EP4090844B1 - Needle stroke switch and fuel injector having such a needle stroke switch - Google Patents

Description

The present invention relates to a needle lift switch and a fuel injector with such a needle lift switch.

In internal combustion engines such as diesel engines or gasoline engines, fuel is usually injected into a combustion chamber in a certain amount and for a certain period of time via an injector. Due to the very short injection times, which are in the microsecond range, it is necessary to open or close the outlet opening of the injector at a very high frequency. In order to precisely control these closing times and to accurately detect an injector state, it is necessary to provide an injector state detection so that a higher-level control unit receives all the information about an individual injector, in particular information regarding its closing or opening times.

Such an injector typically has a nozzle needle (also: injector needle), which allows high-pressure fuel to escape to the outside when an outlet hole in the injector is released. In interaction with this outlet opening, this nozzle needle acts like a plug allows fuel to escape when lifted. It is therefore necessary to lift this needle at relatively short intervals and to allow it to slide back into the outlet opening after a short time. Hydraulic servo valves can be used to trigger this movement. Such valves, in turn, are controlled using an electromagnet. Alternatively, a piezo element can be used that reacts faster than the valve controlled by an electromagnet.

Due to the high injection pressures of over 2500 bar, it is not possible to control or move the nozzle needle directly using a solenoid valve. The force required to open and close the nozzle needle would be too great, so that such a process could only be implemented using very large electromagnets. However, such a construction is not possible due to the limited installation space available in an engine.

Typically, instead of direct control, so-called servo valves are used, which control the nozzle needle and are themselves controlled via an electromagnetic valve or piezo valve. In this case, in a control chamber that interacts with the nozzle needle, a pressure level is built up using the fuel available under high pressure, which acts on the nozzle needle in the closing direction. This control chamber or this control valve is typically connected to the high-pressure area of the fuel via an inlet throttle. Furthermore, this control room has a small, closable outlet throttle from which the fuel can escape to a low-pressure area. If he does this, the pressure in the control chamber and the closing force acting on the nozzle needle are reduced because the high-pressure fuel in the control chamber can flow away. This causes the nozzle needle to move, which opens the outlet opening at the injector tip. In order to be able to control the movement of the nozzle needle, the outlet throttle of the valve is either closed or opened using an anchor element.

Since the general principle of an injector for injecting fuel is known to those skilled in the art, the functionality of this component will not be discussed in more detail below.

As already briefly mentioned above, the injector state detection is of great importance for the controlled operation of the injector. With previous injectors it is not necessary or very complex to provide a seat plate of the injector, which is electrically separated from the injector housing and passes current through at certain points so that the control valve arranged underneath and the nozzle needle are connected to the injector coil arranged above it. However, the ability to pass an electrical signal through the seat plate is advantageous in terms of status detection, since when the injector is closed, an electrical circuit can be generated via which the contact of the nozzle needle in the nozzle needle seat of the injector. The prerequisite for this is of course that this electrical circuit is not already closed at another point, so that, among other things, the seat plate must be electrically insulated from the injector housing. The electrical circuit may only be closed via the nozzle needle and the nozzle needle seat.

The seat plate of the injector is therefore a component which, according to the invention, is used both as a contact element for passing through an electrical signal and at the same time must be insulated from the injector housing. Furthermore, the seat plate contains a passage running from top to bottom, which represents the outlet throttle of an injector. By placing an anchor element and sealing the passage, the control chamber underneath is filled with high-pressure fuel via an inlet, so that the nozzle needle is pushed into its closed position. When the anchor element is lifted from a through opening, the fuel stored under high pressure flows out and reduces the influence of force acting on the nozzle needle, so that it lifts off from its outlet openings and fuel can thereby flow out.

The detailed functionality of an injector can be found, for example, in DE 10 2017 116 383.2 reproduced.

So far it is known as disclosed in WO2019/141863A1 , to implement insulation of the seat plate using a DLC layer (DLC stands for "diamond-like carbon") attached to the seat plate, although it has been shown that the robustness of such a DLC layer is not sufficient for sophisticated injector concepts. Particularly when the seat plate is axially prestressed by means of a screw, improved robustness of the insulating layer is required.

Long-term tests have shown that these layers have a tendency to become electrically conductive under mechanical stress. This is due to their mechanical wear, so that continued electrical isolation cannot be guaranteed over the usual lifespan of an injector. It is therefore the aim of the present invention to create a needle lift switch that overcomes the disadvantage listed and can also be used with challenging injector concepts.

This is achieved with a needle lift switch for an injector according to claim 1. According to the invention it is provided that the needle lift switch for a fuel injector has a seat plate with a plate-like base body and a passage connecting the two flat sides of the plate-like base body, an anchor element which is connected to the passage the seat plate can be lifted off and placed thereon in a sealing manner, and comprises a control valve which is arranged on the side of the seat plate opposite the anchor element and is designed to interact with a nozzle needle, the seat plate being electrically insulated from an injector housing surrounding it and having an electrical connection to it the injector housing can only be achieved via the nozzle needle that interacts with the seat plate. Furthermore, the needle lift switch is characterized in that at least one ceramic and/or plastic part contacting the seat plate is present to insulate the seat plate from the surrounding injector housing.

According to the invention it can further be provided that the at least one ceramic and/or plastic part is an all-ceramic part. Ceramic is dimensionally stable, particularly under high and pulsating pressure loads, and exhibits outstanding wear resistance.

Furthermore, according to the invention, the at least one ceramic and/or plastic part can be designed to be detachable from the seat plate. It is therefore clear that the ceramic and/or plastic part does not merely represent a coating of the seat plate but is a separate part from the seat plate.

According to an optional modification of the present invention, it can be provided that the nozzle needle base body is made of an electrically conductive material, for example a metal, and preferably the plastic and/or ceramic sleeve is made of an electrical insulator, which contains, for example, the components Al ₂ O ₃ , Zr ₂ O ₃ and/or Si ₃ Ni ₃ or consists of at least one of these components.

Zirconium oxide is particularly advantageous in use here because it has a very similar thermal expansion coefficient to steel and is therefore also well suited for press fittings. Due to the almost identical thermal expansion behavior, press fittings can also be realized for applications with high temperature fluctuations (e.g. in injection nozzles). Zirconium oxide is very tough compared to other ceramic materials and can therefore be used particularly advantageously in the event of sudden or pulsating stresses, such as those caused by pressure waves in the injector. Tribologically, zirconium oxide has clear advantages compared to aluminum oxide because it hardly causes any wear on the contact partners.

Furthermore, it can be provided according to the invention that the at least one ceramic and / or plastic part has a sleeve shape, in particular a ring shape or a cylindrical jacket shape, which is suitable for radially surrounding the seat plate, the seat plate preferably being inserted into the sleeve-shaped ceramic and / or plastic part in order to achieve radial centering of the seat plate and to form electrical insulation between the seat plate and the injector housing.

This sleeve-shaped ceramic and/or plastic part essentially serves to protect the current-carrying seat plate from direct electrical contact with the injector housing surrounding the seat plate. Contact with the injector housing should only take place via the nozzle needle and the nozzle needle seat that accommodates the nozzle needle when the injector is closed, in order to easily detect whether the injector is open or closed.

It can be provided that the sleeve-shaped ceramic and/or plastic part is firmly connected to the injector housing for radially surrounding the seat plate, preferably by a material or positive connection such as gluing or soldering.

According to a further development of the invention, it can be provided that the at least one ceramic and / or plastic part is a seat part that cooperates with the anchor element and can be placed sealingly on the passage of the seat plate, the seat part preferably having a cylindrical shape.

The seat part can have rounded corners for placing on the passage of the seat plate in order to avoid the edges breaking off, with the mass finishing process preferably being used to produce the rounded corners. Providing rounded corners is advantageous because it can prevent the edges from breaking off during operation.

Furthermore, the seat part can be a ceramic part, which is preferably produced by hot isostatic pressing. Ceramic also shows excellent wear resistance even when the fuel contains small solid particles that have an abrasive effect when flowing along the seat part achieve. In particular, when the injector injects fuel and the seat part is lifted from the passage of the seat plate, fuel flows out of the passage at a very high speed and comes into contact with the seat part.

Furthermore, it can be provided according to the invention that the seat part electrically insulates the seat plate from the anchor element and from an anchor guide of the anchor element.

A further advantageous development of the invention provides that the at least one ceramic and / or plastic part is a seat plate support, which is arranged on the flat side of the plate-like base body of the seat plate facing the anchor element, and the seat plate is supported by an anchor guide of the anchor element or the Injector housing electrically insulated.

It can be provided that the seat plate support rests on the flat side of the plate-like base body of the seat plate facing the anchor element and preferably has a ring shape.

The seat plate support prevents conductive contact from the anchor guide to the seat plate, so that it is electrically insulated from it.

The invention further relates to a fuel injector with a needle lift switch according to one of the preceding variants.

It can be provided that the fuel injector has an injector state detection, which detects an injector state of a closed injector based on a current flowing through the nozzle needle and injector housing.

The invention also includes an engine with a fuel injector according to one of the above variants.

Fig. 1:

eine schematische Darstellungen zum Erläutern des vorbekannten Stands der Technik,

Fig. 2:

eine schematische Darstellung der erfindungsgemäßen Vorrichtung, und

Fig. 3:

eine vergrößerte Darstellung eines erfindungsgemäßen Ausführungsbeispiels der vorliegenden Erfindung.

Further advantages, features and details of the invention become apparent from the following description of the figures. Show:

Fig. 1:

a schematic representation to explain the known prior art,

Fig. 2:

a schematic representation of the device according to the invention, and

Fig. 3:

an enlarged view of an inventive embodiment of the present invention.

Fig. 1 shows a partial sectional view of an injector 10 from the prior art. You can see the injector 10, which has a housing 14 in which several injector components are arranged. Essential to the function of the injector 10 are the injector needle 15, the valve formed by the armature 11 and seat plate 1 and the electromagnet 12, 13, which has a coil winding 16, an inner magnetic pole 12 and an outer magnetic pole 13. In addition, a recess is provided in the inner magnetic pole 12 for arranging the spring 17, which presses the anchor element 11 in the direction of the valve in order to close the outlet throttle of the valve in a fluid-tight manner when the electromagnet 12, 13 is de-energized.

If the electromagnet 12, 13 is activated, it pulls the anchor element 11 away from the valve with the help of magnetic force, so that high-pressure fuel can flow out of the passage 6 from a control chamber that can be closed by the valve. Since this reduces the pressure in the control chamber that acts on the injector needle 15, it can slide out of a closed position and enables fuel to be dispensed from the injector 10. However, if the electromagnet 12, 13 is put into a de-energized state, the magnetic force acting on the anchor element 11, so that the spring element 17 presses the anchor element 11 onto the outlet opening of the valve and seals the control chamber or the passage 6. This causes the pressure acting on the injector needle 15 to increase, causing it to return to its closed position is pressed. This means that fuel no longer flows out of the outlet opening of the injector 10.

Fig. 2 shows a sectional view of an injector 10 with a needle lift switch 20 according to the invention.

To insulate the seat plate 1, several parts made of ceramic and/or plastic are provided, each of which is in contact with the seat plate 1.

In order to protect the circumferential edge surface of the approximately plate-like seat plate 1 from electrically conductive contact with the injector housing, a sleeve-shaped ceramic and/or plastic part 3 is provided which surrounds the seat plate in the radial circumferential direction. The sleeve 3 can be firmly connected to the injector housing, in particular glued or soldered. In addition to electrical insulation, the sleeve 3 serves to radially center the seat plate 1.

Next to it is in Fig. 2 a seat part 4 can be seen, which preferably consists of ceramic (e.g. Al ₂ O ₃ or Si ₂ Ni ₃ ), and interacts with the anchor element 11 in such a way that it can close the passage 6 of the seat plate. If the anchor element 11 is pulled by the seat plate 1, the passage 6 of the seat plate 1 also opens and high-pressure fuel flows out, so that the pressure in the control chamber drops and the nozzle needle 15 lifts out of its nozzle needle seat comes.

In order to achieve electrical insulation of the seat plate from the anchor element 11, which is usually placed on the passage 6 of the seat plate 1, an insulating seat part 4 is now provided between the anchor element 11 and the seat plate. This generally cylindrical element can have rounded edges and must be checked for cracks due to the dynamic impacting stress. It is also advantageous if it is produced using hot isostatic pressing.

It is particularly advantageous for the seat part if it is made of ceramic, since ceramic has excellent wear resistance and is particularly durable against the abrasive effects of solid particles present in the fuel. Fuel flows at high speed at the underside of the seat part 4 if the injector is in its open position.

The seat part 4 electrically insulates the seat plate 1 from the anchor element 11 and the anchor guide or the injector housing.

A seat plate support 5 is shown as a further ceramic and/or plastic part, which separates the seat plate 1 from the anchor guide or the injector housing 14 on its side facing the anchor element 11.

Here too, due to the pulsating pressure stress, the seat plate support is advantageously made of ceramic. Ceramic remains dimensionally stable even under high pressure loads, so that deformation that changes the armature stroke setting cannot occur.

The seat plate support 5 is advantageously in a ring which has an inner diameter that is larger than the outer diameter of the seat part 4. Finally, both ceramic and/or plastic parts 4, 5 rest on the flat side of the seat plate 1 facing the anchor element 11.

Fig. 3 is an enlarged view Fig. 2 , from which you can see the ceramic and/or plastic parts particularly well.

Claims (15)

1. A needle stroke switch (20) for a fuel injector (10) comprising:

   a seat plate (1) having a plate-like base body and a passage (6) connecting the two areal sides of the plate-like base body;

   an armature element (11) that can be raised from the passage (6) of the seat plate (1) and can be sealingly placed thereon; and

   a control valve (2) that is arranged at the side of the seat plate (1) oppositely disposed the armature element (11) and that is adapted to cooperate with a nozzle needle (15), wherein

   the seat plate (1) is electrically insulated with respect to an injector casing (14) surrounding it; and wherein an electrical connection to the injector casing (14) can only be implemented via the nozzle needle (15) cooperating with the seat plate (1),

   characterized by

   at least one ceramic and/or plastic part (3, 4, 5) contacting the seat plate (1) to generate the insulation of the seat plate (1) with respect to the injector casing (14) surrounding it.
2. A needle stroke switch (20) in accordance with claim 1, wherein the at least one ceramic and/or plastic part (3, 4, 5) is an all-ceramic part.
3. A needle stroke switch (20) in accordance with one of the preceding claims, wherein the at least one ceramic and/or plastic part (3, 4 5) is designed releasably with the seat plate (1).
4. A needle stroke switch (20) in accordance with one of the preceding claims, wherein the at least one ceramic and/or plastic part (3, 4, 5) comprises the components Al₂O₃, Si₃Ni₃ and/or Zr₂O₃ or consists of at least one of these components.
5. A needle stroke switch (20) in accordance with one of the preceding claims, wherein the at least one ceramic and/or plastic part (3) has a sleeve shape, in particular an annular shape or a cylinder jacket shape, that is suitable to radially surround the seat plate (1), with the seat plate (1) preferably being inserted into the sleeve-like ceramic and/or plastic part (3) to achieve a radial centration of the seat plate (1) and to form an electrical insulation between the seat plate (1) and the injector casing (14).
6. A needle stroke switch (20) in accordance with claim 5, wherein the sleeve-like ceramic and/or plastic part (3) for the radial surrounding of the seat plate (1) is fixedly connected to the injector casing (3), preferably by a connection having material continuity or a form fit such as adhesive bonding or soldering.
7. A needle stroke switch (20) in accordance with one of the preceding claims, wherein the at least one ceramic and/or plastic part is a seat part (4) that interacts with the armature element (11) and can be sealingly placed on the passage (6) of the seat plate (1), with the seat part (4) preferably having a cylindrical shape.
8. A needle stroke switch (20) in accordance with claim 7, wherein the seat part (4) has rounded corners for placing on the passage (6) of the seat plate (1) to avoid the edges escaping, with the slide grinding method preferably being used to produce the rounded corners.
9. A needle stroke switch (20) in accordance with one of the preceding claims 7 or 8, wherein the seat part (4) is a ceramic part that is preferably produced by hot isostatic pressing.
10. A needle stroke switch (20) in accordance with one of the preceding claims 7 to 9, wherein the seat part (4) electrically insulates the seat plate (1) toward the armature element (11) and toward an armature guide of the armature element (11).
11. A needle stroke switch (20) in accordance with one of the preceding claims, wherein the at least one ceramic and/or plastic part is a seat plate support (5) that is arranged on the areal side of the plate-like base body of the seat plate (1) facing the armature element (11) and electrically insulates the seat plate (1) from an armature guide of the armature element (11) or the injector casing (14).
12. A needle stroke switch (20) in accordance with claim 11, wherein the seat plate support (5) lies on the areal side of the plate-like base body of the seat plate (1) facing the armature element (11) and preferably has an annular shape.
13. A fuel injector (10) having a needle stroke switch (20) in accordance with one of the preceding claims.
14. A fuel injector (10) in accordance with claim 13, wherein the fuel injector (10) has an injector state recognition that recognizes an injector state of a closed injector (10) with reference to a current flowing through the nozzle needle (15) and the injector casing (14).
15. An engine having a fuel injector (10) in accordance with claim 13 or claim 14.

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