Injection control valve in fuel injector configured for pressure relief

Abstract

A fuel injector includes a nozzle and a nozzle check valve that includes a closing hydraulic surface. The fuel injector also includes a high pressure passage, a low pressure vent, a control passage, a check valve control chamber, and a valve seat. The release passage is formed by at least one of an injector housing or a control valve in the control valve assembly. The control valve is movable between a rest position, a lift injection position, and a lift release position, wherein the high pressure passage is connected to the release passage. A control valve may be operated to selectively connect the high pressure passage to the release passage to release fuel pressure to prevent overpressure. Related apparatus and methods are also disclosed.

Description

Technical Field

[0001] The present invention relates generally to a fuel injector, and more particularly to a control valve in a fuel injector that is movable to a release position to release fuel pressure. Background Art

[0002] Electrically actuated fuel injectors have been used for many years across a range of engine platforms. In conventional designs, an injection valve is selectively opened and closed, controlling the injection of fuel into the engine cylinder at a desired injection timing, injection quantity and sometimes injection rate shape. Some fuel injectors rely primarily on the fuel pressure supplied to the injector to actuate the opening of the injection valve at the desired timing. Other systems employ a separate control valve that operates to directly control the closing hydraulic pressure on the injection valve, thereby more accurately controlling the timing and pattern of fuel injection. Designs are known in which a pressurized fuel reservoir is provided to supply pressurized fuel to multiple fuel injectors at injection pressure. Other strategies, sometimes referred to as unit injectors, pressurize the fuel to the injection pressure within each individual fuel injector, employing a hydraulically actuated or cam-actuated piston or plunger to perform the fuel pressurization. Many different versions and extensions of applications and improvements to these two basic strategies are known, particularly in the field of compression ignition engines.

[0003] In recent years, increasingly stringent regulations have been driving research into improved and alternatively configured fuel injectors. It has long been observed that precise control over the operation of a fuel injector can have various benefits with respect to emissions and fuel efficiency. A well-known factor that improves emissions, at least in part by optimizing fuel spray vaporization and being able to quickly inject precise amounts of fuel, is higher fuel pressure. As a result, engineers have been motivated to design fuel injectors that inject fuel at very high injection pressures in the range of hundreds of megapascals (mPa). While utilizing high injection pressures has proven beneficial in many cases, the hardware capabilities of a fuel injector can be tested under such conditions. U.S. Patent No. 11,105,304B2 to Kim et al. relates to a fuel injector that employs a residually stressed solenoid housing to improve pressure capabilities. Summary of the invention

[0004] In one aspect, a fuel injector includes an injector housing having a nozzle and a nozzle check valve movable to open and close the nozzle, and including a closing hydraulic surface. The fuel injector also includes an electrically actuated control valve assembly having a control valve and an armature. A high pressure passage, a low pressure exhaust port, a control passage, a check valve control chamber fluidly connected to the control passage, and a valve seat are formed in the injector housing, and a release passage is formed by at least one of the injector housing or the control valve. The control valve is movable between a rest position, a lift injection position, and a lift release position, wherein the rest position contacts the control valve seat and blocks the control passage from the low pressure exhaust port to maintain high pressure in the control chamber, the lift injection position is a position where the control passage is fluidly connected to the low pressure exhaust port, and the lift release position is a position where the high pressure passage is fluidly connected to the release passage.

[0005] On the other hand, a fuel system includes a fuel supply and a fuel injector, the fuel injector including a fuel inlet fluidly connected to the fuel supply, and a high pressure passage, a control passage, and a low pressure exhaust port extending from a plunger cavity. The fuel injector also includes an electrically actuated relief valve fluidly located between the fuel inlet and the plunger cavity, a nozzle check valve having a closed hydraulic surface exposed to the fluid pressure of the control passage, and an electrically actuated control valve. The control valve includes a three-position valve that blocks the control passage from the low pressure exhaust port in a static position and fluidly connects the control passage to the low pressure exhaust port in a lift injection position. The fuel injector also includes a release passage therein, and the control valve fluidly connects the high pressure passage to the release passage in a lift release position between the static position and the lift injection position.

[0006] In yet another aspect, a method of operating a fuel system includes: advancing a plunger in the fuel system to increase fuel pressure in a plunger chamber; and during the advancement of the plunger, energizing or de-energizing a solenoid in a fuel injector to move a control valve from one of a rest position blocking a control passage from a low-pressure exhaust port and a lift injection position in which the control passage fluid is connected to the low-pressure exhaust port to a lift release position. The method also includes: based on moving the control valve to the lift release position, fluidly connecting a high-pressure passage extending from the plunger chamber to a release passage to release fuel pressure in the plunger chamber; and during the release of fuel pressure in the plunger chamber, keeping the nozzle check valve closed by fuel pressure on a closing hydraulic surface of the nozzle check valve exposed to fluid pressure in the control passage. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 is a cross-sectional side view of an internal combustion engine system according to one embodiment;

[0008] Figure 2is a cross-sectional side view of a control valve assembly in a fuel injector in a rest position according to one embodiment;

[0009] Figure 3 is a cross-sectional side view of a control valve assembly in a lift-release position;

[0010] Figure 4 is a cross-sectional side view of the control valve assembly in a raised injection position;

[0011] Figure 5 is a conceptual diagram showing a bias spring arrangement for a control valve according to one embodiment;

[0012] Figure 6 is a conceptual diagram showing a bias spring arrangement for a control valve according to another embodiment; and

[0013] Figure 7 is a graph showing control current in a fuel injector for a first strategy compared to a pressure relief strategy according to one embodiment. DETAILED DESCRIPTION

[0014] Reference Figure 1 , an internal combustion engine system 10 according to one embodiment is shown. The engine system 10 includes an internal combustion engine 12 having an engine housing 14, in which a combustion cylinder 16 is formed. The cylinder 16 can be one of any number of cylinders in any suitable arrangement, such as in-line, V-shaped or other. It is understood that, generally in a four-stroke engine cycle, the piston can move between the bottom dead center position and the top dead center position in the cylinder 16. The engine system 10 can be compression-ignited so that the reciprocating motion of the piston in the cylinder 16 increases the fluid pressure therein to the autoignition threshold. Therefore, the engine system 10 can be operated with a suitable compression ignition fuel such as a diesel distillate fuel. Other engine operations, fuel supply and ignition strategies are still within the scope of the present invention. The engine system 10 can be applied to various purposes, from vehicle propulsion of land vehicles or ships to power generation, compressors, pumps or other operations.

[0015] The engine system 10 also includes a fuel system 18 having a fuel supply 20 containing liquid fuel and a fuel pump 22 configured to deliver the fuel to one or more fuel injectors 24, such as Figure 1 As shown. Fuel injector 24 may be one of a plurality of interchangeable fuel injectors, each of which is associated with one of a plurality of cylinders in engine 12 and positioned to directly inject fuel in a practical implementation strategy. The description and discussion herein of a single fuel injector or any component thereof should be understood to be similar to any other fuel injector or corresponding component that may be used in fuel system 18.

[0016] The fuel injector 24 includes an injector housing 26 having a nozzle 28 having a plurality of nozzle outlets 31 formed therein, and each nozzle outlet 31 is fluidly connected to the cylinder 16. The fuel injector 24 also includes a nozzle check valve 30, which has the form of, for example, a nozzle valve, movable to open and close the nozzle outlet 31 in the nozzle 28, and has a closing hydraulic surface 32. The fuel injector 24 also includes an electrically actuated control valve assembly 34 having a control valve 36 and an armature 38. The control valve assembly 34 also includes a first biasing spring 40 and one or more second biasing springs 42, the purpose and function of which are further discussed herein. The solenoid 44 is also part of the control valve assembly 34, and is energized by an electrical control current to magnetically attract the armature 38, thereby moving the control valve 34 between a plurality of different positions, which is also further discussed herein.

[0017] The fuel injector 24 also includes an electrically actuated relief valve assembly 46. The relief valve assembly 46 includes a relief valve 48, an armature 50, a biasing spring 52, and a solenoid 54. A spring stop 56 may be positioned in a fixed position between the spring 40 and the spring 52 in the injector housing 26. In some embodiments, the solenoid 54 and the solenoid 44 may be positioned in a common solenoid assembly, although the invention is not limited thereto. The illustrated design using the spring stop 56 differs from certain other designs using a conventional housing solenoid for a control valve in a relief valve utilizing a conventional biasing spring. The solenoid 54 may be energized by an electrical control current to attract the armature 50, thereby moving the relief valve 46 between an open position and a closed position.

[0018] The high pressure passage 66, the low pressure exhaust port 68, the control passage 70, the check valve control chamber 72 fluidly connected to the control passage 70, and the valve seat 74 are all formed in the injector housing 26. The release passage 76 is formed by at least one of the injector housing 26 or the control valve 36, and in the illustrated embodiment is formed by the injector housing 26. In other embodiments, annular and / or longitudinal or circumferential passages formed in the outer surface of the control valve 36, or even internal passages, can form a pressure relief passage as contemplated herein. The injector housing 26 also has a high pressure branch passage 67, a plunger cavity 60, a fuel inlet 78, and an overflow passage 80 formed therein. In some embodiments, Figure 1 Another branch passage not shown in the drawing may directly fluidly connect the high pressure passage 66 to the check valve control chamber 72. The plunger 58 is movable between an advanced position and a retracted position in the plunger cavity 60 to pressurize the fuel therein. The high pressure passage 66 extends from the plunger cavity 60. The plunger 58 may include a tappet 62 that contacts a rotating cam 64 of the engine 12. In other embodiments, the plunger for fuel pressurization may be hydraulically actuated.

[0019] The relief valve 48 is fluidly located between the fuel inlet 78 and the plunger cavity 60 and is movable between an open position and a closed position, in which the plunger 58 reciprocates to draw fuel into and out of the plunger cavity 60 through the fuel inlet 78. When the relief valve 50 is moved to the closed position, the fluid connection between the fuel inlet 78 and the relief passage 80 is blocked, and moving the plunger 58 toward the advanced position increases the fuel pressure in the plunger cavity 60, the high pressure passage 66, and other locations fluidly connected to the high pressure passage 66.

[0020] Depending on the fuel injection strategy used and possibly other factors, in some cases, when the plunger 58 is advanced to pressurize the fuel, the fuel pressure within the fuel injector 24 may approach or exceed the desired fuel pressure limit. As further discussed herein, the present invention contemplates a unique strategy for selectively releasing or venting fuel pressure to avoid exceeding the desired pressure limit.

[0021] To this end, the control valve 34 may include a multi-position valve, such as a three-position valve movable between a rest position, a lift injection position, and a lift release position. In the rest position, the control valve 36 contacts the control valve seat 74 and blocks the control passage 70 from the low pressure exhaust port 68 to maintain the high pressure in the control chamber 72. At the lift injection position, the control passage 70 is fluidly connected to the low pressure exhaust port 68 so that the high pressure of the fuel applied to the nozzle check valve 30 from the high pressure passage 66 overcomes the hydraulic pressure on the closing hydraulic surface 32 and lifts the nozzle check valve 30 to inject fuel into the cylinder 16. In the rest position in contact with the valve seat 74, the control valve 36 allows the high pressure to prevail in the control chamber 72 and acts on the closing hydraulic maintenance 32 to keep the nozzle check valve 30 closed. In the lift release position, the high pressure passage 66 is fluidly connected to the release passage 76 to enable the discharge of excessive pressure, thereby avoiding over-pressurizing the fuel injector 24. When the relief valve 48 is closed, the discharge of the overpressure occurs during the advancement of the plunger 58. In one embodiment, multiple injections may be performed per engine cycle with pressure relief performed between the multiple injections, as discussed further herein.

[0022] Now also refer to Figure 2 , a schematic diagram of a control valve assembly 34 suitable for use with a fuel injector 24 is shown. Figure 2 The control valve assembly 34 shown may have a Figure 1 For example, in Figure 1 , the release passage 76 is shown above the control valve 36 contacting the valve seat 74 in the rest position, and Figure 2, the release passage 76 is shown below the control valve 36 contacting the injector housing 26 in the rest position. In view of the present disclosure, those skilled in the art will appreciate different control valve and passage piping configurations within the scope of the present invention. Figure 1 The control valve 36 shown in FIG. 1 has a single valve member, but in Figure 2 The control valve 36 shown in FIG. 1 has multiple valve members, including an upper member labeled 36 and a lower member labeled 37. It should be understood that multiple embodiments are contemplated herein where the control valve includes a single valve member, two valve members, a valve with raised edges for establishing or blocking fluid connections based on valve position, internal passages, or other variations as suggested above.

[0023] In the illustrated embodiment, the control valve 36 includes the sealing body 41 and is shown as being present in a rest position in which the sealing body 41 is in contact with the injector housing 26 and in which the control passage 70 is fluidly connected to a high pressure branch passage 69 extending to the high pressure passage 66. In the rest position, the control passage 70 is blocked from the low pressure exhaust port 68 and is also blocked from the release passage 76. Figure 2 Also shown in FIG. 1 is a first biasing spring 40 biasing the control valve 36 toward the rest position, and two second biasing springs 42 biasing the control valve 36 away from the rest position. Figure 2 In the configuration shown, the nozzle check valve 30 remains closed and no fuel injection occurs.

[0024] Reference Figure 3 , shows the control valve 36 moved to the lift release position, wherein the sealing body 41 does not contact the injector housing 26. The third biasing spring 39 is operable to bias the control valve 36 away from the rest position by contacting the valve member 37. In the lift release position, the high pressure branch passage 67, which is fluidly connected to the high pressure passage 66, is fluidly connected to the release passage 76. By having a smaller cross-sectional area than the high pressure passage 66 and the high pressure branch passage 67, the release passage 76 can have a relatively more restricted flow. The control passage 70 remains fluidly connected to the high pressure branch passage 69. In Figure 3 In the illustrated state, high pressure fuel continues to be supplied to the plunger cavity 72 through the control passage 70 and acts on the closing hydraulic surface 32 to keep the nozzle check valve 30 closed. In this configuration, the pressure in the plunger cavity 60 can be reduced by relieving pressure from the branch passage 67 to the relief passage 76. As further discussed herein, when the plunger 58 is advanced and the relief valve 48 is closed, the control valve 36 can be as Figure 3The second biasing spring 42 biases the control valve 36 away from the rest position opposite the biasing force applied by the first biasing spring 40. In the lift release position, the control valve 36 may be substantially balanced between the respective biasing springs such that the control valve 36 may remain positioned in the lift release position until moved by energizing or de-energizing the solenoid 44.

[0025] Now turn to Figure 4 , showing that the control valve 36 has been moved to the lift injection position to perform fuel injection from the fuel injector 24. In this configuration, the high pressure branch passage 69 is blocked from the control passage 70, and the control passage 70 is fluidly connected to the low pressure exhaust port 68. The seal body 41 has moved into contact with the injector housing 26 and now blocks the high pressure branch passage 67 from the control passage 70, the release passage 76, and the low pressure exhaust port 68. Figure 4 As shown, the second biasing spring 42 is disengaged. The control valve 36 is linearly movable between the rest position, the lift spray position, and the lift release position. In the lift release position, the control valve 36 can be linearly movable between the rest position and the lift spray position. Figure 2-4 It can also be seen that the rest position can include a first stop position, and the lift spray position can include a second stop position. The first bias spring 40 can bias the control valve 36 in at least a portion of the travel distance, typically throughout the entire travel distance. One or more second bias springs 42 can bias the control valve 36 in only a portion of the travel distance. The illustrated embodiment includes a first bias spring 40 and a second bias spring 42, the first bias spring 40 acting as a closing bias spring biasing the control valve 36 toward the rest position, and the second bias spring 42 acting as a lift bias spring biasing the control valve 36 away from the rest position.

[0026] Now turn to Figure 5 , showing an operation similar to Figure 2-4 The control valve assembly 134 of the control valve assembly 34 is shown to include a control valve 136 , a first biasing spring 140 , and a second biasing spring 142 . Figure 5 It also shows that Figure 5 140 and 142 are positioned on or associated with opposite ends of the control valve 136. The first biasing spring 140 biases the control valve 136 the entire distance of travel between the rest position and the lift-to-spray position. The second biasing spring 142 biases the control valve 136 for only a portion of the distance of travel and will generally disengage when the control valve 136 moves from the lift-release position toward the lift-to-spray position.

[0027] Reference Figure 6, a control valve assembly 234 is shown that includes a control valve 236, a first biasing spring 240, and a second biasing spring 242. In this embodiment, both biasing springs 240 and 242 can be understood as closing biasing springs acting on or associated with the same end of the control valve 236. The first biasing spring 240 biases the control valve 236 throughout the travel distance between the rest position and the lift spray position, while the second biasing spring 242 biases the control valve only a portion of the travel distance, biasing the control valve 236 toward the rest position, but only beginning to engage in a partial travel position such as the lift release position.

[0028] Figure 5 or Figure 6 Any of the arrangements shown in and other arrangements may be used in a fuel injector according to the present invention to enable different levels of energization of an associated solenoid to actuate a control valve from a rest position to a lift release position relative to actuating the control valve from a lift release position to a lift injection position. In one embodiment, energizing a solenoid according to the present invention moves the control valve from the rest position to the lift release position by energizing the solenoid to a first energy state, and energizing the solenoid to move the control valve from the lift release position to the lift injection position includes energizing the solenoid to a second, higher energy state.

[0029] Industrial Applicability

[0030] Operating the fuel system 18 may include rotating the cam 64 to advance the plunger 58 to increase the fuel pressure in the plunger chamber 60. As described herein, when the relief valve 48 is in the closed position, the fuel pressure in the plunger chamber 60 increases. Operating the fuel system 18 further includes energizing or de-energizing the solenoid 44 during advancement of the plunger 58 to move the control valve 36 from one of the rest position blocking the control passage 70 from the low pressure drain port 68 or the lift injection position fluidly connecting the control passage 70 to the low pressure drain port 68 to the lift release position. Positioning the control valve 36 in the lift release position fluidly connects the high pressure passage 66 to the release passage 76 to release the fuel pressure in the plunger chamber 58.

[0031] As the pressure is released, the control valve 36 can move from the lift release position to the rest position or the lift injection position. Moving the control valve 36 to the lift injection position or returning the control valve 36 to the rest position blocks the high pressure passage 66 from the release passage 70 to the end pressure release. During the release of the fuel pressure in the plunger chamber 60, the nozzle check valve 30 is kept closed by shutting off the fuel pressure on the hydraulic surface 32. As described above, depending on the energy state of the solenoid 44, the control valve 36 can move to different positions. In one embodiment, the solenoid 44 can be energized for the first time in the engine cycle to move the control valve 36 to the lift injection position during the advancement of the plunger 58, and energized for the second time in the same engine cycle to move the control valve 36 to the lift injection position during the advancement of the plunger 58.

[0032] Initially energizing the solenoid 44 to move the control valve 36 from the rest position to the lift release position may include energizing the solenoid 44 to a first energy state, and each of energizing the solenoid 44 for the first time and energizing the solenoid 44 for the second time to move the control valve 36 to the lift injection position in the same engine cycle may include energizing the solenoid 44 to a second higher energy state. In this manner, it is readily contemplated that the control valve 36 may be moved from the rest position to the lift release position with a smaller magnitude of control current against a smaller net spring bias, and then moved from the lift release position to the lift injection position with a larger magnitude of control current against a larger net spring bias. In some applications, the control valve 36 may also be switched between the lift release position and the lift injection position by alternating between a lower magnitude of control current and a larger magnitude of control current, thereby relieving pressure between multiple injections in an engine cycle. Other variations will be apparent to those skilled in the art.

[0033] Now also refer to Figure 7 , a first set of control current traces 300 are shown, which show the spill current 302 and DOC (direct operated check valve) or control valve current 304 in an operating strategy that does not use pressure relief. In this example, the spill valve 48 is initially open and the control valve 36 is initially closed. At about 306, the solenoid 54 can be energized to close the spill valve 48. The rotation of the cam 64 relative to the tappet 62 can advance the plunger 58 and begin to build pressure in the connecting passage in the plunger chamber 60 and the fuel injection 24. At about 310, the solenoid 44 is energized to open the control valve 36 and allow the nozzle check valve 30 to open to begin fuel injection. At about 312, the solenoid 44 is energized again to perform a second fuel injection. Reference numeral 308 represents a period of time when the spill valve 48 is generally closed and the plunger 58 is advanced, so that pressure continues to build, potentially corresponding to a condition where an overpressure may occur. The state represented by the control current trace 300 occurs in the same engine cycle.

[0034] Control current 301 shows the spill current at 402 and the DOC current at 404 during one exemplary engine cycle. In this example, spill valve 48 is initially open and control valve 36 is initially in the lift release position, e.g., in which a lower magnitude control current is applied to solenoid 44. At approximately 406, spill valve 48 is closed. At approximately the same time, or possibly earlier, at 410, the DOC current is reduced to allow nozzle check valve 30 to close. DOC current 404 then increases to a greater magnitude at approximately 411 to move control valve 36 from the rest position to the lift injection position, and then decreases at 412 to move control valve 36 to the rest position (closed) to end fuel injection. At approximately 413, DOC current 404 increases again to move control valve 36 to the lift injection position again to begin a second fuel injection. At 414, DOC current 404 decreases again and thereafter switches between the lift injection position and the lift release position to perform multiple additional fuel injections. Thus, during the time period shown generally at 408 where there is a risk of overpressurization, the pressure relief event between injections may prevent overpressurization.

[0035] This specification is for illustrative purposes only and should not be interpreted as narrowing the scope of the present invention in any way. Therefore, it will be appreciated by those skilled in the art that various modifications may be made to the currently disclosed embodiments without departing from the complete and reasonable scope and spirit of the present invention. Other aspects, features and advantages will become apparent by studying the accompanying drawings and the appended claims. As used herein, the articles "a" and "an" are intended to include one or more items and may be used interchangeably with "one or more". In the case of only wanting one item, the term "one" or similar language is used. In addition, as used herein, the terms "has", "have", "having" etc. are intended to be open terms. In addition, the phrase "based on" is intended to mean "based at least in part on", unless otherwise expressly stated.

Claims

1. A fuel injector, comprising: an injector housing including a nozzle; a nozzle check valve movable to open and close the nozzle and comprising a shutoff hydraulic surface; An electrically actuated control valve assembly comprising a control valve and an armature; a high pressure passage, a low pressure exhaust port, a control passage, a check valve control chamber fluidly connected to the control passage, and a valve seat are formed in the injector housing, and a release passage is formed by at least one of the injector housing or the control valve; and The control valve is movable between a rest position, a lift injection position and a lift release position, wherein the rest position contacts the control valve seat and blocks the control passage from the low-pressure exhaust port to maintain high pressure in the control chamber, the lift injection position is a position in which the control passage is fluidically connected to the low-pressure exhaust port, and the lift release position is a position in which the high-pressure passage is fluidically connected to the release passage.

2. The fuel injector of claim 1 , wherein in the lift release position, the control valve blocks the control passage from both the low pressure drain port and the release passage; and The control valve is linearly movable a travel distance between the rest position, the lift injection position and the lift release position, and at the lift release position, the control valve is located between the rest position and the lift injection position.

3. A fuel injector as described in claim 1 or 2, wherein the rest position includes a first stop position, the lift injection position includes a second stop position, and the fuel injector also includes a first biasing spring and a second biasing spring, the first biasing spring biasing the control valve in at least a portion of the travel distance, and the second biasing spring biasing the control valve only in a portion of the travel distance.

4. The fuel injector of claim 3, wherein the first biasing spring comprises a closing biasing spring that biases the control valve toward the rest position and the second biasing spring comprises a lifting biasing spring that biases the control valve away from the rest position.

5. The fuel injector of claim 3, wherein each of the first biasing spring and the second biasing spring comprises a closing biasing spring that biases the control valve toward the rest position.

6. A fuel injector as claimed in any one of the preceding claims, wherein a plunger cavity is formed in the injector housing and is fluidly connected to the high pressure passage, and the fuel injector further comprises a plunger movable in the plunger cavity, and a tappet coupled to the plunger; and The injector housing defines a low pressure space and further includes an electrically actuated relief valve movable in the injector housing between an open position fluidly connecting the plunger chamber to the low pressure space and a closed position.

7. A fuel system comprising: Fuel supply; a fuel injector including a fuel inlet fluidly connected to said fuel supply, a high pressure passage extending from a plunger cavity, a control passage, and a low pressure drain port therein; The fuel injector also includes an electrically actuated spill valve fluidly located between the fuel inlet and the plunger cavity, a nozzle check valve having a closing hydraulic surface exposed to fluid pressure in the control passage, and an electrically actuated control valve; The control valve includes a three-position valve that fluidly blocks the control passage from the low-pressure exhaust port in a rest position and fluidly connects the control passage to the low-pressure exhaust port in a lift-spray position; and The fuel injector further includes a release passage therein, and the control valve fluidly connects the high pressure passage to the release passage at a lift release position between the rest position and the lift injection position.

8. The fuel system of claim 7, wherein the rest position comprises a first stop position and the lift injection position comprises a second stop position; and The fuel system also includes a biasing spring that biases the control valve only through a portion of the travel distance between a rest position and a lifted injection position.

9. The fuel system of claim 8, wherein the biasing spring comprises a closing biasing spring that biases the control valve toward the rest position.

10. The fuel system of claim 8, wherein the biasing spring comprises a lift biasing spring that biases the control valve away from the rest position.

11. The fuel system of claim 10 further comprising a second biasing spring biasing said control valve over said full travel distance between said rest position and said lift injection position.

12. A method of operating a fuel system, comprising: advancing a plunger in the fuel system to increase fuel pressure in the plunger chamber; energizing or de-energizing a solenoid in the fuel injector during advancement of the plunger to move the control valve from one of a rest position blocking the control passage from the low pressure drain or a lift-injection position fluidly connecting the control passage to the low pressure drain to a lift-release position; upon moving the control valve to the lift release position, fluidly connecting a high pressure passage extending from the plunger chamber to a release passage to release fuel pressure in the plunger chamber; as well as During release of fuel pressure in the plunger chamber, a nozzle check valve in the fuel injector is kept closed by fuel pressure on a closing hydraulic surface of the nozzle check valve exposed to fluid pressure of the control passage.

13. The method of claim 12, further comprising: energizing the solenoid for a first time in an engine cycle to move the control valve to the lift-and-spray position during advancement of the plunger; as well as energizing the solenoid a second time in an engine cycle to move the control valve to the lift-and-spray position during advancement of the plunger; Wherein energizing or de-energizing the solenoid includes energizing the solenoid to a first energy state, and each of energizing the solenoid for a first time and energizing the solenoid for a second time includes energizing the solenoid to a second, higher energy state.

14. The method according to claim 12 or 13, further comprising: applying a small spring bias to the control valve in a portion of a travel path between the rest position and the lift-and-spray position; applying a greater spring bias to the control valve in a portion of the travel path from the lift release position to the lift spray position; as well as A biasing spring is disengaged from the control valve during a portion of the travel path.

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