NOZZLE NEEDLE FOR A FUEL INJECTION DEVICE, AND FUEL INJECTION DEVICE

Abstract

The invention relates to a nozzle needle (10) for a fuel injection device (100), in particular a fuel injector, comprising a nozzle needle tip (12) which is connected to a nozzle needle shaft (11). The nozzle needle tip (12) and the nozzle needle shaft (11) consist of different materials. According to the invention, the nozzle needle shaft (11) has a receiving area (20) formed by a blind bore (21) for the nozzle needle tip (12). The base (22) of the receiving area (20) forms an axial stop for the nozzle needle tip (12), and the nozzle needle tip (12) has an at least approximately constant diameter (d) within the receiving area (20), said diameter simultaneously forming the largest diameter of the nozzle needle tip (12).

Claims

1. A nozzle needle (10) for a fuel injection device (100), the nozzle needle comprising a nozzle needle tip (12) which is connected to a nozzle needle shank (11), wherein the nozzle needle tip (12) and the nozzle needle shank (11) are composed of different materials, wherein the nozzle needle shank (11) has a receptacle (20), formed by a blind bore (21), for the nozzle needle tip (12), wherein a base (22) of the receptacle (20) forms an axial stop for the nozzle needle tip (12), and wherein the nozzle needle tip (12) has, within the receptacle (20), an at least approximately constant diameter (d) which simultaneously forms the largest diameter of the nozzle needle tip (12).

2. The nozzle needle as claimed in claim 1, wherein the nozzle needle tip (12) is composed of a wear-resistant material, and the nozzle needle shank (11) is composed of a solid material composed of steel.

3. The nozzle needle as claimed in claim 1, wherein a surface of the nozzle needle tip (12) which acts hydraulically in the direction of the base (22) of the receptacle (20) is larger than a hydraulic surface of the nozzle needle shank (11) which acts in the same direction, such that the nozzle needle tip (12) is subjected to force in the direction of the base (22) of the receptacle (20) at all times.

4. The nozzle needle as claimed in claim 1, wherein the nozzle needle tip (12) has a conically shaped seat region (25) which adjoins a section (24) of cylindrical form within the receptacle (20).

5. The nozzle needle as claimed in claim 4, wherein the nozzle needle shank (11) has a conical outer surface (28) in a mouth region of the receptacle (20), and wherein an elongation (29) of the seat region (25) running in the direction of the outer surface (28) runs spaced apart from the outer surface (28).

6. The nozzle needle as claimed in claim 1, wherein an interference fit is formed between the nozzle needle tip (12) and the receptacle (20).

7. The nozzle needle as claimed in claim 1, wherein a transition or clearance fit is formed between the nozzle needle tip (12) and the receptacle (20).

8. The nozzle needle as claimed in claim 7, wherein at least one leakage gap is formed between the nozzle needle tip (12) and the receptacle (20).

9. A fuel injection device (100), comprising a housing (18) for guiding a nozzle needle (10), wherein the nozzle needle (10) includes a nozzle needle tip (12) which is connected to a nozzle needle shank (11), wherein the nozzle needle tip (12) and the nozzle needle shank (11) are composed of different materials, wherein the nozzle needle shank (11) has a receptacle (20), formed by a blind bore (21), for the nozzle needle tip (12), wherein a base (22) of the receptacle (20) forms an axial stop for the nozzle needle tip (12), and wherein the nozzle needle tip (12) has, within the receptacle (20), an at least approximately constant diameter (d) which simultaneously forms the largest diameter of the nozzle needle tip (12).

10. The fuel injection device as claimed in claim 9, wherein the nozzle needle tip (12) is composed of a wear-resistant material, and the nozzle needle shank (11) is composed of a solid material composed of steel.

11. The fuel injection device as claimed in claim 9, wherein a surface of the nozzle needle tip (12) which acts hydraulically in the direction of the base (22) of the receptacle (20) is larger than a hydraulic surface of the nozzle needle shank (11) which acts in the same direction, such that the nozzle needle tip (12) is subjected to force in the direction of the base (22) of the receptacle (20) at all times.

12. The fuel injection device as claimed in claim 9, wherein the nozzle needle tip (12) has a conically shaped seat region (25) which adjoins a section (24) of cylindrical form within the receptacle (20).

13. The fuel injection device as claimed in claim 12, wherein the nozzle needle shank (11) has a conical outer surface (28) in a mouth region of the receptacle (20), and wherein an elongation (29) of the seat region (25) running in the direction of the outer surface (28) runs spaced apart from the outer surface (28).

14. The fuel injection device as claimed in claim 9, wherein an interference fit is formed between the nozzle needle tip (12) and the receptacle (20).

15. The fuel injection device as claimed in claim 9, wherein a transition or clearance fit is formed between the nozzle needle tip (12) and the receptacle (20).

16. The fuel injection device as claimed in claim 15, wherein at least one leakage gap is formed between the nozzle needle tip (12) and the receptacle (20).

17. The fuel injection device as claimed in claim 9, wherein the nozzle needle tip (12) is composed of ceramic, hard metal or a sapphire, and the nozzle needle shank (11) is composed of a solid material composed of steel.

18. The nozzle needle as claimed in claim 1, wherein the nozzle needle tip (12) is composed of ceramic, hard metal or a sapphire, and the nozzle needle shank (11) is composed of a solid material composed of steel.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Further advantages, features and details of the invention will emerge from the following description of preferred exemplary embodiments and from the drawing.

[0017] In the drawing:

[0018] FIG. 1 shows a partially sectional side view of a nozzle needle according to the invention for a fuel injection device in the form of a fuel injector,

[0019] FIG. 2 shows a sub-region of the nozzle needle in the region of the nozzle needle tip, in longitudinal section, and

[0020] FIG. 3 shows a sub-region of the nozzle needle as per FIGS. 1 and 2 in an installed position in a fuel injector in its closed position, in longitudinal section.

DETAILED DESCRIPTION

[0021] Identical elements or elements of identical function are denoted by the same reference designations in the figures.

[0022] FIG. 1 illustrates a nozzle needle 10 according to the invention for a fuel injection device 100, shown in FIG. 3, in the form of a fuel injector, in particular a fuel injector for use in an auto-ignition internal combustion engine. The fuel injector is a constituent part of a so-called common-rail system, in which highly pressurized fuel is injected into the combustion chamber of an internal combustion engine, such as is prior art per se and will therefore not be discussed in any more detail below.

[0023] The nozzle needle 10 is composed substantially of two separate components, a nozzle needle shank 11 and a nozzle needle tip 12. The nozzle needle shank 11 is composed of a solid material, in particular of machine steel, and is of substantially cylindrical or bar-shaped form. The nozzle needle shank 11 has, in a central region, multiple guide sections 13 which serve for radial guidance of the nozzle needle shank 11 or of the nozzle needle 10 in the direction of its longitudinal axis 14 by means of abutment against the inner wall 16 of an injector housing 18 illustrated in FIG. 3. In the region of the guide sections 13, there are formed multiple planar surfaces 19 which are formed in particular by grinding and which are preferably arranged at uniform angular intervals with respect to one another and which serve for allowing fuel to flow in the direction of the nozzle needle tip 12 in the region of the inner wall 16.

[0024] The nozzle needle shank 11 has a receptacle 20 in the form of a blind bore 21 for receiving the nozzle needle tip 12. The blind bore 21, which has a constant diameter D, has a base 22 which serves as an axial stop for the nozzle needle tip 12 in the direction of that end 23 of the nozzle needle shank 11 which is situated opposite the nozzle needle tip 12. The end 23 protrudes for example into a control chamber (not illustrated) of the fuel injector in order to control the movement of the nozzle needle 10 for the purposes of opening or closing, in a known manner, injection openings 26 which are formed in the injector housing 18.

[0025] The nozzle needle tip 12 is composed of a different material than the nozzle needle shank 11, in particular of a wear-resistant material such as ceramic, hard metal or a sapphire. The nozzle needle tip 12 has, at least within the receptacle 20, a cylindrical section 24 with an at least approximately constant diameter d, wherein the diameter d of the section 24 and the diameter D of the blind bore 21 are coordinated with one another such that, preferably, a transition or clearance fit is formed between the nozzle needle tip 12 and the nozzle needle shank 11, and wherein the diameter d simultaneously forms the largest diameter of the nozzle needle tip 12. It is however also possible for the diameters d, D to be coordinated with one another such that an interference fit is formed between the nozzle needle tip 12 and the nozzle needle shank 11. It is furthermore possible for leakage grooves or the like (not illustrated) to be formed on the circumference of the section 24 in order to permit a defined throughflow of fuel into the region of the base 22 of the blind bore 21.

[0026] The section 24 of cylindrical form of the nozzle needle tip 12 is adjoined, outside the receptacle 20, by a seat region 25 of conical form. The seat region 25 is designed to close the injection openings 26 when the nozzle needle 10 is in the closed position illustrated in FIG. 3. For this purpose, the seat region 25 bears sealingly against the inner wall 16 of the injector housing 18.

[0027] The nozzle needle shank 11 has a outer surface 28 of conical form in the mouth region of the receptacle 20 or of the blind bore 21. A straight line 29 formed as an elongation of the seat region 25 runs spaced apart from the outer circumference 28 of the nozzle needle shank 11.

[0028] If a transition or clearance fit is formed between the nozzle needle tip 12 and the nozzle needle shank 11 in the region of the receptacle 20, fuel can pass into the region between the base 22 of the blind bore 21 and that face surface of the nozzle needle tip 12 which faces toward the base 22. During the opening of the nozzle needle 10 from the closed position illustrated in FIG. 3 for the purposes of opening up the injection openings 26, from the first moment, the nozzle needle shank 11 begins to move such that an axial gap 30 forms between the base 22 of the blind bore 21 and the nozzle needle tip 12, which axial gap has a size in the region of a few micrometers. Subsequently, the nozzle needle tip 12 also begins to move away from its sealing seat in order to open up the injection openings 26.

[0029] It is also essential that the force acting hydraulically on the nozzle needle tip 12 in the opening direction of the nozzle needle 10 owing to the fuel pressure in the injector housing 18 is always greater than the force acting hydraulically on the nozzle needle shank 11, such that the nozzle needle tip 12 is subjected to force in the direction of the base 22 of the blind bore 21 at all times.

[0030] The nozzle needle 10 thus described, and the fuel injection system 100, may be altered or modified in a variety of ways without departing from the concept of the invention.