GB2254886A

GB2254886A - Ic engine fuel injector with pre and main injections

Info

Publication number: GB2254886A
Application number: GB9208288A
Authority: GB
Inventors: Andreas Kracke; Andreas Iwohan; Alexander Guluk
Original assignee: Volkswagen AG
Current assignee: Volkswagen AG
Priority date: 1991-04-15
Filing date: 1992-04-15
Publication date: 1992-10-21
Anticipated expiration: 2012-04-15
Also published as: DE4210563A1; GB9208288D0; GB2254886B

Description

2 25) 43210 -1DgSCRIPTION FUEL INJECTIC NOZZLES FOR _M INTERNAL COMBUSTION

ENGINE WITH PRE- INJECTION AND MQUR INJECTION OPERATION The invention relates to a fuel injection nozzle for an internal combustion engine, for example a diesel engine, with pre- injection and main injection operation.

A fuel injection nozzle is known from the DE-PS 1 042 964, 46c2 114 in which that separate nozzle needles running adjacent to each other and fitted with different sized locking springs are provided for the main injection and pre-injection, with the pressure space of the nozzle needles being connected to the high pressure fuel supply. As a result of the locking springs being designed differently. the two nozzle needles are displaced into their injection positions when different fuel pressures are achieved. A disadvantage of this construction of nozzle is the fact that the injection timing for the pre-injection and main injection are fixed preset in relation to each other by means of the course of pressure development in the fuel inlet.

This also applies for the fuel injection pump, known from DE-PS 665 886, 46c2 105. with two -2concentrically arranged nozzle needles.

Injection valves built up using piezoelectric transducers are also part of the prior art; see for example DE-OS 17 51 5431 F02M 51106. With this known electrically controllable injection valve, which is however only designed to produce a single injection process, i.e. a main injection process, a pressure space containing the transducers and defined by means of a membrane attached to the nozzle needle is filled with fuel from the fuel inlet up to a certain pressure which still does not cause the nozzle needle to open. By exciting the piezoelectric transducers, these produce a pressure pulse in this pressure space, which causes the single nozzle needle to displace in the sense of producing a connection between the pressure space and a nozzle opening, so that the injection process now begins. The pressure release in the pressure space in conjunction with a return spring influencing the nozzle needle cause the injection process to terminate by moving the nozzle needle back into its position blocking the nozzle opening. This document however does not provide any references to the design of a fuel injection nozzle in accordance with the generic type, i.e. with pre-injection and main injection.

An object of the invention is to produce a fuel injection nozzle with pre-Injection and main injection, which facilitates pre-injection independent from the main injection as far as quantity and time are concerned.

In accordance with the present invention, there is provided a fuel injection nozzle for an internal combustion engine with pre-injection and main injection operations, such as a diesel engine, comprising a main injection needle axially displaceable by Intermittent fuel pressure in a high pressure fuel inlet against the influence of a locking spring for the purpose of connecting a pressure space to a nozzle opening, a further pressure space also supplied by way of the fuel inlet for producing preinjections dependent on the pressure, and piezoelectric transducers arranged in the further pressure space in order to initiate the preinjections independent from the course of pressure development in the fuel inlet.

It is important for the invention that piezoelectric transducers are used only for the preinjection, whereas the main injection is determined in the usual way solely by the intermittent pressure in the high pressure fuel supply. This does not however exclude the use of a single injection needle, which accordingly uncovers the nozzle openings during both -4the main injection processes and the pre-injection processes wherein the further pressure space is flow connected to the pressure space and the main injection needle also acts as the pre-injection needle. It is particularly advantageous however to use two nozzle needles particularly arranged concentrically and used only for the pre-injection or only for the main injection, wherein a pre-injection needle is also provided and is axially displaceable by piezoelectrically produced pressure pulses in the further pressure space for the purpose of connecting same with a further nozzle opening. This enables relatively "easy" construction of the pre-injection needle next to the means of releasing it, so that the pressure pulses required for its axial movement and produced by means of the piezoelectric transducers, need only be small and moreover there is the possibility of ejecting the pre-injection quantity and the main injection quantity in different directions.

As the volume changes produced by means of transducers of this type are per se only relatively small, consideration is also given with the invention to the fact that piezoelectric transducers are only used for the pre-injection, not however for the main injections. However, the volume changes which can be produced in this way in the further pressure chamber -5are sufficient for the relatively small pre-injection quantities. By adjusting accordingly the electric voltage supplied to the transducers, it is possible to determine precisely the quantity for pre-Injection as well as the timing of the pre-injection.

By way of example only, specific embodiments of the present invention will now be described, with reference to the accompanying drawings, in which:

Fig-1 is an axial cross-section through a first embodiment of fuel Injection nozzle, in accordance with the present invention; and Fig.2 is an axial cross-section through a second embodiment of fuel Injection nozzle, in accordance with the present invention.

Figure 1 shows an embodiment of the invention with a single nozzle needle 1. A high pressure fuel supply 3 is incorporated as a channel in the fuel injection nozzle housing, generally designated as 2, comprising several components, and a non-return valve 4 lies in the inlet of the high pressure fuel supply 3 and prevents fuel from returning from the injection nozzle. The fuel supply 3, which is connected to a fuel pump, supplying fuel intermittently, known per se and not illustrated. feeds fuel to a pressure space 5. the fuel being supplied to a combustion chamber, not illustrated, of the internal combustion engine by -6raising the nozzle needle 1 from nozzle opening 6. The nozzle needle 1 is raised for the purpose of the main Injection by the pressure periodically changing in the high pressure fuel supply in the flow direction behind the non-return valve 4, which exerts an opening force, in an upwards direction in Figure 1, on a shoulder 7 of the injection needle 1 against the effect of a locking or return spring 8. As soon as this opening force exceeds the force, active in a downwards direction in Figure 1, produced from the resilient force 8 and the pressure in space 9, the nozzle needle 1 lifts off in an upwards direction in the Figure from the nozzle openings 6 and in so doing connects this to the pressure space 5.

By influencing the pressure in the chamber 9 through appropriate measures in a leakage pipe 10, it is possible to influence the main injection process.

A further pressure space 11 is provided for the pre-injection, this pressure space being connected to the first mentioned pressure space 5 and accommodating piezoelectric transducers 12, whose axial parallel measured length increases when excited, so that through the transducers 12, the volume of the further pressure space 11 is reduced - if only slightly. This represents an increase in pressure also in pressure space 5, so that - at least mainly independent from -7the course of development of pressure in the fuel supply 3 - for the purpose of pre-injection the nozzle needle 1 is moved from its locking position illustrated again against the influence of spring 8 in order to uncover the nozzle openings 6.

The further pressure space 11 is supplied with fuel from the fuel supply 3. Although in an advantageous way only one supply of fuel is necessary, this embodiment of the invention as a result of using piezoelectric transducers 12 offers the possibility of carrying out pre-injections at times which are at least mainly independent from the timings of the main injections.

Whereas the embodiment of the invention just described by way of Figure 1, has only a single nozzle needle for the main injection and pre-injection, the design in accordance with Figure 2 in addition to a main injection needle 20, having a shoulder or collar 21 forming again a pressure surface, has a preinjection needle 22 coaxially incorporated into the main injection needle 20. one advantage of this construction can be seen in that the nozzle openings 23 have for the main injection a different direction of injection from the at least one nozzle opening 24 for the pre-injection, so that the main injection does not occur in the zones of the combustion space with a burned mixture.

The main injection needle 20 is activated in the manner already described by the fuel pressure in a high-pressure fuel supply 25 by exploiting the shoulder 21 as a pressure surface against the influence of a locking or return spring 26 and against the pressure in chamber 27, to which a leakage pipe 28 is connected.

The design of the pre-injection needle 22 is quite similar: a shoulder provided to form a pressure surface is clearly visible at 29 with the pressure in the further pressure space 30 acting finally on this shoulder and with the further pressure space 30 again containing the piezoelectric transducers 31 to change its volume. in this example, the further pressure space 30 is fed by the leakage pipe 28 by means of a non-return valve 32 opening in the supply direction so that in the further pressure space 30 there is a relatively lower pressure.

Furthermore, considering the conditions in the region of the preinjection needle 22, it adjoins the pressure chamber 34 with its rear front surface 33, the pressure chamber 34 being flow connected by means of a channel 35 to the inlet 25 and containing a locking or return spring 36. In view of the relatively high pressure In the pressure chamber 34 it -gis possible for this locking spring to be of a weak construction. As the main needle 20 only is moved, in an upwards direction in Figure 2, to its opening position when there Is a relatively high pressure in the inlet 25, this means that in this particular phase the pressure force exerted in a downwards direction on the pre-injection needle 22 is also high so that the pre-injection needle 22 is definitely prevented from opening during the main injection process.

An increase in pressure is also experienced in the further pressure space 30 in this example when the piezoelectric transducers are excited and in so doing the pressure force acting on the shoulder 29 is increased so that at points in time independent from the pressure in the Inlet 25, preinjection processes can be initiated by raising the pre-injection needle 22. This needle is closed as soon as the pressure in the further pressure space 30 and thus below the shoulder 29 is reduced by the injection process.

The further pressure space is then re-filled by means of the non-return valve 32 during the subsequent main injection process.

The invention accordingly produces a fuel injection nozzle which only requires a fuel supply fitted with one pump, but however offers the possibility of producing in a simple way pre-injection -10processes independent from the main injection processes as far as the timing and quantity are concerned.

Claims

-11CLAIMS

1. A fuel injection nozzle for an internal combustion engine with preinjection and main injection operations, such as a diesel engine, comprising a main injection needle axially displaceable by intermittent fuel pressure in a high pressure fuel inlet against the influence of a locking spring for the purpose of connecting a pressure space to a nozzle opening, a further pressure space also supplied by way of the fuel inlet for producing preinjections dependent an the pressure, and piezoelectric transducers arranged in the further pressure space in order to initiate the preinjections independent from the course of pressure development in the fuel inlet.

2. An injection nozzle as claimed in claim 1, wherein the further pressure space is flow connected to the pressure space and the main injection needle also acts as the pre-injection needle.

3. An injection nozzle as claimed in claim 1 or claim 2, wherein a nonreturn valve is provided in the fuel inlet.

4. An injection nozzle as claimed in claim 1, wherein, in addition to the main injection needle, a pre-Injection needle is provided which is axially displaceable by piezoelectrically produced pressure pulses in the further pressure space for the purpose of connecting same with a further nozzle opening.

5. An injection nozzle as claimed in claim 4, comprising different spray directions from the nozzle opening and from the further nozzle opening.

6. An Injection nozzle as claimed in claim 4 or 5, wherein the preinjection needle is acted on by a resetting force diverted from the pressure in the fuel inlet.

7. An injection nozzle as claimed in any of claims 4 to 6, wherein the pre-injection needle is arranged within the main injection needle.

8. An injection nozzle as claimed in claim 6 or claim 7, wherein the resetting force is produced in a pressure chamber incorporated in the main injection needle and connected to the fuel inlet.

9. An injection nozzle as claimed in any of claims 4 to 8, wherein the further pressure space is flow connected to a leakage pipe by way of a nonreturn valve.

10. A fuel injection nozzle for an internal combustion engine with preinjection and main injection operations, substantially as herein described, with reference to, and as illustrated in Fig.1 or Fig.2 of the accompanying drawings.