Needle travel switch and fuel injector having the same

Abstract

The present invention relates to a needle travel switch and a fuel injector having such a needle travel switch. The needle travel switch for a fuel injector comprises: a seat plate having a plate-shaped base body and a channel connecting two flat sides of the plate-shaped base body; an armature element that can be lifted from the channel of the seat plate and seated thereon in a sealing manner; and a control valve that is arranged on the side of the seat plate opposite the armature element and is designed to cooperate with a nozzle needle. The seat plate is electrically insulated from an injector housing surrounding it and an electrical connection to the injector housing can be achieved solely via the nozzle needle cooperating with the seat plate. The needle travel switch is further characterized by at least one ceramic and / or plastic part that contacts the seat plate to provide insulation of the seat plate from the injector housing surrounding it.

Description

Technical Field

[0001] The present invention relates to a needle travel switch and a fuel injector having the needle travel switch. Background Art

[0002] In internal combustion engines, such as diesel or gasoline engines, fuel is typically injected into the combustion chamber via injectors in a defined amount and over a defined time period. Due to the extremely short injection cycles, typically in the microsecond range, the injector's output openings must be opened and closed very frequently. In order to accurately control these closing times and accurately detect the injector status, injector status detectors are required. This allows the higher-level control unit to obtain comprehensive information about the individual injectors, particularly regarding the closing and opening times.

[0003] Typically, such injectors have a nozzle needle (also called an injector needle) that allows the high-pressure fuel to escape from the injector's outlet opening when it is released. The nozzle needle interacts with the outlet opening like a plug, allowing the fuel to escape when it is lifted. Therefore, the needle must be able to lift in a relatively short period of time and then slide back into the outlet opening after a short time. A hydraulic servo valve can be used to trigger this movement. Such valves are in turn actuated by electromagnets. Alternatively, a piezoelectric element can be used, which responds more quickly than valves actuated by electromagnets.

[0004] Due to the high injection pressures exceeding 2500 bar, it is not possible to directly control or move the nozzle needle using a solenoid valve. The forces required to open and close the nozzle needle would be too great, so this approach can only be implemented using very large electromagnets. However, due to the limited available installation space, this design is not considered in engines.

[0005] Typically, instead of direct actuation, a so-called servo valve is used. This valve actuates the nozzle needle and is itself controlled by a solenoid valve, or more precisely, a piezoelectric valve. In a control chamber interacting with the nozzle needle, a pressure level acting on the nozzle needle in the closing direction is established using available fuel at high pressure. This control chamber, or more precisely, a control valve, is typically connected to the high-pressure fuel area via an intake throttle. Furthermore, this control chamber has a small, closable exhaust throttle, from which fuel can escape toward the low-pressure area. When fuel escapes, the pressure in the control chamber and the closing force acting on the nozzle needle decrease because the fuel in the high-pressure control chamber can flow out. This causes the nozzle needle to move, which releases the outlet opening at the injector tip. Therefore, to control the movement of the nozzle needle, the exhaust throttle of the valve is selectively closed or opened using an armature element.

[0006] Since the general principles of injectors for injecting fuel are known to a person skilled in the art, the functionality of these components will not be explained in detail below.

[0007] As briefly mentioned above, injector status detection is crucial for controlled operation of the injector. Previously, it was unnecessary or extremely costly to provide an injector seat plate that was electrically isolated from the injector housing and directed the current at a specific location, connecting the control valve and nozzle needle, located below the seat plate, to the injector coil, located above the seat plate. However, the ability to route electrical signals through the seat plate is advantageous for status detection because it allows an electrical circuit to be established when the injector is closed, through the contact of the nozzle needle in the injector's nozzle needle seat. This, of course, presupposes that this circuit is not short-circuited at another location, necessitating the seat plate to be electrically insulated from the injector housing. Closing this circuit solely through the nozzle needle and nozzle needle seat is permitted.

[0008] Accordingly, the seat plate of the injector is a component that, according to the present invention, not only serves as a contact element for conducting electrical signals but also must be insulated from the injector housing. Furthermore, the seat plate contains a channel extending from top to bottom, which forms the exhaust throttle of the injector. The armature element seats down and seals this channel, and the control chamber located below is filled with high-pressure fuel via the intake port, thereby pressing the nozzle needle into its closed position. When the armature element is lifted from the passage opening, the high-pressure stored fuel flows out, and the force acting on the nozzle needle is reduced, causing the nozzle needle to lift from its outlet opening, allowing fuel to flow out.

[0009] A more detailed description of the operating principle of an injector is given, for example, in DE 10 2017 116 383.2.

[0010] Previously, it was known to insulate the base plate using a DLC layer (DLC stands for "diamond-like carbon") applied to the base plate. However, such DLC layers have proven insufficiently stable for demanding injector concepts. In particular, when the base plate is axially preloaded using screws, greater stability of the insulation layer is required.

[0011] Endurance tests have shown that this layer has a tendency to become electrically conductive under mechanical load, which is attributed to mechanical wear of the layer, so that continuous electrical insulation cannot be guaranteed over the typical service life of the injector. Summary of the Invention

[0012] The object of the present invention is therefore to create a needle travel switch which eliminates the aforementioned disadvantages and can also be used in challenging injector concepts.

[0013] This is achieved by means of a needle travel switch for the injector.

[0014] According to the present invention, a needle travel switch for a fuel injector comprises: a seat plate having a plate-shaped base body and a channel connecting two flat sides of the plate-shaped base body; an armature element that can be lifted from the channel of the seat plate and sealably seated on the seat plate; and a control valve that is arranged on the side of the seat plate opposite the armature element and is designed to cooperate with a nozzle needle. The seat plate is electrically insulated from an injector housing surrounding the seat plate, and an electrical connection to the injector housing can be achieved solely via the nozzle needle cooperating with the seat plate. The needle travel switch is further characterized by at least one ceramic and / or plastic part that contacts the seat plate to provide insulation of the seat plate from the injector housing surrounding the seat plate.

[0015] According to the invention, it can further be provided that at least one ceramic part and / or plastic part is a solid ceramic part. The ceramic is therefore dimensionally stable, especially under high and even pulsed pressure loads, and exhibits outstanding wear resistance.

[0016] In addition, according to the present invention, at least one ceramic part and / or plastic part can be designed to be separable relative to the seat plate. Accordingly, it is obvious that the ceramic part and / or plastic part does not just represent a coating of the seat plate, but is an independent component relative to the seat plate.

[0017] According to an optional improvement of the invention, it can be provided that the nozzle needle base body is made of an electrically conductive material, for example metal, and preferably the ceramic sleeve and / or the plastic sleeve consists of an electrical insulator, which for example includes the components Al2O3, Zr2O3 and / or Si2Ni3, or consists of at least one of these components.

[0018] Zirconium oxide is particularly advantageous here because it has a coefficient of thermal expansion very similar to that of steel and is therefore also well-suited for press compounds. The nearly identical thermal expansion properties also allow the use of these press compounds in applications with high temperature fluctuations (e.g., in injection nozzles). Compared to other ceramic materials, zirconium oxide is very hard and can therefore be used particularly advantageously under impact or pulsed loads (e.g., caused by pressure waves in injectors). Compared to aluminum oxide, zirconium oxide offers significant tribological advantages because it causes virtually no wear on the contact partners.

[0019] Furthermore, according to the invention, it can be provided that at least one ceramic and / or plastic part has a sleeve-like shape, in particular an annular or cylindrical sleeve-like shape, which is suitable for radially surrounding the seat plate, wherein the seat plate is preferably inserted into the sleeve-like 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.

[0020] 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 it. In order to easily detect whether the injector is open or closed, contact with the injector housing should only occur via the nozzle needle and the nozzle needle seat that accommodates the nozzle needle when the injector is closed.

[0021] In this case, it can be provided that a sleeve-shaped ceramic and / or plastic part for radially surrounding the seat plate is fixedly connected to the injector housing, preferably by a material or form-fitting connection, for example adhesive bonding or welding.

[0022] According to another development of the invention, it can be provided that the at least one ceramic and / or plastic part is a seat part which cooperates with the armature element and is seated sealingly on the channel of the seat plate, wherein the seat part preferably has a cylindrical shape.

[0023] In order to seat on the channel of the seat plate, the seat part can have rounded corners to avoid edge fractures, wherein the rounded corners can preferably be processed by a smooth grinding method. The reason why the rounded corners are provided is advantageous because they can avoid edge fractures during operation.

[0024] Furthermore, the seat element can be a ceramic element, preferably produced by hot isostatic pressing. Furthermore, ceramic also exhibits outstanding wear resistance when the fuel contains small solid particles, which have an abrasive effect as it flows along the seat element. In particular, when the injector injects fuel and the seat element is lifted from the channel in the seat plate, the fuel flows out of the channel at a very high velocity and comes into contact with the seat element.

[0025] Furthermore, according to the invention, it can be provided that the seat part electrically insulates the seat plate with respect to the armature element and with respect to the armature guide of the armature element.

[0026] Another advantageous development of the invention provides that at least one ceramic and / or plastic part is a seat plate support part, which is arranged on the surface side of the plate-shaped base body of the seat plate facing the armature element and the seat plate is electrically insulated from the armature guide device of the armature element or more precisely the injector housing.

[0027] In this case, it can be provided that the seat plate support is located on the flat side of the plate-shaped basic body of the seat plate facing the armature element and preferably has an annular shape.

[0028] The base plate support prevents the armature guide from electrically conductively contacting the base plate, so that the armature guide is electrically insulated relative to the base plate.

[0029] Furthermore, the invention relates to a fuel injector having a needle travel switch according to one of the above-mentioned variants.

[0030] In this case, it can be provided that the fuel injector has an injector state recognition device which recognizes the injector state of the closed injector based on the flow rate through the nozzle needle and the injector housing.

[0031] Furthermore, the invention comprises an engine having a fuel injector according to any of the above variants. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Further advantages, features and details of the present invention can be obtained from the following description of the drawings, in which:

[0033] Figure 1 A schematic diagram for explaining the known prior art is shown.

[0034] Figure 2 shows a schematic diagram of an apparatus according to the invention, and

[0035] Figure 3 An enlarged view of an embodiment of the invention according to the invention is shown. DETAILED DESCRIPTION

[0036] Figure 1 A partial cross-section of an injector 10 from the prior art is shown. The injector 10 can be seen, which has a housing 14 in which several injector components are arranged. Essential for the function of the injector 10 are the injector needle 15, the valve formed by the armature 11 and the seat plate 1, and the electromagnets 12, 13 with the coil winding 16, the inner magnetic pole 12, and the outer magnetic pole 13. Furthermore, a recess is provided in the inner magnetic pole 12 for accommodating a spring 17, which presses the armature element 11 toward the valve in order to fluid-tightly close the exhaust throttle of the valve when the electromagnets 12, 13 are not energized.

[0037] If electromagnets 12 and 13 are activated, they use electromagnetic force to pull armature element 11 away from the valve, allowing high-pressure fuel to flow from the control chamber, which is closable by the valve, through channel 6. Because the pressure in the control chamber acting on injector needle 15 is reduced, the injector needle can slide out of the closed position, allowing fuel to be discharged from injector 10. Conversely, if electromagnets 12 and 13 are de-energized, the magnetic force acting on armature element 11 decreases, causing spring element 17 to press armature element 11 against the valve outlet opening and seal the control chamber or channel 6. This increases the pressure acting on injector needle 15, forcing it back into its closed position. Consequently, fuel no longer flows out of the outlet opening of injector 10.

[0038] Figure 2 A cross-sectional view of an injector 10 is shown having a needle travel switch 20 according to the invention.

[0039] In order to insulate the seat plate 1 , a plurality of components made of ceramic and / or plastic are provided, wherein each component is in contact with the seat plate 1 .

[0040] To protect the circumferential edge of the approximately plate-shaped seat plate 1 from electrically conductive contact with the injector housing, a sleeve-shaped ceramic and / or plastic part 3 is provided that radially surrounds the seat plate. This sleeve 3 can be fixedly connected to the injector housing, in particular, by adhesive bonding or welding. Besides electrical insulation, this sleeve 3 also serves to radially center the seat plate 1.

[0041] In addition, Figure 2 The seat part 4 can be seen in the figure, which is preferably made of ceramic (for example Al2O3 or Si2Ni3) and interacts with the armature element 11 in such a way that it can close the channel 6 of the seat plate. If the armature element 11 is pulled away from the seat plate 1, the channel 6 of the seat plate 1 is opened and the high-pressure fuel can flow out, so that the pressure in the control chamber drops and the nozzle needle 15 is lifted from its nozzle needle seat.

[0042] To electrically insulate the seat plate from the armature element 11 (which typically sits on the channel 6 of the seat plate 1), an insulating seat part 4 is now provided between the armature element 11 and the seat plate. This generally cylindrical element may have rounded edges and, due to dynamic, impact-like loads, must be checked for crack-free conditions. Furthermore, it is advantageous to produce this element by hot isostatic pressing.

[0043] It is particularly advantageous for the seat part to be made of ceramic, since ceramic has excellent wear resistance and is also able to withstand the abrasive effects of solid particles present in the fuel. Thus, the fuel flows at high speed through the underside of the seat part 4 when the injector is in its open position.

[0044] The seat part 4 electrically insulates the seat plate 1 from the armature element 11 and from the armature guide or, more precisely, the injector housing.

[0045] A seat plate support 5 is shown as a further ceramic and / or plastic part, which separates the seat plate 1 on its side facing the armature element 11 from the armature guide or, more precisely, the injector housing 14 .

[0046] Due to the pulsating pressure loads, it is also applicable here that the seat support is advantageously made of ceramic. Ceramics also remain dimensionally stable under high pressure loads, so that no deformation that changes the lifting state of the armature can occur.

[0047] Advantageously, the seat plate support 5 is in the form of a ring having a larger inner diameter than the outer diameter of the seat part 4. Finally, the two ceramic and / or plastic parts 4, 5 rest on the side of the seat plate 1 facing the armature element 11.

[0048] Figure 3 yes Figure 2 The enlarged image from Figure 3 The ceramic and / or plastic parts can be seen particularly clearly.

Claims

1. A needle travel switch (20) for a fuel injector (10), comprising: A seat plate (1) having a plate-shaped base body and a channel (6) connecting two flat sides of the plate-shaped base body; an armature element (11) which can be lifted from the channel (6) of the seat plate (1) and can be seated sealingly on the seat plate (1); as well as A control valve (2) is arranged on the side of the seat plate (1) opposite the armature element (11) and is designed to cooperate with a nozzle needle (15), wherein: The seat plate (1) is electrically insulated from the surrounding injector housing (14) and can be electrically connected to the injector housing (14) only via a nozzle needle (15) cooperating with the seat plate (1). It is characterized by At least one ceramic and / or plastic part (3, 4, 5) contacts the seat plate (1) in order to produce insulation of the seat plate (1) relative to the injector housing (14) surrounding it.

2. The needle travel switch (20) according to claim 1, wherein The at least one ceramic part (3, 4, 5) is a solid ceramic part.

3. The needle travel switch (20) according to any one of the preceding claims, wherein The at least one ceramic and / or plastic part (3, 4, 5) is embodied so as to be separable from the seat plate (1).

4. The needle travel switch (20) according to claim 1 or 2, wherein: The at least one ceramic component (3, 4, 5) comprises the components Al2O3, Si2Ni3 and / or Zr2O3.

5. The needle travel switch (20) according to claim 1 or 2, wherein: The at least one ceramic and / or plastic part (3) has a sleeve shape suitable for radially surrounding the seat plate (1).

6. The needle travel switch (20) according to claim 5, wherein: A sleeve-shaped ceramic and / or plastic part (3) for radially surrounding the seat plate (1) is fixedly connected to the injector housing (14).

7. The needle travel switch (20) according to claim 1 or 2, wherein: The at least one ceramic and / or plastic part is a seat part (4) which cooperates with the armature element (11) and can be seated sealingly on the channel (6) of the seat plate (1).

8. The needle travel switch (20) according to claim 7, wherein: The seat part (4) has rounded corners in order to sit on the channel (6) of the seat plate (1) to avoid edge breakage.

9. The needle travel switch (20) according to claim 7, wherein: The seat component (4) is a ceramic component.

10. The needle travel switch (20) according to claim 7, wherein: The seat part (4) electrically insulates the seat plate (1) relative to the armature element (11) and relative to the armature guide of the armature element (11).

11. The needle travel switch (20) according to claim 1 or 2, wherein: The at least one ceramic and / or plastic part is a seat plate support part (5), which is arranged on the surface side of the plate-shaped base body of the seat plate (1) facing the armature element (11), and the seat plate (1) is electrically insulated from the armature guide device of the armature element (11) or the injector housing (14).

12. The needle travel switch (20) according to claim 11, wherein: The seat plate support (5) is located on the surface side of the plate-shaped base body of the seat plate (1) facing the armature element (11).

13. The needle travel switch (20) according to claim 5, wherein: The at least one ceramic and / or plastic part (3) has an annular shape suitable for radially surrounding the seat plate (1).

14. The needle travel switch (20) according to claim 5, wherein The seat plate (1) is inserted into the sleeve-shaped ceramic part and / or plastic part (3) to achieve radial centering of the seat plate (1) and form electrical insulation between the seat plate (1) and the injector housing (14).

15. The needle travel switch (20) according to claim 7, wherein: The seat component (4) has a cylindrical shape.

16. The needle travel switch (20) according to claim 8, wherein To produce the rounded corners, a smooth grinding method is used.

17. The needle travel switch (20) according to claim 9, wherein The ceramic piece is produced by hot isostatic pressing.

18. The needle travel switch (20) according to claim 12, wherein: The seat plate support member (5) has a ring shape.

19. A fuel injector (10) having a needle travel switch (20) according to any one of the preceding claims.

20. The fuel injector (10) of claim 19, wherein: The fuel injector (10) has an injector state recognition device that recognizes the injector state of the closed injector (10) based on the flow rate through the nozzle needle (15) and the injector housing (14).

21. An engine having a fuel injector (10) according to claim 19 or 20.

Images