GB2234551A

GB2234551A - I.c. engine fuel injector

Info

Publication number: GB2234551A
Application number: GB8917013A
Authority: GB
Inventors: Karl Hofmann
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1989-07-25
Filing date: 1989-07-25
Publication date: 1991-02-06
Anticipated expiration: 2009-07-25
Also published as: GB8917013D0; GB2234551B

Abstract

The two springs 34, 36 or three springs (70, 98, 99, Fig. 4) are arranged to provide two abrupt changes of closing bias after initial opening lift until the maximum opening is achieved. Initial lift occurs against spring 34, a second stage against spring 36 and a final stage against both springs. <IMAGE>

Description

Fuel inection nozzle for internal-combustion engines L Prior art The invention is based on a fuel injection nozzle for internal-combustion engines of the generic type of the main claim. In the case of known injection nozzles of this type (Swiss Patent Specification 329,505), the arrangement is made in such a way that, after the abrupt increase in the spring force at the stroke position of the valve needle associated with the beginning of the part-load range, there is no further jump in spring force, instead the spring force then only increases linearly in accordance with the compression of the second compression spring, which then alone has an effect.Such injection nozzles operate satisfactorily in the idling range below the single jump in spring force, in which a small injection cross-section is established up to a certain quantity of fuel, and thus fuel pressure. In the part-load and full-load range, the valve needle stroke increases with fuel pressure and/or speed and, at relatively high speeds, can already reach the maximum value corresponding to the complete stroke of the valve needle while in the part-load range. Allowing for the requirement of least possible noise generation and other operational requirements, the aim nevertheless is for the valve needle only to perform the complete stroke in the full-load range and at high speeds.

Advantages of the invention The arrangement according to the invention with the characterizing features has the advantage that the valve needle stroke is limited in particular in the partload range at relatively high speeds and consequently the injection period is prolonged, which has a particularly favourable effect on the noise behaviour. With corresponding adjustment of the preliminary strokes, of the spring rigidities and pretensions, a more favourable shape of the injection profile over the entire speed and load range is possible than in the case of the known injection nozzles of the type mentioned at the beginning, with which the effect in the relatively high speed range can only be improved at the expense of the behaviour at lower speeds.

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

The further jump in compressive force, in the part-load range, can be accomplished by concentric arrangement of three compression springs, of which the two outer springs act on thrust pieces, which are supported on stops fixed to the housing and with which the valve needle comes successively into contact. This configuration has the advantage that the overall length of a normal injection nozzle is not increased, or only by a little; however, it causes a not inconsiderable increase in the diameter of the injection nozzle, which in many cases cannot be accomplished due to limited installation space.

A more slender form of the injection nozzle is obtained if three closing springs are arranged and supported according to the features of Claims 2 - 5. In this case, however, as in the prior art, two closing springs are arranged axially one behind the other, as a result of which the overall length of the injection nozzle is increased correspondingly.

Particularly advantageous configurations are produced by the features of Claims 6 - 8, with which the multi-stage characteristic aimed for of the opening stroke of the valve needle is achieved by two compression springs alone, i.e. without any appreciable extra constructional outlay and greater space requirement than in the case of the prior art.

With the arrangements according to the invention, the injection profile of quantity-controlled or crosssection-controlled injection nozzles with a valve needle opening inwards against the fuel flow and with injection holes departing from the valve seat (seating hole nozzles") can be favourably influenced in particular.

Drawing Three exemplary embodiments of the invention are represented in the drawing and explained in more detail in the description which follows. Figure 1 shows a longitudinal section through an injection nozzle according to the first exemplary embodiment, Figure 2 shows a functional circuit diagram of the injection nozzle according to Figure 1, and Figures 3 and 4 each show a partial longitudinal section of the second and third exemplary embodiments.

Description of the exemplary embodiments The injection nozzle according to Figure 1 has a nozzle body 10, which is clamped by a cap nut 12 on a nozzle holder 14.

In the nozzle body 10 there is formed a valve seat, not evident from the drawing, and there is displaceably mounted a valve needle 16, which is provided with a pressure shoulder 18 in the region of a pressure space 20, which is connected via bores 22, 24 and 26 in the nozzle body 10 and nozzle holder 14 to a connection tube 28, fitted on the latter, for a fuel supply line.

A chamber 30, which is open towards the nozzle body 10 and in which a compression spring arrangement, described in more detail below, for the valve needle 16 is accommodated, is formed in the nozzle holder 14. The chamber 30 is connected to an oil leakage connection 32 for the removal of fuel leaking through the guide bore of the valve needle 16 in the nozzle body 10.

The compression spring arrangement contained in the nozzle holder 14 consists of a first compression spring 34 and a second compression spring 36, which are both arranged axially one behind the other. The first compression spring 34 acts via a thrust piece 38 on a plug 40 of the valve needle 16, which plug merges with the guide section of the valve needle 16 at a shoulder 42. The plug 40 passes with play through the bottom of a stop sleeve 44, which is guided displaceably in the chamber 30 of the nozzle holder 14 and surrounds the first compression spring 34. The upper end of the compression spring 34 is supported on a thrust bolt 48, which is provided with a collar 46 and the free end of which adopts a distance a from the thrust piece 38 in the closed position of the valve needle 16, the said distance depending on the complete stroke h8 of the valve needle.

The thrust bolt 48 is, for its part, supported on a disc-shaped annular body 50, which the second compression spring 36 presses against the upper end rim of the stop sleeve 44, the compression spring 36 being supported via an annular collar 52 of a stop bolt 54 on the bottom of the chamber 30 of the nozzle holder 14. The second compression spring 36 presses the stop sleeve 44 against the upper end face 56 of the nozzle body 10, via the annular body 50. The stop sleeve 44 is provided on the outside at its bottom with a depression 58, with the bottom surface of which the shoulder 42 of the valve needle 16 comes into contact when the valve needle has covered a preliminary stroke hV1. In the closed position of the valve needle 16, the free end of the stop bolt 54 adopts a distance from the thrust bolt 48 which corresponds to a second predetermined preliminary stroke hv2 The operating principle of the injection nozzle described is described below with reference to the diagram according to Figure 2. In this diagram, the dependence of the opening stroke h of the valve needle 16 on the fuel pressure p in the pressure space 20 is represented.

The valve needle 16 begins its opening movement when the fuel pressure has increased to the predetermined opening pressure p. During the then following first preliminary stroke he1, the lesser pretensioned first compression spring 34 acts alone on the valve needle 16.

When the fuel pressure has reached the value pl, the valve needle 16 strikes with its shoulder 42 against the stop sleeve 44, which is loaded by the second, greater pretensioned compression spring 36. The compression spring 34 involved in determining the preliminary stroke hvi and the stroke-dependent opening profile of the valve passage cross-section are coordinated with each other in such a way that, up to average speeds, the predetermined idling quantity of fuel is ejected.

After the striking of the valve needle 16 against the stop sleeve 44, the fuel pressure must initially increase beyond the value p2 before the valve needle 16 continues its opening movement. In this case, the stop sleeve 44 is shifted upwards, together with the annular body 50, against the force of the second compression spring 36. In this movement, the thrust bolt 48 remains with its collar 46 in contact with the annular body 50 and thus the first compression spring 34 captured, so that its pretension does not act on the valve needle 16.

When the fuel pressure has increased to the value p3, and at the same time the stop sleeve 44 has covered the stroke hV2, the thrust bolt 48 strikes with its collar 46 against the stop bolt 54. The opening position of the valve needle 16 thereby achieved produces a valve passage cross-section which leads to favourable engine values for this operating range.

After the striking of the thrust bolt 48 against the stop bolt 54, the fuel pressure must initially increase to the value p4 before it can move the valve needle 16 further into its full opening position. The reason for this is that, in the remaining residual stroke, both compression springs 36 and 34 are supported on shoulders, fixed to the housing, of the nozzle holder 14 and of the stop bolt 54 and act in the closing sense on the valve needle 16. The full opening stroke h8 of the valve needle 16 has taken place when the thrust piece 38 moved by the valve needle 16 strikes against the thrust bolt 48, which for its part bears against the stop bolt 54. In the closing movement of the valve needle 16, the operations proceed in the reverse order.

Due to the arrangement of the second pressure stage p3/p4 (sic), the valve passage cross-section is not fully opened in the part-load range at relatively high speeds, but instead of this a longer injection period is enforced, which has a positive effect on the noise behaviour. This advantageous effect is achieved without the arrangement of a third compression spring merely by the first compression spring 34 being brought to alone on the valve needle in the first stroke phase hV1, the second compression spring 36 being brought to bear alone on the valve needle in the second stroke phase hV2 and both compression springs 34 and 36 being brought to bear on the valve needle in the remaining residual stroke.

In the case of the injection nozzle according to Figure 3, the first compression spring 36 acting on the valve needle 16 is supported via the thrust piece 38 on a disc-shaped annular body 60, which for its part bears against an annular collar 62 of a thrust bolt 64, which is pressed by a second compression spring 36a via the annular body 60 against a stop sleeve 66, which for its part is supported on the upper end face of the nozzle body 10.As in the case of the exemplary embodiment described above, in the case of this injection nozzle the first compression spring 34 acts alone during a preliminary stroke hvl of the valve needle 16, while the second compression spring 36a acts alone during a subsequent second preliminary stroke hV2 and then both compression springs 34 and 36a act during the residual stroke, so that the opening characteristic according to the invention is achieved with only two compression springs in the case of this configuration as well.

To be specific, the operations proceed such that firstly the valve needle 16 strikes via the thrust piece 38 against the thrust bolt 64, after which the first compression spring 34 is captured and the valve needle 16 operates by the raising of the thrust bolt 64 alone against the second compression spring 36a. When the annular body 60 comes into contact with a shoulder 68 in the chamber 30a of the nozzle holder, in turn both compression springs 34 and 36a are supported fixedly with respect to the housing and act independently of each other on the valve needle 16. The full opening stroke of the valve needle 16 is ended when the thrust bolt 64 comes into contact with the stop bolt 54 after covering the path b.

In the case of the exemplary embodiment according to Figure 4, a first compression spring 70 acts via a central thrust bolt 72 constantly on a valve needle 74.

The latter is mounted displaceably in a nozzle body 76, which is clamped together with an intermediate disc 78 on a nozzle holder 80. A thrust piece 82 and a flange sleeve 84 are mounted displaceably on the thrust bolt 72.

The thrust piece 82 is located in a stepped bore 86 of the intermediate disc 78 and has at the outer periphery an annular shoulder 88, which together with a matching shoulder 90 limits the complete stroke hg of the valve needle 74 in the stepped bore 86. On the underside, the thrust piece 82 is provided with a recess 91, the bottom surface of which adopts a distance from the rear flat end face 74a of the valve needle 74 when the latter is in its closed position, the said distance corresponding to a predetermined preliminary stroke hV1.

In the nozzle holder 80 there is formed a chamber 92, which goes into a second chamber 94 of smaller diameter, containing the first compression spring 70, at an annular shoulder 93. In the chamber 92 there is formed a second annular shoulder 95 on a stop sleeve 96, which is preferably guiding the flange sleeve 84 and is supported on the intermediate disc 78. The outer annular rim of an annular disc 97, on which a second compression spring 98, which acts on the flange sleeve 84, is supported, is axially movable between the two annular shoulders 93 and 95. A third compression spring 99, which concentrically surrounds the first compression spring 70 and is supported on the bottom of the chamber 94 acts on the top of the annular disc 97, is pretensioned more than the second compression spring 98 and presses the annular disc 97 against the stop sleeve 96.

In the closed position shown of the valve needle 74, the upper end face of the flange sleeve 84 is away from the annular disc 97 by a distance which corresponds to a second, predetermined preliminary stroke hV2.

The injection nozzle according to Figure 4 operates as follows: With increasing fuel pressure, the valve needle 74 firstly operates alone against the first compression spring 70, until the path livi has been covered and the valve needle 74 strikes against the thrust piece 82 at the bottom. Then, the valve needle 74, or the fuel pressure acting on it, must also overcome the opposing force of the second compression spring 98, because the rising valve needle 74 is accompanied by the thrust piece 82 and the flange sleeve 84 moving upwards and the annular disc 97 initially still stays in contact with the stop 95 under the influence of the greater pretensioned third compression spring 99.

When the valve needle 74 has also covered the second preliminary stroke hV2, the flange sleeve 84 strikes against the annular disc 97 at the bottom, after which the influence of the second, then captured compression spring 98 is eliminated and the fuel pressure has to operate against the first compression spring 70 and the third compression spring 99, which produces a higher closing force than the second compression spring 98. At the end of the residual stroke of the valve needle 74, the thrust piece 82 comes into contact with the matching shoulder 90 of the intermediate disc 78, which limits the opening stroke of the valve needle.

Claims

1. Fuel injection nozzle for internal-combustion engines, with a nozzle body, in which a valve seat is formed and a valve needle is displaceably mounted and which is clamped on a nozzle holder, which contains two compression springs, which are supported on stops moved with the valve needle and on shoulders fixed to the housing in such a way that the resultant compressive force acting on the valve needle increases abruptly at a stroke position of the valve needle associated with the beginning of the part-load range, characterized in that at least two compression springs (34, 36 or 70, 98) are supported on stops (38, 48, 50 or 38, 60, 64 or 72, 84, 97) moved with the valve needle (16 or 74) and on shoulders (14, 56 or 76, 80) fixed to the housing, in that the compressive force acting on the valve needle (16 or 74) also increases abruptly at a second stroke position in the part-load range.

2. Injection nozzle according to Claim 1, characterized in that a first compression spring (70, Figure 4) acts via a thrust bolt (72) constantly on the valve needle (74), in that, in addition to the first compression spring (70), a second compression spring (98), surrounding the thrust bolt (74) comes to bear on the valve needle (74) after a first preliminary stroke (hvl) and a third compression spring (99), surrounding the first compression spring (70), comes to bear on the valve needle (74) after a second preliminary stroke ( hV2) .

3. Injection nozzle according to Claim 2, characterized in that the second compression spring (98) acts on a flange sleeve (84), which is preferably guided in the nozzle holder (80), is guiding the thrust bolt (72) and is supported directly or via a further thrust piece (82) on the end face of the nozzle body (76), facing the nozzle holder (80), during the first preliminary stroke (hV1), and in that, in the closed position of the valve needle (74) there is a free distance corresponding to the first preliminary stroke (hvl) between the flange sleeve (84) or the further thrust piece (82) and a shoulder (74a) of the valve needle (74).

4. Injection nozzle according to Claim 3, characterized in that the flange sleeve (84) is supported via a thrust piece (82) on the nozzle body (76), which is mounted in an intermediate disc (78), clamped between nozzle body (76) and nozzle holder (80), and in interaction with a shoulder (90) on the intermediate disc (78) limits the opening stroke of the valve needle (74).

5. Injection nozzle according to Claim 3 or 4, characterized in that the second compression spring (98) is supported on an annular disc (97), which surrounds the thrust bolt (72), is pressed by a greater pretensioned third compression spring (99) against a stop (95) fixed to the housing and with which the flange sleeve (84) comes into contact when the valve needle (74) has covered a partial stroke corresponding to the sum of the preliminary strokes (hV1r he2)'

6.Injection nozzle according to Claim 1, characterized in that a first compression spring (34), acting via a thrust piece (38, Figs. 1 and 3) on the valve needle (16), is supported on a first supporting element (48 or 60), which bears under the action of the first compression spring (34) on a second supporting element (50 or 64), which is pressed by a second compression spring (36 or 36a), which is pretensioned more than the first compression spring (34), against a first stop shoulder (56 or 66) fixed to the housing, in that furthermore a shoulder (42) of the valve needle (16) or the thrust piece (38) comes into contact indirectly or directly with the second supporting element (50 or 64) after a first preliminary stroke (hvl) and lifts the said second supporting element off the first stop shoulder (56 or 66) fixed to the housing is provided, with compression of the second compression spring (36 or 36a), and in that furthermore a stop shoulder (54 or 68) fixed to the housing is provided, with which shoulder the first supporting element (48 or 60) comes into contact after a second preliminary stroke (he2) of the valve needle (16), after which both compression springs (34, 36 or 34, 36a) act on the valve needle (16) in a way producing closing force.

7. Injection nozzle according to Claim 6, characterized in that the first supporting element (60, Figure 3) is a disc-shaped annular body and the second supporting element (64) is a thrust bolt which rests with an annular collar (62) on the first supporting element (60), passes through the latter and the free end of which is opposite the thrust piece (38) in the closed position of the valve needle (16), at a distance corresponding to the first preliminary stroke (hvl), in that furthermore the two stop shoulders (68, 66) fixed to the housing are assigned to the outer annular rim of the first supporting element (60) and are preferably formed on a bore step (68) in the nozzle holder (14a) and on an end face of a stop bush (66) inserted into the nozzle holder (14a), and in that furthermore the complete stroke (hvl + b) of the valve needle (16) is limited by a stop bolt (54) arranged in the second compression spring (36a).

8. Injection nozzle according to Claim 6, characterized in that the first supporting element (48, Figure 1) is a thrust bolt which is provided with an annular collar (46), extends within the first compression spring (34) and the free end of which is opposite the thrust piece (38) in the closed position of the valve needle (16), at a distance (a) dependent on the complete stroke (hs) of the valve needle (16), in that furthermore the second supporting element (50) is a disc-shaped annular body, against which the annular collar (64) of the first supporting element (48) is pressed under the influence of the first compression spring (34), in that furthermore the second compression spring (36), pretensioned more than the first compression spring (34), presses the discshaped second supporting element (50) against a stop sleeve (44) and the latter against the end face (56) of the nozzle body (10), facing the nozzle holder (14), in that furthermore a shoulder (42) on the valve needle (16) strikes against the stop sleeve (44) after a first preliminary stroke (bvi) and then displaces the said stop sleeve against the force of the second compression spring (36) and in that furthermore the complete stroke (h8) of the valve needle (16) and the stroke of the first supporting element (48) are limited by a stop bolt (54) arranged in the second compression spring (36).

9. Injection nozzle according to one of the preceding claims, characterized in that the valve needle is designed as opening inwards against the fuel flow and in that injection holes depart from the valve seat.

10. A fuel injection nozzle for internal combustion engines substantially as hereinbefore described with reference to Figures 1 and 2 of the accompanying drawings.

11. A fuel injection nozzle for internal combustion engines substantially as hereinbefore described with reference to Figure 3 of the accompanying drawings.

12. A fuel injection nozzle for internal combustion engines substantially as hereinbefore described with reference to Figure 4 of the accompanying drawings.