Fuel injector

Abstract

The invention relates to a fuel injector, in particular a common-rail injector (1), comprising an injector housing (2), in which a nozzle needle (8), which is arranged in such a way that the nozzle needle can be moved in a reciprocating manner, is arranged in a high-pressure chamber (6) in order to open and close at least one injection opening (5), which nozzle needle bounds a control chamber (20) by means of one end face and interacts with a nozzle body seat (10) by means of the other end face in order to open and close the injection opening (5). The nozzle needle (8) has a first sleeve-shaped supporting element (14), to which force is applied in the closing direction of the nozzle needle (8). In addition, the nozzle needle (8) has a second sleeve-shaped supporting element, which surrounds the nozzle needle (8) and which is arranged in the direction of the end face of the nozzle needle (8) that is close to the control chamber. The second supporting element (16) is arranged at a distance from the first supporting element (14) axially in the closing direction of the nozzle needle (8). At least one of the stop surfaces (33, 34) of the first (14) sleeve-shaped supporting element or of the second (16) sleeve-shaped supporting element that face each other has at least one cut-out (36).

Claims

1. A fuel injector, comprising an injector housing (2), in which a nozzle needle (8), which is arranged in such a way that the nozzle needle can be moved in a reciprocating manner, is arranged in a high-pressure space (6) in order to open and close at least one injection opening (5), wherein one end of the nozzle needle delimits a control space (20) and an other end of the nozzle needle interacts with a nozzle body seat (10) to open and close the injection opening (5), wherein the nozzle needle (8) has a first supporting element (14), which is sleeve-shaped and is subjected to a force in a closing direction of the nozzle needle (8), and wherein the nozzle needle (8) has a second supporting element (16), which is sleeve-shaped and surrounds the nozzle needle (8) and which is arranged in a direction of the one end of the nozzle needle (8), wherein the second supporting element (16) is arranged at a distance from the first supporting element (14) axially in the closing direction of the nozzle needle (8), wherein the first and second supporting elements (14, 16) have respective mutually facing stop surfaces (33, 34), and wherein at least one of the mutually facing stop surfaces (33, 34) has at least one recess (36).

2. The fuel injector as claimed in claim 1, characterized in that the at least one recess (36) is a groove.

3. The fuel injector as claimed in claim 2, characterized in that a cross section of the groove has the shape of a triangle (136).

4. The fuel injector as claimed in claim 2, characterized in that the at least one of the mutually facing stop surfaces (33, 34) has therein a plurality of grooves arranged parallel to one another (536) and/or radially (636) and/or so as to follow a circumference (736).

5. The fuel injector as claimed in claim 2, characterized in that the at least one of the mutually facing stop surfaces (33, 34) has therein a plurality of grooves arranged so as to be curved (836) and/or so as to intersect (936).

6. The fuel injector as claimed in claim 2, characterized in that the at least one of the mutually facing stop surfaces (33, 34) has therein at least two groove groups (1036), group elements of each of the groove groups being arranged parallel to one another and the groove groups being at an angle to one another.

7. The fuel injector as claimed in claim 1, characterized in that the first supporting element (14) and the second supporting element (16) are arranged within a nozzle body (3), which is adjoined by an injector body (4) in a direction of the end of the nozzle needle (8) remote from the combustion chamber.

8. The fuel injector as claimed in claim 7, characterized in that the second supporting element (16) is fixed on the injector body (2) by an end of the supporting element facing the control space.

9. The fuel injector as claimed in claim 1, characterized in that the second supporting element (16) is of multi-part design.

10. The fuel injector as claimed in claim 1, further comprising a return spring (15), which exerts a restoring force on the first supporting element (14) in a direction of the nozzle body seat (10).

11. The fuel injector as claimed in claim 10, characterized in that the return spring (15) is arranged under prestress between the first supporting element (14) and the second supporting element (16).

12. The fuel injector as claimed in claim 1, characterized in that, in order to limit an opening stroke of the nozzle needle (8), the mutually facing stop surfaces (33, 34) of the first supporting element (14) and of the second supporting element (16) come into contact with one another at a maximum opening stroke of the nozzle needle (8), whereby at least one injection opening (5) is opened, wherein the maximum opening stroke of the nozzle needle (8) is defined by a distance (35) between the mutually facing stop surfaces of the first supporting element (14) and of the second supporting element (16) in a closed position of the nozzle needle (8).

13. The fuel injector as claimed in claim 1, characterized in that the nozzle needle (8) has a radially encircling offset (32), wherein the first supporting element (14) rests axially on the radially encircling offset (32) of the nozzle needle (8).

14. The fuel injector as claimed in claim 2, characterized in that a cross section of the groove has the shape of a semicircle (236).

15. The fuel injector as claimed in claim 2, characterized in that a cross section of the groove has the shape of a rectangle.

16. The fuel injector as claimed in claim 2, characterized in that a cross section of the groove has the shape of a square (336).

17. The fuel injector as claimed in claim 2, characterized in that a cross section of the groove has the shape of a trapezoid (436).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further advantages, features and details of the invention will emerge from the following description of preferred illustrative embodiments and from the drawings, in which:

(2) FIG. 1 shows a longitudinal section through a fuel injector according to the invention,

(3) FIG. 2 shows a partial region of the fuel injector shown in FIG. 1 in the region of a device which is characterized by the first sleeve-shaped supporting element and the second sleeve-shaped supporting element and which defines the maximum opening stroke of the nozzle needle,

(4) FIG. 3 shows the first sleeve-shaped supporting element in perspective view,

(5) FIG. 4 shows the second sleeve-shaped supporting element in a multi-part embodiment with an adjusting ring and a stop ring in perspective view, and

(6) FIG. 5 shows alternative views a through e showing various embodiments of grooves.

(7) FIG. 6 shows alternative views a through e showing, in a plan view of a stop surface of the first sleeve-shaped supporting element or of the second sleeve-shaped supporting element, grooves which are arranged parallel to one another (view a) and/or radially (view c) and/or so as to follow the circumference of the supporting element (view e).

(8) Elements with the same function are provided with the same reference numerals in the figures.

DETAILED DESCRIPTION

(9) FIG. 1 illustrates a fuel injector 1, in this case a common rail injector, which is used to inject fuel into a combustion chamber (not shown) of an internal combustion engine, in particular an auto-ignition internal combustion engine. The fuel injector 1 has a multi-part injector housing 2, which comprises a nozzle body 3 and an injector body 4 adjoining the nozzle body 3. A pressure-tight connection is formed between the nozzle body 3 and the injector body 4 by means of a nozzle clamping nut 50. Formed within the injector housing 2 is a high-pressure space 6, which is continued into the nozzle body 3, where it is formed by a stepped longitudinal bore. On the side facing the combustion chamber, the nozzle body 3 has at least one injection opening 5, starting from the pressure space, for injecting fuel into the combustion chamber of the internal combustion engine. The high-pressure space 6 can be filled with fuel under system pressure via a feed passage 51. In the illustrative embodiment shown, the feed passage 51 is formed in the central region of the high-pressure space 6, perpendicularly to a longitudinal axis 7 of the fuel injector 1.

(10) A piston-shaped nozzle needle 8 is arranged in the high-pressure space 6 in such a way that it can be moved in a reciprocating manner in its longitudinal direction. FIG. 1 illustrates the closed position of the nozzle needle 8, which closes the at least one injection opening 5 formed in the nozzle body 3. For this purpose, a nozzle body seat 10, with which the nozzle needle 8 interacts, is formed on the inside of the nozzle body 3. To open the injection opening 5, the nozzle needle 8 rises from the nozzle body seat 10 and thus allows a fuel flow from the high-pressure space 6, via the at least one injection opening 5, into the combustion chamber of the internal combustion engine.

(11) The nozzle needle 8 is part of a nozzle module 54, which comprises a pin-shaped valve piston 13 on its end remote from the combustion chamber. The nozzle needle 8 and the valve piston 13 are connected to one another by a central piece 55, e.g. by means of laser weld seams. In this case, the nozzle needle 8 is supported in the nozzle body seat 10 in the closed position and can be moved in the longitudinal direction by means of an electromagnet 26, see double arrow 53. In the region of the nozzle needle 8, the nozzle module 54 surrounds a first sleeve-shaped supporting element 14 and a second sleeve-shaped supporting element 16, wherein a return spring 15 is arranged under compressive prestress between the first sleeve-shaped supporting element 14 and the second sleeve-shaped supporting element 16. FIG. 2 shows a partial region of the fuel injector shown in FIG. 1, which shows, on an enlarged scale, the region of the nozzle needle 8 with the first sleeve-shaped supporting element 14, the interposed return spring 15 and the second sleeve-shaped supporting element 16.

(12) On the side of the nozzle module 54 facing away from the combustion chamber, the injector housing 2 comprises a valve piece 18, which has a blind hole 19 on the side facing the valve piston 13. The end region of the valve piston 13 enters this blind hole 19. The valve piston 13 and the blind hole 19 delimit a control space 20, which is connected hydraulically to the high-pressure space 6 by a feed bore 21. An outlet restrictor 22 formed in the valve piece 18 and leading into a low-pressure region 23 of the fuel injector 1 allows hydraulic relief of the control space 20, wherein the outlet restrictor 22 is connected to an outlet passage 52, which is arranged on the opposite side of the injector housing 2 from the feed passage 51.

(13) In order to separate the control space 20 and the low-pressure region 23 hydraulically from one another, the outlet restrictor 22 can be closed by a spherical valve element 24, which is part of a control valve 24. The valve 24 is controlled by means of an electromagnet 26 since the spherical valve element 24 is attached to a magnet armature. Raising of the valve element 24 from the outlet restrictor 22 is initiated by energization of the magnet. The control space 20 and the low-pressure region 23 can thereby be connected hydraulically to one another. This leads to a pressure drop in the control space 20, resulting in a reduction in the hydraulic closing force of the nozzle needle 8. The nozzle needle 8 thus moves by virtue of the force in the high-pressure space 6 acting in the longitudinal direction on the nozzle needle 8. This allows fuel to flow into the combustion chamber of the internal combustion engine via the at least one injection opening 5, which is now open.

(14) As shown in FIG. 2, the first sleeve-shaped supporting element 14 rests on a radially encircling offset 32 of the nozzle needle 8. Together with the first sleeve-shaped supporting element, the second sleeve-shaped supporting element 16, which is arranged on the first sleeve-shaped supporting element 14 via the return spring 15, forms a limit for the maximum opening stroke of the nozzle needle 8. At the maximum opening stroke of the nozzle needle 8, mutually facing stop surfaces 33, 34 of the first sleeve-shaped supporting element 14 and of the second sleeve-shaped supporting element 16 rest against one another. The maximum opening stroke is thereby defined by the axial distance 35 between the mutually facing stop surfaces 33, 34 of the first sleeve-shaped supporting element 14 and of the second sleeve-shaped supporting element 16 in the closed position of the nozzle needle 8. It is a function of the return spring 14 to push the nozzle needle 8 into the nozzle body seat 10 in the direction of the at least one injection opening 5 in order to avoid fuel also flowing into the combustion chamber of the internal combustion engine when the fuel injector is switched off.

(15) FIG. 3 illustrates a possible illustrative embodiment of the first sleeve-shaped supporting element 14 as a one-piece construction element. In this case, recesses 36 are formed at some points on the stop surface 33 of the first sleeve-shaped supporting element 14, and these are explained in detail in the rest of the description. The second sleeve-shaped supporting element 16 is of multi-part construction. FIG. 4 illustrates a possible illustrative embodiment of the second sleeve-shaped supporting element 16 as a two-part component, which has an adjusting ring 56 with through holes 37 for the fuel and a stop ring 38 arranged on the adjusting ring 56. The adjusting ring 56 forms the component of the second sleeve-shaped supporting element 16 which determines the limit of the maximum opening stroke of the nozzle needle 8 and is passed through completely in the axial direction by the nozzle needle 8 in the installed position in the injector. On the side facing away from the adjusting ring 56, the stop ring 38 has a radially encircling collar 57, wherein the collar 57 serves as a support for the return spring 15. Both the first sleeve-shaped supporting element 14 and the second sleeve-shaped supporting element 16 as well as the return spring 15 are mounted on the nozzle needle 8 before the nozzle needle 8 is welded to the central piece 55. Different diameters of the nozzle needle 8 and the central piece 55 lead to the first sleeve-shaped supporting element 14, the second sleeve-shaped supporting element 16 and the return spring 15 being connected to the nozzle module 54 in a manner which prevents loss.

(16) As already shown in FIG. 3, the stop surfaces 33, 34 of the first sleeve-shaped supporting element 14 and of the second sleeve-shaped supporting element 16 have at least one recess 36, which is formed by a groove shape 39. As a result, the stop surfaces 33, 34 of the first sleeve-shaped supporting element 14 and of the second sleeve-shaped supporting element 16 do not rest upon one another over the full area in the open position of the nozzle needle 8, as a result of which the adhesion forces are reduced. Lower adhesion forces allow quicker release of the stop surfaces 33, 34 of the first sleeve-shaped supporting element 14 and of the second sleeve-shaped supporting element 16 from one another and thus allow more precise closing of the nozzle needle 8 and prevent an unintentional afterflow of fuel into the combustion chamber via the at least one injection opening 5. Moreover, the recesses 36 in the stop surfaces 33, 34 of the first sleeve-shaped supporting element 14 and/or of the second sleeve-shaped supporting element 16 allow the fuel under high pressure to flow into precisely these recesses 36 after the closure of the spherical valve element 24 and thus additionally accelerate the release of the stop surfaces 33, 34 of the first sleeve-shaped supporting element 14 and of the second sleeve-shaped supporting element 16.

(17) The recesses 36 have different cross sections. FIG. 5 illustrates possible embodiments of groove cross sections in the form of a triangle 136 (FIG. 5e), of a semicircle 236 (FIG. 5b) or of a rectangle, in particular of a square 336 (FIG. 5a) or of a trapezoid 436 (FIG. 5c and FIG. 5d). Moreover, FIG. 6 shows, in a plan view of a stop surface 33, 34 of the first sleeve-shaped supporting element 14 or of the second sleeve-shaped supporting element 16, grooves which are arranged parallel to one another 536 (FIG. 6a) and/or radially 636 (FIG. 6c) and/or so as to follow the circumference of the supporting element 736 (FIG. 6e). Moreover, the grooves have a curved profile 836, as shown in FIG. 6d, or a mutually intersecting profile 936 (FIG. 6e). As illustrated in FIG. 6b, there can furthermore be at least two groove groups 1036, wherein elements of a groove group are arranged parallel to one another and elements from different groove groups 1036 enclose an angle with one another.

(18) The groove embodiments presented are used for optimization for quicker release of the stop surfaces 33, 34 of the first sleeve-shaped supporting element 14 and of the second sleeve-shaped supporting element 16 and can also be used in combinations on one stop surface 33 or 34 of the first sleeve-shaped supporting element 14 and of the second sleeve-shaped supporting element 16 in each case.

(19) In addition to all these embodiments, additional groove shapes 39 which perform the same function as the groove shapes 39 already mentioned and, for example, ensure the roughness of the stop surfaces 33, 34 of the first sleeve-shaped supporting element 14 and of the second sleeve-shaped supporting element 16 are also possible.

(20) To reduce the contact area of the stop surfaces 33, 34 of the first sleeve-shaped supporting element 14 and of the second sleeve-shaped supporting element 16, conventional methods such as milling, grinding or stamping can be used. It is also possible to remove material with a laser.