Fuel injector for injecting fuel

Abstract

A fuel injector for injecting fuel under high pressure, having a housing (1) in which a longitudinally displaceable nozzle needle (10) is arranged, the nozzle needle (10) opening and closing one or more injection openings (13) with a sealing surface (11), through which the fuel can be ejected. A control chamber (20) that can be filled with fuel applies a hydraulic force in its closing direction to the nozzle needle (10), wherein the pressure in the control chamber (20) can be influenced by a control valve (22) in such a way that the control valve (22) opens and closes the hydraulic connection of the control chamber (20) to a low-pressure chamber (21). The control valve (22) includes an electromagnetic armature (23), which cooperates with a control valve seat (26) to open and close the hydraulic connection, wherein the electromagnetic armature (23) is radially guided in the housing (1) on its outer side (33).

Description

Field of the Invention

[0001] The present invention relates to a fuel injector, such as for use in preferably injecting fuel into the combustion space of an internal combustion engine, wherein the fuel is injected under high pressure. Background Art

[0002] Some fuel injection valves are known, for example, from EP 2 126 331 B1, which are used to inject fuel under high pressure into the combustion space of an internal combustion engine. Such a fuel injection valve has a housing in which a longitudinally movable nozzle needle is arranged. The nozzle needle opens and closes the injection opening by its longitudinal movement, and fuel can be injected into the combustion space under high pressure through the injection opening. Due to the high pressure, the fuel is finely atomized when it exits from the injection opening, so that effective combustion can take place in the combustion space. The movement of the nozzle needle is servo-hydraulically effected, that is, the pressure in the control chamber is regulated by means of a control valve, and the control chamber exerts a hydraulic closing force on the nozzle needle. If the control valve is opened, the pressure in the control chamber is reduced and the nozzle needle moves to its open position. When the control valve is closed, a high pressure is again established in the control chamber, and the nozzle needle is pressed back to its closed position.

[0003] The control valve is, for example, configured as an electromagnetic valve and includes an electromagnet, that is, a coil having a magnetic core that can be energized with a rapid effect. Further, the control valve includes an armature that acts together with the electromagnet. When the electromagnet is energized, the armature moves against the force of the armature spring, thereby releasing the outflow opening through which fuel can flow out of the control chamber into the low-pressure chamber. For this purpose, a closing element having a sealing surface is configured on the armature, and the armature acts together with the control valve seat with the sealing surface. Here, for precise control, it is common to guide the armature in the housing in order to seal and reliably block the outflow throttle. An armature having an angular error or axial misalignment relative to the control valve seat tends to adhere asymmetrically or tends to form an air gap on the stop surface, and when the electromagnet is energized, the armature abuts against the stop surface. In addition, leakage may occur at the control valve seat. In particular, the asymmetric adhesion on the stop surface results in point contact and thus increased friction and wear. To prevent this, the armature having a shank region is guided in a bore or sleeve. However, the corresponding member for guiding the armature in its longitudinal movement is laborious and expensive in production due to the small guiding clearance, which makes the fuel injection valve generally expensive and the production laborious. Summary of the Invention

[0004] In contrast, the fuel injector according to the invention has the advantage that the electromagnetic armature is guided in the fuel injector in a simple manner and without using precision components and thus ensures a reliable function of the fuel injector or the control valve while keeping the manufacturing costs low. For this purpose, the fuel injector has a housing in which a longitudinally movable nozzle needle is arranged, which opens and closes one or more injection openings with a sealing surface, through which the fuel can be ejected. Furthermore, a control chamber that can be filled with fuel is configured in the housing, and the control chamber applies a hydraulic pressure in the closing direction of the nozzle needle to the nozzle needle. The pressure in the control chamber can be influenced by a control valve, in such a way that the control valve opens and closes the hydraulic connection of the control chamber to a low-pressure chamber, wherein the control valve includes an electromagnetic armature that cooperates with a control valve seat to open and close the hydraulic connection. The electromagnetic armature is radially guided in the housing on its outer side.

[0005] The electromagnetic armature has an outer side that is radially guided in the housing with a relatively large clearance. Further guidance of the electromagnetic armature is not necessary because the guidance on the outer side is sufficient to keep the electromagnetic armature in the desired radial position. Since the electromagnetic armature has high mobility within the housing, angular deviation states are automatically compensated, and the radial guidance clearance is so large that clamping of the electromagnetic armature in the housing is reliably avoided.

[0006] In a first advantageous configuration, the electromagnetic armature is rotationally symmetrically configured such that the function is also ensured when the electromagnetic armature rotates within the housing. Here, the radial spacing between the outer edge of the electromagnetic armature and the housing is dimensioned such that the electromagnetic armature cannot move more than 0.1 mm in any direction perpendicular to its movement direction. This guidance clearance is sufficient to keep the electromagnetic armature in its functional position on the one hand. On the other hand, this guidance clearance is so large that, on the one hand, clamping of the electromagnetic armature within the housing is excluded and, on the other hand, it is ensured that the fuel can circulate between the upper and lower sides of the electromagnetic armature, such that the movement of the electromagnetic armature is not significantly affected by the fuel that always flushes the electromagnetic armature.

[0007] In an advantageous configuration, the electromagnetic armature is loaded by an armature spring in the closing direction towards the control valve seat. Here, in an advantageous configuration, the control valve seat can be implemented as a flat seat. The flat seat is insensitive to the radial offset of the electromagnetic armature, such that a good sealing function is also ensured when the electromagnetic armature is slightly offset in the radial direction within the guidance tolerance.

[0008] In a further advantageous configuration, the control valve seat is configured conically and the electromagnetic armature has a closure element in the shape of a spherical segment, which closure element is centered in the control valve seat in the closed state. The possible deviation from the center resulting from the relatively large radial guide clearance is compensated for by centering in the conical control valve seat, or the electromagnetic armature is pressed back into its central state again, such that the function of the control valve is ensured.

[0009] In a further advantageous configuration, the upper side of the electromagnetic armature is configured flat. The upper side faces the electromagnet, such that a flat placement on the electromagnet or on the corresponding abutment surface can compensate for a possible angular deviation state between the stop surface and the upper side of the electromagnetic armature. In an advantageous expansion variant, the lower side of the electromagnetic armature opposite the upper side can also be configured flat and parallel to the upper side. Here, the maximum stroke of the electromagnetic armature is advantageously less than or equal to 0.1 mm, which on the one hand ensures sufficient outflow from the control chamber and on the other hand minimizes a possible tilted state of the electromagnetic armature in the housing. Description of the Drawings

[0010] Different embodiments of the fuel injector according to the invention are shown in the drawings. The drawings show:

[0011] Figure 1 A longitudinal section through the fuel injector (as known from the prior art), wherein only the important components are shown,

[0012] Figure 2 Another fuel injector known from the prior art is shown, wherein only the region of the solenoid valve is shown here,

[0013] Figure 3 and Figure 4 A graphical illustration of the misalignment of the electromagnetic armature in a fuel injector known from the prior art is shown,

[0014] Figure 5 , 6 and 7 show embodiments of the fuel injector according to the invention or of the control valve according to the invention. Detailed Description

[0015] In Figure 1The fuel injector is shown in a longitudinal section as known from the prior art. The fuel injector has a housing 1 which comprises a holding body 2 and a nozzle body 3, the holding body and the nozzle body abutting against each other, wherein the holding body and the nozzle body are clamped relative to each other in a liquid-tight manner by a clamping device not shown in the drawing. A pressure chamber 5 is formed in the holding body 2 and in the nozzle body 3, which pressure chamber can be filled with fuel under high pressure. Here, the filling of the pressure chamber 5 takes place through a high-pressure passage 6 constructed in the housing 1, which high-pressure passage can be connected to a fuel high-pressure source. The pressure chamber 5 is delimited on the lower side in the drawing, i.e., the side facing the combustion space, by a conical nozzle seat 12, and a blind hole 14 adjoins this conical nozzle seat 12, from which a plurality of injection openings 13 start. On the opposite side, the pressure chamber 5 is delimited by a valve block 7, which valve block is fixed by a valve clamping screw 8 screwed into the housing 1. The valve block 7 has a receiving portion for a nozzle needle 10 which is arranged in the pressure chamber 5 in a piston-like and longitudinally displaceable manner. On the nozzle needle 10, a conical sealing surface 11 is formed at its end facing the nozzle seat 12, with which conical sealing surface the nozzle needle 10 cooperates with the nozzle seat 12 to open and close the flow cross-section. If the nozzle needle 10 is lifted from the nozzle seat 12, fuel flows from the pressure chamber 5 through between the sealing surface 11 and the nozzle seat 12, reaches one or more injection ports 13 and is ejected through these injection openings.

[0016] The nozzle needle 10 and the valve block 7 delimit a control chamber 20, which control chamber can be filled with fuel under high pressure through an injection throttle 15. A closing force directed towards the nozzle seat 12 is exerted on the nozzle needle 10 by the hydraulic pressure in the control chamber 20. The movement of the nozzle needle 10 takes place servo-hydraulically, that is to say, by adjusting the pressure in the control chamber 20. For this purpose, an outflow throttle 16 is constructed in the valve block 7, which outflow throttle leads into a low-pressure chamber 21 in the holding body 2. Here, the low-pressure chamber 21 is always filled with fuel at a low fuel pressure, although always completely, through a return line not shown.

[0017] The outflow throttle part 16 is opened or closed by the control valve 22. The control valve 22 includes an electromagnetic armature 23, on which an armature disk 24, a guide section 28, and a closing element 25 are constructed. The electromagnetic armature 23 extends through a drill hole 27 constructed in the valve clamping screw 8. A closing force is applied to the electromagnetic armature 23 by the armature spring 34 in the direction of the conical control valve 26 constructed on the valve block 7. In this embodiment, the closing element 25 is constructed, for example, spherically and cooperates with the conical control valve seat 26 to open and close the outflow throttle part 16. The electromagnet 30 is used to move the electromagnetic armature 23, and the electromagnet includes a coil 31 and a magnetic core 32. If the electromagnet 30 is energized, the electromagnet exerts a magnetic attraction force on the electromagnetic armature 23 and pulls the electromagnetic armature away from the control valve seat 26 contrary to the force of the pre-tightened armature spring 34, so that the outflow throttle part 16 is opened and a connection is established between the control chamber 20 and the low-pressure chamber 21. Then, the fuel waiting in the control chamber 20 flows out into the low-pressure chamber 21, so that the pressure in the control chamber 20 drops slightly and the valve needle 10 is pressed away from the nozzle seat 12 by the hydraulic pressure in the pressure chamber 5, and the connection between the pressure chamber 5 and the blind hole 14 or the injection opening 13 is released. If the fuel injection is to be ended, the energization of the electromagnet 30 is ended and the armature spring 34 presses the electromagnetic armature 23 back into its closed state, in which the closing element 25 locks the outflow throttle part 16 again. The fuel flowing into the control chamber 20 through the injection throttle part 15 raises the pressure to the pressure level of the pressure chamber 5, so that the nozzle needle 10 is pressed back into its closed state.

[0018] Figure 2 shows another fuel injector known from the prior art, where only the area of the control valve is shown in longitudinal section here. The remaining areas of the fuel injector correspond to Figure 1 the illustration in. Here, the electromagnetic armature 23 has a guide section 28, and the guide section is closely guided in a drill hole 27 constructed in the valve clamping screw 8. Here, the radial clearance in the drill hole 27 is selected to be very small to prevent the center line deviation or angular deviation state of the electromagnetic armature 23. The drill hole 27 and the guide section 28 must be manufactured very precisely to ensure good guidance on the one hand and not cause unnecessary wear on the other hand, which may damage the service life of the control valve 22. In Figure 2 the embodiment shown, the control valve seat 26 is constructed as a flat seat and the closing element 25 accordingly has a flat sealing surface, and the closing element cooperates with the flat control valve 26 with this sealing surface.

[0019] In Figure 3The influence of the angular deviation position of the electromagnetic armature 23 is shown. If an angular deviation position of the electromagnetic armature 23 occurs due to manufacturing tolerances or due to thermal expansion that may occur in the fuel injector, the guide section 28 is loaded with a tilting moment in the bore 27, which is visually illustrated by the force F and the corresponding arrow in Figure 3 . This deviation position of the angle α (which is shown here extremely magnified for clarity) results in a one-sided load on the guide section 28 and thus in a point contact of the guide section 28 of the bore 27. This results in increased wear in the corresponding position and thus in a reduced service life of the control valve 22. In order to seal the outflow throttle 16, a closing element 25 rotatably supported in the receiving part is required here. A similar situation can also occur in the spherical closing element 25 and the conical control valve seat 26, as shown in Figure 4 . Since the position of the spherical sealing element 25 is determined by the conical control valve seat 26, in addition to the angular deviation, it must also be possible to achieve position compensation between the electromagnetic armature guide and the valve seat to ensure the sealing of the control valve. Here, this is achieved by the separating surface between the guide body 29 and the guide section 28 of the electromagnetic armature 23.

[0020] In Figure 5 , a first embodiment of a control valve according to the invention is shown. The electromagnetic armature 23 is constructed substantially disc-shaped and has a flat upper side 123 facing the electromagnet 30. Opposite the flat upper side 123, a flat lower side 223 is likewise constructed on the electromagnetic armature 23, which flat lower side cooperates with the control valve seat 26 constructed as a flat seat. The electromagnetic armature 23 is guided on its outer side in a sleeve 17, which sleeve 17 determines the spacing between the electromagnet 30 or the magnetic core 32 and the valve clamping screw 8. Here, the guide gap d is relatively large compared to the guide in the bore (as in the embodiment shown in Figure 1 ), for example 0.1 mm or slightly less. Thereby, on the one hand, sufficient guidance of the electromagnetic armature 23 in the sleeve 17 is ensured, and on the other hand, fuel can flow freely between the upper side 123 and the lower side 223 so as not to impede the movement of the electromagnetic armature 23. In order to make this fuel flow even easier, it can also be provided that a bore is introduced into the electromagnetic armature 23, which bore connects the upper side to the lower side.

[0021] Figure 5Also shown is the angular deviation position of the electromagnetic armature 23 relative to the longitudinal axis or the lower side of the electromagnet 30, where, for the sake of clarity, this angle is drawn significantly larger than it actually is. If the electromagnet 30 is energized in this embodiment, the magnetic force pulls the electromagnetic armature 23 against the magnetic core 32 and lies flat against this magnetic core. Here, possible angular deviation positions of the phase difference angle α (as shown here) can be compensated because the electromagnetic armature 23 is always placed flat on the magnetic core 32. At the end of the power-on, the armature spring 34 presses the electromagnetic armature 23 back onto the flat control valve seat 26, where the angular deviation position can be compensated again. Here, the stroke h of the electromagnetic armature 23 is relatively small, for example 0.1 mm.

[0022] In Figure 6 an additional embodiment of a control valve according to the invention is shown. Here, the electromagnetic armature 23 does not have a flat surface on its lower side parallel to the upper side, but rather has a spherical closing element 25 that interacts with the conical control valve seat 26, as this has already been shown in Figure 1 . Since the electromagnetic armature 23 has a relatively large radial clearance in the sleeve 17, the electromagnetic armature 23 is centered by the closing element 25 such that the electromagnetic armature always returns to its central position again, and no additional guiding elements are necessary.

[0023] Figure 7 As Figure 5 shown, there is an additional embodiment with a flat seat, that is, the closing element 25' interacts with the flat control valve seat 26. Here, the closing element 25' is configured as a cylindrical member, thereby reducing the requirements on the electromagnetic armature in terms of wear. Thereby, the material of the electromagnetic armature 23 can be optimized in terms of magnetic properties with reduced requirements for mechanical stability and thus with greater design freedom. Further improvements can be achieved hereby: The sleeve 17, the closing element 25', and the upper stroke stop are made of a non-magnetizable or only slightly magnetizable material. Here, the upper stroke stop is realized in the form of a disk 36 that is clamped between the sleeve 17 and the magnetic core 32 and against which the armature disk 24 abuts in the open position of the control valve.

Claims

1. A fuel injector for injecting fuel under high pressure, the fuel injector having a housing (1) in which a longitudinally displaceable nozzle needle (10) is arranged, the nozzle needle opening and closing one or more injection openings (13) with a sealing surface (11), fuel being able to be ejected through the one or more injection openings, and the fuel injector having a control chamber (20) that can be filled with fuel, the control chamber applying a hydraulic pressure in the closing direction of the nozzle needle to the nozzle needle (10), and the fuel injector having a control valve (22) by means of which the pressure in the control chamber (20) can be influenced in such a way that the control valve (22) opens and closes the hydraulic connection of the control chamber (20) to a low-pressure chamber (21), wherein, The control valve (22) comprises a magnetic armature (23) having an armature disk (24), wherein the magnetic armature (23) co-operates with a control valve seat (26) for opening and closing the hydraulic connection, characterized in that the magnetic armature (23) is radially guided in the housing (1) only on the outside of the armature disk (24), and a closing element (25') is formed on the magnetic armature (23), wherein the closing element (25') co-operates with the control valve seat (26) and the control valve seat (26) is designed as a flat seat, and the closing element (25') is made of a non-magnetizable or only slightly magnetizable material.

2. The fuel injector according to claim 1, characterized in that, The magnetic armature (23) is rotationally symmetrically configured.

3. The fuel injector according to claim 1 or 2, characterized in that, The spacing between the outer edge (33) of the armature disk (24) and the housing (1) is dimensioned such that the armature disk (24) cannot be displaced from its central position by more than 0.15 mm (d) in any direction perpendicular to the direction of movement of the armature disk.

4. The fuel injector according to claim 1, characterized in that, The magnetic armature (23) is loaded by an armature spring (34) in the closing direction of the magnetic armature towards the control valve seat (26).

5. The fuel injector according to any one of claims 1, 2, and 4, characterized in that, The maximum stroke (h) of the magnetic armature (23) is less than or equal to 0.1 mm.

6. The fuel injector according to any one of claims 1, 2, and 4, characterized in that The sleeve (17) and the upper stroke stop limiting the movement of the magnetic armature (23) of the fuel injector are made of a non-magnetizable or only slightly magnetizable material, wherein the magnetic armature (23) is guided on its outside in the sleeve (17), and the upper stroke stop for the magnetic armature (23) is clamped between the sleeve (17) and the solenoid valve (30) of the fuel injector.

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