Fuel injector for gaseous or liquid fuels

Abstract

The invention relates to a fuel injector for gaseous or liquid fuels with a housing (1), in which a longitudinally movable valve needle (7) is arranged which interacts with a valve seat (10) in order to open and close a flow cross section (11), wherein to open the flow cross section (11) the valve needle (7) carries out an outward opening movement out of the housing (1). The valve needle (7) is at least partially surrounded by a lubricant chamber (26) which is separated from the fuel chamber (5) by a corrugated bellows (25) which surrounds the valve needle (7), wherein the end portion of the corrugated bellows (25) facing the valve seat (10) is connected to the valve needle (7) in a fluid-tight manner at a sealing point (27). A preloaded closing spring (30) which urges the valve needle (7) in a closing direction is arranged between the valve seat (10) and the sealing point (27).

Description

[0001] title

[0002] Fuel! Injector for gaseous or liquid fuels

[0003] The invention relates to a fuel injector, as it is used in particular to meter gaseous or liquid fuels into a combustion chamber or an intake tract of an internal combustion engine.

[0004] State of the art

[0005] In internal combustion engines powered by gaseous or liquid fuel, the fuel is metered either directly into the combustion chamber or into the engine's intake tract. The fuel injectors used for this purpose have a movable valve element that interacts with a valve seat to open and close a flow cross-section. The movement of the valve element is precisely controlled by an electrical actuator, such as an electromagnet or a piezo actuator, to adapt the amount and timing of fuel delivery to the current requirements of the internal combustion engine. Because the valve element is mounted on a movable bearing, friction occurs, so the valve element bearings must be lubricated for a long service life.Since gaseous and many liquid fuels lack a lubricating effect, it is known to create a lubricant chamber in the fuel injector and fill it with a lubricant, such as mineral oil. This lubricant chamber is sealed against the fuel to prevent contamination of the fuel with lubricant. Such a fuel injector is known, for example, from DE 10 2022 206 220 A1.

[0006] The lubricant chamber in these fuel injectors is defined, among other things, by a corrugated bellows surrounding the valve element, which is shaped like a piston-shaped valve needle. Since the fuel injector is designed to be as narrow as possible due to the limited installation space in the internal combustion engine, the valve needle must be correspondingly long. The production of a long valve needle incurs high costs due to complex machining and the tolerances that must be maintained. Furthermore, it is highly sensitive to transverse forces acting on the valve needle due to manufacturing tolerances or thermal expansion.

[0007] Advantages of the invention

[0008] The fuel injector according to the invention has the advantage that the piston-shaped valve needle is less sensitive to transverse forces, thus enabling robust and cost-effective production of the fuel injector. For this purpose, the fuel injector for gaseous or liquid fuels has a housing in which a longitudinally movable valve needle is arranged. The valve needle interacts with a valve seat to open and close a flow cross-section, wherein the valve needle executes an opening movement directed out of the housing to open the flow cross-section. A lubricant chamber is formed in the housing, which surrounds at least part of the valve needle and is separated from a fuel chamber by a corrugated bellows surrounding the valve needle, wherein the corrugated bellows is connected to the valve needle in a fluid-tight manner at a sealing point at its end section facing the valve seat.A pre-tensioned closing spring is arranged between the valve seat and the sealing point, which acts on the valve needle in a closing direction.

[0009] The closing spring presses the valve needle with a sealing surface against the valve seat through its preload. Since the closing spring is arranged between the corrugated bellows and the valve seat, the closing force is applied to the valve needle close to the valve seat. This allows the use of a multi-part valve needle, with the individual valve needle sections abutting one another with their end faces. In particular, one valve needle section, on which the sealing surface that interacts with the valve seat is formed, can extend into the corrugated bellows. There it rests against a second valve needle section, which also transfers the opening force to the first valve needle section. In this way, the function of the valve needle and the application of closing and opening forces can be implemented in a simple manner, avoiding the need for a long and therefore expensive valve needle.In a first advantageous embodiment, the closing spring surrounds the valve needle. The closing spring can, for example, be in the form of a helical compression spring. This allows for a symmetrical application of force to the valve needle.

[0010] In a further advantageous development of the invention, the valve needle is constructed in several parts and consists of at least two piston-shaped valve needle sections, wherein the valve needle sections abut one another with their end faces at a separation point. This allows several shorter sections to be manufactured, which is simpler in terms of production technology and can also be used to achieve angle compensation between the individual valve needle sections. Advantageously, the first valve needle section, which interacts with the valve seat, projects into the corrugated bellows and there abuts the second valve needle section at the first separation point. The separation point is thus within the corrugated bellows and thus in the lubricant chamber, so that wear at the first separation point can be minimized. Advantageously, the end face of one of the valve needle sections is convexly curved.The convex end face is preferably designed as a spherical section that rests against the end face of the other valve needle section along an annular line. This allows for angle compensation between the two valve needle sections. The spherical section advantageously contacts the opposite end face at two points when viewed in longitudinal section, with the angle formed by the two contact points and the center of the spherical section being between 20 and 120 degrees. This angle allows for optimized force transmission without compromising the stability of the valve needle.

[0011] In a further advantageous embodiment, the end face of the adjoining valve needle section adjacent to the convex end face is concavely curved inward. This prevents the valve needle sections from sliding off their end faces. Advantageously, one of the end faces can be conical, and the adjacent end face of the opposite valve needle section can be shaped like a spherical segment or also conical.

[0012] In a further advantageous embodiment, the closing spring is arranged under compressive preload between a contact surface in the housing and a clamping ring, with the clamping ring surrounding the valve needle and being firmly connected to the valve needle. This allows for a symmetrical application of force from the closing spring to the valve needle, thus ensuring a secure seal at the valve seat.

[0013] drawing

[0014] The drawing shows a fuel injector according to the invention. Fig. 1 shows a longitudinal section through such a fuel injector, with only the parts of the fuel injector essential to the invention being shown, and

[0015] Fig. 2 is an enlarged view of the section marked II in Fig. 1.

[0016] Description of the embodiments

[0017] Fig. 1 shows a fuel injector according to the invention in longitudinal section, as it is used for injecting gaseous or liquid fuel into a combustion chamber or into an intake tract of an internal combustion engine. For the sake of clarity, the fuel injector is only shown in its essential components. The fuel injector has a housing 1 which comprises a valve body 2, a valve tube 3 and a nozzle body 4. These parts of the housing 1 are tightly connected to one another to prevent fuel from escaping. The valve tube 3 is essentially tubular and is connected at one end to the nozzle body 4, which forms the combustion chamber-side end of the fuel injector or of the housing 1. The opposite end section of the valve tube 3 projects into the valve body 2 and is likewise connected to it in a gas-tight manner.The end of the valve tube 3 facing away from the nozzle body 4 is received in a magnetic body 20 which is arranged within the valve body 2 and between which and the valve body 2 an annular space 14 is formed.

[0018] A fuel chamber 5 is formed inside the valve body 2 and the valve tube 3, which is filled with a gaseous or liquid fuel during operation. Furthermore, a piston-shaped valve needle 7 is arranged longitudinally displaceably in the fuel chamber 5. The valve needle 7 comprises a first valve needle section 107, a second valve needle section 207, and a third valve needle section 307, all of which are essentially piston-shaped. The first valve needle section 107 is guided in a guide bore 16 of the valve tube 3 and, at its end facing the combustion chamber, forms a valve disk 17 that protrudes from the nozzle body 4. On the outer edge of the valve disk 17, an annular sealing surface 9 is formed, which interacts with a valve seat 10 at the end of the nozzle body 4 to open and close a flow cross-section 11, through which fuel can flow out of the fuel chamber 5.In the area of ​​the guide bore 16, several bores 12 are formed in the valve tube 3, which ensure the flow of the gaseous or liquid fuel in the fuel chamber 5 in the direction of the valve seat 10.

[0019] The first valve needle section 107 rests against the second valve needle section 207 at a first separation point 8. The second valve needle section 207 is guided in a guide body 15 at its end facing away from the first separation point 8 and is surrounded by a corrugated bellows 25, so that a lubricant chamber 26 is formed between the second valve needle section 207 and the corrugated bellows 25. At its end facing away from the first valve needle section 107, the second valve needle section 207 rests against the third valve needle section 307 at a second separation point 18. The third valve needle section 307, which forms the end of the valve needle 7 facing away from the nozzle body 4, is connected at its end to a magnet armature 23, which is movably arranged in the magnet body 20.Furthermore, an inner pool 21 and an electromagnet 22 are arranged in the magnet body 20 and surround the third valve needle section 307, so that by energizing the electromagnet 22, a longitudinal force can be exerted on the magnet armature 23 and thus also on the valve needle 7 in the direction of the nozzle body 4.

[0020] The corrugated bellows 25 is attached at one end to a support ring 28, which is attached to the first valve needle section 107, where it forms a sealing point 27, so that the lubricant chamber 26 is sealed. At its other end, the corrugated bellows 25 is also sealingly connected to the guide body 15. The lubricant chamber 26 delimited by the corrugated bellows 25 extends through the guide body 15 into the magnet body 20, so that the guide of the second valve needle section 207 in the guide body 15 and also the guides of the third valve needle section 307 are lubricated, as are the first separation point 8 and the second separation point 18. For this purpose, the lubricant chamber 25 is filled with lubricating oil, for example, and is thus sealed off from the fuel chamber 5 and the annular chamber 14 to prevent contamination of the fuel.

[0021] A closing spring 30 is arranged under compressive preload between the support ring 28 and a shoulder 19 on the guide bore 16. This closing spring is designed here as a helical compression spring and surrounds the first valve needle section 107. Since the support ring 28 is firmly connected to the valve needle 7, the closing spring 30 exerts a closing force on the valve plate 17 in the direction of the valve seat 10, so that the flow cross-section 11 is closed by the force of the closing spring 30 when the electromagnet 22 is not energized. The closing spring 30 also ensures that the three valve needle sections 107, 207, 307 are always pressed together at the separation points 8, 18 and do not separate.

[0022] The fuel is supplied via the annular space 14, which is formed between the magnet body 20 and the valve body 2. The fuel flows through the annular space 14 via several transverse bores 13 in the valve tube 3 into the fuel chamber 5 and further through the bores 12 to the valve seat 10.

[0023] The fuel injector functions as follows: If the electromagnet 22 is not energized, the valve needle 7 is pressed with the valve plate 17 against the valve seat 10 by the force of the pre-tensioned closing spring 30, thereby closing the flow cross-section 11 between the sealing surface 9 and the valve seat 10. If fuel is to be dispensed, the electromagnet 22 is energized and the magnet armature 23 is thereby pulled towards the valve body 2 against the force of the closing spring 30. As a result, the valve needle 7 and thus also the valve plate 17 move out of the nozzle body 4, opening up a flow cross-section 11 between the sealing surface 9 and the valve seat 10, through which fuel flows out of the fuel chamber 5.If the gas injection is to be ended, the current supply to the electromagnet 22 is interrupted, and the closing spring 30 presses the first valve needle section 107 and thus the entire valve needle 7 back into its closed position in contact with the valve seat 10. The first valve needle section 107 rests against the second valve needle section 207 at the first separation point 8. This area, designated II in Fig. 1, is shown again enlarged in Fig. 2. The second valve needle section 207 has an end face 207a which is convexly curved outwards, wherein the imaginary sphere forming the spherical section has a center point M which lies on the longitudinal axis of the valve needle 7.The end face 107a of the first valve needle section 107 facing the second valve needle section 207 is conical and directed inward, so that the end face 207a, viewed in longitudinal section, rests against the end face 107a at two points Pi, P2; in actual fact, the contact naturally occurs in the form of a circular line K with radius R. The center point M and the two points Pi, P2 form an angle a that is between 20° and 120° and can be adjusted via the circle radius and the opening angle of the cone. This design of the first separation point 8 enables angle compensation between the first valve needle section 107 and the second valve needle section 207 in order to compensate for possible axial errors due to manufacturing tolerances or thermal expansion. The second separation point 18, which is formed between the second valve needle section 207 and the third valve needle section 307, can also be designed in the same way.The separation points 8, 18 can also have other shapes: For example, it is also possible for both end faces 107a, 207a to be shaped like spherical segments, with one of the end faces being concave and the other convex. Pairs of two conical surfaces are also possible.

Claims

Claims 1 . Fuel injector for gaseous or liquid fuels with a housing (I), in which a longitudinally movable valve needle (7) is arranged, which is connected to a valve seat (10) for opening and closing a flow cross-section (II), wherein the valve needle (7) executes an opening movement directed out of the housing (1) to open the flow cross-section (11), and with a lubricant chamber (26) which surrounds at least part of the valve needle (7) and which is separated from a fuel chamber (5) by a corrugated bellows (25) surrounding the valve needle (7), wherein the corrugated bellows (25) is connected to the valve needle (7) in a fluid-tight manner at a sealing point (27) at its end section facing the valve seat (10), characterized in that a prestressed closing spring (30) is arranged between the valve seat (10) and the sealing point (27), which spring acts on the valve needle (7) in a closing direction.

2. Fuel injector according to claim 1, characterized in that the closing spring (30) surrounds the valve needle (7).

3. Fuel injector according to claim 1 or 2, characterized in that the valve needle (7) is constructed in several parts and consists of at least two piston-shaped valve needle sections (107, 207, 307), the valve needle sections (107, 207, 307) abutting one another with their end faces (107a, 207a) at a separation point (8, 18).

4. Fuel injector according to claim 3, characterized in that the first valve needle section (107), which cooperates with the valve seat (10), projects into the bellows (25) and there bears against a second valve needle section (207) at a separation point (8).

5. Fuel injector according to claim 3 or 4, characterized in that the end face (107a; 207a) of a valve needle section (107; 207; 307) is concavely curved.

6. Fuel injector according to claim 5, characterized in that the concave end face (207a) is formed in the shape of a spherical segment.

7. Fuel injector according to claim 6, characterized in that the spherical segment-shaped end face (207a) rests on the end face (107a) of the other valve needle section (107) along an annular line.

8. Fuel injector according to claim 7, characterized in that, viewed in longitudinal section, the spherical portion (207a) touches the opposite end face (107a) at two points (Pi; P2), the angle (a) formed by the two contact points (Pi; P2) and the center point (M) of the spherical portion (207a) being 20° to 120°.

9. Fuel injector according to one of claims 5 to 8, characterized in that the end face (107a) of the other valve needle section (107) which bears against the convex end face (207a) is concavely curved inwards.

10. Fuel injector according to one of claims 3 to 9, characterized in that one of the end faces (107a; 207a) is conical and the adjacent end face (107a; 207a) of the opposite valve needle section (107; 207; 307) is spherical segment-shaped or likewise conical.

11. Fuel injector according to one of claims 1 to 10, characterized in that the closing spring (30) is arranged between a shoulder (19) in the housing (1) and a support ring (28) under compressive prestress, wherein the support ring (28) surrounds the valve needle (7) and is firmly connected to the valve needle (7).

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