Fuel injector

Abstract

A fuel injector (10) for delivering gaseous fuel to an internal combustion engine includes a needle coupling member (64) engageable with a needle assembly to cause an opening movement of a needle (16); a first actuator (20a) operable to generate a first opening force acting on the valve needle assembly by engagement between the first actuator (20a) and the valve needle coupling member (64); and a second actuator (20b) operable to generate a second opening force acting on the valve needle assembly by engagement between the second actuator (20a) and the valve needle coupling member (64), whereby the valve needle coupling member (64) defines a spacing distance (D) from the engagement surface (81) of the valve needle assembly, the valve needle (16) has an engagement surface (81) such that when the valve needle coupling member (64) has moved through the spaced distance after actuation, the valve needle coupling member (64) impinges only on the engagement surface (81), whereby the valve needle coupling member (64) and the engagement surface (81) remain engaged throughout the course of movement of the valve needle (16) to the full lift position.

Description

Technical Field

[0001] The present invention relates to a fuel injector for use in a gaseous fuel injection system. Specifically, the present invention relates to a fuel injector for a gaseous fuel (such as hydrogen) that is used to deliver fuel to an internal combustion engine. Background Art

[0002] In a fuel injection system for liquid fuel, it is known that a fuel pump supplies fuel to a high-pressure accumulator (or common rail), and the fuel is delivered from the high-pressure accumulator to each cylinder of the engine by means of a dedicated fuel injector. Generally, the fuel injector has: an injection nozzle that is received in a hole provided in the cylinder head of the cylinder; and a valve needle that is actuated to control the release of high-pressure fuel from an injection hole provided in the injection nozzle into the cylinder.

[0003] A simple way to open and close the valve needle is to directly connect the actuator to the valve needle by attaching the armature of a solenoid actuator to the valve needle (or by providing a valve needle with an integral armature). The valve needle is biased towards a seating surface such that when the solenoid is not energized, the valve needle prevents fuel from flowing through the injection hole. When the solenoid is actuated, the valve needle is lifted from its seating surface and fuel injection occurs.

[0004] The fuel injector and injection system can be configured in a similar manner for gaseous fuels, such as hydrogen. In this case, hydrogen is typically held in a vehicle's storage tank at a high pressure (e.g., up to 700 bar). At the same time, the injector can operate, for example, at approximately 300 bar. Therefore, fuel can be delivered directly from the storage tank to the fuel injector, eliminating the need for an accumulator. However, the complexity of this method is that the fuel pressure decreases as the storage tank is depleted. For example, as the storage tank empties, the fuel pressure may drop to 150 bar or lower. Since the force required to open the valve needle is affected by the fuel pressure, the opening force varies according to the filling state of the storage tank.

[0005] The present invention has been designed in this context. Summary of the Invention

[0006] One aspect of the present invention provides a fuel injector for delivering gaseous fuel to an internal combustion engine. The fuel injector includes: an injection nozzle including a nozzle body provided with nozzle holes; a valve needle assembly received within the nozzle holes and including a valve needle that can engage a seat region to control the delivery of gaseous fuel through at least one outlet of the injection nozzle; a valve needle coupling member that can engage the valve needle assembly to cause an opening movement of the valve needle; a first actuator that can be operated to generate a first opening force that acts on the valve needle assembly through engagement between the first actuator and the valve needle coupling member; and a second actuator that can be operated to generate a second opening force that acts on the valve needle assembly through engagement between the second actuator and the valve needle coupling member.

[0007] When the second actuator is not operating, the valve needle coupling member can move relative to the second actuator. The engagement surface between the valve needle coupling member and the valve needle assembly defines a spacing distance such that when the valve needle coupling member has moved through the spacing distance after actuation, the valve needle coupling member only impacts the engagement surface, whereby the valve needle coupling member and the engagement surface remain engaged throughout the entire movement of the valve needle to the fully lifted position.

[0008] The second actuator can be configured such that the second opening force urges the second actuator into engagement with the valve needle coupling member.

[0009] The second actuator can include a first thrust surface configured to engage a second thrust surface that is fixed relative to the valve needle coupling member. Optionally, the valve needle coupling member includes the second thrust surface.

[0010] The second actuator can include a second armature, in which case the valve needle coupling member can move relative to the second armature when the second actuator is not operating. The first thrust surface can be fixed relative to the second armature. For example, the first thrust surface can be defined by the surface of a component attached to the second armature.

[0011] The second actuator can be configured to disengage from the valve needle coupling member when not operating.

[0012] The first actuator can be fixed to the valve needle coupling member.

[0013] The first actuator may include a first armature carried by a valve needle coupling member. In such an embodiment, the fuel injector may include a first stop member that defines a first stop surface against which the first armature is forced into engagement when the valve needle is forced closed against the seat region. Optionally, the first stop member also defines an abutment surface for a spring that is operative to urge the valve needle against the seat region to close the valve needle when the first actuator and the second actuator are deactivated. The stop member may also be formed of a damping material such that the stop member absorbs movement of the first armature when the first armature is forced into engagement with the stop member.

[0014] The valve needle coupling member may be a pull tube within which a portion of the valve needle is received. The pull tube may define a flow path for gaseous fuel through the injection nozzle. The pull tube may be provided with at least one opening to permit gaseous fuel flowing within the pull tube to flow radially out of the pull tube for delivery to downstream components of the injection nozzle.

[0015] The valve needle coupling member may define an internal engagement surface that is capable of engaging an engagement surface of the valve needle assembly. The internal engagement surface of the valve needle coupling member and the engagement surface of the valve needle assembly may be frustoconical surfaces.

[0016] The engagement surface of the valve needle assembly may be defined by a lift member carried on the valve needle. The lift member may be a tubular part carried on the valve needle.

[0017] The fuel injector may also include a first stop surface and a second stop surface for the first armature and the second armature, respectively, against which the first armature and the second armature may engage when the valve needle moves to a full lift position.

[0018] Another aspect of the present invention provides a method of operating a fuel injector for delivering gaseous fuel to an internal combustion engine. The fuel injector includes: an injection nozzle including a nozzle body provided with nozzle holes; a valve needle assembly received within the nozzle holes and including a valve needle that can engage a seat region to control the delivery of gaseous fuel through at least one outlet of the injection nozzle; and a valve needle coupling member that can engage the valve needle assembly to cause an opening movement of the valve needle. The engaging surfaces of the valve needle coupling member and the valve needle assembly define a spacing distance such that when the valve needle coupling member has moved through the spacing distance after actuation, the valve needle coupling member only impacts the engaging surface, whereby the valve needle coupling member and the engaging surface remain engaged throughout the movement of the valve needle to the fully lifted position. The method includes: operating a first actuator of the injector to generate a first opening force that acts on the valve needle assembly through the engagement between the first actuator and the valve needle coupling member. The method further includes: when the pressure of the fuel exceeds a pressure threshold, operating a second actuator of the injector to generate a second opening force that acts on the valve needle assembly through the engagement between the second actuator and the valve needle coupling member; and when the pressure of the fuel is below the pressure threshold, moving the valve needle coupling member relative to the second actuator.

[0019] It should be understood that the various features of each aspect of the present invention, either alone or in suitable combination, are equally applicable to other aspects of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] For a better understanding of the present invention, preferred non-limiting embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings, in which:

[0021] Figure 1 is a cross-sectional view of a fuel injector according to an embodiment of the present invention;

[0022] Figures 2 to 4 shows the continuous injection stage of the fuel injector when the injector is in the high-pressure mode Figure 1 ; and

[0023] Figure 5 corresponds to Figure 1 , but shows the valve needle of the injector fully lifted away from its valve seat when the injector is in the low-pressure mode.

[0024] In the drawings and in the following description, the same features are assigned the same reference numerals.

[0025] DETAILED DESCRIPTION

[0026] Throughout the specification, terms such as "top", "bottom", "upper", and "lower" and other directional markers are used with reference to the orientation of the fuel injector as shown in the accompanying drawings. However, it should be understood that these markers are not restrictive, and the fuel injector according to the present invention can be used in any orientation. Detailed Description

[0027] Generally, embodiments of the present invention provide a fuel injector for gaseous fuel used in an internal combustion engine, wherein a variable opening force can be applied to the valve member of the injector to account for changes in the force required to open the valve member due to fluctuations in fuel pressure.

[0028] Figure 1 A first embodiment of a fuel injector 10 for gaseous fuel used in an internal combustion engine is shown. The fuel injector 10 is of the inward-opening type and includes an injection nozzle 12 having a generally cylindrical nozzle body 14, through which a valve needle 16 of a valve needle assembly extends downwardly towards a nozzle tip 18.

[0029] The fuel injector further includes actuator means generally designated 20 for the injection nozzle 12. The injector 10 has a longitudinal axis L, and the injection nozzle 12 and thus the valve needle 16 extend along the longitudinal axis L.

[0030] The nozzle tip 18 defines a chamber volume 22 which, in use, receives gaseous fuel for delivery to a combustion chamber (not shown) of an engine. In the region of the chamber volume 22, the wall of the nozzle body 14 is provided with a plurality of nozzle outlets 24 which extend through the thickness of the wall of the nozzle body 14 to effect fluid communication between the nozzle holes 26 and the environment external to the fuel injector 10 (i.e., the combustion chamber). Since it is a sectional view, three nozzle outlets 24 are fully visible in the drawing, and three others are partially visible, but it should be understood that the group of nozzle outlets 24 can include any suitable number of such outlets and may include a single outlet.

[0031] At the end of the injection nozzle 12 opposite the nozzle tip 18, the nozzle body 14 defines a shoulder region 28 which has an increased outer diameter when compared to the remainder of the nozzle body 14. The nozzle body 14 is received within a tubular housing 30 which defines an inner bore 32 which also receives other parts of the injector 10. The shoulder region 28 engages a step in the inner surface of the tubular housing 30, and the elongate stem of the nozzle body 14 extends and projects through an opening 34 at the lower end of the housing 30.

[0032] The enlarged head end 36 of the nozzle body 14 remote from the tip 18 is received within an insert 37 located within the lower section of the tubular housing 30. The insert 37 defines a spring chamber 38 which houses a nozzle spring 40 for biasing the valve needle 16 into engagement with the valve needle seat 42. The nozzle spring 40 is configured to provide a relatively high force to counteract the force generated by the high pressure in the combustion chamber over a relatively large seat area 42.

[0033] The valve needle assembly is operable to control the fuel delivery through the nozzle outlet 24. The valve needle 16 is received within the nozzle bore 26 and is engageable with a seat area 42 defined by the frustoconical surface of the nozzle bore 26 of the injection nozzle 10.

[0034] In the case where the valve needle 16 is engaged with the seat area 42, this defines the "closed" position of the valve needle 16, in which fuel flow through the nozzle outlet 24 from the fuel injector 10 is prevented. Conversely, when the valve needle 16 is moved away from the seat area 42, the "open" position of the valve needle 16 is defined, in which fuel is permitted to flow out of the nozzle outlet 24 through the nozzle bore 26 by means of a flat, slot or groove provided on the surface of the valve needle 16.

[0035] The operation of the fuel injector 10 will be further described later.

[0036] Within the upper section of the housing 30, a first actuator and a second actuator (hereinafter referred to as first actuator means 20a and second actuator means 20b) are arranged axially in series along the longitudinal axis L of the fuel injector 10, the first actuator means 20a being located Figure 1 below the second actuator means 20b in the orientation shown.

[0037] The first actuator means 20a includes a solenoid defining a first coil 44 which is concentrically arranged about a first core member 46 in a radially outer region of the first actuator means 20a. The first coil 44 is mounted in a known manner on a first coil former 47. The first actuator means 20a further includes a first armature 52 which is arranged to move axially upwardly to engage the first core member 46 when the first coil 44 is energized.

[0038] Correspondingly, the second actuator means 20b includes a solenoid defining a second coil 54 which is concentrically arranged about a second core member 56 in a radially outer region of the second actuator means 20b. The second coil 54 is mounted in a known manner on a second coil former 57. The second actuator means 20b further includes a second armature 60 which is arranged to move axially upwardly to engage the second core member 56 when the second coil 54 is energized.

[0039] Each core member 46, 56 includes an upper region 46a, 56a and a lower region 46b, 56b, wherein the lower regions 46b, 56b project into the space surrounded by the respective coils 44, 54 and are thus located radially inside the respective coils 44, 54. The lower regions 46b, 56b of each core member 46, 56 have a flat lower side defining top stop surfaces 61, 62 which limit the upward movement of the respective one of the armatures 52, 60, as will be described in further detail below.

[0040] The valve needle assembly further includes a valve needle coupling member in the form of a pull tube 64 which extends coaxially along the longitudinal axis L of the injector 10. The pull tube 64 defines a bore 66 which is shaped towards the lower end so as to define a relatively thick wall portion 67 compared to the wall thickness of the remaining part of the length of the pull tube 64. The relatively thick wall portion 67 of the pull tube 64 defines a frustoconical inner engagement surface 80.

[0041] The first armature 52 and the second armature 60 are arranged on the pull tube 64, spaced apart along the pull axis L.

[0042] The first armature 52 is fixed to the pull tube 64 such that the movement of the first armature 52 and the movement of the pull tube 64 are coupled together. When the first coil 44 is energized, the first armature 52 is moved upward (in the illustrated drawing), thus pulling the pull tube 64 upward.

[0043] The second armature 60 is slidably mounted on the pull tube 64 since the pull tube 64 is received in the central opening 63 of the second armature 60 in a sliding fit such that the second armature 60 can move axially relative to the pull tube 64. When the second coil 54 is energized, the engagement between a first thrust surface (which is fixed relative to the second armature 60) and a second thrust surface (which is fixed relative to the pull tube 64) transfers an upward acting force from the second armature 60 to the pull tube 64 to effect movement of the pull tube 64. Conversely, when the second coil 54 is not energized such that the second actuator device 20b is not operative, the pull tube 64 can move relative to the second armature 60.

[0044] The lower end of the central opening 63 of the second armature 60 is enlarged to define a recess 65 within the second armature 60 which receives a bearing sleeve 68 which is fixed to the second armature 60, for example, by welding, interference fit, threading, adhesive or a combination of these methods. The bearing sleeve 68 is generally tubular except for an annular end wall 69 which extends radially inwardly at the lower end of the sleeve 68. The end wall 69 includes a central opening sized to slidably mate with the pull tube 64. A portion of the flat upper surface of the end wall 69 within the sleeve 68 defines a first thrust surface 90.

[0045] Accordingly, the second thrust surface 91 is defined by the planar, radially extending lower end surface of the enlarged portion 92 of the pull tube 64, the enlarged portion 92 being received within the bearing sleeve 68. The enlarged portion 92 includes a radially projecting tube flange 93 at its upper end, and a downwardly tapering conical portion 94 extends from the lower side of the tube flange 93. The conical portion 94 terminates in a lower end surface extending in a radial plane, which lower end surface defines the second thrust surface 91. Thus, in this example, the second thrust surface 91 is integral with the pull tube 64.

[0046] The lower side of the tube flange 93 overhangs the conical portion 94 to define an upper spring seat for the thrust spring 95, the thrust spring 95 being disposed between the tube flange 93 and the end wall 69 of the bearing sleeve 68. Thus, a portion of the end wall 69 defines a lower spring seat that surrounds that portion of the end wall 69 that defines the first thrust surface 90. The thrust spring 95 serves to bias the bearing sleeve 68 and the tube flange 93 apart to hold the second armature 60 against the second bottom stop 89 when the second coil 54 is de-energized, and thus to resist the engagement between the thrust surfaces 90, 91.

[0047] The interface between the thrust surfaces 90, 91 is more clearly shown in the detailed view provided in Figure 1 which shows that when the second coil 54 is de-energized, the first thrust surface 90 and the second thrust surface 91 are axially spaced apart to define a small gap therebetween. Conveniently, using the bearing sleeve 68 as a separate component to define the first thrust surface 90 enables the size of the gap to be adjusted according to the requirements of the application, the reason for which will become clear in the following description.

[0048] The bearing sleeve 68 may be made of a material harder than the second armature 60, thereby providing a correspondingly hard surface for the first thrust surface 90.

[0049] However, in other embodiments, the first thrust surface 90 may be defined by the surface of the second armature 60 itself.

[0050] It should be noted that the thrust surfaces 90, 91 and the associated features are located at an axial position that lies between the flux paths generated by the coils 44, 54 when energized, these flux paths being represented by dashed lines in Figure 1 which. Since the features providing the thrust surfaces 90, 91 consume most of the volume of the second armature 60, positioning these features away from the flux paths avoids restricting the flux area and thus minimizes the effect of accommodating the thrust surfaces 90, 91 on the performance of the actuator devices 20a, 20b.

[0051] The armature return spring 70 is mounted on the support plate 71, which bears at the upper end of the pull tube 64. The armature return spring 70 serves to push the combined mass of the first armature 52, the second armature 60, and the pull tube 64 in the downward direction toward the integral collar 72 on the valve needle 16.

[0052] At the upper end of the valve needle 16 remote from the tip 18, the valve needle 16 includes a reduced-diameter upper stem 74 located directly above the integral collar 72, and the upper stem 74 extends into the pull tube 64. The upper stem 74 carries in interference fit a tubular member in the form of a lifting member 76. The lower surface of the lifting member 76 defines an engagement surface 81 that is shaped to cooperate with the engagement surface 80 on the pull tube 64. In the case where the valve needle 16 is seated against the valve seat 42, as Figure 1 shown, the lower regions of the pull tube 64 and the corresponding engagement surfaces 80, 81 of the lifting member 76 are spaced apart by a spacing distance D. The lifting member 76 can take any convenient form, but in the illustrated example is an annular member within which the upper end of the valve needle 16 is received.

[0053] In Figure 1 the lower part of the lowering, the clearance D between the engagement surface 80 of the pull tube 64 and the engagement surface 81 of the lifting member 76 is more clearly shown, and the lifting member 76 contacts the pull tube 64 such that the pull tube 64 can be accelerated upward to transmit the impact force to the valve needle 16.

[0054] Since the pull tube 64 is a tubular member and defines an inner bore 66, it conveniently provides a flow path for the gaseous fuel through the middle of the injector 10. Fuel is introduced into the upper end of the housing 30 from a high-pressure fuel source. The fuel flows through and around the armature return spring 70 at the upper end of the pull tube 64 and then forward through the pull tube 64 itself. The pull tube 64 is provided with a plurality of holes 82 that extend radially through the wall of the tube 64 to define a flow path for the fuel from the inside of the pull tube 64 into the spring chamber 38 and then forward to the downstream parts of the fuel injector 10. The valve needle 16 is provided with a plurality of grooves or slots on its outer surface to allow the fuel delivered to the nozzle body 14 to flow between the spring chamber 38 and the cavity volume 22 when the valve needle 16 is lifted away from the seat region 42.

[0055] The nozzle spring 40 is operatively engaged with the valve needle 16 via a spring seat 84. The upper stem of the valve needle 16 is received through the nozzle spring 40, and the nozzle spring 40 provides a return force acting on the valve needle 16 via the spring seat 84 to push the valve needle 16 into the closed position, i.e., engaging with the seat region 42.

[0056] The nozzle spring 40 is mounted at its lower end on a spring seat 84 which is formed by a collar carried by an integral collar 72 of the valve needle 16. The pull tube 64 is received within the collar defining the spring seat 84 and is slidable relative to the collar. At the upper end of the nozzle spring 40, the end of the nozzle spring 40 engages the lower abutment surface of a member defining a first bottom stop 86 for the first armature 52. The nozzle spring 40 presses the first bottom stop 86 into engagement with a support ring 87 which is fixed to the housing 30 below the first coil 44, so that the support ring 87 prevents the first bottom stop 86 from moving upward, such that the first bottom stop 86 is held in place by the nozzle spring 40 against the support ring 87.

[0057] The first bottom stop 86 is positioned below the first armature 52 to define a stop surface for the first armature 52 when the first armature 52 moves downward (in the illustrated view) under the force of the armature return spring 70. Since the first bottom stop 86 is conveniently held in place by the nozzle spring 40, this enables the first bottom stop 86 to absorb the impact from the first armature 52 when the nozzle valve needle 16 is closed. When the armature 52 contacts the first bottom stop 86, there is a gap below the pull tube 64.

[0058] The first bottom stop 86 is typically made of a material (such as a polymer) having damping characteristics to minimize the bounce of the armature at the end of its stroke. An annular ring 88 is mounted on the first bottom stop 86 to provide further damping when the first armature 52 is forced to stop as soon as it engages the first bottom stop 86. The annular ring 88 can also provide the function of a seal to prevent gas from escaping from the injector 10. The annular ring 88 can be made of an elastomeric material or any material having suitable damping characteristics. As previously described, although the first armature 52 is provided with the first bottom stop 86 to limit the extent of downward travel, the top stop for the first armature 52 is defined by the surface 61 of the first core member 46.

[0059] Accordingly, a second bottom stop 89 is provided below the second armature 60, and when the second coil 54 is not energized, the second armature 60 is held in contact with the second bottom stop 89 by a thrust spring 95. The second bottom stop 89 is defined by an annular member which is fixed to the upwardly facing surface of the lower region 46b of the second core member. Like the first bottom stop 86, the second bottom stop 89 is typically made of a material (such as a polymer) having damping characteristics to minimize the bounce of the armature at the end of its travel. A radial clearance is provided between the bearing sleeve 68 and the second bottom stop 89 to ensure that the bearing sleeve 68 does not interfere with the engagement between the second armature 60 and the second bottom stop 89.

[0060] Figure 1The clearance between the lower side of the bearing sleeve 68 and the upper surface of the lower region 46b of the first core member is shown. This clearance allows the pull tube 64 to move downward even when the second armature 60 is engaged with the second bottom stop 89. Thus, the interface between the first armature 52 and the first bottom stop 86 defines the point at which the pull tube 64 stops. Accordingly, the second actuator device 20b and the second bottom stop 89 are configured to avoid interfering with the interface between the first actuator 52 and the first bottom stop 86, and the first bottom stop 86 thus defines the main control point for the pull tube 64.

[0061] The top stop surfaces 61, 62 are sized and dimensioned such that the movement of the first armature 52 and the second armature 60 is stopped substantially simultaneously when the first armature 52 and the second armature 60 move upward when the actuator devices 20a, 20b are actuated.

[0062] Figure 1 The injector 10 is shown in a position where the valve needle 16 is engaged with the valve seat 42 and is thus in its closed position. The armature return spring 70 pushes the pull tube 64 downward, and thus the first armature 52 engages with the first bottom stop 86. In this position, no gaseous fuel can escape from the chamber volume 22 through the outlet 24 because the valve needle 16 is seated against the valve seat 42.

[0063] The injector 10 can operate in two different modes: a high-pressure mode, which is used when the pressure of the fuel entering the injector 10 is higher than a pressure threshold, which corresponds to the fuel tank being filled to at least a threshold fill level; and a low-pressure mode, which is used when the fuel pressure is lower than the pressure threshold, which corresponds to the fuel tank being filled to a level below the threshold fill level. In this example, the pressure threshold can be, for example, approximately 150 bar, although the threshold can vary for each implementation.

[0064] Figures 2 to 4 A series of stages of the fuel injection operation of the injector 10 when in the high-pressure mode is shown. In this mode, current is applied to the first coil 44 and the second coil 54, which generates magnetic flux controlled and guided by the first core member 46 and the second core member 56 to cause an electromagnetic force to act on the armatures 52, 60. Further, once each armature 52, 60 is coupled to the pull tube 64, each armature 52, 60 transfers the force acting on it to the pull tube 64. Thus, once coupled, the first actuator device 20a generates a first opening force acting on the pull tube 64 through the first armature 52, and the second actuator device 20b generates a second opening force acting on the pull tube 64 through the second armature 60.

[0065] Initially, only the first armature 52 is connected to the pull tube 64, and the first opening force generated by the first actuator device 20a is not sufficient to overcome the reaction force provided by the armature return spring 70. At this stage, as Figure 2 shown, the first armature 52 and the pull tube 64 remain stationary.

[0066] Meanwhile, since the force generated by the second actuator device 20b is sufficient to overcome the thrust spring 95, the second armature 60, which is not yet connected to the pull tube 64, can be lifted. As the second armature 60 is lifted, the first thrust surface 90 and the second thrust surface 91 engage.

[0067] Once the thrust surfaces 90, 91 engage, the second armature 60 is effectively connected to the pull tube 64 through the thrust surfaces 90, 91. Thus, the second opening force is applied to the pull tube 64 and is thus combined with the first opening force. At this stage, the first opening force and the second opening force generated by both the first actuator device 20a and the second actuator device 20b act on the pull tube 64 combinedly, such that the armatures 52, 60 are pulled upward together and simultaneously against the force of the armature return spring 70. This combined force is sufficient to overcome the force of the armature return spring 70, and thus the first armature 52 and the second armature 60 start to move together, causing the pull tube 64 to be pulled upward.

[0068] As can be seen from the above, the second opening force is also used to connect the second armature 60 to the pull tube 64 through the thrust surfaces 90, 91. Once connected, the second opening force then transfers from the second armature 60 to the pull tube 64 through the interface between the thrust surfaces 90, 91 and further acts on the valve needle assembly.

[0069] Figure 3 The injector 10 is shown at the moment when the nozzle valve needle 16 is about to open. As the first armature 52 moves away from the first bottom stop 86 in the upward direction and the second armature 60 also moves upward, the armature return spring 70 is compressed, and the gap D between the frustoconical engagement surface 80 of the pull tube 64 and the engagement surface 81 of the lifting member 76 on the valve needle stem 74 closes. Thus, the combined moving mass of the pull tube 64 and the first armature 52 and the second armature 60 contacts the lifting member 76. This transfers an impact force or impulse to the valve needle 16 via the engagement surfaces 80, 81, causing the valve needle 16 to move away from the valve seat 42 and move through the lift stroke. This can be considered similar to a "hammering" action. In this way, the combined first opening force and second opening force act on the valve needle 16 through the pull tube 64. Since both the armatures 52, 60 are moving at the moment of impact when in the high-pressure mode, this can generally provide twice the impact force of a single armature.

[0070] The lifting member 76 can be made of any material capable of withstanding the impact provided by the "hammering" when lifting the pull tube 64.

[0071] As the pull tube 64 continues to move through the lift stroke, the valve needle 16 moves further away from the valve seat 42. Once the valve needle 16 has moved away from the valve seat 42, the gaseous fuel delivered through the inner bore 66 of the pull tube 64 to the chamber volume 22 can flow out through the nozzle outlet 24.

[0072] Figure 4 An injector 10 is shown at the moment when the nozzle valve needle 16 is in the full lift position. Both the armature return spring 70 and the nozzle spring 40 are compressed, wherein the nozzle spring 40 maintains contact between the pull tube 64 and the lift member 76. Both the first armature 52 and the second armature 60 are in contact with their respective top stop surfaces 61, 62. Importantly, at this time, the engagement surfaces 80, 81 are still engaged, thereby coupling the pull tube 64 to the lift member 76 and thus applying the combined first opening force and second opening force to the valve needle assembly.

[0073] Therefore, it can be understood from the foregoing description that throughout the lift stroke, the frustoconical engagement surface 80 of the pull tube 64 and the engagement surface 81 of the lift member 76 remain coupled together until the end of the stroke, at which time the first armature 52 reaches its stop surface 61 and the second armature 60 reaches its stop surface 62. Since the lift member 76 and the pull tube 64 remain coupled together, when the fuel pressure is high, all the available forces from both the first actuator device 20a and the second actuator device 20b thus maintain a high force requirement throughout the entire stroke of the valve needle 16.

[0074] To generate a similar amount of force using a single solenoid actuator, a larger diameter would be required to provide a coil with more turns, which would increase the size and total weight of the injector and thus increase the manufacturing cost and complexity of the injector. Therefore, it is highly desirable to use two actuator devices. However, it should be understood that the present invention is not limited to the first actuator device and the second actuator device. In other embodiments, more than two actuator devices may be used to generate the lift force required to lift the valve needle.

[0075] When fuel injection is complete, the first coil 44 and the second coil 54 are de-energized, causing the valve needle 16, the pull tube 64, and the first armature 52 and the second armature 60 to return to their rest positions under the action of the nozzle spring 40 and the actuator return spring 70. Thus, the injector 10 returns Figure 1 to the

[0076] the state shown. Figure 5, when the fuel pressure is lower than the pressure threshold, the force required to lift the valve needle 16 from its valve seat 42 is correspondingly lower. In this case, the first opening force generated by the first actuator device 20a is sufficient to lift the valve needle 16. Therefore, operating both the first actuator device 20a and the second actuator device 20b will generate a lifting force higher than that required to lift the valve needle 16, thereby imparting excess kinetic energy to the valve needle 16.

[0077] Therefore, only the first actuator device 20a is used in the low-pressure mode. Since the second armature 60 is not permanently coupled to the pull tube 64, the second armature 60 can be separated from the pull tube 64, such that the first actuator device 20a does not need to lift the mass of the second armature 60. Since the coupling engagement between the second armature 60 and the pull tube 64 is achieved by the second opening force, deactivating the second actuator device 20b effectively separates the second armature 60 from the pull tube 64 to allow the pull tube 64 to move relative to the second armature 60.

[0078] In this regard, Figure 5 the valve needle 16 shown in full lift, but the second armature 60 remains engaged with the second bottom stop 89 under the action of the thrust spring 95 and is thus separated from the pull tube 64. As the pull tube 64 has been lifted upward, the spacing between the thrust surfaces 90, 91 increases relative to the injector 10 at the Figure 1 closed position shown.

[0079] By operating only the first actuator device 20a in the low-pressure mode, only the first opening force is applied to the valve needle 16. Therefore, the total force acting on the valve needle 16 is lower than the combination of the first opening force and the second opening force generated in the high-pressure mode, such that as the valve needle 16 is lifted, the kinetic energy imparted to the valve needle 16 decreases. Further, the valve needle 16 tends to bounce to a lesser extent when reaching full lift, thereby enhancing the control of fuel injection.

[0080] Since the second armature 60 is separated from the pull tube 64 in the low-pressure mode, when the first armature 52 engages its stop surface 61, the total mass of the impact feature decreases, thereby reducing noise.

[0081] Another benefit of the low-pressure mode is that the electrical power consumed by the injector 10 is reduced because only the first coil 44 is energized.

[0082] In summary, providing the second armature 60 that can be selectively coupled to the pull tube 64 via the thrust surfaces 90, 91 enables the fuel injector 10 to apply a variable opening force to the valve needle 16 via the pull tube 64 and thus reduce the excess kinetic energy in the valve needle 16 when the fuel pressure is low. Advantageously, this is achieved without changing the control of the actuator devices 20a, 20b when activated, noting that slowing down the operation of the actuator devices may complicate the control.

[0083] The actuator devices 20a, 20b can have their coils connected in series or parallel and be driven by a single circuit, saving the cost of electronics compared to driving the two coils separately. Then, appropriate switching can be provided such that the second coil 54 can be deactivated when the first coil 44 is energized in the low-pressure mode. Alternatively, each actuator device can be provided with a separate drive circuit.

[0084] As previously described, when the injector 10 is stationary and the first coil 44 and the second coil 54 are not energized, the size of the gap between the thrust surfaces 90, 91 can be changed by varying the position of the bearing sleeve 68 relative to the second armature 60. In some embodiments, the bearing sleeve 68 can be positioned such that the thrust surfaces 90, 91 are in engagement when the coils 44, 54 are not energized. In other embodiments, the gap between the thrust surfaces 90, 91 can be less than or greater than Figure 1 the gap shown in. The size of the gap affects the kinetic energy in the second armature 60 when the thrust surfaces 90, 91 engage during a fuel injection event and thus affects the impact force between the thrust surfaces 90, 91. This impact force can provide a hammering effect to assist in the opening of the valve needle 16 and may thus be desirable in some applications. Accordingly, the size of the gap between the thrust surfaces 90, 91 can be varied to provide a desired impact force.

[0085] It should be understood that various other embodiments of the present invention are also contemplated without departing from the scope of the appended claims.

[0086] For example, in other embodiments, a solid cylindrical body can be used instead of the coupling member in the form of a pull tube. In such a case, a flow path can be defined radially around the body and / or by means of a passage drilled through the solid cylindrical body, and the flow path can be continued by passages formed in the first core member and the second core member and / or the first armature and the second armature.

[0087] The selective coupling between the armature and the coupling member (such as a pull tube) can be achieved in various ways different from using the thrust surfaces of the interface, as in the above examples. Additionally, in the case of using thrust surfaces, these can be implemented in various other ways. For example, the thrust surfaces can be frustoconical instead of planar as in the above examples. Further, the second thrust surface can not be integral with the pull tube as in the above examples and can instead be provided by a separate component (such as a collar fixed relative to the coupling member).

[0088] In other examples, more than one armature is arranged to selectively couple to a coupling member such as a pull tube. This can be particularly useful where two or more actuator devices are different and arranged to produce different lifting forces acting on the valve needle, thereby providing further flexibility in the lifting force applied to the valve needle. For example, in an arrangement of two actuator devices with selectively couplable armatures, three different lift forces can be produced.

[0089] The engagement surfaces 80, 81 are not limited to the frustoconical shape as described in the present invention. Other embodiments may have modified shapes of the engagement surfaces 80, 81 shown in the drawings such that the surfaces of the pull tube 64 and the lifting member are at different angles, ranging from being completely perpendicular to the pull tube axis L to being nearly parallel.

[0090] Parts List

[0091] 10 - Fuel injector

[0092] 12 - Injection nozzle

[0093] 14 - Nozzle body

[0094] 16 - Valve needle

[0095] 18 - Nozzle tip

[0096] 20a - First actuator device

[0097] 20b - Second actuator device

[0098] 22 - Chamber volume

[0099] 24 - Nozzle outlet

[0100] 26 - Nozzle hole

[0101] 28 - Shoulder region of the nozzle body

[0102] 30 - Tubular housing

[0103] 32 - Inner bore of the tubular housing

[0104] 34 - Opening of the tubular housing

[0105] 36 - Head end of the nozzle body

[0106] 37 - Insert

[0107] 38 - Spring chamber

[0108] 40 - Nozzle spring

[0109] 42 - Valve seat region

[0110] 44, 54 - First coil and second coil

[0111] 46, 56 - First core member and second core member

[0112] 46a, 56a - Upper regions of the first core member and the second core member

[0113] 46b, 56b - Lower regions of the first core member and the second core member

[0114] 47, 57 - First coil former and second coil former

[0115] 52, 60 - First armature and second armature

[0116] 61, 62 - Stopping surfaces of the first armature and the second armature

[0117] 63 - Central opening of the second armature

[0118] 64 - Pulling tube (valve needle connecting member)

[0119] 65 - Second armature recess

[0120] 66 - Inner hole of the pulling tube

[0121] 67 - Thick - walled part of the pulling tube

[0122] 68 - Bearing sleeve

[0123] 69 - End wall of the bearing sleeve

[0124] 70 - Armature return spring

[0125] 71 - Support plate

[0126] 72 - Integral collar of the valve needle

[0127] 74 - Upper rod of the valve needle

[0128] 76 - Lifting member

[0129] 80 - Engaging surface of the pulling tube

[0130] 81 - Engaging surface of the lifting member

[0131] 82 - Pulling tube hole

[0132] 84 - Spring seat

[0133] 86 - First bottom stop

[0134] 87 - Support ring

[0135] 88 - Annular ring

[0136] 89 - Second bottom stop

[0137] 90 - First thrust surface

[0138] 91 - Second thrust surface

[0139] 92 - Enlarged portion of the pulling tube

[0140] 93 - Tube flange

[0141] 94 - Conical portion

[0142] 95 - Thrust spring

[0143] D - Spacing distance

Claims

1. A fuel injector (10) for delivering gaseous fuel to an internal combustion engine, the fuel injector (10) comprising: An injection nozzle (12), the injection nozzle (12) comprising a nozzle body (14), the nozzle body (14) being provided with nozzle holes (26); A valve needle assembly received within the nozzle hole (26) and including a valve needle (16), the valve needle (16) being engageable with a seat region (42) to control the delivery of gaseous fuel through at least one outlet (24) of the injection nozzle (12); A valve needle coupling member (64) engageable with the valve needle assembly to effect an opening movement of the valve needle (16); A first actuator (20a) operable to generate a first opening force acting on the valve needle assembly through an engagement between the first actuator (20a) and the valve needle coupling member (64); And A second actuator (20b) operable to generate a second opening force acting on the valve needle assembly through an engagement between the second actuator (20a) and the valve needle coupling member (64); Wherein the valve needle coupling member (64) is movable relative to the second actuator (20b) when the second actuator (20b) is not operating; and Wherein an engagement surface (81) of the valve needle coupling member (64) with the valve needle assembly defines a spacing distance (D) such that when the valve needle coupling member (64) has moved through the spacing distance after actuation, the valve needle coupling member (64) only impacts the engagement surface (81), and thereby the valve needle coupling member (64) and the engagement surface (81) remain engaged throughout the movement of the valve needle (16) to a fully lifted position.

2. The fuel injector (10) according to claim 1, wherein, The second actuator (20b) is configured such that the second opening force urges the second actuator (20b) into engagement with the valve needle coupling member (64).

3. The fuel injector (10) according to any one of the preceding claims, wherein, The second actuator (20b) includes a first thrust surface (90) configured to engage a second thrust surface (91) that is fixed relative to the valve needle coupling member (64).

4. The fuel injector (10) according to claim 3, wherein, The valve needle coupling member (64) includes the second thrust surface (91).

5. The fuel injector (10) according to any one of the preceding claims, wherein, The second actuator (20b) includes a second armature (60), and wherein the valve needle coupling member (64) is movable relative to the second armature (60) when the second actuator (20b) is not operating.

6. The fuel injector according to claim 5 when dependent on claim 3 or claim 4, wherein, The first thrust surface (90) is fixed relative to the second armature (60).

7. The fuel injector (10) according to any one of the preceding claims, wherein, The second actuator (20b) is configured to be disengaged from the valve needle coupling member (64) when not operating.

8. The fuel injector (10) according to any one of the preceding claims, wherein, The first actuator (20a) is fixed to the valve needle coupling member (64).

9. The fuel injector (10) according to any one of the preceding claims, wherein, The first actuator (20a) includes a first armature (52) carried by the valve needle coupling member (64).

10. The fuel injector (10) according to claim 9, the fuel injector (10) including a first stop member (86), the first stop member (86) defining a first stop surface, when the valve needle (16) is forced against the seat area (42) to close, the first armature (52) is forced into engagement with the first stop surface.

11. The fuel injector (10) according to claim 10, wherein, The first stop member (86) further defines an abutment surface for a spring (40), the spring (40) for urging the valve needle (16) against the seat area (42) to close the valve needle (16) when the first actuator (52) and the second actuator (60) are deactivated.

12. The fuel injector (10) according to any one of the preceding claims, wherein, The valve needle coupling member (64) is a pull tube, a portion of the valve needle (16) being received within the pull tube.

13. The fuel injector (10) according to claim 12, wherein, The pull tube (64) defines a flow path for gaseous fuel through the injection nozzle (12).

14. The fuel injector (10) according to claim 12 or claim 13, wherein, The pull tube (64) is provided with at least one opening (82) to allow gaseous fuel flowing within the pull tube (64) to flow radially out of the pull tube (64) for delivery to downstream components of the injection nozzle (12).

15. The fuel injector (10) according to any one of the preceding claims, wherein, The valve needle coupling member (64) defines an internal engagement surface (80) capable of engaging the engagement surface (81) of the valve needle assembly.

16. A method of operating a fuel injector (10) for delivering gaseous fuel to an internal combustion engine, the fuel injector (10) including: An injection nozzle (12), the injection nozzle (12) including a nozzle body (14), the nozzle body (14) being provided with nozzle holes (26); A valve needle assembly received within the nozzle holes (26) and including a valve needle (16), the valve needle (16) capable of engaging a seat area (42) to control the delivery of gaseous fuel through at least one outlet (24) of the injection nozzle (12); And A valve needle coupling member (64) capable of engaging the valve needle assembly to cause an opening movement of the valve needle (16), wherein the engagement surface (81) of the valve needle coupling member (64) and the valve needle assembly defines a spacing distance (D) such that when the valve needle coupling member (64) has moved through the spacing distance after actuation, the valve needle coupling member (64) only impacts the engagement surface (81), and thereby the valve needle coupling member (64) and the engagement surface (81) remain engaged throughout the movement of the valve needle (16) to the full lift position; Wherein the method includes: Operating a first actuator (20a) of the injector (10) to generate a first opening force, the first opening force acting on the valve needle assembly through the engagement between the first actuator (20a) and the valve needle coupling member (64); When the pressure of the fuel exceeds a pressure threshold, operate a second actuator (20b) of the injector to generate a second opening force that acts on the valve needle assembly through an engagement between the second actuator (20a) and a valve needle coupling member (64); and When the pressure of the fuel is below the pressure threshold, move the valve needle coupling member (64) relative to the second actuator (20b).

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