GB2564869B

GB2564869B - Fuel injector with a closed metallic tube

Info

Publication number: GB2564869B
Application number: GB1711913.2A
Authority: GB
Inventors: P Cooke Michael
Original assignee: Delphi Technologies IP Ltd
Current assignee: Delphi Technologies IP Ltd
Priority date: 2017-07-24
Filing date: 2017-07-24
Publication date: 2019-11-13
Anticipated expiration: 2037-07-24
Also published as: GB201711913D0; GB2564869A

Description

Fuel injector with a closed metallic tube

TECHNICAL FIELD

The present invention relates to a direct acting solenoid diesel fuel injector.

BACKGROUND OF THE INVENTION

Making a direct acting solenoid injector work at the pressures needed for modern diesel fuel injection equipment is a challenge because it is difficult for a solenoid to generate the high force needed to overcome the seat pressure imbalance of a conventional diesel nozzle when the needle valve member is seated in a closed position. Most approaches concentrate on multiplying the force on the solenoid (e.g. EP2530293, WO2013189636, DEI02012222043, EP2295785). These suffer from complexity and high inertia forces because the only way to get more force than the solenoid can provide is to use some form of mechanical advantage which multiplies the force using a “lever” ratio, but this also means the solenoid must move more distance and at higher velocity by the same ratio. A few attempts have been made to reduce the force imbalance from the nozzle. GB2526273 has a balancing piston which reduces the seat force, but these pistons entail guide leakage which consumes power and requires measures to catch the leakage. EP 2660457 provides a leak-free balancing force using a composite tube, but problems with this include making a composite tube with thermal expansion matched to the surrounding metal and that the feeding of fuel to the inside of this tube during injection gives a reservoir of fuel which can leak into the engine cylinder after injection.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to resolve the above mentioned problems in providing a fuel injector adapted to be part of a direct fuel injection equipment of an internal combustion engine. Said injector has an elongated shape extending along a main axis and comprising a body, defining an inner space wherein, in use, fuel at high pressure enters via an inlet and wherein, an actuation device is adapted to generate sufficient forces to reciprocally move a needle valve member between a closed position of a valve seat, preventing fuel injection and, an open position of said valve seat enabling said fuel injection through spray holes drilled at a bottom end of the injector body.

Sard actuation device comprises a coil fixed to said body cooperating with a magnetic armature fixed to said needle valve member and, a metallic tube extending in said body inner space from a first end fixed to the body to a second end fixed to the head of the needle valve member, a pressure difference being generated between the tube inner volume remaining at substantially atmospheric pressure and the tube outside being subject to the high pressure of the actuation chamber.

Also, said inner space is divided by a core member in an actuation chamber wherein extends the tube and in a nozzle chamber wherein extends the needle, said core member being provided with a through hole for the second end of the tube and the head of the needle to be fixed together.

Also, the coil is positioned around said core.

Also, the fuel injector further comprises a fluid communication enabling fuel to flow between said actuation chamber and said nozzle chamber.

Also, said fluid communication partially extends through the core.

Also, said fluid communication partially extends through the armature.

Also, the fluid communication evolves from an open state when the needle is in closed position to a restricted state when the needle is in open position OP.

Also, the fluid communication comprises a first path defined by a first hole and a throttle having a fixed section generating, in use, a pressure difference between said actuation chamber and said nozzle chambers and, a second path defined partially by a second hole, said second path having a section of passage for the fuel to flow from the actuation chamber (26) to the nozzle chamber (90) varying from the sum of the sections of the throttle (116) and the second hole (118), when the needle is in closed positron (CP) to, the section of the throttle (116) only when the needle reaches the open position (OP) and the second hole (118) is closed.

Also, the magnetic armature cooperates with the core to define together said second path of the fluid communication.

Also, the opening section of said second path increases continuously from a first state when the needle is in open position to a second state when the needle moves to the closed position.

Also, in said first state, said second path is fully closed, the open state of the fluid communication being the fixed section of the throttle.

Also, the fuel injector further comprises an adjusting member fixed to the first end of the tube and also to the injector body.

Also, said adjusting member is a cylinder fixed in a bore extending through the body of the injector, said cylindrical adjusting member extending from an outer end opposed to an inner end to which is fixed said first end of the tube.

Also, said cylindrical adjusting member is press fitted in said bore.

Also, the adjusting member is provided with engagement means for complementary attachment of a tool enabling a positioning adjustment of the adjusting member in said bore.

Also, the adjusting member is further provided with a hole defining the fuel inlet.

Also, said hole extends from an opening in its outer end to a blind bottom end that is in the vicinity to the inner end of said adjusting member.

Also, said inner end of the cylindrical adjusting member protrudes in the actuation chamber.

Also, the adjusting member further comprises a filter arranged in said hole. Also, said filter comprises a plurality of micro-drillings extending from said hole to said actuation chamber.

Also, in an embodiment the tube is straight.

Also, in another embodiment the tube is bent or wavy.

Also, the tube is made of steel or of a titanium alloy.

Moreover, the needle valve member is axially guided between a lower guiding means and an upper guiding means defines between an armature peripheral face and a complementary face of the injector body.

Also, the injector body comprises a tubular portion defining said inner space.

Also, said tubular portion has a thin wall thickness.

Also, the injector body is wrapped in carbon fibre woven perpendicularly to the main axis.

In a further aspect, the invention discloses a method for tuning a fuel injector lift, said method comprising the following steps: a) providing a tube to be arranged in a fuel injector as previously described; b) to reduce the tube axial stiffness, waving or bending the tube by pressing it between the jaws of a press provided with complementary wavy grooves; or c) to increase the tube axial stiffness straightening the tube by pressing it between the jaws of a press provided with complementary straight grooves.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is now described by way of example with reference to the accompanying drawings in which:

Figure 1 is an axial view of a fuel injector as per the invention.

Figure 2 is a first embodiment of the injector of figure 1.

Figure 3 is a second embodiment of the injector of figure 1.

Figures 4, 5 and 6 are a detail sections of the injector of figure 1.

Figures 7 and 8 are illustration of a method step for adjusting the injector of figure 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In reference to the figures 1, 2 and 3 is generally described a diesel fuel injector 10 of a direct injection equipment of an internal combustion engine which is to be inserted and clamped in a well provided in the engine block. Said injector 10 has an elongated shape extending along a main axis X and it comprises an actuation assembly 12, show on the upper part of the figure, and a nozzle assembly 14 fixed together by an injector capnut 16 abutting at an end against a shoulder of the nozzle and firmly tightened, at the other end, onto the actuation assembly. In use, fuel at high pressure is delivered to the injector entering via a fuel inlet 18 arranged in the top of the actuation assembly 12 and flowing inside the injector toward spray holes 20 arranged in the opposite tip end 22 of the injector, for said fuel to be sprayed in the cylinder of the engine.

The actuation assembly 12 comprises a tubular actuator body 24 defining an inner actuation chamber 26 surrounded by a peripheral wall 28 having a wall thickness T28 and, extending about said main axis X from an upper end 30, where are provided said fuel inlet 18 and an electric connector 32, to a lower end 34 defining a transverse lower face 35 wherein opens said actuation chamber 26, said lower face 35 being limited to the annular area surrounding said opening. In the embodiment represented, the connector 32 runs through the gap of a C-shaped clamping tube 33 in which is inserted the actuator body 24.

In an alternative, the peripheral wall has a normal wall thickness T28 comprised between 30 and 50% of the internal bore diameter, or diameter of the actuation chamber 26 and, in another alternative, the peripheral wall 28 has a very thin wall thickness T28 which is only 15 to 20% of said bore diameter. In the alternative of a normal wall thickness, said wall may be wrapped within carbon fibers woven in the hoop stresses direction that is perpendicular to the main axis X. Advantages of said alternatives is detailed afterward. A solenoid assembly 36 comprising an electrical coil 38 arranged around a core member 40, or magnetic pole piece, is inserted in the lower part of said actuation chamber 26. The core member 40, better shown on figure 5, is substantially cylindrical axially extending from an upper face 42, inside the actuation chamber 26 to, an opposed transverse under face 44. Between said opposed faces 42, 44 the core member defines a peripheral face complementary inserted in the lower end 34 of the actuator body, the core under face 44 being in approximately flush surface continuity with the lower face 35 of the actuator body. The coil 38 has an annular shape and is engaged around said core peripheral face in an annular recess defined between the core and the inner face of the body 24. The core 40 is further provided with an axial through hole 46 comprising a top conical portion 48 largely opening in said upper face 42 and narrowing down for joining a central cylindrical portion 50 downwardly joining a steeper lower conical portion 52 slightly widening to an opening in said under face 44.

The coil 38 is electrically connected to terminals of the connector 32 via connecting wires 54 extending in said outer clamping tube 33 arranged around the actuator body 24.

The clamping tube 33 is provided with flats 58 arranged in the upper part in the vicinity to the inlet 18 and the connector 32 and it extends to a lower end abutting on a shoulder arranged in the lower end 34 of the actuator body 24. When placed in the engine, the fuel inlet 18, the connector 32 and said flats 58 protrude outside the well enabling clamping of the injector to the engine, the clamping force being transmitted from said flats 58 down to the actuator body 24 then to the nozzle assembly.

Inside the actuation chamber 26 is arranged a tube 60, straight in a first embodiment of figure 2 and, smoothly wavy in a second embodiment of figure 3. In another alternative not shown, the tube may be bent in several areas. The tube 60 defines an inner volume 61 and it extends from a first end 62, or tube upper end, fixed to the upper end of the body 24 to a second end 64, or tube lower end, freely engaged in the through hole 46 of the core member.

In reference to figure 4, said tube first end 62 is fixed to the actuation body 24 via a cylindrical adjusting member 66 press fitted with interference in an axial bore 68 drilled at the injector body upper end 30 and defining the fuel inlet 18. Said adjusting member 66 extends from an outer end 72, that is inside the bore 68 to an inner end 74 protruding inside the actuation chamber 26 and, it is provided with an axial blind hole 70 opening in said outer end 72 and downwardly extending to a bottom face 76 that is in vicinity to said member inner end 74.

From said inner end 74 a smaller plug member 78 inserted and sealingly closing the tube first end 62 protrudes in the actuation chamber 26.

Moreover, in the part of the adjusting member 66 that protrudes in the actuation chamber 26, a filter 80 defined by a plurality or micro-holes radially drilled through the peripheral wall of the adjusting member form a fluid communication between said fuel inlet 18 and said actuation chamber 26 so that, in use, fuel entering the fuel inlet 18 flows in the bore 68, in the blind hole 70, through said filter 80 prior to fill the actuation chamber 26. Particles and debris present in the fuel are trapped at the bottom of said blind hole 70.

In an alternative not shown, said hole 70 is a through hole wherein are inserted a filter member.

Also, the blind hole 70 is internally threaded 84 for complementary engagement of a tool, not shown, adapted to axially push-in or pull-out the adjusting member 66 in the bore 68 therefore enabling fine tuning of the position of the tube first end 62. Other complementary tool engagement means can be chosen.

In an alternative the tube 60 is made of titanium alloy such as 6-AF-4V or 3-AF-2.5V and, in a second alternative it is made if stainless steel such as 17-7 or 304 having about 1000 MPa compressive hoop stress, the advantages being presented afterward.

In the lower part of the injector 10, the nozzle assembly 14 has a nozzle body 86 extending along the main axis X from a transverse upper face 88 down to said tip end 22. The upper face 88 is arranged in sealing surface contact against the transverse lower face 35 of the actuator body and, the nozzle body is internally provided with a nozzle chamber 90 surrounded by a peripheral wall 92 that comprise a large upper portion defining a large portion 94 of the nozzle chamber and, a narrow lower portion defining a narrow portion 96 of the nozzle chamber ending with said tip end 22.

In said nozzle chamber 90 is axially X guided a needle valve member 98 having a generally thin cylindrical core extending from a head 100 that is fixedly inserted in the tube lower end 64, down to a pointy end 101 that cooperates with a seating face 102 provided on the inner side of the peripheral wall 92 and defining a valve seat 103 right above said spray holes 20.

The needle head 100 defines a shoulder 104 joining the core to a narrower upper extension 105. A magnetic armature 106 is fixed to said needle 98 and, more precisely, said armature 106 has a general disc-like shape defining a cylindrical peripheral face 108 extending between a flat upper face 110 facing the under face 44 of the core member and, an opposed under face 112 facing said large portion 94 of the nozzle chamber. The armature 106 is provided with the axial through hole 113 extending between said opposed faces 110, 112 and in which is inserted the needle head upper extension 105, the armature under face 112 abutting the shoulder 104 of the needle. On the other side, said upper extension 105 protrudes out of the hole 113 above the upper face 110 and is fixed by insertion in the lower end 64 of the tube, sealingly closing said lower end. Being sealed at the upper end 62 by the adjusting member and at the lower end 64 by the needle head, the inner volume 61 of the tube is sealingly isolated from the actuation chamber 26.

In an alternative shown on figure 5, the magnetic armature 106 is provided with a first through hole 114, on the right side of the figure, extending from an opening in the upper face 110, facing the lower conical portion 52 of the hole arranged in the core member 40, to an opening in the under face 112, said through hole 114 further defining a throttle 116 having a restricted cross-section.

In said alternative of figure 5, the magnetic armature 106 is further provided with a larger second through hole 118 also extending between said armature upper 110 and under 112 faces..

In another alternative presented in figure 6, the magnetic armature 106 is only provided with the first through hole 114 defining the throttle 116. It does not have any second though hole.

In practice there would be a plurality of holes 118 equispaced on a pitch circle around the armature in order to avoid non-axial magnetic and hydraulic forces. There would also be a plurality of holes 114,116 as well to minimise the radial space they take up so that the hole 52 through the solenoid does not need to be too big, which would lose solenoid force.

As it is shown on figure 5, the needle 98 is axially guided via a lower guiding means 120 and an upper guiding means 122, both means defining enlarged portions of the needle adjusted to slide against the inner face of the narrow portion 96 of the nozzle chamber.

In the alternative of figure 6, the upper guiding means 122 is defined in the large portion 94 of the nozzle chamber, between the peripheral face 108 of the armature adjusted to slide against the inner face of the peripheral wall 92 of the nozzle.

The combination of alternatives presented is not limited to those shown and described. The solutions for the tube shape, the tube material, the armature and the upper guiding means being all compatible with each other’s.

Tube alternatives (straight, wavy or bent) can be combined with armature alternatives (two holes - figure 5 - or one hole - figure 6) which can also be combined with upper guide alternatives (narrow chamber - figure 5 - or large chamber - figure 6). For instance, a steel made straight tube (fig. 2) can be arranged with a one hole armature (Fig. 6) and an upper guiding in the narrow chamber (fig. 5) and, a titanium made wavy tube (fig. 3) can be arranged with a two holes armature (fig. 5) and an upper guiding in the large chamber (fig. 6).

In use, the injector 10 is arranged in a fuel injection equipment provided on an internal combustion engine and, fuel at high pressure, that can be 3000 bars and above, is delivered and enters the injector 10 via the fuel inlet 18 wherein it is filtered 80 from particles prior to fill the actuation chamber 26 and to flow around the tube 60 in the through hole 46 of the core member, then through the holes and throttle 116 of the armature and in the nozzle chamber 90, large 94 and narrow 96 portions. Because hydrostatic forces generated by the pressure difference between the tube inner volume 61, that remains at substantially atmospheric pressure and, the tube outside subject to the high pressure of the actuation chamber 26, the tube 60 tends to shrink. Since the upper end 62 of the tube is fixed to the actuator body 24, said tube shrinkage pulls the lower end 64 and the needle 98 trying to open the valve seat 103.

Three consecutive steps of the injector 10 operation are now briefly described.

In a first step, the coil 38 is not energised, the needle 98 is a closed position CP wherein the valve seat 103 is closed preventing fuel injection through the spray holes 20. The opening force generated on the needle by the shrinkage of the tube is not sufficient to move the needle. The actuation chamber 26 and the nozzle chamber 90 are both at an identical high pressure.

In a subsequent second step, the coil 38 is energised generating a magnetic field that upwardly attracts the armature 106 and the needle 98 toward the core member 40. As being pulled by both the shrinkage force and the magnetic force, the needle 98 lifts up toward an open position OP of the valve seat 103 enabling fuel passage between the pointy end 101 of the needle and the seating face 102 of the body. As soon as the needle lifts up from the seating face, said high pressure fuel generates on the needle further forces opening the valve seat 103. Injection event through the spray holes 20 occurs and, the fuel having difficulties to flow through the armature, the actuation chamber 26 remains at high pressure while, in the nozzle chamber 90 the pressure drops.

In the embodiment of figure 5 where the armature is provided with the first through holel 14, defining the throttle 116, and with the second through hole 118, said upper face 110 may come in surface contact against said under face 44 closing the second through hole 118. In said embodiment, the section of the passage for the fuel to flow from the actuation chamber to the nozzle chamber varies from the sum of the sections of the throttle 116 and the second hole 118 when the needle is in closed position CP to, the section of the throttle 116 only when the needle reaches the open position OP and the second hole 118 is closed.

In a third step, energisation of the coil 38 is stopped. The needle is in open position OP. After the injection event, the pressure in the nozzle chamber 90 has dropped while the pressure in the actuation chamber 26 has substantially remained at its previous high level. The pressure difference across the armature 106 downwardly pushes the armature generating on the armature 106 and on the needle 98 a closing force pushing the armature 106 away from the core member 40, and the needle 98 toward the closed position CP, stretching the tube 60 back to the length it had during the first step.

The actuator body is also subject to a pressure difference between the high pressure in the actuation chamber 26 and the atmospheric pressure on the outside.

Lift of the needle 98 can be improved in choosing an actuator body with a peripheral wall 28 having said thin wall thickness T28. Indeed, said peripheral wall 28 also being subject to presurisation forces tends to elongate the actuator body which in combination with the tube shrinkage increases the needle maximum lift. In said thin thickness T28 alternative, the elongation may be up to 0.07 mm per 100 mm axial length of the wall further adding to the tube shrinkage in pulling the needle 98.

In the alternative where said wall has a normal thickness T28 as described above, the pressure in the actuation chamber 26 still tends to dilate the actuator body 24 and, a solution to improve the needle lift is to prevent, at least partially, the dilation of the actuator body for instance, the peripheral wall 28 of the actuator body may be wrapped within said carbon fibers woven around the peripheral wall 28 in the hoop stresses direction that is perpendicular to the main axis X.

In reference to figures 7 and 8 is presented a method 130 to adjust the axial stiffness of the tube 60. Indeed, thanks to the embodiment and alternatives described, a single tube 60 may be utilised for several families of injectors requiring different forces to move the needle 98. Indeed, the stiffness of the tube 60 can be increased by straightening the tube and reducing its waviness and, it can be lowered by increasing said waviness.

As shown on figure 7, increasing the stiffness can be done by pressing a wavy tube 60 between the opposite jaws 132 of a press, said jaws having complementary straight grooves 134.

As shown on figure 8, lowering the stiffness can be done by pressing a straight tube 60, or not sufficiently wavy tube 60, between the opposite jaws 136 of a press, said jaws having complementary wavy grooves 138. LIST OF REFERENCES X main axis T28 wall thickness of the actuator body CP closed position OP open position θ gap 10 fuel injector 12 actuation assembly 14 nozzle assembly 16 capnut 18 fuel inlet 20 spray holes 22 tip end 24 actuator body 26 actuation chamber 28 actuator body peripheral wall 30 upper end 32 electric connector 33 clamping tube 34 lower end 35 lower face of the actuator body 36 solenoid assembly 38 coil 40 core member - magnetic pole piece 42 upper face 44 under face 46 hole 48 top conical portion 50 central cylindrical portion 52 lower conical portion 54 wires 58 clamping flats 60 tube 61 tube inner volume 62 tube first end - tube upper end 64 tube second end - tube lower end 66 adjusting member 68 bore 70 blind hole 72 outer end of the adjusting member 74 inner end of the adjusting member 76 bottom face of the hole 78 plug member 80 filter 84 thread 86 nozzle body 88 upper face of the nozzle body 90 nozzle chamber 92 peripheral wall of the nozzle 94 large portion of the nozzle chamber 96 narrow portion of the nozzle chamber 98 needle valve member 100 head of the needle 101 pointy end of the needle 102 seating face 103 valve seat 104 shoulder 105 narrow extension of the needle head 106 magnetic armature 108 peripheral face of the armature 110 upper face of the armature 112 under face of the armature 113 central hole 114 first through hole 116 throttle 118 second through hole 130 method 132 jaws of a press 134 straight groove 136 jaws of a press 138 wavy groove

Claims

1. Luel injector (10) adapted to be part of a direct fuel injection equipment of an internal combustion engine, said injector having an elongated shape extending along a main axis (X) and comprising a body (24, 86) defining an inner space (26, 90) wherein, in use, fuel at high pressure enters via an inlet (18) and wherein an actuation device is adapted to generate sufficient forces to reciprocally move a needle valve member (98) between a closed position (CP) of a valve seat (103) preventing fuel injection and, an open position (OP) of said valve seat (103) enabling said fuel injection through spray holes (22) drilled at a bottom end of the injector body; said actuation device comprising a coil (38) fixed to said body cooperating with a magnetic armature (106) fixed to said needle valve member (98) and, a metallic tube (60) extending in said body inner space (26) from a first end (62) fixed to the body to a second end (64) fixed to the head (100) of the needle valve member, a pressure difference being generated between the tube inner volume (61) remaining at substantially atmospheric pressure and the tube outside being subject to the high pressure of the actuation chamber (26).

2. Luel injector (10) as claimed in the preceding claim wherein, said inner space (26, 90) is divided by a core member (40) in an actuation chamber (26) wherein extends the tube (60) and in a nozzle chamber (90) wherein extends the needle (98), said core member (40) being provided with a through hole (46) for the second end (64) of the tube and the head (100) of the needle to be fixed together.

3. Luel injector (10) as claimed in claim 2 wherein the coil (38) is positioned around said core (40).

4. Luel injector (10) as claimed in any one of the claims 2 or 3 further comprising a fluid communication (46, 114, 116, 118) enabling fuel to flow between said actuation chamber (26) and said nozzle chamber (90).

5. Fuel injector (10) as claimed in claim 4 wherein said fluid communication (46) partially extends through the core (40).

6. Fuel injector (10) as claimed in any one of the claims 4 or 5 wherein said fluid communication (114, 116, 118) partially extends through the armature (106).

7. Fuel injector (10) as claimed in claim 6 wherein the fluid communication (114, 116, 118) evolves from an open state when the needle (98) is in closed position (CP) to a restricted state when the needle is in open position (OP).

8. Fuel injector (10) as claimed in claim 7 wherein the fluid communication (114, 116, 118) comprises a first path defined by a first hole (114) and a throttle (116) having a fixed section generating, in use, a pressure difference between said actuation chamber (26) and said nozzle chambers (90) and, a second path defined partially by a second hole (118), said second path having a section of passage for the fuel to flow from the actuation chamber (26) to the nozzle chamber (90) varying from the sum of the sections of the throttle (116) and the second hole (118), when the needle is in closed positron (CP) to, the section of the throttle (116) only when the needle reaches the open position (OP) and the second hole (118) is closed.

9. Fuel injector (10) as claimed in claim 8 wherein the magnetic armature (106) cooperates with the core (40) to define together said second path of the fluid communication.

10. Fuel injector (10) as claimed in claim 9 wherein the opening section of said second path increases continuously from a first state when the needle (98) is in open position (OP) to a second state when the needle (98) moves to the closed position (CP).

11. Fuel injector (10) as claimed in claim 10 wherein in said first state, said second path is fully closed, the open state of the fluid communication being the fixed section of the throttle (116).

12. Fuel injector (10) as claimed in any one of the preceding claims further comprising an adjusting member (66) fixed to the first end (62) of the tube and also to the injector body (24).

13. Fuel injector (10) as claimed in claim 12 wherein said adjusting member (66) is a cylinder fixed in a bore (68) extending through the body of the injector, said cylindrical adjusting member (66) extending from an outer end (72) opposed to an inner end (74) to which is fixed said first end (62) of the tube.

14. Fuel injector (10) as claimed in claim 13 wherein said cylindrical adjusting member (66) is press fitted in said bore (68).

15. Fuel injector (10) as claimed in any one of the claims 13 or 14 wherein the adjusting member (66) is provided with engagement means for complementary attachment of a tool enabling a positioning adjustment of the adjusting member (66) in said bore (68).

16. Fuel injector (10) as claimed in any one of the claims 12 to 15 wherein the adjusting member (66) is further provided with a hole (70) defining the fuel inlet (18).

17. Fuel injector (10) as claimed in claim 16 wherein sard hole (70) extends from an opening in its outer end (72) to a blind bottom end (76) that is in the vicinity to the inner end (74) of said adjusting member (66).

18. Fuel injector (10) as claimed in claim 17 wherein said inner end (74) of the cylindrical adjusting member protrudes in the actuation chamber (26).

19. Fuel injector (10) as claimed in any one of the claims 16 to 18 wherein the adjusting member (66) further comprises a filter (80) arranged in said hole (70).

20. Fuel injector (10) as claimed in claim 19 wherein said filter (80) comprises a plurality of micro-drillings extending from said hole (70) to said actuation chamber (26).

21. Fuel injector (10) as claimed in any one of the preceding claims wherein the tube (60) is straight.

22. Fuel injector (10) as claimed in any of the claims 1 to 21 wherein the tube (60) is bent or wavy.

23. Fuel injector (10) as claimed in any of the preceding claims wherein the tube (60) is made of steel.

24. Fuel injector (10) as claimed in any of the claims 1 to 20 wherein the tube (60) is made of a titanium alloy.

25. Fuel injector (60) as claimed in any of the preceding claims wherein the needle valve member (98) is axially guided between a lower guiding means and an upper guiding means defined between an armature peripheral face (108) and a complementary face of the injector body (86).

26. Fuel injector (10) as claimed in any of the preceding claims wherein the injector body (24, 86 ) comprises a tubular portion defining said inner space (26).

27. Fuel injector (10) as claimed in claim 26 wherein said tubular portion has a thin wall thickness (T28).

28. Fuel injector (10) as claimed in any of the preceding claims wherein the injector body (24, 86) is wrapped in carbon fibre woven perpendicularly to the main axis (X).

29. Method (130) for tuning a fuel injector lift, said method comprising the following steps: a) providing a tube (60) to be arranged in a fuel injector (10) as set in any one of the preceding claims; b) to reduce the tube axial stiffness, waving or bending the tube by pressing it between the jaws (136) of a press provided with complementary wavy grooves (138) or; c) to increase the tube axial stiffness straightening the tube by pressing it between the jaws (132) of a press provided with complementary straight grooves (134).