EP1076772B1 - Fuel injection nozzle for an internal combustion engine - Google Patents

Description

The invention relates to a fuel injection nozzle for an internal combustion engine, in particular a common rail injection system, in which the injection nozzle is permanently acted upon by fuel held at high pressure in a preliminary store, the fuel injection nozzle having a nozzle needle coupled to an actuating element which serves to control a nozzle opening process Contains the needle tip and a valve seat interacting with the needle tip of the nozzle needle, the valve seat having a conical sealing surface with an opening angle α ₁ and the needle tip having a conical sealing surface with an opening angle α ₂ in the closed state of the injection valve, and the needle tip and needle housing having an annular flow channel limit.

One problem with fuel injectors of this type is that often severe damage due to cavitation below the valve seat after a short running time Nozzle needle tip and needle housing are to be determined, which lead to leaks in the Valve seat and lead to failure of the nozzle. Such cavitation damage come into play particularly in common rail injection systems, because due to the permanent application of the high pressure of that stored in the preliminary storage Fuel significantly longer cavitation phases during the opening and closing of the Injector occur compared to more conventional injectors Fuel injection systems.

DE 36 05 082 A1 describes a fuel injection nozzle for internal combustion engines known which is provided for a conventional injection system and in which an annular groove in the sealing surface of the needle tip interacting with the valve seat is provided, which serves to form a turbulent boundary layer of the flow. Downstream of the sealing surface there is initially a convex shape at the needle tip Sheath surface section provided, on which a concavely shaped Shell surface section follows. This should prevent the tendency for the flow to separate The area of the valve passage is reduced and the flow or the jet formation be improved.

DE 196 34 933 A1 shows a fuel injection valve in which two Areas of a valve sealing surface in the transition that have different cone angles have a groove-shaped extension downstream of the valve seat. The extension serves to increase the metering accuracy of the injection quantity by a defined position the sealing edge is generated. DE 195 47 423 A1 also uses a groove Extensions below the valve seat in the nozzle body or nozzle needle by one create defined contact line. The circumferential one representing an extension radial recess is very flat and is specified with 0.01 to 0.06 mm. It's like that assume that this expansion increases the cavitation and the nozzle needle and the nozzle body is affected by erosion in the adjacent walls, which ultimately leads to the destruction of the injection valve.

From DE 38 10 467 A1 a fuel injection nozzle emerges as known, in which the injection-side end of the nozzle needle with a rotationally symmetrical constriction is provided. Through this design, a flow deflection of the fuel in Direction of the spray hole. A rapid drop in pressure is avoided, so that Occurrence of cavitation in the nozzle area is reduced.

In the injection nozzle shown in GB 2 029 508 A, the flow cross section between the valve seat and the injection holes by suitable shaping of Nozzle needle tip and nozzle housing gradually changed to separate the flow and avoid instabilities. The flow cross section is based on the valve seat gradually increased and gradually reduced again after a flow deflection.

The object of the invention is to provide a fuel injector which a low susceptibility to cavitation damage in the area of the valve seat on the nozzle needle and has needle housing.

This object is achieved by the fuel injector specified in claim 1. Advantageous developments of the fuel injector according to the invention are in the Subclaims marked.

The invention provides a fuel injection nozzle for an internal combustion engine, in particular a common rail injection system, in which the injection nozzle is permanently acted upon by fuel held at high pressure in a preliminary store. The fuel injection nozzle contains a nozzle needle with a needle tip, which nozzle is coupled to an actuating element for controlling a nozzle opening process, and a valve seat which interacts with the needle tip of the nozzle needle, the valve seat having a conical sealing surface with an opening angle α ₁ and the needle tip resting against the latter in the closed state of the injection valve have a conical sealing surface with an opening angle α ₂ and the needle tip and needle housing delimit an annular flow channel. It is envisaged that the opening angle α _{2 of} the sealing surface of the needle tip is smaller than the opening angle α _{1 of} the sealing surface of the valve seat, and that an expansion of the annular flow channel between the needle tip and the needle housing is formed in the flow direction of the fuel following the sealing surfaces, such that Both on the needle tip and on the needle housing, extensions in the form of recesses form a cavitation space in which the implosion of cavitation bubbles occurs away from the wall. In other words, the size and shape of the cavitation space are deliberately kept so that the cavitation bubbles are guided and disintegrate at a distance from the walls of the annular flow channel formed by the nozzle needle and needle housing, and as a result there is no erosion of the walls.

Due to the inverse seat angle difference, the narrowest point of the Needle sealing seat at the downstream end, where cavitation forms, whose Cavitation bubbles then have no possibility in the subsequent expansion to knock down the wall of the needle tip or needle housing and therefore none Can cause damage. Cavitation at the nozzle needle is more critical than at Needle housing. Erosion at the nozzle needle affects the function of the Injector by changing the opening behavior.

According to a particularly preferred embodiment, it is provided that the Extension of the flow channel between the needle tip and the needle housing immediately following the sealing surfaces of the needle tip and valve seat.

Preferably, the expansion of the flow channel between the needle tip and Needle housing due to a concave cross section of the surfaces of Needle tip and needle housing formed.

A particularly advantageous embodiment of this provides that the concave Course of the surface of the needle tip and / or needle housing through a radius is formed.

According to a preferred embodiment it is provided that the concave course of the Surface on the upstream side with an edge in the sealing surface of Needle tip and / or valve seat merges.

Furthermore, it can be provided that the concave course of the surface on the downstream side with an edge in the surface of the needle tip and / or Needle housing merges.

According to a particularly preferred embodiment of the invention Fuel injection nozzle is provided that in each case on the surface of the needle tip and needle housing an expansion of the flow channel with a concave course is provided, and that the center of the expansion of the needle housing at closed valve towards the center of the extension of the needle tip is offset upstream.

According to a preferred embodiment it is provided that the extensions on The needle housing and the needle tip are formed by the same radii.

The opening angle α _{1 of} the valve seat is advantageously between 50 ° and 60 °, preferably between 55 ° and 65 °.

According to a particularly preferred embodiment, the opening angle is Valve seat around 60 °.

The opening angle α _{2 of} the sealing surface of the needle tip is advantageously between 0.5 ° and 3 °, preferably between 1 ° and 2 °, smaller than the opening angle α _{1 of} the valve seat.

It is particularly advantageous to make the opening angle α _{2 of} the sealing surface of the needle tip 1.5 ° smaller than the opening angle α _{1 of} the valve seat.

According to an advantageous development of the invention, it is provided that a transition surface is formed on the needle tip upstream of the sealing surface, which has an angle α ₃ between that of the needle body and that of the sealing surface of the nozzle needle. This transition surface improves the flow behavior at the transition from the needle body to the sealing surface.

This transition surface is advantageously formed by a conical surface.

Preferably, the transition surface is designed so that it the angle between the Sealing surface of the nozzle needle and the needle body approximately halved.

According to a preferred development of the fuel injection nozzle according to the invention it is provided that the needle tip has a tapered end section. this has the advantage that the nozzle needle with its end portion far in at the downstream End of the needle housing trained blind hole extends, which the Blind hole volume is reduced.

The tapered end section is preferably formed by a cone.

According to a preferred embodiment, it is provided that the cone forming the tapering end section has an opening angle α ₄ that is smaller than the opening angle α _{2 of} the sealing surface of the needle tip.

The opening angle α _{4 of} the end section is advantageously between 40 ° and 65 °, preferably between 50 ° and 55 °.

According to a development of the invention, it is provided that the needle tip upstream of the sealing surface against the diameter of the needle body has widened bead-shaped section.

This bead-shaped section can be formed by successive conical and / or cylindrical ring surfaces can be formed.

Alternatively, the bead-shaped portion may be lenticular or spherical Be formed.

The diameter of the bead-shaped section is advantageously 1.05 times up to 1.2 times, preferably 1.1 times to 1.15 times the diameter of the Needle body of the nozzle needle.

The longitudinal extent of the bead-shaped section in the direction of the needle axis is advantageously 0.2 times to 0.6 times, preferably 0.25 times to 0.35 times the diameter of the needle body of the nozzle needle.

Figur 1 eine geschnittene Seitenansicht einer Kraftstoffeinspritzdüse im Bereich der Nadelspitze gemäß einem Ausführungsbeispiel der Erfindung;

Figur 2 eine Darstellung der Nadelspitze der Düsennadel des in Figur 1 gezeigten Ausführungsbeispiels mit einer vergrößerten Einzelheit X;

Figur 3 die Nadelspitze einer Düsennadel gemäß einem weiteren Ausführungsbeispiel der Erfindung mit Einzelheiten X und Y.

Preferred exemplary embodiments of the invention are explained below with reference to the drawing. Show it:

Figure 1 is a sectional side view of a fuel injector in the area of the needle tip according to an embodiment of the invention;

FIG. 2 shows the needle tip of the nozzle needle of the exemplary embodiment shown in FIG. 1 with an enlarged detail X;

Figure 3 shows the needle tip of a nozzle needle according to another embodiment of the invention with details X and Y.

In Figure 1 is the sectional side view of an injection nozzle of a common rail injection system shown in the area of the needle tip of the nozzle needle. In one Needle housing 14 is a nozzle needle, the needle body of which is identified by reference number 11 is provided, slidably mounted in the axial direction. Located on the needle tip 12 a conical sealing surface 13, which with the sealing surface 16 one on the needle housing 14 provided valve seat 15 in the sense of opening and closing the injector interacts when the nozzle needle 11 moves. On the needle tip 12 opposite end is the nozzle needle 11 with one for controlling a Coupled actuator serving actuator, which is not in the figure is shown.

At the front of the nozzle needle 11, a blind hole 110 is formed in the needle housing 14, from which injection openings 120 emanate, which serve to inject the fuel into the combustion chamber of the internal combustion engine. The needle tip 12 of the nozzle needle 11 is provided with an end section 121 in the form of a tapered cone which extends deep into the blind hole 110. Between the sealing surface 13 and the conical end section 121, an enlargement of the annular flow channel 17 formed between the needle tip 12 and the needle housing 14 in the form of a course 19 with a concave cross section is produced on the surface of the needle tip 12. Opposite this concave course 19 of the needle tip 12, an enlargement of the annular flow channel 17 formed between the needle tip 12 and the needle case 14 in the form of a course 18 which is also concave in cross section is produced on the inner wall of the needle housing 14. A transition surface 111 is formed between the sealing surface 13 and the needle body 11, which has an angle α ₃ and essentially halves the angle between the cylindrical outer surface of the needle body 11 and the sealing surface 13. The sealing surface 16 of the valve seat 15 has an opening angle α ₁ , which is 60 ° in the illustrated embodiment, while the sealing surface 13 of the needle tip 12 has an opening angle α ₂ , which is smaller than the opening angle α _{1 of} the sealing surface 16 of the valve seat 15 and is 58.5 ° in the illustrated embodiment. The narrowest point of the needle sealing seat is thus between the sealing surface 13 of the nozzle needle tip 12 and the sealing surface 16 of the valve seat 15 in the front region of the needle tip 12, which means an inverse seat angle difference compared to conventional sealing seat geometries. After this constriction, the annular flow channel 17 formed between the needle tip 12 and the needle housing 14 widens through the concave courses 18, 19, whereby a "cavitation trap" or cavitation space is formed for the cavitation bubbles, which due to the inverse seat angle difference in a defined manner at the narrowest point of the Needle sealing seat are formed immediately upstream of the concave courses 18, 19. For comparison with a conventional needle tip geometry, such is shown in dashed lines in FIG. The recess on the nozzle needle and needle housing represents a sudden expansion in which cavitation bubbles form. The recess is designed or dimensioned such that the subsequent implosion of the cavitation bubbles does not take place in the immediate vicinity of the walls, but rather in the middle of the flow or at least at a distance from the nozzle needle. The gap width formed by the expansion is more than 0.05 mm at the widest point. Gap widths of 0.5 mm or more are more favorable. In the downstream connection to the cavitation space follows a flow channel, the cross section of which is preferably designed such that the flow speed remains approximately constant. The conical wall of the needle housing in connection with the cavitation space is preferably inclined somewhat more steeply than in the upstream region, which causes the flow to be deflected in the direction of the spray holes.

The needle tip 12 of the nozzle needle 11 from FIG. 1 is enlarged again in FIG shown. As can be seen in particular from the enlarged section X, the concave course 18 formed by a radius, which in the shown Embodiment is 0.5 mm. This radius creates a flute-shaped, annular recess formed by a first edge 191 on the sealing surface 13 to a second edge 192 on the front end portion 121 of the needle tip 12 runs. The concave course 18 on the inside of the needle housing 14 is also formed by a radius extending from an upstream edge 181 to one downstream 182 runs, see Figure 1. As also from Figure 1 can be seen, the center of the concave extension 18 of the needle housing 14 at closed valve opposite the center of the concave extension 19 of the Needle tip 12 moved upstream. In this embodiment, the two extensions 18, 19 on the needle housing 14 and needle tip 12 by the same radii formed so that a width of the cavitation space at the widest point of approx. 1 mm results.

In a second exemplary embodiment of a nozzle needle, as shown in FIG can be combined with a needle housing of the type shown in FIG Needle tip 32 upstream of a sealing surface 33 compared to the diameter of the Needle body 31 formed widened bead-shaped section 320. This bead-shaped section 320 is formed by successive annular surfaces 321, 322, 323 formed, of which the annular surfaces 321 and 323 are designed as conical surfaces, while the annular surface 322 is formed in the form of a cylindrical annular surface, compare Detail Y. The diameter of the bulge portion 320 is at its widest point, i.e. on the ring surface 322 around 1.15 times the diameter of the Needle body 31 of the nozzle needle. The longitudinal extent of the bead portion 320 in the direction of the needle axis is approximately 0.25 times the diameter of the Needle body 31. Deviating from the configuration of the bead-shaped section 320 by successive conical and cylindrical ring surfaces the bead-shaped Section 320 can also be formed by a lenticular or spherical surface 324, as shown in dashed lines in detail Y.

Immediately following the sealing surface 33 of the needle tip 32 is an expansion in Formed a conical shape 39, which is formed by a radius, such as shown in detail X. The conical extension 39 goes on the one hand with an edge 391 in the sealing surface 33 and on the other side with an edge 392 in the end section 321 of the Nozzle tip 32 over.

As shown in Figure 3, the sealing surface 33 of the needle tip 32 has an opening angle α ₂ of 59.8 °, compared to an opening angle α ₁ of 60 ° of the sealing surface of the valve seat of the needle housing combined therewith. The opening angle α _{4 of} the end section 321 is 55 °. The conical ring surface 323 of the bead-shaped section 320 is formed with an opening angle of 45 ° as a transition surface between the sealing surface 33 and the cylindrical ring surface 322 of the bead-shaped section 320.

LIST OF REFERENCE NUMBERS

1

injection

11; 31

Nozzle needle, needle body

12; 32

pinpoint

13; 33

sealing surface

14

needle housing

15

valve seat

16

sealing surface

17

flow channel

18

Concave course

19

Concave course

110

blind

120

Injection port

181

edge

182

edge

191; 391

edge

192; 392

edge

111

Transition surface

121; 321

end

320

beaded section

321

ring surface

322

ring surface

323

ring surface

324

Spherical surface

Claims (26)

1. Fuel injection nozzle for an internal combustion engine, in particular of a common-rail injection system, in which the injection nozzle is acted upon permanently by fuel reserved under high pressure in a prestore, containing a nozzle needle (11; 21; 31) coupled to an actuating element serving for controlling a nozzle-opening operation, with a needle tip (12; 22; 32), and a valve seat (15; 25) cooperating with the needle tip (12; 22; 32) of the nozzle needle (11; 21; 31), the valve seat (15; 25) having a conical sealing surface (16; 26) with an aperture angle α₁, and the needle tip (12; 22; 32) having a conical sealing surface (13; 23; 33) coming to bear on the conical sealing surface (15; 26) in the closed state of the injection valve, with an aperture angle α₂, and the needle tip (12; 22; 32) and the needle housing (14; 24) delimiting an annular flow duct (17; 27), the aperture angle α₂ of the sealing surface (13; 23; 33) of the needle tip (12; 22; 32) being smaller than the aperture angle α₁ of the sealing surface (16; 26) of the valve seat (15; 25), and, following the sealing surfaces (13; 23; 33, 16; 26) of the needle tip (12; 22; 32) and valve seat (15; 25) in the direction of flow of the fuel, a widening of the annular flow duct (17; 27) being formed between the needle tip (12; 22; 32) and the needle housing (14; 24), characterized in that setbacks forming the widening of the flow ducts (17) are provided on the needle tip (12) and on the needle housing (14; 24), said setbacks together forming a cavitation space, in which the implosion of cavitation bubbles takes place at a distance from the wall.
2. Fuel injection nozzle according to Claim 1, characterized in that the widening of the flow duct (17; 27) between the needle tip (12; 22; 32) and the needle housing (14; 24) is provided, directly following the sealing surfaces (13; 23; 33, 16; 26) of the needle tip (12; 22; 32) and valve seat (15; 25).
3. Fuel injection nozzle according to Claim 1 or 2, characterized in that the widening of the flow duct (17; 27) between the needle tip (12; 22; 32) and the needle housing (14; 24) is formed by a cross-sectionally concave profile (18; 28; 19; 39) of the surfaces of the needle tip (12; 22; 32) and needle housing (14; 24).
4. Fuel injection nozzle according to Claim 3, characterized in that the concave profile (18; 28; 19; 39) of the surface of the needle tip (12; 22; 32) and/or needle housing (14; 24) is formed by a radius.
5. Fuel injection nozzle according to Claim 3 or 4, characterized in that the concave profile (18; 28; 19; 39) of the surface merges on the upstream side, with an edge (181; 191; 281; 391), into the sealing surface (13; 16; 26; 33) of the needle tip (12;22;32) and/or valve seat (15; 25).
6. Fuel injection nozzle according to Claim 3, 4 or 5, characterized in that the concave profile (18; 19; 28; 39) of the surface merges on the downstream side, with an edge (182; 192; 282; 392), into the surface of the needle tip (12; 22; 32) and/or needle housing (14; 24).
7. Fuel injection nozzle according to Claims 3 to 6, characterized in that, with the valve closed, the centre of the widening (18) of the needle housing (14) is offset upstream in relation to the centre of the widening (19) of the needle tip (12).
8. Fuel injection nozzle according to one of Claims 4 to 7, characterized in that the widenings (18; 19) on the needle housing (14) and needle tip (12) are formed by identical radii.
9. Fuel injection nozzle according to one of Claims 1 to 8, characterized in that the aperture angle α₁ of the valve seat (15; 25) is between 50° and 70°, preferably between 55° and 65°.
10. Fuel injection nozzle according to Claim 9, characterized in that the aperture angle α₁ of the valve seat (15; 25) is around 60°.
11. Fuel injection nozzle according to Claim 9 or 10, characterized in that the aperture angle α₂ of the sealing surface (13; 23; 33) of the needle tip (12; 22; 32) is between 0.5° and 3°, preferably between 1° and 2°, smaller than the aperture angle α₁ of the valve seat (16; 26).
12. Fuel injection nozzle according to Claim 11, characterized in that the aperture angle α₁ of the sealing surface (13; 23; 33) of the needle tip (12; 22; 32) is 1.5° smaller than the aperture angle α₁ of the valve seat (16; 26).
13. Fuel injection nozzle according to one of Claims 1 to 12, characterized in that the needle tip (12; 22) has formed on it, upstream of the sealing surface (13; 23), a transitional surface (111; 211) which has an angle α₃ between that of the needle body (11; 21) and that of the sealing surface (13; 23) of the nozzle needle (10; 20).
14. Fuel injection nozzle according to Claim 13, characterized in that the transitional surface (111; 211) is formed by a conical surface.
15. Fuel injection nozzle according to Claim 14, characterized in that the transitional surface (111; 211) approximately bisects the angle between the sealing surface (13; 23) of a nozzle needle (10; 20) and the needle body (11; 21).
16. Fuel injection nozzle according to one of Claims 1 to 15, characterized in that the needle tip (12; 22; 32) has a tapering end portion (121; 221; 321).
17. Fuel injection nozzle according to Claim 16, characterized in that the tapering end portion (121; 221; 321) is formed by a cone.
18. Fuel injection nozzle according to Claim 17, characterized in that the cone forming the tapering end portion (121; 221; 321) has an aperture angle α₄ which is smaller than the aperture angle α₂ of the sealing surface (13; 23; 33) of the needle tip (12; 22; 32).
19. Fuel injection nozzle according to Claim 18, characterized in that the aperture angle α₄ of the end portion (121; 221; 321) is between 40° and 65°, preferably between 50° and 55°.
20. Fuel injection nozzle according to one of Claims 1 to 19, characterized in that the needle tip (32) has, upstream of the sealing surface (33), a bead-like portion (320) widened in relation to the diameter of the needle body (31).
21. Fuel injection nozzle according to Claim 20, characterized in that the bead-like portion (320) is formed by successive conical and/or cylindrical annular surfaces (321; 322; 323).
22. Fuel injection nozzle according to Claim 20, characterized in that the bead-like portion (320) is formed by a lenticular or spherical surface (324).
23. Fuel injection nozzle according to Claim 20, 21 or 22, characterized in that the diameter of the bead-like portion (320) is 1.05 times to 1.2 times , preferably 1.1 times to 1.15 times, the diameter of the needle body (31) of the nozzle needle.
24. Fuel injection nozzle according to one of Claims 20 to 23, characterized in that the longitudinal extent of the bead-like portion (320) in the direction of the needle axis is 0.2 times to 0.6 times, preferably 0.25 times to 0.35 times, the diameter of the needle body (31) of the nozzle needle.
25. Fuel injection nozzle according to one of Claims 1 to 24, characterized in that the cross-sectional profile following the widening downstream and formed by the needle tip and the needle housing is designed for an essentially constant flow velocity.
26. Fuel injection nozzle according to Claim 25, characterized in that that part of the needle housing which is located downstream of the valve seat is designed as a conical surface, with an aperture angle, measured in relation to the longitudinal axis of the fuel injection nozzle, which is smaller than the aperture angle α₁ of the sealing surface (16, 26) located upstream.

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