EP2062338B1 - Spark plug - Google Patents

Abstract

The invention relates to a spark plug for igniting a combustible gas mixture in an internal combustion engine, comprising an ignition electrode (4), an electrical supply line (5), to which the ignition electrode (4) is connected, an insulator body (6), through which the supply line (5) is passed, a housing head (2), which rests in sealing fashion on the insulator body (6) and bears an outer thread (3) for the purpose of screwing it into an internal combustion engine, a tube housing (9), which is fixed on the housing head (2), surrounds the insulator body (6) and has a hexagon head (13). The invention provides that the tube housing (9) surrounds an insulator body holder (7), which is welded to the housing head (2) and presses the insulator body (6) with a prestress against the housing head (2).

Description

The invention relates to a spark plug for igniting a combustible gas mixture in an internal combustion engine, comprising an ignition electrode, an electrical supply line to which the ignition electrode is connected, an insulator body, through which the supply line is passed, and a housing head which sits sealingly on the insulator body and an external thread for screwing into an internal combustion engine carries. Such a spark plug is for example from the EP 1 265 328 B1 known.

In internal combustion engines, peak pressures of the order of 150 bar can occur. These peak pressures load the spark plug during operation and, even with dimensionally accurate manufacture and careful sealing, can cause combustion gases to exit the engine. In particular, in gas engines occurring peak pressures can also cause the insulator body is squeezed and explosively shoots out of the plug housing.

In order to improve the pressure resistance of spark plugs and to prevent the pressing out of the insulator body was in the EP 1 265 328 B1 proposed to clamp the insulator body between the housing head and the pipe housing and to weld housing head and pipe housing together. In this way, the extrusion of the insulator body could be effectively countered and an improved seal can be achieved.

The object of the invention is to increase life and reliability of a spark plug of the type mentioned on.

This object is achieved by a spark plug having the features specified in claim 1.

While at the out of the EP 1 265 328 B1 known spark plug, the tubular housing on the one hand has the function to protect the spark plug from damage by external influence and to screw the spark plug torque to transmit, and on the other hand clamp the insulator, this clamping function is taken in a spark plug according to the invention by an insulator body holder, the Insulator body with a bias against the housing head presses. In this way, in a spark plug according to the invention, the tubular housing and the insulator body holder can be optimized separately with respect to their respective functions. Therefore, very high torques can be transmitted via the hexagon of the tube housing of a spark plug according to the invention for screwing in the spark plug into an engine block, without thereby impairing the seal between insulator body and housing head. Preferably, the tube housing and the insulator body holder are made of different materials.

In particular, in known Vorkammerzündkerzen for gas engines occurs as a result of the usual large maintenance and replacement intervals and the problem that due to contamination and corrosion of the threaded surface particularly large torques for changing the spark plug of a motor are necessary. Therefore, very high forces must be transmitted via the plug housing, which in known When unscrewing a defective spark plug, spark plugs can lead to breakage, which makes replacement of a spark plug extremely difficult. In a spark plug according to the invention, the housing can be optimized independently of the insulator body holder and thus the risk of breakage can be substantially reduced.

In a spark plug according to the invention, the insulator body holder is preferably made of a metallic material having a thermal expansion coefficient α _M , the in the temperature range from 0 ° C to 400 ° C with the thermal expansion coefficient α _{K of} the insulator body the inequality α _M - α _K <1 × 10 ^-6 / K. The thermal expansion coefficient α _{M of} the insulator body holder is thus smaller than the thermal expansion coefficient α _{K of} the insulator body or exceeds it by less than 1 · 10 ^-6 / K. In this way, the bias voltage with which the insulator body is pressed sealingly against the housing head, even when a heating operation of the spark plug is maintained as far as possible, so that it is ensured even at elevated temperatures that the housing head is sealingly seated on the insulator body.

In the context of the invention it has been found that the insulator body of a spark plug and surrounding metal parts can heat up to 400 ° C and more during operation. The steels commonly used in the art have a coefficient of thermal expansion in the relevant temperature range of from about ^{12.10 -6} / K to ^{15x10 -6} / K, while the temperature coefficient of the insulator body typically made of alumina is typically about ^{3.10 -6} / K is up to 8 · 10 ^-6 / K. In the case of spark plugs according to the prior art, this leads to the fact that at higher temperatures, the contact force with which the insulator body is pressed against the housing head, so that gases from the combustion chamber through a joint between the housing head and the insulator body into the interior of the Candle can get. Such leakage gases lead to deposits in the interior of the spark plug, increase the risk of shunts and can affect the functionality of a spark plug over time and cause their premature failure.

In a spark plug according to the invention, the materials of the insulator body and the insulator body holder with respect to the thermal expansion coefficient coordinated, so that permanently a better seal is achieved. Impairment by leakage gases can therefore be avoided in a spark plug according to the invention, so that results in a longer life. The insulator body may be made of a ceramic material customarily used in the state of the art, for example aluminum oxide, or in particular also of aluminum nitride, which has an advantageously high thermal expansion coefficient. Matching coefficients of expansion have in particular nickel-iron alloys with a nickel content of 25% by weight to 50% by weight. Steel, for example ST37 steel, is preferred as the material for the tubular housing.

Preferably, the insulator body holder is welded to the housing head via a butt weld or a wedge seam, a butt weld being particularly preferred. Wedge seams are sometimes referred to as V-seams and butt welds as I-seams. In particular, when the insulator body holder and the housing head overlap, high-precision manufacturing can be performed by welding with a wedge or butt weld.

Welding is particularly preferably carried out as arc welding, particularly preferably as inert gas welding, in particular as TIG welding (tungsten inert gas). In arc welding, the material is heated up around the weld to be formed. During the subsequent cooling, therefore, there is a length contraction, by which the insulator body is clamped with great force between the housing head and the insulator body holder. The length contraction caused by the welding thus provides for a higher contact force with which the insulator body is pressed against the housing head, and consequently also for a better seal against the ingress of gases from the combustion chamber of the engine.

The EP 1 265 328 B1 teaches the use of laser welding techniques for spark plug production. Laser welding has the advantage of very high precision, making it predestined for high-precision manufacturing, as required for spark plugs. Surprisingly, can be produced by arc welding spark plugs, which provides an improved seal between the insulator body and Show housing head. This improved sealing is effected by the contraction occurring during cooling of the weld.

The measure according to the invention of pressing the insulator body against the housing head welded to it by means of an insulator body holder and arranging a vent opening in the tubular housing prevents impast of candle parts from the tubular housing in the event of dangerous peak pressures in a simple and reliable manner. Namely, if such high peak pressures occur that the insulator body is pressed into the interior of the pipe housing despite the insulator body holder being welded to the housing head, the pressure can be discharged through the at least one vent opening in the jacket surface of the pipe housing without causing dangerous acceleration the insulator body and its imposition comes.

In the context of the invention it was recognized that even with dimensionally accurate production and careful sealing even in normal engine operation combustion gases from the engine in small quantities as leakage gases, for example, at sealing points between an insulating body and a guided through him electrode connection (center electrode) in a surrounded by the pipe housing Interior of the spark plug can get. Such leakage gases, which are always inevitable to a greater or lesser extent, increase the risk of shunts and can affect in this way spark plugs. Leakage gases can, for example, also lead to a pressure building up in the pipe housing which can lead to an accumulation of insulation layers and thus premature failure of the spark plug. By means of a venting channel according to the invention, leakage gases can be led out of the pipe housing. Harmful effects of the leakage gases can be avoided in this way and consequently the service life of a spark plug can be increased.

Fig. 1

ein Ausführungsbeispiel einer erfindungsgemäßen Zündkerze in einem Längsschnitt.

Further details and advantages of the invention will be explained with reference to an embodiment with reference to the accompanying drawings. The features described may be used alone or in combination to provide preferred embodiments of the invention. It shows:

Fig. 1

An embodiment of a spark plug according to the invention in a longitudinal section.

In the Fig. 1 illustrated spark plug 1 has a housing head 2 with an external thread 3 for screwing in an internal combustion engine and an ignition electrode 4, which is arranged in the housing head 2. The ignition electrode 4 is connected to an electrical supply line 5, which is also referred to as the center electrode. The supply line 5 is passed through an insulator body 6, which is pressed by an insulator body holder 7 with a bias against the housing head 2. The housing head 2 is seated with the interposition of a seal 8 in the form of a copper sealing ring sealingly on the insulator body 6. The insulator body holder 7 and the insulator body 6 are surrounded by a tubular housing 9 which is fixed to the housing head 2 by welding and carries a hexagon 13, with which the necessary for screwing the spark plug 1 in an internal combustion engine torque can be transmitted. The hexagon 13 is welded to the tubular housing 9. The insulator body holder 7 includes an annular space 20 which surrounds the insulator body 6 and is filled with a filling material for dissipating heat arising.

The filler material contains ceramic powder or may even consist entirely of ceramic powder. The ceramic powder may be mixed with a binder and / or a heat-conductive additive, preferably in the form of a metal powder, for example copper. The filler material preferably comprises at least 50% by weight, more preferably at least 75% by weight, in particular at least 90% by weight, of ceramic powder, for example aluminum oxide and / or aluminum nitride. In particular, aluminum nitride has the advantage of good thermal conductivity.

The insulator body 6 has an annular bead 11 around which the insulator body holder 7 engages. The insulator body holder presses in this way against an annular surface 12 of the insulator body 6 and thus exerts on the insulator body 6, the bias with which the insulator body 6 is pressed against the seal 8 and the annular surface 10 of the housing head 2. The insulator body holder 7 is welded to the housing head 2. As Fig. 1 shows the insulator body holder 7 and the housing head 2 are arranged overlapping in a partial area, in which also the housing head 2 with the insulator body holder 7 connecting weld 25 is arranged. In a corresponding manner, the tubular housing 9 and the housing head 2 are arranged overlapping in a partial area in which there is a weld 26 connecting the tubular housing 9 and the housing head 2.

The housing head 2 has a first cylindrical surface, on which the insulator body holder 7 rests, and a second cylindrical surface, on which the tubular housing 9 rests on. By attaching the insulator body holder 7 on the first cylinder surface and the tube housing 9 to the second cylindrical surface with exact means an exact positioning possible. The two cylindrical surfaces are each bounded by a step, against the annular surface of the insulator body holder 7 and the tubular housing 9 abut. The joint between the annular surface of the housing head 2 and the adjoining end of the insulator body holder 7 and the tubular housing 9 is filled during welding by the weld 25 and 26 respectively.

Welds 25, 26 are butt welds produced by arc welding, namely TIG welding. Upon cooling of the welds 25, 26, the material contracts, so that the insulator body 6 is pressed by the insulator body holder 7 against the housing head 2. This leads to an improved seal.

The insulator body 6 is made of a ceramic material, such as alumina or aluminum nitride, which has a coefficient of thermal expansion between 4 · 10 ^-6 / K and 8 · 10 ^-6 / K in the temperature range of 0 ° C to 400 ° C. In addition to the use of technically pure aluminum oxide or aluminum nitride, it is also possible to use composite ceramics, for example ceramic materials which consist of at least 50% by weight, in particular at least 75% by weight, of aluminum nitride. The insulator body holder 7 is made of a metallic material whose coefficient of thermal expansion α _M the thermal expansion coefficient α _{K of} the insulator body 6 in the relevant temperature range of 0 ° C to 400 ° C at most by 1 · 10 ^-6 / K, preferably at most 5 · 10 ^-7 / K, exceeds or is slightly smaller. It is particularly favorable, in particular, when the thermal expansion coefficient α _{M of} the insulator body holder 7 is slightly smaller than the thermal expansion coefficient α _{K of} the insulator body 6 then heating leads to an increase in the preload and thus to an even better seal. Preferably, therefore, the thermal expansion coefficient α _{M of} the metallic material of the insulator body holder 7 is chosen such that the metallic material when heated from 20 ° C to 400 ° C, in total less expands than the ceramic material of the insulator body 6 when heated from 20 ° C. at 400 ° C. In particular, it is favorable if the total thermal expansion of the material of the insulator body holder 7 in the temperature range from 0 ° C. to 400 ° C. is not more than 3 × 10 ^-3 , in particular not more than 2.5 × 10 ^-3 .

In the illustrated embodiment, the metallic material of the insulator body holder 7 is a nickel-iron alloy having a nickel content of 25 wt .-% to 50 wt .-%. Suitable nickel-iron alloys are offered, for example, by Deutsche Nickel AG under the names Dilaton 36, Dilaton 41, Dilaton 42, Dilaton 46 and Dilaton 48. Dilaton 36, whose coefficient of thermal expansion in the temperature range from 0 ° C. to 400 ° C. is only approximately 5.5 × 10 ^-6 / K, and Dilaton 42, whose coefficient of thermal expansion is in the temperature range from 0 ° C. to 400 °, are particularly well suited C is about 6 · 10 ^-6 / K.

In view of the different functions of the insulator body holder 7 and the tubular housing 9, it is advantageous to manufacture these from different metallic materials. The tubular housing 9 is made of a commercially available steel, for example ST37 steel.

In the illustrated spark plug 1 is a pre-chamber spark plug, since the ignition electrode 4 is arranged in an antechamber 14, which can communicate through openings 15 with the combustion chamber of an internal combustion engine (not shown). Vorkammerzündkerzen are for example from the EP 0 675 272 A1 to which reference is made for further details and particularities of prechamber spark plugs. In the illustrated embodiment, the pre-chamber 14 is formed by a cap 16 which is inserted into the housing head 2. As the material for the cap 16, in particular nickel is suitable, wherein the remaining housing head 2 with the external thread 3 is preferably made of steel, in particular ST52-3 or S355 steel.

In the event that it should come despite the measures described leakage of leakage gases, the tube housing 9 in its lateral surface gas outlet openings 21 for the discharge of leakage gases. Corresponding gas outlet openings 22 can in principle also be arranged in the insulator body holder 7, but leakage gases within the annular space 20 are far less problematical since there are no live parts in the annular space 20 and consequently there is no risk of shunts. By contrast, leakage gases are particularly harmful in the region in which the supply line 5 (center electrode) emerges from the ceramic body 6 and is connected, for example, to a strand of a cable, since deposits there increase the risk of shunts.

Penetration of leakage gases in the rear (ie, away from the head 2) region in which the supply line 5 emerges from the ceramic body 6 is counteracted by a seal 23. This seal 23 is in the illustrated embodiment, a sealing ring surrounding the protruding from the insulator body holder 7 part of the insulator body 6. The sealing ring 23 is in the illustrated embodiment, a plastic ring, such as a Teflon ring. Any leakage gases which seep out of the annular space 20 between the insulator body holder 7 and the insulator body 6 resting against the annular surface 12 are prevented from penetrating further by the sealing ring 23 and are discharged through the vent openings 21 out of the tube housing.

LIST OF REFERENCE NUMBERS

1

spark plug

2

housing head

3

external thread

4

ignition electrode

5

Supply line (center electrode)

6

insulator body

7

Insulator body holder

8th

poetry

9

tube housing

10

Ring bead of the insulator body

11

Ring surface of the insulator body

12

ring surface

13

hexagon

14

antechamber

15

chamber port

16

cap

20

annulus

21

Gas outlet

23

seal

24

annulus

25

Weld

26

Weld

Claims (15)

1. A spark plug for igniting a combustible gas mixture in an internal combustion engine, comprising

   an ignition electrode (4),

   an electrical supply line (5) to which the ignition electrode (4) is connected,

   an insulator body (6) through which the supply line (5) is passed,

   a housing head (2) that rests in sealing fashion on the insulator body (6) and bears an outer thread (3) for the purpose of screwing it into an internal combustion engine, a tube housing (9) that is fixed on the housing head (2), surrounds the insulator body (6) and has a hexagon (13) head,

   characterized in that

   the tube housing (9) surrounds an insulator body holder (7) that is welded by means of a weld seam (25) to the housing head (2) and presses the insulator body (6) with a prestress against the housing head (2).
2. A spark plug according to claim 1, characterized in that the weld seam (25) is either a butt seam or a V-seam.
3. A spark plug according to any of above claims, characterized in that the tube housing (9) is welded to the housing head (2).
4. A spark plug according to any of above claims, characterized in that the tube housing (9) is provided on its surface with at least one vent hole (21) for discharging combustion gases from the tube housing (9).
5. A spark plug according to claim, characterized in that the insulator body (6) is surrounded by a sealing ring (23).
6. A spark plug according to claim 5, characterized in that seen from the housing head (2), the sealing ring (23) is mounted behind the at least one vent aperture (21).
7. A spark plug according to any of above claims, characterized in that the insulator body holder (7) is made out of a metallic material having a thermal expansion coefficient α_M that fulfills in the temperature range of 0° C to 400° C with the thermal expansion coefficient α_K of the insulator body (6) the inequation α_M - α_K < 1 · 10^-6/K, especially the inequation α_M - α_K < 0.5 · 10^-6/K.
8. A spark plug according to claim 7, characterized in that the thermal expansion coefficient α_M of the metallic material of the insulator body holder (7) is chosen in such a manner that, at a heating up from 20° C to 400° C, the metallic material expands less than the ceramic material of the insulator body (6) at a heating up from 20° C to 400° C.
9. A spark plug according to any of above claims, characterized in that the insulator body holder (7) comprises an annular space (20) that surrounds the insulator body (6) and is filled with a filling material comprising at least 50% of weight of ceramic powder.
10. A spark plug according to any of above claims, characterized in that between the housing head (2) and the insulator body (6) is a gasket (8), in particular a copper gasket.
11. A spark plug according to any of above claims, characterized in that the insulator body holder (7) is manufactured out of a different material than the tube housing (9).
12. A spark plug according to any of above claims, characterized in that the insulator body holder (7) presses against an annular surface (12) of the insulator body (6).
13. A spark plug according to any of above claims, characterized in that the insulator body holder (7) and the housing head (2) are arranged overlapping in a subsection.
14. A spark plug according to any of above claims, characterized in that the tube housing (9) and the housing head (2) are arranged overlapping in a subsection.
15. A method for the manufacture of a spark plug (1) in which
    a housing head (2) is placed on an insulator body (6) through which an electrical supply line (5) is passed to which an ignition electrode (4) is connected and an insulator body holder (7) is welded to the housing head (2),
    wherein by means of the welding is caused a longitudinal contraction by which the insulator body (6) is tightly pressed against the housing head (2) and a tube housing (9) is fixed to the housing head (2), said tube housing (9) surrounding the insulator body (6).

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