INJECTION NOZZLE FOR INJECTING FUEL UNDER HIGH PRESSURE

Abstract

The invention relates to an injection nozzle for injecting fuel under high pressure, comprising a nozzle body (2) in which a pressure chamber (9), which can be filled with fuel under high pressure, is formed and in which a conical body seat (25) is formed which opens into a blind hole (32), forming a transition edge (35), from which blind hole a plurality of injection holes (30) originate and the total of the flow cross-sections of all injection holes forms a total injection hole cross-section (A.sub.SL). A nozzle needle (14) is arranged in the pressure chamber (9) so as to be longitudinally movable, said nozzle needle interacting, by means of a conical sealing surface (27), with the body seat (25) in order to open and close a flow cross-section, wherein the nozzle needle (14) has, on the end thereof facing the body seat (25), a needle tip (28) which protrudes into the blind hole (32) when the sealing surface (27) contacts the body seat (25). A seat cross-section area (A.sub.S) is formed between the sealing surface (27) and the transition edge (35) when the nozzle needle (14) is raised from the body seat (25), through which seat cross-section area fuel can flow from the pressure chamber (9) into the blind hole (32). The needle tip (28) is conical and has an opening angle (13) that is smaller than the opening angle (a) of the conical sealing surface (27), and the blind hole (32) has a conical portion (132) having an opening angle (a) that is formed between the transition edge (35) and an intermediate edge (36), wherein the needle tip (28) is arranged in a partial stroke of the nozzle needle (14) at the height of the conical portion (132) of the blind hole (32).

Claims

1. An injection nozzle for injecting fuel under high pressure, the injection nozzle comprising a nozzle body (2) in which a pressure chamber (9), that is configured to be filled with fuel under high pressure, is formed and in which a conical body seat (25) is formed, wherein the body seat (25) opens into a blind hole (32), forming a transition edge (35), wherein a plurality of injection holes (30) originate from the blind hole and a total of flow cross-sections of all of the injection holes forms a total injection hole cross-section (A.sub.SL), and a nozzle needle (14) which is arranged in the pressure chamber (9) so as to be longitudinally movable, and which interacts, via a conical sealing surface (27), with the body seat (25) in order to open and close a flow cross-section between the sealing surface (27) and the body seat (25), wherein the nozzle needle (14) has, on the an thereof facing the body seat (25), a needle tip (28) which protrudes into the blind hole (32) when the sealing surface (27) contacts the body seat (25), wherein a seat cross-section area (A.sub.S) is formed between the sealing surface (27) and the transition edge (35) when the nozzle needle (14) is raised from the body seat (25), through which seat cross-section area fuel can flow from the pressure chamber (9) into the blind hole (32), wherein the needle tip (28) is conical and has an opening angle (β) that is smaller than an opening angle (α) of the conical sealing surface (27), and the blind hole (32) has a conical portion (132) having an opening angle (σ) which adjoins the transition edge (35), wherein the needle tip (28) is arranged in a partial stroke of the nozzle needle (14) at a height of the conical portion (132) of the blind hole (32).

2. The injection nozzle as claimed in claim 1, characterized in that the partial stroke of the nozzle needle (14) is a needle stroke region in which a ratio of the seat cross-section area (A.sub.S) and the total injection hole cross-section (A.sub.SL) is no more than 1.3 (A.sub.S/A.sub.SL≤1.3).

3. The injection nozzle as claimed in claim 2, characterized in that a flow cross-section between the needle tip (28) and a wall of the blind hole (32) as far as an injection hole upper edge (33) is at most twice the seat cross-section area (As), wherein the injection hole upper edge (33) is an imaginary line which circulates around the blind hole (32) and which is marked by an inlet edge of the injection holes (30) facing the body seat (25) in the wall of the blind hole (32).

4. The injection nozzle as claimed in claim 1, characterized in that a shoulder (26) is formed at a transition of the sealing surface (27) to the needle tip (28).

5. The injection nozzle as claimed in claim 1, characterized in that a transition cone (24) is configured on the nozzle needle (14) between the needle tip (28) and the sealing surface (27), an opening angle (τ) of the transition cone being different from the opening angle (a) of the sealing surface (27) and the opening angle (β) of the needle tip (28).

6. The injection nozzle as claimed in 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 of the same size.

7. The injection nozzle as claimed in claim 1, characterized in that a diameter (A.sub.SO) of the injection hole upper edge (33) is larger than a diameter (D.sub.S) of the transition edge (35).

8. The injection nozzle as claimed in claim 1, characterized in that a flow cross-section between the nozzle needle (14) and the wall of the blind hole (32) is constant between the transition edge (35) and the injection hole upper edge (33).

9. The injection nozzle as claimed in claim 1, characterized in that a cylindrical portion or a dome (34) adjoins the conical portion (132) in the blind hole (32).

10. The injection nozzle as claimed in claim 3, characterized in that a shoulder (26) is formed at a transition of the sealing surface (27) to the needle tip (28).

11. The injection nozzle as claimed in claim 3, characterized in that a transition cone (24) is configured on the nozzle needle (14) between the needle tip (28) and the sealing surface (27), an 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).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Various exemplary embodiments of the injection nozzle according to the invention are shown in the drawing, in which:

[0017] FIG. 1 shows an injection nozzle as known from the prior art in a longitudinal section,

[0018] FIG. 2 shows an enlargement of the blind hole known from the prior art with the nozzle needle and a definition of the geometric sizes,

[0019] FIG. 3 shows a nozzle also known from the prior art, wherein further flow cross-sections are defined herein,

[0020] FIG. 4 shows a first embodiment according to the invention of the injection nozzle according to the invention in the same view as in FIG. 2 and

[0021] FIGS. 5, 6, 7 and 8 show further exemplary embodiments of the invention.

DETAILED DESCRIPTION

[0022] In FIG. 1 a fuel injector 1 is shown in longitudinal section, as is known from the prior art, wherein only the region of the injection nozzle of the fuel injector which is sufficient for the following description of the invention is shown. The injection nozzle has a nozzle body 2 which is clamped by the interposition of a throttle plate 3 in a fluid-tight manner by means of a clamping nut 7 against a holding body 5. A pressure chamber 9 is formed in the nozzle body 2, said pressure chamber being able to be filled with fuel at high pressure via a high-pressure bore 12 which is configured in the holding body 5 and the throttle plate 3. A piston-shaped nozzle needle 14 is arranged in the pressure chamber 9 so as to be longitudinally movable. The nozzle needle 14 in this case is guided in a guide portion 15 inside the pressure chamber 9, wherein the flow of fuel into this guide portion 15 is ensured by a plurality of polished sections 16 on the nozzle needle 14, which are configured to be sufficiently large that it does not result in the fuel flow being throttled in this region. A body seat 25 is formed at the end of the nozzle body 2 on the combustion chamber side in the pressure chamber 9, said body seat being conically shaped and interacting with a conical sealing surface 27 which is configured on the nozzle needle 14. A blind hole 32 adjoins the conical body seat 25, a plurality of injection holes 30, through which the fuel exits, emerging from said blind hole.

[0023] At the end remote from the combustion chamber, the nozzle needle 14 is guided in a sleeve 18. The sleeve 18 is pressed by a closing spring 19 surrounding the nozzle needle 14 against the throttle plate 3 and thus is held fixedly in this position. The nozzle needle 14, the sleeve 18 and the throttle plate 3 define a control chamber 22 which is connected via an inlet throttle 23 to the high-pressure bore 12. In order to control the pressure in the control chamber 22, the control chamber 22 may be connected via an outlet throttle 21 to a low pressure chamber in the holding body 5, not shown in more detail in the drawing. To this end, a control valve 20 is configured in the holding body 5, said control valve opening and closing this connection, driven by an electromagnetic actuator or piezo-electrical actuator. If an injection of fuel is intended to take place, the control valve 20 opens the connection of the control chamber 22 to the low pressure chamber by the outlet throttle 21 being opened up. Due to the pressure drop in the control chamber 22 the hydraulic closing force acting in the direction of the body seat 25 is reduced and the nozzle needle 14 is raised from the body seat 25 and opens up a flow cross-section between the sealing surface 27 and the body seat 25, through which fuel may flow out of the pressure chamber 9 into the blind hole 32 and from there to the injection openings 30. The fuel passes through the injection holes 30, is finely atomized at the same time and forms a combustible mixture together with the air in the combustion chamber. For terminating the fuel injection, the control valve 20 is closed again and the fuel flowing via the inlet throttle 23 from the high pressure bore 12 pushes the nozzle needle 14 back into its closed position, i.e. in contact with the body seat 25.

[0024] For the further explanation, FIG. 2 shows an enlarged view of the detail of FIG. 1 denoted by II. Since the nozzle body and also the nozzle needle 14 are configured to be rotationally symmetrical relative to a longitudinal axis 10, for the sake of clarity, only one side of the injection nozzle is shown here. 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 a blind hole 32, forming a transition edge 35, wherein the blind hole 32 has a conical portion 132 and is defined by a dome 34 at the end on the combustion chamber side. The opening angle of the conical blind hole 32 is denoted here by a 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 conically configured and interacts with the body seat 25. The opening angle of the sealing surface 27 is denoted by a and in this exemplary embodiment is slightly larger than the opening angle γ of the body seat 25. The injection holes 30 are configured so as to be distributed over the circumference of the blind hole 32, for example five or six injection holes 30, wherein the injection holes 30 form an upper inlet edge 31, i.e. the region of the round inlet edge of the injection holes 30 which is closest to the body seat 25.

[0025] The flow of the fuel from the pressure chamber 9 into the blind hole 32 and onward into the injection holes 30 takes place through different flow cross-sections as shown in FIG. 3. The flow cross-section between the sealing surface 27 and the transition edge 35 forms a seat cross-section area A.sub.S. This seat cross-section area A.sub.S forms the smallest flow cross-section when the nozzle needle is located in a partial stroke, i.e. when it has been moved away only slightly from the body seat 25 at the start of the opening stroke movement. The fuel flows through the seat cross-section area A.sub.S into the blind hole 32 and at the same time passes the surface A.sub.SO which is formed by the injection hole upper edge 33. The injection hole upper edge 33 in this case is defined as the imaginary line on which the inlet edges 31 are located. This forms the flow cross-section before the fuel flows into the injection holes 30. All of the injection holes 30 together form a total injection hole cross-section A.sub.SL so that the flow inside the blind hole 32 is determined, in particular, by the ratio of these flow cross-sections to one another. Moreover, other geometric sizes also influence the flow of fuel, in particular the so-called L-dimension, which is identified in FIG. 3 by L and which marks the distance from the transition edge 35 to the center of the injection holes 30. If the nozzle needle 14 has only performed a small part of its maximum opening stroke, the cross-section area A.sub.S forms the smallest cross-section, whilst the surface of the injection upper edge A.sub.SO accordingly is relatively large. Only when the nozzle needle 14 has exceeded a specific stroke does the total injection hole cross-section A.sub.SL form the smallest flow cross-section, so that the fuel flow is decelerated only when entering the injection hole, which does not lead to cavitation in the blind hole 32.

[0026] FIG. 4 shows a first exemplary embodiment of the injection nozzle according to the invention in the same view as FIG. 3. A needle tip 28 which protrudes into the blind hole 32 is configured on the nozzle needle 14 adjoining the conical sealing surface 27. The needle tip 28 is also conically configured and has an opening angle β which is smaller than the opening angle α of the sealing surface 27. In this exemplary embodiment, the opening angle β corresponds approximately to the opening angle σ of the blind hole wall so that a substantially constant flow cross-section is formed between the needle tip 28 and the wall of the blind hole 32. This flow cross-section extends as far as the height of the injection hole upper edge 33 so that an equalization of the flow is achieved in this region between the seat cross-section area A.sub.S and the injection holes 30. Thus it does not lead to a pressure drop when the fuel enters the blind hole 32, and thus to no cavitation formation, at least a significant reduction in the tendency to cavitation, which prevents cavitation damage in the region of the blind hole 32 and the injection holes 30. For forming this flow cross-section, the diameter D.sub.B1 of the offset edge 17 which is formed between the sealing surface 27 and the needle tip 28 is smaller than the diameter D.sub.S of the transition edge 35 (see FIG. 2) which marks the transition between the body seat 25 and the blind hole 32.

[0027] In FIG. 5 a further exemplary embodiment of the injection nozzle according to the invention is shown. Here a transition cone 24 is configured on the nozzle needle 14 between the sealing surface 27 and the needle tip 28. The opening angle β of the transition cone 24 is larger than the opening angle α of the sealing surface 27 and smaller than the opening angle β of the needle tip 28, so that an edge is also formed at the transition of the sealing surface 27 to the transition cone 24. The diameter D.sub.A of this transition edge 37 between the sealing surface 27 and the transition cone 24 is larger than the diameter of the transition edge 35 in order to form the corresponding flow path to the injection holes 30.

[0028] FIG. 6 shows a further variant of the blind hole of an injection nozzle according to the invention. In this case, the injection hole 30 has a cylindrical portion 232 adjoining the conical portion 132, which is defined by the transition edge 35 and an intermediate edge 36, a rounded dome 34 adjoining said cylindrical portion. The interaction with the correspondingly shaped nozzle needle 14 is shown in FIG. 7. In this case, over a large part of the needle stroke the conical needle tip 28 is opposite the conical portion 132 of the blind hole 32 and thus forms the flow cross-section which leads to a calming of the flow. In particular, in this case a nozzle needle 14 which has a transition cone 24 between the sealing surface 27 and the needle tip 28 may be used. A further exemplary embodiment of the injection nozzle according to the invention is shown in FIG. 8. In this case, a shoulder 26 is configured at the transition of the sealing surface 27 to the needle tip 28, the offset edge 17 being formed thereby.

[0029] In the injection nozzle according to the invention, the corresponding angles and distances have to be matched such that during the partial stroke of the nozzle needle the seat cross-section area A.sub.S is only slightly larger than the total injection hole cross-section AK so that no flow deceleration occurs when entering the blind hole 32, but only when entering the injection holes 30. In this case it is advantageous, in particular, if the diameter D.sub.s of the transition edge 35 is larger than the diameter of the intermediate edge 36 and at most 1.6 times this diameter D.sub.S2. It is also advantageous if the cone angle β of the needle tip 28 is in the region of +/−20° of the opening angle σ of the conical portion 132 of the blind hole 32.