EP1527276B1 - Fuel-injection valve for internal combustion engines - Google Patents

Abstract

The invention relates to a fuel-injection valve for internal combustion engines comprising a valve body (1), in which a plunger-shaped valve needle (5) is located in a bore (3). The bore (3) is delimited at the combustion chamber end by a valve seat (9), which co-operates with a valve sealing surface (7) that is configured on the valve needle (5) in such a way that the opening of at least one injection orifice (11) configured at the combustion chamber end of the valve body (1) is controlled by the longitudinal displacement of the valve needle (5). Micro-depressions are configured on the valve sealing surface (7) and/or the valve seat (9).

Description

State of the art

The invention is based on a fuel injection valve for internal combustion engines, as is known from the prior art, for example from the published patent application DE 196 18 650 A1. In a valve body, a bore is formed, in which a piston-shaped valve needle is arranged to be longitudinally displaceable, which has a valve sealing surface at its end on the combustion chamber side. At the combustion chamber end, the bore is delimited by a valve seat with which the valve sealing surface of the valve needle interacts and thus controls by its longitudinal movement the opening of at least one injection opening, which is formed at the combustion chamber end of the valve body.

The valve seat and the valve sealing surface are at least substantially conical. Due to the short opening times of the fuel injection valve, the valve needle must be moved with very large forces in order to achieve correspondingly short switching times. As a result, the valve needle reaches high speeds, with which it strikes the valve seat during the closing movement with the valve sealing surface. In particular, in so-called common-rail injection systems, as they are known for example from DE 198 27 267 A1, therefore, high demands on the valve seat and the valve needle, to a long service life of the fuel injection valve and a possible over to achieve a consistent injection characteristic throughout the entire service life.

The movement of the valve needle in the bore is done, for example, by acting on the valve needle in the direction of the valve seat, a closing force. The closing force of the opposing opening force on the valve needle is obtained by pressurizing the valve needle with fuel, whereby a part of the valve sealing surface in this case undergoes a hydraulically effective force. In the previously known fuel injection valves, there is a seat wear in operation, that is, the valve sealing surface and the valve seat with time align with each other and changes the hydraulically effective surface area of the valve sealing surface. As a result, the injection is no longer optimal and can lead to increased exhaust emissions.

In the high pressure range of common rail fuel injection valves, including the range of the valve seat counts, it comes as a result of the injection processes usually to pressure oscillations. Between two injections occur thereby oscillating forces on the valve seat and the valve sealing surface, which is superimposed on the high constant base load by the constantly applied high pressure. As a result, wear occurs between the valve sealing surface and the valve seat, which impairs the service life of the fuel injection valve.

Advantages of the invention

The fuel injection valve according to the invention with the characterizing features of claim 1, in contrast, has the advantage that the fuel injection valve has a better drift behavior of the injection quantity and a longer life. The valve sealing surface of the valve needle and / or the valve seat have micro-recesses in the contact area, which lead to improved lubrication between the valve seat and valve needle in the highly loaded area. By a targeted adaptation of the micro-wells, which form a microstructure in its entirety, to the tribologically relevant stress, the wear on the valve seat is reduced and thus increases the life of the injection system.

In an advantageous embodiment of the object of the invention, the microwells are formed as individual, separate wells. With a diameter of the individual wells of for example 5 microns, which are arranged at a distance of also 5 microns in a rectangular grid, up to 10,000 lube deposits per mm ^{2 can be} formed. With a larger diameter of the wells correspondingly less per unit area are available. The arrangement of the wells can also be optimized in such a way that the distance between the wells in the circumferential direction of the valve sealing surface or the valve seat is different from the distance in the longitudinal direction.

In a further advantageous embodiment, the microwells are formed as grooves or groove segments, which are either separated from each other or partially overlap or intersect. It may be advantageous in this case if the grooves extend over the entire circumference of the valve sealing surface of the valve needle and / or the valve seat, which can be produced easily.

Due to the small depth of the Mikrovertierfungen these can be formed with various methods on the sealing surface of the valve member. For example, laser processing, hard turning, spark erosion or lithographic methods are suitable for this purpose. With these methods can be Produce a large number of lubrication depots cost-effectively and in a short time.

Further advantages and advantageous embodiments of the subject matter of the invention can be taken from the description and the drawing.

drawing

Figur 1

ein Kraftstoffeinspritzventil im wesentlichen Bereich im Längsschnitt,

Figur 2

eine Vergrößerung des mit II bezeichneten Ausschnitts der Figur 1,

Figur 3a, Figur 3b Figur 3c

und
eine Vergrößerung von Figur 2 im mit III bezeichneten Ausschnitt verschiedener Ausführungsbeispiele und

Figur 4

dieselbe Ansicht wie Figur 2 mit Nuten als Mikrovertiefungen.

In the drawing, an embodiment of the fuel injection valve according to the invention is shown. It shows the

FIG. 1

a fuel injector substantially in longitudinal section,

FIG. 2

an enlargement of the section of FIG. 1 denoted by II,

Figure 3a, Figure 3b Figure 3c

and
an enlargement of Figure 2 in the designated III section of various embodiments and

FIG. 4

the same view as Figure 2 with grooves as microwells.

Description of the embodiment

1 shows an embodiment of the fuel injection valve according to the invention is shown in its essential section in longitudinal section. In a valve body 1, a bore 3 is formed, in which a piston-shaped valve needle 5 is arranged longitudinally displaceable. The valve body 1 is in this case arranged in an internal combustion engine, not shown in the drawing, so that it projects with its combustion chamber end into the combustion chamber of the internal combustion engine or forms part of the wall of the combustion chamber. The valve needle 5, away from the combustion chamber, has a guide section 15, which is located in a guide region 23 the bore 3 is guided sealingly. Starting from the guide section 15, the valve needle 5 tapers to the combustion chamber to form a pressure shoulder 13, which surrounds the valve needle 5 over its entire circumference. At its combustion chamber end, the valve needle 5 passes into a substantially conical valve sealing surface 7, which cooperates with a valve seat 9, which is also substantially conical in shape and which limits the bore 3 at its combustion chamber end. In the valve seat 9, at least one injection opening 11 is formed, which connects the valve seat 9 with the combustion chamber of the internal combustion engine. Between the valve needle 5 and the wall of the bore 3, a pressure chamber 19 is formed which is radially expanded at the level of the pressure shoulder 13, wherein a valve body 1 formed in the inlet channel 25 opens into this radial extension. Via the inlet channel 25, the pressure chamber 19 can be filled with fuel under high pressure, which then flows through the pressure chamber 19 and thus reaches the valve seat 9.

By a device, not shown in the drawing, a constant or temporally variable closing force is exerted on the combustion chamber facing away from the end of the valve needle 5, so that the valve needle 5 is pressed with its valve sealing surface 7 in abutment against the valve seat 9. This closing force counteracts the hydraulic force which acts on the pressure shoulder 13 and on parts of the valve sealing surface 7 due to the fuel pressure in the pressure chamber 19. To control the longitudinal movement of the valve needle 5 in the bore 3, these two forces are used. Exceeds the hydraulic force on the valve needle 5, the closing force, the valve needle 5 lifts with its valve sealing surface 7 from the valve seat 9, and fuel flows from the pressure chamber 19 through the injection openings 11 into the combustion chamber of the internal combustion engine. If the closing force is increased or the hydraulic force is reduced, then the closing force on the valve needle 5 prevails, and the valve needle 5 comes with its Valve sealing surface 7 again in contact with the valve seat 7, whereby the injection openings 11 are closed.

FIG. 2 shows an enlargement of the section of FIG. 1 denoted by II, that is to say an enlargement of the valve seat area of the fuel injection valve. The valve sealing surface 7 is subdivided into two conical surfaces, of which the first conical surface 107 directly adjoins the cylindrical section of the valve needle 5, while the second conical surface 207 adjoins the first conical surface 107 and forms the tip of the valve needle 5. The first conical surface 107 has a larger opening angle than the second conical surface 207, so that a sealing edge 30 is formed at the transition of the two conical surfaces 107 and 207. The valve seat 9 has an opening angle which lies between the opening angle of the first conical surface 107 and that of the second conical surface 207, so that the sealing edge 30 comes into contact with the valve seat 9 in the closed position of the valve needle 5. The injection openings 11, of which several are generally distributed over the circumference of the valve body 1, are arranged downstream of the sealing edge 30, so that they can be closed by the valve needle 5.

The switching times of the valve needle 5 are very short: Since in high-speed internal combustion engines, such as those used in passenger cars, more than 2000 injections per minute can take place, an injection process takes only about 1 ms. Therefore, act on the valve needle 5 large forces and thus high accelerations that can open the valve needle 5 at high speed on the valve seat 9, wherein during operation of the fuel injection valve, the sealing edge 30 will hit something in the valve seat 9, so that there is an adjustment between valve sealing surface 7 and valve seat 9 comes. The valve sealing surface 7 and the valve seat 9 are therefore mechanically extremely heavily loaded. On the one hand, the seating area of the valve body 1 must not be too hard to prevent breakage in this area. On the other hand, the sealing edge 30 must not impact too much in the valve seat 9 during operation, since then also the fuel surface in the pressure chamber 19 acted upon partial surface of the valve sealing surface 7 changes and thus the pressure at which the valve needle 5 against the closing force in Opening direction is moved. A change of this opening pressure also causes a change in the total opening dynamics, so that a precise injection is no longer guaranteed.

In injection valves, in which constantly high pressure fuel in the pressure chamber and thus also rests on the valve seat, resulting from pressure vibrations another load. By closing the valve needle, the fuel in the pressure chamber, which flows toward the valve seat, abruptly decelerated, so that the kinetic energy converts into compression work and as a result pressure oscillations occur, resulting in a periodic load in the valve seat and valve sealing area. Fuel injectors claimed in this manner are mainly used in common rail injection systems. In addition, in fuel injection valves in which the closing force is generated on the valve needle by the hydraulic pressure in a control chamber, pressure oscillations occur in this control chamber, which can also lead to periodic forces on the valve needle in its closed position.

In order to reduce the wear on the interface between the valve sealing surface 7 and the valve seat 9 and thus to increase the service life, it is provided to form 7 microwells on the valve seat 9 or on the valve sealing surface 7. FIG. 3 a shows a first exemplary embodiment, in which an enlarged detail of the valve sealing surface 7 is shown, which is designated III in FIG. The Valve sealing surface 7 is covered with wells 32 which are individually formed and spaced from each other. The wells 32 are circular microwells, which in this example are arranged in a rectangular pattern. The depth of the wells is 0.5 microns to 50 microns, with a depth of 3 microns to 20 microns is particularly advantageous. The wells have a diameter between 5 microns and 100 microns, with a size of 10 microns to 50 microns has been found to be particularly advantageous. The distance of the wells 32 from each other is in the range of 5 .mu.m to 500 .mu.m, but may in certain cases also outside this range.

Through the wells 32, a fuel lubricating film is held on the valve sealing surface 7, so that even when the valve needle 5 is closed, that is, when it rests on the valve seat 9, sufficient lubrication between these components is ensured. It is the wear between the valve sealing surface 7 and the valve seat 9 is reduced when it comes to pressure oscillations in the pressure chamber 19 through the various operating conditions of the fuel injection valve and thus to deformations of the valve body 1 in the region of the valve seat 9. The same, wear-reducing effect is achieved if such wells 32 are also formed in the valve seat 9 in addition to the valve sealing surface 7. It can also be provided only in the valve seat 9 cup 32 and thus form a microstructure, but it will be generally easier to form a microstructure on the valve sealing surface 7 of the valve needle 5, as it is more easily accessible.

FIG. 3b shows a further exemplary embodiment of microwells in the valve sealing surface 7, the section shown being identical to that of FIG. 3a. Instead of cups here groove segments 35 are formed, which are arranged concentrically around a center in this example. The groove segments 35 result in a preferred direction, so that the Lubricating effect of these microwells can be optimized by a suitable orientation on the valve sealing surface 7. Again, it can be provided, the groove segments 35 also or exclusively on the valve seat 9 form, depending on what is more suitable for the lubricating effect or causes less costs.

FIG. 3 c shows a further exemplary embodiment of the microwells, which are designed here as grooves 38. The section shown corresponds in size to the figure 3a and 3b. The grooves 38 extend, for example, parallel to one another and in the tangential direction on the valve sealing surface 7. In FIG. 4, this is shown by way of example on the first conical surface 107. However, it can also be provided that the grooves intersect, as shown in FIG. 4 on the second conical surface 207. Due to the orientation of the grooves 38, their width and their depth, the lubricating properties can be adjusted and thus optimized.

The production of the microwells 32, 35, 38 can be done by various techniques. Thus, for grooves 38 fine turning, hard turning or beam machining is suitable. Wells 32 may be introduced, for example, by microembossing, spark erosion or by lithographic or electrochemical methods. The same methods are also suitable for the production of the groove segments 35. After the introduction of the microstructure in valve sealing surface 7 or valve seat 9, it is provided to post-treat the surface, for example by lapping, fine grinding or finishing. Which method is selected depends on the type of microwells, the material and the size of the surface to be treated.

Claims (15)

1. Fuel injection valve for internal combustion engines, having a valve body (2) in which a piston-shaped valve needle (5) is arranged in a bore (3), and having a valve seat (9) which is formed at the combustion-chamber-side end of the bore (3) and interacts with a valve sealing face (7) which is formed on the valve needle (5), so that the opening of at least one injection opening (11) which is formed at the combustion-chamber-side end of the valve body (1) is controlled by the longitudinal movement of the valve needle (5), characterized in that the valve sealing face (7) and/or the valve seat (9) has microdepressions (32; 35; 38) which have a depth of between 0.5 µm and 50 µm, preferably between 3 µm and 20 µm.
2. Fuel injection valve according to Claim 1, characterized in that the microdepressions (32; 35; 38) are formed individually and separately from one another.
3. Fuel injection valve according to Claim 2, characterized in that the microdepressions (32; 35; 38) are formed as wells (32).
4. Fuel injection valve according to Claim 3, characterized in that the wells (32) are spaced apart from one another to a lesser extent in the peripheral direction of the valve needle (5) than in the longitudinal direction of the valve needle (5).
5. Fuel injection valve according to Claim 3, characterized in that the wells (32) are spaced apart from one another to a greater extent in the peripheral direction of the valve sealing face (7) than in the longitudinal direction of the valve needle (5).
6. Fuel injection valve according to Claim 2, characterized in that the microdepressions (32; 35; 38) are spaced apart from one another with a spacing (a) of between 5 µm and 500 µm.
7. Fuel injection valve according to Claim 1, characterized in that the microdepressions (32; 35; 38) are formed as grooves (38).
8. Fuel injection valve according to Claim 1, characterized in that the microdepressions (32; 35; 38) are formed as groove segments (35).
9. Fuel injection valve according to Claim 7 or 8, characterized in that the microdepressions (32; 35; 38) at least partially intersect one another.
10. Fuel injection valve according to Claim 7 or 8, characterized in that the microdepressions (32; 35; 38) run in concentric circles around the entire circumference of the valve sealing face (7) and/or of the valve seat (9).
11. Fuel injection valve according to Claim 1, characterized in that the microdepressions (32; 35; 38) at least partially overlap one another.
12. Fuel injection valve according to Claim 1, characterized in that the microdepressions (32; 35; 38) have a width (b) of between 5 µm and 100 µm, preferably between 10 µm and 50 µm.
13. Fuel injection valve according to one of the preceding claims, characterized in that the microdepressions (32; 35; 38) are produced by means of blasting machining, laser machining, hard-turning, microstamping, electrical discharge machining or by means of lithographic or electrochemical methods.
14. Fuel injection valve according to Claim 7, characterized in that the grooves (38) are produced by means of precision turning.
15. Fuel injection valve according to Claim 13 or 14, characterized in that the microdepressions (32; 35; 38) are formed after the precision machining of the valve seat face (7) and of the valve seat (9), and the faces are subsequently remachined by means of lapping, precision grinding or finishing.

Images