Hydraulic valve

Abstract

A hydraulic valve comprises a rod (58) guided slidingly in a bushing along a guidance zone (ZG) comprising a convergence zone (ZC) in which the forces acting on the rod tend to recentre it in the bushing and, a divergence zone (ZD) in which the forces acting on the rod tend to move it away from the axis, the two zones joining along a line of separation (M) situated in a second clamping zone, the functional clearance for sliding defined between the bushing and the rod being increased in the divergence zone (ZD).

Description

TECHNICAL FIELD

[0001] The present invention relates to a hydraulic valve and more particularly to the valve of a diesel fuel injector. TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0002] In a diesel fuel injector, injections are controlled by a solenoid valve that opens or closes a leak channel, thereby controlling the pressure in a control chamber. This solenoid valve comprises a rod sliding within a sleeve that is press-fitted into a bore in the valve body, with a magnetic armature attached to one end of the rod.

[0003] This leak channel opens into an annular groove surrounding the bushing, limiting the bushing's clamping force to the extreme areas of the bore located on either side of this annular groove. Furthermore, the bushing is radially drilled, allowing pressurized fuel to pass from the groove into the bushing.

[0004] Within the sleeve, the rod is guided along a guide zone extending between the radial hole and the end of the sleeve opposite the magnetic armature. Despite the limited clearance between the rod and the sleeve, during operation the pressurized fuel deforms the sleeve and the rod, displacing it radially so that the rod approaches the sleeve or even makes direct contact, thus preventing the correct operation of the valve and injector. DE 10 2016 000 350 describes an injector control valve with a sleeve in which a rod slides, the end of which has a magnetic armature attached. The opposite end of the rod extends from the sleeve and slides into an annular socket axially spaced from the sleeve, forming an axial fuel supply channel. The rod includes an annular groove which, in the closed position, lies within the annular socket: the valve is closed.When the armature is attracted to the solenoid, the rod moves and the annular groove positions itself in the axial space; this is the open position. An internal channel extends within the rod from the annular groove to the free end face of the rod (opposite the armature). In the open position, fuel enters the annular groove, which is in the axial space, and is expelled through the end face of the rod.

[0005] EP2620632 discloses an injector control valve comprising a sleeve in which a rod slides, the end of which is fitted with a magnetic armature. The sleeve is press-fitted into a bore provided in the valve body. The sleeve includes two projecting end bearings, thus forming an annular space with the bore between two clamping zones. A radial hole is provided in the sleeve to allow pressurized fuel to pass from the annular space into the sleeve. The rod extends over only a portion of the so-called guide zone extending between the radial hole and the end of the sleeve opposite the magnetic armature. The rod includes two annular grooves on its guide portion.

[0006] EP2960485 discloses an injector control valve comprising a sleeve in which a rod slides, with a magnetic armature attached to one end of the rod. The sleeve is press-fitted into a bore provided in the valve body. A radial hole is provided in the sleeve to allow pressurized fuel to pass into the sleeve. The rod has a reduced diameter cross-section forming a return chamber between the rod and the sleeve. A return line is placed in the return chamber through the sleeve so that when the rod is in the open position, fuel can leave the inside of the sleeve and flow into the return line. SUMMARY OF THE INVENTION

[0007] The present invention aims to remedy the aforementioned drawbacks by proposing a hydraulic control valve for a fuel injector, the valve comprising a body provided with a bore in which a tubular sleeve is clamped, a valve stem being guided sliding in the sleeve.

[0008] The sleeve extends between a first end and a second end and is clamped in the bore in a first clamping zone and a second clamping zone, said zones being located at opposite ends of the sleeve. These zones are separated by an annular space provided in the bore and surrounding the sleeve, into which, during use, high-pressure fuel enters and passes inside the sleeve through a hole passing through the sleeve, said hole being arranged in the vicinity of the first clamping zone.

[0009] The valve stem extends between a first end emerging from the first clamping zone and a second end emerging from the second clamping zone, and is guided in the sleeve along a guide zone extending between the second end of the sleeve and said through hole.

[0010] In operation, the pressurized fluid deforms the sleeve and radially displaces the rod such that the guiding zone comprises a convergence zone of length LC in which the forces acting on the rod tend to recenter it within the sleeve, this convergence zone being proximal to the through hole, and a divergence zone of length LD in which the forces acting on the rod tend to misalign it, this divergence zone being proximal to the second end of the sleeve. The two zones meet along a separation line located in the second clamping zone. The sleeve and the rod are configured so that the defined functional sliding clearance between them is increased in the divergence zone, the clearance increase being at a distance between LD / 3 and 2LD / 3 from the separation line. This design feature cancels or equalizes the forces in the divergence zone.In addition, the defined functional sliding clearance between the bushing and the rod is also increased in the convergence zone by means of an annular groove provided in the rod and / or the bushing.

[0011] This annular groove provided in the convergence zone is advantageously positioned at a distance greater than LC / 2 from the separation line, for example in some variants at a distance greater than or equal to 3LC / 4. Thus positioned, this annular groove minimizes friction related to the formation of a deposit on the rod, while maintaining maximum recentering force.

[0012] Furthermore, at the divergence zone, the increase in functional clearance is achieved by a decrease in the section of the rod and / or by an increase in the section of the bushing.

[0013] According to a first embodiment, the rod and / or the socket is provided with an annular groove defining said increase.

[0014] According to a second embodiment, the stem and / or the socket is provided with a shoulder marking the beginning of said increase.

[0015] According to a third embodiment, the rod and / or the socket is provided with a truncated cone defining said increase.

[0016] The invention also covers a fuel injector in which a control valve made according to the preceding lines is arranged between an actuator holder and an injection nozzle. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Other features, purposes and advantages of the invention will become apparent from the detailed description that follows and with regard to the accompanying drawings given by way of non-limiting example. There figure 1 (A and B) is an axial section of a fuel injector, along with a zoom on the injector's control valve. figure 2 (A, B, C, D, E) is an axial section of a prior art control valve, similar to that of the figure 1 , as well as test and modeling results. The figure 3 (A, B, C) presents a model and a 3D view of a valve stem according to a first embodiment of the invention. figure 4 (A, B, C) presents a model and a 3D view of a valve stem according to a second embodiment of the invention. figure 5 (A, B, C) presents a model and a 3D view of a valve stem according to a third embodiment of the invention. figure 6 (A, B, C, D, E) presents a model and a 3D view of a valve stem according to a fourth embodiment of the invention. DESCRIPTION OF PREFERRED IMPLEMENTATION METHODS

[0018] A fuel injector 10, part of the injection system of an internal combustion engine, is shown in figure 1A in axial section along a longitudinal axis X. The injector 10 includes a control valve 12 held tight by an injector nut 14 between an actuator carrier 16 and an injection nozzle 18.

[0019] The injector includes a high pressure (HP) circuit 20 and a return circuit 22.

[0020] The HP 20 circuit has a main channel running through the injector from an inlet port to the injection holes and a bypass branch supplying a control chamber 24. In said main channel is arranged a flow restriction, known by its English acronym NPO, creating a pressure drop between upstream and downstream, the bypass branch extending from upstream of the NPO to the control chamber 24.

[0021] The return circuit 22 extends from the control chamber 24 to an outlet. This return circuit 24 incorporates another restriction, known by the acronym SPO, and the control valve 12, which opens or closes the circuit. When the circuit is closed, the pressure in the control chamber increases, pushing a needle into a position that prevents fuel injection. When the valve 12 opens the return circuit 22, pressurized fuel can escape from the control chamber, where the pressure drops, allowing the needle to move to a fuel injection position.

[0022] Control valve 12, more easily detailed by the figures 1B And 2Aincludes a cylindrical body 26 extending along the longitudinal axis X between a first transverse face 28, or upper face, arranged against the injector holder and, a second transverse face 30, or lower face, arranged against the injection nozzle, the HP circuit 20 extending in an eccentric area of ​​the body 26 and including the NPO arranged in the vicinity of the lower face 30.

[0023] The return circuit 22 includes a hydraulic bore 32 extending along the longitudinal axis X from a blind bottom 34, close to the lower face 30, to an opening 36 located in the center of the bottom 38 of a recess 40 opening more widely in the upper face 28. In addition, an annular groove 42 surrounding said bore 32 is provided in the body, the groove 42 separating a first clamping zone ZS1 located between the groove 42 and the opening 36 and, a second clamping zone ZS2 located on the other side of the groove, at the bottom of the bore, between the groove 42 and a lower limit 48 located before said blind bottom 34.

[0024] In the lower face 30 of the body opens a hollow hemisphere in direct connection with the control chamber 24 and from which a restricted channel forming the SPO leads to a return channel extending obliquely in the body from a blocked lower end to the groove 42 surrounding the bore 32.

[0025] A sleeve 50 having a cylindrical tubular wall held tight in the two clamping zones ZS1, ZS2 is inserted into the bore 32, the groove 42 then defining an annular space surrounding the sleeve, a space into which said return channel opens.

[0026] The sleeve 50 extends within the bore from a first end 52, flush with the bottom 38 of the recess, to a second end 54 located at the lower limit 48 of the second clamping zone. Furthermore, the sleeve is provided with holes 56 passing through the wall, creating a permanent fluidic connection between the annular space of the groove and the interior of the sleeve.

[0027] The valve 12 further comprises a stem-armature assembly including a generally cylindrical stem 58 inserted and crimped into the center of a disc-shaped magnetic armature 60. The stem 58 is slidably mounted in the sleeve 50 and extends from a first end 62 emerging in the recess, to which the magnetic armature 60 is attached, to a second end 64 flush with the second end 54 of the sleeve.

[0028] The rod 58 is guided against the inner face of the sleeve along a guide zone ZG located towards the bottom of the bore between the opening of the through holes 56 and the second end 54 of the sleeve. At the opening in the recess, the rod 58 and the sleeve 50 cooperate to define a hydraulic seat 68, and between this seat 68 and the guide zone ZG, in the portion facing the through holes 56, the rod 58 is thinned.

[0029] The operation of injector 10 is now summarized in two key steps: Step 1: A coil arranged in the actuator holder 16 is not energized, and a valve spring located within the coil pushes the stem 58 into the closed position of the seat 68, thus blocking the return circuit 22. High-pressure fuel enters the control chamber where the pressure increases, pushing the needle to a position that prevents fuel injection. Step 2: The coil is energized and generates a magnetic field that attracts and moves the armature 60, thereby opening the seat 68. The fuel can then exit the control chamber, passing successively through the hollow hemisphere, the SPO, the return channel, the groove 42, and the hole(s) 56, before exiting through the seat 68 into the recess 40 and flowing through the return circuit to an outlet.

[0030] All figures of the type of the figure 2B, 2C They illustrate a specific case of a valve where the guide zone is 3 mm long. This valve is representative, and the lessons learned can be applied to other valves with different dimensions.

[0031] There figure 2B is a graph of the guide zone ZG, located on the x-axis from an origin "0" near holes 56 to an end of zone ZG "3 mm" located at the second end 54 of the sleeve. The y-axis shows the profile of the rod 58 and the conical profile of the inner face 51 of the sleeve. Thus, the radial functional clearance J between the rod and the sleeve decreases regularly. The figure 2B represents the situation without pressure.

[0032] During use, as the two steps indicated above follow one another and repeat at high frequency, high-pressure fuel deforms the bushing and rod and radially displaces the rod.

[0033] There figure 2C illustrates, using the same abscissa and ordinate, these deformations during operation. The functional clearance J passes through a minimum marked by a line M around the abscissa 2 mm, this minimum separating a convergence zone ZC located between the origin and this minimum clearance and a divergence zone ZD located beyond, between this minimum M and the end of the zone.

[0034] There figure 2D is a model of the rod in use, deformed by fuel pressure but also radially displaced, with one edge of the rod therefore being closer to the inner face of the bushing than the diametrically opposite edge. In the modeling of the figure 2D The radial displacement occurs in the direction indicated by arrow F, such that the upper edge AS (in the direction of the figure) is closer to the socket than the opposite lower edge AI. This deformation and displacement of the rod results in an uneven distribution of pressures along and around the rod. These pressures generate asymmetrical radial forces on the rod, producing a torque that tends to deform it. From the origin (on the left of the figure 2D ) at the end of the stem (on the right) the pressure exerted on the stem decreases constantly, the extreme areas being both dark.

[0035] Thus we observe that, in the convergence zone ZC, the darkest area (high pressure) is larger on the upper edge AS than on the lower edge AI, this difference in size of the high pressure areas resulting in forces which tend to push the stem of the socket and therefore to recenter this convergence zone ZC in the socket.

[0036] However, in the divergence zone ZD, the dark area is larger (this time the dark area indicates a low pressure zone) on the upper edge AS than on the lower edge AI, this difference in size of the low pressure zones resulting in forces that tend to decenter this divergence zone ZD by approaching it from the socket.

[0037] The opposing forces applied to the rod create a torque that deforms the rod or displaces it so that it bends at an angle.

[0038] There figure 2E This illustrates, on a graph with the same x-axis from 0 to 3 mm, the variation of pressures P, measured in bar on the y-axis. The curves of the upper edge AS and the lower edge AI evolve from a high value equal to the origin until they both vanish at the end of zone ZG, but between these extreme points the curves separate such that, on the upper edge AS, the pressure is higher in the convergence zone ZC and lower in the divergence zone ZD, which generates these forces of recentering or misalignment.

[0039] In order to reduce, or even cancel or equalize the forces in the divergence zone ZD, the functional clearance J is artificially increased in the divergence zone ZD.

[0040] According to a first embodiment represented and analyzed in figure 3 (A, B, C), this increase in functional clearance J is achieved by means of an annular groove 70 made in the divergence zone ZD of the rod. By artificially moving the upper edge AS of the sleeve away from the rod in a part of the rod where the pressures are already low, the faces of the rod and the sleeve are too far apart and the pressures no longer generate significant forces. Only the forces in the convergence zone ZC remain on the rod 58, tending to recenter the rod and thus balance it between the opposing edges. An isometric view of the rod and armature is shown in figure 3C allowing you to see this 70mm groove at the end of the stem.

[0041] Several tests and modeling studies have demonstrated that the optimal location for the groove, and therefore for increasing the functional clearance J, is at a distance of LD / 2 from the boundary M, which marks the limit between the convergence zones ZC and the divergence zones ZD. LD is the length of the divergence zone ZD, approximately 1 mm in the chosen example. These tests and modeling studies showed that an acceptable result was obtained if the groove 70 was located at a distance from the boundary M between LD / 3 (slightly closer to the boundary M) and 2LD / 3 (slightly further away). Beyond this zone [LD / 3 - 2LD / 3], the desired effect of canceling the off-center forces is not achieved.

[0042] The graph of the figure 3B clearly indicates that in the divergence zone ZD the forces compensate and balance each other, forming a plateau and then decreasing until they cancel each other out.

[0043] A second embodiment is represented and analyzed in figure 4 (A, B, C), the increase in functional clearance J being achieved by significantly reducing the diameter of the end of the rod 58 from a shoulder 72 located, as in the first embodiment, at a distance from the limit M between LD / 3 and 2LD / 3, the final part 74 of the rod located beyond this shoulder 72 being too far from the bushing to be significantly influenced by pressure differences.

[0044] The graph of the figure 4B clearly indicates that in the divergence zone ZD the forces balance and decrease until they cancel each other out more rapidly than in the case of the throat of the figure 3 An isometric view of the rod and armature is shown in figure 4C allowing us to see the shoulder 72 and the stepped diameter of part 74 at the end of the stem.

[0045] A third embodiment is represented and analyzed in figure 5 (A, B, C), the increase in functional clearance J being achieved by progressively decreasing the diameter of the end of the rod 58 by making a conical end 76 whose widest section of connection with the rest of the rod is located, just at the level of the limit M so that the increase in functional clearance only becomes significant at a distance from said limit M between LD / 3 and 2LD / 3, the surface of the final conical part 76 being too far from the bushing to be significantly influenced by pressure differences.

[0046] The graph of the figure 5B This clearly indicates that in the divergence zone ZD, the forces cancel each other out at the beginning of the ZD zone. An isometric view of the rod and reinforcement is shown in figure 5C allowing you to see the conical part 76 at the end of the rod.

[0047] It has been observed that for proper rod alignment, it is advantageous to also modify the configuration of the convergence zone. Two scenarios are described below: they concern compensation for misalignment due to the mechanical force of the spring (variant 1); and for the appearance of a deposit (variant 2). Variante 1

[0048] A fourth embodiment of the invention is presented in figure 6 (A to E) and wherein the rod 58 is provided at its second end 64 with a reduced stepped diameter 74, similar to the second embodiment previously presented and shown in figure 4 , is further equipped in the convergence zone ZC with an annular groove 78.

[0049] The forces applied to the stem are not solely due to pressure differences in the functional clearance J between opposing edges AS, AI. The valve spring, for example, which is compressed at the core of the coil and continuously pushes the stem toward the closed position of seat 68, does not push exactly along the longitudinal axis X. The direction and magnitude of the offset of the pushing force vary during operation. As the two previously described steps 1 and 2 follow and repeat, the spring compresses and expands at a high frequency, which changes the direction of the force it applies to the stem, causing it to tend to shift at an angle within the bushing.It then became apparent that the forces generated in the convergence zone ZC were reversed and, rather than creating a centering / decentering force couple between the ZC and ZD zones, the stem was only subjected to the influence of divergent forces which tended to press the stem against the sleeve and thus block the operation of the valve 12. In this sense, the arrangement of the annular groove 78 in the convergence zone ZC, close to the line M, has the effect of moving the stem away from the wall of the sleeve and thus equalizing the pressures around the stem and therefore the forces applied to it.

[0050] This equalization of pressures and forces is clearly shown by the figure 6A where the different pressures are identified by symmetrical gray areas of equal width at the upper edge AS and at the lower edge AI. This is also reflected on the pressure graph in figure 6B where the curves representing the pressures on the opposite edges AS, AI are almost coincident resulting in zero radial forces.

[0051] To counter this effect, several tests and modeling were carried out which demonstrated that the optimal place to place the groove 78 and therefore this increase in the functional clearance J in the convergence zone ZC is at a distance of LC / 3 from the limit M marking the limit between the convergence zones ZC and divergence zones ZD, LC being the length of the convergence zone ZC.

[0052] In the example shown, the length LC is approximately 2 mm, and therefore LC / 3 is a distance of approximately 0.66 mm. These tests and modeling also showed that an acceptable result was obtained if the groove 78 was located at a distance from the limit M between LC / 4, slightly closer to the limit M, and LC / 2, slightly further away. Beyond this zone [LC / 4 - LC / 2], the desired effect of canceling the off-center forces is not achieved.

[0053] THE figures 6C et 6D They present the profiles of the sleeve and the rod according to the fourth embodiment, without any pressure (6C) and under pressure (6D). Under pressure, the sleeve and the rod still deform but always remain a distance from each other. Variante 2

[0054] Tests have shown that another problem with the alignment of the valve stem 58 in the sleeve 50 is related to the formation of a deposit on the valve stem. This deposit is due to fuel degradation caused by temperature and / or various types of additives in diesel fuel. The deposit, which is generally viscous, generates friction proportional to a coefficient of friction, the cross-section of the stem 58, and the length of the guide zone (LC+LD).

[0055] In this context, it appeared advantageous to position an annular groove (of the type of annular groove 78 of the Fig.6A ) in the convergence zone ZC, in the region where the pressure field difference between the two sides of the rod 58 (between the two edges AI and AS) is small. Thus, the annular groove is placed at a distance greater than LC / 2 from the separation line (M). Such an annular groove minimizes friction while maintaining maximum recentering force.

[0056] Depending on the configuration, a particularly desirable throat position is greater than or equal to 3LC / 4.

[0057] The two effects presented in variants 1 and 2 can coexist, but in practice, the deposit issue has been observed to be predominant. It is therefore advisable to compensate for the effect of this deposit as a priority. Specifically, this will result in a valve stem that includes two functional clearance increases in the guide area: an increase in clearance in the divergence zone, in the form of a groove or other types of configuration shown above; and an annular groove in the convergence zone, at a distance greater than LC / 2 (according to variant 2).

[0058] It will be understood, however, that depending on the type of effect to be countered, the annular groove in the convergence zone is placed according to the indications of variant 1 or variant 2. It is also possible to consider a combination of the two grooves (variants 1 and 2) in the convergence zone.

[0059] It should be noted that several alternatives to the embodiments presented are not shown, although they are part of the invention.

[0060] Thus, symmetrical arrangements in which the groove 70 of the first mode, or the shoulder 72 and the stepped diameter 74 of the second mode, or the conical part 76 of the third mode, are made in the sleeve, and no longer in the stem, have a similar effect of increasing the functional clearance J and equalizing the radial forces in the divergence zone ZD. A combination of embodiments is also possible, in which part of the increase in clearance J is achieved in the stem via a groove, a cone, or a stepped diameter, and a complementary part is achieved opposite it in the sleeve via another groove, another cone, or another stepped diameter, with one groove possibly facing another groove, cone, or stepped diameter.

[0061] The same applies to the fourth embodiment; similar results can be achieved by replacing the groove 78 in the stem with a symmetrical groove made in the socket or even by combining a groove in the stem facing a groove in the socket.

[0062] THE figures 6C et 6D They also provide dimensions, to be noted as an example, for the valve shown in which the convergence zone ZC has a length LC of 2 mm and the divergence zone ZD has a length LD of 1 mm.

[0063] In the convergence zone, the groove 78 has a width of 0.5mm and is at 0.5mm, i.e. LC / 4 of the limit M and, in the divergence zone ZC the shoulder 72 is at 0.5 mm of the limit M, i.e. LD / 2.

[0064] There figure 6E presents an isometric view of the frame and rod assembly produced according to the fourth embodiment. REFERENCES

[0065] X longitudinal axis NPOrestriction SPOrestriction J functional clearance ZS1 first clamping zone ZS2 second clamping zone ZG guiding zone ZC converging zone ZD diverging zone M separation line A rod edge AI rod edge Ppressure 10 injector 12 control valve 14 injector nut 16 actuator holder 18 injection nozzle 20 high-pressure circuit 22 return circuit 24 control chamber 26 valve body 28 first face - upper face 30 second face - lower face 32 bore 34 blind bottom 36 opening 38 bottom of recess 40 recess 42 groove 48 lower limit of second clamping zone 50 bushing 51 inner face of bushing 52 first end of bushing 54 second end of bushing 56 hole 58 stem 60 armature 62 first end of stem 64 second end of stem 68 seat 70 groove 72 shoulder 74 stepped diameter 76 tapered section 78 groove

Claims

1. A hydraulic control valve (12) for a fuel injector (10), the valve comprising a body (26) provided with a bore (32) in which a tubular bush (50) is clamped, a valve stem (58) being guided slidingly in the bush, the bush (50) extending between a first end (62) and a second end (64) and being clamped in the bore in a first clamping zone (ZS1) and a second clamping zone (ZS2), said zones being situated at opposite ends of the bush, said zones being separated by an annular space (42) provided in the bore and surrounding the bush and at which, when in use, highly pressurised fuel arrives and passes into the interior of the bush via a hole (56) passing through the bush, said through-hole being arranged in the vicinity of the first clamping zone and, the valve stem extending between a first end (62) emerging from the first clamping zone (ZS1) and a second end (64) emerging from the second clamping zone (ZS2), and being guided in the bush along a guide zone (ZG) extending between the second end (54) of the bush and said through-hole, characterised in that said guide zone comprises a convergence zone (ZC) of length LC in which, when in use, the forces acting on the stem tend to recentre the latter in the bush, this convergence zone being proximal to the through-hole, and a divergence zone (ZD) of length LD in which the forces acting on the stem tend to displace it out of centre, this divergence zone being proximal to the second end of the bush, the two zones meeting up along a dividing line (M) located in the second clamping zone; in that the bush and the stem are configured such that the functional sliding play (J) defined between them increases in the divergence zone (ZD), said increase in play (J) being at a distance of between LD / 3 and 2LD / 3 from said dividing line (M); and in that the functional sliding play (J) defined between the bush and the stem also increases in the convergence zone (ZC) in the form of an annular groove provided in the stem (58) and / or the bush (50), positioned at a distance greater than LC / 2 from said dividing line (M).

2. The hydraulic valve (12) according to claim 1, wherein said annular groove provided in the convergence zone (ZC) is at a distance greater than or equal to 3LC / 4 from said dividing line (M).

3. The hydraulic valve (12) according to claim 1 or 2, wherein the increase in functional play (J) is brought about by reducing the section of the stem (58) and / or by increasing the section of the bush (50).

4. The hydraulic valve (12) according to claim 3, wherein the stem (58) and / or the bush (50) are / is provided with an annular groove (70) defining said increase.

5. The hydraulic valve (12) according to claim 3, wherein the stem and / or the bush are / is provided with a shoulder (72) marking the start of said increase.

6. The hydraulic valve (12) according to claim 3, wherein the stem and / or the bush are / is provided with a truncated cone (76) defining said increase.

7. A fuel injector (10), wherein a control valve (12) produced according to any one of the preceding claims is arranged between an actuator mount (16) and an injection nozzle (18).

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