WO2008055483A1 - Ignition device, in particular spark plug for an internal combustion engine and method for production - Google Patents

Abstract

The invention relates to an ignition device for an internal combustion engine, comprising at least one spark plug body made of an electrically conductive material, at least one electrical insulating element, which is arranged centrally in the spark plug body, at least one central electrode which is arranged centrally in the insulating element and protrudes from the base tip of the insulating element and at least one ground electrode which is positioned laterally with respect to the central electrode and is connected to the spark plug body, wherein the ground electrode and/or the central electrode is reinforced with precious metal.

Description

 Ignition device, in particular spark plug for an internal combustion engine and method of manufacture

The invention relates to an ignition device for igniting combustible mixtures, in particular a spark plug for generating the spark for a, in particular gas-fired internal combustion engine according to the preamble of patent claim 1 and a method for producing a spark plug.

From DE 101 22 938 a spark plug for a motor is known in which the center electrode has a tip made of precious metal.

Furthermore, a spark plug from DE 101 29 040 is known, which comprises a region with a step-shaped cross-sectional change of the ground electrode.

Among other things, from the GB 587437 also as a result of the work of Dr. Ing. Llewellyn-Jones has known to use stainless steel reinforced electrodes in spark plugs, particularly in aircraft engines.

Furthermore, one can refer to the Platinum Metals Rev., 1963, 7 (2), 58-65, a contribution by Professor Llewllyn-Jones, who has the basics of the erosion rate of platinum metals, especially in use as an electrode, the subject.

Reinforced spark plug electrodes, in particular with metals from the series of platinum metals are known from P.M. The growing use of platinum group metals for spark plug electrodes. Raw from the company Engelhard Ltd., Iselin, New Jersey, published at the meeting from 14.10.1992 to 17.10.1992 in Nice.

According to DE 195 03 223 A1, an ignition device, in particular a spark plug, with at least two ground electrodes fixed in the same bending height with respect to the tip of the center electrode is known, in which several types of discharge take place. Thus, when a high voltage is applied between the center electrode and the at least two ground electrodes, a first discharge is performed, the so-called air spark, at a first wide spark gap between the center electrode facing end surface of the ground electrode and the outer surface of the center electrode. According to the conventional technology, a second discharge takes place at a second wide spark gap, the so-called air sliding spark, between the ground electrode, the insulating member and the center electrode. In order for air slip to be formed, a relatively wide electrode spacing is needed to allow the air sliding spark to slide over the surface of the insulator element. This embodiment of the ignition device is not applicable in particular for gas-fired industrial engines with high compression pressures, as with such igniters a small located in the micrometer range electrode spacing to reduce the voltage requirement increase over time is not displayed and thus a production of arranged close to the center electrode ground electrodes by punching , is not feasible. At present, the life expectancy requirements for internal combustion engine igniters are increasing significantly, in particular for igniters intended for use in gas-fired stationary, large volume and high compression internal combustion engines. Ignition devices for this purpose should have a long duration of at least 1,000 to 2,000 hours. Because such

Internal combustion engines operate with high compression pressure, special importance must be attached to the smallest possible electrode spacing. The currently available ignition devices do not meet the requirement for a long life, resulting in a costly spark plug change.

The invention is based on this prior art, the task of providing an ignition device for an internal combustion engine, which has a long service life in a simplified and cost-effective production, and to provide an economically optimized method for inexpensive precious metal reinforcement of a mass and / or center electrode in the ignition device ,

This object is achieved with respect to the ignition device according to the invention with the features of claim 1 and solved in relation to the process to be created with the features of claim 13. Further advantageous embodiments and modifications of the invention will become apparent from the dependent claims and the description.

The solution according to the invention is given by an ignition device for an internal combustion engine comprising:

A spark plug body of an electrically conductive material,

An electrical insulation layer, which is arranged centrally in the spark plug body,

A center electrode, which is arranged centrally in the insulating element and projects from the tip of the insulating element and at least one

• Ground side of the center electrode employed ground electrode which is connected to the spark plug body. The ignition device according to the invention can be used for example in a gas-powered industrial engine with a high compression pressure.

With regard to its design and the positioning of the ground electrodes in the ignition device, the ignition device according to the invention has considerable advantages over the prior art, because spark gaps projecting far into the combustion space without thermal overheating or vibration fractures at the ground electrode can be realized by the frontal application of a noble metal tip , A further significant advantage of the ignition device according to the invention is then that, in the case of the height-offset arrangement of the ground electrodes, a nearly 360 ° burnup surface can preferably be provided on the lateral surface of the center electrode. In the arrangement according to the invention, mutual contact between the ground electrodes is essentially ruled out. With the enlargement of the Abbrandfläche the spark exit surface is simultaneously increased and thus achieved an increased life

Another advantage of the ignition device according to the invention is that the electrode spacing between each ground electrode and the center electrode is set so that it is substantially equal. The electrode spacing is preferably in the micrometer range to avoid undesirable misfire. Since the inventive ignition device requires a high discharge voltage, this small micrometer range satisfies the requirement for stable operation without misfire

In another embodiment of the invention, the center electrode and the ground electrodes are formed substantially of a non-noble metal

According to a further embodiment of the inventive ignition device, the center electrode and the ground electrodes consist essentially of a nickel-based alloy, comprising elements such as Al, Si, Mn, Cr, Y, Hf. The advantage of using nickel-based alloys is the reduced material costs

According to a further preferred embodiment of the invention, each end face of the ground electrode of the lateral surface of the center electrode is opposite and the electrode distance is less than the distance of the ground electrode to the isoher element. This has the advantage that a plurality of ground electrode pairs can be arranged offset in height with respect to the tip of the center electrode. The burning surface of the ignition device is thus increased

In a further embodiment of the invention, the electrode spacing between each ground electrode and the center electrode is substantially equidistant. This leads to a uniform burn of the ground electrodes and the center electrode. In addition, with each individual ground electrode, a micrometre reduced electrode spacing between the ground electrode and center electrode is possible, which can lead to a reduction in the voltage requirement increase over time. Furthermore, the spark is formed directly as air sparks A gliding of the air spark on the toe of the insulating does not take place

In another preferred embodiment of the invention, the electrode spacing is approximately between 200 .mu.m to 600 .mu.m, preferably at 300 .mu.m. The small electrode spacing in the micrometer range is of great importance in particular for ignition devices for use in gas-operated industrial engines with high compression pressures, since a particularly small electrode spacing leads to a reduction in the discharge voltage requirement In a further preferred embodiment of the ignition device according to the invention, the electrode spacing can be readjusted by bending the ground electrodes. The advantage of this embodiment allows a readjustment to small electrode spacings, preferably 300 .mu.m, during engine operation at regular intervals of maintenance. A repeated use of these ignition devices is given.

According to a further advantageous embodiment of the invention, each ground electrode forms an air gap with the center electrode over the electrode gap. The height-offset arrangement of the ground electrode pairs preferably results in at least four air gaps ranging in size between 200 .mu.m and 600 .mu.m, preferably 300 .mu.m. The distance between the air gap between the ground electrode and the center electrode corresponds essentially to the distance between the electrodes.

A significant advantage of the method according to the invention is that can be set by the erfiπdungsgemäße positioning of the ground electrode pairs predefined electrode distances in the micrometer range cost and with a minimum of process steps. In addition, the small electrode spacings in conjunction with an increase in burnup area allow for an increase in the life of the igniter without the use of precious metals.

A further advantage of the method according to the invention is that the height-offset attachment of the laterally arranged ground electrodes makes it possible to use a large burnup area, which makes it possible to reduce the rise in the voltage requirement over the runtime.

The object of the invention shows the significant advantage that the electrode spacing can also be readjusted by attaching lateral ground electrodes.

In a particularly advantageous embodiment of the method according to the invention, a substantially equal electrode spacing is formed between each ground electrode and the center electrode. The electrode spacing is set between 200μm and 600μm, preferably 300μm, to avoid misfire. Since the ignition device according to the invention enables a low discharge voltage, the requirement for stable operation without misfire is met by means of an electrode spacing of between 200 μm and 600 μm.

In an advantageous embodiment of the method according to the invention, a third ground electrode pair to the first and the second ground electrode pair with respect to the tip of the center electrode mounted in such a height offset, that the third ground electrode pair is arranged lower than the first ground electrode pair, which additionally increases the burning surface.

In a further advantageous embodiment of the method according to the invention, the ground electrodes are bent in such a way that the electrode spacing is readjusted. The advantage of the erfgπdungsgβmäßen method allows in motor operation, as needed, a readjustment to small micro-scale electrode distances, preferably 300 .mu.m, so that low raw emissions are possible until the end of life. Thus, the ignition devices according to the invention can be used several times with the ground electrodes positioned according to the invention.

An advantage of this embodiment is that a uniform erosion of the ground electrodes and the center electrode takes place.

The objects according to the invention will be explained in more detail below on the basis of the exemplary embodiments and FIGS. 1 to 3. Here are from the figures and their description further features and advantages of the invention. Showing:

Figure 1: A schematic view of a spark plug device with a laterally arranged

ground electrode

Figure 2 ¹ A schematic representation of a cross-sectional view of a combustion chamber end of an ignition device with two laterally arranged ground electrodes

FIG. 3: The stepwise formation of an electrode with a noble metal tip

FIG. 4: reinforcement of the electrode

FIG. 5: Side electrode variants

Figure 6: an embodiment with stainless steel sleeve

1 schematically illustrates an exemplary embodiment of the ignition device according to the invention for an internal combustion engine, which is designed as a spark plug. The ignition device 10 has a cylindrical spark plug body 1 made of metal, in which a ceramic insulating element 2 is arranged centrally. From the insulating member 2, the tip of the center electrode 3 formed of a non-noble metal projects into the combustion chamber (not shown) of the internal combustion engine. The ceramic insulating member 2 includes the center electrode 3 of the igniter. The center electrode 3 is disposed axially in the ceramic insulating member 2 and protrudes from the toe of the insulating member 2. Through the center electrode 3, the center axis of the ignition device runs centrally. On the end surface of the cylindrical spark plug body 1, a ground electrode 4 is mounted such that the leading end is fixed to the end face of the cylindrical spark plug body 1 by welding. For the ground electrode 4 formed of a non-noble metal, made of a nickel-based alloy, electrode wire z. B. used with dimensions of the order of 1.7mm x 2.7mm. After welding, the ground electrode 4 is bent in the direction of the center axis of the ignition device such that the ground electrode is positioned at the same bending height with respect to the tip 5 of the center electrode 3. The invention is not limited only to the examples described, but other ground electrodes can z B arranged offset in height with respect to the tip of the center electrode

An additional possibility is that possible further ground electrodes are arranged offset on the end face of the cylindrical spark plug body to another than 90 ° or 60 ° -Wιnkel

In addition, electrode wires with other dimensions can be used for the ground electrodes. Furthermore, the stamp with which the Masseeie- electrodes are punched, have different diameters

The invention is generally applicable to igniters

Figure 1 shows a partial view of the spark plug according to the invention, which consists essentially of a metallic body (1), a ceramic insulator (2), a center electrode (3) and a ground electrode (4). The ground electrode (4) is designed as a side electrode and forms a spark gap (EA) with the center electrode (3).

The center electrode (3) is centrally inserted in the insulator (2) and pressure-tightly embedded in the step-shaped insulator bore by means of an electrically conductive glass mass, not shown, and a firing pin. The center electrode (3) is formed with an annular shaped tip, the so-called corona tip (9). The center electrode (3) looks in the zundseitigen end and is provided at the end with a noble metal tip (5). The noble metal tip can consist of a platinum or lithium alloy , The noble metal tip (5) is connected to the center electrode (3) by means of an alloying zone (7). The alloying zone (7) is formed by laser welding. The alloy zone (7) compensates for the different coefficients of linear expansion of the two metals nickel alloy from the center electrode (3) and indium or platinum alloys from the noble metal tip (5), so that during engine operation no stress cracks occur in the joint plane and therefore premature end of life is avoided.

The ground electrode (4) is formed from a round wire (0 1, 5 - 2,0 mm) and bent in the direction of spark plugs central axis to the noble metal tip (5) of the center electrode (3) in the form of a side electrode The ground electrode (4) is zünseitig verünt and The precious metal tip (6) is welded onto the ground electrode (4) by means of a laser welding, so ) and the ground electrode (4) forms an alloying zone (8) for the purpose of compensating for the different coefficient of longitudinal expansion of the nickel base alloy of the ground electrode (4) and iridium or platinum alloy of the noble metal tip (6) The noble metal tips (5) of the center electrode (3) and the noble metal tip (6) of the ground electrode (4) form a spark gap (EA). The ground electrode (4) is above the Isolatorfußspitze (10) with the distance G, wherein the distance G is always greater than the electrode spacing (EA). FIG. 2 shows a spark plug having the features of FIG.

The spark plug according to the invention in FIG. 2 differs essentially from the spark plug described in FIG. 1 in that it is formed with at least one additional auxiliary electrode (11). The auxiliary electrode is arranged to form a sliding air gap (GLF) with the center electrode (12). The sliding air gap (GLF) consists of a sliding spark gap (GF) and a Luftfun kenstreckθ (LF).

The center electrode (12) is cylindrical in the region of the insulator bore (13) and tapers only outside the insulator bore (13). This geometry ensures that the sparks are formed at the appropriate engine operating state or contaminated insulator foot tips on the sliding air gap (GLF).

For proper functioning of the spark plug according to the invention, the distance between the sliding air gap section (GLF) is greater than the air gap gap (EA). The air gap (LF) of the sliding air gap (GLF) is smaller than the air gap of the center electrode (12) and the ground electrode (4). The distance G between the lower edge of the ground electrode (4) and the Isolatorfußspitze is greater than that of the air gap (EA) of the center electrode (12) and the ground electrode (4). FIG. 3 shows the production sequence when attaching the noble metal tip (6) to the ground electrode (4). The noble metal tip (6) is applied to the ground electrode (4) in such a way that the noble metal tip (6) in the form of a blank (15) is applied on the end face (14) of the ground electrode (4).

The ground electrode (4) has the geometric shape of a round wire instead of conventional flat wires. This allows a mechanical processing, for example by means of turning. At the ground electrode (4), a tapered step (16) is mounted on the end face (14) a Ronde (15) is applied by means of resistance welding. The step (16) which receives the blank (15) is larger in diameter than the blank (16). Subsequently, an alloy zone (8) is produced by laser welding between the blank (15) and the step (16) of the center electrode (4), and the ground electrode (4) is formed with a noble metal tip (6). The ground electrode (4) with the noble metal tip (6) can then be welded onto the body (1) and bent. Furthermore, FIG. 1 shows a spark plug with a noble-metal-reinforced center electrode (3) and a noble-metal-reinforced ground electrode (4) in the form of a side electrode, wherein the noble metal reinforcement (6) is welded onto the side electrode on the front side. Between precious metal (6) and ground electrode (4), an alloy zone (8) is formed. The alloy zone (8) is formed for example by means of beam welding, preferably by laser welding. The ground electrode (4) consists of a round wire. The ground electrode (4) is tapered on the ignition side and provided with a step ((16). The center electrode (3) is formed with a noble metal tip (5) and a Alierungszoπe (7). The distance G, which is shown in Figures 1 and 2, is greater than the air gap (EA). An additional auxiliary electrode (11) can be seen in an alternative embodiment in Figure 2. The distance of the sliding air gap (GLF), as shown in FIG. 2, is greater than the air gap (EA). The air gap (LF) of the sliding air gap (GLF) is smaller than the air gap (EA) between the center electrode (12) and the ground electrode (4). The distance G between the lower edge of the ground electrode (4) and the Isolatorfußspitze is greater than that of the air gap (EA) of the center electrode (12) and the ground electrode (4).

FIG. 4 shows a further manufacturing possibility of the noble metal reinforcement on the ground electrode. This provides that on the end face of the ground electrode, a noble metal piece is welded as described below:

a. Resistance welding Ground electrode, preferably round wire, on body b. Bending the ground electrode c. Cutting the ground electrode d. Resistance welding Precious metal piece (5) e. Laser welding precious metal piece f. Assembly of body and insulator completely

The noble metal piece in FIG. 5 can be applied to the end face in the form of a round blank, a cylindrical wire piece, a rivet form or as a ball (with subsequent flat embossing), preferably by means of resistance welding. In order to produce a thick alloy layer, a radiation welding process, preferably a laser welding process, is additionally used.

FIG. 6 shows a spark plug with stainless-steel-reinforced electrodes 3, 4. The center electrode 3 has a tubular sleeve 5, which is friction-welded, for example. Such a sleeve 5 can also be arranged on the sides and / or auxiliary electrode.

LIST OF REFERENCE NUMBERS

1 body

2 insulator

3 center electrode

4 side electrode

5 precious metal point

6 precious metal blanks

7 alloy zone

8 alloy zone

9 Corona point

10 insulator toe

11 auxiliary electrode

12 center electrode

13 insulator bore

14 front side earth electrode

15 plate

16 level

G Distance of insulator foot tip / ground electrode

EA electrode distance

LF air gap

GF sliding spark gap

GLF G conductive air gap

G Distance side electrode / insulator foot

Claims

claims 1. Ignition device, in particular spark plug for an internal combustion engine, comprising at least one Ziindkerzenkörper of an electrically conductive material, at least one electrical insulating element, which is arranged centrally in the spark plug body, at least one center electrode which is centrally disposed in the insulating member and projecting from the toe of the insulating element and at least one ground electrode positioned laterally with respect to the center electrode, which is connected to the spark plug body, the ground electrode and / or the center electrode having a noble metal reinforcement. 2. Ignition device according to claim 1, characterized in that the precious metal reinforcement is arranged on the front side of the ground electrode. 3. Ignition device according to claim 1 and 2, characterized in that the precious metal reinforcement is arranged on the front side on the center electrode. 4. Ignition device according to one or more of the preceding claims, characterized in that the Edelstahlarmierung is designed substantially tubular. 5. Ignition device according to claim 1 to 3, characterized in that the noble metal reinforcement consists of a platinum alloy. 6. Ignition device according to claim 1 to 4, characterized in that the noble metal reinforcement consists of an iridium alloy. 7. firing direction according to one or more of the preceding claims, characterized in that the Edelstahlarmierung has up to 90 weight percent of an iridium-rhodium alloy. 8. Ignition device according to one or more of the preceding claims, characterized in that the iridium alloy has a rhodium content of about 30 - 60 weight percent and / or a rhodium content of about 1 to 3 weight percent. 9. Ignition device according to one or more of the preceding claims, characterized in that the center electrode (3) and the ground electrodes are formed substantially from a nickel-based alloy. 10. Ignition device according to one or more of the preceding claims, characterized in that the ground and / or center electrode is tapered towards the ignition side. 11. Ignition device according to one or more of the preceding claims, characterized in that the ground and / or center electrode has a substantially round cross-section. 12. Ignition device according to one or more of the preceding claims, characterized in that the middle and / or ground electrode has a noble metal tip and an adjoining alloy zone (7). 13. A method of making a connection between a center and / or ground electrode of a spark plug and a noble metal tip, comprising the steps of: temporarily placing the noble metal tip on the face of a substantially circular electrode wire, then forming a joint between the electrode wire and the noble metal tip, in particular by laser welding. 14. A method of making a center and / or ground electrode comprising the steps of: Producing a taper on a substantially round wire, temporary application of a noble metal tip, in particular in the form of a Ronde and / or a particular aufzusteckendes tube and / or around and / or over the end face of the taper of the round wire, then generating a joint connection between precious metal tip and the end face of the tapered wire. 15. A method for producing an ignition device, in particular a spark plug, characterized in that at least one ground and / or center electrode is used according to one or more of the preceding claims. 16. Internal combustion engine with an ignition device according to one of claims 1 to 5.