FUEL INJECTION VALVE

Abstract

Fuel injection valve having a magnet armature (18) which interacts with a valve seat (19), which is formed on a valve piece (15), in order to open and close an outflow opening (20), wherein the magnet armature (18) can be moved away from the valve seat (19) by an electromagnet (24). A valve piece (15) delimits a control chamber (12), wherein the outflow opening (20) opens into the control chamber (12), and the control chamber (12) can be charged with fuel at high pressure that exerts a hydraulic force on the valve piece (15). Between the magnet armature (18) and the valve piece (15), there is arranged a bracing element (30) which is preloaded against the valve piece (15) and which exerts a force on the valve piece (15) in the region of the outflow opening (20) in the direction of the control chamber (12).

Claims

1. A fuel injection valve having a magnet armature (18) which interacts with a valve seat (19), which is formed on a valve piece (15), in order to open and close an outflow opening (20), wherein the magnet armature (18) is movable away from the valve seat (19) by an electromagnet (24), and having a control chamber (12) which is delimited by the valve piece (15), wherein the outflow opening (20) opens into the control chamber (12), and the control chamber (12) is configured to be charged with fuel at high pressure, wherein pressure in the control chamber (12) exerts a hydraulic force on the valve piece (15) in a region of the outflow opening (20) in a direction of the magnet armature (18), wherein a bracing element (30) is arranged between the magnet armature (18) and the valve piece (15), and wherein the bracing element (30) is preloaded against the valve piece (15) and exerts a force on the valve piece (15) in the region of the outflow opening (20) in a direction of the control chamber (12).

2. The fuel injection valve according to claim 1, characterized in that the bracing element is formed as a holed disk (30) which has a central opening (32) through which the magnet armature (18) extends.

3. The fuel injection valve according to claim 2, characterized in that the valve seat (19) is in the form of a ring-shaped disk and surrounds the outflow opening (20).

4. The fuel injection valve according to claim 1, characterized in that the bracing element (30) is preloaded against the valve piece (15) by a sleeve (28) which is supported with an end on the electromagnet (24).

5. The fuel injection valve according to claim 4, characterized in that the electromagnet (24) is preloaded in a direction of the valve piece (15) by a magnet spring (27).

6. The fuel injection valve according to claim 1, characterized in that the magnet armature (18) is preloaded against the valve seat (19) by an armature spring (22).

7. The fuel injection valve according to claim 6, characterized in that the armature spring (22) is arranged in an interior of the electromagnet (24).

8. The fuel injection valve according to claim 1, characterized in that the bracing element (30) lies on a circular-ring-shaped region on the valve piece (15), wherein the circular-ring-shaped region surrounds the valve seat (19) and the outflow opening (20).

9. The fuel injection valve according to claim 1, characterized in that the valve seat (19) is formed as a flat seat.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The drawing schematically illustrates various exemplary embodiments of the fuel injection valve according to the invention in longitudinal section. In the drawing:

[0016] FIG. 1 shows a longitudinal section through a fuel injection valve such as is known from the prior art,

[0017] FIG. 2 shows the same fuel injection valve, in this case likewise in a schematic illustration, with only the main parts being illustrated, and the influence of the internal pressure in the control chamber on the deformation of the adjacent components being illustrated on an exaggerated scale,

[0018] FIG. 3 shows a first exemplary embodiment of the fuel injection valve according to the invention,

[0019] FIG. 4 shows, in the same illustration as FIG. 3, the effects of a deformation of the valve piece by the internal pressure in the control chamber, and

[0020] FIG. 5 shows a second exemplary embodiment of the fuel injection valve according to the invention, with only the region of the bracing element being illustrated.

DETAILED DESCRIPTION

[0021] FIG. 1 schematically illustrates a fuel injection valve known from the prior art in longitudinal section, with only the main parts of the fuel injection valve being illustrated. The fuel injection valve has a housing 1 which comprises a valve body 2, a holding body 3 and a nozzle body 5, which are braced against one another in liquid-tight fashion in said sequence by bracing devices (not shown). In the holding body 3 there is formed a bore 7 which extends into the nozzle body 5 and in which a piston-like nozzle needle 8 is arranged in longitudinally displaceable fashion. Here, the nozzle needle 8 interacts with a nozzle seat 9 formed in the nozzle body 5, such that, when the nozzle needle 8 bears against the nozzle seat 9, injection openings 10 which are formed on the combustion-chamber-side end of the nozzle body 5 are closed off with respect to a pressure chamber 6 which surrounds the nozzle needle 8 in the region of the nozzle body 5. The pressure chamber 6 is in this case charged with fuel at high pressure, which is compressed, and supplied to the fuel injection valve, by a high-pressure pump (not shown in any more detail).

[0022] The fuel pressure in the pressure chamber 6 exerts on the nozzle needle 8 an opening force which is directed in an opening direction, that is to say away from the nozzle seat 9, but which counteracts a hydraulic closing force which is generated by the fuel pressure in a control chamber 12. Here, the control chamber 12 is delimited by that face side of the nozzle needle 8 which is averted from the nozzle seat 9, and at the opposite side by a valve piece 15. The control chamber 12 is connected via a feed line (not shown) to the pressure chamber 6, such that it can always be charged with fuel at high pressure via said feed line. The hydraulic forces exerted on the nozzle needle 8 by the pressure in the pressure chamber 6 and in the control chamber 12 are configured such that, when an equal pressure prevails in the control chamber 12 and in the pressure chamber 6, the nozzle needle 8 is pushed hydraulically against the nozzle seat 9 and thus closes off the injection openings 10.

[0023] A control valve 14 serves for the regulation of the pressure in the control chamber 12. Here, the control valve 14 comprises a magnet armature 18 which is arranged in longitudinally displaceable fashion in an outflow chamber 16 formed in the valve body 2. The magnet armature 18 interacts with a valve seat 19 in order to open and close an outflow opening 20, wherein the valve seat 19 is formed on the valve piece 15 and surrounds the opening-out point of the outflow opening 20 into the outflow chamber 16 in the manner of a ring-shaped disk, such that, when the magnet armature 18 bears against the valve seat 19, the outflow opening 20 is closed off with respect to the outflow chamber 16. For the movement of the magnet armature 18, an electromagnet 24 is used which comprises a magnet core 25 with a magnet coil 26 formed therein. If the magnet coil 26 is electrically energized, the electromagnet 24 exerts an attractive force on the magnet armature 18, such that said magnet armature is pulled away from the valve seat 19 in the direction of the electromagnet 24. The movement of the magnet armature 18 occurs in this case counter to the force of an armature spring 22 which is arranged in a recess in the electromagnet 24. The armature spring 22 also ensures that, when the electrical energization of the magnet coil 26 is interrupted, the magnet armature 18 moves back into its closed position again, that is to say into contact with the valve seat 19.

[0024] The axial spacing between the electromagnet 24 and the valve piece 15 denotes the maximum stroke H of the magnet armature 18. To keep said maximum stroke constant, a sleeve 28 is arranged between the electromagnet 24 or the magnet core 25 and the valve piece 15, the axial length of which sleeve ultimately defines the maximum stroke H. To hold the electromagnet 24 in place, a magnet spring 27 is provided which preloads the electromagnet 24 against the valve piece 15 via the sleeve 28. If the electromagnet 24 is now electrically energized, it moves the magnet armature 18 away from the valve seat 19 and opens up the outflow opening 20. As a result, the pressure in the control chamber 12 falls, because fuel flows out via the outflow opening 20 into the outflow chamber 16, and the hydraulic closing force on the nozzle needle 8 correspondingly falls. Said nozzle needle is thus moved away from the nozzle seat 9 by hydraulic forces in the pressure chamber 6, and opens up the injection openings 10 such that fuel passes from the pressure chamber 6 via the injection openings 10 into the combustion chamber of the internal combustion engine. To end the injection, the electrical energization of the electromagnet 24 is ended, such that the armature spring 22 pushes the magnet armature 18 back into contact with the valve seat 19, which closes the outflow opening 20 again. The fuel pressure that builds up again in the control chamber 12 owing to the follow-up inflow of fuel pushes the nozzle needle 8 back into its closed position against the nozzle seat 9, such that the injection openings 10 are closed again.

[0025] The fuel pressures used in the case of normal fuel injection are very high, and temporarily amount to 2000 bar (200 MPa) or even considerably higher. This results in a small but nevertheless significant deformation of the valve piece 15 by the fuel pressure in the control chamber 12, because it is always the case that only a very low fuel pressure prevails in the outflow chamber 16 on that side of the valve piece 15 which is averted from the control chamber 12. As a result, the valve piece 15 deforms, as illustrated by means of the dashed line in FIG. 2, such that the valve seat 19 is displaced by a distance h in the direction of the electromagnet 24. The maximum stroke H of the magnet armature 18 is thus also reduced by said distance h, because the spacing of the magnet armature 18 to the electromagnet 24 when the control valve is closed is also decreased. Since the magnetic force on the magnet armature 18 is very sensitive to the spacing to the electromagnet 24, the magnetic force on the magnet armature 18 is now increased, which changes the opening dynamics in the event of electrical energization of the electromagnet 24. This results in different injection dynamics, and thus in a change in quantity and injection time.

[0026] FIG. 3 illustrates a first fuel injection valve according to the invention, wherein only the region of the control valve is illustrated in detail. The construction of the control valve 14 is, aside from the details discussed below, identical to the construction known from the prior art and shown in FIGS. 1 and 2. Instead of a sleeve 28 which supports the electromagnet 24 directly on the valve piece 15, a bracing element 30 is provided between the electromagnet 24 and the valve piece 15. The bracing element 30 is supported by the sleeve 28 on the electromagnet 24 and lies, at the other side, on the valve piece 15 in a circular-ring-shaped region surrounding the valve seat 19. As a result, the bracing force which is transmitted by means of the magnet spring 27 to the electromagnet 24, the bracing sleeve 28 and the bracing element 30 is exerted on the valve piece 15 in the region of the outflow opening 20. If a deformation of the valve piece 15 now occurs owing to the pressure in the control chamber 12, the state as illustrated in FIG. 4 arises. The valve piece 15 deforms, as has also already been shown in FIG. 2, in the direction of the electromagnet 24 in particular in the region of the outflow opening 20, and thereby displaces the valve seat 19 in the direction of the electromagnet 24. Owing to the bracing element 30, said electromagnet is also moved by the distance h in the direction of the electromagnet 24, such that, via the sleeve 28, the electromagnet 24 is also moved by the distance h counter to the force of the magnet spring 27. It is thus ultimately the case that the spacing between the valve seat 19 and the electromagnet 24, and thus also the maximum stroke H of the magnet armature 18, remain constant. If, in the event of such a deformation, the electromagnet 24 is electrically energized, then the spacing between the electromagnet 24 and the magnet armature 18 is of the same size as in the absence of said deformation. Thus, the magnetic forces, and thus the opening characteristic of the control valve 14, also remain the same. As a result of this independency of the injection pressure, a control valve 14 of said type can be used even in the case of very high injection pressures, which lead to an intense deformation of the valve piece 15. The distance h by which the valve seat 19 is moved here typically amounts to a few micrometers.

[0027] To ensure that the bracing element 30 sets down on the valve piece 15 only in the region of a circular-ring-shaped disk which surrounds the outflow opening 20, the region of the valve seat 19 is of elevated form and projects beyond the otherwise flat side, facing toward the outflow chamber 16, of the valve piece. FIG. 5 illustrates an alternative embodiment in this regard. Here, the valve piece 15 has been ground so as to be completely flat on the side facing toward the outflow chamber 16. To nevertheless exert the forces in the region of the outflow opening 20, the bracing element 30 has a protrusion such that the axial forces are exerted on the valve piece 15 only in the region of the outflow opening 20. The functionality of this exemplary embodiment is otherwise identical to that shown in FIGS. 3 and 4.

[0028] The embodiment of the bracing element 30 as a holed disk is the simplest possibility for realizing a bracing element of said type in an electromagnet shown here. It is however also possible for some other form of the bracing element 30 to be provided which ensures that the force exerted on the electromagnet 24 by means of a magnet spring 27 or some other device is exerted on the valve piece 15 only in the region of the outflow opening 20.