Injection nozzle for injecting fuel at high pressure

Abstract

Injection nozzle for injecting fuel under high pressure, having a nozzle body (2) in which a pressure chamber (9) is configured which can be charged with fuel under high pressure and in which a conical body seat (25) is configured which opens into a blind hole (32) by means of a transition edge (35), a plurality of injection holes (30) leading out of the blind hole and the flow cross sections of all injection holes adding up to a total injection hole cross section (A SL ). A nozzle needle (14) is arranged movably in longitudinal direction in the pressure chamber (9), which nozzle needle cooperates with the body seat (25) with a conical sealing surface (27) in order to open and close the flow cross section, wherein the nozzle needle (14) has a needle tip (28) on its end facing the body seat (25), which needle tip projects into the blind hole (32) when the sealing surface (27) is resting on the body seat (25). When the nozzle needle (14) is lifted from the body seat (25), a seat cross section (As) is formed between the sealing surface (25) and the transition edge (35), through which seat cross section fuel can flow from the pressure chamber (9) into the blind hole (32). The needle tip (28) is conically shaped and has an opening angle (β) which is smaller than the opening angle (α) of the conical sealing surface (27), and the blind hole (32) has a conical section (132) with an opening angle (σ) which is configured between the transition edge (35) and an intermediate edge (36), wherein the needle tip (28) is arranged at the height of the conical section (132) of the blind hole (32) in a partial stroke of the nozzle needle (14).

Description

TECHNICAL FIELD

[0001] The invention relates to an injection nozzle for injecting fuel under high pressure, for example for introducing fuel under high pressure into a combustion chamber of an internal combustion engine. BACKGROUND

[0002] For a long time, injection nozzles for introducing fuel under high pressure have been known from the prior art. Such injection nozzles preferably form part of a fuel injector, which can introduce electrically controlled, highly compressed fuel into a combustion chamber of an internal combustion engine. The fuel is finely atomized when injected into the combustion chamber, so that a combustible fuel-air mixture is produced there. In self-igniting internal combustion engines, the combustible fuel-air mixture ignites by compression of the fuel-air mixture in the combustion chamber and burns with high efficiency due to the good atomization of the fuel.

[0003] Injection holes, through which the fuel finally comes out, are located in the injection nozzle, which controls the opening and closing of these injection openings by means of a piston-like, longitudinally movable nozzle needle, which is arranged in a nozzle body of the injection nozzle. Here, the movement of the nozzle needle takes place at least hydraulically, that is to say, the closing force is generated by the hydraulic pressure in a control chamber. By adjusting the pressure in this control chamber and being driven by the hydraulic pressure of the fuel surrounding the nozzle needle, the longitudinal movement of the nozzle needle can be controlled. Here, the pressure in the control chamber is controlled, for example, by a solenoid valve, so that the injection can ultimately be precisely controlled by the electromagnet.

[0004] The nozzle needle has a conical sealing surface on its end facing the injection openings. The nozzle needle cooperates with a body seat constructed in the injection nozzle with this sealing surface in order to open and close the flow cross section. In the injection nozzles of the type considered here, a blind hole follows the conical body seat, which is constructed as a blind bore and from which the actual injection opening comes out. The blind hole is mainly used to supply all injection openings with the same amount of fuel and thus to ensure uniform combustion.

[0005] If the nozzle needle is in its closed position, that is to say, bears against the body seat, it blocks the blind hole and thus also the injection opening relative to the pressure chamber, which is filled with compressed fuel and surrounds the nozzle needle. At the beginning of the opening stroke of the nozzle needle, the gap between the sealing surface and the body seat constitutes the narrowest cross section for the fuel flow into the blind hole. The fuel flowing through the gap reaches the blind hole, where a pressure drop occurs and a suppression of the flow due to the significantly larger flow cross section. This promotes the generation of a vortex structure in the fuel flow and the transition from laminar to turbulent flow. Furthermore, the pressure drop when the fuel enters the blind hole promotes the generation of cavitation bubbles, which implode further on and can lead to damage on the sealing surface of the nozzle needle and on the body seat.

[0006] In fuel injection, different requirements must be taken into account. On the one hand, ever higher injection pressures are striven for, since high injection pressures lead to good atomization of the fuel and thus to a good combustion process. At the same time, a high fuel flow should also be achieved in order to produce a high efficiency (downsizing), i.e. to obtain as much efficiency as possible with a given stroke space. This, however, leads to a nozzle geometry which promotes the generation of cavitation and thus cavitation erosion resulting therefrom.

[0007] A large total injection hole cross section, that is to say, the sum of the cross sections of all injection openings, leads to the fact that the gap between the sealing surface and the body seat constitutes the smallest flow cross section over a relatively large needle stroke, which correspondingly lengthens the period in which cavitation can occur. A large blind hole face, that is to say, a blind hole which has a large flow cross section within the blind hole, which leads to the injection opening, likewise has a disadvantageous effect, since the pressure drop when the fuel flows into the blind hole is thus enhanced and promotes the generation of cavitation. A large volume of the blind hole also promotes the formation of vortices, which lengthens the residence time of the cavitation bubbles inside the blind hole and increases the likelihood that they implode there and cause damage.

[0008] From EP 1 891 324 B1 a fuel injection nozzle for introducing fuel into a combustion chamber of an internal combustion engine is known, which works according to the principles described above. The nozzle needle has a conical sealing surface which cooperates with a likewise conical body seat in order to open and close the flow cross section. On the nozzle needle a nozzle needle tip is configured which partially protrudes into the blind hole of the injection nozzle. The transition of the conical sealing surface to the needle tip is configured rounded, so that the flow cross section expands relatively quickly from the gap between the sealing surface and the body seat and thus the pressure drop explained above already occurs before the fuel enters the blind hole.

[0009] A jet nozzle of this type is also known from DE 10 2005 037 955 Al, in which the sealing face has a significantly different cone angle from the body seat, so that the lying of the sealing face on the body seat essentially takes place on the surrounding sealing edge. A further, narrow cross section is formed between the second portion of the sealing face and the edge configured on the transition of the body seat to the blind hole, so that here the flow flows from a region with a high flow velocity into a region with a low flow velocity and then again into a region with a high flow velocity. SUMMARY

[0010] In contrast thereto, the jet nozzle according to the application has the advantage that the formation of cavitation or its reduction to an extent that excludes harmful cavitation corrosion in the jet nozzle, in particular below the sealing seat and in the blind hole, is prevented. The service life of the fuel injection valve is thereby increased and also the accuracy of the injection is improved over a longer service life. To this end, the jet nozzle has a nozzle body in which a pressure chamber which can be charged with fuel at high pressure and a conical body seat are configured. The conical body seat transitions into a blind hole by means of a transition edge, from which a plurality of injection holes emerge, wherein the sum of the flow cross sections of all injection holes constitutes a total injection hole cross section. A nozzle needle is arranged movably in longitudinal direction in the pressure chamber, which interacts with the body seat with a conical sealing face in order to open and close the flow cross section, wherein the nozzle needle has a needle tip on its end facing the body seat, which extends into the blind hole when the sealing face lies against the body seat. Here, between the sealing face and the transition edge a jet cross section is formed when the nozzle needle is lifted from the body seat, through which the fuel can flow from the pressure chamber into the blind hole. The needle tip is conically shaped and has an opening angle which is smaller than the opening angle of the conical sealing face, and in the blind hole a conical section is configured which has an opening angle and which is situated directly next to the transition edge, wherein the needle tip is arranged at the height of the conical section of the blind hole in the partial stroke of the nozzle needle.

[0011] Due to the shaping of the jet nozzle, in particular of the nozzle needle, in the region of the sealing face according to the application, a flow cross section is formed between the nozzle needle or the nozzle needle tip and the blind hole, which is largely constant and which constitutes in particular in the region of the partial stroke of the nozzle needle, i.e. at the beginning of the opening stroke movement, a flow cross section which leads to a calming of the flow and thus to a laminar inflow of the fuel into the injection holes. This is achieved by the configuration of the nozzle needle tip on the one hand and of the blind hole on the other hand, between which the flow cross section is fixed. Since no or only a small pressure drop occurs when the fuel flows into the injection holes, in this case cavitation formation is suppressed, which could otherwise lead to the well-known cavitation damage in the region of the injection holes or the blind hole.

[0012] The partial stroke of the nozzle needle is in particular a region of the stroke of the nozzle needle in which the ratio of the seat cross section to the total injection hole cross section is not more than 1.3. Only when the total injection hole cross section is more than 1.3 times the seat cross section is there a risk of cavitation formation in the blind hole, because then the injection hole constitutes the smallest flow cross section and thus a pressure drop occurs when fuel flows from the pressure chamber into the blind hole. Thus, the shaping of the sealing surface according to the invention effectively prevents the tendency to cavitation in the region of the partial stroke of the nozzle needle. In an advantageous manner, the flow cross section between the tip of the needle and the wall of the blind hole up to the upper edge of the injection hole is at most 2 times the seat cross section, wherein the upper edge of the injection hole is an imaginary line which is marked by the entry edge of the injection hole in the wall of the blind hole which faces the body seat.

[0013] In an advantageous configuration of the invention, a shoulder is configured on the transition of the sealing surface of the nozzle needle to the tip of the needle which, in interaction with the transition edge on the transition of the body seat to the blind hole, results in an advantageous configuration of the flow cross section in this region.

[0014] In a further advantageous configuration, a transition cone is configured on the nozzle needle between the tip of the needle and the sealing surface, the opening angle of which is different from the opening angle of the sealing surface and the opening angle of the tip of the needle. In interaction with the transition edge at the beginning of the blind hole, a flow optimization can likewise be achieved in order to adapt the nozzle needle to different configurations of the injection hole or the body seat.

[0015] In a further advantageous configuration, the opening angle of the conical tip of the needle and the opening angle of the conical blind hole are the same. Thereby, a uniform flow cross section and thus a flow equalization is produced between these components. Here, in an advantageous configuration, the diameter of the upper edge of the injection hole can be greater than the diameter of the transition edge. Thereby, it can be achieved that the flow cross section between the nozzle needle and the wall of the blind hole is constant between the transition edge and the upper edge of the injection hole, thus achieving a flow equalization. BRIEF DESCRIPTION OF DRAWINGS

[0016] Different embodiments of the injection nozzle according to the invention are shown in the drawings. The drawings show

[0017] Figure 1 The injection nozzle is shown in longitudinal section, as is known from the prior art,

[0018] Figure 2 An enlarged view of the blind hole with the nozzle needle and the geometric parameters defined is shown, as is known from the prior art,

[0019] Figure 3 A nozzle is shown which is likewise known from the prior art, wherein here a further flow cross section is defined,

[0020] Figure 4 The same is shown in the same illustration for a first configuration according to the application of the injection nozzle according to the application, and Figure 2

[0021] Figure 5 6, 7 and 8 show further embodiments of the application. DETAILED DESCRIPTION

[0022] In Figure 1 longitudinal section, a fuel injector 1 is shown, as is known from the prior art, wherein only the injection nozzle region of the fuel injector is shown, which is sufficient for the subsequent explanation of the application. The injection nozzle has a nozzle body 2, which is tensioned liquid-tightly with respect to a holding body 5 by means of a tensioning nut 7 in the case of an intermediate layer at a throttle disc 3. In the nozzle body 2 a pressure chamber 9 is configured, which can be charged with fuel at high pressure by means of high-pressure bores 12 configured in the holding body 5 and the throttle disc 3. In the pressure chamber 9 a piston-like nozzle needle 14 is arranged displaceable in the longitudinal direction. Here, the nozzle needle 14 is guided in a guide section 15 within the pressure chamber 9, wherein a fuel flow in this guide section 15 is ensured by a plurality of grinding blades 16 on the nozzle needle 14, which are configured so large that no fuel flow throttling occurs in this region. On the end of the nozzle body 2 on the combustion chamber side of the nozzle body 2, in the pressure chamber 9 a body seat 25 is configured, which is conically shaped and which cooperates with a conical sealing surface 27 configured on the nozzle needle 14. On the conical body seat 25 a blind hole 32 is connected, from which a plurality of injection holes 30 lead, through which the fuel comes out.

[0023] ​At the end away from the combustion chamber, the nozzle needle 14 is guided within the sleeve 18. The sleeve 18 is pressed against the throttle disc 3 by a closing spring 19 surrounding the nozzle needle 14 and is thus held fixedly in this position. The nozzle needle 14, sleeve 18, and throttle disc 3 define a control chamber 22, which is connected to the high-pressure borehole 12 via an injection throttle section 23. To control the pressure in the control chamber 22, it can be connected via an outflow throttle section 21 to a low-pressure chamber in the retainer 5 (not shown in more detail in the drawings). For this purpose, a control valve 20 is constructed in the retainer 5, which opens and closes this connection by an electromagnetic or piezoelectric actuator. If fuel injection occurs, the control valve 20 opens the connection between the control chamber 22 and the low-pressure chamber by releasing the outflow throttle section 21. As the pressure in the control chamber 22 decreases, the hydraulic closing force acting towards the body seat 25 decreases, and the nozzle needle 14 lifts off the body seat 25, releasing the flow cross-section between the sealing surface 27 and the body seat 25. Fuel can then flow through this flow cross-section from the pressure chamber 9 into the blind orifice 32 and from there to the injection opening 30. The fuel exits through the injection orifice 30, where it is finely atomized and forms an ignitable mixture with the air in the combustion chamber. To terminate fuel injection, the control valve 20 closes again, and the fuel injected from the high-pressure borehole 12 via the throttling section 23 pushes the nozzle needle 14 back into its closed position, that is, against the body seat 25.

[0024] To further explain, Figure 2 Show Figure 1 A magnified view of a portion marked II. Because the nozzle body 2 and nozzle needle 14 are constructed with rotational symmetry about the longitudinal axis 10, only one side of the injection nozzle is shown here for clarity. The conical body seat 25 has an opening angle γ, which is defined here as the angle between the longitudinal axis 10 and the body seat 25. The body seat 25 transitions into the blind orifice 32 by forming a transition edge 35, wherein the blind orifice 32 has a conical section 132 and is limited at its combustion chamber side end by a dome 34. Here, the opening angle of the conical blind orifice 32 is denoted by σ and is significantly smaller than the opening angle γ of the body seat 25. The sealing surface 27 on the nozzle needle 14 is also conical and interacts with the body seat 25. The opening angle of the sealing surface 27 is denoted by α and, in this embodiment, is slightly larger than the opening angle γ of the body seat 25. The injection holes 30 are configured to be distributed around the blind holes 32, for example, five or six injection holes 30, wherein the injection holes 30 form the upper inlet edge 31, that is, the area of ​​the circular inlet edge of the injection hole 30 closest to the body seat 25.

[0025] The flow of fuel from pressure chamber 9 to blind orifice 32 and further to injection orifice 30 occurs across different flow cross sections, such as in... Figure 3As shown in the diagram, the flow cross section between the sealing surface 27 and the transition edge 35 constitutes the seat cross section As. When the nozzle needle is in partial stroke, that is, when the nozzle needle moves only slightly away from the body seat 25 at the start of the opening stroke, this seat cross section As constitutes the minimum flow cross section. Fuel flows through the seat cross section As into the blind orifice 32 and then through the surface A formed by the upper edge 33 of the injection orifice. SO Here, the upper edge 33 of the injection orifice is defined as an imaginary line, and the inlet edge 31 lies on said imaginary line. This inlet edge constitutes the flow cross-section before fuel flows into the injection orifice 30. All injection orifices 30 together constitute the total injection orifice cross-section A. SL This means that the flow within the blind orifice 32 is determined, in particular, by the proportions of these flow cross sections relative to each other. Furthermore, other geometric parameters also influence fuel flow, especially the so-called L-dimension, which... Figure 3 The dimension L is used to mark the distance from the transition edge 35 to the center of the injection hole 30. If the nozzle needle 14 first moves a small portion of its maximum opening stroke, the seat cross-section A... S To form the smallest cross-section, while spraying the upper edge A SO Its area is relatively large in comparison. The total injection orifice cross-section A only increases when the nozzle needle 14 exceeds a defined stroke. SL This constitutes the minimum flow cross section, so that the fuel flow is only suppressed when it enters the injection hole, which will not cause cavitation in the blind hole 32.

[0026] Figure 4 With Figure 3 The same illustration shows a first embodiment of the injection nozzle according to the invention. A needle tip 28 is constructed on the nozzle needle 14, adjacent to the tapered sealing surface 27, the needle tip extending into the blind orifice 32. The needle tip 28 is also tapered and has an opening angle β smaller than the opening angle α of the sealing surface 27. In this embodiment, the opening angle β is approximately equivalent to the opening angle σ of the blind orifice wall, such that a largely constant flow cross-section is formed between the needle tip 28 and the wall of the blind orifice 32. This flow cross-section extends to the height of the upper edge 33 of the injection orifice, thereby achieving the desired cross-section A. S The flow in the region between the blind orifice 30 and the injection orifice 30 is homogenized. Therefore, no pressure drop occurs when fuel enters the blind orifice 32 and thus no cavitation forms, but at least the tendency for cavitation is significantly reduced, preventing cavitation damage in the region between the blind orifice 32 and the injection orifice 30. To form this flow cross-section, the diameter D of the interrupted edge 17 between the sealing surface 27 and the needle tip 28 is constructed. B1 Less than the transition edge 35 (see Figure 2 The diameter D S The transition edge is marked at the transition between the body seat 25 and the blind hole 32.

[0027] A further embodiment of a spray nozzle according to the application is shown in Figure 5 Here, a transition cone 24 is configured on the nozzle needle 14 between the sealing face 27 and the needle tip 28. The opening angle τ of the transition cone 24 is greater than the opening angle a of the sealing face 27 and smaller than the opening angle β of the needle tip 28, so that an edge is likewise configured on the transition from the sealing face 27 to the transition cone 24. The diameter D A of the transition edge 37 between the sealing face 27 and the transition cone 24 is greater than the diameter of the transition edge 35, in order to form a corresponding flow path towards the spray hole 30.

[0028] A further variant of a blind hole of a spray nozzle according to the application is shown in Figure 6 Here, the spray hole 32 has a cylindrical section 232 next to a conical section 132, which is delimited by the transition edge 35 and the intermediate edge 36, next to which a rounded dome 34 is configured. The interaction with a correspondingly shaped nozzle needle 14 is shown in Figure 7 Here, the conical needle tip 28 is opposite the conical section 132 of the blind hole 32 over a large part of the needle stroke and thus constitutes a flow cross section which leads to a flow calming. Here, in particular, a nozzle needle 14 can be used which has a transition cone 24 between the sealing face 27 and the needle tip 28. The interaction with a correspondingly shaped nozzle needle 14 is shown in Figure 8 A further embodiment of a spray nozzle according to the application is shown in. Here, a shoulder 26 is configured on the transition from the sealing face 27 to the needle tip 28, through which an interrupted edge 17 is constituted.

[0029] In a spray nozzle according to the application, the respective angles and spacings must be coordinated in such a way that during a part stroke of the nozzle needle, in which the seat cross section A S is only slightly greater than the total spray hole cross section A SL , no flow deceleration occurs on entry into the blind hole 32, but only on entry into the spray hole 30. Here, it is particularly advantageous if the diameter D S of the transition edge 35 is greater than the diameter of the intermediate edge 36 and at most 1.6 times the diameter D S2 . It is further advantageous if the cone angle β of the needle tip 28 lies in the range of + / - 20° of the opening angle σ of the conical section 132 of the blind hole 32.

Claims

1. An injection nozzle for injecting fuel under high pressure, the injection nozzle having a nozzle body (2) in which a pressure chamber (9) capable of being filled with fuel under high pressure is constructed, and a conical body seat (25) is constructed in the nozzle body, the body seat opening into a blind orifice (32) with a transition edge (35) formed, from which a plurality of injection holes (30) originate, and the sum of the flow cross sections of all the injection holes constitutes the total injection hole cross section (A). SL The injection nozzle has a nozzle needle (14) arranged longitudinally within the pressure chamber (9), the nozzle needle interacting with the body seat (25) via a tapered sealing surface (27) to open and close the flow cross section, wherein... The nozzle needle (14) has a needle tip (28) at its end facing the body seat (25). When the sealing surface (27) is against the body seat (25), the needle tip extends into the blind hole (32). When the nozzle needle (14) is lifted from the body seat (25), a seat cross section (As) is formed between the sealing surface (27) and the transition edge (35), through which fuel can flow from the pressure chamber (9) into the blind hole (32). The needle tip (28) is tapered and has an opening angle (β) smaller than the opening angle (α) of the tapered sealing surface (27), and the blind hole (32) has a tapered section (132) with an opening angle (σ) connecting to the transition edge (35), wherein the needle tip (28) is positioned at the height of the tapered section (132) of the blind hole (32) during a portion of the stroke of the nozzle needle (14), the portion of the stroke of the nozzle needle (14) being a needle stroke region in which the seat cross-section (A) is... S ) and total injection hole cross-section (A SL The proportion of A is no more than 1.3 and greater than 1, i.e., 1 < A S / A SL ≤1.

3.

2. The injection nozzle according to claim 1, characterized in that, The flow cross-section between the needle tip (28) and the wall of the blind hole (32) up to the upper edge (33) of the injection hole is the largest of the seat cross-section (A). S Twice that of the injection hole, wherein the upper edge (33) of the injection hole is an imaginary line that surrounds the blind hole (32), the imaginary line being marked by the inlet edge of the injection hole (30) facing the body seat (25) in the wall of the blind hole (32).

3. The injection nozzle according to claim 1 or 2, characterized in that, A shoulder (26) is constructed on the transition from the sealing surface (27) to the needle tip (28).

4. The injection nozzle according to claim 1 or 2, characterized in that, Between the needle tip (28) and the sealing surface (27), a transition cone (24) is constructed on the nozzle needle (14), the opening angle (τ) of the transition cone being different from the opening angle (α) of the sealing surface (27) and the opening angle (β) of the needle tip (28).

5. The injection nozzle according to claim 1, characterized in that, The opening angle (β) of the conical needle tip (28) and the opening angle (σ) of the conical blind hole (32) are the same.

6. The injection nozzle according to claim 1, characterized in that, The flow cross section between the walls of the nozzle needle (14) and the blind hole (32) is constant between the transition edge (35) and the upper edge (33) of the injection hole.

7. The injection nozzle according to claim 1, characterized in that, In the blind hole (32), a cylindrical section or a dome (34) is connected on the conical section (132).

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