The arrangement includes a combined injection and ignition device which has an attachment that is fastened in a through-penetrating opening in the cylinder head of the engine and that includes an effective or active part that projects out from said attachment part and has an end portion which when the device is fastened in the cylinder head projects into the compression chamber, said end portion including an injection nozzle and an ignition electrode connected therewith and forming a central electrode in said device, wherein the device also functions as an sparking plug.

DESCRIPTION OF THE BACKGROUND ART A similar arrangement is known from SE C 502 604 for instance. Such an arrangement provides an injection device that is combined with a single-pole sparking plug whose single pole forms a central electrode. This type of sparking plug combined with an injection device has a single, centrally positioned electrode and thus lacks a side electrode (earth electrode).

In the case of this known arrangement, the earth electrode required to produce an ignition spark is mounted on the top of the piston.

The distance between the fixedly mounted central electrode and the piston-mounted earth electrode thus changes as a function of piston movement in the cylinder.

This known arrangement provides a very attractive construction solution from a space/technical aspect, particularly when using so-called four valve technology in combination with direct fuel injection into the combustion chamber, since it avoids the problem of also finding room for a space-demanding sparking plug in the roof of the combustion chamber (the cylinder top) on the underside of the cylinder head.

OBJECT OF THE INVENTION As will be evident from the above, ignition electrode arrangements that include a fixed and a moveable ignition electrode in each cylinder of an engine are known to the art. However, one drawback with such an electrode arrangement in which the size of the spark gap varies is that positive sparking (an effective ignition spark) cannot always be guaranteed, particularly in the case of a large spark gap. For several reasons, it is not possible to work in practice with ignition voltages that exceed 30-40 kV.

For instance, in respect of advanced ignition (where ignition shall take place at a given number of degrees of crankshaft rotation prior to the upper dead centre position), it may be problematic to achieve positive ignition because the spark gap (the distance between the piston-mounted electrode and the sparking plug electrode attached to the cylinder head) is excessively large with respect to the available ignition voltage. There is a danger that the spark will choose the"wrong path"and jump between the sparking plug electrode and the nearest surrounding outer surface of the cylinder head, i. e. the surface area adjacent to the sparking plug instead of the piston electrode. This can result in the spark being insufficient to provide positive ignition, and may also result in damage to the insulator (ceramic) surrounding the sparking plug electrode.

Among other things, the present invention aims at eliminating the aforesaid problems associated with an electrode arrangement that includes a spark gap which varies with the position of the piston in the cylinder. A general object of the invention is to provide an ignition electrode arrangement that has properties with which: -improved combustion conditions can be achieved; -good ignition quality can be obtained; -the limits with respect to the range within which acceptable ignition combustion conditions can be achieved are extended, also when concerning engine operation with the use of a gas mixture in which the gasified fuel constitutes a small part of the gas mass taken into the compression chamber for ignition; -improved fuel economy is achieved; -fuel economy is improved;

-the useful life/durability of the ignition electrode part of the combined injection and ignition device is improved; -the amounts of harmful emission products generated in the combustion process are reduced; and -ignition of the fuel-air mixture can also be ensured when the spark gap dependent on piston position is much too large to effect positive ignition with a spark that travels from the fixed central electrode to the piston-mounted earth electrode.

SUMMARY OF THE INVENTION These objects can be achieved in accordance with the present invention with a fuel injection and ignition arrangement of the kind described in the introduction and having the significant features set forth in the characterising clause of Claim 1.

Further developments of the arrangement and preferred embodiments thereof may have the features set forth in the dependent Claims 2-8.

A primary characteristic feature of the inventive arrangement is that it includes an electrically conductive ring-like part which is provided with an earth electrode and which can be mounted in the front part of the opening that accommodates said device (said front part opening into the compression chamber). This ring-like part is constructed and positioned to surround the effective part or active part of the injection and ignition device, wherewith the earth electrode fixed to the ring-like part forms a side electrode relative to the central electrode connected to the injection nozzle.

The accommodation opening provided in the cylinder head of the engine and in which the combined injection and ignition device can be fastened corresponds to the cavity in the cylinder head which in the case of engines fitted with conventional sparking plugs is normally referred to as the"sparking plug well".

Because the ring-like part that carries the earth electrode is mounted in the same through- penetrating accommodation opening as the combined injection and ignition device, there is no need to find suitable room in the cylinder top (the roof of the combustion chamber) for a

separate attachable side electrode (fixed earth electrode). There is normally no suitable place for fitting a separate side electrode, particularly when applying so-called four valve technology.

The combined injection and ignition device-hereinafter referred to solely as the"device" for the sake of simplicity-has an attachment part which is comprised of electrically conductive material, preferably metal. This attachment part includes in practice an external thread which enables the device to be secured in the accommodation opening by screwing said threaded portion into a section of the accommodation opening that includes a corresponding internal thread.

The attachment part is suitably provided with a ring-shaped front end surface that surrounds the effective part of the device and forms an abutment surface that enables the ring-shaped part to be fixed axially in the accommodation opening (by screwing in the attachment part).

In practice, the ring part is suitably comprised of a tubular sleeve part which is provided at some point on its circumference with a thickened electrode part which externally of the end- edge of the sleeve part facing towards the compression chamber transforms into an axially directed electrode part, this electrode part being the part that forms the side electrode and whose end portion is preferably curved inwards towards the centre axis of the sleeve part.

The front part of the accommodation opening (in which part the sleeve part is fitted) is preferably a circular-cylindrical opening whose cylindrical defining wall includes an axially extending groove intended for accommodating the electrode-root portion of the tubular sleeve part (i. e. to provide room for said electrode root part). As a result of the shape- bound fixation obtained by the engagement of the electrode root portion in the accommodation groove extending axially in the cylindrical defining wall of the accommodation opening, it is ensured that the sleeve part (and therewith the side electrode) will be held firmly against rotation relative to the cylinder head and the piston. As a result of this shape-bound locking effect, the sleeve part can only be fitted in the cylinder in one specific rotational position, meaning that the side electrode fixed to the sleeve part will always be located in a given specific position in the compression chamber/combustion chamber. It is therewith possible to fasten the earth electrode (the piston electrode) in a

non-centre position on the top of the piston. Such non-central positioning of the piston electrode is not possible when using a sleeve part that is non-rotatably connected to the device, since in this case the side electrode would be situated in an unpredictable rotational position in the compression chamber, depending on how"hard"the device is screwed into the accommodation opening. Since the position of the side electrode in the compression chamber cannot therefore be anticipated with any degree of certainty, there is a risk that a non-centrally positioned piston electrode on the piston top will"collide"with the side electrode.

The sleeve part is conveniently provided at its end-edge distal from the compression chamber with a circumferentially extending and radially outwardly projecting ring flange that functions as an axial stop that governs the extent to which the sleeve part can be inserted into the accommodation opening. Thus, the ring flange is intended to abut a ring- shaped abutment surface in the accommodation opening on the one hand and to be in contact with the front end surface of the attachment part on the other hand, wherewith the ring flange can be locked firmly to the ring-shaped abutment surface.

The moveable earth electrode is preferably an electrode which is fixedly mounted on the top of the piston and which, depending on the placement of the sleeve part and therewith the side electrode, may be positioned centrally on the piston top or at a radial distance from the centre of the piston. In order to avoid compressed gas mixture or combustion gases from leaking from the compression chamber/combustion chamber to the accommodation opening, pressure-tight packings or seals are suitably fitted between the ring flange of the sleeve part and the abutment surface of the accommodation opening on the one hand and between the ring flange and the front end surface of the attachment part on the other hand.

In one particular embodiment of the inventive arrangement, the combined injection and ignition device may, for instance, include a fixedly mounted valve housing which houses a movable valve needle that includes a fuel supply channel. In this case, the end of the valve housing located in the compression chamber includes a valve seat for coaction with a valve element provided at the end of the valve needle, wherein said valve element can be brought into sealing contact with the valve seat as a result of movement of the valve needle. In this

particular embodiment, the valve housing and the valve needle together form the injection nozzle and the central electrode of said device.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be further illustrated and explained with reference to exemplifying embodiments thereof and also with reference to the accompanying drawings, in which Fig. 1 is an axial longitudinally sectioned view of part of a cylinder head and an associated cylinder in which a piston is arranged, in accordance with a first embodiment of an inventive fuel injection and ignition arrangement; Fig. 2 is a cross-sectional view taken on the line 2-2 in Fig. 1 and showing the sleeve part and its side electrode of the embodiment of Fig. 1; Fig. 3 is an axial longitudinally sectioned view of a second embodiment of an inventive arrangement, said view being shown in larger scale than Fig. 1; Fig. 4 is a in perspective view in still larger scale of the sleeve part and its side electrode according to the embodiment of Fig. 3; Fig. 5 is an axial longitudinally sectioned view of the effective or active part of the combined injection and ignition electrode of a combined injection and ignition device principally of the same kind as those shown in Figs. 1 and 3; and Fig. 6 is a cross-sectional view taken on the line 6-6 in Fig. 5 and showing the effective or active end of said device.

DESCRIPTION OF EMBODIMENTS Fig. 1 illustrates part of a cylinder head 10 in a multi-cylinder internal combustion engine, particularly an Otto cycle engine. The illustrated part of the cylinder head is situated immediately above an associated cylinder 12 in the engine cylinder block and functions as a cylinder cover, among other things. The cylinder head also includes the cylinder induction and exhaust valves with associated gas passageways. Only the orifices of two of said gas passageways are shown in the Figure, where the valve seats of the passageways are respectively referenced 14,16. A piston 18 is moveable in the cylinder. The piston is provided with piston ring grooves 20 for receiving piston rings (not shown), and a lubricating groove 22 for a lubricating ring (not shown). The piston rings and the oil rings

are intended to seal against the inside 24 of the cylinder wall 26. The piston 18, which is shown in its upper dead centre position in the Figure, includes a gudgeon pin hub which accommodates a gudgeon pin (not shown). The upper side of the piston 18 includes a concave recess or cavity 28 which forms the lowermost part of the compression chamber/combustion chamber in the cylinder 12. An upwardly extending earth electrode 30 that forms an integral part of the piston is located in the piston top cavity 28.

Provided in the cylinder head 10, directly above the cylinder 12, is a vertical accommodation opening 32 which extends from the upper side 34 of the cylinder head down to the recess or cavity 36 formed adjacent the underside of the cylinder head and building the uppermost part of the compression chamber/combustion chamber in the cylinder 12. The accommodation opening 32 corresponds to the sparking plug well of a cylinder of an internal combustion engine where each cylinder is typically provided with a two-pole sparking plug whose side electrode forms an integral part of the plug.

The vertical accommodation opening 32 removably accommodates a combined injection and ignition device 38 that effects both direct injection of fuel into the cylinder and the ignition of the fuel-air mixture in the compression chamber/combustion chamber of the cylinder concerned. The combined device 38 includes a metallic attachment part 40 that has an external thread 42 and that surrounds the central body 44 of the device 38. The bottom part of the central body 44 extending onto the compression chamber forms the effective or active part 46 of the device which performs fuel ejection and, in certain cases, also spark ignition of the fuel-air mixture in the compression chamber. The lower end-part 48 of the effective part 46 includes an injection nozzle 50 to which there is connected a central electrode 52.

The accommodation opening 32 narrows stepwise down towards the recess 36 in the top of the cylinder. The device 38 is secured in the opening 32 accommodating said device, by screwing the externally threaded attachment part 40 of said device into that section 56 of the opening 32 which has a corresponding internal thread 54. An electrically conductive ring-part 62 provided with an earth electrode 60 that projects axially forwards is fitted non- rotatably into the front portion or section 58 of the accommodation opening 32 that opens out into the uppermost part 36 of the compression chamber. The ring-part 62 has the form

of a tubular sleeve which surrounds the effective or active part 46 of the device 38, wherewith the earth electrode 60 of said ring-part forms a side electrode which is separate from the central electrode 52 of the device 38. The combined ignition device 38 thus has a fixed spark gap 64 between the outside of the central electrode 52 and the end surface of the inwardly curved end-part 66 of the side electrode 60 facing towards the common centre axis A of the ring-part and the device 38.

The sleeve-like ring-part 62 will now be described in more detail with reference to Figs. 2,3 and 4. As will be seen from these Figures, the rear end-edge of the sleeve 62 (the upper end-edge in Fig. 3) is provided with a circumferentially extending and radially outwardly projecting ring flange 68 which lies against a ring-shaped abutment surface 74 in the accommodation opening 32 via annular packings 70,72 on the one hand, and against a ring- shaped front end surface 76 at the bottom (forward) end of the attachment part 40 on the other hand. The sleeve 62 is thus fixed axially in the accommodation opening 32, by screwing/tightening the combination device 38 in the opening 32, against the ring flange 68.

For the reasons mentioned above in the general part of the present description, it is often necessary, particularly when the piston-earth electrode 30 is not positioned centrally, as in the case of Fig. 1, to ensure that the side electrode 60 (and thus also the sleeve 62) will have an unchangeable, predetermined rotational setting in relation to the cylinder head 10 and the piston 18.

As will best be seen from Figs. 2 and 4, the sleeve 62 is provided externally to this end with an axially extending electrode root part 78 which passes into the actual side electrode 60, outside the front end-edge 80 of said sleeve. In order to provide space for the electrode root part 78, the cylindrical defining wall of the opening section 58 is provided with an axially extending groove 82 for receiving said root part 78. Positioning of the root part 78 in the groove 82 thus ensures that the sleeve 62, and therewith the side electrode 60, will be held in a fixed setting relative to the piston and its earth electrode 30.

Finally, Figs. 5 and 6 show an example of how the lower end-part 48 of the combined injection and ignition device 38 may be constructed to achieve both fuel injection and the

requisite ignition spark in those cases when the spark shall travel from the central electrode 52 to the side electrode 60 instead of to the piston-mounted earth electrode 30.

The effective or active part 46 of the device 38 is through-passed axially by a tubular valve housing 84 which is centred and fixedly mounted in said effective part 46. In turn, there extends axially through the valve housing 84 a valve shaft which is constructed as a valve needle 86 and which includes a central passageway 88 for supplying fuel batch-wise to the combustion chamber. Formed in the free end-part 84'of the valve housing is a valve seat 90 which connects with the fuel passageway 88 in the valve needle 86. The valve seat 90 accommodates a valve element 92 which is fastened in the end of the valve needle 86 and which can be brought into abutment with the seat 90. The valve element may be fastened in the end of the valve needle 86 or may form the outermost terminating part of the valve needle. Because the valve needle 86 can be moved axially in the valve housing 84, the valve element 92 can be manoeuvred relative to the end seat 90 of the valve housing, as particularly shown in Fig. 5, where the upper half of the Figure shows the valve element 92 in a valve-closing position whereas the bottom half of the Figure shows the valve element distanced from the seat 90 and in a valve opening position in which a ring-shaped gap 94 is formed between the seat 90 and the valve element delimiting surface 96.

The valve housing 84, the valve needle 86 and the valve element 92 are comprised of an electrically conductive material and together form a central electrode in the combined injection and ignition device 38. In this case, the ignition device 38 thus forms a single-pole sparking plug which is intended to generate an ignition spark in co-action with either the piston-mounted earth electrode 30 or the side electrode 60. As will be seen from Fig. 5, the valve element 92 has a central pin-like end part 98 that forms the spark generating part of the ignition device 38.

As will also be seen from Fig. 5, the fuel supply passageway 88 in the valve needle 86 extends axially up to the rear part of the valve element 92, where the passageway 88 communicates with the outside of the needle via four radial holes 100 which open out immediately adjacent the conical rear side 96 of the valve element 92. The valve housing 84 has a ring-shaped groove 102 in its inner wall surface adjacent the valve needle 86, in the region of the innermost part of the valve seat 90. This groove 102 is laterally in open communication with the radially innermost part of the valve seat 90. The upper half of Fig.

5 shows the sealing state in which the conical surface 96 of the valve element 92 is in sealing abutment with a corresponding conical surface of the valve seat 90.