EP2062338A1

EP2062338A1 - Spark plug

Info

Publication number: EP2062338A1
Application number: EP07801622A
Authority: EP
Inventors: Georg Maul; Dieter Kuhnert
Original assignee: Multitorch GmbH
Current assignee: Multitorch GmbH
Priority date: 2006-09-16
Filing date: 2007-08-13
Publication date: 2009-05-27
Anticipated expiration: 2027-08-13
Also published as: WO2008031482A1; DK2062338T3; DE102006043593B3; DE502007002224D1; ES2337524T3; PT2062338E; EP2062338B1; US20100001626A1; US8053964B2; ATE450911T1

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

spark plug

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 known, for example, from EP 1 265 328 B1.

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, it was proposed in EP 1 265 321 B1 to clamp the insulator body between the housing head and the pipe housing and to weld the 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.

Whereas in the case of the spark plug known from EP 1 265 328 B1, the tubular housing has the function of protecting the spark plug from damage by external action and transmitting torque for screwing in the spark plug, and, on the other hand, clamping the isolator, this clamping function is achieved in the case of an inventive spark plug Take the spark plug through an insulator body bracket that presses the insulator body against the housing head with a preload. 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 the case of known When unscrewing a defective spark plug, spark plugs can lead to breakage, which makes the 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 (XM in the temperature range of 0 ⁰ C to 400 ⁰ C with the thermal expansion coefficient α «of the insulator body the inequality OCM - OCK < 1 -10 ^"6 ZK fulfilled. the thermal expansion coefficient CCM of the insulator body holder is thus smaller than the thermal expansion coefficient ocκ of the insulator body or exceeds less than 1 ^• ^{10" 6} ZK. In this way remains the bias voltage at which the insulator body sealing against the housing head is pressed, as far as possible preserved even during an ongoing heating of the spark plug, so that it is ensured even at elevated temperatures that the housing head 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 metal parts surrounding it can heat up to 400 ^° C. and more during operation. The steels commonly used in the prior art have a coefficient of thermal expansion in the relevant temperature range of about ^{12.times.10.sup.-} ⁶ to ^{15.times.10.sup.-} ⁶ Z.sup.K, while the temperature coefficient of the insulator body, usually made of aluminum oxide, is typically about ^{3.times.10.sup.-} ⁶ 8 ^■ 10 ^"6 ZK. 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 from a ceramic material commonly used in the art, for example aluminum oxide, or in particular also from aluminum nitride, which has an advantageously high coefficient of thermal expansion. Suitable expansion coefficients in particular have 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 ensures a higher pressing 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.

EP 1 265 328 B1 teaches the use of laser welding methods for producing spark plugs. 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 impasting of candle parts from the tubular housing in the event of dangerous peak pressures in a simple and reliable manner. 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 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 ignition can reach. 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.

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 shows an embodiment of a spark plug according to the invention in a

Longitudinal section.

The spark plug 1 shown in FIG. 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 prestressing with which the insulator body 6 is pressed against the gasket 8 and the annular surface 10 of the housing head 2. The insulator body holder 7 is welded to the housing head 2. As shown in FIG. 1, the insulator body holder 7 and the housing head 2 are overlappingly arranged in a partial region, in which the insulator body holder 7 and the housing head 2 are also overlapped. 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 thermal expansion coefficient between 4 ^• 10 ^"6 ZK and 8 ^■ ^{10" 6} ZK in the temperature range of 0 ⁰ C to 400 ⁰ 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 thermal expansion coefficient a _M the thermal expansion coefficient α «of the insulator body 6 in the relevant temperature range from 0 ⁰ C to 400 ⁰ C at most by 1 ^■ 10 ^{" 6} ZK, preferably at most by 5 ^• 10 ^" ⁷ / K, exceeds or is slightly smaller. It is particularly favorable, in particular, if the thermal expansion coefficient α, M of the insulator body holder 7 is slightly smaller than the thermal expansion coefficient α 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 ot _{M of} the metallic material of the insulator body holder 7 is selected such that the metallic material when heated from 20 ⁰ C to 400 ° C, in total less expands than the ceramic material of the insulator body 6 when heated from 2O ⁰ C. to 400 ⁰ C. It is particularly advantageous if the total thermal expansion of the material of the insulator body holder 7 in the temperature range from ^{0 0} C to 400 ° C not more than 3 ^• 10 ^'3 , in particular not more than 2.5 ^• 10 ^{~ 3} , is.

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 the Deutsche Nickel AG under the names Diaton 36, Dilaton 41, Dilaton 42, Dilaton 46 and Dilaton 48. In particular Dilaton 36, the coefficient of thermal expansion in the temperature range from 0 ⁰ C to 400 ⁰ C is only about 5.5 ^■ 10 ^ / K, and Dilaton 42, whose thermal expansion coefficient in the temperature range from 0 ⁰ C to 400 ° C. is about 6 ^• 10 ^"6 ZK.

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). Prechamber spark plugs are known, for example, from EP 0 675 272 A1, to which reference is made for further details and special features 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. Nickel is particularly suitable as the material for the cap 16, the remaining Housing head 2 with the external thread 3 preferably made of steel, in particular ST52-3 or S355 steel, is made.

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 problematic, since there are no live parts in the annular space 20 and consequently there is no danger 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. In the exemplary embodiment illustrated, this seal 23 is a sealing ring which surrounds the part of the insulator body 6 protruding from the insulator body holder 7. 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 threads

4 ignition electrode

5 supply line (center electrode)

6 insulator body

7 insulator body holder

8 seal

9 tubular housing

10 torus of the insulator body

11 ring surface of the insulator body

12 ring surface

13 hexagon

14 antechamber

15 prechamber opening

16 cap

20 annulus

21 gas outlet opening

23 sealing ring

24 annulus

25 weld

26 weld

Claims

claims

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) a housing head (2) which sits sealingly on the insulator body (6) and carries an external thread (3) for screwing into an internal combustion engine, a tube housing (9) which is fastened to the housing head (2), the insulator body ( 6) and carries a hexagon (13), characterized in that the tube housing (9) surrounds an insulator body holder (7), which is welded to the housing head (2) via a weld seam (25) and the insulator body (6). with a bias against the housing head (2) presses.

2. Spark plug according to claim 1, characterized in that the weld (25) is a butt weld or a wedge seam.

3. Spark plug according to one of the preceding claims, characterized in that the weld (25) is an arc weld seam, preferably a TIG weld.

4. Spark plug according to one of the preceding claims, characterized in that the tubular housing (9) to the housing head (2) is welded.

5. Spark plug according to one of the preceding claims, characterized in that the tubular housing (9) has in its lateral surface at least one vent opening (21) for discharging combustion gases from the tubular housing (9).

6. Spark plug according to claim 5, characterized in that the insulator body (6) by a sealing ring (23) is enclosed.

7. Spark plug according to claim 6, characterized in that the sealing ring (23) from the housing head (2) from behind the at least one vent opening (21) is arranged.

8. Spark plug according to one of the preceding claims, characterized in that the insulator body holder (7) is made of a metallic material having a thermal expansion coefficient CXM, in the temperature range from ^{0 0} C to 400 ⁰ C with the coefficient of thermal expansion α «of the insulator body (6) satisfies the inequality CXM - α« <1 -10 ^"6 ZK, in particular the inequality α _M - α« <0.5 -10 ^"6 ZK.

9. Spark plug according to claim 8, characterized in that the coefficient of thermal expansion (XM of the metallic material of the insulator body holder (7) is selected such that the metallic material when heated from 2O ⁰ C to 400 ⁰ C in total less expands than that ceramic material of the insulator body (6) when heated from 20 ° C to 400 ° C.

10. Spark plug according to one of the preceding claims, characterized in that the insulator body holder (7) includes an annular space (20) which surrounds the I-solatorkörper (6) and is filled with a filling material which is at least 50 wt.% made of ceramic powder.

11. Spark plug according to one of the preceding claims, characterized in that between the housing head (2) and the insulator body (6) a seal (8), in particular a copper sealing ring, is arranged.

12. Spark plug according to one of the preceding claims, characterized in that the insulator body holder (7) is made of a different material than the tubular housing (9).

13. Spark plug according to one of the preceding claims, characterized in that the insulator body holder (7) presses against an annular surface (12) of the insulator body (6).

14. Spark plug according to one of the preceding claims, characterized in that the insulator body holder (7) and the housing head (2) are arranged overlapping in a partial area.

15. Spark plug according to one of the preceding claims, characterized in that the tubular housing (9) and the housing head (2) are arranged overlapping in a partial area.

16. Spark plug according to claim 15, characterized in that the insulator body holder (7) and the housing head (2) overlap on a cylindrical surface.

17. A spark plug according to claim 16, characterized in that 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.

18. Spark plug according to one of the preceding claims, characterized in that the housing head (2) an antechamber (14) is formed, in which the ignition electrode (4) is arranged.

19. Spark plug according to one of the preceding claims, characterized in that the insulator body (6) consists of at least 50 wt.% Of aluminum nitride.

20. A method for producing a spark plug (1), in which a housing head (2) is placed on an insulator body (6) through which an electrical supply line (5), to which an ignition electrode (4) is connected, passed , and an insulator body holder (7) with the housing head (2) is welded, characterized in that the welding causes a length contraction, by which the insulator body (6) sealingly against the housing head (2) is pressed.