GB2226362A

GB2226362A - I.c. engine fuel injection nozzle

Info

Publication number: GB2226362A
Application number: GB8926524A
Authority: GB
Inventors: Karl Hofmann; Rolf-Juergen Giersch
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1988-12-22
Filing date: 1989-11-23
Publication date: 1990-06-27
Anticipated expiration: 2009-11-23
Also published as: DE3843235A1; GB2226362B; JPH02196159A; GB8926524D0

Description

t 0 - 1 Fuel Injection Nozzle for Internal-Combustion Engines

Prior art

The invention is based on a fuel injection nozzle of the generic type of the main claim. In the case of known injection nozzles of this type, the mouth of the injection hole lies within the conical valve seat face of the nozzle body, the grummet of the valve needle in its closed position covering the mouth completely and interrupting the connection between injection hole and blind hole. By this isolation of the injection hole from the blind hole volume, a complete termination of the in- dividual injections is achieved and thereby the formation of harmful residues is counteracted. On the other hand, in the case of this design, the unavoidable concentricity tolerances of the components and the guide play of the valve needle may cause the grummet of the valve needle to assume a different distance from the mouth regions of the individual injection holes during the opening stroke and, as a result, cause the injection quantities to deviate from the specified values to an extent adversely affecting the engine performance. In the case of injec- tion nozzles having a needle stroke control which is provided for the purpose of a pre-injection and can be realized, for example, by an arrangement with two closing springs or an escape plunger, the spray formation at all of the injection holes of a nozzle has an inten- sified influence on the engine performance in idling and at part load in a pre-stroke range which corresponds functionally to the pre-injection and may be between 0.01 and 0.06 mm. With an unfavourable coincidence of production tolerances, it is possible in this pre-stroke - 2 range that the valve needle covers the mouth region of an injection hole and a discharge of fuel through this injection hole is Largely prevented.

Advantages of the invention The arrangement according to the invention with the characterizing features of the main claim has, in comparison, the advantage that a full spray formation at all the injection holes of the injection nozzle is ensured in the entire stroke range of the valve needle and that a defined metering cross-section is produced in the pre-stroke range. The diameter step at the transition from the grummet to the dome of the valve needle can be produced exactly and with small deviations from item to item by shaped grinding with a correspondingly sharp- ened grinding wheel.

Advantageous further developments of the arrangement according to the main claim are possible by the features listed in the subclaims.

For further restriction of the tolerances, it is proposed that the cone angle of the valve needle dome coincides at least approximately with the grummet angle or the seat angle of the valve seat face on the nozzle body.

The effect of the isolation between injection hole and blind hole volume upon closing or in the closed position of the valve needle is not markedly impaired if the width of the annular gap produced in the closed position of the valve needle between the valve needle dome and the conical inside watt region of the nozzle body ties in the range from 0.01 to 0.05 mm.

The arrangement according to the invention is particularly advantageous in the case of injection nozzles for pre-injection and main injection with nozzle stroke control, because the maintaining of a minimum gap in front of all the injection hole mouths in the prestroke range is particularly important in the case of these injection nozzles - as already mentioned above.

- 3 D r a w i n g An exemplary embodiment of the invention is represented in the drawing and explained in more detail in the following description. Figure 1 shows a Longitud- inaL section through an injection nozzLe with needle stroke control by two closing springs, Figure 2 shows, enlarged, a section through the end, on the combustion chamber side, of the injection nozzLe according to Figure 1 and Figure 3 shows a representation correspond- ing to Figure 2 of a variant of the injection nozzle according to Figures 1 and 2.

Description of the exemplary embodiment

An injection nozzle has a nozzle body 10, which is clamped together with a shim 12 by a union nut 14 on a nozzLe holder 16. In the nozzLe body 10 there is dispLaceabLy mounted a valve needle 18, which interacts with an inwardly turned valve seat face 19 in the nozzle body 10, in front of which there are a plurality of injection openings 20. As usual, the guide bore of the valve needle 18 is widened at one point into a pressure space 21, in the region of which the valve needle 18 has a pressure shoulder 22 and which is connected via a channeL 23 to a connection piece 24 on the nozzle holder 16 for the connecting of a fuel feed Line. The fuel acting on the pressure shoulder 22 pushes the valve needle 18 upwards against the graduated force variation of a cLosing spring arrangement described below, the fueL-being discharged through the injection openings 20 in a preinjection phase and a main-injection phase.

In the nozzLe holder 16 there is formed a first chamber 26 for receiving a first closing spring 28, which is supported via a disc 30 on the bottom of the chamber 26 and constantly acts via a thrust piece 32 and a thrust bolt 34 on the valve needle 18. The chamber 26 merges at a housing shoulder 36 with a second chamber 38, in which a second closing spring 40 is arranged, which surrounds - 4 the thrust bolt 34. The closing spring 40 is supported via discs 42, 44 on the housing shoulder 36 and via a thrust piece 46 on the upper end face of the shim 12.

The thrust piece 46 is guided displaceably on the wall of the chamber 38 with the necessary movement play. The end 48, facing the valve needle 18, of the thrust bolt 34 is of a smooth design and is guided displaceabLy in the thrust piece 46. The valve needle 18 is provided with an end pin 50, which protrudes into the shim 12 and on which the thrust bolt 34 acts directty. The end pin 50 is dimensioned such that, in the closed position of the valve needle 18, it lies underneath the upper end face of the shim 12 by the amount of the pre-stroke hv. After covering the pre-stroke hv, the end pin 50 strikes the thrust piece 46, after which both closing springs 28, 40 act on the valve needle 18 in the closing sense. The overall stroke hg of the valve needle is limited, as known, by the annular shoulder 52, formed at the transition to the end pin 50, of the valve needle 18 and by the lower end face of the sh im 12.

The valve seat 19 is formed on an inside wall region 56 of the nozzle body 10, which region conically bounds the pressure space 21 and merges without steps or edges with the wall of a blind hole 58. The valve needle 18 has a grummet 60, which merges downstream at a stepped edge 62 with a dome 64, entering into the blind hole 58. The injection holes 20 open out from the nozzle body 10 directly underneath the valve seat face 19, interacting with the grummet 60. In the closed position of the valve needle 18, the distance between the flattened-off dome apex 66 of the valve needle 18 and the blind hole base 68 is smaller than the distance between the blind hole base 68 and the injection holes 35 20.

The dome 64 of the valve needle 18, adjoining the grummet 60 with a stepped edge 62, is likewise of a conical design. The cone angle of the dome 64 corresponds to the cone angle of the inside wall region 56 or of the 1 - 5 vaLve seat face 19 of the nozzLe body 10, so that, in the cLosed position of the vaLve needLe 18, an annuLar gap 72 which is of the same width throughout is produced between the remaining bLind hoLe voLume 70 and the injec5 tion hoLes 20. The gap width may be between 0.01 and 0.05 mm, it being possibLe to maintain these vaLues exactLy by shaped grinding of the vaLve needLe 18.

In the cLosed position shown of the vaLve needLe 18, a certain isoLating effect between the residuaL bLind hoLe voLume 70 and the injection hoLes 20 is maintained by the narrow annuLar gap 72 and the formation of harmfuL residues is thereby counteracted. When the vaLve needLe 18 is opening, the annuLar gap 72 ensures that the vaLve needLe 18 cannot cover any of the injection hoLes 20 if there happens to be any offset from centre, so that a discharge from aLL the injection hoLes 20 is ensured aLso in the pre-stroke range in particuLar.

The variant according to Figure 3 differs from the design described above mereLy in that the conicaL inside waLL region 56 of the nozzLe body 10a merges at an annuLar edge 74 with a cyLindricaL bLind hoLe 58a.

6 -

Claims

1. Fuel injection nozzle for internal-combustion engines, having a nozzle body, in which a valve needle, provided with a grummet and a dome adjoining the latter, is mounted displaceably and a fuel pressure space surrounding the valve needle is formed, adjoining which space downstream is a conical inside wall region of the nozzle body, which region merges with the wall of a blind hole and at which a valve seat face, interacting with the grummet of the valve needle, is formed and at least one injection hole opens out at a point which is further away from the blind hole base than the dome apex of the valve needle when the latter is in the closed position, characterized in that the injection hole (20) opens out downstream of the valve seat face (19) at the conical inside wall region (56) of the nozzle body (10), and the (sic) the valve needle dome (64) adjoining the grummet (60) of the valve needle (18) adjoins the grummet (60) with a diameter step (62) and is designed as a cone or truncated cone.

2. Injection nozzle according to Claim 1, characterized in that the cone angle of the valve needle dome (64) coincides at least approximately with the grummet angle of the valve needle (18) or the seat angle of the valve seat face (19) of the nozzle body (10).

3. Injection nozzle according to Claim 1 or 2, characterized in that the width of the annular gap (72), produced in the closed position of the valve needle (18), between the valve needle dome (64) and the conical inside watt region (56) of the nozzle body (10) lies in the range from 0. 01 to 0.05 mm.

4. Injection nozzle according to one of the a, 0 7 preceding claims, characterized by means for needle stroke control, preferably by a closing spring arrangement with two springs (28, 40) of different length during the open ing stroke or acting on the valve needle (18) at different times.

5. A fuel injector nozzle substantially as herein described with reference to Figures 1 and 2, or Figures 1 and 2 as modified by Figure.3.

-- Published 1990 at The Patent Office. State Hoise-66 71Higl,.Hcl.borr..

London WC1P 4TP Further copies maybe obtaine,' from The Paten'. OL,e