chamber 18, and therefore the nozzle chamber 18 may be filled with the high-pressure fuel.

[0048] The nozzle chamber 18 may be formed in a lower part of the injector body 11. The nozzle chamber 18 may communicate with the nozzle orifices 11a.

[0049] The needle 15 may move upward or downward in the nozzle chamber 18. The needle 15 may move between the open position at which the needle 15 opens the nozzle orifices 11a and the closed position at which the needle 15 closes the nozzle orifices 11a. A spring 15a may be mounted on the needle 15. The spring 15a may be configured to urge the needle 15 downward.

[0050] The middle chamber 19 may extend long in a middle part of the injector body 11, and the control rod 16 may move upward or downward in the middle chamber 19.

[0051] The solenoid coil 12 may be mounted in the injector body 11. The solenoid coil 12 may be mounted in an upper part of the injector body 11 through a coil bobbin 12a. A spring 13f may be disposed in a hollow portion of the coil bobbin 12a to urge the armature 13 downward.

[0052] The armature 13 may be disposed below the solenoid coil 12 so as to be adjacent to the solenoid coil 12. The armature 13 may have a valve part 13a and a disk part 13b formed on an upper end of the valve part 13a.

[0053] A shaft 13c may be mounted in a hollow portion of the valve part 13a through a busing 13d. A lower end of the spring 13f may make contact with an upper surface of the disk part 13d, and therefore the armature 13 may be moved downward by spring force of the spring 13f.

[0054] The control chamber 14 may be formed below the armature 13, and fuel pressure in the control chamber 14 may be varied depending on a movement of the armature 13. The control chamber 14 may have an inlet passage 23 and an outlet passage 24. The inlet passage 23 may communicate with the high-pressure fuel passage 17, and the outlet passage 24 may communicate with an inner drain chamber 31. The high-pressure fuel may flow into the control chamber 14 from the high-pressure fuel passage 17 through the inlet passage 23, and the control chamber 14 may be filled with the high-pressure fuel.

[0055] If the armature 13 moves upward to allow the valve part 13a of the armature 13 to open the outlet passage 24 of the control chamber 14, the high-pressure fuel may be drained from the control chamber 14 to the inner drain chamber 31 through the outlet passage 24, and thus the fuel pressure in the control chamber 14 may decrease. If the armature 13 moves downward to allow the valve part 13a of the armature 13 to close the outlet passage 24 of the control chamber 14, high-pressure fuel may be introduced into the control chamber 14 through the inlet passage 23, and thus the fuel pressure in the control chamber 14 may increase. The variation in the fuel pressure in the control chamber 14 may cause an imbalance in force exerted on the control rod 16 and the needle 15. Accordingly, the control rod 16 and the needle 15 may move upward or downward, and the needle 15 may open or close the nozzle orifices 11a.

[0056] The control chamber 14 may be formed by a valve block 20. The valve block 20 may be mounted in the injector body 11. The valve block 20 may be spaced apart downward from the solenoid coil 12.

[0057] The valve block 20 may have a first sleeve 21 extending downward and a second sleeve 22 extending upward.

[0058] The first sleeve 21 may have the control chamber 14 and the inlet passage 23 formed therein, and the inlet passage 23 may be configured to communicate with the high-pressure fuel passage 17. An upper end of the control rod 16 may slide in the first sleeve 21, and therefore the control chamber 14 may be defined by the first sleeve 21 and the control rod 16.

[0059] Drain chambers 31 and 32 may be located between the control chamber 14 and the solenoid coil 12. The drain chambers 31 and 32 may be formed by the second sleeve 22 of the valve block 20 and a cavity of the injector body 11.

[0060] The inner drain chamber 31 may be formed in the second sleeve 22, and the outlet passage 24 may be formed in the valve block 20. The valve part 13a of the armature 13 may slide in the second sleeve 22, and therefore the inner drain chamber 31 may be defined by the second sleeve 22 and the valve part 13a.

[0061] The control chamber 14 and the inner drain chamber 31 may communicate with each other through the outlet passage 24, and an outlet orifice 25 may be formed in the outlet passage 24. The outlet orifice 25 may have a fixed gap T2.

[0062] The outer drain chamber 32 may be formed outside the second sleeve 22. The outer drain chamber 32 may be defined by the second sleeve 22 and a cavity of the injector body 11. A drain passage 26 may be formed in the second sleeve 22, and the inner drain chamber 31 and the outer drain chamber 32 may communicate with each other through the drain passage 26. Furthermore, the outer drain chamber 32 may communicate with the middle chamber 19 through a connecting passage 19a.

[0063] A seat portion 44 may be formed around an upper opening of the outlet passage 24. The seat portion 44 and/or a lower end surface 43 of the valve part 13a may be formed to be flat. The lower end surface 43 of the valve part 13a may be brought into contact with, or spaced apart from, the seat portion 44 by a movement of the armature 13 to close or open the outlet passage 24.

[0064] If the solenoid coil 12 is energized, the armature 13 may be attracted upward toward the solenoid coil 12 by electromagnetic force of the solenoid coil 12. At this time, the electromagnetic force of the solenoid coil 12 may overcome the spring force of the spring 13f. The lower end surface 43 of the valve part 13a may be spaced apart from the seat portion 44 by the upward movement of the armature 13 to open the outlet passage 24. The high-pressure fuel may be drained from the control chamber 14 to the inner drain chamber 31 by the opening of the outlet passage 24, and the fuel pressure in the control chamber 14 may relatively decrease. Accordingly, the fuel pressure in the control chamber 14 may be lower than that in the nozzle chamber 18. A force to push the needle 15 upward may be generated by the difference between the fuel pressure in the nozzle chamber 18 and the fuel pressure in the control chamber 14, and the needle 15, together with the control rod 16, may be moved upward by the force. Accordingly, the needle 15 may open the nozzle orifices 11a, and thus the high-pressure fuel may be injected through the nozzle orifices 11a. The amount of fuel to be injected may be adjusted depending on energizing time of the solenoid coil 12.

[0065] If the solenoid coil 12 is de-energized, the armature 13 may be moved downward by the spring force of the spring 13f so that the lower end surface 43 of the valve part 13a may be brought into contact with the seat portion 44 to close the outlet passage 24 of the control chamber 24. Since the high-pressure fuel is not drained from the control chamber 14 by the closing of the outlet passage 24, the fuel pressure in the control chamber 14 may be higher than that in the nozzle chamber 18. The difference between the fuel pressure in the nozzle chamber 18 and the fuel pressure in the control chamber 14 may generate a force to push the needle 15 downward, and the needle 15, together with the control rod 16, may be moved downward by the force. Accordingly, the needle 15 may close the nozzle orifices 11a. In this case, the sum of the fuel pressure in the control chamber 14 and the spring forces of the springs 13f and 15a may be greater than the fuel pressure in the nozzle chamber 18.

[0066] The fuel injector 10 according to an embodiment of the present disclosure may include an adjustment unit 50 for adjusting a fuel injection rate based on a load condition of an engine.

[0067] The adjustment unit 50 may be configured to adjust a fuel injection rate by adjusting the opening rate shape slope of the nozzle orifices 11a. Referring to FIG. 5, the opening rate shape slope of the nozzle orifices 11a (see SL1, SL2, and SL3 of FIG. 5) may be a fuel injection rate slope while the needle 15 is being completely moved from the closed position to the open position.

[0068] As illustrated in FIG. 5, as the opening rate shape slope of the nozzle orifices 11a increases (SL3>SL2>SL1), the nozzle orifices 11a may be more rapidly opened, and therefore an initial fuel injection rate and the amount of fuel to be injected may increase. Furthermore, as the opening rate shape slope of the nozzle orifices 11a decreases, the nozzle orifices 11a may be more slowly opened, and therefore an initial fuel injection rate and the amount of fuel to be injected may decrease.

[0069] According to an embodiment, the adjustment unit 50 may be configured to vary a reduction rate (variation) of the fuel pressure in the control chamber 14 by varying the amount of fuel drained from the control chamber 14 based on a load condition of an engine when the needle 15 opens the nozzle orifices 11a, and the opening rate shape slope of the nozzle orifices 11a may be adjusted by varying the reduction rate (variation) of the fuel pressure in the control chamber 14. That is, when the nozzle orifices 11a are opened, the adjustment unit 50 may adjust a reduction rate (variation) of the fuel pressure in the control chamber 14 to adjust the opening rate shape slope of the nozzle orifices 11a (see SL1, SL2, and SL3 of FIG. 5). Accordingly, the nozzle orifices 11a may be more rapidly or slowly opened, and thus the initial fuel injection rate and the amount of fuel to be injected may be adjusted.

[0070] According to an embodiment, the adjustment unit 50 may include a piezoelectric actuator 55 interposed between the solenoid coil 12 and the disk part 13b of the armature 13.

[0071] The piezoelectric actuator 55 may have a piezoelectric material. As illustrated in FIG. 2, the piezoelectric actuator 55 may contract to a minimum thickness of P1 if the piezoelectric actuator is de-energized. As illustrated in FIG. 3, the piezoelectric actuator 55 may expand to a thickness of P2 if the piezoelectric actuator 55 is energized. The expansion thickness P2 of the piezoelectric actuator 55 may be adjusted depending on the magnitude of applied input voltage.

[0072] The piezoelectric actuator 55 may have an insulation layer coated on an outer surface thereof, and the insulation layer may prevent electric interference, electromagnetic interference, and the like between the piezoelectric actuator 55 and the solenoid coil 12. An upper surface of the piezoelectric actuator 55 may be attached to the bottom of the solenoid coil 12.

[0073] An insulator 56 may be preferably interposed between the solenoid coil 12 and the piezoelectric actuator 55, and the insulator 56 may prevent electric interference, electromagnetic interference, and the like between the solenoid coil 12 and the piezoelectric actuator 55. The insulator 56 may be attached to the bottom of the solenoid coil 12, and the piezoelectric actuator 55 may be attached to the bottom of the insulator 56.

[0074] If the solenoid coil 12 is energized, as illustrated in FIG. 3, to open the nozzle orifices 11a, the armature 13 may move toward the solenoid coil 12, and the valve part 13a of the armature 13 may move upward so that the lower end surface 43 of the valve part 13a may be spaced apart from the seat portion 44 by an opening gap T1. The distance by which the armature 13 moves upward may be adjusted depending on the contraction thickness P1 and the expansion thickness P2 of the piezoelectric actuator 55, and therefore the opening gap T1 may be varied.

[0075] As described above, the opening gap T1 between the lower end surface 43 of the valve part 13a and the seat portion 44 may be adjusted to be greater or smaller than the fixed gap T2 of the outlet orifice 25 according to the contraction or expansion of the piezoelectric actuator 55. Accordingly, as the amount of high-pressure fuel drained from the control chamber 14 is varied, a variation in the fuel pressure in the control chamber 14 may be adjusted, and the opening rate shape slope of the nozzle orifices 11a (see SL1, SL2, and SL3 of FIG. 5) may be adjusted by the adjustment of the fuel pressure variation in the control chamber 14.

[0076] Meanwhile, not only the opening rate shape slope but also a closing rate shape slope may be adjusted as the opening gap T1 is adjusted according to the contraction or expansion of the piezoelectric actuator 55. This allows adjustment of the distance by which the needle 15 moves downward. Accordingly, the nozzle orifices 11a may be more rapidly or slowly closed, and thus a last fuel injection rate and the amount of fuel to be injected may be adjusted. Referring to FIG. 5, the closing rate shape slope of the nozzle orifices 11a (see SL4, SL5, and SL6 of FIG. 5) may be a fuel injection rate slope while the needle 15 is being completely moved from the open position to the closed position.

[0077] As illustrated in FIG. 5, as the closing rate shape slope of the nozzle orifices 11a increases (SL6>SL5>SL4), the nozzle orifices 11a may be more slowly closed, and therefore a last fuel injection rate may increase. Furthermore, as the closing rate shape slope of the nozzle orifices 11a decreases, the nozzle orifices 11a may be more rapidly closed, and therefore a last fuel injection rate may decrease.

[0078] For example, in FIG. 5, a line OT1 represents a state in which the opening gap T1 has been adjusted to be smaller than the fixed gap T2 of the outlet orifice 25 by the piezoelectric actuator 55. When the needle 15 opens the nozzle orifices 11a by energizing of the solenoid coil 12 in the state in which the opening gap T1 has been adjusted to be smaller than the fixed gap T2 of the outlet orifice 25, the armature 13 may move a short distance upward, which results in a reduction in the amount of high-pressure fuel drained from the control chamber 14. Accordingly, a reduction rate of the fuel pressure in the control chamber 14 may decrease (that is, the fuel pressure in the control chamber 14 may gradually decrease), and thus opening of the nozzle orifices 11a may be delayed. Since the opening of the nozzle orifices 11a is delayed, the opening rate shape slope SL1 of the nozzle orifices 11a may be relatively small. Furthermore, when the needle 15 closes the nozzle orifices 11a by de-energizing of the solenoid coil 12 in the state in which the opening gap T1 has been adjusted to be smaller than the fixed gap T2 of the outlet orifice 25, the armature 13 may move a relatively short distance downward, and thus the nozzle orifices 11a may be rapidly closed. Since the nozzle orifices 11a are rapidly closed, the closing rate shape slope SL4 of the nozzle orifices 11a may be relatively small. Since the nozzle orifices 11a are slowly opened and rapidly closed as described above, injection duration time may be short, which results in a reduction in the amount of fuel to be injected.

[0079] In FIG. 5, a line OT2 represents a state in which the opening gap T1 has been adjusted to be equal to or slightly greater than the fixed gap T2 of the outlet orifice 25 by the piezoelectric actuator 55. When the needle 15 opens the nozzle orifices 11a by energizing of the solenoid coil 12 in the state in which the opening gap T1 has been adjusted to be equal to or slightly greater than the fixed gap T2 of the outlet orifice 25, the distance by which the armature 13 moves upward may be longer than that in the case of the line OT1, which results in an increase in the amount of high-pressure fuel drained from the control chamber 14. Accordingly, a reduction rate of the fuel pressure in the control chamber 14 may increase (that is, the fuel pressure in the control chamber 14 may rapidly decrease), and thus the nozzle orifices 11a may be more rapidly opened in the case of the line OT2 than in the case of the line OT1. Since the nozzle orifices 11a are more rapidly opened, the opening rate shape slope SL2 of the nozzle orifices 11a may be greater than the operating rate shape slope SL1 of the line OT1. Furthermore, when the needle 15 closes the nozzle orifices 11a by de-energizing of the solenoid coil 12 in the state in which the opening gap T1 has been adjusted to be equal to or slightly greater than the fixed gap T2 of the outlet orifice 25, the armature 13 may move a relatively long distance downward, and thus the nozzle orifices 11a may be more slowly closed in the case of the line OT2 than in the case of the line OT1. Since the nozzle orifices 11a are more slowly closed, the closing rate shape slope SL5 of the nozzle orifices 11a may be greater than the closing rate shape slope SL4 of the line OT1. Since the nozzle orifices 11a are more rapidly opened and more slowly closed in the case of the line OT2 than in the case of the line OT1, injection duration time may be longer than that in the case of the line OT1, which results in an increase in the amount of fuel to be injected.

[0080] In FIG. 5, a line OT3 represents a state in which the opening gap T1 has been adjusted to be greater than the fixed gap T2 of the outlet orifice 25 by the piezoelectric actuator 55. When the needle 15 opens the nozzle orifices 11a by energizing of the solenoid coil 12 in the state in which the opening gap T1 has been adjusted to be greater than the fixed gap T2 of the outlet orifice 25, the distance by which the armature 13 moves upward may be longer than that in the case of the line OT2, which results in an increase in the amount of high-pressure fuel drained from the control chamber 14. Accordingly, a reduction rate of the fuel pressure in the control chamber 14 may be greater than that in the case of the line OT2 (that is, the fuel pressure in the control chamber 14 may rapidly decrease), and thus the nozzle orifices 11a may be more rapidly opened in the case of the line OT3 than in the case of the line OT2. Since the nozzle orifices 11a are more rapidly opened, the opening rate shape slope SL3 of the nozzle orifices 11a may be greater than the operating rate shape slope SL2 of the line OT2. Furthermore, when the needle 15 closes the nozzle orifices 11a by de-energizing of the solenoid coil 12 in the state in which the opening gap T1 has been adjusted to be greater than the fixed gap T2 of the outlet orifice 25, the armature 13 may move a relatively long distance downward, and thus the nozzle orifices 11a may be more slowly closed in the case of the line OT3 than in the case of the line OT2. Since the nozzle orifices 11a are more slowly closed, the closing rate shape slope SL6 of the nozzle orifices 11a may be greater than the closing rate shape slope SL5 of the line OT2. Since the nozzle orifices 11a are more rapidly opened and more slowly closed in the case of the line OT3 than in the case of the line OT2, injection duration time may be longer than that in the case of the line OT2, which results in an increase in the amount of fuel to be injected.

[0081] The solenoid coil 12 and the piezoelectric actuator 55 may be electrically connected to a controller 60, and the controller 60 may control energizing or de-energizing of the piezoelectric actuator 55, the magnitude of applied voltage, and the like, as well as controlling energizing or de-energizing of the solenoid coil 12, energizing time, and the like.

[0082] The controller 60 may receive position information of an accelerator pedal or a throttle pedal from an ECU of a vehicle to determine a full load condition (or full throttle condition) or a partial load condition (or partial throttle condition) of an engine.

[0083] In the case where the nozzle orifices 11a are open and the engine is under the full load condition, the controller 60 may de-energize the piezoelectric actuator 55 to maintain the thickness of the piezoelectric actuator 55 at the minimum thickness P1. Accordingly, the opening gap T1 may be greater than the fixed gap T2 of the outlet orifice 25, and thus an initial fuel injection rate and the amount of fuel to be injected may increase.

[0084] Since the piezoelectric actuator 55 contracts to the minimum thickness P1 under the full load condition of the engine and the opening gap T1 is greater than the fixed gap T2 of the outlet orifice 25, the amount of high-pressure fuel drained from the control chamber 14 may relatively increase. Accordingly, a reduction rate of the fuel pressure in the control chamber 14 may relatively increase (that is, the fuel pressure in the control chamber 14 may rapidly decrease), and thus the nozzle orifices 11a may be rapidly opened. That is, the opening rate shape slope of the nozzle orifices 11a may increase. As the opening rate shape slope of the nozzle orifices 11a increases, an initial fuel injection rate and the amount of fuel to be injected may increase, and thus output performance may be improved.

[0085] In the case where the nozzle orifices 11a are open and the engine is under the partial load condition, the controller 60 may energize the piezoelectric actuator 55 to expand the piezoelectric actuator 55 to the expansion thickness P2. At this time, the controller 60 may vary the expansion thickness P2 of the piezoelectric actuator 55 by controlling the magnitude of voltage applied to the piezoelectric actuator 55 according to the position of the accelerator pedal or the throttle pedal. Accordingly, the opening gap T1 may be smaller than or equal to the fixed gap T2 of the outlet orifice 25, and thus an initial fuel injection rate and the amount of fuel injected may decrease.

[0086] Since the expansion thickness P2 of the piezoelectric actuator 55 is adjusted depending on the magnitude of voltage under the partial load condition of the engine and the opening gap T1 is smaller than the fixed gap T2 of the outlet orifice 25, the amount of high-pressure fuel drained from the control chamber 14 may relatively decrease. Accordingly, a reduction rate of the fuel pressure in the control chamber 14 may decrease (that is, the fuel pressure in the control chamber 14 may slowly decrease), and thus the nozzle orifices 11a may be slowly opened. That is, the opening rate shape slope of the nozzle orifices 11a may decrease. As the opening rate shape slope of the nozzle orifices 11a decreases, an initial fuel injection rate and the amount of fuel to be injected may decrease. As a result, NOx may be reduced, and thus emission regulations may be assuredly satisfied.

[0087] FIG. 6 is a flowchart illustrating a method of controlling a fuel injector according to an embodiment of the present disclosure.

[0088] If an ECU for a vehicle sends a fuel injection signal to the controller 60, the controller 60 may energize the solenoid coil 12 (Step S1).

[0089] As the solenoid coil 12 is energized, the armature 13 may be attracted upward toward the solenoid coil 12 by electromagnetic force of the solenoid coil 12. The lower end surface 43 of the valve part 13a may be spaced apart from the seat portion 44 by the upward movement of the armature 13 to open the outlet passage 24 of the control chamber 14. High-pressure fuel may be drained from the control chamber 14 to the inner drain chamber 31 by the opening of the outlet passage 24, and the fuel pressure in the control chamber 14 may relatively decrease. Accordingly, the control rod 16 and the needle 15 may move upward, and therefore the nozzle orifices 11a of the injector body 11 may be opened to inject the high-pressure fuel through the nozzle orifices 11a. The amount of fuel to be injected may be adjusted depending on energizing time of the solenoid coil 12.

[0090] The controller 60 may receive position information of an accelerator pedal or a throttle pedal from the ECU of the vehicle to determine a full load condition or a partial load condition of an engine (Step S2).

[0091] If the engine is under the full load condition, the controller 60 may de-energize the piezoelectric actuator 55 to contract the piezoelectric actuator 55 to the minimum thickness P1 (Step S3). Accordingly, the opening gap T1 may be greater than the fixed gap T2 of the outlet orifice 25, and thus an initial fuel injection rate and the amount of fuel to be injected may increase. As described above, under the full load condition of the engine, the fuel injection rate and the amount of fuel to be injected may increase, and thus output performance may be improved.

[0092] If the engine is under the partial load condition, the controller 60 may energize the piezoelectric actuator 55 to expand the piezoelectric actuator 55 to a predetermined thickness (Step S4). At this time, the controller 60 may vary the expansion thickness P2 of the piezoelectric actuator 55 by controlling the magnitude of voltage applied to the piezoelectric actuator 55 according to the position of the accelerator pedal or the throttle pedal. Accordingly, the opening gap T1 may be smaller than or equal to the fixed gap T2 of the outlet orifice 25, and thus a fuel injection rate may decrease. As described above, under the partial load condition of the engine, the fuel injection rate and the amount of fuel to be injected may decrease, and thus NOx may be reduced. As a result, emission regulations may be satisfied.

[0093] Logical blocks, modules or units described in connection with embodiments disclosed herein can be implemented or performed by a computing device having at least one processor, at least one memory and at least one communication interface. The elements of a method, process, or algorithm described in connection with embodiments disclosed herein can be embodied directly in hardware, in a software module executed by at least one processor, or in a combination of the two. Computer-executable instructions for implementing a method, process, or algorithm described in connection with embodiments disclosed herein can be stored in a non-transitory computer readable storage medium.

[0094] Although the present disclosure has been described with reference to embodiments and the accompanying drawings, the present disclosure is not limited thereto, but may be variously modified and altered by those skilled in the art to which the present disclosure pertains without departing from the spirit and scope of the present disclosure.

[0095] Therefore, embodiments of the present disclosure are provided to explain the spirit and scope of the present disclosure, but not to limit them, so that the spirit and scope of the present disclosure is not limited by the embodiments. The scope of the present disclosure can be construed on the basis of the original claims, and all the technical ideas within the scope equivalent to the original claims are included in the scope of the present disclosure.