FUEL INJECTOR FOR FUEL INJECTION

Description

[0001] The invention relates to a fuel injector as used for injecting fuel, preferably into a combustion chamber of an internal combustion engine, wherein the fuel is injected under high pressure. State of the art

[0002] Fuel injection valves, such as those used for high-pressure fuel injection into the combustion chamber of an internal combustion engine, are known, for example, from EP 2 126 331 B1. Such a fuel injection valve has a housing in which a longitudinally displaceable nozzle needle is arranged, which, through its longitudinal movement, opens and closes injection openings through which fuel can be injected into a combustion chamber under high pressure. The high pressure finely atomizes the fuel as it emerges from the injection openings, allowing effective combustion to take place in the combustion chamber. The movement of the nozzle needle is servo-hydraulically, i.e. the pressure in a control chamber, which exerts a hydraulic closing pressure on the nozzle needle, is regulated by a control valve. When the control valve opens, the pressure in the control chamber is reduced and the nozzle needle moves into its open position.When the control valve is closed, the high pressure in the control chamber builds up again, and the nozzle needle is pushed back into its closed position. Other fuel injection valves are known, for example, from document DE 10 2010 000 244 A1 or EP 2 749 800 A1.

[0003] The control valve is designed, for example, as a solenoid valve and comprises an electromagnet, i.e. a coil with a magnetic core that can be switched in rapid succession. The control valve also comprises a magnet armature that interacts with the electromagnet. When the electromagnet is energized, the magnet armature is moved against the force of an armature spring, opening a drain opening through which fuel can flow from the control chamber into a low-pressure chamber. For this purpose, a closing element with a sealing surface is formed on the magnet armature, with which the magnet armature interacts with a control valve seat. For precise control, it is common practice to guide the magnet armature in the housing so that the drain throttle is closed tightly and reliably. A magnet armature that has an angular error or an axial misalignment with respect to the control valve seat tends to have an asymmetrical installation orto form an air gap at the stop surface, against which the armature rests when the electromagnet is energized. Leaks can also occur at the control valve seat. In particular, the asymmetrical contact with the stop surface leads to point contact and thus to increased friction or wear. To prevent this, magnet armatures with a shaft area are guided in a bore or sleeve. However, the corresponding components that guide the magnet armature during its longitudinal movement are complex and expensive to manufacture due to the small guide clearance, which makes the fuel injection valve as a whole expensive and complex to manufacture. Disclosure of the invention Advantages of the invention

[0004] The fuel injector according to the invention has the advantage that the magnet armature is guided in the fuel injector in a simple manner and without the use of precision components, thus ensuring reliable function of the fuel injector or control valve while simultaneously keeping manufacturing costs low. For this purpose, the fuel injector has a housing in which a longitudinally displaceable nozzle needle is arranged. The nozzle needle, with a sealing surface, opens and closes one or more injection openings through which the fuel can be sprayed. Furthermore, a fuel-fillable control chamber is formed in the housing, which exerts a hydraulic force on the nozzle needle in its closing direction.A control valve can be used to influence the pressure in the control chamber by opening and closing a hydraulic connection between the control chamber and a low-pressure chamber. The control valve comprises a magnet armature that interacts with a control valve seat to open and close the hydraulic connection. The magnet armature is radially guided on its outer surface within the housing. A cylindrical closing element (25') is formed on the magnet armature and interacts with the flat control valve seat. The closing element is made of a non-magnetizable or only slightly magnetizable material.

[0005] The outer surface of the armature is radially guided within the housing with a relatively large amount of play. No further guidance of the armature is necessary, as the guidance on the outer surface is sufficient to hold the armature in the desired radial position. As the armature has a high degree of mobility within the housing, angular misalignments are automatically compensated for, with the radial guide play being so large that jamming of the armature in the housing is reliably prevented. The flat design of the control valve seat makes it insensitive to radial displacement of the armature, ensuring good sealing even if the armature is slightly displaced radially within the guide tolerance.

[0006] In a first advantageous embodiment, a magnet armature is designed to be rotationally symmetrical, so that function is ensured even if the magnet armature rotates within the housing. The radial distance between the outer edge of the magnet armature and the housing is dimensioned such that the magnet armature cannot move by more than 0.1 mm in any direction perpendicular to its direction of movement. This guide play is sufficient to hold the magnet armature in its functional position. On the other hand, it is large enough to prevent the magnet armature from jamming within the housing and to ensure that the fuel can circulate between the top and bottom of the magnet armature, so that the movement of the magnet armature is not significantly influenced by fuel that is constantly flowing around the magnet armature.

[0007] In an advantageous embodiment, a magnetic armature is acted upon by an armature spring in the closing direction towards the control valve seat.

[0008] In a further advantageous embodiment, the upper side of the magnet armature is flat. The upper side faces the electromagnet, so that a flat resting surface on the electromagnet or on a corresponding contact surface can compensate for any angular misalignment between the stop surface and the upper side of the magnet armature. In an advantageous further development, the underside of the magnet armature, which is opposite the upper side, can also be flat and parallel to the upper side. The maximum stroke of the magnet 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 any possible misalignment of the magnet armature in the housing. drawing

[0009] The drawing shows various embodiments of the fuel injector according to the invention. Figure 1 shows a longitudinal section through a fuel injector as is known from the prior art, with only the essential components being shown, Figure 2 shows another fuel injector known from the prior art, with only the area of ​​the solenoid valve being shown here, Figures 3 and 4 show illustrations of incorrect positions of the magnet armature in the fuel injector known from the prior art, Figures 5 and 6 show solenoid valves not according to the invention for functional illustration, and Figure 7 shows an embodiment of the fuel injector according to the invention or of the control valve according to the invention. Description of the embodiments

[0010] In Figure 1a fuel injector is shown in longitudinal section, as is known from the prior art. The fuel injector has a housing 1 which comprises a holding body 2 and a nozzle body 3 which bear against one another and are clamped against one another in a liquid-tight manner by a clamping device (not shown in the drawing). A pressure chamber 5 which can be filled with fuel under high pressure is formed in the holding body 2 and in the nozzle body 3. The pressure chamber 5 is filled via a high-pressure channel 6 formed in the housing 1 which can be connected to a high-pressure fuel source. The pressure chamber 5 is delimited on the lower side in the drawing, i.e. the side facing a combustion chamber, by a conical nozzle seat 12 which is adjoined by a blind hole 14 from which a plurality of injection openings 13 extend.On the opposite side, the pressure chamber 5 is delimited by a valve piece 7, which is fixed by a valve clamping screw 8 screwed into the housing 1. The valve piece 7 has a receptacle for a piston-shaped nozzle needle 10, which is arranged so as to be longitudinally displaceable in the pressure chamber 5. On the nozzle needle 10, at its end facing the nozzle seat 12, a round sealing surface 11 is formed, with which the nozzle needle 10 interacts with the nozzle seat 12 to open and close a flow cross-section. If the nozzle needle 10 lifts off the nozzle seat 12, fuel flows from the pressure chamber 5 between the sealing surface 11 and the nozzle seat 12 to one or more injection openings 13 and is sprayed out through these.

[0011] The nozzle needle 10 and the valve piece 7 define a control chamber 20, which can be filled with fuel under high pressure via an inlet throttle 15. The hydraulic pressure in the control chamber 20 exerts a closing force on the nozzle needle 10 in the direction of the nozzle seat 12. The movement of the nozzle needle 10 is servo-hydraulically, i.e., by regulating the pressure in the control chamber 20. For this purpose, an outlet throttle 16 is formed in the valve piece 7, which opens into a low-pressure chamber 21 in the holding body 2. The low-pressure chamber 21 is always at a low fuel pressure via a return line (not shown), but is always completely filled with fuel.

[0012] The outlet throttle 16 is opened or closed by a control valve 22. The control valve 22 comprises a magnet armature 23 on which an armature plate 24, a guide section 28, and a closing element 25 are formed. The magnet armature 23 extends through a bore 27 formed in the valve clamping screw 8. An armature spring 34 exerts a closing force on the magnet armature 23 in the direction of a conical control valve seat 26 formed on the valve piece 7. In this exemplary embodiment, the closing element 25 is spherical and interacts with the conical control valve seat 26 to open and close the outlet throttle 16. The electromagnet 30, which comprises a coil 31 and a magnetic core 32, serves to move the magnet armature 23.When the electromagnet 30 is energized, it exerts a magnetic force of attraction on the magnet armature 23 and pulls it away from the control valve seat 26 against the force of the preloaded armature spring 34, so that the outlet throttle 16 opens and a connection is established between the control chamber 20 and the low-pressure chamber 21. Fuel present in the control chamber 20 then flows into the low-pressure chamber 21, so that the pressure in the control chamber 20 drops slightly and the valve needle 10, driven by the hydraulic pressure in the pressure chamber 5, is pushed away from the nozzle seat 12, opening the connection between the pressure chamber 5 and the blind hole 14 or the injection openings 13. If the fuel injection is to be stopped, the current supply to the electromagnet 30 is stopped and the armature spring 34 pushes the magnet armature 23 back into its closed position, in which the closing element 25 closes the outlet throttle 16 again.The fuel flowing into the control chamber 20 via the inlet throttle 15 increases the pressure to the pressure level of the pressure chamber 5, so that the nozzle needle 10 is pushed back into its closed position.

[0013] Figure 2 shows another fuel injector known from the prior art, whereby only the area of ​​the control valve is shown in longitudinal section. The other areas of the fuel injector are shown in the illustration of the Figure 1. The magnet armature 23 has a guide section 28 which is tightly guided in the bore 27 formed in the valve clamping screw 8. The radial play in the bore 27 is selected to be very small in order to prevent any misalignment or angular misalignment of the magnet armature 23. The bore 27 and the guide section 28 must be manufactured with great precision in order to ensure good guidance on the one hand and to prevent unnecessary wear on the other, which would impair the service life of the control valve 22. The control valve seat 26 is Figure 2 shown embodiment is designed as a flat seat and accordingly the closing element 25 has a flat sealing surface with which it interacts with the flat control valve seat 26.

[0014] In Figure 3The effect of an angular misalignment of the magnet armature 23 is shown. If an angular misalignment of the magnet armature 23 occurs due to manufacturing tolerances or thermal expansions that can occur in the fuel injector, the guide section 28 in the bore 27 is subjected to a tilting moment, which is represented by the forces F and the corresponding arrows in the Figure 3Such a misalignment by an angle α, which is shown extremely enlarged here for the sake of clarity, causes a one-sided load on the guide section 28 and thus a point-like contact of the guide section 28 of the bore 27. This leads to increased wear at the corresponding points and thus to a reduced service life of the control valve 22. To seal the outlet throttle 16, a closing element 25 rotatably mounted in the receptacle is required. A similar situation can also occur with a spherical closing element 25 and a conical control valve seat 26, as in Figure 4shown. Since the position of the spherical sealing element 25 is determined by the conical control valve seat 26, in addition to the angular deviation, position compensation between the armature guide and the valve seat must also be enabled to ensure the tightness of the control valve. This is achieved here by a parting plane between the guide body 29 and the guide section 28 of the magnet armature 23.

[0015] In Figure 5A control valve not according to the invention is shown. The magnet armature 23 is essentially plate-shaped and has a flat upper side 123 facing the electromagnet 30. Opposite the flat upper side 123, a likewise flat lower side 223 is formed on the magnet armature 23, which interacts with the control valve seat 26 designed as a flat seat. The magnet armature 23 is guided on its outer side in a sleeve 17, which determines the distance between the electromagnet 30 or the magnetic core 32 and the valve clamping screw 8. The guide play d is in this case relative to the guide in a bore, as in the case of the Figure 1In the embodiment shown, the gap is relatively large, for example, 0.1 mm or slightly less. This ensures, on the one hand, adequate guidance of the magnet armature 23 in the sleeve 17, and, on the other hand, allows the fuel to flow freely between the top side 123 and the bottom side 223 so as not to impede the movement of the magnet armature 23. To further facilitate this fuel flow, it may also be provided to introduce bores into the magnet armature 23 that connect the top side to the bottom side.

[0016] Figure 5also shows an angular misalignment of the magnet armature 23 with respect to the longitudinal axis or the underside of the electromagnet 30, whereby the angle is drawn significantly larger than it actually is for the sake of clarity. If the electromagnet 30 is switched on in this embodiment, the magnetic force draws the magnet armature 23 into contact with the magnet core 32 and lies flat against it. Any angular misalignment by the angle α, as shown here, is compensated for because the magnet armature 23 always lies flat against the magnet core 32. When the current supply is discontinued, the armature spring 34 presses the magnet armature 23 back onto the flat control valve seat 26, whereby the angular misalignment can be compensated for again. The stroke h of the magnet armature 23 is relatively small, for example 0.1 mm.

[0017] In Figure 6Another embodiment of a control valve is shown, not according to the invention. The magnet armature 23 does not have a flat surface parallel to the top on its underside, but rather a spherical closing element 25 that interacts with a conical control valve seat 26, as already shown in Figure 1 is shown. Since the magnet armature 23 has a relatively large radial play in the sleeve 17, the magnet armature 23 is centered by the closing element 25 so that it always returns to its central position without the need for additional guide elements.

[0018] Figure 7shows an inventive embodiment of a control valve with a flat seat, i.e. the closing element 25' interacts with a flat control valve seat 26. The closing element 25' is designed here as a cylindrical component, whereby the demands on the magnet armature with regard to wear are reduced. This allows the material of the magnet armature 23 to be optimized with regard to the magnetic properties with reduced demands on mechanical stability and thus with greater design freedom. Further improvements can be achieved by manufacturing the sleeve 17, the closing element 25' and the upper stroke stop from material that is not or only slightly magnetizable. The upper stroke stop is realized here in the form of a disk 36 which is clamped between the sleeve 17 and the magnet core 32 and against which the armature plate 24 rests when the control valve is in the open position.

Claims

1. Fuel injector for injecting fuel at high pressure, having a housing (1) in which there is arranged a longitudinally displaceable nozzle needle (10) which, by way of a sealing surface (11), opens and closes one or more injection openings (13) via which the fuel can be ejected, and having a control chamber (20) which is fillable with fuel and exerts a hydraulic force on the nozzle needle (10) in the closing direction thereof, and having a control valve (22) by way of which the pressure in the control chamber (20) can be influenced in that the control valve (22) opens and closes a hydraulic connection of the control chamber (20) to a low-pressure chamber (21), wherein the control valve (22) comprises a magnet armature (23) with an armature disc (24), wherein the magnet armature (23) interacts with a control-valve seat (26) for the purpose of opening and closing the hydraulic connection, wherein the magnet armature (23) is guided radially in the housing (1) only at the outer side (33) of the armature disc (24), and the fuel injector is characterized in that a cylindrical closing element (25') is formed on the magnet armature (23), wherein the closing element (25') interacts with the control-valve seat (26) and the control-valve seat (26) is formed as a flat seat, and the closing element (25') is made of a material which is non-magnetizable or is magnetizable only to a small degree.

2. Fuel injector according to Claim 1, characterized in that the magnet armature (23) is of rotationally symmetrical form.

3. Fuel injector according to Claim 1 or 2, characterized in that the spacing between the outer edge (33) of the armature disc (24) and the housing (1) is dimensioned such that, perpendicular to its direction of movement, the armature disc (24) is not deflectable from its central position by more than 0.15 mm (d) in any direction.

4. Fuel injector according to Claim 1, characterized in that the magnet armature (23) is loaded by an armature spring (34) in its closing direction in the direction of the control-valve seat (26).

5. Fuel injector according to Claim 1, characterized in that the top side (123), facing towards the electromagnet (30), of the magnet armature (23) is of flat form.

6. Fuel injector according to Claim 5, characterized in that the bottom side (223), opposite the top side (123) and facing towards the control-valve seat (26), of the magnet armature (23) is formed to be flat and parallel to the top side (123).

7. Fuel injector according to one of Claims 1 to 6, characterized in that the maximum travel (h) of the magnet armature (23) is less than or equal to 0.1 mm.

8. Fuel injector according to one of Claims 1 to 7, characterized in that some or all the components (7; 17; 36) which limit the movement of the magnet armature (23) consist of material which is non-magnetizable or is magnetizable only to a small degree.