EP3377754B1

EP3377754B1 - Fuel injector

Info

Publication number: EP3377754B1
Application number: EP16794598.9A
Authority: EP
Inventors: Philippe Legrand
Original assignee: Delphi Technologies IP Ltd
Current assignee: Delphi Technologies IP Ltd
Priority date: 2015-11-16
Filing date: 2016-11-09
Publication date: 2020-04-29
Anticipated expiration: 2036-11-09
Also published as: WO2017084948A1; CN108291510B; JP2018537610A; EP3377754A1; JP6763634B2; GB201520124D0; CN108291510A

Description

Technical field

The present invention relates to a fuel injector for use in delivering high pressure fuel to an internal combustion engine.

Background

Both indirect and direct acting injectors are known for use in fuel injection systems. In an indirect acting injector, a control valve arrangement is operable to control the pressure of fuel within a control chamber which acts on an upper end of an injector valve needle. The pressure level within the control chamber determines the balance of forces on the needle, and hence controls the precise timing of needle movement away from the seating for the valve needle to commence injection. An actuator such as an electromagnetic actuator controls the control valve arrangement. The force applied by the actuator is not linked directly to the valve needle movement, but controls the control valve arrangement which in turn controls the force which is consequently applied to the valve needle via a hydraulic circuit.
In a direct acting injector, an actuator is coupled directly to the valve needle to control needle movement. Both piezoelectric and electromagnetic direct acting injectors are known. JP H02 112664 A and DE 199 43 253 A1 disclose fuel injectors comprising a valve needle moving within a bore, by means of piezoelectric actuators which apply a radial force to a force convertor.
In an electromagnetic direct acting injector, a solenoid-operated actuator controls movement of a plunger, having a plunger diameter, by applying a current through a solenoid. The plunger acts on a chamber of fuel arranged at the upper end of a valve needle of a second, reduced diameter. The arrangement acts as a hydraulic amplifier arrangement by which the force of the plunger is transmitted to the valve needle with an amplification factor determined by the ratio of the plunger diameter to the diameter of the valve needle. As the plunger is actuated and pulled upwards, the volume of the chamber increases causing fuel pressure within the control chamber to reduce and hence reducing the force tending to act to seat the valve needle. If the actuation force is removed by removing or reducing the current applied to the solenoid, the plunger moves downwardly under a spring force, reducing the volume of the control chamber and increasing fuel pressure in the control chamber so as to seat the valve needle.
It is desirable to provide an injector that can withstand the application of large forces. This is because large forces allow the needle to react more quickly, enable the system to accommodate more complex injection sequences, allow the use of higher pressure fuels, and place fewer limitations on the components that can be used within the injection system. However, the amount of force that can be applied using conventional direct acting injectors is limited by geometry of the fuel injector. In particular, the opening force applied to the needle is counteracted by resistive forces; these resistive forces increase as the diameter of the plunger increases. This means that in practice the plunger diameter cannot exceed a maximum threshold, typically around 8 mm. As a result the maximum force that can be applied to the needle is typically around 110 N.
It is an object of the invention to provide an injector which addresses the shortcomings of the prior art.

Summary of the invention

Against this background, the invention resides in a fuel injector for use in an internal combustion engine. The fuel injector comprises a valve needle having a needle axis and being reciprocally movable within a bore in a nozzle housing towards and away from a needle seat along the needle axis; and a needle actuator comprising a force applicator and a force convertor. The force applicator is configured to apply a radial force to the force convertor in a direction transverse to the needle axis. The force convertor is configured to convert the radial force to a longitudinal force substantially parallel to the needle axis. The needle actuator is configured to apply the longitudinal force to the needle, thereby to effect movement of the needle along the needle axis.
In this way, the invention provides a fuel injector in which the movement of the needle is controlled by applying a radial force by the applicator, which is converted into a longitudinal force by the force convertor. The needle is therefore what may be referred to as "side-actuated". This side actuation is advantageous because it allows the force applicator to be arranged around the outside of the needle, rather than at the end of the needle, meaning that the actuator need not take up space in the longitudinal direction.
The force convertor may comprise at least one pivot member configured to pivot about a pivot point to convert the radial force to the longitudinal force. Using a pivot member in this way provides a particularly simple means of converting the radial force into the longitudinal force. Furthermore, the force applied to the needle can be finely tuned by selecting the dimensions of the pivot member and the location of the pivot, allowing the actuator of the invention to be adapted to apply many different forces as required by different applications.
The at least one pivot member may comprise a first lever portion at an applicator side of the pivot point and a second lever portion at a needle side of the pivot point. The force applicator may be configured to apply the radial force to the first lever portion, and the pivot member may be configured to pivot about the pivot point to move the second lever portion in a direction having a component that is substantially parallel to the needle axis.
The at least one pivot member may comprise a lever arm having an elbow that acts as the pivot point. Providing an elbow in this way allows for a particularly compact configuration of the pivot member.
The force convertor may comprise a plurality of pivot members. The pivot members may have flow paths therebetween. Each pivot member may be at least partially defined by a segment of a substantially cylindrical shell. This arrangement is particularly advantageous as the cylindrical shell configuration allows the force convertor to fit snugly into the bore, while the flow paths permit flow of oil through and around the pivot members, and the use of a plurality of pivot members results in a balanced force being applied to the needle, encouraging smooth operation of the fuel injector.
The housing may define a shoulder, and the pivot member is located such that the pivot point bears against the shoulder during pivoting of the pivot member. The shoulder provides a particularly secure means of fixing the location of the force convertor within the bore of the housing.
The pivot member may comprise a pivot region in the vicinity of the pivot point, and the pivot region may be made of a material that is mechanically harder than the material of a remainder of the pivot member. Making the pivot region of a harder material than the remainder of the pivot member means that the pivot region is particularly wear resistant, which improves the lifetime of the fuel injector.
The force applicator includes an electromagnetic coil. In this case, a part of the force convertor that is adjacent to the coil may be made of magnetic material, and the electromagnetic coil may be configured such that activating the electromagnetic coil causes the radial force to be applied to the force convertor. The combination of the electromagnetic coil and the side actuation described above is particularly advantageous when compared to conventional axial actuation, because demagnetisation of the system occurs faster when the system is magnetised radially rather than axially, which allows greater control over the delivery of fuel into the combustion chamber.
Other actuation means for applying the radial force are also envisaged.
The force convertor may comprise a head portion that applies the longitudinal force to the needle. The head portion is coupled to the needle via a first damping means, such as a hydraulic lash adjuster (HLA). The damping means provides a damping effect, and may also act to locate the head portion in a desired position. The head portion may be is sandwiched between first and second damping means, such as first and second HLAs.
The fuel injector may comprise a return means configured to apply a return force to the needle to urge the needle towards the needle seat. The return means may comprise a needle spring and/or a boost flange.
The fuel injector may comprise a needle guide for guiding movement of the needle within the bore. In embodiments that include a boost flange, the boost flange may act as the needle guide.
The actuator described above may be used in conjunction with a hydraulic amplifier. In this case, the needle comprises a plunger portion and a needle portion. The force convertor is configured to apply the longitudinal force to the plunger portion, and the plunger portion is coupled to the needle portion via a hydraulic amplification system, such that longitudinal movement of the plunger portion effects movement of the needle portion along the needle axis.

Brief description of the drawings

In order that the present invention may be more readily understood, an example of the invention will now be described in detail with reference to the accompanying figures, in which:

Figure 1 is a schematic cross section of a fuel injector of one embodiment of the invention in the closed position, including a valve needle actuated by an actuator;
Figure 2 is a partial cross section taken along the line A-A of the fuel injector in the closed position in Figure 1, to illustrate the relative positions of component parts of the injector when the injector is in the closed position;
Figure 3 is a partial cross section showing a close-up of a part of the fuel injector of Figure 1;
Figure 4 is a schematic cross section of the fuel injector of Figure 1 in the 'open' position, where fuel is allowed to flow from a plurality of outlets to a combustion chamber;
Figure 5 is a partial cross section taken along the line B-B of the fuel injector in the open position in Figure 4, to illustrate the relative position of component parts of the injector when the injector is in the open position;
Figure 6 is a schematic cross section of an alternative embodiment of a fuel injector in the closed position according to the present invention;
Figure 7 is a schematic cross section of a second alternative embodiment of a fuel injector in the closed position according to the present invention;
Figure 8 is a schematic cross section of a third alternative embodiment of a fuel injector in the closed position according to the present invention; and
Figure 9 is a schematic cross section of a fourth alternative embodiment of a fuel injector in the closed position according to the present invention.

Detailed description

For the purpose of the following description it will be appreciated that references to upper, lower, upward, downward, above and below, for example, are not intended to be limiting and relate only to the orientation of the injector as shown in the illustration.
The present invention relates to a fuel injector 10 of the type generally shown in Figure 1. The injector 10 is a direct acting fuel injector that is suitable for use in a fuel injection system of an internal combustion engine, and particularly a diesel engine in which fuel is typically injected into the engine at high pressure levels in excess of 2000 bar, and as commonly as high as 3000 bar.
The injector 10 includes an injection nozzle 12 at its lower end including a valve needle 14. The valve needle 14 defines a longitudinal needle axis L, and the needle 14 is slidable within a blind bore 16 provided in an injection nozzle housing 18 under the influence of an actuator 20, which also forms a part of the injector 10. Fuel under high pressure is delivered to an internal injector volume 24 defined within the bore 16 through a high pressure supply passage (not shown). The valve needle 14 is engageable with a valve needle seating 22, defined at the blind end 24 of the bore 16, to control the flow of fuel from the injector 10 into a combustion chamber of the engine (not shown).
The injection nozzle housing 18 includes an upper injection nozzle housing 26 and a lower injection nozzle housing 28. The lower injection nozzle housing 28, the upper housing 26 and the actuator 20 are housed within a cap nut 30 to retain the parts securely in position relative to one another.
Considering the actuator 20 in more detail, the actuator 20 comprises a force applicator 32 and a force convertor 34. The force applicator 32 is configured to apply a radial force to the force convertor 34 in a direction transverse to the needle axis L, and the force convertor 34 is configured to convert the radial force to a longitudinal force that is substantially parallel to the needle axis L. The force convertor 34 is configured to apply the longitudinal force to the needle 14, which causes the needle 14 to move along the needle axis L away from the valve seat 22.
As best seen in Figure 3, the force convertor 34 includes a plurality of pivot members 36 configured to pivot about a pivot point 38 to convert the radial force to the longitudinal force. Each pivot member 36 is defined by a lever arm 40, which includes first and second lever portions 42 and 44 joined at an elbow 46. In use, the elbow 46 acts as the pivot point 38. The first lever portion 42 is arranged generally at an applicator side of the pivot point 38, and the second lever portion 44 is arranged generally at a needle side of the pivot point 38. The pivot point 38 rests against a shoulder 48 that is defined by the housing 18.
As best seen in Figure 2, the pivot members 36 encircle the needle 14, such that together the pivot members 36 define a substantially cylindrical shell that is coaxial with the valve needle 14. In this way, the each pivot member 36 is at least partially defined by a segment of a substantially cylindrical shell. The pivot members 36 have flow paths between them, to allow oil to pass between and around the segments of the force convertor 34.
Referring back to Figure 3, the first and second lever portions 42 and 44 are substantially perpendicular to one another. At an end of the first lever portion 42 that is remote from the needle seat 22, the first lever portion 42 is provided with a movement stop 50 that, in use, abuts the needle 14 to limit the pivoting movement of the pivot member 36. At an end of the second lever portion 44 that is closest to the valve needle 14 the second lever portion 44 is provided with a head portion 52 that, in use, applies the longitudinal force to the needle 14.
At least a part of the first lever portion 42 of the force convertor 34 is made of a magnetic material. In particular, the part of the force convertor 34 that is adjacent to the force applicator 32 is made of a magnetic material such as FeSi or FeCo. The force convertor 34 may also be coated with a non magnetic material.
The pivot member 36 comprises a pivot region 54 that lies in the vicinity of the elbow 46 or pivot point 38. In this pivot region 54, the pivot member 36 comprises a material that is mechanically harder than the material of the remainder of the pivot member 36. For example, the pivot region 54 may be made of a carbon or stainless steel, or another material having a suitably high mechanical hardness.
The pivot members 36 of the force convertor 34 may be made by any suitable method, for example by metal injection moulding or by a sintering process. Different material may be integrated into the pivot members during the process of manufacture to form regions having different properties (for example, the magnetic region near the force applicator, or the material having a high mechanical hardness in the pivot region). Additionally or alternatively, different regions of the pivot members may be treated differently after moulding or sintering, for example by heat treating certain regions.
The force applicator 32 includes an electromagnetic coil 56. The electromagnetic coil 56 encircles the force convertor 34 and the needle 14, such that the coil 56, the force convertor 34 and the needle 14 are coaxial with one another. In use, an electric current can be applied to the coil 56 to induce a magnetic field in the housing which attracts the magnetic material of the force convertor 34.
The force applicator 32 is housed in a recess 58 defined between the upper and lower injection nozzle housings 26 and 28. A non-magnetic, annular spacer 60 is provided inboard of the coil 56, between the coil 56 and internal injector volume 24. In operation, the spacer 60 separates the coil 56 and the high-pressure oil, ensuring the coil 56 is kept dry.
Turning now to the valve needle 14, and referring back to Figure 1, the valve needle 14 includes a lower tip region 62 nearest the valve seat 22, a top region 64 at an end that is remote from the valve seat 22, and an intermediate region 66 between the top region 64 and the tip region 62. The tip region 62 is of a relatively small diameter and sits against the valve needle seating 22 when the valve is closed. The top region 64 of the valve needle is attached to an interior surface of the housing by a needle spring 67.
The intermediate region 66 is of enlarged diameter compared to the lower tip region 62. Moving from the bottom of the intermediate region 66 as shown in Figure 1 towards the top, the intermediate region 66 is surrounded by a needle guide 68 in the form of a ring that is attached to the housing 18. The needle guide 68 is provided with through-passages 70 that permit the flow of oil through the ring. In this way, the needle guide 68 serves to guide the needle 14 without disturbing the flow of oil within the bore 16.
Continuing upward, the needle 14 is provided with a boost flange 72. The boost flange 72 comprises an annular collar 74 that is fixed to the valve needle 14 and a flange section 76 at the lower edge of the collar 74 that extends radially away from the collar 74 towards the injection nozzle housing 18. The flange section 76 is configured to define a minimal clearance with the injection nozzle housing 18 and is provided with at least one through-passage 78 that defines a flow path for high pressure fuel flowing through the injector 10. The through-passage 78 is configured such that there is some resistance to flow of fuel through the flange 76.
The flange 76 provides a pressure seat 80 on which high-pressure oil acts to bias the flange 76, and hence the needle 14 attached to the flange 76, towards the valve needle seat 22, as will be described in more detail below. The flange 76 also provides a guiding function for the valve needle 14 to keep it aligned with the valve needle seat 22.
Continuing further up the needle 14, the needle 14 is provided with an upper collar 82 that sits between the pivot members 36 of the force convertor 34.
A first damping means 84 in the form of a first hydraulic lash adjuster (HLA) 86, best seen in Figure 3, is mounted on the upper collar 82 via a push-fitting. The HLA 86 includes an annular HLA piston 88 that consists of a collar 90 and an internal flange 92 that extends from the collar 82 towards the needle 14 and an HLA spring 94 that sits between the internal flange 92 of the HLA piston 88 and the upper collar 82. In use, the gap between the internal flange 92 of the HLA piston 88 and the upper collar 82 is filled with oil. The valve needle 14 passes through the centre of the piston 88 and spring 94 of the HLA 86. The inner diameter of the internal flange 92 is marginally greater than the diameter of the valve needle 14, such that the needle 14 can slide freely through the internal flange 92.
A second damping means 96 in the form of a second hydraulic lash adjuster (HLA) 98 is mounted on the collar 74 of the boost flange 72. The second HLA 98 is of substantially the same construction as the first HLA 86, having an annular HLA piston 100 that consists of a collar 102 and an internal flange 104 that extends from the collar 102 towards the needle 14 and an HLA spring 106 that sits between the internal flange 104 of the HLA piston 100 and the collar 102 of the boost flange 72. In use, the gap between the internal flange 104 of the HLA piston 100 and the collar 102 is filled with oil.
The first and second HLAs 86 and 98 are positioned such that the head portions 52 of the pivot members 36 are sandwiched between the first and second HLAs 86 and 98. The first and second HLA springs 94 and 106 are in a state of compression so as to sandwich the pivot members. The spring force generated by the spring 94 of the first HLA 86 is slightly greater than the spring force generated by the spring 106 of the second HLA 98, so that the HLAs 86, 98 are configured to bias the pivot members downwardly towards the shoulder 48, thus retaining contact between the pivot region 54 and the pivot point 38. In this way, the HLAs 86 and 98 act to damp motion of the head portions 52, and also act to bias the head portions 52 into a predetermined position. However, the spring force applied by the HLAs is lower than the spring force provided by the needle spring 67.
The operation of the fuel injector 10 will now be described with reference to Figures 1 to 5. Figures 1, 2 and 3 illustrate the fuel injector 10 when the valve needle 14 is in the closed position. When the needle 14 is in the closed position, the force convertor 34 adopts a closed configuration. Figures 3 and 4 illustrate the fuel injector 10 when the valve needle 14 is in the open position. When the needle 14 is in the open position, the force convertor 34 adopts an open configuration.
In operation of the injector 10, movement of the valve needle 14 between the closed position and the open position is controlled by controlling the current that is applied to the coil 56 of the actuator 20.
Referring to Figures 1, 2 and 3, when the valve needle 14 is in the closed position there is no current running through the coil 56 of the actuator 20, and thus no magnetic force applied to the force convertor 34.
Pressurised fuel in the bore 16 tends to exert forces on the surfaces of the needle 14, the HLAs 86, 98 and the boost flange 72. The pressure forces act equally on all these exposed surfaces. However, when the needle 14 is seated against the valve seat 22 the tip region 62 is not exposed to the pressurised fuel in the closed configuration, and thus when the needle is closed there is no force applied to the tip region 62 of the needle 14. Thus, a net downward force acts on the needle 14, causing the needle to be biased downwardly, towards the valve seat 22. In addition, the needle spring 67 acts to further bias the needle 14 downwardly, towards the valve seat 22. Thus, in the closed configuration, the needle 14 is seated against the valve seat 22 under the influence of the fuel pressure on the needle surfaces and the force applied by the needle spring 67. The presence of the spring 67 therefore reduces the likelihood of a leak from the injector 10 in the combustion chamber during periods of inactivity.
The first HLA 86, which is attached to the needle 14 via the upper collar 82, is also biased downwardly by the action of the fuel pressure on the boost flange 72. The first HLA 86 acts on the head portions 52 of the pivot members 36 to bias the head portions downwardly, which biases the pivot members 36 into a closed configuration.
In the closed configuration, the head portions 52 are located at a downward position that is generally towards the needle seat 14. The first lever portions 42 are tilted generally inwards and towards the needle axis L. The inward tilt is limited by the movement stops 50 which abut the needle 14. The inward tilt of the first lever portions 42 defines a fuel-filled gap 110 between the pivot members 36 and the upper injection nozzle housing 26, as is best seen in Figure 2.
To move the needle 14 from the closed position to the open position, a current is applied to the coil 56. When the current is applied, an electromagnetic field is induced in both the upper and lower injection nozzle housings 26 and 28 which attracts the magnetic portions of the pivot members 36 in a radial direction generally towards the coil. Hence, the inducing a magnetic field using the coil 56 causes a force to be applied to the pivot member 36 in a direction that is generally radial, i.e. transverse to the needle axis L. In particular, the coil 56 induces the radial force that is applied to the first lever portion 42 of the pivot member 36.
The applied radial magnetic force causes the first lever portion 42 to move in a radially outward direction, towards the housing 18. This outward radial movement of the first lever portion 42 causes the pivot members 36 to pivot around the pivot point 38, such that the pivot point 38 bears against the shoulder 48 of the lower injection nozzle housing 28. The pivoting motion causes the second lever portion 44 and hence the head portion 52 to move upwardly in a longitudinal direction, with at least component of the movement being along the needle axis L.
The upward movement of the head portion 52 lifts the first HLA 86 in a direction along the needle axis L which in turn exerts a force on the upper collar 82. The needle 14 is thereby pushed upwards by the first HLA 86, against the force of the needle spring 67 and the pressure force exerted on the pressure seat 80 by the fuel, causing displacement of the needle 14 away from the needle seat 22 in a direction along the needle axis L. The compression of the second HLA spring 106 in its rest position causes the second HLA 98 to remain in contact with the head portion 52 throughout the motion from closed to open configuration.
Once the valve needle 14 has lifted away from the valve needle seating 22, fuel is able to flow out through the injector into the combustion chamber, and the needle 14 is now in the open position, shown in Figures 4 and 5.
In the open position of Figures 4 and 5, the pivot members 36 are arranged in the open configuration. In the open configuration, the first lever portions 42 are biased outwardly, such that the first lever portions 42 lie against the internal surface defined by the bore 16. The head portions 52 have been displaced upwardly, and are located in a position that is away from the needle seat 22 relative to the open configuration. Oil can flow easily between within flow paths defined between the segments of the pivot members 36.
When it is required to terminate injection, the current applied to the coil 56 is removed. Removing the current removes the magnetic force that was applied to the first lever portions 42 of the pivot members 36 in the radial direction. As a result, there is no force causing the upward displacement of the second lever portions 44, and hence no force causing upward displacement of the head portion 52.
The force applied to the needle 14 from the first HLA 86 is therefore removed when the current is turned off. In the absence of any upward force applied to the needle by the actuator 20, the fuel pressure acting on the pressure seat 80 of the boost flange 74, coupled with the force from the needle spring 67, overcomes the upwardly-directed forces acting on thrust surfaces of the valve needle 14, and the needle 14 is caused to move downwards and into the closed position.
The first HLA 86, which is attached to the needle 14 via the upper collar 82, is also moved downwardly as the needle 14 moves downwards. The first HLA 86 acts on the head portions 52 of the pivot members 36 to push the head portions 52 downwards and thereby move the pivot members 36 into the closed configuration, as shown in Figures 1 to 3.
By controlling the current that is applied to the coil 56, injection can therefore be controlled to deliver single or multiple injections of fuel accurately. Particularly advantageously, the demagnetization of the system occurs faster when the magnetic field is radial as in the invention than it does when the magnetic field is axial, because the force convertor 34 insulates the eddy currents. The radial actuator of the invention therefor provides for faster demagnetisation, and hence faster closing of the valve, allowing greater control over the delivery of fuel into the combustion chamber.
Because of the configuration of the force convertor 34, the longitudinal displacement of the needle 14 is equal to the radial displacement of the first lever portion 42 of the pivot member 36. Thus, the longitudinal displacement can be accurately controlled by controlling the dimensions of the pivot members 36.
Furthermore, the force applied to the needle 14 via the force convertor 34 can be finely tuned by controlling the dimensions of the convertor 34. The principle of levers can be applied to the first and second lever portions, and the relative dimensions of the first and second lever portions 42 and 44 can be varied to increase or decrease the force applied. For example, the length of the first lever portion 42 can be increased. This increases the distance from the pivot 38 at which the radial force is applied. Furthermore, increasing the length of the first lever portion 42 increases the volume to which the magnetic force is applied, thereby increasing the total radial magnetic force. In particular, by using the lever principle, forces of more than 200 N can be easily achieved by refining the geometry of the pivot members 36.
The non-magnetic layer on the outer surface of the pivot members 36 guards against magnetic sticking with the housing 18 when pivot members 36 are in open fully outwardly. Furthermore, contact between the pivot regions of the pivot members 36 and the housing 28 means that the pivot members 36 are connected to the magnetic circuit, which increases the applied force and helps faster magnetic switching.
Higher lifting forces applied to the needle means that the fuel injector can be used at higher fuel pressures.
The first and second HLA 86 and 98 are included to account for expansion of components under the heat and high pressure that are experienced under operation. Both HLAs 86 and 98 also retain the head portion 52 in close proximity to the valve needle 14 during movement. Another function of the second HLA 98 is to dampen the movement of the pivot members 36. The speed of seating the valve needle 14 may cause unwanted vibration of the pivot members 36 about the pivot shoulder 48 and result in unnecessary wear. In high performance systems that require multiple injection patterns, the coupling between the valve needle 14 and pivot members 36 must not be compromised by wear, and the second HLA 98 damps the system appropriately so that the wear is minimised.
In lower performance systems, the stresses applied to the system and the speed of movement of the component parts is reduced. Figure 6 illustrates a fuel injector 112 that is particularly suitable for use in such lower performance systems in accordance with a second embodiment of the present invention. The embodiment of Figure 6 is similar to the embodiment of Figures 1 to 5, except that the second HLA 98 is omitted. In this second embodiment, the head portions 52 of the pivot members 36 bear against the first HLA 86. In this way, the first HLA 86 still acts to bias the head portions 52 into a predetermined position, and to damp the motion of the head portion 52 in transition from closed to open configurations. The second HLA 98 can be omitted, since in the lower performance system the injector 112 can cope more readily without the damping effects of the second HLA 98. The embodiment of Figure 6 is therefore a simpler fuel injector that is easier to manufacture and maintain.
Figure 7 illustrates a fuel injector 114 in accordance with a third embodiment of the present invention. The embodiment of Figure 7 is similar to the embodiment of Figures 1 to 5, except that in this embodiment, the boost flange 174 is incorporated into the top region 64 of the valve needle 14, thereby providing a pressure seat 80 on which high-pressure oil acts to bias the needle 14 towards the valve seat 22, as noted above. The boost flange 74 also provides a guiding function for the valve needle 14 to keep it aligned with the valve needle seat 22. In this way, the area of the pressure seat 80 acted upon by the oil is increased, providing a larger downwards-acting force to bias or, in operation, to urge the needle 14 towards the needle seat 22. Larger forces enable more complex injection patterns and results in a higher performance injector.
While the present invention has been described in relation to a direct acting fuel injector with a single needle, it will be appreciated that a number of different systems can be combined in conjunction with the actuator of the embodiments detailed in relation to Figures 1 to 7. It is in accordance with this that Figure 8 illustrates a fuel injector 116 in accordance with a fourth embodiment of the present invention, which utilises a combination of mechanical and hydraulic amplification methods to exploit the invention. In this embodiment, the needle 14 comprises a plunger portion 118 and a needle portion 120, wherein the force convertor 34 is configured to apply the longitudinal force to the plunger portion 118 along the needle axis L. The plunger portion 118 is coupled to the needle portion 120 via a hydraulic amplification system 122, such that longitudinal movement of the plunger portion 118 effects movement of the needle portion 120 along the needle axis L.
In conventional indirect acting fuel injectors, the combination of mechanical and hydraulic amplification systems is known. However, the reliance of these systems on axial actuators that provide relatively low upward forces results in high amplification ratios being required. In particular, such a conventional system would need an amplification ratio of between 3 and 4. By using radial actuation, in accordance with the present invention, a higher initial force can be achieved on the plunger, such that the same output force can be achieved with a smaller amplification ratio, typically be between 1.05 and 2. A small amplification ratio is particularly advantageous because it allows a greater degree of component design flexibility, and allows for the design of smaller components that are less sensitive to hydraulic waves.
Figure 9 illustrates a fuel injector 124 in accordance with a fifth embodiment of the present invention. The embodiment of Figure 9 is similar to the embodiments of Figures 1 to 5, except that in this embodiment, the force applicator 32 comprises an annular, magnetic sleeve 126 that further enhances the performance of the fuel injector 124. The sleeve 126 is integrated into the upper injection nozzle housing 26, such that it surrounds at least a part of the magnetic region of the pivot members 36. At least a part of the sleeve 126 is manufactured from a magnetic material such as FeSi or FeCo, such that the sleeve 126 increases the radial magnetic force applied to the pivot members 36 during injection.
Although in the embodiments described and illustrated the force convertor comprises four pivot arms, any suitable number of pivot arms may be used. In the embodiments described, a movement stop is provided on each pivot arm to limit pivoting of the pivot member. However, embodiments are envisaged where the pivot stop is provided on the needle, for example as a collar surrounding the needle, against which the pivot members abut to limit pivoting of the pivot members.
Any suitable components of the injection system may be integrated with one another if desired. For example, collar components or the boost flange may be integrated with the valve needle. The second HLA may be integrated with the boost flange if desired.
Other variations and modifications will be apparent to the skilled person, without departing from the scope of the appended claims.

Claims

A fuel injector (10) for use in an internal combustion engine, the fuel injector (10) comprising:
a valve needle (14) having a needle axis (L) and being reciprocally movable within a bore (16) in a nozzle housing (18) towards and away from a needle seat (22) along the needle axis (L) ; and

a needle actuator (20) comprising a force applicator (32) and a force convertor (34);

wherein the force applicator (32) is configured to apply a radial force to the force convertor (34) in a direction transverse to the needle axis (L), and the force convertor (34) is configured to convert the radial force to a longitudinal force substantially parallel to the needle axis (L); and

wherein the needle actuator (20) is configured to apply the longitudinal force to the valve needle (14), thereby to effect movement of the valve needle (14) along the needle axis (L); characterized in that the force applicator (32) includes an electromagnetic coil (56) which encircles the force convertor (34) and the needle (14), such that the coil (56), the force convertor (34) and the needle (14) are coaxial with one another and,

wherein the force convertor (34) comprises a head portion (52) that applies the longitudinal force to the needle (14), and wherein the head portion (52) is coupled to the needle (14) via a first damping means (84).
The fuel injector as claimed in claim 1, wherein the force convertor (34) comprises at least one pivot member (36) configured to pivot about a pivot point (38) to convert the radial force to the longitudinal force.
The fuel injector as claimed in claim 2, wherein the at least one pivot member (36) comprises a first lever portion (42) at an applicator side of the pivot point (38) and a second lever portion (44) at a needle side of the pivot point (38), wherein the force applicator (32) is configured to apply the radial force to the first lever portion (42), and the pivot member (36) is configured to pivot about the pivot point (38) to move the second lever portion (44) in a direction having a component that is substantially parallel to the needle axis.
The fuel injector as claimed in claim 2 or claim 3, wherein the at least one pivot member (36) comprises a lever arm (40) having an elbow (46) that acts as the pivot point (38).
The fuel injector as claimed in any of claims 2 to 4, wherein the force convertor (34) comprises a plurality of pivot members (36) having flow paths therebetween, each pivot member (36) being at least partially defined by a segment of a substantially cylindrical shell.
The fuel injector of any of claims 2 to 5, wherein the housing (18) defines a shoulder (48), and the pivot member (36) is located such that the pivot point (38) bears against the shoulder (48) during pivoting of the pivot member (36).
The fuel injector of any of claims 2 to 6, wherein the pivot member (36) comprises a pivot region (54) in the vicinity of the pivot point (38), the pivot region (54) being made of a material that is mechanically harder than the material of a remainder of the pivot member.
The fuel injector of any preceding claim, wherein the force applicator (32) comprises an electromagnetic coil (56), wherein a part of the force convertor (34) that is adjacent to the electromagnetic coil (56) is made of magnetic material, and wherein the electromagnetic coil (56) is configured such that activating the electromagnetic coil (56) causes the radial force to be applied to the force convertor (34).
The fuel injector of claim 1, wherein the head portion (54) is sandwiched between first and second damping means (84, 96).
The fuel injector of any preceding claim, comprising a return means (67, 72) configured to apply a return force to the needle (14) to urge the needle (14) towards the needle seat (22).
The fuel injector of claim 10, wherein the return means comprises a boost flange (72).
The fuel injector of any preceding claim, further comprising a needle guide (68, 72) for guiding movement of the needle (14) within the bore (18).
The fuel injector of claim 12, when dependent on claim 11, wherein the boost flange (72) acts as the needle guide.
The fuel injector of any preceding claim, wherein the needle (14) comprises a plunger portion (118) and a needle portion (120), wherein the force convertor (32) is configured to apply the longitudinal force to the plunger portion (118), and wherein the plunger portion (118) is coupled to the needle portion (120) via a hydraulic amplification system (122), such that longitudinal movement of the plunger portion (118) effects movement of the needle portion (120) along the needle axis (L).