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(11) | EP 2 944 797 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | VALVE ACTUATOR OF A FUEL INJECTOR |
| (57) A control valve (14, 26) arrangement of a fuel injector (10), the control valve (14,
26) comprises a cylindrical solenoid (14), extending along a main axis (A1) and being
provided with an axial cylindrical bore, a biasing means (24) arranged in the bore
and, a magnetic armature (28) facing the lower face of the solenoid, the armature
(28) being moveable between a first position close to the solenoid (14), when the
solenoid (14) is energized and, a second position distant from the solenoid (14),
where it is biased by the biasing means (24) when the solenoid (14) is not energized.
The biasing means (24) comprises pressurized gas (G) contained in a deformable envelope.
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TECHNICAL FIELD
[0001] The present invention relates to an electromagnetic actuator of a control valve of a fuel injector. It more particularly focuses on a biasing means pushing the magnetic armature of the actuator, away from the solenoid.
BACKGROUND OF THE INVENTION
[0002] A fuel injector of the prior art is represented on figure 1 and it comprises an electromagnetic actuator that displaces a control valve enabling hydraulic control of a valve needle. The actuator comprises a solenoid and a magnetic armature, the latter having an integral axial stem forming a control valve. The actuator further comprises a compression spring that is inserted in an axial bore of the solenoid and that permanently biases the armature away from the solenoid.
[0003] In use, when the solenoid is not energized, the armature is only subject to the spring force and it is therefore pushed away from the solenoid. To the contrary, when the solenoid is energized, the armature is attracted toward the solenoid with a magnetic force superior to the opposed force of the spring.
[0004] The spring is a relatively long coil spring and is subject to buckling where it may contact and rub the side wall of the bore which disrupts the displacements of the armature and control valve stem.
[0005] Furthermore, on the manufacturing line, fuel injectors are tuned and sorted to their respective engine applications. The injector can be tuned for a maximum pressure of 1600 bars while another similar-injector made with same components, coming from the same line, may be tuned for working with a 2000 bars engine or more. Part of the tuning is done by selecting the spring having the appropriate stiffness. Therefore the springs are also sorted in a plurality of classes of stiffness's and such classification does not ease the manufacturing.
SUMMARY OF THE INVENTION
[0007] The invention is particularly related to a control valve assembly of a fuel injector, the control valve comprising a cylindrical solenoid, extending along a main axis, and being provided with an axial cylindrical bore, a biasing means arranged in the bore and, a magnetic armature facing a face of the solenoid. Said face is known as the lower face of the solenoid.
[0008] The armature is moveable between a first position upward position, close to the solenoid, when the solenoid is energized and, a second position downward position, distant from the solenoid, where it is biased by the biasing means when the solenoid is not energized. Advantageously, the biasing means comprises pressurized gas contained in a deformable envelope arranged inside the cylindrical bore.
[0009] Also, the solenoid is wound on a core provided with the cylindrical bore. The bore is a blind hole opening on the lower face of the solenoid and, the opening is closed by a wall arranged on said lower face. Alternatively, the core can be provided with a through bore, one extremity of which being plugged. The closing wall is a deformable membrane and, under the influence of the pressurized gas contained in the bore, said closing wall deforms to bias the armature.
[0010] Alternatively to a closing membrane, the biasing means comprises a metallic cylindrical cartridge of pressurized gas, the cartridge being arranged into the cylindrical bore. The cartridge can be of cylindrical shape, provided with features enabling axial deformation of the cartridge.
[0011] Additionnally, the biasing means further may comprise a pressure adjusting means to adjust the pressure of gas inside said envelop. The pressure adjusting means comprises an aperture, provided in the envelop, and a means to open or close said aperture, said means being normally closed for holding the pressurized gas inside the envelope and, being opened, for instance to insert a needle to inject pressurized gas.
[0012] The invention also relates to a fuel injector comprising a control valve, assembly as set in any of the preceding lines.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] The present invention is now described by way of example with reference to the accompanying drawings in which:
Figure 1 is an axial section of an injector of the prior art.
Figure 2 is an axial section of a control valve arrangement of a fuel injector as per the invention.
Figures 3 to 8 are different embodiments of a biasing means used in the control valve of figure 2.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0014] To ease and clarify the following description the top-down orientation of the figures is arbitrarily chosen and, words and expressions such as "above, under, over, below..." may be utilized without any intention to limit the invention.
[0015] As per figure 1 is represented a fuel injector 10 of the prior art. The injector 10 extends along a main axis A1 and it has a body 12 in which is fixedly arranged a solenoid 14 substantially cylindrical extending along an actuator axis A2 parallel and distinct from the main axis A1 or, in another embodiment coincident to the main axis A1. As it is known in the art, the body 12 normally comprises several components fixedly maintained together for instance by a capnut. The core of the invention not being focused on the body of the injector, for the purpose of this description, said body 12 will not be detailed in individual components and will be identified as a whole, referenced as "the injector body 12".
[0016] The solenoid 14 is electrically connected to an electronic control unit, not represented, via electrical links upwardly extending toward an electrical connector 16. The solenoid 14 is wound around a core 18 and comprises an axial blind bore 20 which opens centrally in the lower face 22 of the actuator and, inside of which is arranged a biasing member 24. In the injector 10 of figure 1, the biasing member 24 is an elongated compression spring.
[0017] Below the solenoid 14 is arranged a mushroom-like control valve 26 having a magnetic disc armature 28, the "head" of the mushroom and, downwardly axially extending from the centre of the armature is an integral cylindrical stem forming the valve member 30. The stem 30 is slidably arranged in a bore provided in the body 12. As can be seen on the figure, the spring 24 is permanently compressed between the top blind end of the bore 20 and the armature 28 therefore; it permanently downwardly biases the control valve 26. The top blind end of the bore may be either integrally made or, alternatively, a plug may be arranged in a through bore. In use, the armature 28 magnetically cooperates with the solenoid 14 and mechanically with the spring 24.
[0018] The lowest part of the injector 10 is a nozzle 32 wherein a needle 34 is axially A1 slidably guided in a main bore 36 of a nozzle body and therein displaces between an open position, enabling injection of fuel through spray holes and, a closed position forbidding such fuel injection.
[0019] In the body 12 a high pressure circuit conduit enables fuel to flow from an inlet to said spray holes and, a return low pressure circuit enables the fuel not injected, also identified as back leak, to flow back toward an outlet.
[0020] The top of the needle 34 protrudes in a control chamber 38 which inside pressure varies as a function of the displacements of the control valve 26.
[0021] When the solenoid 14 is energized, it generates on the armature 28 an upwardly oriented attraction force predominant over the downwardly oriented pushing spring force. Consequently, the armature 28 lifts-up to an upper position UP close to the solenoid 14 and the spring 24 is compressed. In upper position UP the valve control 26 opens a fluid path between the control chamber 38 and the return low pressure circuit so, the pressure inside the control chamber 38 decreases and the needle 34 upwardly slides in open position enabling fuel injection.
[0022] To the contrary, when the solenoid 14 is not energized, the armature 28 is solely subject to the spring force which downwardly solicits and displaces the control valve 26 in a lower position LP. In said lower position LP of the control valve 26, the fluid path, previously open, closes enabling the pressure inside the control chamber 38 to built-up again and to exercise a closing force on the needle 34 in order to stop fuel injection.
[0023] A first embodiment of the invention is represented on figure 2, wherein the biasing member 24 is a cylindrical cartridge 40 filled with compressed gas G. The cartridge 40 is a hollow cylindrical and resiliently deformable envelop, having a peripheral cylindrical wall 42 closed at both extremities by substantially circular end walls 44.
[0024] While precise characteristics will be chosen according to the injector, typically the cartridge 40 could be metallic such as steel, while a plastic envelope is possible and, the cartridge 40 could be approximately from 3 mm to 5 mm in diameter, from 5 mm to 8 mm in axial height and, it could be pressurized with Argon (Ar), or another neutral gas, at a pressure to be adjusted between 10 and 30 bars.
[0025] In use, as shown on figure 2, and detailed in figures 3, 5 and, 7, the armature 28 is in contact with the bottom end wall 44 of the biasing member 24 and, when upwardly moving from the lower position LP to the upper position UP, the armature 28 solicits the cartridge 40 which axially deforms further compressing the inside gas G. When stopping energizing the solenoid 14, the control valve 26 solicited by the cartridge 40 downwardly moves from the upper position UP to the lower position LP.
[0026] Typically, the axial displacement of the control valve 26 between the upper position UP and the lower position LP is less than 0.1 mm and, to enable this resilient deformation of the envelop, the bottom end wall 44 of the cartridge 40 may be convex when the control valve 26 is in lower position LP and, it may flatten, either totally or only partially, when the armature 28 is upwardly attracted by be solenoid 14.
[0027] Numerous alternatives to the convex bottom can be chosen to accommodate such 0.1mm deformation. For instance, another possibility is to provide the cylindrical wall 42 of the cartridge 40 with a series of peripheral folds enabling envelope length variation.
[0028] In a second embodiment of the invention, the deformable biasing member 24 comprises gas G directly pressurized in the axial bore 20 of the solenoid 14 while said bore 20 is sealed at the bottom face 22 by a deformable membrane 44 that, for instance, is naturally curved convex and which can flatten, partially or totally, when solicited by the armature 28.
[0029] In the preceding lines, the pressure of gas G is chosen and set when manufacturing the biasing member 24. In alternative embodiments, the biasing means 24 can be further provided with a pressure adjusting means 46. In reference to figures 3 to 8 several embodiments of pressure adjusting means 46 are sketched and described. The pressure adjusting means 46 comprises an aperture 48 provided in the envelope and, a closing means 50 adapted to open or close said aperture 48. The closing means 50 can be a simple ball or a check valve, a simple pivotable or flexible flap or, a double lip seal or any other feature normally and naturally closed. This means that when not solicited, the closing means 50 closes the aperture 48, for instance under the solicitation of the gas pressure, and therefore the pressurized gas G is held inside the cartridge 40. This enables to inflate the envelope when the cartridge 40 is manufactured then, to adjust the inner pressure to specific values.
[0030] To adjust the pressure in the cartridge 40, the closing member 50 is initially maintained in closed position by the pressurized gas inside the cartridge 40 and, as the sketches of figures 4, 6 or 8, an inlet needle 52 is introduced through the aperture 48 to adjust the pressure. When inserted through the aperture 48, the inlet needle 52 pushes the closing means 50 in an open position and gas G can be added or removed. Once the pressure is set inside the cartridge 40 to a desired value, the inlet needle 52 is removed and the closing member 50 closes again. Afterward, said pressure adjusting means 46 can be permanently sealed in closed position.
[0031] The following references have been used in this description:
- 10
- fuel injector
- 12
- body
- 14
- actuator
- 16
- electrical connector
- 18
- core
- 20
- bore
- 22
- lower face of the solenoid
- 24
- biasing member
- 26
- control valve
- 28
- armature
- 30
- valve member
- 32
- nozzle
- 34
- needle
- 36
- bore
- 38
- control chamber
- 40
- cartridge
- 42
- cylindrical wall
- 44
- end surfaces
- 46
- pressure adjusting mean
- 48
- aperture
- 50
- closing mean
- 52
- inlet needle
- A1
- main axis
- A2
- actuator axis
- UP
- upper position of the control valve
- LP
- lower position of the control valve
- G
- gas
1. Control valve assembly (14, 26) of a fuel injector (10), the control valve (14, 26)
comprising
- a cylindrical solenoid (14), extending along a main axis (Al) and being provided with an axial cylindrical bore (20),
- a biasing means (24) arranged in the bore (20) and,
- a magnetic armature (28) facing a face (22) of the solenoid, the armature (28) being
moveable between a first position (UP) close to the solenoid (14), when the solenoid
(14) is energized and, a second position (LP) distant from the solenoid (14), where
it is biased by the biasing means (24) when the solenoid (14) is not energized, characterized in that
the biasing means (24) comprises pressurized gas (G) contained in a deformable envelope.
2. Control valve assembly (14, 26) as set in the preceding claim, wherein the deformable
envelope is arranged inside the cylindrical bore (20).
3. Control valve assembly (14, 26) as set in claim 2, wherein the solenoid (14) is wound
on a core (18) provided with the cylindrical bore (20), said bore (20) being a blind
hole opening on said face (22) of the solenoid, said opening being closed by a wall
arranged on said face (22), the closing wall being deformable under the influence
of the pressurized gas (G) contained in the bore.
4. Control valve assembly (14, 26) as set in claim 1, wherein the biasing means (24)
comprises a metallic cylindrical cartridge (40) of pressurized gas (G), said cartridge
being arranged into the cylindrical bore.
5. Control valve assembly (14, 26) as set in any of the preceding claims, wherein the
biasing means (24) further comprises pressure adjusting means (46) to adjust the pressure
of gas inside said envelop.
6. Control valve assembly (14, 26) as set in claim 5 wherein the pressure adjusting means
(46) comprises an aperture (48) provided in the envelop and, closing means (50) to
open or close said aperture (48), said closing means being normally closed.
7. Fuel injector (10) comprising a control valve (14, 26) arrangement as set in any of
the preceding claim.