Fuel injectors with improved long-term sealing performance

Abstract

The invention relates to a fuel injector (1) comprising a valve piece (2) with a valve seat area (20) provided with a diffuser opening (21), the valve piece (2) having a groove (23) around the diffuser opening (21), the groove (23) being substantially in the form of the side of a spherical belt arranged circumferentially covering the outer surface of a spherical sealing member (30) in the sealing position, the groove (23) being obtained by coining the valve seat area (20) axially towards the diffuser opening (21). The invention further proposes a method for obtaining said fuel injector (1).

Description

[Technical field]

[0001] The present invention relates to the technical field of fuel injectors, and more particularly to improving the long term sealing performance of fuel injectors, including those having solenoid valves. [Background technology]

[0002] In the common rail system used in automotive engineering, a fuel injection system having a fuel injector is adopted. Each type of fuel injector is provided with a valve such as a solenoid valve for adjusting the hydraulic pressure of the fuel and for controlling the fuel injection performance of each fuel injection system.

[0003] Typically, fuel injector valves comprise a spherical sealing element which, in a first sealing position, covers and seals the diffuser opening on the relief chamber side of the valve piece so as to prevent fuel flow through the diffuser opening. In a second position, where the sealing element is temporarily spaced from the diffuser opening, no sealing is performed and the hydraulic pressure profile around the valve allows fuel to flow from the diffuser opening towards the control chamber. In the first position, a mechanical force causes the sealing element to abut against the valve piece. The mechanical force can be applied, for example, by a resilient means, such as a compression spring, across a guide piece for centering the sealing member relative to the valve stem. If the fuel injector comprises a solenoid valve, the sealing in the first position can be temporarily prevented by energizing the respective coils so as to magnetically overcome the force of the resilient means and reach the second position.

[0004] As a set parameter, the axial trajectory of the sealing element back and forth between the first and second positions has an initial length value that affects the injection profile and injection performance. During long-term use, as the sealing element moves back and forth millions of times along the valve stem, the sealing surface on the valve piece plastically deforms. This causes the relative position of the sealing element in its first position to shift along the valve stem. This phenomenon may be referred to as "armature lift drift" and results in a deviation from the initial injection profile.

[0005] Furthermore, the plastic deformation generally occurs unevenly across the sealing surface around the valve stem, thus unevenly altering the microstructure and mechanical stability around the sealing surface on the valve piece, which can cause the trajectory to shift from the valve stem.

[0006] Furthermore, during use of the fuel injector, the sealing surfaces on the valve piece and the surfaces around the diffuser opening typically undergo cavitation erosion, which during long-term use can deteriorate the valve's tightness, causing leakage and changes in the injection profile.

[0007] A further problem with fuel injectors, especially in off-highway vehicle conditions, is particulate erosion. Although fuel is typically filtered before entering the fuel injector, an unavoidable amount of particulate remains in the fuel, which can erode the sealing surfaces on the valve seat area. Several solutions have been proposed to this problem, including the application of an anti-erosion coating layer on the surfaces of the valve seat area that are susceptible to particulate erosion. However, the application of an anti-erosion coating layer increases manufacturing costs.

[0008] It may therefore be believed that there is a long felt need in the fuel injector industry for improved fuel injection profile stability. Summary of the Invention [Problem to be solved by the invention]

[0009] A primary object of the present invention is to propose a fuel injector with improved long term injection profile stability. Another object of the present invention is to provide an inexpensive solution to the problem of injection profile stability. A further object of the present invention is to minimize or eliminate the problem of armature lift, as well as particle and cavitation erosion around the sealing surfaces on valve pieces used in fuel injectors. [Means for solving the problem]

[0010] The present invention provides a fuel injector including a valve piece for conditionally providing fluid flow communication between a relief chamber and a control chamber, the valve piece having a generally frusto-conical seat area facing the relief chamber, the seat area adapted to receive a generally spherical sealing member and to support the sealing member in a first position in which the sealing member is in mechanical contact with the valve piece.

[0011] The valve piece further has a diffuser opening which allows fluid to flow between the relief chamber and the control chamber through the diffuser in a second position in which the sealing member is spaced from the diffuser opening such that said mechanical contact is no longer made.Around the periphery of the diffuser opening, a groove substantially in the form of a profile of a spherical belt is provided in the valve seat area, the groove being arranged to circumferentially cover an outer surface of the sealing member when the sealing member is in the first position.

[0012] The grooves provide an increased contact surface area between the sealing member and the valve piece, which improves sealing capability compared to prior art circular contact valves. Furthermore, the degree of mechanical pressure applied by the sealing member to the groove's sealing surface on the valve seat area is distributed over a larger surface area compared to prior art circular contact valves, thus minimizing the occurrence of mechanical damage on the valve seat area due to mechanical impact by the sealing member. Thus, the grooves reduce the occurrence of cavitation erosion around the diffuser opening and on the valve seat area.

[0013] In a possible embodiment, the grooves may be axially spaced from the diffuser opening such that a frustoconical spacing is disposed between the diffuser opening and the grooves, which further reduces the occurrence of damage and cavitation erosion.

[0014] In a possible embodiment, the diffuser opening may be in the form of a circumferential chamfer, which further reduces the occurrence of damage and cavitation erosion.

[0015] In another possible embodiment, the grooves and / or diffuser openings are provided with one or more anti-erosion coating layers.

[0016] The invention further proposes a method for obtaining a fuel injector as described above, comprising forming a groove around the diffuser opening on the valve seat area, said groove being in the form of a substantially spherical belt profile arranged to circumferentially cover the corresponding outer surface of the sealing member in the first position, in this way making it possible to realize the fuel injector according to the invention.

[0017] A possible aspect of the method may further include axially spacing the groove from the diffuser opening such that a frustoconical spacing is disposed between the diffuser opening and the groove. This version of the method allows the advantages of the corresponding above-mentioned embodiment to be realized, and thus the resulting fuel injector is further reduced in damage and cavitation erosion.

[0018] A possible version of the method of the present invention may further include shaping the diffuser opening such that it defines a circumferential chamfer, the resulting fuel injector being even more resistant to damage and cavitation erosion.

[0019] In a possible version of the method according to the invention, forming the groove is performed by coining the valve seat area axially towards the diffuser opening.

[0020] In a possible version, the method further includes providing one or more anti-erosion coating layers on the grooves and / or the diffuser openings.

[0021] The present application further proposes a fuel injector obtained by a method comprising forming a groove by coining in the valve seat area, axially towards the diffuser opening. [Brief description of the drawings]

[0022] The drawings briefly described herein are intended only for a better understanding of the invention and are not intended as such to define the scope of protection or to define the context in which said scope may be interpreted without the description. [Figure 1] 1 shows an axial cross-sectional view of an exemplary fuel injector according to the present invention; [Diagram 2] A detailed enlarged view of "J" in Figure 1 is shown. [Diagram 3] A detailed enlarged view of the "X" in Figure 2 is shown. [Figure 4] 3, where the sealing member and exemplary guide pieces have been extracted and not shown in order to better visualize the geometrical aspects of the groove and its surroundings. [Figure 5a] FIG. 1 is an SEM image in the direction along the valve axis towards the diffuser showing cavitation erosion on the valve seat area around the diffuser opening of a prior art valve piece after a 60 hour experimental study (cavitation flow test: fuel is continuously flowed through the diffuser opening). [Figure 5b]FIG. 1 is an SEM image in the direction along the valve axis towards the diffuser showing cavitation erosion on the valve seat area around the diffuser opening of a prior art valve piece after an 80 hour experimental study (cavitation flow test: fuel is continuously flowed through the diffuser opening). [Figure 6a] FIG. 1 is an SEM image in the direction along the valve axis towards the diffuser showing no or minimal cavitation erosion on the grooved seat area around the diffuser opening of the valve piece in an injector according to the present invention after 60 hours of experimental study (cavitation flow test: fuel is continuously flowed through the diffuser opening). [Figure 6b] FIG. 1 is an SEM image in the direction along the valve axis towards the diffuser showing no or minimal cavitation erosion on the grooved seat area around the diffuser opening of the valve piece in an injector according to the present invention after 80 hours of experimental study (cavitation flow test: fuel is continuously flowed through the diffuser opening). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] With reference to the above figures, the present invention proposes a fuel injector (1) comprising a valve piece (2) for conditionally establishing fluid flow communication between a relief chamber (3) and a control chamber (4). The valve piece (2) has a substantially frusto-conical valve seat area (20) facing the relief chamber (3). The valve seat area (20) accommodates a substantially cylindrical sealing member (30) and is arranged to support the sealing member (30) in a first position in which the sealing member (30) is in mechanical contact with the valve piece (2). The valve piece (2) further comprises a diffuser opening (21) which allows fluid to flow between the relief chamber (3) and the control chamber (4) through a diffuser (22) in a second position in which the sealing member (30) is spaced from the diffuser opening (21) (e.g. along the valve axis (A)) such that said mechanical contact is no longer made.

[0024] In the context of this application, the term "first position" corresponds to a sealed position in which fluid flow through the diffuser opening (21) is prevented by the sealing member (30), and the term "second position" corresponds to an open position in which fluid flow is permitted to flow around the sealing member (30) and into the diffuser opening (21).

[0025] Figure 1 shows an overall view of a fuel injector (1) according to the present invention. Figure 1 shows an axial cross-section of an exemplary fuel injector (1) according to the present invention. Figure 2 shows an enlarged detail of "J" in Figure 1. Figure 3 shows an enlarged detail of "X" in Figure 2, which visualizes the vicinity of the sealing member (30) and the valve seat area (20) with the diffuser opening (21).

[0026] Around the periphery of the diffuser opening (21), a groove (23) substantially in the shape of the side of a spherical belt is provided in the valve seat area (20), which is arranged to cover the outer surface of the sealing member (30) in the circumferential direction (i.e. around the valve axis (A)) in the first position.

[0027] FIG. 4 shows a version of FIG. 3 in which the sealing member (30) and exemplary guide piece (71) have been extracted and not shown in order to better visualize the geometrical aspects of the groove (23) and its surroundings.

[0028] The geometrical features of the groove (23) described above provide a longer flow path for the fuel over the seal compared to prior art fuel injectors not having the groove (23) described herein. In other words, the seal of such prior art fuel injectors occurs simply in a circular locus on the corresponding valve seat area, rather than in a locus having the shape of a spherical belt as in the present invention. The longer flow path allows the seal to be achieved with reduced pressure and axial mechanical forces applied to the sealing member (30) compared to what would be required to achieve an equivalent seal over a circular mechanical contact in the case of the sealing member of the prior art fuel injector. Thus, the present invention provides a fuel injector (1) with a longer lifespan by reducing mechanical degradation with respect to future fuel leakage around the sealing surface.

[0029] The mechanical force may be understood to be applied by elastic means (72), such as a compression spring, across a guide piece (71) for centering the sealing member (30) with respect to the axis (A). If the fuel injector (1) comprises a solenoid valve, the force of the elastic means (72) can be overcome, thereby temporarily preventing sealing in the first position, by energizing the respective coils (73) so as to reach the second position.

[0030] In a possible embodiment, the grooves (23) may be axially spaced from the diffuser opening (21) such that a frustoconical interval (24) is disposed between the diffuser opening (21) and the grooves (23). The frustoconical interval (24) disposed between the diffuser opening (21) and the grooves (23) is highlighted in FIG. 4 as a shaded area.

[0031] Due to the frustoconical shape of the valve seat area (20), the groove (23) is axially spaced from the diffuser opening (21), which also corresponds to the groove (23) and the diffuser opening (21) being radially spaced from each other. Thus, the groove (23) and the diffuser opening (21) are not adjacent / juxtaposed to each other. This measure protects the diffuser opening (21) from mechanical damage or plastic deformation during the formation of the groove (23), especially when the groove (23) is formed by coining. This measure is particularly effective when the diffuser opening (21) includes a circumferential chamfer form, as described herein.

[0032] Considering the conical and spherical side shapes, the spherical outer surface of the sealing member (30) is substantially prevented from contacting the latter frustoconical surface or the surfaces of the frustoconical intervals (24). It can therefore be seen that the sealing member (30) is prevented from mechanically contacting the diffuser opening (21) during use of the fuel injector (1). This measure further extends the life of the fuel injector (1) by further preventing mechanical damage at the diffuser opening (21).

[0033] Furthermore, the non-juxtaposition of the diffuser opening (21) and the grooves (23) improves the flow profile and fuel pressure distribution around the diffuser opening (21) during use of the fuel injector (1), which results in a greater distance of the implosion trajectory of the cavitation bubble from the diffuser opening (21), thus further extending the life of the fuel injector (1).

[0034] In a possible embodiment of the fuel injector (1) according to the invention, the diffuser opening (21) may be in the form of a circumferential chamfer. The circumferential chamfer at the diffuser opening (21) may be understood to be formed around the valve axis (A). The chamfer may have the shape of a circumferential flank of a truncated cone with a sharper apex angle compared to the truncated cone shape of the valve seat area (20). The circumferential chamfer may be understood as a so-called "Helget chamfer". The circumferential chamfer orients the fluid flow direction in such a way that the local fuel pressure is better distributed, thus preventing the formation of cavitation bubbles around the diffuser opening (21). Thus, in this embodiment, the occurrence of cavitation erosion around the diffuser opening (21) is reduced, thereby increasing the life of the fuel injector (1).

[0035] The invention further proposes a method for obtaining a fuel injector (1) comprising a valve piece (2) conditionally providing fluid flow communication between a relief chamber (3) and a control chamber (4), the valve piece (2) comprising a valve seat area (20) with a substantially frustoconical surface facing the relief chamber (3), the valve seat area (20) accommodating a substantially cylindrical sealing member (30), i.e. a valve ball, arranged to support the sealing member (30) in a first position in which the sealing member (30) is in mechanical contact with the valve piece (2), the valve piece (2) further comprising a diffuser opening (21) which allows fluid to flow between the relief chamber (3) and the control chamber (4) through a diffuser (22) (e.g. along the valve axis (A)) in a second position in which the sealing member (30) is spaced (e.g. along the valve axis (A)) from the diffuser opening (21) such that said mechanical contact is no longer made.

[0036] The method according to the invention comprises forming a groove (23) in the vicinity of the diffuser opening (21) on the valve seat area (20) such that the groove (23) is substantially in the form of a lateral surface of a spherical belt arranged to circumferentially cover a corresponding outer surface of a sealing member (30) in a first position. The sealing member (30) in this embodiment of the invention is a valve ball, and the lateral surface of the spherical belt corresponds to the outer surface of the valve ball in intimate contact with which it achieves the seal.

[0037] The method therefore makes it possible to realise the fuel injector (1) according to the invention, which achieves the above-mentioned advantages provided by the grooves (23).

[0038] A possible embodiment of the method according to the invention may further comprise arranging the groove 23 axially spaced from the diffuser opening 21 such that a frustoconical spacing 24 may be disposed between the diffuser opening 21 and the groove 23. This version of the method allows for the manufacture of the above-mentioned embodiments of the fuel injector 1 with avoidance of mechanical damage at the diffuser opening 21 and with a greater distance of the implosion trajectory of the cavitation bubble from the diffuser opening 21.

[0039] A possible version of the method according to the invention may further comprise shaping the diffuser opening (21) such that the diffuser opening (21) is provided with a circumferential chamfer. This version of the method allows for the manufacture of each embodiment of the fuel injector (1) according to the invention.

[0040] In a possible version of the method according to the invention, the formation of the grooves (23) may be performed by coining the valve seat area (20) axially towards the diffuser opening (21). In the context of the present application, the axial direction may correspond to the direction along the valve axis (A), towards the diffuser (22).

[0041] According to the above information, the present application further proposes a fuel injector (1) obtained by any of the above-mentioned versions of the method according to the invention. In particular, the present application proposes a fuel injector (1) obtained by a method comprising forming a groove (23) in a valve seat area (20) by coining in the axial direction towards the diffuser opening (21). In other words, the present invention proposes a fuel injector (1) comprising a valve piece (2) having a valve seat area (20) provided with a diffuser opening (21). The valve piece (2) has a groove (23) in the vicinity of the diffuser opening (21), the groove (23) being substantially in the form of a flank of a spherical belt arranged so as to cover in the circumferential direction the outer surface of the spherical sealing member (30) in the sealing position, the groove (23) being obtained by performing a coining operation in the valve seat area (20) in the axial direction towards the diffuser opening (21).

[0042] Considering that the valve piece (2) and also the valve seat area (20) may be made of a metallic material, the coining press results in a microstructural change on the valve seat area (20) thereby forming the grooves (23). The microstructural change achieved by the coining process can be observed by metallographic imaging. The microstructural change further results in an improvement in the local mechanical properties at the grooves (23) compared to other surfaces of the valve seat area (20) that have not been subjected to the coining process.

[0043] According to the invention, a controlled and uniform microstructural change in the circumferential direction can be achieved during the manufacturing process of the valve piece 2. The mechanical strength of the manufacturing material of the valve piece 2 is uniformly increased during the formation of the groove 23, and no significant shape changes of the sealing surface (here the groove 23) occur even after long-term use, especially compared to valve pieces of the prior art manufactured without the groove 23.

[0044] In other words, the pressure applied by the coining process on the valve seat area (20) during the formation of the groove (23) compresses and hardens the body material in the respective areas of the valve piece (2) and the sealing surfaces (surfaces that the sealing member 30 contacts in the first position) are displaced axially. As a result, the groove (23) is hardened to provide a radially symmetrical sealing surface that is substantially mechanically deformed by the impact of the sealing member (30) during use. The potential range of "armature drift" is already determined during the manufacturing stage of the valve piece (2), thus stabilizing the long-term valve sealing (or sealing performance) and maintaining the injection profile of the fuel injector (1) over its extended life. The coining process makes it possible to prevent radially asymmetrical mechanical deformation of the sealing surfaces on the valve seat area (20).

[0045] Experimental Study 1: Figures 6a and 6b, in comparison with Figures 5a and 5b respectively, show that the grooves (23) minimize or prevent cavitation erosion around the diffuser openings (21) of the fuel injector (1) according to the present invention. Figures 5a, 5b, 6a and 6b are SEM images of each of the four valve pieces (2) in a direction along the valve axis (A) towards the diffuser (22) showing the vicinity of the valve seat area (20) around the diffuser openings (21) at the end of each experimental test, which may be understood as a cavitation flow test involving a continuous flow of fuel through each diffuser opening (21) under fuel pressure around each surface of the valve pieces (2).

[0046] Figure 5a shows the cavitation erosion around the diffuser opening (21) of a prior art valve piece (2) without the grooves (23) described above after 60 hours of experimental study. Figure 5b shows the cavitation erosion around the diffuser opening (21) of a prior art valve piece (2) without the grooves (23) described above after 80 hours of experimental study. It should be noted that even the presence of a circumferential chamfer in each valve piece (2) without grooves (23) does not completely eliminate cavitation erosion around the diffuser opening (21) (and around each sealing surface).

[0047] Figures 6a and 6b show that after 60 and 80 hours of this experimental study, respectively, no cavitation was observed around the diffuser opening (21) of the valve piece (2) having grooves (23) in the fuel injector (1) according to the present invention.

[0048] These advantageous results are achieved even without any anti-erosion coating layer on the valve seat area (20) shown in Figures 6a and 6b. It is envisaged that the life span of the fuel injector (1) according to the invention may be significantly increased if the diffuser opening (21) (and thus also the groove 23) is provided with an anti-erosion coating.

[0049] In the context of this application, the term "anti-erosion coating" corresponds to one or more known coating layers, such as nitrides, that are used to minimize erosion around the sealing surfaces of fuel injector valves.

[0050] Experimental Study 2: After testing was performed as described in Experimental Study 1, the valve pieces (2) were cut axially to check the cavitation erosion results on the fuel flow surfaces of the diffuser (22) and the throttles within each valve piece (2).

[0051] Cavitation erosion is observed to occur within the diffuser (22) rather than around the diffuser opening (21) and sealing surface (here groove 23). Thus, the presence of the groove (23) (and thus the presence of the frustoconical spacing (24) disposed between the diffuser opening (21) and groove (23)) axially shifts the implosion trajectory of the cavitation bubble away from the surface of the valve seat area (20) and thus away from the diffuser opening (21).

[0052] Experimental Study 3: The erosion caused by fuel contaminated with micron-sized particles, such as may occur in suburban conditions, was confirmed by carrying out the "Dust Contaminated Fuel" (DCF) test, which may also be interpreted as the "Off-Highway Vehicle Test".

[0053] The characteristics of the valve pieces (2) installed inside the fuel injectors that are the subject of this test are different. The valve pieces (2) used in the four different fuel injectors (1) can be classified as follows: a) A valve piece (2) for a fuel injector (1) according to the present invention, without an anti-erosion coating around the diffuser opening (21) and around the grooves (23). b) A first prior art valve piece (i.e., no grooves 23) that does not have any anti-erosion coating around each diffuser opening. Fuel injectors having such valve pieces are intended for use with high performance particulate filters, which would otherwise have a reduced lifespan, to increase their lifespan. c) A second prior art valve piece (i.e. without grooves 23) with a first anti-erosion coating around each diffuser opening. Fuel injectors having such valve pieces may be used with low performance particulate filters for increased life. d) A third prior art (i.e., no grooves 23) valve piece provided with a second state-of-the-art erosion protection coating around each diffuser opening.

[0054] The following was confirmed: The rate and extent of particle-related erosion was highest for sample (b) (i.e., the first prior art valve piece). The lowest rate and extent of particle-related erosion was observed for sample (d) (i.e., the third prior art valve piece). The rate and extent of particle related erosion was very similar between sample (c) and sample (a). Thus, due to the grooves (23), the fuel injector (1) of the present invention exhibits favorable particle erosion resistance comparable to that of the prior art fuel injector having a coated second prior art valve piece.

[0055] This advantageous result is achieved by eliminating the costs associated with providing an anti-erosion coating due to the presence of the groove (23) (and by extension the presence of the frustoconical spacing 24 disposed between the diffuser opening 21 and the groove 23) while still achieving a desirable degree of particle erosion prevention. It is envisaged that even commonly used (low cost) anti-erosion coatings, such as those used in sample (c) above, can improve the degree of particle erosion prevention in the fuel injector (1) according to the invention to a degree that was only possible with the state of the art (high cost) anti-erosion coating used in sample (d) above. Thus, maximum particle erosion prevention can be achieved in a fuel injector (1) having a valve piece (2) provided with a low cost anti-erosion coating, without the need for a high cost anti-erosion coating layer. Thus, the present invention achieves particle erosion prevention with minimal manufacturing costs.

[0056] Thus, possible versions of the method according to the invention may include providing one or more anti-erosion coating layers on the groove (23) and / or the diffuser opening (21). As a result, in possible embodiments of the fuel injector (1) according to the invention, the groove (23) and / or the diffuser opening (21) may be provided with one or more anti-erosion coating layers. For example, the one or more anti-erosion coating layers may comprise a material that is harder, tougher or has a higher mechanical strength compared to the body material of the valve piece (2). [Explanation of symbols]

[0057] 1 Fuel Injector 2 Valve Pieces 3 Relief Chamber 4. Control Chamber 20 Valve seat area 21 Diffuser opening 22 Diffuser 23 Groove 24 Cone Trapezoid Spacing 30 Sealing member 71 Guide Piece 72 Elastic means 73 Coil

Claims

1. a valve piece (2) for conditionally providing fluid flow communication between a relief chamber (3) and a control chamber (4); The valve piece (2) has a substantially frustoconical valve seat area (20) facing the relief chamber (3), the valve seat area (20) is arranged to receive a generally spherical sealing member (30) and support the sealing member (30) in a first position in which the sealing member (30) is in mechanical contact with the valve piece (2); 1. A fuel injector (1), wherein the valve piece (2) further comprises a diffuser opening (21) which allows fluid to flow between the relief chamber (3) and the control chamber (4) through a diffuser (22) in a second position where the sealing member (30) is spaced from the diffuser opening (21) such that the mechanical contact is no longer made, 1. A fuel injector (1), characterized in that a groove (23) substantially in the form of a profile of a spherical belt is arranged in the valve seat area (20) around the diffuser opening (21), the groove (23) being arranged to circumferentially cover and seal against an outer surface of the sealing member (30) when the sealing member (30) is in the first position.

2. 2. The fuel injector (1) of claim 1, wherein the groove (23) is arranged axially spaced from the diffuser opening (21) such that a frustoconical spacing (24) is arranged between the diffuser opening (21) and the groove (23).

3. A fuel injector (1) as claimed in claim 1 or 2, wherein the diffuser opening (21) is in the form of a circumferential chamfer.

4. a valve piece (2) for conditionally providing fluid flow communication between a relief chamber (3) and a control chamber (4); The valve piece (2) has a substantially frustoconical valve seat area (20) facing the relief chamber (3), the valve seat area (20) is arranged to receive a generally cylindrical sealing member (30) and support the sealing member (30) in a first position in which the sealing member (30) is in mechanical contact with the valve piece (2); 1. A method for obtaining a fuel injector (1), wherein the valve piece (2) further comprises a diffuser opening (21) which allows fluid to flow between the relief chamber (3) and the control chamber (4) through a diffuser (22) in a second position where the sealing member (30) is spaced from the diffuser opening (21) such that the mechanical contact is no longer made, comprising the steps of: forming a groove (23) around the diffuser opening (21) on the valve seat area (20), such that the groove (23) is in the form of a substantially spherical belt profile arranged to circumferentially cover a corresponding outer surface of the sealing member (30) in the first position.

5. 5. The method of claim 4, further comprising: axially spacing the groove (23) from the diffuser opening (21) such that a frustoconical spacing (24) is disposed between the diffuser opening (21) and the groove (23).

6. The method of claim 4 or 5, further comprising shaping the diffuser opening (21) such that the diffuser opening (21) is formed with a circumferential chamfer.

7. 7. The method according to claim 4, wherein forming the groove (23) is performed by coining the valve seat area (20) axially towards the diffuser opening (21).

8. 1. A fuel injector (1), comprising a valve piece (2) having a valve seat area (20) provided with a diffuser opening (21), the valve piece (2) having a groove (23) around the diffuser opening (21), the groove (23) being substantially in the form of the side of a spherical belt arranged so as to circumferentially cover an outer surface of a spherical sealing member (30) in a sealing position, the groove (23) being obtained by coining the valve seat area (20) axially towards the diffuser opening (21).

Images