A valve for metering liquid, in particular a fuel injection valve

Abstract

To provide a fuel injector in which the strength of a valve seat body is improved.SOLUTION: A valve comprises an excitable actuator for actuating a valve closing body which forms a seal seat in cooperation with a valve seat surface (6) formed on a valve seat body (5), and injection openings (7) which are formed downstream of the valve seat surface (6) and are arranged in a dome-shaped center area (44) of the valve seat body (5), which projects outward in the injection direction. The dome-shaped center area (44) of the valve seat body (5) has a curved outer contour, and the curved contour has, in a radially inner area of the dome shape, a larger radius than the radius of the curved contour in a radially outer area of the dome shape. The dome shape ends in a recessed depression (47) which is radially outside of the outlet area of all the injection openings (7), and a peripheral edge area (48) of the valve seat body (5), which similarly projects in the axial direction, is continuously provided radially outside of the depression (47). A fuel injection valve is particularly suited for directly injecting fuel into a combustion chamber of an air-fuel mixture compression and spark ignition type internal combustion engine.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The invention relates to a valve for metering liquid, in particular a fuel injection valve, according to the preamble of the main claim. [Background technology]

[0002] In figures 1, 2a, 2b and 2c, known embodiments of the valve seat body are shown. Figures 2a, 2b and 2c show three basic and typical constructional forms of the valve seat body with injection orifices in schematic form. In the known embodiment according to figure 2c, the flat, planar end face of the valve seat body is the downstream valve end of the fuel injector facing the combustion chamber, whereas in the likewise known embodiments according to figures 2a and 2b, the valve seat body is formed with a central region of the valve seat body, which is provided with the injection orifices and which projects dome-shaped outwards in the injection direction. This is a conical top with a conical casing surface in the central region (for example DE 102013219027 A1) or a conical top with a rounded, convex outwards curvature (for example EP 2333306 A1). In both cases, the dome-shaped central region of the valve seat body merges smoothly and continuously into the flat, planar end face of the valve seat body. Summary of the Invention [Problem to be solved by the invention]

[0003] In such a valve seat body, the entire dome-shaped area is a stiffness-critical area. This area is subjected to heavy use by millions of impacts from the valve closing body of the valve needle. Furthermore, the fuel system pressure acts on the entire inside of the dome-shaped central area. This load has a negative effect on the quality of the valve seat surface and on the requirements for the tightness and fatigue strength of the valve seat body in the dome-shaped area, with the risk of distortion of the dome-shaped area. [Means for solving the problem]

[0004] In addition to its simple and inexpensive manufacture, the valve according to the invention for metering liquids with the features of claim 1 has numerous other advantages: According to the invention, a dome-shaped, axially projecting central region of a valve, in particular a fuel injection valve, is realized in such a way that it has a curved outer shape, the shape of the curvature in the radially inner region of the dome has a larger radius than the shape of the curvature in the radially outer region of the dome, the dome ends in a concave recess radially outer than the outlet regions of all the injection orifices, from which a similarly axially projecting peripheral region of the valve seat body is adjoined radially outward, so that in cross section a dome-shaped contour of the valve seat body is formed which appears generally wavy but flattened in the central region.

[0005] The stiffness-related stresses are effectively reduced in the domed central area of ​​the valve seat body according to the prior art. The structural separation of the load-diverting area (the "base" of the peripheral area) and the area for the injection orifices (the "functional area") results in a significantly improved load-bearing capacity for the domed central area in the center of the dome.

[0006] Due to the high load-bearing capacity, it is possible to reduce the wall thickness in the domed central region radially inwards, without increasing the risk of fatigue failure. In this way, it is conceivable to achieve a small wall thickness in the central region of 200-300 μm. In contrast, in the region of the injection port, the wall thickness of the dome can be increased by thickening, which increases the overall stiffness of the valve seat body and, due to the length of the injection port, advantageously allows the injected liquid, especially the fuel, to penetrate deeper into the combustion chamber.

[0007] It is further emphasized that uncontrolled fuel leakage immediately after the end of injection is prevented. Normally, when closing the fuel injector, the valve closing body of the valve needle hits the valve seat surface, so that the closing process is followed for a short time by an undesired opening phase. This uncontrolled release of fuel quantity leads to small deviations of the injected fuel quantity from the setpoint, which cannot be prevented from having adverse effects when the engine is running. With the design according to the invention of the dome-shaped central region, the probability of strong impacts is significantly reduced due to the inherent high stiffness of the wavy dome.

[0008] A further advantage of the present invention is that, during engine operation, less carbon deposits form on the outer surface of the dome-shaped central region than in known fuel injectors. The design of the valve closing body according to the present invention provides a temperature distribution within the component which prevents the rapid build-up of a soot film.

[0009] Due to the low degree of coating on the surface of the valve seat body, the design according to the invention offers higher safety against clogging of the injection orifices ("carbonization"). In view of the large variations in fuel quality worldwide, this robust behavior is highly advantageous.

[0010] Further advantageously, the rise in particulate emissions in the exhaust caused by continuous engine operation is smaller than with prior art fuel injectors (reduced PN drift).

[0011] Advantageous developments and improvements of the fuel injector according to claim 1 are possible by means of the measures recited in the dependent claims.

[0012] It is particularly advantageous that the geometric design of the lower end face of the valve seat body facing the combustion chamber can be adapted very flexibly to the desired installation conditions and the requirements for the engine operation. [Brief description of the drawings]

[0013] An embodiment of the invention is shown in a simplified manner in the drawings and is explained in detail in the following description. [Figure 1] 1 shows a schematic cross-sectional view of a fuel injection valve according to a known design, comprising a valve seat body with an injection port at the downstream valve end; [Figure 2a] 2 shows a schematic diagram of a known construction of a valve seat body with injection ports as section II-III of FIG. 1 in an enlarged view. [Figure 2b] 2 shows a schematic diagram of a known construction of a valve seat body with injection ports as section II-III of FIG. 1 in an enlarged view. [Figure 2c] 2 shows a schematic diagram of a known construction of a valve seat body with injection ports as section II-III of FIG. 1 in an enlarged view. [Diagram 3] 3 shows a cross-sectional view, comparable to FIG. 2, of a valve seat body according to an embodiment of the invention; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] The known example of a fuel injector 1 shown in Fig. 1 is realized in the form of a fuel injector 1 for a fuel injection system of a spark-ignition internal combustion engine of the mixture compression type. This fuel injector 1 is particularly suitable for injecting fuel directly into a combustion chamber (not shown) of the internal combustion engine. The invention can be applied in general in valves for metering liquids.

[0015] The fuel injector 1 comprises a nozzle body 2, in which a valve needle 3 is arranged. The valve needle 3 is operatively connected to a valve closing body 4, which cooperates with a valve seat surface 6 arranged on a valve seat body 5 to form a sealing seat. The valve seat body 5 and the nozzle body 2 can also be realized as one piece. In this embodiment, the fuel injector 1 is an inward-opening fuel injector 1, which has at least one injection port 7, typically at least two injection ports 7. However, the fuel injector 1 is ideally realized as a multi-hole fuel injector, and therefore has 4 to 30 injection ports 7. The nozzle body 2 is sealed against the valve housing 9 by a seal part 8. As the driving part, for example, an electromagnetic circuit including an electromagnetic coil 10 functions as an actuator, and the electromagnetic coil 10 is wound around a coil housing 11 and a coil body 12 in contact with an inner pole 13 of the electromagnetic coil 10. The inner pole 13 and the valve housing 9 are separated from each other by a narrow portion 26 and are connected to each other by a non-ferromagnetic connecting part 29. The electromagnetic coil 10 is excited by a current supplied via a conductor 19 through an electrical male contact 17. The male contact 17 is surrounded by a synthetic resin jacket 18 which can be integrally molded to the inner pole 13. Alternatively, piezoelectric or magnetostrictive actuators can also be used.

[0016] The valve needle 3 is guided in a valve needle guide 14 which is embodied in the shape of a disk. A paired adjusting disk 15 serves for stroke adjustment. On the opposite side of the adjusting disk 15 there is an armature 20 which is frictionally connected to the valve needle 3 via a first flange 21, to which the valve needle 3 is connected by a welded seam 22. A return spring 23 is supported against this first flange 21 and which, in the fuel injector 1 according to this design, is preloaded by an adjusting sleeve 24.

[0017] Fuel passages 30, 31, 32 pass through the valve needle guide 14, the armature 20 and the guide body 41. Fuel is supplied via a central fuel supply pipe 16 and is filtered by a filter element 25. The fuel injector 1 is sealed to a fuel distribution pipe, not shown in detail, by a seal 28 and to a cylinder head, not shown in detail, by a further seal 36.

[0018] Downstream of the armature 20 there is arranged an annular damping element 33 made of elastomeric material. The damping element 33 rests on a second flange 34 which is frictionally connected to the valve needle 3 via a welded seam 35.

[0019] When the fuel injection valve 1 is at rest, the armature 20 is loaded by the return spring 23 against its stroke direction, i.e. so that the valve closing body 4 is held in a sealed state on the valve seat surface 6. When the electromagnetic coil 10 is energized, it establishes a magnetic field which moves the armature 20 against the spring force of the return spring 23 in the stroke direction, said stroke being preset by the working gap 27 which exists between the inner pole 13 and the armature 20 in the rest position. The armature 20 also lifts up in the stroke direction the first flange 21 which is welded to the valve needle 3. The valve closing body 4 which is connected to the valve needle 3 is lifted up from the valve seat surface 6 and fuel is injected through the injection orifice 7.

[0020] When the coil current is stopped, the armature 20 falls from the inner pole 13 due to the pressure of the return spring 23 after the magnetic field is sufficiently eliminated, so that the first flange 21 connected to the valve needle 3 moves against the stroke direction, and the valve needle 3 moves in the same direction, so that the valve closing body 4 rests on the valve seat surface 6 and the fuel injection valve 1 is closed.

[0021] 1, 2a, 2b and 2c show an embodiment of a known valve seat body 5. In Figure 3 In order to specifically explain the configuration and contour of the valve seat body 5 according to the present invention, a comparative cross section II-II of FIG. III is selected by zooming in.

[0022] 2a, 2b and 2c show three basic typical constructional forms of the valve seat body 5 with the injection orifices 7 in a very schematic view. Whereas in the known embodiment according to FIG. 2c a flat, planar end face 43 of the valve seat body 5 constitutes the downstream valve end of the fuel injector 1 facing the combustion chamber, in the likewise known embodiments according to FIGS. 2a and 2b the valve seat body 5 is formed with a central region 44 of the valve seat body 5, said central region 44 being provided with the injection orifices 7 and projecting dome-shaped outwards in the injection direction and formed rotationally symmetrically with respect to the valve longitudinal axis 40. In the embodiment according to FIG. 2a this is a cone top with a conical outer surface in the central region 44, whereas the central region 44 according to the embodiment according to FIG. 2b is realized as a cone top, curved outwards in a rounded, convex manner. In both cases, the dome-shaped central region 44 of the valve seat body 5 merges smoothly and continuously into the flat, planar end face 43 of the valve seat body 5, as in the realization according to FIG. 2c.

[0023] The object of the invention is to create a valve seat body 5 for a fuel injection valve 1 having a plurality of injection ports 7, which, despite the dome-shaped central region 44, has a particularly high structural strength, i.e. is not as susceptible to bending stresses as in the prior art.

[0024] Measurements have shown that the thin wall thickness in the central region 44 of the valve seat body 5 and the short injection orifice have a positive effect on the particle emissions of an internal combustion engine. However, with this fuel injector 1, which is optimized for the lowest possible particle emissions, there is a risk of a significant increase in component stresses within the valve seat body 5. By means of the geometrical measures according to the invention for increasing the stiffness, it is envisaged that the material volume or material thickness of the valve seat body 5 is increased in the stiffness-critical areas.

[0025] According to the invention, the dome-shaped central region 44 of the valve seat body 5 has a curved outer shape, with the radius of curvature of the radially inner region of the dome being greater than the radius of curvature of the radially outer region of the dome. Furthermore, the dome-shaped axially projecting central region 44 of the valve seat body 5 thus ends in a concave recess 47 radially outward of the outlet regions of all the injection holes 7, which recess 47 is ideally circumferentially formed and radially outwardly adjoins a similarly axially projecting peripheral region 48 of the valve seat body 5, so that in cross section the valve seat body 5 forms an overall wave-shaped dome-shaped contour. Due to the change in radius, the dome-shaped axially projecting central region 44 appears as a flattened dome, i.e. as a dome with a limited radial extent and which projects axially only slightly beyond the end face 43, if at all. The radius of the curved shape refers to the radius of curvature of the curve formed by the curved shape.

[0026] In Fig. 3 an embodiment of the valve seat body 5 according to the invention is shown in a cross-section comparable to Fig. 2. The dome-shaped central region 44 is ideally formed rotationally symmetrically with respect to the valve longitudinal axis 40 and ends in a circumferential concave recess 47 radially outward of the outlet region of all the jets 7, which recess 47 is arranged as an annular recess. A similarly axially projecting peripheral region 48 of the valve seat body 5 adjoins radially outward from the recess 47, so that in cross section the valve seat body 5 is formed with an overall wave-shaped dome-shaped contour. In this embodiment, the recess 47 and the transition of the radially outer edge of the recess to the peripheral region 48 are each formed with a radius of a fairly small radius. The peripheral region 48 here has a flat, planar end face 43. Instead of being radiused, the transition can also be formed with an angle.

[0027] The dome-shaped contour of the central region 44 at the nozzle 7 connection region has an inherent small radius so that the additional material volume does not directly lead to a longer nozzle 7, thus reducing the stresses inside the components between the nozzles 7. This special contour also results in an improved spray break-up of the liquid flow emerging through the 3D ellipse obtained at the nozzle 7 exit region and an optimized penetration into the combustion chamber. The 3D ellipse results in a longer jet guide in the circumferential direction or tangential to the valve seat and a shorter length of the nozzle 7 in the radial direction, which is favorable for spray break-up. This applies in particular to cylindrically extending nozzles 7 without a pre-stage arranged towards the injection side.

[0028] In the following, in order to explain the dimensions specifically, some specific sizes representing the central region 44 of the valve seat body 5 are shown by way of example, but the invention is not limited thereto. When the diameter of the valve seat body 5, and therefore the diameter of the valve tip of the fuel injector 1, is about 6 mm, the radius of the curved shape of the central region 44 centered on the valve longitudinal axis 40 is, for example, 3 mm to 7 mm. Towards the radially outward direction, the radius of the curved shape of the central region 44 decreases, for example, to 1 to 5 mm. In the outlet region of the injection port 7 of the dome part, the radius can be reduced to 0.2 to 0.6 mm by a certain material thickening, and thus by additional curving locally. The recess 47 is preferably realized very small, i.e. with a radius that should not be larger than 0.5 mm.

[0029] In the present design, the wall thickness of the central region 44 of the valve seat body 5 varies between about 0.2 and 0.3 mm in the region of the valve longitudinal axis 40 and between 0.35 and 0.7 mm in the thickened region near the jet orifice 7. The wall thickness in the radially outer region of the central region 44 can be approximately 20 to 250% thicker than the wall thickness in the radially inner region of the central region 44. In the case of variants with thicker walls, the difference between the thinnest and thickest wall thicknesses is smaller, since otherwise the dome would be too flat.

[0030] From the recess 47 acting as a load relief groove, the contour extends radially outwards at an angle α of 0° to a maximum of 70° with respect to the valve longitudinal axis 40 perpendicular to the end face 43 of the valve seat body 5. Depending on the design, said angle can also be replaced by a radius larger than 0.5 mm.

[0031] In the embodiment shown in Fig. 3, the central region 44, which is also the region which projects most axially on the valve longitudinal axis 40, is advantageously set back from the end face 43. Alternatively, the central region 44 may end its axially projecting extension at the level of the end face 43 or may project axially slightly beyond the end face 43. In all cases, however, the recess 47 is present axially set back with respect to the end face 43 of the valve seat body 5. A setback in this manner provides a decisive advantage in terms of stiffness for the valve seat body 5.

[0032] The combination of the greater wall thickness at the nozzle 7 and the recess 47 injection port The maximum stresses occurring locally at the outlet are minimized because the introduced forces can be better distributed by the added material. These stresses are: injection port If the inclination is large, it interacts with the recess 47 in the radial direction with respect to the jets 7. In order to achieve an improved stiffness between the recess 47 and the jets 7, the radius of the recess 47 must therefore be designed as small as possible. If the inclination is small, the maximum stresses are present between the jets 7. Here, the thickened area in the radially outer central region 44 reduces the stresses generated there. The optimum stiffness is achieved by the geometric design of the recess 47 and the thickened area in the region of the jets 7.

[0033] Furthermore, the recess 47 serves to circulate air which is favorable for the breakup of the liquid spray. Furthermore, the recess 47 serves to protect the nozzle 7 from the accumulation of combustion products and combustion chamber gases. The flat dome portion of the central region 44, in combination with the flow in the combustion chamber influenced by the recess 47, also serves to evaporate the fuel accumulated on the dome portion.

[0034] A slight wall thickness protruding outward in the region of the jets 7 can be designed so that the jets 7 pass exactly through it. This increases the length of the jets 7 and guides the jet flow over a longer distance, advantageously improving the penetration. In such a design, the jets 7 run at an angle of approximately 45° to the longitudinal axis of the valve. However, it is also conceivable that the jets 7 run at a steeper inclination to the longitudinal axis of the valve, i.e. at an angle smaller than 45°, so that the jets 7 of the dome run radially inward from the wall thickness.

[0035] The nozzle 7 of the valve seat body 5 can be formed with a front step with an enlarged diameter extending towards the injection side as shown in all embodiments, but can also extend cylindrically, conically with a positive or negative opening angle, or with several steps etc. All cross-section shapes for the nozzle 7 are conceivable, from circular through elliptical to polygonal. The nozzle 7 is produced by electro-discharge machining, laser drilling or punching. The nozzle 7 can be produced with sharp edges at the nozzle inlet or outlet or can be rounded, for example by hydroerosiv erosion.

[0036] Steel may be utilized as a typical material for the valve seat body 5. Thus, the manufacture of the dome-shaped central region 44 may be performed by means of machining (e.g. turning, grinding, honing), by deformation (e.g. extrusion) or even by one-way molding (e.g. metal injection molding). However, other metallic or ceramic materials besides steel are also of interest for the valve seat body 5.

[0037] The invention is not limited to the embodiment described above but can be applied, for example, for other arranged injectors and for inward opening multi-hole fuel injectors 1 with any constructional form.

Claims

1. A valve (1) for metering liquid for a fuel injection system of an internal combustion engine, comprising: an excitable actuator (10) for operating a valve closure body (4) which cooperates with a valve seat surface (6) formed on the valve seat body (5) to form a sealing seat; at least one injection port (7) formed downstream of the valve seat surface (6), the injection port (7) being arranged in a dome-shaped central area (44) of the valve seat body (5) protruding outwardly in an injection direction; The valve comprising: When the valve longitudinal axis (40) is set as the radial center, The dome-shaped central region (44) of the valve seat body (5) has a curved outer surface profile; the radius of curvature of the radially inner region of the central region (44) is greater than the radius of curvature of the radially outer region of the central region (44) on both the inner surface of the central region (44) in the direction of the valve longitudinal axis (40) and on the outer surface of the central region (44) in the direction of the valve longitudinal axis (40); A wall thickness of a radially outer region of the central region (44) is made thicker than a wall thickness of a radially inner region of the central region (44), and an outlet region of an injection port (7) arranged in the central region (44) is made thicker; said central region (44) ends in a concave recess (47) radially outward of the exit regions of all the jets (7); a peripheral region (48) extending radially outwardly from the recess (47) to the valve seat body (5) and projecting outwardly in the direction of the valve longitudinal axis (40); A valve comprising:

2. 2. The valve according to claim 1, characterized in that the valve is a fuel injection valve (1) for direct injection of fuel into a combustion chamber.

3. 3. A valve according to claim 1 or 2, characterized in that in cross section, the valve seat body (5) is formed with a generally wave-shaped dome-shaped contour, the central region (44) appearing as a flattened dome due to the change in radius.

4. 4. The valve according to claim 1, wherein the dome-shaped central region (44) is formed rotationally symmetrically relative to the valve longitudinal axis (40) and the recesses (47) extend correspondingly circumferentially.

5. A valve according to claim 4, characterized in that the circumferential concave recess (47) is provided as an annular recess.

6. A valve according to any one of claims 1 to 5, characterized in that the transition of the recess (47) and / or of its radially outer edge to the peripheral region (48) is formed in an angular or rounded manner.

7. A valve according to any one of the preceding claims, characterised in that the peripheral area (48) has a flat, planar end face (43).

8. 8. The valve according to claim 1, characterized in that the wall thickness of the central region (44) of the valve seat body (5) varies in the radial direction, the wall thickness being thinner in a radially inner region of the central region (44) than in a radially outer region of the central region (44).

9. 9. The valve of claim 8, wherein the wall thickness in the radially outer region of the central region (44) is about 20-250% thicker than the wall thickness in the radially inner region of the central region (44).

10. the central region (44) which is radially surrounded by the recess (47) is recessed or protruding in its axial extension with respect to the peripheral region (48) of the valve seat body (5) which extends radially outward, or both regions (44, 48) are at the same level as the end face (43), A valve according to any one of the preceding claims, characterized in that said recess (47) always has its bottom recessed relative to said end face (43).

11. Valve according to any one of the preceding claims, characterised in that 2 to 30 injection orifices (7) are provided in the valve seat body (5).

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