EP0980474A1

EP0980474A1 - Fuel injector for auto-ignition internal combustion engines

Info

Publication number: EP0980474A1
Application number: EP98936237A
Authority: EP
Inventors: Karl Hofmann; Friedrich Boecking
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1997-12-11
Filing date: 1998-06-19
Publication date: 2000-02-23
Anticipated expiration: 2018-06-19
Also published as: JP4223077B2; JP2001511231A; EP0980474B1; DE59810346D1; DE19755057A1; US6257506B1; WO1999030028A1

Abstract

The invention relates to a fuel injector for auto-ignition internal combustion engines. Said injector comprises a body (30) with a conical seat surface (32) from which injection openings (34) originate. It also comprises a valve needle which is slidably guided in the entry zone of the blind bore, through a guiding section, against a closing force and against the direction of fuel flow. The valve needle has a closing cone (12) disposed at the end of a valve spindle connected to the guiding section and co-operating with the seat surface (32). The valve spindle (10) circumferentially defines an annular space (40) for fuel feeding. The inventive injector is characterised in that a throttle device with a variable throttle cross section is placed in the transition zone between the valve spindle (10) and the closing cone (20). Said throttle device allows for a varying amount of injected fuel, depending on the axial displacement of the valve needle.

Description

Fuel fine spray nozzle for self-igniting

Internal combustion engines

State of the art

The invention relates to a fuel injection nozzle for self-igniting internal combustion engines with a nozzle body, in which a conical seat is formed in the bottom of a blind bore, from which spray openings originate, and with a valve needle, which can be displaced with a guide section in the entrance region of the blind bore against a closing force and against the fuel flow direction is guided and which at the end of a valve stem adjoining the guide section has a closing cone which interacts with the seat surface, the valve stem delimiting an annular space on the circumference for the force supply. Such fuel injection nozzles emerge, for example, from DE-OS 37 34 587 and from German utility model 93 01 992.0. In the fuel injector resulting from DE-OS 37 34 587, a control passage for the injection fuel, which is influenced by the stroke of the valve needle, is provided to prevent the so-called back-blowing of the combustion gases, the passage cross section of which, during the closing stroke of the valve needle, decouples the pump-side relief shaft from the fuel pressure in the blind hole Throttle cross section reduced.

In the fuel injector resulting from the German utility model 93 01 992.0, a guide sleeve which surrounds the valve shaft and which has a conically shaped end face and in its section near the conical end face has several recesses reaching to the conical end face, to prevent the closing cone from being caused by Clearance or an eccentricity of the valve needle or even with lateral forces acting on the valve needle with a small opening stroke or with the preliminary stroke partially or completely covers the spray holes, which results in an impairment of the combustion process.

A problem with such fuel injection nozzles is that a small stroke of the valve needle already causes large flow rates. In the pre-stroke area in particular, the stroke-dependent flow characteristic curve is very steep.

Apart from negative combustion processes, this is particularly problematic because it results in different, with different tolerances fueled fuel injectors cause very different flow rates with the same stroke.

In addition, it has been shown that a staged or at least slowly increasing injection at the start of injection generally leads to an improvement in the emission values of the internal combustion engine.

The invention is therefore based on the object of developing a generic fuel injection nozzle in such a way that the above-mentioned manufacturing tolerances do not adversely affect the injection process, in particular in the area of the advance stroke, and that a slowly increasing injection is achieved at least at the start of injection.

Advantages of the invention

This object is achieved in a fuel injection nozzle of the type described in the introduction in that a variable throttle device is arranged in the transition area between the valve stem and the closing cone, by means of which the injection quantity can be varied depending on the axial displacement of the valve needle.

The arrangement of such a throttle device has the particularly great advantage that not only is it possible to vary the injection quantity in such a way that it increases continuously at the beginning of the injection process, but that the injection quantity can also be varied such that only small flow changes occur, particularly in the pre-stroke area a lifting movement of the Valve needles arise and, as a result, manufacturing tolerances occur far less disruptively than in known fuel injection nozzles.

A wide variety of embodiments are conceivable with regard to the design of the throttle device.

An advantageous embodiment provides that the throttle device comprises a shoulder formed in the annular space and a control edge arranged at a distance from it and formed on the valve needle and adjoining it at least one conical surface downstream. The shoulder, the control edge arranged at a distance from it, and the at least one conical surface adjoining the control edge downstream enable a throttle with a throttle cross-section that decreases by axial movement of the valve needle in a very advantageous, technically simple manner.

An advantageous embodiment provides that the control edge of the shoulder is substantially opposite. In this way, a defined initial throttle cross section is advantageously realized.

In another embodiment, the control edge is located slightly downstream of the shoulder. This ensures that, in the event of a slight axial displacement, the initial throttle cross section is initially maintained until the control edge runs over the shoulder. As far as the formation of the conical surface adjoining the control edge is concerned, a wide variety of embodiments are also conceivable here.

The conical surface is advantageously determined depending on the arrangement of the control edge with respect to the shoulder.

An advantageous embodiment provides that the conical surface adjoining the control edge has a smaller conical angle than the conical seat surface. In conjunction with the initial throttle cross-section determined by the distance of the control edge from the shoulder, a start of the injected fuel injection quantity is achieved, in which the conical seat surface of the valve needle is also included in the throttling process in a very advantageous manner.

In addition, it is also possible that the conical surface adjoining the control edge has a larger conical angle than the conical seat surface.

In a further embodiment of a throttle device which is advantageous with regard to its manufacture, it is provided that a sleeve which is axially displaceable against the restoring force of a spring is arranged in the annular space and has a conically shaped end face on the outer annular surface of the conical seat surface is present and in the at least two axially displaceable valve pins are successively provided for controllable openings with different opening cross-sections. Such a sleeve has in particular the very great advantage that it is not only easy to manufacture, but also easy to assemble, especially outside the nozzle body.

As far as the arrangement and design of the openings with different opening cross-sections, which can be opened one after the other by axial displacement of the valve needle, it could in principle have a very different shape. An advantageous embodiment provides that a first opening above a control edge formed on the valve stem in the jacket of the sleeve and a second opening with a smaller opening cross-section than that of the first opening are arranged below the control edge formed on the valve stem. The opening provided in the conical front face takes over an initial throttling, whereas the opening provided in the jacket enables the throttle cross-section to decrease depending on the valve needle stroke by axially displacing the valve needle. The opening provided in the jacket can have an elliptical, oval, round, triangular, quadrangular or polygonal shape.

In another advantageous embodiment it is provided that two rows of holes lying one above the other are arranged in the casing of the sleeve, the downstream row of holes having a smaller total opening cross section than that upstream row of holes. This embodiment of the throttle device advantageously also enables filtering of the injected fuel cross section.

A further advantageous embodiment provides that an axially displaceable sleeve is arranged in the annular space against the restoring force of a spring, which has a conically shaped end face which bears against the outer annular surface of the conical end face and that the sleeve opposite in the valve stem cooperates with at least one sleeve Recess is arranged, the opening cross section increases steadily towards the conical seat surface at the end of the sleeve facing the guide portion of the valve needle.

Yet another advantageous embodiment provides that a sleeve which is axially displaceable against the restoring force of a spring and which can be taken along by the axial displacement of the valve needle is arranged in the annular space, which sleeve rests with a conically shaped end face on the outer annular surface of the conical seat surface and in which is conical Front side has at least one recess open to the front side.

In the latter embodiment, the sleeve is particularly simple and can be produced with a few manufacturing steps. drawing

Further features and advantages of the invention are the subject of the following description and the drawing of some exemplary embodiments.

The drawing shows:

Fig. 1 jweils in half sectional view, and partially broken away, two embodiments of a solubilizing use of the invention Kraftstoffeinspritzduse, ^•

2 each in a half-sectional view and partially broken away, two further exemplary embodiments of a fuel injector making use of the invention;

3 shows a half-sectional view of a throttle device of a fuel injector making use of the invention;

3a shows an enlarged detail of the throttle device shown in FIG. 3;

4 each in a half-sectional view and partially broken away, two further exemplary embodiments of a fuel injection valve according to the invention;

5 each in a half-sectional view and partially broken away, two further exemplary embodiments of a fuel injection valve according to the invention. Description of the exemplary embodiments

The lower area of an exemplary embodiment of a fuel injector for self-igniting internal combustion engines is shown in FIG. 1 on the left half of the figure.

As is apparent from FIG. 1, the fuel injection nozzle has a nozzle body 30, in which a conical seat surface 32 is formed in the bottom of a blind bore 31, from which spray openings 34 extend. A valve needle is axially displaceably arranged in the blind bore 31, which is guided axially displaceably with a guide section (not shown) in the entrance region of the blind bore against a closing force and against the direction of fuel flow and which at the end of a valve stem 10 adjoining the guide section has a seat 32 cooperating closing cone 12.

The valve stem 10 delimits an annular space 40 on the circumference, which serves to supply fuel. A throttle device with a variable throttle cross section is arranged in the transition area between the valve stem 10 and the closing cone 12, by means of which the injection quantity can be varied depending on the axial displacement of the valve needle. The throttle device comprises a shoulder 31, which is formed in the annular space on the nozzle body 30, and a control edge 20, which is formed slightly downstream on the valve stem 10 of the valve needle and against which connect two conical surfaces 21, 22 downstream with different cone angles.

The function of such a throttle device with a variable throttle cross-section is as follows: First, a first throttle cross-section is realized by the distance between the shoulder 31 and the control edge 20 and thus that between the shoulder 31 and the valve stem 10. By axially displacing the valve stem 10 against the direction of flow of the fuel to be injected, i.e. 1 upwards, the throttle cross section does not initially change until the control edge 20 has carried out a lifting movement designated by U in FIG. 1 and the control edge passes over the shoulder 31. At this moment, the first conical surface 21 lies opposite the shoulder 31, which due to its conicity leads to a reduction in the throttle cross section when the valve needle is displaced further axially.

This decreases further as soon as the second conical surface 22 begins to drive over the shoulder 31, so that the cross-sectional area from the annular space 40 to the spray openings 34 increases with the further opening stroke movement of the valve needle.

The exemplary embodiments shown in FIG. 1 on the right half of the figure and the exemplary embodiments shown in FIG. 2 on the left and right half of the picture differ from the exemplary embodiment shown above in FIG. 1 on the left half of the picture by the different arrangement of control edge 20 and shoulder 31 Here are the elements that are identical to those of the first exemplary embodiment shown in FIG. 1 on the left half of the figure, provided with the same reference numerals, so that with regard to their description, reference is made in full to the statements relating to the first exemplary embodiment.

A further exemplary embodiment of a nozzle with a variable throttle cross section, which is used in particular in injectors for common rail injection systems, is shown in FIGS. 3 and 3a.

In FIG. 3, those elements that are identical to those of the exemplary embodiments shown in FIGS. 1 and 2 are provided with the same reference numerals, so that reference is made to the explanations for these exemplary embodiments with regard to their description. The embodiment shown in FIG. 3 from a common rail fuel injector differs in that the valve seat, known per se, is used in common rail nozzles. The embodiment shown in FIG. 3 also differs from the embodiments shown in FIGS. 1 and 2 in that the control edge 20 formed on the valve needle 10 is located directly opposite the shoulder 31 formed on the valve body 30 at a distance d1. A conical surface 23 adjoins the control edge 20, the conical angle δ1 of which is smaller than the angle δ2 of the closing cone. The gap formed due to the distance d1 makes the transition from the opening area to the forward stroke area Fuel injector set. This can also be changed in that the control edge 20 is arranged slightly at a distance h.2 under the shoulder 21.

With such a design of the throttle device, the closing cone 12 is included in the throttle function of the throttle device in the manner described below.

The function of the fuel injection nozzle shown in FIGS. 3 and 3a is as follows: First, the closing cone 12 lifts slightly from the valve seat 32, as a result of which a gap is formed between the closing cone 20 and the valve seat 32, the width of which is smaller than the distance d1 between the control edge 20 and the shoulder 31. Because of these spacing relationships, the gap between the closing cone 12 and the valve seat 32 initially forms a throttle. With a further axial movement of the valve needle, the gap between the shoulder 31 and the control edge 20 on the valve stem 10 increases continuously, approximately until the conical surface 23 adjoining the control edge 20 moves along the shoulder 31, i.e. until the valve needle 10 has performed an axial stroke of height hl. This initially enables a flat increase in the injection quantity with increasing stroke of the valve needle, which increases after increasing the axial stroke of size h1 with increasing axial stroke.

This not only enables injection course shaping in a particularly advantageous manner, but it does In particular, disadvantageous variations in the injection quantity due to manufacturing tolerances are eliminated.

Further exemplary embodiments of throttle devices for fuel injection nozzles are shown in FIGS. 4 and 5 as half-sectional views.

In the exemplary embodiments shown in FIGS. 4 and 5, those elements which are identical to those of the exemplary embodiments described above are provided with the same reference numerals, so that with regard to their description reference is made to the explanations regarding the exemplary embodiments described above. The exemplary embodiments shown in FIGS. 4 and 5 differ from the exemplary embodiments shown in FIGS. 1 to 3 in that instead of forming a shoulder 31 in the annular space 40, a sleeve 50 which is axially displaceable counter to the restoring force of a spring (not shown) is arranged, which rests with a conical end face on the outer ring surface 32a of the conical seat surface 32.

In the sleeve 50 shown in FIG. 4 on the left half of the figure, two openings 52, 53 which can be opened one after the other by axial displacement of the valve needle and consequently of the valve stem 10 are provided in the sleeve, the first opening 52 of which is arranged in the jacket of the sleeve 50 and the second opening thereof 53 is provided on the conical end face 51, for example in the form of grooves. On the valve stem 10, a control edge 70 is provided which, when the fuel injector is closed, is arranged at a predetermined distance U below the first opening 52 with a larger opening cross section. In such a fuel injection nozzle, the opening 53 provided in the conical end face 51 initially acts as a throttle, which leads to an injection quantity determined by the opening cross section of the second opening 53 when the valve stem 10 is slightly displaced axially. In the event of a further axial displacement of the valve stem 10, the control edge 70 passes over the opening 52, which is arranged in the casing of the sleeve 50 and has a larger opening cross section, as a result of which the amount of fuel injected increases continuously with increasing stroke movement of the valve stem 10.

4, the two openings of different opening cross-sections are each formed by a row of holes 61, 62, the downstream row of holes 61 having a smaller overall cross-section than the upstream row of holes 62.

In this case, the control edge 70 lies between the first and the second row of holes 61, 62. By axially displacing the valve stem 10, the control edge 70 passes over the upstream row of holes 61 and opens it continuously with increasing stroke movement, as a result of which the throttle cross section decreases continuously. The embodiment shown in FIG. 5 on the left half of the figure differs from the embodiment shown in FIG. 4 in that a plurality of recesses 80 cooperating with the sleeve 50 are arranged opposite the sleeve 50 in the valve stem 10, the opening cross section of which is on the closing cone 12 facing away and a (not shown) guide portion of the valve needle facing end of the sleeve 50 increases steadily towards the conical seat. This area 81 represents a throttle with a variable throttle cross section, which is continuously reduced by a lifting movement of the valve stem 10.

In the embodiment shown in FIG. 5 on the right half of the figure, the sleeve 50 is designed such that it can be taken along by the valve stem 10 by an axial displacement of the valve needle and thus of the valve stem 10. For this purpose, the valve stem 10 has a shoulder 17 which engages on a projection 57 of the sleeve 50. The sleeve 50 has in the conically shaped end face 51 toward the end face open recesses 55, which represent a throttle cross section that decreases with increasing axial displacement of the valve stem 10. As shown in FIG. 5, the projection 57 is arranged at a distance from the shoulder 17 formed on the valve needle 10 in such a way that the sleeve 50 is initially not carried along when the valve needle is moved. In this case, the amount of fuel injected is determined by the conical end face 51 trained openings 55, which perform a throttle function.

The distance of the projection 57 over the shoulder 17 corresponds to a forward stroke of the fuel injector.

The above description relates to a spray nozzle, but it is understood that the invention is not limited to such a spray nozzle, but can also be used in a corresponding manner in a blind nozzle.

Claims

claims

Fuel injection nozzle for self-igniting internal combustion engines with a nozzle body (30), in which a conical seat surface (32) is formed in the bottom of a blind bore (37), from which spray openings (34) extend, and with a valve needle, which has a guide section in the entrance region of the blind bore (37) is displaceably guided against a closing force and against the direction of fuel flow and which at the end of a valve stem (10) adjoining the guide section has a closing cone (12) which interacts with the seat surface (32), the valve stem (10) having an annular space ( 40) for the fuel supply limited, characterized in that a throttle device with a variable throttle cross section is arranged in the transition region between the valve stem (10) and the closing cone (20), by means of which the injection quantity can be varied depending on the axial displacement of the valve needle.

2. Fuel injection nozzle according to claim 1, characterized in that the throttle device has a shoulder (31) formed in the annular space (40) and a control edge arranged adjacent to it at a distance and on the valve stem (10)

(20), to which at least one conical surface (21, 22) is connected downstream.

3. Fuel injection nozzle according to claim 2, characterized in that the control edge (20) of the shoulder (31) is substantially opposite.

4. Fuel injection nozzle according to claim 2, characterized in that the control edge (20) is arranged slightly downstream of the shoulder (31).

5. Fuel injection nozzle according to claim 3 or 4, characterized in that the at least one conical surface (21, 22) adjoining the control edge (20) has a smaller conical angle than the conical seat surface (20).

6. Fuel injection nozzle according to claim 3 or 4, characterized in that the at least one conical surface (21, 22) adjoining the control edge (20) has a larger conical angle than the conical seat surface (20).

7. Fuel injection nozzle according to claim 1, characterized in that in the annular space (40) against the restoring force of a spring axially displaceable sleeve (50) is arranged, which with a conical end face (51) bears against the outer ring surface (32a) of the conical seat surface (32) and in which at least two openings (52, 53; 61, 62) with different opening cross-sections that can be opened one after the other by axial displacement of the valve needle are provided.

8. Fuel injection nozzle according to claim 7, characterized in that a first opening (52) above a control edge formed on the valve stem (70) in the jacket of the sleeve (50) and a second opening (53) with a smaller opening cross section than that of the first opening

(52) are arranged in the end face (51) formed on the sleeve (50).

9. Fuel injection nozzle according to claim 7, characterized in that in the shell of the sleeve (50) two rows of holes (61, 62) one above the other are arranged, wherein the downstream row of holes (61) has a smaller total opening cross section than the upstream row of holes (62) and a control edge (70) formed on the valve stem (10) is arranged between the two rows of holes (61, 62) in the closed state of the fuel injector.

10. Fuel injection nozzle according to claim 1, characterized in that in the annular space (40) against the restoring force of a spring axially displaceable sleeve (50) is arranged, which with a conical end face rests on the outer annular surface (32a) of the conical seat surface (32) and that the sleeve (50) is arranged opposite in the valve stem (10) at least one recess (80) cooperating with the sleeve (50), the opening cross section of which at the end of the sleeve (50) facing the guide section increases steadily towards the conical seat surface.

11. A fuel injector according to claim 1, characterized in that in the annular space (40) against the restoring force of a spring axially displaceable, by an axial displacement of the valve needle removable sleeve (50) is arranged, which with a conically shaped end face (51) on the outer ring surface (32a) of the conical seat surface (32) and the conical end face (51) has at least one recess (55) open towards the end face.