Method for manufacturing an open/close element for servo valves of a fuel injector

Abstract

 The manufacturing method regards an open/close element for servo valves of a fuel injector, wherein the open/close element (47) is made in a single piece with a bushing (41), which is designed to move for a certain axial travel along a fixed stem (38) for opening/closing the servo valve (5). The bushing (41) is axially movable for a travel greater than the travel of the open/close element (47) under the control of an anchor (17) actuated by an electric actuator (15). The method comprises a step of providing the bushing (41) with a guide portion (61) designed to engage the guide hole (59) for a relative displacement of the anchor (17) with respect to the bushing (41) between two stop elements (62, 65), and a step of providing an intermediate body (12a) for supporting a spring (23) acting on the bushing (41), which comprises a flange (24) provided with at least one radial notch (71). Then, the bushing (41) is arranged so as to bring the flange (24) into contact with an end edge (66) of the bushing (41), and finally the flange (24) is welded on said edge (66) in a position corresponding to the notch (71) so that a weld is made in view between the bushing (41) and the intermediate body (12a).

Description

[0001] The present invention relates to a method for manufacturing an open/close element for servo valves of a fuel injector, in which the open/close element comprises a bushing designed to move for a certain axial travel along a fixed stem for opening and closing said servo valve. The invention moreover relates to an open/close element manufactured applying the aforesaid method.

[0002] In servo valves of the type described, the discharge duct of the servo valve gives out onto a lateral surface of the stem in such a way that, in the closing position, the bushing is subject to a substantially zero axial pressure. Consequently, the servo valve is of a balanced type and requires relatively small forces for its displacement. The bushing is brought into the closing position by a corresponding spring and is controlled, against the action of the spring, for opening the servo valve by an anchor, generally a disk-shaped anchor, actuated by an electric actuator.

[0003] In order to reduce or eliminate the rebounds of the bushing when it is brought into the closing position, the need is felt to separate the anchor from the bushing and to displace the anchor axially for a travel greater than the travel of the bushing so as to strike against the latter when it rebounds.

[0004] The production of this type of servo valve presents the problem of providing two stop or impact elements for the travel of the anchor, which will be fixed with respect to the bushing and must be located on the latter with extreme precision. In addition, said type of production presents the problem of mounting the anchor in a slidable way on the bushing and of fixing thereon an intermediate body, on which the spring acts. Since said intermediate body has a flange that must be fixed in contact with an end edge of the bushing, fixing of the flange by means of welding, for example laser welding, presents difficulties of access to the area to be welded.

[0005] The aim of the invention is to provide a method for manufacturing an open/close element for servo valves of the type described above that will solve the problems referred to above and presents a high reliability and a limited cost.

[0006] According to the invention, the above purpose is achieved by a method for manufacturing an open/close element for servo valves of a fuel injector, as defined in Claim 1.

[0007] For a better understanding of the invention, described herein is a preferred embodiment, provided by way of example with the aid of the annexed drawings, wherein:

• Figure 1 is a partial median section of a servo valve, the open/close element of which is manufactured applying the method according to the invention;
• Figure 2 is a perspective view of a component of the open/close element;
• Figure 3 is a perspective view of the open/close element of Figure 1 assembled with the corresponding control anchor;
• Figure 4 is a median section of a servo valve according to a variant of Figure 1;
• Figure 5 is a median section of a servo valve according to another variant of Figure 1; and
• Figure 6 is a partially sectioned perspective view of the open/close element of Figure 5 assembled with the corresponding control anchor.

[0008] With reference to Figure 1, designated as a whole by 2 is a hollow body or casing of a fuel injector for an internal-combustion engine, in particular a diesel engine. The casing 2 extends along a longitudinal axis and terminates with a nozzle or nebulizer (not visible in the figure) for injection of the fuel at a high pressure.

[0009] The casing 2 has an axial cavity 34, housed in which is a dosage servo valve 5 comprising a valve body 7 having an axial hole axially slidable in which is a rod for control of the injection (not visible in Figure 1 either). This rod is controlled by the pressure of the fuel in a control chamber, which is contained in the valve body 7 and is not visible in Figure 1 either. Housed in a portion of the cavity 34 is an electric actuator 15, comprising an electromagnet 16, designed to control an anchor 17 in the form of a notched disk. In particular, the electromagnet 16 comprises a magnetic core 19, which has a polar surface 20 perpendicular to the axis 3 of the casing 2 and is held in position by a support or jacket 21.

[0010] The electric actuator 15 has an axial cavity 22 in communication with the discharge of the servo valve 5 towards the usual fuel tank. Housed in the cavity 22 is a helical compression spring 23, pre-loaded so as to exert an action of thrust on the anchor 17 in a direction opposite to the attraction exerted by the electromagnet 16. The spring 23 acts on the anchor 17 through an intermediate body, designated as a whole by 12a, which comprises a flange 24 made in a single piece with a pin 12 for guiding one end of the spring 23. A thin lamina 13 made of non-magnetic material is located between a plane top surface 17a of the anchor 17 and the polar surface 20 of the core 19, in order to guarantee a certain gap between the anchor 17 and the core 19.

[0011] The valve body 7 comprises a flange 33, housed in the cavity 34, which is kept fixed, in a fluid-tight way, against a shoulder not visible in the figure by a threaded ring nut 36 screwed on an internal thread 37 of the cavity 34. The anchor 17 is associated to a bushing 41, guided axially by an axial stem 38, which is made in a single piece with the flange 33 of the valve body 7 and extends in cantilever fashion from the flange 33 itself towards the cavity 22. The stem 38 has a cylindrical lateral surface 39, which guides axial sliding of the bushing 41. In particular, the bushing 41 has a cylindrical internal surface 40, coupled to the lateral surface 39 of the stem 38 substantially in a fluid-tight way, for example with a diametral play of less than 4 µm, or else by means of interposition of annular seal elements.

[0012] The control chamber of the body 7 has an outlet duct 43 for the fuel, made axially inside the flange 33 and the stem 38. The duct 43 is in communication with at least one substantially radial stretch of duct 44. Advantageously, two or more radial stretches 44 can be provided, set at constant angular distances apart, which give out into an annular chamber 46, formed by a groove of the lateral surface 39 of the stem 38. In Figure 1, two stretches 44 are provided, inclined in the direction of the anchor 17.

[0013] The annular chamber 46 is obtained in an axial position adjacent to the flange 33 and is opened/closed by a terminal portion of the bushing 41, which forms the open/close element 47 for said annular chamber 46 and hence also for the radial stretches of duct 44. The open/close element 47 is consequently made in a single piece with the bushing 41 and co-operates with a corresponding stop for closing the servo valve 5. In particular, the open/close element 47 terminates with a stretch having an internal frustum conical surface 45 flared downwards and designed to stop against a frustum conical joint 49 between the flange 33 and the stem 38.

[0014] Advantageously, the joint 49 has two frustum conical surface portions 49a and 49b, separated by an annular groove 50, which has a cross section shaped substantially like a right angle. The frustum conical surface 45 of the open/close element 47 engages in a fluid-tight way the frustum conical surface portion 49a, against which it stops in the closing position. On account of the wear between these surfaces 45 and 49a, after a certain time the closing position of the open/close element 47 requires a greater travel of the bushing 41 towards the joint 49, once again defining as maximum diameter of the surface the diameter of the cylindrical stretch of the annular groove 50.

[0015] The anchor 17 is made of a magnetic material and is formed by a distinct piece, i.e., a piece separate from the bushing 41. It has a central portion 56 having a plane bottom surface 57, and a notched annular portion 58, with cross section tapered outwards. The central portion 56 has an axial hole 59, by means of which the anchor 17 engages with a certain radial play along an axial portion of the bushing 41 formed by a collar 61, obtained on a flange 60 of the bushing 41. The collar 61 has a smaller diameter than the bushing 41 and hence also than the flange 60.

[0016] The flange 24 of the intermediate body 12a has a plane surface 65, designed to engage a surface 17a of the anchor 17 opposite to the surface 57. The bushing 41 is made in a single piece with a first stop element of the anchor 17, defined by a shoulder 62, formed between the collar 61 and the flange 60 of the bushing 41. In addition, the intermediate body 12a comprises an axial pin 63 for connection of the bushing 41, which is made in a single piece with the flange 24 and must be fixed rigidly to the bushing 41 so that the surface 65 of the flange 24 of the intermediate body 12a is fixed with respect to the bushing 41. The connection pin 63 is designed to be housed in a corresponding seat 40a of the bushing 41, which has a diameter slightly greater than the internal surface 40 of the bushing 41 in order to reduce the portion to be ground so as to ensure fluid tightness with the surface 39 of the stem 38.

[0017] Between the surface 39 of the stem 38 and the surface 40 of the bushing 41 there occurs in general a certain leakage of fuel, which leaks out into a compartment 48 between the end of the stem 38 and the connection pin 63. In order to enable discharge of the fuel leaking into the compartment 48 towards the cavity 22, the intermediate body 12a is provided with an axial hole 64.

[0018] The connection pin 63 extends axially from the plane surface 65 of the flange 24 in a direction opposite to the guide pin 12. In turn, the shoulder 62 is located in a position such as to create an axial play of a pre-set amount for the anchor 17 to enable a relative axial displacement between the anchor 17 and the bushing 41. The distance or space between the surface 65 of the flange 24 and the shoulder 62 of the bushing 41 defines the housing of the anchor 17. The plane surface 65 of the flange 24 bears upon an end surface or edge 66 of the collar 61 of the bushing 41 so that the housing of the anchor 17 is uniquely defined.

[0019] Normally, the anchor 17 rests against the shoulder 62 in the position indicated in Figure 1. The surface 65 of the flange 24 projects from the lamina 13 downwards by a distance equal to a certain travel, or lift, of the open/close element 47. The bushing 41 can be drawn axially by the anchor 17 upwards when it engages the flange 24. The anchor 17 can, however, perform a travel greater than the travel of the bushing 41, performing along the collar 61 an overtravel equal to the aforesaid play, between the two stop elements represented by the shoulder 62 of the bushing 41 and by the surface 65 of the flange 24.

[0020] When the electromagnet 16 is not energized, the spring 23 acts on the body 12a and held the open/close element 47 with its frustum conical surface 45 against the frustum conical portion 49a of the joint 49 so that the servo valve 5 is closed. Normally, the anchor 17 is detached from the lamina 13 and rests against the shoulder 62. In the annular chamber 46 there is hence set up a pressure of the fuel, the value of which is equal to the supply pressure of the injector. When the electromagnet 16 is energized to perform an opening stroke of the servo valve 5, the core 19 attracts the anchor 17, which at the start performs a loadless travel until it is brought into contact with the surface 65 of the flange 24, without affecting the displacement of the bushing 41. Next, the action of the electromagnet 16 on the anchor 17 overcomes the force of the spring 23 and, via the flange 24 and the fixing pin 63, draws the bushing 41 towards the core 19 so that the open/close element 47 opens the servo valve 5.

[0021] When energization of the electromagnet 16 ceases, the spring 23, via the body 12a, causes the bushing 41 to perform the travel towards the closing position of the servo valve 5. During a first stretch of this closing travel, the flange 24, with the surface 65, draws the anchor 17 along with it, which hence moves together with the bushing 41. At the end of its travel, the open/close element 47 strikes, with its conical surface 45, against the frustum conical surface portion 49a of the joint 49 of the valve body 7.

[0022] On account of the type of stresses involved, the small area of contact, and the hardness of the open/close element 47 and of the valve 7, after impact, the open/close element 47 rebounds, overcoming the action of the spring 23. Instead, the anchor 17 continues its travel towards the valve body 7, recovering the play that is formed between the plane surface 57 of the portion 56 of the anchor 17 and the shoulder 62 of the flange 60. After a certain time from the first impact of the open/close element 47, the anchor 17 continues its travel towards the valve body 7 until there is an impact of the plane surface 57 of the portion 56 against the shoulder 62 of the bushing 41. As a result of this impact, the rebounds of the bushing 41 are markedly reduced or even eliminated.

[0023] By appropriately sizing the weights of the anchor 17 and of the bushing 41, the travel of the anchor 17, and the travel of the open/close element 47, it is possible to obtain impact of the anchor 17 against the bushing 41 during the first rebound, immediately following upon de-energization of the electromagnet 16 so that both the first rebound and the rebounds subsequent to the first rebound are attenuated. The impact between the anchor 17 and the shoulder 62 of the bushing 61 can also occur upon return of the open/close element 47 into the closing position, following upon the first rebound. In this case, the rebounds of the open/close element 47 subsequent to the first rebound are completely blocked.

[0024] Advantageously, the intermediate body 12a is fixed on the bushing 41 by welding the flange 24 on the edge 66 of the bushing 41 with a purposely provided autogenous welding device 70, schematically indicated with dashed lines in Figure 1. For this purpose, according to the invention the flange 24 is provided with at least one substantially radial notch 71 or with a plurality of radial notches 71, angularly set at the same distance apart from one another. In particular, in the example of Figures 1-3 two diametrally opposite notches 71 are provided. Each notch 71 has two parallel walls 72 connected by a wall 73 perpendicular to the walls 72.

[0025] Advantageously, the two parallel walls 72 are set at a distance so as to enable access of the welding device 70 on the edge 66 of the bushing 41, along the edge of the surfaces 72 and 73 of the notch 71. For this purpose, the distance between the walls 72 can be chosen substantially equal to the thickness of the flange 24, for example in the region of 3 mm.

[0026] Obviously, before said welding it is necessary to insert the collar 61 into the hole 59 of the anchor 17 and then insert the pin 63 of the intermediate body 12a into the seat 40a of the bushing 41. To weld the intermediate body 12a, it is also necessary to phase it, i.e., orient it, so as to bring the notches 71 successively into a position corresponding to the welding device 70. In the case of an automatic production and welding plant, the phasing of the intermediate body 12a can be performed automatically in any known way.

[0027] The method for manufacturing the open/close element 47 of the servo valve 5 of Figures 1-3 is performed as described in what follows.

[0028] First, the anchor 17 is provided with the central guide hole 59, and the bushing 41 is provided with a guide portion 61 and the shoulder 62. Then, the intermediate body 12a is provided with the flange 24 for supporting the spring 23 and with the radial notches 71. The intermediate body 12a can also be provided with the two pins 12 and 63, respectively, for guiding the end of the spring 23 and for insertion in the bushing 41. Then, the anchor 17 is inserted on the collar 61 of the bushing 41, and the fixing pin 63 is inserted into the hole 40a of the bushing so as to bring the flange 24 into contact with the edge 66 of the bushing 41. The radial play between the fixing pin 63 with respect to the hole 40a can be in the region of 0.1 mm.

[0029] Finally, via the welding device 70, the flange 24 is welded on said edge 66, in a position corresponding to the notches 71, i.e., along the edge of the walls 72 and 73 of each notch 71 in contact with the edge 66. There is thus obtained, between the bushing 41 and the intermediate body 12a, a weld in view of the operator, without varying the external profile of the bushing 41 and of the intermediate body 12a.

[0030] In the variants of Figures 4-6, the parts that are similar to the ones of the embodiment illustrated in Figures 1-3 are designated by the same reference numbers and will not be described any further herein.

[0031] In the variant of Figure 4, the anchor 17 has a constant thickness for the two portions 56 and 58, whilst the shoulder 62 is not made on a flange, but on the thickness of the bushing 41. Inserted between the bottom surface 57 of the anchor 17 and the shoulder 62 of the bushing 41 is a ring of calibrated thickness 55, which can be chosen from a series of modular classes of calibrated thicknesses in order to adjust the additional travel of the anchor 17, i.e., the relative play between the two stop elements. For the corresponding manufacturing method, before the pin 63 of the intermediate body 12a and the anchor 17 is fitted on the bushing 41, it is necessary to fit the ring of chosen calibrated thickness 55 on the collar 61.

[0032] In the variant of Figure 5, the bushing 41 has an annular flange 74 projecting outwards, which forms an stop element for the anchor 17 made in a single piece with the bushing 41. A bottom surface 75 of the flange 74 (see also Figure 6) is designed to engage a shoulder 76 formed by an annular depression 77 of the plane top surface 17a of the anchor 17. The central portion 56 of the anchor 17 can here slide on an axial portion 82 of the bushing 41, adjacent to the flange 74. The flange 74 has a top surface that forms the end edge 80 of the bushing 41 and is in contact with the surface 65 of the flange 24. Obviously, the annular depression 77 has a depth greater than the thickness of the edge 74 to enable the whole travel of the anchor 17 towards the core 19 of the electromagnet 16.

[0033] The shoulder 76 of the anchor 17 is normally held in contact with the plane surface 75 of the flange 74 by a compression spring 52, located between the plane surface of the portion 56 of the anchor 17 and a depression 51 in the top surface of the flange 33 of the valve body 7. The spring 52 is pre-loaded so as to exert a force far smaller than that of the spring 23, but sufficient to keep the anchor 17 with the shoulder 76 in contact with the bottom surface 75 of the flange 74 of the bushing 41.

[0034] The other stop element of the travel of the anchor 17 is fixed with respect to the bushing 41 and is designed to stop the anchor 17 in the travel towards the closing position of the servo valve 5. Said stop element is represented herein by a C-shaped ring 78, housed in an annular groove 79 of the bushing 41 itself and is designed to block the anchor 17 on the bushing 41. Advantageously, between the C-shaped ring 78 and the anchor 17, there can be a ring 81 which has a calibrated thickness and can be chosen from a series of classes of modular thickness for adjusting the additional travel of the anchor 17 with respect to the bushing 41. In particular, a bottom surface of the ring 81 is kept in contact with the top surface of the C-shaped ring 78. The play between the anchor 17 and the bushing 41 is formed here by the difference of the distance between the surface 75 of the flange 74 and a top surface 85 of the ring 81, with the thickness of the anchor 17 itself.

[0035] Also in this embodiment, the intermediate body 12a is connected to the bushing 41 by means of welding, performed by means of the welding device that acts in a position corresponding to radial notches 71 of the flange 24 on the surface of the flange 44 of the coil 41, as in the case of the two variants of Figures 1-4.

[0036] The method for manufacturing the open/close element of Figures 5 and 6 differs from that of Figures 1-4 in that the anchor 17 must be mounted on the bushing 41 after welding of the flange 24 on the edge 80. In fact, the bushing 41 thus welded can be slid into the hole 59 of the anchor 17 and into the hole of the ring 81, which is subsequently blocked on the bushing 41 by means of the C-shaped ring 78. In this way, there does not exist the minimum risk of thermal alteration of the anchor 17 during the process of welding.

[0037] The method for manufacturing the open/close element 47 of the servo valves 5 according to the invention is characterized by the following steps:

• the bushing (41) is provided with a guide portion, designed to engage the guide hole (59) for a relative displacement of the anchor 17 between two stops (62, 65; 75, 78), said bushing (41) being equipped with at least one (62, 75) of said stops (62, 65; 75, 78);
• an intermediate body (12a) is provided between the spring (23) and the bushing (41), said body (12a) comprising a flange (24) for supporting said spring (23);
• at least one radial notch (71) is provided on said flange (24);
• said bushing (41) is arranged so as to bring said flange (24) into contact with an edge (66, 80) of said bushing (41); and
• said flange (24) is welded on said edge (66, 80) in a position corresponding to said at least one notch (71) so that a weld is obtained in view between said bushing (41) and said intermediate body (12a).

[0038] From what has been seen above, the advantages of the manufacturing method according to the invention emerge clearly as compared to the known art. In particular, the welding operation can be performed in view. In addition the weld does not cause any variation of the external profile of the bushing 41 and of the flange 24, and above all does not cause any variation of the surface 17a of the anchor 17 so that the entire travel of the anchor 17 itself is not precluded.

[0039] It may be understood that various modifications and improvements may be made to the manufacturing method described above, without thereby departing from the scope of protection of the claims. For example, in the embodiment illustrated in Figure 1, the shoulder 62 can be represented by a C-shaped ring mounted removably on the bushing, or one or both of the rings 78 and 81 mounted removably on the bushing 41. In addition, in the variant of Figures 1-3 a ring can be provided of a thickness chosen from classes of modular thickness for adjusting the travel of the anchor 17. These modular shims can be of a C-shaped type that can be fitted on the collar 61 after insertion of the anchor 17.

[0040] In the variant of Figure 4, the ring 55 can be replaced with a ring of a C-shaped type. In this case, in the manufacturing method, a step for the positioning of the C-shaped ring after the process of welding is necessary. The advantage of said solution is not only that of enabling adjustment of the size of the housing for the anchor 17 after welding, but also that of performing the welding operation with the anchor 17 at a sufficient distance from the notch 71, there thus being reduced the risk of thermal alteration of the anchor 17 itself. Likewise, in the variant of Figure 6 the shim ring 81 can be of a C-shaped type, which can be inserted after welding. In both of the variants of Figures 4 and 6, said insertion can be performed in the assembly step, after measurement of the effective value of the housing of the anchor 17. Finally, in the variants of Figures 4-6 the shim rings 55 and 81 can be eliminated.

Claims

1. A method for manufacturing an open/close element for a servo valve (5) of a fuel injector, wherein the open/close element (47) is made in a single piece with a bushing (41) that is designed to move for a certain axial travel along a fixed stem (38) for opening/closing said servo valve (5); a discharge duct (43, 44) of the servo valve (5) giving out onto a lateral surface (39) of said stem (38), a spring (23) being designed to keep said bushing (41) in the closing position, where said bushing (41) is subject to a substantially zero axial pressure; said bushing (41) being movable under the control of an anchor (17) actuated by an electric actuator (15) against the action of said spring (23); said anchor (17) being provided with a central hole (59) and being axially movable for a travel greater than said certain travel; said method comprising the following steps:

- the bushing (41) is provided with a guide portion (61, 82), designed to engage said central hole (59) for a relative displacement of the anchor (17) between two stop elements (62, 65; 75, 78), said bushing (41) being equipped with at least one (62, 75) of said stop elements (62, 65; 75, 78);

- an intermediate body (12a) is provided, comprising a flange (24) for supporting said spring (23);

- at least one radial notch (71) is provided on said flange (24);

- said intermediate body (12a) is located on said bushing (41) so as to bring said flange (24) into contact with an edge (66, 80) of said bushing (41); and

- said flange (24) is welded on said edge (66, 80) in a position corresponding to said at least one notch (71) so that a weld is made in view between said bushing (41) and said intermediate body (12a).

2. The manufacturing method according to Claim 1,
characterized in that said intermediate body (12a) is moreover provided with a connection pin (63) that can be inserted in said bushing (41) and a guide pin (12) for guiding an end of said spring (23), said guide pin (12) being coaxial to said connection pin (63) and opposite to the latter.

3. The manufacturing method according to Claim 1 or Claim 2, characterized in that said flange (24) is provided with a series of notches (71) located at the same angular distances from one another.

4. The manufacturing method according to any one of the preceding claims, characterized in that said notch (71) has two parallel sides (72) connected by a transverse side (73), said parallel sides being set at a distance so as to enable welding of an edge of said sides (72, 73) on said edge (66, 80) by means of an autogenous welding device (70).

5. The manufacturing method according to Claim 4,
characterized in that said parallel sides (72) are set at a distance of at least 2 mm apart.

6. The manufacturing method according to any one of the preceding claims, characterized in that one of said stop elements (62, 74) is made in a single piece with said bushing (41).

7. The manufacturing method according to Claim 6,
characterized in that said integral stop element is defined by a shoulder (62) of said bushing (41), said anchor (17) being fitted on said guide portion (61) before said welding.

8. The manufacturing method according to Claim 7,
characterized in that said guide portion is formed by a collar (61) of said bushing (41) located between said shoulder (62) and said edge (66) of the bushing (41), the other of said stop elements being formed by said flange (24).

9. The manufacturing method according to Claim 8,
characterized in that a ring (55) of a thickness chosen from classes of modular thickness is located between said shoulder (62) and said anchor (17).

10. The manufacturing method according to Claim 8,
characterized in that a removable ring (78) of a thickness chosen from classes of modular thickness is located between said shoulder (62) and said anchor (17), said ring being of a C-shaped type.

11. The manufacturing method according to any one of Claims 1 to 6, characterized in that said stop element made of a single piece is formed by a flange (74) of said bushing (41) bearing said edge (80).

12. The manufacturing method according to Claim 11,
characterized in that the other of said stop elements comprises a removable ring (78), designed to block said anchor (17) on said bushing (41), said anchor (17) being fitted on said guide portion (82) after said welding.

13. The manufacturing method according to Claim 12,
characterized in that said guide portion (82) is located between said flange (74) of said bushing (41) and said removable ring (78).

14. The manufacturing method according to Claim 12 or Claim 13, characterized in that said removable ring is a C-shaped ring (78) located in an annular groove (79) of said bushing (41).

15. The manufacturing method according to Claim 14,
characterized in that said C-shaped ring (78) is designed to support an annular shim (81) chosen from classes of modular thickness, said annular shim (81) being fitted on said bushing (41) before said C-shaped ring (78).

16. The manufacturing method according to Claim 14 or Claim 15, characterized in that said C-shaped ring (78) is inserted in said groove (79) after insertion of said anchor (17).

17. The manufacturing method according to Claim 9 or 15, characterized in that said C-shaped ring (55, 81) is inserted after insertion of said anchor (17).

18. An open/close element for a servo valve of a fuel injector, manufactured applying the method according to any one of the preceding claims.

Drawing