Spark plug of an internal combustion engine

The present invention relates to a spark plug of an internal combustion engine, in particular for use in gasoline engines, with an insulator body, with at least one stationary ground electrode support arrangement and with at least one stationary center electrode support, with a spark plug housing comprising at least two parts surrounding the insulator body.

The spark plugs currently available for industrial gas engines are often products which have been derived from the automotive industry and have been adapted for preferred use in industrial gas engines through corresponding improvements. These candles usually have a fixed, cylindrical central electrode, which is provided with a noble metal pin. With the fixed ground electrodes, both the hook electrode and two to four laterally attached electrode fingers are used. Such ground electrodes can also be provided with a noble metal plate. Spark plugs of this type are known from EP 0834973 A2, EP 0859436 A1, EP 1049222 A1, DE 19641856 A1 and from WO 95/25372. Generic spark plugs with multi-part spark plug housings are known from GB 156,087 A or from US Pat. No. 6,152,095 A, for example. A major disadvantage of the spark plugs known in the prior art is that their compressive strength is not sufficiently good for long-term operation. In the case of spark plugs according to the prior art, the insulator body or the base center electrode is often pressed out unintentionally. If this happens in operating states in which a high internal pressure prevails in the cylinder of the internal combustion engine, an explosive imposition of the insulator body and / or base center electrode in spark plugs according to the prior art can occur, which, among other things, can also pose a risk to the operating personnel present.

The object of the invention is therefore to create a spark plug in which the disadvantages of the spark plugs according to the prior art are eliminated. In addition, a method for producing the spark plugs according to the invention is to be made available.

This is achieved according to the invention in that the spark plug housing has a lower housing part and an upper housing part, at least the part of the insulator body on the combustion chamber side being pressure-proof, preferably completely, of the lower housing part together with the upper housing part.

Due to the inventive design of the spark plug housing with a lower housing part and an upper housing part, the individual parts can be made very pressure-resistant, then pushed onto the insulator body and thus assembled in such a way that a very pressure-resistant spark plug is created.

Here, the composite of lower housing part and upper housing part comprises the insulator body of the spark plug in such a way that an unintentional pressing out of the insulator body or the base center electrode from the spark plug housing constructed in this way is effectively prevented. The terms lower and upper part of the housing refer to the normal installation position of a spark plug, in which the lower part of the housing points downwards in the direction of the combustion chamber and the upper part of the housing points upwards in the direction of the spark plug connector.

With regard to the connection of the individual parts of the spark plug housing, it is particularly favorable that these are pushed over one another in their contact area and / or pressed and / or welded. This type of connection in the contact area between the individual parts of the spark plug housing creates a particularly pressure-resistant spark plug.

To fasten the spark plug in the cylinder, it is particularly favorable that at least part of the spark plug housing has a thread for screwing into a cylinder head.

Favorable embodiments provide that the individual parts of the spark plug housing are made of electrically conductive material and / or the connections between the individual parts of the spark plug housing are designed to be conductive in their respective contact areas. As a result, the spark plug housing can be used as an electrically conductive connecting piece between at least one ground electrode and the cylinder or engine block.

Favorable variants provide that the individual parts of the spark plug housing preferably each have at least one seal against the insulator body. Such seals prevent gas from escaping or the pressure drop through the spark plug.

In particularly preferred exemplary embodiments, the compressive strength of the spark plug is further enhanced by the fact that the insulator body has at least one bead, preferably extending over its entire circumference, which is preferably in at least one contact area

AT 410 150 B rich of at least two housing parts is arranged.

Favorable design variants of the multi-part and electrically conductive spark plug housing provide that the ground electrode carrier arrangement is arranged on the spark plug housing and has at least one ground electrode. The designation ground electrode carrier arrangement here refers to an arrangement of at least one earth electrode carrier on which in turn at least one earth electrode is arranged.

In order to ensure a long service life of the spark plug, individual preferred exemplary embodiments provide that the ground electrode carrier arrangement preferably has four flat, preferably inward-facing, ground electrodes arranged perpendicular to one another. Here it is again favorable that at least one ground electrode and / or at least one ground electrode carrier arrangement is welded to at least one part of the spark plug housing and / or integrated into at least one part of the spark plug housing.

In the case of the central electrode carrier designed as a counterpart to the ground electrodes and the mass electrode carrier arrangement, it is particularly favorable that at least one, preferably four, perpendicular to one another - flat - preferably outwardly facing - central electrodes is (are) arranged on the central electrode carrier. Here, the center electrode carrier as well as the ground electrode carrier arrangement can have one or more individual electrode carriers and electrodes. It is particularly favorable that the electrodes of the center electrode carrier and the mass electrode carrier arrangement are arranged in pairs, plane-parallel opposite one another, with an insulating air gap between one another. Such an arrangement achieves a very good and reliable ignition of the fuel-air mixture as well as a long service life of the pressure-resistant spark plug.

A particularly pressure-resistant variant is achieved in that the center electrode carrier is shouldered on the insulator body and / or surrounds the base center electrode and / or is preferably completely welded to the base center electrode. Above all, this prevents the base center electrode from being accidentally pushed out of the spark plug.

In terms of a long service life of the spark plug, particularly favorable design variants provide that the edge length of the center electrodes and / or the ground electrodes is greater than 4 mm, preferably greater than 6 mm. A further improvement in the service life of the electrodes is achieved in that the electrodes of the center electrode support arrangement have a coating of noble metal and / or noble metal platelets.

To manufacture such a spark plug, it is particularly favorable that the individual parts of the spark plug housing are manufactured individually, pushed over a commercially available standard insulator body and / or pushed one above the other and / or pressed and / or welded. As a result, a standard insulator body can be used to manufacture a spark plug according to the invention, which significantly reduces the production costs for such spark plugs. In addition, it is particularly favorable that the center electrode carrier is manufactured in advance, pushed flush onto a base center electrode of the insulator body up to the insulator base and welded.

Further favorable embodiments provide that the ground electrode carrier arrangement is welded to at least one part of the spark plug housing or is manufactured integrated in at least one part of the spark plug housing and that a pulsed and / or continuously operating laser welding process and / or electron beam welding process and / or plasma welding process and / or high vacuum soldering process is used for welding and / or resistance welding technology is used.

Further features and details of the present invention emerge from the following description of the figures. It shows:

Fig. 1 is a sectional view of a spark plug according to the invention.

In the case of the spark plug according to the invention, a standard insulator body such as is used commercially by various spark plug manufacturers is used.

This insulator body 1 (mostly made of ceramic) is pushed into a spark plug housing upper part 3 with a seal 2 enclosed on both sides. The spark plug housing lower part 4 is also pushed onto the insulator body 1. In a further production step, the upper part 3 and the lower part 4 are pressed together, preferably in the area of ​​the insulator bead 15. In the pre-tensioned state, the housing parts are welded to one another by means of a laser 5.

With this construction, the upper housing 3 can be designed to be very pressure-stable. One engine3

AT 410 150 Β pressure-related pushing out of the insulator body 1 is thus prevented. As a result of the welding process in the contact area 5 on the pre-stressed housing 3, the housing components are permanently pre-stressed and a seal is thus created between the housing 3, 4 - seal 2 and insulator body 1.

Weldable structural steels, stainless steels and their alloys, but also nickel-based alloys or brass alloys, can be used as materials for the upper and lower housing parts 3, 4. The advantage of the brass housing is the better heat dissipation.

A very compact high-pressure candle with, for example, M18 x 1.5 thread 13 can be produced by the selected two-shell shape of the housing.

A ground electrode carrier arrangement 6 can be applied to the lower housing part 4 on the motor side. In the specific case, for reasons of temperature and hot corrosion resistance, a ground electrode carrier arrangement 6 made of Inco Alloy 600 (WNr 2.4816) is welded to the housing in area 7 by means of a laser. Other nickel-based alloys or high-temperature stainless steels can also be used as alternatives. The ground electrode carrier arrangement 6 could optionally also be manufactured in one piece, that is to say as an integral part of the lower housing part 4.

The implementation of the ground electrode carrier arrangement 6 with 4 electrode fingers ensures good mixture accessibility.

The ground electrode support arrangement 6 are provided with precious metal plates (= ground electrodes 9); these are welded to the support 6 on one or both sides by means of a laser. The weld is made in such a way that the gap is closed on the electrode sides. This means that there is no open gap (or opening) through which gas can enter between the noble metal plate and the electrode carrier fingers.

This construction makes it possible to produce very long electrode erosion edges in relation to the compact overall component size. Noble metal plates 9 with an edge length greater than 4.0 mm are used on the ground electrode carrier arrangement.

In the specific case, the edge length of the ground electrode 9 is 6.25 mm.

In the case of the ground electrodes 9, small plates with the dimensions 6.25 x 1.6 x 0.5 mm (other dimensions can also be used) are used. Pt Rh alloys (90/10, 95/5, 80/20, 75/25), for example, can be used as the noble metal.

Pulsed lasers, continuously operating lasers (CW lasers), electron beam welding processes or vacuum and high vacuum soldering processes as well as plasma welding or resistance welding technology can be used as welding processes.

The base center electrode 12 of the insulator body 1 is welded to a center electrode carrier 10 in the area 11. The spark position can be determined by the center electrode carrier 10 in coordination with the ground electrode carrier arrangement 6. The center electrode carrier 10 is pushed onto the base center electrode 12 until it rests flush on the insulator base 14. In this position it is welded to the base center electrode in area 11. As a result of this arrangement, the center electrode carrier 10 and the base center electrode 12 are safe from high pressure. It is not possible to press the base center electrode out of the insulator base due to the engine pressure, since the center electrode carrier 10, which is welded to the base center electrode 12, is shouldered 14 on the insulator base 14. The welded connection 11 between the electrode carrier and the electrode is produced by welding with a pulsed laser. However, a continuously operating laser (CW laser), electron beam welding, soldering or resistance welding can also be used.

The weld 11 can take place along the entire length of the base center electrode 12, with welding being carried out from the outside through the center electrode carrier 10 onto the base center electrode 12. One or more spot welds as well as one or more seam welds can be arranged several times on the circumference in the longitudinal axis, if necessary, or several times radially on the circumference if necessary.

The center electrode carrier 10 is designed so that it enables good mixture accessibility. The design according to the invention enables easy readjustment. The center electrode carrier is designed in such a way that center electrodes 8 with a length of more than 4 mm can be welded on. In the specific invention, the edge length of the center electrode 8 is 6.25 mm. The center electrode carrier 10 is designed with 4 separate electrode fingers

AT 410 150 B which noble metal electrodes are welded on as center electrodes 8.

The center electrode arrangement 10 is provided with noble metal plates as center electrodes 8, these are welded to the carrier on one or both sides by means of a laser. The weld is made in such a way that the gap is closed on the electrode sides. This means that there is no open gap (or opening) through which gas can enter between the precious metal plate and the electrode carrier fingers.

In the specific case, Inco Alloy 600 (WNo. 2.4816) is used as the center electrode carrier material. Other nickel-based alloys or high-temperature stainless steels can also be used as alternatives.

In the case of the center electrodes 8, small plates with the dimensions 6.25 x 2.0 x 0.5 mm (other dimensions can also be used) are used. Pt Rh alloys (90/10, 95/5, 80/20, 75/25), for example, can be used as the noble metal.