FUEL INJECTOR

Description

Technical field

[0001] The invention relates to a fuel injector, such as is used in particular as a component of a common-rail injection system for injecting fuel into the combustion chamber of a self-igniting internal combustion engine. State of the art

[0002] A fuel injector having the features of the preamble of claim 1 is made from the Fig. 2 The known fuel injector is known from DE 102 42 685 A1 of the applicant. It is characterized by a nozzle needle whose tip has two conical sections with different cone angles extending towards the bottom of a blind hole in the nozzle body. In the region of a valve seat surface of the needle tip, which, in the lowered state of the nozzle needle, forms a sealing seat with a conical surface in the nozzle body, an annular groove is formed radially around a longitudinal axis of the nozzle needle. In the region of the annular groove is an inlet of a bore, which has an outlet either in the region of the end face of the needle tip facing the bottom of the blind hole or laterally near the region of the end face of the needle tip. The bore provided in the known fuel injector is designed to achieve the most constant possible opening dynamics of the nozzle needle over the entire service life of the fuel injector.Document CN 108 533 432 A also reveals a fuel injector. Disclosure of the invention

[0003] The fuel injector according to the invention, with the features of claim 1, has the advantage that, in addition to simplified manufacturing of the nozzle needle, it reduces the tendency for cavitation due to fuel bubble formation, particularly at small strokes or during the opening and closing of the nozzle needle, to such an extent that no cavitation damage results in the area below the sealing seat in the area of ​​the blind hole and, in particular, also not in the area of ​​the injection orifices. Furthermore, the fuel injector has the advantage that it counteracts misalignment of the nozzle needle during opening.

[0004] The invention is based on the idea that the described advantages can be achieved by either reducing the flow velocity when opening the nozzle needle and thus the tendency to form vortices with resulting cavitation phenomena, and / or by better guiding the fuel flow at small nozzle needle strokes, and / or by subjecting the fuel to less severe deflections, and / or by realizing a modified fuel flow path.

[0005] Against this background, the teaching of the invention according to claim 1 proposes that the nozzle needle has a conical or frustoconical needle tip with a constant angle from the region of the valve seat surface to an end face facing the blind hole, that the bore inlet opens in the region of the valve seat surface, and that the blind hole in the region of the sealing seat has a first section with a first angle to the longitudinal axis of the nozzle body, to which a second section with a second angle is attached in the direction of a blind hole base, wherein the second angle is smaller with respect to the longitudinal axis than the first angle.

[0006] In contrast to the prior art mentioned above, such a design of the nozzle needle thus dispenses with a longitudinal groove running radially around the longitudinal axis of the nozzle needle and with different large angles in the area of ​​the needle tip of the nozzle needle, which makes its manufacture relatively simple.

[0007] Advantageous further developments of the fuel injector according to the invention are listed in the dependent claims.

[0008] In a first design embodiment or arrangement of the at least one bore in the nozzle needle, the at least one bore is designed as a straight bore and arranged at an oblique angle to the longitudinal axis of the nozzle needle. Such an arrangement optimizes the flow of the fuel through the bore by resulting in only minimal deflections of the fuel flow path. Furthermore, such a bore is also relatively easy to manufacture.

[0009] In the last described design or arrangement of the bore in the nozzle needle, it is particularly advantageous if the inclined angle of the at least one bore is adapted to or corresponds to the inclined angle of the at least one injection opening in the nozzle body. This ensures that the flow is not deflected, or only slightly deflected, as it exits the bore towards the at least one injection opening, resulting in optimized flow guidance and thus a reduction in vortex formation.

[0010] For this purpose, it is particularly advantageous if the bore outlet of the at least one bore is located at the level of the injection port or between the injection port and the bottom of the blind hole when the nozzle needle is in its lowered position. This minimizes the vertical offset between the bore outlet of the at least one bore and the at least one injection port, viewed along the longitudinal axis of the nozzle needle, when the nozzle needle opens.

[0011] A further optimization of the alignment of the bore outlet of the at least one bore with the at least one injection port in the nozzle body provides that the nozzle needle is arranged to be rotationally fixed with respect to its longitudinal axis, and that the bore outlet of the at least one bore is aligned with an inlet area of ​​the at least one injection port in the nozzle body. In other words, this means that the bore outlet of the bore in the nozzle needle is aligned with the inlet area of ​​the at least one injection port with respect to its angular position around the longitudinal axis, so that an almost direct flow of fuel from the area of ​​the nozzle needle into the area of ​​the injection port is enabled.

[0012] In an alternative arrangement of the at least one bore, the bore outlet of the at least one bore can be located in the area of ​​the end face of the needle tip facing the bottom of the blind hole. Such a design or arrangement of the at least one bore may be even simpler to implement from a manufacturing perspective than the proposals made above, where the bore outlet is located on a side surface of the needle tip.

[0013] Particularly when multiple holes are provided in the jet needle, it can be advantageous if the holes do not intersect the longitudinal axis of the jet needle. This allows for independent fuel flow in each individual hole.

[0014] Another advantageous embodiment of the bore, in which its bore outlet is located in the area of ​​the end face of the needle tip facing the base of the blind hole, provides that the at least one bore has several bore sections, wherein a first bore section facing the end face of the needle tip runs concentrically to the longitudinal axis of the nozzle needle.

[0015] In a first embodiment, such a bore section can terminate on the side of the needle tip facing away from the end face in a transverse bore perpendicular to the longitudinal axis, passing through the nozzle needle, forming a second bore section. Such an arrangement or design of the second bore section is relatively easy to manufacture. However, to optimize flow guidance, it can alternatively be provided that the first bore section on the side facing away from the end face of the needle tip is connected to at least one bore arranged at an oblique angle to the longitudinal axis, which opens into the valve sealing surface.

[0016] In order to enable the nozzle needle to be supplied with flow from below or from the side of the blind hole base when opening strokes are small, it is provided that the end face of the needle tip is arranged on the side of an upper injection hole edge of the injection hole facing the blind hole base when the nozzle needle is partially open, where the ratio of the annular flow cross-section between the nozzle needle and the nozzle body is less than 1.5 times the total area of ​​the cross-sectional areas of the injection openings.

[0017] Finally, irrespective of the specific arrangement or design of the at least one bore in the nozzle needle, it proposes a further embodiment of the invention in which the bore inlet of the at least one bore is arranged in the transition area between the seat surface arranged at different angles and the section of the nozzle body adjoining it in the direction of the blind hole base, when a sealing seat has formed.

[0018] Finally, it proposes a further constructively preferred embodiment in which the diameter of the at least one bore in the nozzle needle is less than or equal to the diameter of the at least one injection opening.

[0019] Further advantages, features and details of the invention will become apparent from the following description of preferred embodiments and from the drawings. Brief description of the drawings

[0020] Figures 1 to 4 each show an axial end section of a fuel injector with different embodiments of bores in a nozzle needle in longitudinal section, and Figure 5 shows the fuel injector according to Fig. 3 with its jet needle in a partially raised position. Embodiments of the invention

[0021] Identical elements or elements with the same function are provided with the same reference numbers in the figures.

[0022] In the Fig. 1 Figure 1 shows the axial end region of a fuel injector 10 facing a combustion chamber (not shown) of a self-igniting internal combustion engine. The fuel injector 10 has a nozzle body 12 in the wall of which at least one, preferably several, injection openings 14 are formed. Fuel under high pressure can be injected from a high-pressure chamber 16 of the nozzle body 12 into the combustion chamber of the internal combustion engine via the at least one injection opening 14. The injection opening 14 extends at an oblique angle α to a longitudinal axis 18 of the nozzle body 12.The nozzle body 12 further comprises a recess 20 for forming the high-pressure chamber 16. On the side facing the injection port 14, this recess has a conically shaped seating surface 21 with a first angle β 1 relative to the longitudinal axis 18. This seating surface transitions into a conical section 22 with a second angle β 2 towards the base 23 of a blind hole 19 in the recess 20. The second angle β 2 is smaller than the first angle β 1. The injection port 14 extends, by way of example, from the region of section 22.

[0023] The nozzle body 12 interacts with a nozzle needle 25 which is movable in the direction of the longitudinal axis 18 and arranged concentrically to the longitudinal axis 18.

[0024] The nozzle needle 25, which is moved in a manner known per se by means of an actuator (not shown), for example a magnetic actuator, is depicted in the figures in a lowered position, forming a sealing seat 26 with the nozzle body 12 in the area of ​​the seat surface 21. In this position, the at least one injection opening 14 is at least indirectly closed, so that no fuel from the area of ​​the high-pressure chamber 16 enters the area of ​​the injection opening 14.

[0025] The nozzle needle 25 has a needle tip 28 which has a conical or frustoconical, or longitudinally conical, valve seat surface 29 with an angle γ / 2 to the longitudinal axis 18, which is adapted to or corresponds to the angle β 1 of the seat surface 21 of the nozzle body 12. The needle tip 28 has a flat end face 30 on the side facing the base of the blind hole 23.

[0026] In the region of the needle tip 28, at least one straight bore 34 is formed in the nozzle needle 25, which is arranged at an oblique angle Δ with respect to the longitudinal axis 18, wherein the angle Δ is preferably adapted to or corresponds to the angle α of the injection opening 14. The diameter of the at least one bore 34 is at most as large as the diameter of the injection opening 14.

[0027] The bore 34 has a bore inlet 36, which, when the nozzle needle 25 is lowered, is located in the transition area between the seat surface 21 and the section 22 of the nozzle body 12. Furthermore, the bore inlet 36 extends from the conical valve seat surface 29. Preferably, a longitudinal axis 38 of the bore 34 intersects the transition between the seat surface 21 and the section 22. In the illustrated embodiment, a bore outlet 40 of the bore 34 opens approximately at the level of the injection opening 14 on the side of the nozzle body 12 facing the blind hole 19.

[0028] Furthermore, it can be provided that the nozzle needle 25 is arranged in a rotationally fixed manner with respect to the longitudinal axis 18, wherein the bore outlet 40 of the bore 34 is aligned with the opening of the injection port 14 in the area of ​​the nozzle body 12 with respect to the angular position about the longitudinal axis 18.

[0029] In the Fig. 2 A nozzle needle 25a is shown, in which the straight bore 34a opens into the end face 30 of the nozzle needle 25a with its bore outlet 40. The bore inlet 36 is arranged in relation to the nozzle body 12 when the nozzle needle 25a is lowered, corresponding to the nozzle needle 25.

[0030] The Fig. 3 Figure 1 shows a nozzle needle 25b in which the bore 34b has a first bore section 41 that runs concentrically to the longitudinal axis 18 and opens in the region of the end face 30 of the needle tip 28. On the side of the first bore section 41 facing away from the end face 30, it opens into (at least) two bores 42, 43, each arranged at an oblique angle to the longitudinal axis 18, which form second bore sections 45. The bore inlets 36 are arranged in relation to the nozzle body 12 when the nozzle needle 25b is lowered, corresponding to the nozzle needles 25 and 25a.

[0031] In the Fig. 4 A nozzle needle 25c is shown, which differs from the nozzle needle 25b in that the bore 34c also has the first bore section 41, but this opens into a transverse bore 48, arranged perpendicular to the longitudinal axis 18 and passing through the needle tip 28, as the second bore section 45. Here too, the bore inlets 36 are arranged in relation to the nozzle body 12 when the nozzle needle 25c is lowered, corresponding to the nozzle needles 25, 25a and 25b.

[0032] Most recently, in the Fig. 5 the fuel injector according to Fig. 3The figure shows the nozzle needle 25b lifted from the sealing seat 26, but not fully raised. In this position of the nozzle needle 25b, the area ratio between a seating surface Aseat in the region of an annular inlet gap 50 between the nozzle needle 25b and the nozzle body 12 and the total cross-sectional areas ASI of the injection opening(s) 14 is less than 1.5, i.e., Aseat < 1.5 × ASI. The end face 30 of the nozzle needle 25b is located on the side facing the base of the blind hole 23 of an upper inlet edge 51 of the at least one injection opening 14.

[0033] The fuel injector 10 described so far can be modified or adapted in a variety of ways without deviating from the inventive concept. For example, the geometry of the recess 20 in the area of ​​the blind hole 19 can be designed differently. The bore inlet 36 can also be arranged just below or above the transition from the seat surface 21 to the section 22.

Claims

1. Fuel injector (10), having a nozzle body (12) in which a blind hole (19) is formed, from which at least one injection opening (14) starts, having a nozzle needle (25; 25a to 25c) arranged so as to be able to perform a stroke movement along a longitudinal axis (18), wherein the nozzle needle (25; 25a to 25c) has a valve seat surface (29), which forms a sealing seat (26) with a seat surface (21) in the nozzle body (12) when the nozzle needle (25; 25a to 25c) is in a lowered position, and having at least one bore (34; 34a to 34c) in the nozzle needle (25; 25a to 25c), wherein, when the sealing seat (26) is formed, at least certain regions of a bore inlet (36) of the at least one bore (34; 34a to 34c) are arranged in the region of the seat surface (21) and a bore outlet (40) of the at least one bore (34; 34a to 34c) is arranged below the valve seat surface (29) of the nozzle needle (25; 25a to 25c) in the direction of the longitudinal axis (18), characterized in that the nozzle needle (25; 25a to 25c) has, from the region of the valve seat surface (29) to a flat end face (30) facing the blind hole (19), a frustoconical needle tip (28) with a constant angle (γ), in that the bore inlet (36) starts from the frustoconical valve seat surface 29 and in that the blind hole (19) has, in the region of the sealing seat (26), a first angle (β1) with respect to the longitudinal axis (18), adjoined by a portion (22) with a second angle (β2) in the direction of a blind hole base (23), wherein the second angle (β2) relative to the longitudinal axis (18) is smaller than the first angle (β1).

2. Fuel injector according to Claim 1, characterized in that the at least one bore (34) is in the form of a rectilinear bore (34; 34a) and arranged at an oblique angle (Δ) with respect to the longitudinal axis (18).

3. Fuel injector according to Claim 2, characterized in that the oblique angle (Δ) of the at least one bore (34) corresponds to an oblique angle (α) of the at least one injection opening (14) in the nozzle body (12).

4. Fuel injector according to Claim 2 or 3, characterized in that the bore outlet (40) of the at least one bore (34) is arranged at the level of the injection opening (14) or between the injection opening (14) and the blind hole base (23) when the nozzle needle (25) is in the lowered position.

5. Fuel injector according to one of Claims 2 to 4, characterized in that the nozzle needle (25) is rotationally fixed in relation to the direction of the longitudinal axis (18), and in that the bore outlet (40) of the at least one bore (34) is located at the level of the at least one injection opening (14) in the nozzle body (12) on the side facing the blind hole (19) when the nozzle needle (25) is in the lowered position.

6. Fuel injector according to Claim 1 or 2, characterized in that the bore outlet (40) of the at least one bore (34a; 34b; 34c) opens out in the region of the end face (30) of the needle tip (28) facing the blind hole base (23).

7. Fuel injector according to one of Claims 2 to 6, characterized in that the at least one bore (34) does not intersect the longitudinal axis (18).

8. Fuel injector according to Claim 6, characterized in that the at least one bore (34b; 34c) has a plurality of bore portions (41; 45), wherein a first bore portion (41) facing the end face (30) of the needle tip (28) is concentric with the longitudinal axis (18).

9. Fuel injector according to Claim 8, characterized in that the first bore portion (41), on the side of the needle tip (28) facing away from the end face (30), opens out in a transverse bore (48), which runs perpendicular to the longitudinal axis (18) and extends through the nozzle needle (25c), as a second bore portion (45).

10. Fuel injector according to Claim 8, characterized in that the first bore portion (41), on the side facing away from the end face (30) of the needle tip (28), is connected to at least one bore (42, 43) arranged at an oblique angle to the longitudinal axis (18) as a second bore portion (45).

11. Fuel injector according to one of Claims 6 to 10, characterized in that, when the nozzle needle (25b; 25c) is partially open, in which case the following relationship is true: ASitz < 1.5 x ASI, the end face (30) of the needle tip (28) is arranged on the side of an upper inlet edge (51) of the injection opening (14) facing the blind hole base (23), wherein ASitz is an annular throughflow cross section between the nozzle needle and the nozzle body and ASI is the total surface area of the cross-sectional areas of the injection opening (14) or of the injection openings (14).

12. Fuel injector according to one of Claims 1 to 11, characterized in that, when the sealing seat (26) is formed, the bore inlet (36) of the at least one bore (34; 34a to 34c) is arranged in the transition region between the seat surface (21) and the portion (22) of the nozzle body (12).

13. Fuel injector according to one of Claims 1 to 12, characterized in that the diameter of the at least one bore (34; 34a to 34c) in the nozzle needle (25; 25a to 25c) is less than or equal to the diameter of the at least one injection opening (14).