FUEL INJECTOR

Abstract

The invention relates to a fuel injector (10), comprising a nozzle body (12) in which a blind hole (19) is formed, wherein at least one injection opening (14) leads off same, comprising a nozzle needle (25; 25a to 25c) that is reciprocatingly movable along a longitudinal axis (18), wherein the nozzle needle (25; 25a-25c) has a valve seat (29) which forms a sealing seat (26) with a seating surface (21) in the nozzle body (12) in a lowered position of the nozzle needle (25; 25a-25c), and comprising at least one borehole (34; 34a-34c) in the nozzle needle (25; 25a-25c), wherein at least some portions of a borehole inlet (36) of the at least one borehole (34; 34a-34c) are located in the region of the seating surface (21) when the sealing seat (26) is formed, and a borehole outlet (40) of the at least one borehole (34; 34a-34c) is located below the valve seat (29) of the nozzle needle (25; 25a-25c) in the direction of the longitudinal axis (18).

Claims

1. A fuel injector (10) comprising a nozzle body (12), in which a blind hole (19) is formed, wherein at least one injection opening (14) leads off from the blind hole, a nozzle needle (25; 25a to 25c), configured to be moved in a reciprocating manner 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) in a lowered position of the nozzle needle (25; 25a to 25c), and at least one bore (34; 34a to 34c) in the nozzle needle (25; 25a to 25c), wherein at least some portions of a bore inlet (36) of the at least one bore (34; 34a to 34c) are arranged in a region of the seat surface (21) when the sealing seat (26) is formed, and a bore outlet 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 a direction of the longitudinal axis (18), wherein the nozzle needle (25; 25a to 25c) has, from a region of the valve seat surface (29) to an end face (30) facing the blind hole (19), a conical or frustoconical needle tip (28) with a constant angle (γ), wherein the bore inlet (36) emerges in the region of the valve seat surface (29), and wherein the blind hole (19) has, in a region of the sealing seat (26), a section with a first angle (β.sub.1) with respect to the longitudinal axis (18), which is adjoined in the direction of a blind hole bottom (23) by a section (β.sub.2) with a second angle (β.sub.2), wherein the second angle (β.sub.2) is smaller than the first angle (β.sub.1) in relation to the longitudinal axis (18).

2. The fuel injector as claimed in claim 1, wherein the at least one bore (34) is a rectilinear bore (34; 34a) and is arranged at an oblique angle (Δ) with respect to the longitudinal axis (18).

3. The fuel injector as claimed in claim 2, wherein 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. The fuel injector as claimed in claim 2, wherein the bore outlet (40)-of the at least one bore (34) is arranged at a height of the injection opening (14) or between the injection opening (14) and the blind hole bottom (23) when the nozzle needle (25) is in the lowered position.

5. The fuel injector as claimed in claim 2, wherein the nozzle needle (25) is arranged in a rotationally fixed manner in relation to the direction of the longitudinal axis (18), and wherein the bore outlet of the at least one bore (34) is located at a height of the at least one injection opening (14) in the nozzle body (12) on a side facing the blind hole (19) when the nozzle needle (25) is lowered.

6. The fuel injector as claimed in claim 1, wherein the bore outlet of the at least one bore (34a; 34b; 34c) emerges in a region of an end face (30) of the needle tip (28) which faces the blind hole bottom (23).

7. The fuel injector as claimed in claim 2, wherein the at least one bore (34) does not intersect the longitudinal axis (18).

8. The fuel injector as claimed in claim 6, wherein the at least one bore (34b; 34c) has a plurality of bore sections (41; 45), wherein a first bore section (41) of the plurality of bore sections faces the end face (30) of the needle tip (28) and extends concentrically with respect to the longitudinal axis (18).

9. The fuel injector as claimed in claim 8, wherein, on a side of the needle tip (28) which faces away from the end face (30), the first bore section (41) opens into a transverse bore (48) as a second bore section (45) of the plurality of bore sections, wherein the second bore section extends perpendicularly to the longitudinal axis (18) and passes through the nozzle needle (25c).

10. The fuel injector as claimed in claim 8, wherein, on a side which faces away from the end face (30) of the needle tip (28), the first bore section (41) is connected to at least one bore (42, 43) as a second bore section (45) of the plurality of bore sections, wherein the second bore section is arranged at an oblique angle with respect to the longitudinal axis (18).

11. The fuel injector as claimed in claim 6, wherein the end face (30) of the needle tip (28) is arranged on a side of an upper inlet edge (51) of the injection opening (14) which faces the blind hole bottom (23) when the nozzle needle (25b; 25c) is partially open, in which case a ratio A.sub.Sitz is <1.5×A.sub.SI, wherein A.sub.Sitz is an annular flow cross section between the nozzle needle and the nozzle body and A.sub.SI is the a total area of cross-sectional areas of the injection opening (14) or injection openings (14).

12. The fuel injector as claimed in claim 1, wherein the bore inlet (36) of the at least one bore (34; 34a to 34c) is arranged in a transitional region between the seat surface (21) and the section (22) of the nozzle body (12) when the sealing seat (26) is formed.

13. The fuel injector as claimed in claim 1, wherein a 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 a diameter of the at least one injection opening (14).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Further advantages, features and details of the invention will become apparent from the following description of preferred exemplary embodiments and with reference to the drawings.

[0019] FIG. 1 to FIG. 4 each show an axial end section of a fuel injector with different embodiments of bores in a nozzle needle in longitudinal section and

[0020] FIG. 5 shows the fuel injector according to FIG. 3 in a partially raised position of its nozzle needle.

DETAILED DESCRIPTION

[0021] In the figures, identical elements or elements having the same function are provided with the same reference numerals.

[0022] FIG. 1 illustrates the axial end region of a fuel injector 10 which faces a combustion chamber (not shown) of a self-ignition internal combustion engine. The fuel injector 10 has a nozzle body 12, in the wall of which at least one, preferably a plurality of, injection openings 14 is formed. Fuel at high pressure can be injected into the combustion chamber of the internal combustion engine from a high-pressure chamber 16 of the nozzle body 12 via the at least one injection opening 14. The injection opening 14 extends at an oblique angle α with respect to a longitudinal axis 18 of the nozzle body 12. In addition, to form the high-pressure chamber 16, the nozzle body 12 has a recess 20, which, on the side facing the injection opening 14, has a conical seat surface 21 with a first angle β.sub.1, which is formed in relation to the longitudinal axis 18, and which, in the direction of a blind hole bottom 23 of a blind hole 19 of the recess 20, merges into a conical section 22 with a second angle β.sub.2. In this case, the second angle β.sub.2 is smaller than the first angle β.sub.1. Furthermore, by way of example, the injection opening 14 extends from the region of the section 22.

[0023] The nozzle body 12 interacts with a nozzle needle 25, which is arranged so as to be movable in the direction of the longitudinal axis 18 and concentrically with the longitudinal axis 18. The nozzle needle 25, which is moved in a manner known per se by means of an actuator (not illustrated), for example a magnetic actuator, is illustrated in the figures in a lowered position, forming a sealing seat 26 with the nozzle body 12 in the region of the seat surface 21. In this position, the at least one injection opening 14 is at least indirectly closed, ensuring that no fuel passes from the region of the high-pressure chamber 16 into the region of the injection opening 14.

[0024] The nozzle needle 25 has a needle tip 28, which has a valve seat surface 29 of conical or frustoconical shape or of conical design in longitudinal section with an angle γ/2 with respect to the longitudinal axis 18 which is matched to or corresponds to the angle β.sub.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 blind hole bottom 23.

[0025] In the region of the needle tip 28, at least one rectilinear bore 34 is formed in the nozzle needle 25, which bore is arranged at an oblique angle Δ in relation to the longitudinal axis 18, wherein the angle Δ is preferably matched to the angle α of the injection opening 14 or corresponds thereto. The diameter of the at least one bore 34 is at most as large as the diameter of the injection opening 14.

[0026] The bore 34 has a bore inlet 36 which is arranged in the transitional region between the seat surface 21 and the section 22 of the nozzle body 12 when the nozzle needle 25 is lowered. Furthermore, the bore inlet 36 starts from the conical valve seat surface 29. A longitudinal axis 38 of the bore 34 preferably intersects the transition between the seat surface 21 and the section 22. In the exemplary embodiment illustrated, a bore outlet 40 of the bore 34 emerges at approximately the height of the injection opening 14 on the side of the nozzle body 12 which faces the blind hole 19.

[0027] Furthermore, provision can be made for the nozzle needle 25 to be arranged in a rotationally fixed manner in relation to the longitudinal axis 18, in which case the bore outlet 40 of the bore 34 is then aligned with the opening of the injection opening 14 in the region of the nozzle body 12 in respect of the angular position about the longitudinal axis 18.

[0028] FIG. 2 illustrates a nozzle needle 25a in which the rectilinear bore 34a emerges with its bore outlet 40 in the region of the end face 30 of the nozzle needle 25a. In relation to the nozzle body 12, the bore inlet 36 is arranged in a manner corresponding to nozzle needle 25 when the nozzle needle 25a is lowered.

[0029] FIG. 3 shows a nozzle needle 25b in which the bore 34b has a first bore section 41, which extends concentrically with the longitudinal axis 18 and emerges in the region of the end face 30 of the needle tip 28. On the side of the first bore section 41 which faces away from the end face 30, it opens into (at least) two bores 42, 43, which are each arranged at an oblique angle with respect to the longitudinal axis 18 and form second bore sections 45. In relation to the nozzle body 12, the bore inlets 36 are arranged in a manner corresponding to nozzle needles 25 and 25a when the nozzle needle 25b is lowered.

[0030] FIG. 4 shows a nozzle needle 25c that differs from nozzle needle 25b in that the bore 34c likewise has the first bore section 41, but the latter opens into a transverse bore 48, as the second bore section 45, that passes through the needle tip 28 and is arranged perpendicular to the longitudinal axis 18. Here too, the bore inlets 36 are arranged in a manner corresponding to nozzle needles 25, 25a and 25b in relation to the nozzle body 12 when the nozzle needle 25c is lowered.

[0031] Finally, FIG. 5 shows the fuel injector according to FIG. 3 with the nozzle needle 25b raised from the sealing seat 26 but not completely raised. In this position of the nozzle needle 25b, an area ratio between a seat surface A.sub.Sitz 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 A.sub.SI of the injection opening(s) 14 is less than 1.5, that is to say A.sub.Sitz<1.5×A.sub.SI. In this case, the end face 30 of the nozzle needle 25b is located on that side of an upper inlet edge 51 of the at least one injection opening 14 which faces the blind hole bottom 23.

[0032] The fuel injector 10 described so far can be changed or modified in a variety of ways without departing from the concept of the invention. For example, the geometry of the recess 20 in the region of the blind hole 19 can be designed differently. Moreover, the bore inlet 36 can be arranged just below or above the transition from the seat surface 21 to the section 22.