A FUEL INJECTOR WITH ENHANCED LONG-TERM SEALING BEHAVIOUR

Technical Field of the Invention

The present invention relates to the technical field of fuel injectors. In particular, the present invention relates to enhancement of long-term sealing behaviour of fuel injectors, including those comprising solenoid valves.

Background of the Invention

Fuel injection systems that include fuel injectors are employed in common rail systems that are used in automotive engineering. Various types of fuel injectors include valves, such as solenoid valves for regulation of hydraulic pressure of fuel, as well as for controlling fuel injection behaviour of respective fuel injection systems.

A fuel injector valve generally includes a spherical sealing element for covering and sealing a diffusor opening that is provided on a relief chamber-side of a valve piece, to block fuel flow through the diffusor opening when in a sealed, first position. In a second position where the sealing element is temporarily diverged from the diffusor opening, the sealing is ceased and hydraulic pressure profile around the valve cause the fuel flow through the diffusor opening towards a control chamber. In the first position, the sealing element abuts onto the valve piece under a mechanical force. Said mechanical force can be exerted by an elastic means such as a compression spring; for instance, over a guide piece for centering of the sealing member in accordance with a valve axis. In the case where the fuel injector includes a solenoid valve, the sealing at the first position can be momentarily ceased by energizing a respective coil to magnetically overcome the force of the elastic means, thereby reaching to the second position.

As a setting parameter, axial trajectory of the sealing element at reciprocations between the first and second positions has an initial length value affects the injection profile and injection behaviour. Upon a long-term use that corresponds to millions of reciprocations of the sealing element along the valve axis, sealing surface on the valve piece undergoes plastic deformation. As a result, the relative position of the sealing element at its first position shifts along the valve axis. This phenomenon can be named as "armature lift drift" and causes deviation from the initial injection profile.

Furthermore, said plastic deformation usually unevenly takes place throughout the sealing surfaces around the valve axis. Thus, the microstructure and mechanical stability around the sealing surfaces on the valve piece undergoes an uneven change. This fact can cause deviation of said trajectory from the valve axis.

In addition, the sealing surfaces on the valve piece and surfaces around the diffusor opening are generally subjected to cavitation erosion when the fuel injector is in use. This phenomenon weakens the tightness of the valve, causes leakages and changes the injection profile upon a long-term use.

Particle erosion is a further problem that is observed in fuel injectors, in particular under off- highway vehicle conditions. Although fuel is normally subjected to a filtering process prior to entering the fuel injector, an inevitable extent of microparticles remain in the fuel, that erodes the sealing surfaces on valve seat areas. Several solutions are proposed for overcoming this problem, including the provision of erosion-preventive coating layers onto valve seat area's surfaces that are prone to undergo particle erosion. Yet, the provision of erosion-preventive coating layers increases the production costs.

Hence, the enhancement of stability in fuel injection profile can be considered as a long-felt need in fuel injectors industry.

Summary of the Invention

Primary object of the present invention is to propose a fuel injector with an enhanced longterm injecton profile stability. Another object of the present invention is to a low cost solution for injection profile stability problem. Further objects of the present invention are to minimize or eliminate the armature lift drift problem, particle erosion and cavitation erosion around the sealing surfaces on valve piece that are used in fuel injectors. The present invention proposes a fuel injector comprising a valve piece for conditional provision of fluid flow communication between a relief chamber and a control chamber. The valve piece comprises a valve seat area with a substantially frustoconical form facing the relief chamber. The valve seat area is arranged for accommodating a substantially spherical sealing member and for supporting said sealing member at a first position in which the sealing member is in mechanical contact with the valve piece.

The valve piece further comprises a diffusor opening for allowing fluid flow between the relief chamber and the control chamber through a diffusor at a second position in which the sealing member is diverged from the diffusor opening to cease said mechanical contact. Around the diffusor opening, the valve seat area is provided with a groove that is substantially in the form of a side surface of a spherical belt, the groove being arranged to circumferentially cover an outer surface of the sealing member when the sealing member in the first position.

The groove corresponds to an increased extent of contact surface area between the sealing member and the valve piece, thereby enhancing the sealing performance when compared to circular-contact prior art valves. Furthermore, the extent of mechanical pressure exerted by the sealing member onto the sealing surfaces which are formed by the groove on the valve seat area is distributed throughout an increased surface area when compared to that in circular-contact prior art valves; and thus the occurrence of mechanical damages on the valve seat area due to mechanical impacts by the sealing member, is minimized. Therefore, the groove decreases the occurrence of cavitation erosion around the diffusor opening and on the valve seat area.

In a possible embodiment, the groove can be axially separate from the diffusor opening, such that a frustoconical interval is disposed between the diffusor opening and the groove. With this embodiment, the occurrence of damage and cavitation erosion is further decreased. In a possible embodiment, the diffusor opening can be in the form of a circumferential chamfer. With this embodiment, the occurrence of damage and cavitation erosion is even further decreased.

In an alternative possible embodiment, the groove and/or the diffusor opening are provided with one or more erosion-preventive coating layers.

The present invention further proposes a method for obtaining a fuel injector as described above. The method includes a formation of a groove around the diffusor opening on the valve seat area, such that the resulting groove is substantially in the form of a side surface of a spherical belt that is arranged to circumferentially cover a corresponding outer surface of the sealing member when in the first position. The method thus enables the fuel injector according to the present invention.

A possible application of the method can further comprise arrangement of the groove to be axially separate from the diffusor opening, such that a frustoconical interval is disposed between the diffusor opening and the groove. This version of the method enables the achievement of the advantages of the corresponding embodiment described above. Hence, the occurrence of damage and cavitation erosion is further decreased with the resulting fuel injector.

A possible version of the method according to the present invention can further comprise shaping of the diffusor opening such that a circumferential chamfer is formed at the diffusor opening. With the resulting fuel injector, the occurrence of damage and cavitation erosion is even further decreased.

In a possible version of the method according to the present invention, the formation of the groove is performed by a coining that is applied onto the valve seat area in an axial direction towards the diffusor opening.

In a possible version, the method further includes provision of one or more erosionpreventive coating layers onto the groove and/or the diffusor opening. The present application further proposes a fuel injector obtained by a method that includes formation of the groove by a coining that is applied onto the valve seat area in an axial direction towards the diffusor opening.

Brief Description of Figures

The figures, whose brief explanations are herewith provided, are solely intended for providing a better understanding of the present invention and are as such not intended to define the scope of protection or the context in which the scope is to be interpreted in the absence of the description.

Fig.l shows an axial section of an exemplary fuel injector according to the present invention.

Fig.2 shows a close-up view of the detail "J" from Fig.l.

Fig.3 shows a close-up view of the detail "X" from Fig.2.

Fig.4 shows a version of Fig.3 where the sealing member and the exemplary guide piece are extracted and not shown, for better visualising the geometric aspects of the groove and periphery thereof.

Fig.5a is a SEM image in a direction along the valve axis towards the diffusor, showing cavitation erosion on the valve seat area around the diffuser opening of a prior art valve piece, upon an experimental study of 60 hours (cavitation flow test: continuous flow of fuel through the diffusor opening).

Fig.5b is a SEM image in a direction along the valve axis towards the diffusor, showing cavitation erosion on the valve seat area around the diffuser opening of a prior art valve piece, upon an experimental study of 80 hours (cavitation flow test: continuous flow of fuel through the diffusor opening). Fig.6a is a SEM image in a direction along the valve axis towards the diffusor, showing nonexistence or minimization of cavitation erosion on the grooved valve seat area around the diffuser opening of a valve piece for an injector according to the present invention, upon an experimental study of 60 hours (cavitation flow test: continuous flow of fuel through the diffusor opening).

Fig.6b is a SEM image in a direction along the valve axis towards the diffusor, showing nonexistence or minimization of cavitation erosion on the grooved valve seat area around the diffuser opening of a valve piece for an injector according to the present invention, upon an experimental study of 80 hours (cavitation flow test: continuous flow of fuel through the diffusor opening).

Detailed Description of the Invention

Referring to the figures described above, the present invention proposes a fuel injector (1) comprising a valve piece (2) for conditional provision of fluid flow communication between a relief chamber (3) and a control chamber (4). The valve piece (2) comprises a valve seat area (20) with a substantially frustoconical form facing the relief chamber (3). The valve seat area

(20) is arranged for accommodating a substantially cylindrical sealing member (30) and for supporting said sealing member (30) at 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 diffusor opening (21) for allowing fluid flow between the relief chamber (3) and the control chamber (4) through a diffusor (22) at a second position in which the sealing member (30) is diverged from the diffusor opening (21) (e.g., along the valve axis (A)) to cease said mechanical contact.

Within the context of the present application, the term "first position" corresponds to a sealing position in which the fluid flow through the diffusor opening (21) is blocked by a sealing member (30), and the term "second position" corresponds to an open state in which the fluid flow is allowed to flow around the sealing member (30) into the diffusor opening

(21). A general view of a fuel injector (1) according to the present invention is shown in Figure-1. Fig.l shows an axial section of the exemplary fuel injector (1) according to the present invention. Figure shows a close-up view of the detail "J" from Fig.l. Figure3 shows a closeup view of the detail "X" from Fig.2, visualising the vicinity of the sealing member (30) and the valve seat area (20) with the diffusor opening (21).

Around the diffusor opening (21), the valve seat area (20) is provided with a groove (23) that is substantially in the form of a side surface of a spherical belt. The groove (23) is being arranged to circumferentially cover an outer surface of the sealing member (30) (that is, around the valve axis (A)) when in the first position.

Figure4 shows a version of Fig.3 where the sealing member (30) and the exemplary guide piece (71) are extracted and not shown, for better visualising the geometric aspects of the groove (23) and periphery thereof.

The above-mentioned geometric features of the groove (23) prolong the flow path of the fuel to overcome the sealing, when compared to a prior art fuel injector that does not comprise the groove (23) described herein. In other words, the sealing on such prior art fuel injector takes place at a merely circular locus on a corresponding valve seat area, instead of at a locus that has the form of a spherical belt as in the present invention. The prolonged flow path enables sealing with a lower extent of pressure forces axial mechanical force exerted onto the sealing member (30), when compared to that required for obtaining a comparable extent of sealing over a circular mechanical contact of the sealing member in a prior art fuel injector. Thus, the present invention decreases mechanical depreciation that relate to future fuel leakages around sealing surfaces and provides a fuel injector (1) with an enhanced service life.

The above-mentioned mechanical force can be considered as that exerted by an elastic means (72) such as a compression spring; for instance, over a guide piece (71) for centering of the sealing member (30) onto the axis (A). In the case where the fuel injector (1) includes a solenoid valve, the sealing at the first position can be momentarily ceased by energizing a respective coil (73) to overcome the force of the elastic means (72), thereby reaching to the second position.

In a possible embodiment, the groove (23) can be axially separate from the diffusor opening (21), such that a frustoconical interval (24) is disposed between the diffusor opening (21) and the groove (23). Such frustoconical interval (24) disposed between the diffusor opening (21) and the groove (23) is emphasized in Fig.4 as a shaded region.

Because of the fact that the valve seat area (20) has a frustoconical geometry, the groove (23) being axially separate from the diffusor opening (21) also corresponds to that the groove (23) and diffusor opening (21) are radially separate from each other. Thus, the groove (23) and diffusor opening (21) are not adjacent/juxtaposed with each other. This measure protects the diffusor opening (21) from being mechanically damaged or plastically deformed at the formation of the groove (23), in particular in the case where the groove (23) is formed by coining. This measure is particularly useful in the case where the diffusor opening (21) includes the form of a circumferential chamfer as discussed in the present specification.

Considering the conical and spherical side surface geometries, the spherical outer surface of the sealing member (30) is substantially prevented from contacting onto the latter frustoconical surface or onto the surface of the frustoconical interval (24). Thus, it can be considered that, the sealing member (30) is prevented from mechanically contacting to the diffusor opening (21) when the fuel injector (1) is in use. This measure further enhances the service life of the fuel injector (1) by further preventing mechanical damage at the diffusor opening (21).

Furthermore, that the diffusor opening (21) and groove (23) are not juxtaposed to each other enhances the flow profile and fuel pressure distribution around the diffusor opening (21) when the fuel injector (1) is in use, and results in further distancing of the cavitation bubbles implosion locus from the diffusor opening (21). From that aspect, the service life of the fuel injector (1) is further enhanced. In a possible embodiment of the fuel injector (1) according to the present invention, the diffusor opening (21) can be in the form of a circumferential chamfer. The circumferential chamfer at the diffusor opening (21) can be considered to be formed around the valve axis (A). The chamfer can have a geometry of a circumferential side surface of a frustum of a cone, that has an apical angle that is more acute when compared to that of the frusto- conical geometry of the valve seat area (20). Said circumferential chamfer can be considered as a so-called "Helget chamfer". The circumferential chamfer arranges the fluid flow directions to ameliorate the distribution of the local fuel pressures, thereby impeding the formation of cavitation bubbles around the diffusor opening (21). Thus, such embodiment reduces the occurrence of the cavitation erosion around the diffusor opening (21), thereby increasing the service life of the fuel injector (1).

The present invention further proposes a method for obtaining a fuel injector (1) that comprises a valve piece(2) for conditional provision of fluid flow communication between a relief chamber (3) and a control chamber (4); wherein the valve piece(2) comprises a valve seat area (20) with a substantially frustoconical surface facing the relief chamber (3), the valve seat area (20) is arranged for accommodating a substantially cylindrical sealing member (30) i.e. a valve ball and for supporting said sealing member (30) at 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 diffusor opening (21) for allowing fluid flow between the relief chamber (3) and the control chamber (4) through a diffusor (22) (e.g., along a valve axis (A)) at a second position in which the sealing member (30) is diverged from the diffusor opening (21) (e.g., along the valve axis (A)) to cease said mechanical contact.

The method according to the present invention includes a formation of a groove (23) in the vicinity of the diffusor opening (21) on the valve seat area (20), such that the groove (23) is substantially in the form of a side surface of a spherical belt that is arranged to circumferentially cover a corresponding outer surface of the sealing member (30) when in the first position. The sealing member (30) in an application of the invention, is a valve ball and the side surface of a spherical belt corresponds to an outer surface of the valve ball in a close contact, providing sealing. Hence, the method enables the fuel injector (1) according to the present invention, achieving the advantages that are attributed to the groove (23) as discussed above.

A possible application of the method according to the present invention can further comprise arrangement of the groove (23) to be axially separate from the diffusor opening (21), such that a frustoconical interval (24) can be disposed between the diffusor opening (21) and the groove (23). Such version of the method enables the production of the abovedisclosed respective embodiment of the fuel injector (1) in which the mechanical damage is prevented at the diffusor opening (21) and in which the cavitation bubbles implosion locus is further distanced from the diffusor opening (21).

A possible version of the method according to the present invention can further comprise shaping of the diffusor opening (21) such that a circumferential chamfer is formed at the diffusor opening (21). This version of the method enables the production of the respective embodiment of the fuel injector (1) according to the present invention.

In a possible version of the method according to the present invention, the formation of the groove (23) can be performed by a coining that is applied onto the valve seat area (20) in an axial direction towards the diffusor opening (21). Within the context of the present application, the axial direction can correspond to a direction along the valve axis (A), towards the diffusor (22).

In accordance with the information submitted above, the present application further proposes a fuel injector (1) that is obtained by any of the above-mentioned versions of the method according to the present invention. In particular, the present application proposes a fuel injector (1) obtained by a method that includes formation of the groove (23) by a coining that is applied onto the valve seat area (20) in an axial direction towards the diffusor opening (21). In other words, the present invention proposes a fuel injector (1) comprising a valve piece (2) with a valve seat area (20) provided with a diffusor opening (21); wherein the valve piece (2) includes a groove (23) in the vicinity of the diffusor opening (21), said groove (23) is substantially in the form of a side surface of a spherical belt arranged to circumferentially cover an outer surface of a spherical sealing member (30) when in a sealing position; and the groove (23) is obtained by coining that is applied onto the valve seat area (20) in an axial direction towards the diffusor opening (21).

Considering that the valve piece (2) and also the valve seat area (20) can be made of a metallic material, the coining press results in a microstructural change on the valve seat area (20) to form to the groove (23). The microstructural change achieved by coining can be observed by metallographic imaging. Such microstructural change also results in a local enhancement of mechanical properties at the groove (23) when compared to remaining surfaces of the valve seat area (20) that were not subjected to coining process.

With the present invention, a controlled and circumferentially uniform microstructural change can be achieved at the production stage of the valve piece (2). The mechanical strength of the valve piece (2) production material is uniformly increased at the stage of formation of the groove (23), and no significant geometric change of the sealing surfaces (here, groove 23) takes place throughout long-term use, in particular when compared to prior art valve pieces that are not produced with such groove (23).

In other words: The pressure forces exerted at the forming of the groove (23) onto the valve seat area (20) by coining, compresses and compacts the body material at the respective zones of the valve piece (2) and shifts the sealing surfaces (surface to be contacted by the sealing member 30 when at the first position) in the axial direction. As a result, the groove (23) provides a hardened and radially symmetrical sealing surface, that is substantially no longer prone to mechanical deformation at impacts of the sealing member (30) when in use. A potential extent of "armature lift drift" is already achieved at the production phase of the valve piece (2); so, the long-term valve tightness (or sealing behaviour) is stabilized and the injection profile of the fuel injector (1) is maintained throughout a prolonged service life. Coining allows the prevention of radially asymmetrical mechanical deformations at sealing surfaces on the valve seat area (20).

Experimental study 1:

Fig.6a and Fig.6b in comparison with Fig.5a and Fig.5b respectively, show that the groove (23) provides a minimisation or prevention of cavitation erosion around the diffusor opening (21) of a fuel injector (1) according to the present invention. Fig.5a, Fig.5b, Fig.6a and Fig.6b are respective SEM images of four valve pieces (2), in a direction along the valve axis (A) towards the diffusor (22), showing the vicinity of valve seat areas (20) around respective diffuser openings (21) at the end of respective experimental tests. Said experimental tests can be considered as cavitation flow tests that include continuous flow of fuel through respective diffusor openings (21), under operating fuel pressures around the respective surfaces of the valve piece (2).

Fig.5a shows cavitation erosion around the diffuser opening (21) of a prior art valve piece (2) without the above-disclosed groove (23), upon 60 hours duration of such experimental study. Fig.5b shows cavitation erosion around the diffuser opening () of a prior art valve piece (2) without the above-disclosed groove (23), upon 80 hours duration of such experimental study. It is noted that, in respective valve pieces (2) without groove (23), even the presence of circumferential chamfer cannot eliminate the cavitation erosion around the diffusor openings (21) (and around the respective sealing surfaces) to the full extent.

Fig.6a and Fig.6b respectively show that no cavitation is observed around the diffuser opening (21) of a valve piece (2) with the groove (23) for a fuel injector (1) according to the present invention, upon 60 hours and 80 hours durations of such experimental study.

These positive results are achieved without the presence of any erosion-preventive coating layers on the valve seat area (20) shown in Fig.6a and Fig.6b. It is envisaged that the service life of a fuel injector (1) according to the present invention can be prolonged to an even greater extent in the case where the diffusor opening (21) (and possibly, also the groove 23) are provided with an erosion-preventive coating.

Within the context of the present application, the term "erosion-preventive coating" corresponds to one or more coating layers that are known to be used for minimisation of erosion around sealing surfaces of fuel injector valves, such as nitrides. Experimental study 2:

After the tests conducted as described in Experimental study 1, the valve pieces (2) are axially cut to observe the cavitation erosion results on fuel flow surfaces of diffusors (22) and throttles inside the respective valve pieces (2).

It is observed that, cavitation erosion takes place inside the diffusor (22) instead of occurring around the diffuser opening (21) and sealing surfaces (here: groove 23). So, the presence of the groove (23) (and possibly, also the presence of the frustoconical interval (24) disposed between the diffusor opening (21) and the groove (23)) axially shifts the implosion loci of cavitation bubbles away from the valve seat area (20) surfaces, and even away from the diffusor opening (21).

Experimental study 3:

"Dust contaminated fuel" tests (abbreviated as DCF) are performed for observing erosion due to micron-sized particles contaminated fuel such as that can be encountered at rural conditions. This test can be also considered as "off highway vehicles test".

The fuel injectors that are subjected to the present test differ by the features of the respective valve pieces (2) provided therein. The valve pieces (2) used in four different fuel injectors (1) can be classified as follows: a) a valve piece (2) for the fuel injector (1) according to the present invention, without erosion-preventive coating around the diffusor opening (21) and around the groove (23); b) a first prior art valve piece (i.e., without groove 23), that is not provided with any erosion-preventive coating around the respective diffusor opening; fuel injectors with such valve pieces shall be used with high-performance particle filters for a prolonged service life, otherwise they have a short service life; c) a second prior art valve piece (i.e., without groove 23), that is provided with a first erosion-preventive coating around the respective diffusor opening; fuel injectors with such valve pieces can be used with low-performance particle filters for a prolonged service life; d) a third prior art valve piece (i.e., without groove 23), that is provided with a second, advanced-technology erosion-preventive coating around the respective diffusor opening.

The following observations are made:

- The highest rate and extent of particle-related erosion is observed with the sample (b) (that is, the first prior art valve piece).

- The lowest rate and extent of particle related erosion is observed with the sample (d) (that is, the third prior art valve piece).

- The rate and extent of particle-related erosion observed with the sample (c) and sample (a) are highly similar. Hence, thanks to the groove (23) the fuel injector (1) according to the present invention shows an acceptable particle erosion resistance that is comparable with the prior art fuel injector with coated, second prior art valve piece.

This advantageous result shows that the presence of the groove (23) (and possibly, also the presence of a frustoconical interval 24 disposed between the diffusor opening 21 and the groove 23) eliminates the costs related to provision of an erosion-preventive coating and yet achieves an acceptable extent of particle erosion prevention. It is envisaged that, even with a commonly used (low cost) erosion-preventive coating such as that used in sample (c) above, the extent of particle erosion prevention in a fuel injector (1) according to the present invention can be increased to a level that was only available with an advanced- technology (high-cost) erosion-preventive coating that is used in sample (d) above. So, a maximized extent of particle erosion prevention can be achieved with a fuel injector (1) with a valve piece (2) provided with a low-cost erosion-preventive coating, without necessitating a high-cost erosion-preventive coating layer. Hence, the present invention provides prevention of particle erosion with minimized production costs.

Accordingly, in a possible version of the method according to the present invention can include provision of one or more erosion-preventive coating layers onto the groove (23) and/or the diffusor opening (21). As a result, in a possible embodiment of the fuel injector (1) according to the present invention, the groove (23) and/or the diffusor opening (21) can be provided with one or more erosion-preventive coating layers. For instance, said one or more erosion-preventive coating layers can include a material that has a higher hardness, toughness, or mechanical strength when compared to a body material of the valve piece (2).

Reference signs

1 fuel injector

2 valve piece

3 relief chamber

4 control chamber

20 valve seat area

21 diffusor opening

22 diffusor

23 groove

24 frustoconical interval

30 sealing member

71 guide piece

72 elastic means 73 coil