GB2186632A

GB2186632A - Fuel injection nozzle for i.c. engines

Info

Publication number: GB2186632A
Application number: GB08701149A
Authority: GB
Inventors: Klaus Wolf
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1986-02-18
Filing date: 1987-01-20
Publication date: 1987-08-19
Also published as: JPS62210259A; GB8701149D0; DE3605082A1

Abstract

A blind hole 16 is located downstream of the valve seat 14 from which spray bores 18, 19 lead and the needle tip 30 has a convex surface portion 36 and, downstream of this, a concave surface portion 40. This needle tip counteracts a breakaway of the flow and the formation of stagnant areas in the blind hole. The valve needle can be provided with an annular slot 32 in the sealing surface 34. The transition 44 between the valve seat 14 and the blind hole 16 can be rounded-off and bores (76, 78, 84, Fig. 2) provided in the valve needle. The tip may have further surface portions (Figs. 1a, 1b and 3). <IMAGE>

Description

SPECIFICATION Fuel injection nozzle for internal-combustion engines State of the Art The invention starts from a fuel injection nozzle according to the pre-characterizing clause of the main claim. In known injection nozzles of this type, the needle tip is designed over its entire length as a uniformly tapering cone.

In this design, in part ranges of the field of operating characteristics it is not possible completely to prevent the flow from breaking away and so-called dead-water areas from forming in the blind hole and in the adjacent portions of the spray bores, and as a result of this notable differences in fuel consumption and in the formation of black smoke occur in these part ranges of the field of operating characteristics. Where injection nozzles of the type mentioned in the introduction are concerned, it is also known to provide the needle tip over its entire length with a convex or a concave outer surface (DE-A-3,014,958).

However, these measures taken in relation to another object in themselves still do not result in any reduction in the disadvantages mentioned above, especially because they do not lessen the dead blind hole volume, but instead enlarge it. As regards blind hole nozzles with spray bores starting from the valve seat (DE A-2,710,217), it is known to relieve the blind hole via a longitudinal bore and a transverse bore in the valve needle and provide the valve needle with an annular groove in the sealing surface in order to seal off the spray bores more effectively.

Advantages of the Invention In contrast to this, the advantage of the arrangement according to the invention, which has the characterizing features of the main claim, is that the tendency of the flow to break away in the region of the valve passage and in the blind hole or at the valve-needle tip and the formation of so-called dead-water areas are reduced, thereby improving the flow and the formation of the jet.

The arrangement according to the main claim can be developed advantageously by means of the measures indicated in the subclaims.

As a result of the constructive features according to claims 2 to 7, the form of the needle tip can be adapted to meet the requirements of the particular use as closely as possible. The end of the needle tip itself can be of varying design, for example it can be flattened or rounded to a greater or lesser extent.

It is especially advantageous if, in addition to the features contained in the main claim, according to claim 8 the transition formed between the valve seat of the nozzle body and the blind hole is well rounded off or chamfered. This particularly effectively prevents the flow from breaking away in this region also. In addition to this, measures can be taken to lessen the blind hole volume and thus reduce HC emission. For this purpose, according to claim 9 the geometry of the blind hole can be matched approximately to the form of the needle tip.

Furthermore, according to claim 10, in order to lessen the blind hole volume and further improve the flow, the bottom of the blind hole is provided with flow-guiding wall portions. To form these wall portions, the blind hole bottom can have a conical or hemispherical contour which causes the flow to divide and be guided or deflected towards the spray bores.

The contour of the cone can be limited by a straight line or a curve.

A design of the injection nozzle according to claims 11 and/or 12 is especially advantageous. An annular slot or annular groove in the sealing surface of the valve needle assists the formation of a turbulent flow boundary layer which, as it streams round an edge or a set-back contour, rests against this for longer than a laminar flow. Consequently, in injection nozzles of the present generic type, the measure according to claim 11 results in an improved flow behaviour and the prevention of so-called dead-water areas in the valve gap and in the blind hole. The measure according to claim 12 is based on the principle of the sucking-off of low-energy boundary layers located near the wall. In the present case, this measure also makes it more difficult for the flow to break away from the surface of the valve-needle tip.The low-energy boundary layer will be sucked off through the bores in the valve needle immediately behind the valve cone. The suction effect necessary for this is produced, in a similar way to a jet pump, as a result of the increased flow speed in the bores.

The measures according to claims 11 and 12 can be combined with the measures of claim 1 in an especially advantageous and effective way.

Drawing Three exemplary embodiments of the invention are illustrated in the drawing and explained in detail in the following description.

Figure 1 shows the first exemplary embodiment in an enlarged partial longitudinal section, Figs. 1a and 1b each show an alternative form of the exemplary embodiment according to Fig. 1 by means of contour lines of the needle tip, and Figures 2 and 3 show the second and third exemplary embodiments in a representation corresponding to that of Fig. 1.

Description of the Exemplary Embodiments The injection nozzle according to Fig. 1 has a nozzle body 10 provided with a central bore 12, into which opens a fuel feed line (not shown). On the same side as the combustion space, the bore 12 merges via a conical valve seat 14 into a blind hole 16, from which at least two spray bores 18, 19 lead outwards.

Mounted displaceably in the bore 12 is a valve needle 20 which, upstream of the valve seat 14, limits an annular space 21, via which the fuel reaches the valve seat 14. The valve needle 20 has a conical portion 23 which starts at an annular edge 22 and which merges at an annular edge 24 into a valve cone 26. The latter has a somewhat larger cone angle than the portion 23 and interacts with the valve seat 14 of the nozzle body 10 as the closing member of the latter.

At an annular edge 28, the valve cone 26 adjoins a needle tip 30 which penetrates completely into the blind hole 16 when the valve needle 20 is in the closing position. The annular space 22 is limited at the top by a pressure shoulder (not shown) of the valve needle 20, at which pressure shoulder the fuel exerts on the valve needle 20 a force which acts in the opening direction. A closing spring also acts on this valve needle and is accommodated in a nozzle-holder, against which the nozzle body 10 is clamped in the conventional way by means of a nozzle nut.

According to the invention, the valve needle 20 is provided, in the region of its valve cone 26, with an annular slot 32 which interrupts locally the sealing surface 34 formed on the valve cone 26. A cross-sectional profile of the annular slot 32 can be limited by straight lines, as in the exemplary embodiment, or by a curved baseline. The needle tip 30 has a convex outer-surface portion 36 which immediately adjoins the annular edge 28 and which merges directly, at a turn line 38, into a concave outer-surface portion 40. The latter terminates in a rounded-off end 42 of the needle tip 30. The transition 44 between the valve seat 14 and the blind hole 16 is well rounded or chamfered, and the bottom of the blind hole 16 is provided with flow-guiding wail portions 46, 48. These are formed on an elevation 50 which reduces the volume of the blind hole 16.The conventional form of the blind hole is indicated by a broken line 52.

The fuel flowing through the valve gap 54 when the valve needle 20 is opened acquires, as a result of the annular slot 32, a turbulent boundary layer which appreciably reduces the tendency of the flow to break away from the valve needle 20 at the annular edge 28 and downstream of the latter. The above-described design of the needle tip 30 and the pronounced rounding-off of the transition 44 also counteract the tendency of the flow to break away. Furthermore, the flow-guiding wall portions 46, 48 on the bottom of the blind hole ensure that the flow is deflected into the spray bores 18, 19 with very little loss. The interaction of all the measures according to the invention effectively prevents the flow from breaking away and so-called dead-water areas forming over relatively wide part ranges of the field of operating characteristics.

The alternative forms according to Figs. 1 a and 1 b each differ from the above-described exemplary embodiment in slightly modified contours of the needle tip 30a and 30b. In the needle tip 30a, a convexly curved outersurface portion 36a merges tangentially into the sealing surface 34 of the valve cone 26, so that there is no annular edge between the two surface portions and the needle tip 30a starts at an imaginary cross-sectional plane 56 in an outwardly imperceptible way. The outersurface portion 36a has adjoining it tengentially in turn a conical outer-surface portion 58, a concave outer-surface portion 40a and then again a conical portion 60 which extends up to a relatively sharp tip 62.

The needle tip 30b differs from that according to Fig. 1 in that the annular edge 28b is first followed by a conical outer-surface portion 63 which has a somewhat larger cone angle than the sealing surface 34. The portion 63 has adjoining it a convex portion 36b and then a concave portion 40b which itself merges tangentially into a conical portion 64 extending up to a tip 66. Other combinations of conical, convex and concave surface portions are possible, but it is always essential to the invention that a convex portion should be followed downstream by a concave portion.

In the injection nozzle according to Fig. 2, which is of basically the same design as that according to Fig. 1, a valve needle 70 is provided, in the region of the valve cone 72, with an annular slot 74 and a transverse bore 76 opening into this on both sides. A longitudinal bore 78 branches off from this transverse bore and opens out on the end face 79, located on the same side as the combustion space, of a needle tip 82 starting at the cross-sectional plane 80. In the region of the needle tip 82, the valve needle 70 is provided with a second transverse bore 84 which intercepts the longitudinal bore 78. The outer contour of the needle tip 82 is defined by a convex outer-surface portion 86 starting at the cross-sectional plane 80 and by a concave outer-surface portion 88 which directly adjoins it and which extends up to the flattened end face 79.

When the valve needle 70 is opened, the fuel flows through the valve gap 89 and through the bores 76, 78, a vacuum being generated in the transverse bore 84 in the manner of a jet pump. As a result of this vacuum, low-energy boundary layers of the flow streaming past the needle tip 82 are sucked up, thereby likewise counteracting a breakaway of flow from the needle tip 82.

In the injection nozzle according to Fig. 3, a valve needle 90 has a needle tip 92 which, in turn, has a convex outer-surface portion 94 and, downstream of this, a concave outer-surface portion 96. When the valve needle 90 is in the closing position, the needle tip 92 penetrates into a blind hole 98, the counter of which corresponds approximately to the form of the needle tip 92. The dead volume of the blind hole 98 is further minimized as a result, and this has a favourable effect on the HC emission.

Claims

1. Fuel injection nozzle for internal-combustion engines, with a nozzle body provided with a central bore which, on the same side as the combustion space, merges via a conical valve seat into a blind hole, from which at least one spray bore leads outwards, and also with a valve needle which is mounted displaceably in the central bore and which, upstream of the valve seat, limits in the bore an annular space serving for the fuel supply and, on the same side as the combustion space, is provided with a valve cone which interacts with the valve seat and which adjoins, without a step in diameter, a needle tip penetrating into the blind hole when the valve needle is in the closing position, characterized in that, as seen in the direction of flow of the fuel, the needle tip (30, 82, 92) has a convex outer-surface portion (36, 88, 94) and, downstream of this, a concave outer-surface portion (40, 88, 96).

2. Injection nozzle according to claim 1, characterized in that the two outer-surface portions (36, 40) of the needle tip (30) merge directly into one another at a turn line (38) (Figs. 1 and 1b).

3. Injection nozzle according to claim 1, characterized in that the convex outer-surface portion (36a) is followed immediately by a conical outer-surface portion (58) (Fig. 1a).

4. Injection nozzle according to one of claims 1 to 3, characterized in that an annular edge (28) is formed between the valve cone (26) and the needle tip (30) of the valve needle (20) (Figs. 1 and 1b).

5. Injection nozzle according to claim 4, characterized in that the annular edge (28b) is followed by a conical outer-surface portion (63) of the needle tip (30b) (Fig. 1b).

6. Injection nozzle according to one of claims 1 to 3, characterized in that the valve cone (26) of the valve needle (20) merges into the needle tip (30a) without steps or edges (Fig. la).

7. Injection nozzle according to one of the preceding claims, characterized in that the concave outer-surface portion (40b) of the needle tip (30b) is followed by a conical outer-surface portion (64) (Fig. 1b).

8. Injection nozzle according to one of the preceding claims, characterized in that the transition (44) formed between the valve seat (14) and the blind hole (16) of the nozzle body (10) is rounded off or chamfered (Fig.

1).

9. Injection nozzle according to one of the preceding claims, characterized in that the geometry of the blind hole (98) is matched approximately to the form of the needle tip (92) (Fig. 3).

10. Injection nozzle according to one of claims 1 to 8, characterized in that the bottom of the blind hole (16) is provided with flowguiding wall portions (46, 48) (Fig. 1).

11. Injection nozzle especially according to one of the preceding claims, characterized in that the valve needle (20) is provided, on the valve cone (26), with at least one annular slot (32) or annular groove which interrupts the sealing surface (34).

12. Injection nozzle especially according to one of the preceding claims, characterized in that the valve needle (70) is provided, in the valve cone (72) and in the needle tip (82), with at least one transverse bore (76, 84) each and is provided with a longitudinal bore (78) which connects the transverse bores (76, 84) and which opens out on the end face (79) of the needle tip (82) located on the same side as the combustion space (Fig. 2).

13. Any of the fuel injection nozzles substantially as herein described with reference to the accompanying drawings.