WO2014193356A1

WO2014193356A1 - Fuel injector

Info

Publication number: WO2014193356A1
Application number: PCT/US2013/043054
Authority: WO
Inventors: William Yunbiao SHEN; Abhijit P. UPADHYE
Original assignee: International Engine Intellectual Property Company, Llc
Priority date: 2013-05-29
Filing date: 2013-05-29
Publication date: 2014-12-04

Abstract

An amplified needle control to provide faster response times when an injection event is to be terminated, such as faster response times when stopping the injection of fuel by a fuel injector into a combustion chamber of an internal combustion engine. The system includes a primary control chamber and a secondary control chamber. Pressure differentials between the primary control chamber and a secondary control chamber may be used to control the displacement of a piston and associated displacement of a needle of a nozzle assembly.

Description

FUEL INJECTOR

BACKGROUND

[0001] Embodiments are directed to a fuel injector for use with a combustion engine. More specifically, embodiments are related to the use of amplified needle control to provide faster response times when an injection event is to be terminated, such as faster response times when stopping the injection of fuel by a fuel injector into a combustion chamber of an internal combustion engine.

[0002] High-pressure fuel injection systems are often used in combustion engines to deliver fuel to a combustion chamber. Fuel may be supplied through a common rail to a series of unit fuel injectors. The fuel injectors typically utilize a nozzle assembly to inject fuel into the combustion chamber. When pressurized fuel that will be injected into the combustion chamber is supplied to a nozzle chamber of the injector, the pressurized fuel may act against a needle of the nozzle assembly in a direction that attempts to lift the needle to an unseated, or open, position. To counteract such forces, fuel injectors may include an area above the needle where a control volume of pressurized fuel is accumulated. This control volume provides a force against an upper surface of the needle that at least assists in preventing the pressurized fuel from lifting the needle. When fuel in the nozzle chamber is to be injected into the combustion chamber, the control volume may be drained so as to remove or reduce this force above the needle, thereby allowing the pressurized fuel in the nozzle chamber to lift the needle from the valve seat. The fuel may then be forced out of a small opening or outlet in a nozzle assembly of the fuel injector under high pressure, thereby typically atomizing the fuel that is delivered to the combustion chamber of the combustion engine. When fuel injection is to stop, a control volume of fuel may again accumulate above the needle to again provide a force to at least assist in counteracting the force on the needle from the fuel pressure in the nozzle chamber, and thereby, with the assistance of a spring, move the needle back to the closed position.

[0003] Often, with common rail fuel injectors having hydraulic needle control, the actuation of the needle control valve and the subsequent displacement of the needle may control the injection event and associated response times. Further, often, when an injection event is to be terminated, the supply of electrical current to a solenoid that is used in the operation of the needle control valve is terminated. However, the needle may not begin to be displaced from the unseated position to the seated position until pressure inside the control volume is equal to or slightly less than the fuel pressure inside the nozzle body. Thus, while pressure in the control volume is building, there may be a delay between the time when the injection event is intended to stop and when the needle is actually returned to its seated position to end the injection event.

BRIEF SUMMARY

[0004] According to an embodiment, a fuel injector is provided that includes a primary control chamber and a secondary control chamber. The primary control chamber may be separated from the secondary control chamber by a piston. The piston includes a bottom surface that is configured to abut against a needle of a nozzle assembly at least when the needle is to be moved from an unseated position to a seated position against a valve seat. Additionally, an inlet throttle line is configured to deliver fuel to the primary control chamber. Further, the secondary control chamber receives at least a portion of the fuel delivered to the primary control chamber.

[0005] According to another embodiment, a fuel injector is provided that includes a piston that is slideably positioned in an piston guide bore of the fuel injector to at least assist in displacing a needle of a nozzle assembly from an unseated position to a seated position. The piston has a top portion and a bottom surface. Additionally, a primary control chamber is positioned to allow fuel in the primary control chamber to exert a force against a top portion of the piston. Further, the primary control chamber has a primary volume. A secondary control chamber is positioned at least adjacent to the bottom surface of the piston. The secondary control chamber has a secondary volume that is larger than the primary volume. Further, fuel is provided to the primary control chamber through an inlet throttle line. Additionally, a drain throttle configured for the removal of fuel from the primary control chamber when a control valve is in an open position.

[0006] According to another embodiment, a method is provided for displacing a needle of a nozzle assembly of a fuel injector. The method includes evacuating fuel from a primary control chamber to decrease a first pressure in the primary control chamber. Fuel is also evacuated from a secondary control chamber to decrease a second pressure in the secondary control chamber. Additionally, the primary control chamber is separated from the secondary control chamber by a piston. The needle is lifted from a seated position against the valve seat to an unseated position when the net force provided by the first and second pressure and a spring are less than a lifting force being exerted against the needle. Fuel is also supplied to the primary control chamber to elevate the first pressure. The piston is displaced toward the needle by, at least in part, a pressure differential between the first pressure and the second pressure. Additionally, the needle is displaced by the displacement of the piston, the needle being displaced from the unseated position to the seated position against the valve seat.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

[0007] Figure 1 illustrates a portion of a hydraulically actuated, electronically controlled, fuel injection system using a fuel injector with an amplified needle control system.

[0008] Figure 2 illustrates a cross sectional view of a portion of a fuel injector that includes an amplified needle control system.

[0009] Figure 3 illustrates a cross sectional view of a portion of a fuel injector.

[0010] Figure 4 illustrates a cross sectional view of a portion of a fuel injector with the needle in a seated, or closed, position.

[0011] Figure 5 illustrates a cross sectional view of a portion of a fuel injector having a needle guide plate.

[0012] Figure 6 illustrates a cross sectional view of a portion of a fuel injector that includes an amplified needle control system having a drain line.

DETAILED DESCRIPTION

[0013] Figure 1 illustrates a portion of a hydraulically actuated, electronically controlled, fuel injection system 10 in which fuel is supplied at high pressure through a common rail 12 to each of a series of fuel injectors, including the depicted individual fuel injector 14. As shown, fuel is delivered via a supply line 16 to the fuel injector 14. Referencing Figures 1 and 2, fuel may be transported through the fuel injector 14 through a fuel line 18. At least a portion of the fuel flowing through the fuel line 18 may be delivered to a nozzle chamber 20 positioned within the injector body 19 that contains at least a portion of a needle 22 of a nozzle assembly 21. Additionally, at least a portion of the fuel in the fuel line 18 upstream of the nozzle chamber 20 may flow into an inlet throttle line 24. As shown in Figure 2, according to certain embodiments, the fuel line 18 may pass through a valve body 26, a throttle plate 28, and a piston guide plate 30 before delivering fuel to the nozzle chamber 20, which may be located in a nozzle body 32. Additionally, according to certain embodiments, the inlet throttle line 24 may extend along the throttle plate 28 and deliver fuel to a primary control chamber 34 in the piston guide plate 30.

[0014] At least a portion of the primary control chamber 34 may be positioned about at least a portion of a piston guide bore 35 in the piston guide plate 30. More specifically, at least a portion of the primary control chamber 34 may be positioned in, or extend into, the piston guide bore 35 and be separated from a portion of the secondary control chamber 38 that, according to certain embodiments, may also extend into the piston guide bore 35. As shown in Figure 2, according to certain embodiments, the primary control chamber 34 may extend between a top portion 39 of a piston 36 and into a portion of the throttle plate 28. As shown in Figures 2-3, according to certain embodiments, at least a portion of the secondary control chamber 38 may include an aperture 40 in a floating sleeve 42 that is positioned in the nozzle chamber 20. The aperture 40 may be provided in a portion of the sleeve 42 that provides for a clearance between the sleeve 42 and the needle guide 23. Additionally, the volume of the secondary control chamber 38 may be expanded by extending the secondary control chamber 38 into a cavity 44 in the piston 36, the cavity 44 being in fluid communication with the aperture 40. Alternatively, rather than have a floating sleeve 42, according to other embodiments, at least a portion of the secondary control chamber 38' may be positioned in a needle guide plate 45 that is positioned above and adjacent to the nozzle body 32, as shown for example in Figures 5 and 6. Moreover, the needle guide plate 45 may also include an aperture 40^' configured to provide at least a portion of the for the secondary control chamber 38^'. Further, according to certain embodiments, the volume of the primary control chamber 34 is smaller than the volume of the secondary control chamber 38, 38^'. [0015] The sleeve 42 may also include a needle guide bore 43 that is sized to guide the movement of the sleeve 42 about a needle guide 23 of the needle 22, and/or vice versa, as the needle 22 is displaced between seated and unseated positions. Similarly, the needle guide plate 45 may include a needle guide bore 43 ^' that is sized to guide the movement of the needle guide 23 of the needle 22. In order to prevent the needle guide bore 43, 43 ^' from interfering with the movement of the needle 22, the needle guide bore 43, 43 ^' and/or needle guide 23 may be configured so that there is sufficient distance or clearance between interior walls of the needle guide bore 43, 43 ^' and the adjacent portion of the needle guide 23 while still minimizing and/or preventing fuel from entering into the space between the needle guide bore 43, 43 ^' and the needle guide 23. For example, according to certain embodiments, the needle guide bore 43, 43 ^' and/or needle guide 23 may be configured for a tight clearance fit, such as, for example, a 3 μιη diametric clearance between the needle guide bore 43, 43 ^' and the needle guide 23.

[0016] The piston 36 may be sized for a relatively tight fit in the piston guide bore 35. For example, the piston 36 may be sized for a tight match clearance fit in the piston guide bore 35, such as, for example, a 3 μιη diametric clearance between the outer diameter of the piston 36 and an adjacent wall 37 of the piston guide bore 35. Such sizing may allow the piston 36 to be displaced along the piston guide bore 35 while also preventing and/or minimizing fuel in the primary control chamber 34 from passing into and/or through the area between the outer diameter of the piston 36 and the adjacent wall 37 and into the secondary control chamber 38, 38', and vice versa. Additionally, the top portion 39 of the piston 36 may have an outer diameter that is larger than the outer diameter of the adjacent portion of the needle guide 23 that a bottom portion 41 of the piston 36 may contact and/or press against during operation of the injector 14, such as, for example, the proximal portion 46 of the needle 22. For example, according to certain embodiments, the top portion 39 of the piston 36 may have a diameter of approximately 4 mm, while the needle guide 23 of the needle 22 that the piston 36 contacts has an approximately 3 mm diameter. More specifically, the surface area of the top portion 39 of the piston 36 upon which fuel in the primary control chamber 34 may exert a force against may be larger than the surface area of the top portion of the needle guide 23 that the piston 36 contacts. Such differences in surface area, and the resulting increase in the force exerted upon the top portion 39 by fuel, may increase the force that the piston 36 may exert upon the needle 22, and thereby provide a relatively fast end to the injection event, particularly when compared to traditional needle controlled fuel injectors that lack the amplified needle control system provided by the supply and removal of fuel from the above-discussed primary and secondary control chambers 34, 38, 38^'.

[0017] As shown in Figures 2 and 3, the piston 36 may also include a drain passage 46. The drain passage 46 may provide a passageway for fuel to flow from the primary control chamber 34 and to the secondary control chamber 38, 38^', and vice versa. For example, when the needle 22 is in a seated, or closed, position, at least a portion of the fuel delivered to the primary control chamber 34 through the inlet throttle line 24 may pass through the drain passage 46 and into the secondary control chamber 38, 38^'. Further, when the needle 22 is being displaced toward the seated, or closed, position and/or when the piston 36 is being displaced generally in a direction toward the secondary control chamber 38, 38^', fuel in the secondary control chamber 38, 38' may flow through the drain passage 46 and, at least temporarily, into the primary control chamber 34. Such passage of fuel through the drain passage 46 may at least assist in maintaining a relatively low fuel pressure in the secondary control chamber 38, 38^'. According to certain embodiments, the drain passage 46 may have a size, such as a diameter, that is smaller than the size, such as the diameter, of at least the portion of the inlet throttle line 24 that is adjacent to the primary control chamber 34.

[0018] Fuel passing from the secondary control chamber 38, 38' through the drain passage 46 may enter into the primary control chamber 34 before entering into a drain throttle 48. The opening and closing of the drain throttle 48 may be controlled by a control valve 15. When in the closed position, fuel may be able to accumulate in the primary control chamber 34, and, as a result, may also enter into the secondary control chamber 38, 38'. However, when the control valve 15 is in an open position, fuel in the primary control chamber 34 may be evacuated through the drain throttle 48, which may deliver the evacuated fuel to an area of relatively low pressure, such as, for example, a fuel tank 17. Thus, when the control valve 15 opens, a pressure differential between the pressure of fuel in the primary control chamber 34 and the pressure of the drain throttle 48 and/or fuel tank 17 may influence the flow of fuel from the primary control chamber 38, 38^' to the drain throttle 48. Additionally, due to the pressure differential between the primary control chamber 34 and secondary control chamber 38, 38', fuel may flow from the secondary control chamber 38, 38^' and through passage 46 to primary control chamber 34 before also passing along to the tank 17. Such removal of fuel from the secondary control chamber 38, 38' to the primary control chamber 34 may reduce the pressure inside the secondary control chamber 38, 38^'. Additionally, according to certain embodiments, the drain throttle 48 may be operably connected to a check valve 50 that prevents fuel from flowing through the drain throttle 48 and into the primary control chamber 34. According to certain embodiments, fuel in the fuel tank 17 may be subjected to one or more pumps, such as low and high pressure pumps 19a, 19b that may be used to deliver fuel from the tank 17 to the common rail 12, as well as provide the elevated pressure of the fuel in the common rail 12.

[0019] When the needle 22 is at a seated, or closed, position the needle 22 is seated on a valve seat 52 of the nozzle body 32 to prevent fuel from being injected through an opening 54 in the nozzle body 32 and into a combustion chamber. While the needle 22 is in the seated, or closed, position, relatively high pressure fuel from the common rail 12 is delivered along the supply line 16 and the fuel injector 14. Moreover, at least a portion of the fuel entering into the injector 14 is delivered by the fuel line 18 to the nozzle chamber 20 while at least another portion of the delivered by the fuel line 18 is diverted into the inlet throttle line 24 and delivered to the primary control chamber 34. During this time, the fuel in the primary control chamber 34 and nozzle chamber 20 may have a fuel pressure that is at or around the fuel pressure in the common rail 12, less any pressure losses experienced during delivery of the fuel to the primary control chamber 34 and/or the nozzle chamber 20.

[0020] When pressurized fuel that will be injected into the combustion chamber is supplied to the nozzle chamber 20 of the injector 14, the pressurized fuel may act against the needle 22 in a direction that attempts to lift the needle 22 from the valve seat 52 and to an unseated, or open, position. However, the fuel delivered to the primary and/or secondary control chambers 34, 38, 38^' provides a pressure against the piston 36 and/or the needle guide 23 that prevents the needle 22 from being lifted away from the valve seat 52. Moreover, as shown in Figures 1-4, the piston 36 and/or the needle guide 23 may have a size, such as diameter, that is larger than the diameter of the needle 22 seated on the valve 52. Such differences in sizes, such as differences in diameters, may provide the piston 36 and needle guide 23 with surface areas for fuel to exert a downward force against the needle 22 that is larger than the surface area of the needle 22 that the fuel pressure is acting against in an attempt to lift the needle 22. More specifically, such differences in surface areas may result in a downward force being exerted against the needle 22 by the piston 36 and/or against the needle guide 23 that is/are greater than the force that is attempting to lift the needle 22 away from the valve seat 52. Thus, the needle 22 may remain in the seated, or closed, position. Additionally, the needle 22 may also be biased in the seated, or closed, position, by a spring 56 positioned in the nozzle chamber 20 that assists in retaining the needle 22 in the closed position.

[0021] When an injection event is to commence, the control valve 15 may be opened so that fuel may be evacuated from the primary control chamber 34 through the drain throttle 48 to a lower pressure area, such as, for example, the fuel tank 17. Such removal of fuel from the primary control chamber 34 may result in a reduction in fuel pressure in the primary control chamber 34. This reduction in pressure may cause the fuel pressure in the primary control chamber 34 to drop below the fuel pressure in the secondary control chamber 38, 38^'. As a result of such pressure differences between the primary and secondary control chambers 34, 38, 38^', the piston 36 may be displaced in the piston guide bore 35 toward the primary control chamber 34. Thus, as the piston 36 is displaced, the volume of the secondary control chamber 38, 38^' increases while the volume of the primary control chamber decreases 34, which may result in a reduction in the fuel pressure in the secondary control chamber 38, 38'. Additionally, pressure differences between the primary and secondary control chambers 34, 38, 38' may result in fuel passing from the secondary control chamber 38, 38' and into the primary control chamber 34, such as, for example, through the drain passage 46 in the piston 36. Such removal of fuel from the secondary control chamber 38, 38' may result in a decrease in fuel pressure in the secondary control chamber 38, 38^'. Fuel entering into the primary control chamber 34 from the secondary control chamber 38, 38' may then also be evacuated from the primary control chamber 34 through the drain throttle 48.

[0022] The reduction in fuel pressure in the primary and secondary chambers 34, 38, 38' may result in the net force acting to retain the needle in the seated position being smaller than the forces acting to lift the needle 22 to an unseated position. Thus, once the net force acting to lift the needle 22 is greater than the biasing force of the spring 56 and any remaining pressure in the primary and secondary control chambers 34, 38, 38^', the needle 22 is lifted from the valve seat 52, and fuel is injected out of the fuel injector 14 through the opening 54.

[0023] During the injection event, fuel that enters into the primary control chamber 34 continues to be evacuated through the drain throttle 48, while fuel in the secondary control chamber 38, 38' may continue to flow into the primary control chamber 34, such as through the drain passage 46 in the piston 36, and also be evacuated through the drain throttle 48. Such removal of fuel from the primary and secondary control chambers 34, 38, 38' may retain those chambers 34, 38, 38^' at relatively low fuel pressures. However, fuel in the nozzle chamber 20 may continue to be at or around the common rail 12 fuel pressure. Thus, differences between the fuel pressure in the nozzle chamber 20 and the primary and secondary control chambers 34, 38, 38^' may allow the needle 22 to remain at an unseated, or open, position so fuel continues to be injected from the fuel injector 14 through the opening 54. Moreover, such pressure differentials, and the resulting net lifting force, may allow the needle 22 to be biased in the lifted position during the injection event.

[0024] When the injection event is to be terminated, the control valve 15 may be closed. Fuel may then accumulate in the primary control chamber 34 so as to provide a force against the top portion 39 of the piston 36 that presses the piston 36 against the needle 22 in a direction generally toward the valve seat 52. Moreover, such pressure may cause the piston 36, along with the spring 56, to push the needle 22 back to its seated position against the valve seat 52.

[0025] While fuel pressure in the primary control chamber 34 is building, the injector 14 may be configured to slow and/or prevent the accumulation of fuel pressure in the secondary control chamber 38, 38'. Moreover, the injector 14 may be configured to prevent fuel pressure in the secondary control chamber 38, 38' from interfering with the ability of fuel pressure in the primary control chamber 34 to displace the piston 36 toward the needle 22 so that the piston 36 at least assists in returning the needle 22 to the seated, or closed, position. For example, according to certain embodiments, the inlet throttle line 24 may be sized larger than the drain passage 46 so that the primary control chamber 34 receives high pressure fuel at a faster rate than the secondary control chamber 38, 38' receives fuel from the primary control chamber 34. Additionally, the primary control chamber 34 may have a smaller volume than the secondary control chamber 38, 38' so that the secondary control chamber 38, 38^' requires a longer time before the secondary control chamber 38, 38^' can attain the generally same fuel pressure as the primary control chamber 34. Thus, the resulting difference in pressure between the primary and secondary control chambers 34, 38, 38^' when the lifted needle 22 is to return to the seated position prevents or minimizes pressure in the secondary control chamber 38, 38' from interfering with the ability of the fuel pressure in the primary control chamber 34 to exert a force against the piston 36 that displaces the needle 22 back to the seated position.

[0026] Further, to assist in the displacement of the needle 22 from the lifted to the closed position, the surface area of the piston 22 upon which the fuel in the primary control chamber 34 exerts a force may be larger than the surface area atop the needle guide 23 that comes into contact with the piston 36. This difference in surface area may allow for an amplified net force on the needle 22 that displaces the needle 22 back to the seated position. Further, as the piston is not pressure balanced anymore, the response time for the close end motion may be significantly faster than compared to non-amplified needle control. More specifically, with traditional fuel injectors that do not include an amplified needle control system, the needle starts to move from an open, unseated position to a seated, closed, position when the pressure above the needle and spring preload generally equal the relatively high pressure inside the nozzle chamber (high pressure). In such situations, the needle may be in a balanced or equilibrium condition that may result in a delay between when the nozzle assembly 21 was to close, such as when current used to provide an injection event (EOC), and when the injection event is actually terminated (EOI). However in an amplified system, such as that described above using the primary and secondary control chambers 34, 38, 38^', once pressure inside the primary control chamber 34 equals the pressure inside the secondary control chamber 38, 38^' (low pressure), the piston 36 starts to move in a direction generally toward the needle 22, and, if not already in contact with the needle 22, the piston 36 contacts the needle 22 and moves the needle 22 toward the seated, closed position. Thus, in the amplified system, the time required to overcome all the forces acting upwards to lift the needle 22 and/or retain the needle 22 in the lift position is comparatively shorter. Moreover, the amplified control system may provide a faster EOC-EOI time because the relatively low pressure of the secondary control chamber 38, 38^' being overcome so as to move the needle 22 to the seated position is less than the relatively high pressure of the nozzle assembly 21 than an injector lacking the amplified control system needs to overcome.

[0027] When the needle 22 reaches its seated position on the valve seat 52, the fuel pressure inside the primary control chamber 34 may continue to increase. The fuel pressure inside the secondary control chamber 38, 38^' may also continue to increase, including through the tight clearance fit between the outer portion of the piston 36 and the wall 37 of the piston guide bore 35, as well as through the tight clearance fit between the needle guide 23 and the adjacent portions of the interior walls of the needle guide bore 43. Again, the drain throttle 48 may also act as an inlet for fuel from the primary control chamber 34 to enter into the secondary control chamber 38, 38^'.

[0028] Referencing Figure 6, in an alternative design, rather than providing a drain passage 46 in the piston 36, the aperture 40, 40^' of the secondary control chamber 38, 38^' may be operably connected to a drain line 58. According to certain embodiments, the drain line 58 extends from the aperture 40, 40' to a portion of the drain throttle 48. According to such embodiments, the drain line may terminate along the drain throttle 48 at a position that is downstream of the check valve 50 of the drain throttle 48. Additionally, the drain line 58 may also include a check valve 60 that prevents the flow of fuel in the drain throttle 48 from entering into the secondary control chamber 38, 38' through the drain line 58. By removing the drain passage 46 and using a drain line, fuel that enters into the secondary control chamber 38, 38^' may be limited to the fuel that passes through the tight match clearance fit between the sidewall of the piston and the adjacent wall 37 of the piston guide bore 35. Thus, typically, the secondary control chamber 38, 38^' may be maintained at a relatively low pressure, thereby further minimizing the potential of the secondary control chamber 38, 38' from interfering with the ability of fuel pressure in the primary control chamber 34 to displace the piston 36 toward and against the needle 22 when the needle 22 is to be displaced from an unseated position to a seated position.

Claims

1. A fuel injector comprising: a primary control chamber and a secondary control chamber, the primary control chamber separated from the secondary control chamber by a piston, the piston having a bottom surface, the bottom surface configured to abut against a needle of a nozzle assembly at least when the needle is to be moved from an unseated position to a seated position against a valve seat; and an inlet throttle line configured to deliver fuel to the primary control chamber, and wherein the secondary control chamber receives at least a portion of the fuel delivered to the primary control chamber.

2. The fuel injector of claim 1, wherein the secondary control chamber has a volume that is larger than a volume of the primary control chamber.

3. The fuel injector of claim 2, wherein the secondary control chamber includes a cavity in the piston.

4. The fuel injection of claim 2, wherein at least a portion of the secondary control chamber is housed in a floating sleeve positioned in the nozzle chamber, the floating sleeve including a needle guide bore that is configured to guide the slidable displacement of a needle guide portion of the needle.

5. The fuel injector of claim 2, wherein the piston includes a drain passage configured to allow the passage of fuel between the primary control chamber and the secondary control chamber, the drain passage having a diameter that is smaller than the diameter of the portion of the inlet throttle line that is adjacent to the primary control chamber.

6. The fuel injector of claim 5, wherein the piston has a top portion, the top portion having a diameter that is larger than a diameter of the needle guide against which the piston abuts.

7. The fuel injector of claim 4, further including a drain throttle, the drain throttle being operated by a control valve, the drain throttle configured for the removal of fuel from the primary control chamber when the control valve is in an open position.

8. The fuel in injector of claim 7, further including a drain line that operably extends between from the secondary control chamber and the drain throttle, the drain line including a check valve configured to prevent fuel in the drain throttle from entering into the secondary control chamber through the drain line.

9. A fuel injector comprising: a piston slideably positioned in an piston guide bore of the fuel injector to at least assist in displacing a needle of a nozzle assembly from an unseated position to a seated position, the piston having a top portion and a bottom surface; a primary control chamber positioned to allow fuel in the primary control chamber to exert a force against the top portion of the piston, the primary control chamber having a primary volume; a secondary control chamber positioned at least adjacent to the bottom surface of the piston, the secondary control chamber having a secondary volume, the secondary volume being larger than the primary volume; an inlet throttle line configured to deliver fuel to the primary control chamber; and a drain throttle configured for the removal of fuel from the primary control chamber when a control valve is in an open position.

10. The fuel injector of claim 9, wherein the secondary volume includes a cavity in the piston.

11. The fuel injector of claim 9, wherein the piston includes a drain passage configured to allow the passage of fuel between the primary control chamber and the secondary control chamber, the drain passage having a diameter that is smaller than the diameter of the portion of the inlet throttle line that is adjacent to the primary control chamber.

12. The fuel injector of claim 8, wherein the bottom portion is configured to abuts against the needle when the needle is to be moved from the unseated position to the seated position, the top portion of the piston having a diameter that is larger than a diameter of the needle guide against which the bottom portion abuts.

13. The fuel injector of claim 8, further including a drain throttle, the drain throttle being operated by a control valve, the drain throttle configured for the removal of fuel from the primary control chamber when the control valve is in an open position.

14. A method of displacing a needle of a nozzle assembly of a fuel injector comprising:

evacuating fuel from a primary control chamber to decrease a first pressure in the primary control chamber;

evacuating fuel from a secondary control chamber to decrease a second pressure in the secondary control chamber, the primary control chamber being separated from the secondary control chamber by a piston;

lifting the needle from a seated position against the valve seat to an unseated position when the net force provided by the first and second pressure and a spring are less than a lifting force being exerted against the needle;

supplying fuel to the primary control chamber to elevate the first pressure; displacing the piston toward the needle by, at least in part, a pressure differential between the first pressure and the second pressure; and

displacing the needle by the displacement of the piston, the needle being displaced from the unseated position to the seated position against the valve seat.

15. The method of claim 14, wherein the step of evacuating the fuel from the secondary control chamber includes delivering fuel from secondary chamber to primary control chamber and evacuating the delivered fuel from the primary control chamber.