CA2320415A1 - Spark plug - Google Patents
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- CA2320415A1 CA2320415A1 CA 2320415 CA2320415A CA2320415A1 CA 2320415 A1 CA2320415 A1 CA 2320415A1 CA 2320415 CA2320415 CA 2320415 CA 2320415 A CA2320415 A CA 2320415A CA 2320415 A1 CA2320415 A1 CA 2320415A1
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Abstract
In a spark plug 100, when a side of the spark plug 100 in which a spark discharge gap g is formed in an axial direction of a center electrode 3 is a front side thereof by definition, a distance "a" along the axial direction from the surface of one end of a metallic shell 1, with which one end of a ground electrode 4 is joined, to the outermost point of a front end portion of the ground electrode 4 is 6 mm or more and at least a surface layer portion of the ground electrode 4 is made from a sulfur corrosion resistant metal. As the sulfur corrosion resistant metal, an iron-based alloy can be employed, containing: iron as a main component: and at least one of chromium and cobalt in total content of 10 mass % or more. The spark plug is hard to suffer electrode consumption through a reaction with a sulfur constituent or other inconveniences even in a working environment in which contact with the sulfur constituent at a high concentration can arise and thereby, capable of ensuring a sufficiently long lifetime of an electrode even when being employed in a direct-injection type engine or the like.
Description
SPARK PLUG
Technical Field The present inventxox~ relates to a spark plug for an internal combuct~on engine and an internal combustion engine with the spark plug ~ooiowoted thereon_ Background of the Art Electrodes (a center electrode and a ground electrode) o~ a spark plug for an internal combustion engine have heretofore been manufactured from nickel-based material in order to ensure high temperature strength and high temperature oxidation resistivity. Especially in order to improve high temperature oxidation resistivity, it is necessary to compound a relatively large amount of chromium into an alloy anal among alloys of this kind, INCONEL 600 (a trade name of INCO Co. in U.K., having a composition of Ni - X5.5 mass % Cr - 8_0 mass % Fe), which is one of nickel-based heat resistant alloys, is excellent in balance between performance acrd cost therefoze haring been widely employed as a spark 2U plug electrode material.
Studies performed by the present inventors have revelled, howevez, that while nickel-based alloys such as INCO1V~L 600 are excellent in high temperature oxidation reci.ativity, they have high reactivity with a sulfur (S) constituent axad therefore, especially when an electrode protrudes by 6 mm yr more in length into a high temperature environ.~oae~at allowing contact with a sulfur constituent at a high concentration> zz~conveni.eu.ces such as abnormality ix~ consumption of an electrode (in turn resulting ixa a wzdex spark discharge gap) and melting damage thereon arise with extreme ease.
Technical Field The present inventxox~ relates to a spark plug for an internal combuct~on engine and an internal combustion engine with the spark plug ~ooiowoted thereon_ Background of the Art Electrodes (a center electrode and a ground electrode) o~ a spark plug for an internal combustion engine have heretofore been manufactured from nickel-based material in order to ensure high temperature strength and high temperature oxidation resistivity. Especially in order to improve high temperature oxidation resistivity, it is necessary to compound a relatively large amount of chromium into an alloy anal among alloys of this kind, INCONEL 600 (a trade name of INCO Co. in U.K., having a composition of Ni - X5.5 mass % Cr - 8_0 mass % Fe), which is one of nickel-based heat resistant alloys, is excellent in balance between performance acrd cost therefoze haring been widely employed as a spark 2U plug electrode material.
Studies performed by the present inventors have revelled, howevez, that while nickel-based alloys such as INCO1V~L 600 are excellent in high temperature oxidation reci.ativity, they have high reactivity with a sulfur (S) constituent axad therefore, especially when an electrode protrudes by 6 mm yr more in length into a high temperature environ.~oae~at allowing contact with a sulfur constituent at a high concentration> zz~conveni.eu.ces such as abnormality ix~ consumption of an electrode (in turn resulting ixa a wzdex spark discharge gap) and melting damage thereon arise with extreme ease.
As a case to cause such inconveniences, exemplified is use of a spark plug in a direct-injection type engine. In the direct-injection type engine, a fuel is directly injected into a combustion chamber from a nozzle by a fuel injection.
pump; therefore, a high temperature firing section protruding into the combustion channber is exposed directly to a highly concentrated fuel mist, such that the firing section is subject to be attacked by a sulfur constituent in. the fuel._ Especially ix~. cases where low grade ~uel rich in sulfur is used. or much of sulfur is contained in an engine oil. electrode consumption and the like inconvenience caused by a reaction with sulfur advance rapidly, to sometimes leading to an early termination o~ the lifetime.
In another case, a creeping-discharge type spark plug for an internal combustion engine, improved on cazbon/oil fouling resistivity, has a chance to suffer damage from sulfur attack on a center electrode for a reason described below. In a creeping-discharge type spark plug, sparks produced in a spark discharge gap are propagated along an insulator surface in the form of creeping discharge all the time or depending on a conditi.on_ Fox example, a so-called sezni-cxeepin.g-dzschaxge type spaxJ~ plug ixzcludes a center electrode, az~ insulator surrounding the center electrode and, a ground electrode disposed such that a firing surface of a front end thereof faces a aide surface of the center electrode, wherein the front end portion of the insulator is positioned so as to be inserted between the center electrode and the fiz-ing surface of the ground electrode (that is, a spark discharge gap). Whew creeping discharge za released, aerial discharge occurs only in a gap between the gxou~a.d electrode firing surface and an insulator surface, while discharge sparks leap along the surface of the front end of the insulator. In such a 5emi-creeping-discharge type spark plug, since as shaven in FICI. 6(b), sparks S creeping the surface of the insulator 2 aze frequently generated, there is a case where the surface of the insulator 2 made of aluzn,ina or the like is partly eroded off_ The dusts J generated due to the erosion of the insulator 2 are, in a case, deposited in a clearance K betwreen the center electrode 3 and an inner surface of an insulator through-hole 2d together with a reaction product from the electrodes due to the discharge.
Since the dusts J absorb a sulfur constituent in a busnizxg gas with ease, the suJ_fur constituent is coz~ce~atxated zz~ the dusts deposited in the clearance K.
thereby eventually leading to damage by melting on the external surface of the center electrode 3.
It is accordingly an object of the present invention is to provide a spark plug hard to suffer electrode consumption through a reaction with a sulfur constituent or other inconveniences even in a working environment in which contact with the sulfur constituent at a high concentration can arise and thereby, capable of ensuring a sufficiently long lifetime of an electrode even when being employed in a direct-injection type engine or the like and i5 an internal combustion engine adopting the spark plug.
SUMMARY OF THE INVENTION
In order to solve the above described problem, a first aspect of the pre9ent invention is directed to a spark plug includes= a center electrode an insulator provided outside the center electrode; a cylindrical metallic shell further pxovided outside the insulator; and a ground electrode, a base end of which. is joiuaed with a surface of one end of the metallic shell and ~.
distal end of which is bent towazd the cez~ter electrode to Porxa a spark discharge gap therebetween, wherein when a side of the spark plug in which the spark discharge gap is formed in an axial direction of the center electrode is a front side thereof by definition, a distance along the axial direction from the surface of one end of the metallic shell to the outermost point of a front end portion of the ground electrode is 6 mm or more arid at least a surface layer portion of the ground electrode is made from a sulfur corxocion resistant metal.
When the distance "a" along the axial direction ~xom. the surface of oz~e end of the zaetaJ_Lic shell to the outerzx~ost point of a front end portion of the ground electrode exceeds 6 ~oo,za, temperature of the found electrode rises in a combustion chamber with extreme ease therefore, an adverse influence of sulfur corrosion is apt to act on the ground electrode very easily when the electrode is attacked by a sulfur constituent in the fuel. Vfxth a surface Iayer portion of the ground electrode made from a sulfur corrosion resistant metal, however, corrosion caused by a reaction with a sulfur constituent is alleviated even when the attack of the sulfur constituent arises and a long lifetime of the ground electrode of a spark plug can be ensured even in an environment under which the ground electrode has a chance to be put into contact with a high concentration sulfur constituent. It should be noted that in the above described first aspect, the effect is especially greatly exezted when the distance "a" exceeds 7.5 mm.
A construction of the above described first aspect is applicable to both of a so-called parallel type spark plug in which a side surface of one D ound electrode face9 a front end surface of a center electrode and a so-called multi-electrode type spark plug in which front end surfaces of a plurality of ground electxodec surrounding a center electzode ~ace a tide surface of the center electxode_ Of the two types, in the parallel type sparlt plug, the -round electrode inevitably protrudes ixato a combustion chazr~bez beyond the front end of the center electrvde~ therefore, temperature of the ground electrode is easier to rise. with the result that the effect of applicatiorx of the first aspect construction of the present invention is especially greatly exerted.
A second aspect of the present invention is directed to a sp~.rk plug includes'- a center electrode: an insulator provided outside the center electrode: a cylindrical metallic shell further provided outside the zx~sulator~
~.ad a ground electrode, a base end of which is joined with a suz~~ace o~ one s ex~.d of the ~oaetallac shell azxd a distal end of whzch faces the center electrode to ~ozxn a spank discharge gap thezebetween, wherein a difference d - D1 between an outer diameter D 1 of the center electrode and an inner diameter d of a through-hole of the insulator in which the center electrode is inserted is ensured to be 0_07 mm or more and at least a surface layer portion of the l0 center electrode is made from a sulfur corrosion resistant metal.
When the center electrode is subjected to sulfur corrosion, a corrosion product in the fornn of powder is, in a case, deposited as dusts in a clearance between an outer surface of the center electrode and an inner surface of the through-hole of the insulator. The above described difference d - D1 is a parameter reflecting a magnitude oP the clearance. When a magnitude of the clearance is small, generated dusts deposit in the clearance with a high density; for example, when a cold-hot cycle is repeated, an inconvenience can also tabe place since a difference in thermal expansion between the center electrode and the insulator causes cracking in the insulator_ With at least the surface layer portion of the center electrode made from a sulfur corrosion resistant metal, however, generation of dusts in company with sulfiir cozxocion is suppressed: thereby suppressing the very phezaoxnenon that the dusts fall down into the clearance. NZoxeovex, with the parameter d - D1 ensured to be 0.07 mm or more. high density 26 packing of the dusts in the clearar~ce, i~ the dusts fall down into the clearance, is suppressed therefore, cracking or the like in the insulator becomes harder to occur even when a cold-hot cycle is repeated. However, when the parameter d - D1 is larger than 0.2 mm, hest resistivity of the center electrode is reduced or eccentric positioning of the center electrode in assembly is easy to take place; therefore, the parameter d - D1 is preferably 0.2 mm or less and more preferably in the range of 0_07 to 0.15 z~axz~. '_fhis second aspect construction can be combined with the fizst aspect construction. In the case of the co~oabination, at least the surface layer poztion of the gzound electzvde is also made from the sulfux corrosion resistant metah therefore, the sulfur corrosion of the ground electrode can be effectively prevented or suppressed_ The second aspect of the present invention has a construction applicable to a creeping-discharge type spark plug, that is a spark plug in which an insulator is disposed outside of a center electrode while a surface of a front end of the center electrode is exposed so as to be flush with a suzface of a front end of the insulator, and a positional relation between the front ends of the insulator and the center electrode is deterncxi.ned such that 16 not only can a spark discharge gap be formed between the ground electrode and a portion including the front end of the center electrode, but creeping spark discharge along a surface of a portion including the front end of the insulator can also be effected in the spark discharge gap. In this case, dust generated due to the erosion of the insulator fall down into a clearancE as described above therefore, cracking in the insulator or the like, when a cold-hot cycle is repeated, can be more e$ectively auppxessed by coatrolli_ng the parameter d - D1 within the above described range. Furthex, z ~rolume of the dust gez~erated due to the erosion of the insulator ixxczeases absorbing a sulfur constituent. but when the param.etex' d - Dl is controlled within the abo~re desexibed range, no worry about generation of cracking or the like arises. On the other hand, since dusts have a function to absorb and concentrstte the sulfur constituent, a surface of the center electrode exposed to the clearance is further apt to suffer aulfux corroaion_ Accordingly, when an outer surface portion of the center electrode is at least made from a sulfur corrosion resistant metal, it is more effective for prevez~.tion of sulfur corrosion.
It chould be noted that the ground electrode or tk~e center electzode s may be made from a sulfur corrosion resistazxt ~oaetal i~a the entizety thereof ox alternatively, only a surface layer portion which is attacked by corrosion can be made from a aul.fur corrosion resistant metal. In the latter case, for example, a heat conduction accelerating material section whose maize constituent is at least one of copper and nicbel is formed in each of the bulks IO of the ground electrode and the metallic shell, and heat dissipation during actual use of a spark plug is promoted, thereby enabling further improvement of a lifetime of an electrode.
As a sulfur corrosion resistant metal, to be concrete, there can be employed an iron-based alloy eantaining iron as a main constituent and at t5 least one of chromxunn and cobalt in total content of 10 mass % or more.
Iron is basically zxxuch more excellent in sulfur corrosion resistivity than nickel and e~fectivelry contributes to improvement on electrode lifetime in the presence of sulfur, which is the object of the present invention. The reason is speculated to be as follows: That is, according to the Ni-S binary phase 20 diagram, an outectic with a sulfur compound (~TisSa~ is formed on the nickel side and an eutectic temperature is e~ctremely as low as about 630°C>
therefore, not only does a reaction between sulfur and nickel cozxetituezxts progress rapidly, but melting damage also occurs with ease due to reduction in melting point. In contrast to this> according to the Fe-S biuaxy phase 25 diagram, an eutectic with a sulfizr compound (FeS) is Formed on the iron side, whereas an eutectic terr~perature is as high as near 1000°C~
therefore, not only is a reaction with sulfur cons7picuously su~pQressed, but melting damage is harder to occur due to a high melting point of a sulfur compound, a if the compound arises.
HowevEr, iron-based alloys ti.e., alloys whose main component is iron are generally poor in oxidation resistivity~ therefore, at least one of chromium and cobalt is compounded in total content of 10 mass % or m.oxe co a~ to ensure sufficient oxidation resistivity even at a high tempexatu7ce_ Chromium and cobalt can be compounded at LO mass % oz more singly or in cozubination_ Zt should be noted that the term "main constituent" in the present specification means a component with the highest mass content.
In the above described iron alloy, when a content of chromium or cobalt is excessively high, embrittlement of the alloy may occur and therefore, machinability thereof may be reduced, with the result that, for example, machining iota a desired electrode shape may be, in a case, difficult: therefore, a total content thereof is set to 30 mass % or less and desirably 27 mass °~° of less.
It should be noted that when an iron-based alloy is adopted as a sulfur corrosion resistant metal, a case might arise in which a sulfur corrosion resistivity is degraded by a xeactxozi between nickel and sulfur if nickel is much contained_ Nickel, however, has an effect increasing oxidation resistivity of iron as well therefore, the metal can be compounded in a range where the sulfur corrosion resistivity is not degz~aded. In this case, a content o~ xxickel is set to 30 mass % or less and desirably 25 mass % or less_ Fuzther, to the above described ixon-based alloy, aluminum is effectively added in. order to improve oxidation. resistivity at bagh temperature. A content of aluminum is preferab),y in the range of. for example, 2 to 5 mass °~b. When a content of aluminum exceeds S mass %.
embrittlement of the alloy may occur and therefore, reduction in machinability thereof may be effected therefore, for example, a case may arise where machining into a desired shape of an electrode becomes hard, while when less than 2 mass %, the effect to improve oxidation resistivity comes to be not conspicuous. A content of alun~.inum is desirably in the range of 2 to d mats %.
For example, when chromium and cobalt axe simultaneously added, a~a iron-based alloy more e~zcellent x~o. oxidation resistivity can be obtained.
In this case, the iron-based alloy preferably contains I5 to 25 mass chromium and 2 to 5 mass % aluminum. When a content of chromium exceeds 25 mass 36 or a content of aluminum exceeds S mass %, embrittlement of the alloy may occur and therefore, reduction in z~nachinability may be effected, wherein, for example, a case may arise where machining into a desired electrode shape becomes hard. On the other hand, when a content of chromium is 15 mass % or less or a content of aluminum is 2 mass % or less, a case may arise where oxidation resistivity at high temperature is not sufficiently ensured. Desirably, the iron-based alloy contains 16 to 19 mass % chromium and 2 to 4 mass % aluminum. Further, as such an irvn-based alley, for example. an electrical heating alloy can be ezxaployed, which contains 15 to 25 mass % chromium, 2 to 6 mass °Y
aluminum and the balance being iron and inevitable impurities.
On the other hand, also in a nickel-based alloy containing nickel as a main constituent, resistirrity to sulfur corrosion is conspicuously improved by compounding chromium in content of 25 mass % or more and such a nzckel-based alloy can be adopted as sulfur corrosion resistant nxetal, being referred to as in the present inveratioz~._ Sauace nickel is inherently excellent 2s in high temperature o~dation resistivity and in addition to this, the high temperature oxidation resistivity is further i.zn~pzoved in the presence of chxomium~ by using the nickel-based alloy, not only is sulfur corrosion rosistivity improved, but a long lifetime of a spark plug can be en.;ured even under a severe working envirorxment_ When a nickel-based alloy is used, a content of chromium is desirably 30 mass % or more_ Furthex, a coz~positi.oxz may be adopted which contains, for example, 1 to 3 mass % aluxaix~uxn and, for example, 3 to 20 mass % iron for ensuring high temperature strength 5 az~d high tem.pexature oxidation xesisti.vity_ As such a nickel based alloy, there can be used a heat resistant nickel-based alloy having chromium in content of 25 mass % or more.
Next, by using a spark plug of the present invention, an internal combustion engine can be constructed in which a combustion chamber is 10 formed in a cylinder head and not only can a spark plug be mounted on the cylinder head such that a spark discharge gap is positioned in the combustion chamber, but a fuel injection system for injecting a fuel direct into the combustion chamber is also provided. By applying a spark plug of the present invention to such a dizect-injection type internal combustion engine, sulfur corrosion on electrodes of a spark plug to take place due tv fuel injection can be prevented with extreme effectiveness, thereby enabling frequency of exchanges to decrease.
Further, an internal combustion engi-ne can also be constructed in which a spsrk plug relating to the second aspect of the present invention of a creeping discharge type (a spark plug in which at least the surface layer portion of the center electrode is made from the sulfur corrosion resistant ~oo.etal) is ~aaounted such that the combustion chamber is fozzxxed in the cylinder head and the spaxk discharge gap is positioned i.n the combustion chamber. The center electrode is harder to be affected by sulfur corrosion even when dusts generated due to the erosion of the insulator are deposited in the clearance between an outer surface of the center electrode of the 9psrk plug and an izxner surface of the through-hale of the insulator, and a sulfur constituent is concentrated in the deposited dusts thereby ensuring a lI
longEr Lifetime of a spark plug and enabling frequency of exchanges o~ spark plugs to decrease.
BRIEF DESCRIPTION OF TITS DR.A.WINGS
FIG. 1 is a longitudinal sectional view showing a spark plug of a first example of the present invention and an enlarged sectional view including a partial front view showing a main part of the spark plug;
FIG. 2 is an enlarged sectional view of a main part showing a first modification of the first example of the spark plug of FIG. 1;
FIG. 3 is an enlarged sectional view of a main part showing a second modification of the first example of the spark plug of FIG. l~
FIG. 4 is a front view showing a spark plug of a second example of the present invention;
FIG. 5 is a sectional view of a main part of FIG_ 4;
FIGS. 8(a) and 6(b) are sectional views illustrating an action of the spark plug of FIG. 4 in compazison with an comparative example;
FIG. 7 is a simplified sectional view of a direct-injection type gasoline engine on which the spark plug of FIG. 1 is mounted FIG_ 8 is a simplified sectional view of a gssoline engine on which the spsxrk plu$ of FIG. 4 is mounted>
FIGS- 9(a) to 9(d) are magnified photographs showing sectional views of ground electzodes after a test oaf test pieces of zuaterials nwoabered 1 to 4 (inventive electrodes) used in a first experiment 26 FIGS. 10(a) to 7.0(c) are magnified photographs showing sectional views of ground electrodes after a test of test pieces of materials nuna,bexed to 7 (outside of the scope of the inventions used in the first experiment; and FIGs. lI(a) and 11(b) are photobraphs showing outer appearances of peripherals of spark discharge gaps o~ an example and a comparative example, respectively, after a test in a second e;cperiment.
PREFERRED EMBODIEMNTS OF THE INVENTION
Descz-iption will be given of ezabod~i.~oaen.ts o~ the present invention below with zefere~ace to exazaples shown in the accompanying drawings.
(First Example) l0 A spark plug 100 shown in FIG. l, as an example of the present invention, has a construction of a so-called parallel electrode type spark plug and includes: a cylindrical metallic shell 1; an insulator 2 fittingly inserted into the interior of the metallic shell I such that a front end portion 21 thereof protrudes from the metallic shell 1i a center electrode 3 provided in the interior of the insulator 2 such that a high melting point metal firing section ~1 formed at a front end thereof is protruded from the insulator 2; a ground electrode 4. one end of which joined with the metallic shell 1 by means of welding or the like, the ether of end of which is bent sideways such that a side surface of the ground electrode 4 faces the front end of the center electrode 8. A distsnce "a" measured from a surface of one end of the metallic shell 1 to the outermost point of a front end portion of the gxound electrode 4 along an axial direction O of the center electrode 3 is 6 u~m or zaoze ox ?_5 mm or more.
The high welting zaetal ~Zxiuag section 31 is made &oxaa a metal containing at least one selected from the group consisting of Ir. Pt. Rh. W.
Re and Ru, fox example Ir, as a main component. or a composite material containing the metal as a main constituent. Fuxther, a Pt-based metal firing section 32 fscing the high melting metal firing section 31 is formed on the J.3 ground electrode 4 and a gap between the high zzxelting point metal firing section 31 and the Pt-based metal firing section 32 works as the spaxl~
discharge gap g.
The insulator 2 is made from a ceramic sintered body, fox example Of ~nmi a, aluminum nitride or the like, and has, il~. the interior thereof. a through-hole 6 for fitti~agly inserting the centez electrode 3, extending along an axial direction thereof. Further, the metallic shell 1 has a cylindrical shape and is zxxade from. a metal such as low carbon steel or the like and not only serves as a housing for the spark plug 100, but also has a threaded l0 portion '7 for mounting the spark plug 100 on the cylinder head 53 (FIG_ 7), which is formed on an outer surface thereof.
At least surface layer portions of the center electrode 3 and the ground electrode 4 are formed from a sulfur corrosion resistant metal described above. Concrete examples of iron-based alloys preferably usable in m the present invention as a sulfur corrosion resistant metal are exemplified as follows:
*FCHW1 (JZS C 2520 Electrical heating iron chromium alloy Class No. 1) main composition containing 23 to 26 mass °i6 Cr~ 4 to 6 mass °r6 Ah and the balance o~ Fe, and traces of additive elements or inevitable impurities, and 20 '~FCHW2 (JIS C 2620 Electrical heating iron chromium alloy Class No. 2) main composition containixzg I7 to 21 mass % Cr~ 2 to ~1 mass % Ah and the balance of Fe, and traces of additive elements or inevitable xxnpurities_ .
Further, concrete examples of a nickel-based alloy preferably usable in the present invention as a sulfur cozzosion x'esistant metal are 25 exemplified as follows:
* II~CONEL s9o maze composition containing 30 mass °r~ Cr~ 9.5 mass % Fe~ arxd the balance of Ni, and traces of additive elements or inevitable impurities.
1~
* Haatelloy G80 main composition containing 29.5 mass % Cr~ 2.0 mass % Co; 5.5 mass Mo: 2.5 mass % W: 15.0 mass % Fe~ and the balance of Ni, and traces of additive elements or inevitable impurities.
In this example, a heat cozxduction accelerating mate~rzal secti.ox~ He made from copper or a copper alloy is formed zn the ixatexior of the center electrode 3 along an axial direction thereof axed the rest including the electrode surface layer portion is a sulfur corrosion resistant metal section 3d. The ground electrode 4 is made from a sulfur corrosioxi resistant metal l0 in the entirety. It should he noted that a similar heat conduction accelerating material section 4c can also be formed in the bulk of the ground electrode 4 as shown in FIG_ 2. Further, contrary to those cases, the heat conduction accelerating material section 3c and 4c can be omitted in a working environment where temperature rise of the electzodes is not so much of a problem.
Moreover, as shown in FIG. 3, a modification is allowed that the fi-ring sections 31 and 32 are ozuztted az~d a spark gap g is formed between a side surface of the ground electrode 4 and the front end surface of the cezxtez electrode ~_ FIG. ? shows an example of a direct-injection type engine (an internal combustion engine) with the Spark plug 100 mounted thereon. In the dixect-injection type engine 40, the spark plug 100 is screwed with the threaded portion 7 to fasten into a plug hole 53a formed in a cylinder head 58. By doing so, the spark plug 1.00 is mou~ated such that a spark discharge gap g is positioned in a combustion chamber 52 and a front end portion thereof protrudes into the chamber_ On the othez hand. a jet nozzle 50 jetting a fuel F in a mist directly into the combustion chamber 52 with a fuel injection pump 54 is mounted on the cylinder head o2. The jetted fuel F is Fprayed directly over the front end section of the spark plug 100_ When the direct-injection type engi.~ne 40 is activated, the front end section of the spark plug 100, including the ground electrode 4 and the center electrode 3, is heated to a higb. temperature by combustion of the ~uel 5 F. EspecialJy> the ~cound electrode 4 protzudxng from the ane end surface of the metallic shell 1 by a distance "a" as large as 6 mm or more is heated to a considerably high temperature and in this condition, the ground electrode 4 is kept exposed repeatedly to a jetted mist of the fuel F containing sulfur.
The grouxxd electrode 4 and the center electrode 3 are, however, made from 10 the above described sul~ux corrosion resistant metal; therefore, no inconvenience such as increase in the spark discharge gap g or melting damage is hard to occur even if there arises an attack by a sulfur constituent. It should be noted that when the center electrode H side does not have so much of rise in tez~apezature and therefore, sulfur corrosion 1~ thereof is not problematic either, only the center electrode 3 may be made from a common electrode metal such as INCONEL 600, which is not a sulfur corrosion resistant metal.
(Second Example) The spark plug 200 shown in FIC_ 4 ig constructed as a so-called semi-creeping- discharge type spark plug rind includes= a cylindrical metallic shell 1: an insulator 2 fittimgly inserted in the zzxetalLic shell 1 with a front end portion thereof protruding from the metal mezr~ber~ a center electrode ~
provided in the insulator 2; a plurality of gzou~ad electrodes 4 disposed such that base ends thereof are joined with the metallic shell 1, intermediate portions thereof surround the front end portion o~ the insulator 2, and front ends thereof face a side surface of the center electrode 3_ The insulator 2 is made from a cersmic sintered body such as alun~i.na or sluminum nitride and has, in the inberior thereof, a hole Section (a thxough-hole) 2d for fittingly inserting the center electrode 3, formed along an axial direction of the insulator 2. Further, the metallic shell 1 is made from lover carbon steel in a cylindrical shape and serves as a housing of the spark plug_ Further, a threaded portion 7 ~ox mountiz~.g the spark plug 200 on the cy~uader head is formed on an outer surface of the metallic shell 1 as showb. in FIG_ 4_ '~vo of the ground electrodes ~ axe, as shown in FZGs. ~ aza.d 5, provided on both sides of the center electrode 3 one on. each side (that is. one kind of multi-electrode type spark plug) and are bent inward such that front end surfaces 4a thereof face a side surface of the center electrode 3 in parallel thereto with the insulator 2 interposed therebetween, while the base ends of the ground electrodes 4 are fixed to the metallic shell J. into one body by welding or the like means. A front end portion of the insulator 2 is located so as to be inserted between the side surface of the center electrode 3 and the front end surfaces 4a of the ground electrodes 4.
The center electrode 3 and the ground electrodes 4 in this example are made from the sulfur corrosion resistant metal in the entirety thereof. It should be noted that the above described heat conduction accelerating material section can be inserted in each of the bulks of the center electrode and the ground electrode 4 for improvement on heat dissipation according to a necessity.
Description will be given of a function of the spark plug 200 below:
The spark plug 200 is, as shown in FIG. $, mounted on a gasoline engine (an internal coz~abusti.ozx engine) 41 by a threaded portion 7 thereof and works as an ignition source for a mixed gas supplied into the combustion ebaxnber 52_ Fox example, a high discharge voltage is applied across the center electrode 3 and the ground electrodes 4 so as to have a negative potential and a positive potential, respectively, and thereby, sparks S are, as shown in FIG.
6(a), generated betwoen the froxxt end surfaces 4a of the ground electrodes 4 snd the center electrode 3, thereby setting fire to a mixed gas. The sparks S
are propagated on routes along a surface of the front end portion of the insulator 2.
When the internal combustion engine dl is operated at a prescribed or higher speed, or under a prescribed or higher load, the surface of the front e~.d portxoz~ o~ the insulator 2 is øxaduaJJ,y ezoded i.n company with spark discharge_ Moreover, ions are driven by an electric field (a potential gradient) formed between the electrodes 3 and 4 to impinge on surfaces o~
the electrodes 3 and 4 to sputter a metal constituent of the electrodes, which, in a case, produces a reaction product by oxidation thereof. As a result, removed stock of the insulator or a reaction product concurrently formed flies off in the form of dusts J to settle into a clearance K between an outer surface of the center electrode 3 and an inner surface of the through-hole 2d as deposits. The dusts J come to be in contact with the outer surface of the center electrode 3, while absorbing a sulfur constituent included in the fuel to a higher concentration, but since the center electrode 3 is made from a sulfur corrosion resistant metal. corrosion or melting damage of the center electrode 3 can be hard to occur.
Here, a difference d - D1 between an outer diameter D1 of the center electrode 3 and an inner diameter d of the through-hole 2d through which the center electrode 3 penetrates is ensured to be 0.07 mm or more. 'When the front end portion of the center electrode 3 is smaller in diameter than the base ex~d portion 3c thereof, a difference d - D1 between the outer diameter D1 of the base exi.d portzon 3c and the in~aer di.ax~aeter d of the thzough hole 2d is only required to be ensured 0.07 mm or more. When the clearance K is small in magnitude, the dusts J generated are, as shown in FIG. 6(b), deposited and packed in the clearance K at a high density, r~rhich can, in a case, cruse arx inconvEnience such as to produce cracks C in the 1~
insulator 2, for example, in repetitions of the cold-hot cycle. By ensuring the difference d - D 1 to be 0.0? mxn or more, however, the dusts ~1 have a lizxxitation in high density packing in the clearance K, whereby cracki.~ag or the like is hard to occur even in repetitions of a cold-hot cycle.
Further, in the spark plug 200, poztiozts i.ucluding parts of firing surfaces of the gxou~ad electrode ~ and/or the center electrode 3 can be each transformed into a consumption resistant section made from a metal containing at least one selected from the group consisting of Ir, Pt, Rh, W, Re and Ru, as a main component, or alternatively from a composite material containing the metal as a main constituent. For instance, in an example shown in FIG. 5, the spark plug 200 has a construction in which a band-like consumption resistant section 31 is formed in the outer peripheral portion of the front end surface of the center electrode 3. To be concrete, a material of the consumption resistant section ~1 in use can be a Pt-Ni alloy, far example 16 an alloy containing Pt as a main component and 15 mass % or more Ni_ A gasoline engiz~.e 41 of FIG. 8 adopts a construction in which a fuel is atomized and mixed with intake air through a carburetor not shown by a negative pressure created in a cylinder expansion, whereas the engine 41 xnay also be of a direct-injection type, similar to FIG. ?. In tk~ia csse, since a fuel is sprayed direct onto the electrodes 2 and 4 in additioz~ to croncentration of a sulfur constituent in the dubts d, the electrodes 3 and 4 are exposed to a very severe environment considering from the viewpoint of sulfur corroeion_ However, the electrodes 3 azzd 4 axe ncaade :6rom. a suJ.fuz coxrosi~on resistant metal therefore, corrosion is hard to advance even in such an environment, 26 thereby enabling a longer lifetime of the spark plug 200.
Also in this construction, a distance "a" from the one end surface of the metallic shell 1 to the outermost point of a front end portion of the ground electrodes 4 can be 6 mm or more. In this case, ovhile a temperature . x9 of the ground electrode 4 rises more conspicuously, sulfur corrosion can be effectively suppressed by forming at least a surface layer portion of the ground electrodes 4 with a sulfur corrosion resistant metal.
Experiments The following experiments below were co~aducted ix~ oxder to confirm the effect of the present invention_ (First Experiment) x0 First of all, wires (of a rectangle of 1.5 mm x 2_8 mm in section) made of vazious kinds of alloy were prepared as base materials of the ground electzode, which is one of main parts of the spark plug of FIG_ 1_ The wires were each cut into pieces of 20 mm in length to form test pieces_ .Alloy compositions of wires used in the first experiment are shown in Table 1.
I
c~ ~ U
('~ ~ U
v ~ v ~ O O O
rC"~Ci~ Jn ~ T~ r1 r1 I p ~ ~-.--aH 1--~a O O p C
r~
JG"~O O ..r O
~ ~
z Z
U U ~
~, a~
c~
C~..LL ,-, ~--, .~ -;
~., ~C
..., tt~ o N N i.n -i ,-1 I I O O O
V V
0 o um .n o0 _ _ I I O O O
Ca Cl7 p ....O O O 1 '~' y' ~ ICJ C~'JCTj I I O ~
~
U
p ..-.
Q O O O O tl~ O O U b I
~
U ~n a~ cfl C u~ c~
p c~ ~ ,~ m .-a N cw7 ~
U rn .
~
p G I I I ~ ~ ~ N c~
I .~
' U
,~ ~ _.
cc5 .-, .~ ...~W p r-, --, '-d .f~ 'z'~
U c~ :~ c~
4~ t=. ~ ~ ~ G~ ca C' ~. '-.--,I ,-s #
"~ N n'7 d' l~7 Cfl h Next, 9 parts by wt sodium sulfate and 1 part by ~srt sodium chloxide were compounded and a mixture is heated at 900°C using a heater into a molten salt bath_ The test pieces were immersed in the moltex~ salt bath as a su1~uac coxxosioza test bath for 10 hr and then take~a out ~6cona the bath, followed by cleaning the test pieces with distilled water and then drying the test pieces. Thereafter, the test pieces (of the ground electrode) were each cut along a cross section perpendicular to the axial direction thereof and the cut pieces were further polished to observe czoss sections under an optical microscope. yIicrophotographs of observed images are shown in FIG2. 9(~ to l0 9(d) and IO(a) to 10(c). FIGs. 9(a) to 9(d) are microphotographs of ground electrodes made of alloys having desirable compositions of sulfur corrosion resistant metals, and correspond to respective materials numbered 1 to 4 in Table 1. Neither corrosion nor melting damage is observed in each photograph and it is understood that electrode surface layer portions were 1~ mainta_i_ned in good conditions. After the corrosion test, surface portions of the test pieces (of ground electrodes) were further investigated using an electron probe micro-analyzer (EPMA) to obtain distributions of a sulfur constituent, rwith the result that almost no sulfur constituent was detected in each test piece. That is, it was found that almost no advance in corrosion 20 by sulfur took place vn each test piece_ On the other hand, FZGs. 10(a) to 10(c) are microphotographs of test pieces from alloys having a Chemical composition outside the desirable ran.~e described above as ground electrode raaterzals and the test pieces correspond to respective materials numbered 5 to ? in Table 1. Cvnspicuvus 2s corrosions or melting damage are observed in electrode surface layer portions of the test pieces. After the corrosion test, suxface portions of the test pieces were further investifatcd using an. electron probe micro-analyaer (EPNIA) to obtain dic~tributions of a sulfur constituent, with the result that 2.'~.
much of a sulfur constituent was detected in each text piece, leading to understanding that the corrosion and melting damage observed on. the microphotographs were caused by sulfur corrosion.
(Seco~ad Expexaxaent) The following exper.~oaent was conducted on the spark plug shown in FIG. 1 in order to confirm the effect of the first aspect of the present invention. As a material of the center electrode, a material 2 of Table 1 (FCHW-2~ example) and a material 5 of Table 1 (INCONEL 600 comparative example) were adopted. Not only was a value of an initial spark discharge gap g adjusted in the range of 0.8 to l.5mm, but also a length of the ground electrode 4 was varied to adjust the distance "a" of FIG_ 1 to obtain various values in the range of 6 to 8 mm_ The spark plugs were mounted on a direct-injection type 6-cylinder gasoline engine with a cylinder volume of 2000cc and an engine oil having a sulfur constituent in content of 1 mass % was used. The engine was operated for a continuous 100 hr at a revolution speed of 5500 rpm with a full-vpen throttle valve before testing sulfur corrosion. After the operation of the engine for the 100 hr, sulfur corrosion produced on the ground electrode portion of each tested spark plug was observed with the naked eye, Evaluation. results were indicated as follows: ~,vhen almost no sulfur corrosion arises, it is given "very good'' with a xaark of O> when. although some sulfur corrosion arnses, no trouble was encountered in operation, it is given " good" with a m.axk of O, azzd when sulfur corrosion is great and troubles such as misfire frequently occur, it is given "bad" with a mark of X. The results are shown in Table 2_ From the results in Table 2, it is found that the comparative examples suffer Sulfur corrosion, and inconvenience due to sulfur corrosion is very much severe ix~. the cozuxparative e~camples when the distance "a"
exceeds 7.5 mm, while in the examples no sulfur corrosion occurs at all even when the distance increases up to the order of 8 mm_ FIGs_ 11(a) and 11(b) chov~r a:fter-test outer appearances of a comparative example azxd ate.
example of this invention, respectively_ VVb.ile the comparative example receives co~aspicuous da~oaage to the ground electrode due to sulfur corrosion. the example of the invention is influenced a little by sulfur corrosion and maintains a good outer appearance.
(Third Experiment) The following experiment was conducted on a spark plug of the same type as the first experiment in order to confirm the effect of the second aspect of the present invention. First of all, both of ground electrodes 4 and center electrode 3 were prepared with the material 2 of Table 1 (FCHW-2~
example) and a value of the distance "a" of each was set to 8 mm.
Furthermore, an outer diameter D 1 of each of the center electrode 3 was fixed at 2.60 mm, while an inner diameter d of the through-hole 6 of an insulator 2 was adjusted to various values in the range of 2.65 to 2.6~ mm such that the difference d -DI assume various values in the range of 0.05 to 24 0.08 mm_ Thus prepared spsrk plugs esch were mounted on a direct-injection type 6-cylinder gasoline engine to perform, as eold-hot cycle test, 3000 time repetitions of an operating cycle including operatiox~ for 1 min with a full-open throttle valve at an engine revolutiozx speed o~ 5500 rpm, followed by idling for 1 mix~_ The ~aumber hT o:f test spark plugs ix~
the 2s same condition is 5. Evaluation results were indicated as fellows= when no cracking occurs in the insulators of test spark plugs after test, it is given "good" arid when cracking occurs even in one of the insulators of test spark plugs, it i9 given 'dad"_ The results are shown in Table 2.
As seen from the results, it is found that by adjusting the difference d - D 1 to be 0.07 mm or more, generation of cracl~n.g can be effectively prevente d from occurring.
Tab 1 a 2 FCHW-2 I NCOl~iEL 6 O ~1 O D
7. 5 0 x Tab 1 a 3 c~
r- c~-~w-0. 0 5 X
0. 0 6 x 0. 0 7 0. 0 8 ~ O
pump; therefore, a high temperature firing section protruding into the combustion channber is exposed directly to a highly concentrated fuel mist, such that the firing section is subject to be attacked by a sulfur constituent in. the fuel._ Especially ix~. cases where low grade ~uel rich in sulfur is used. or much of sulfur is contained in an engine oil. electrode consumption and the like inconvenience caused by a reaction with sulfur advance rapidly, to sometimes leading to an early termination o~ the lifetime.
In another case, a creeping-discharge type spark plug for an internal combustion engine, improved on cazbon/oil fouling resistivity, has a chance to suffer damage from sulfur attack on a center electrode for a reason described below. In a creeping-discharge type spark plug, sparks produced in a spark discharge gap are propagated along an insulator surface in the form of creeping discharge all the time or depending on a conditi.on_ Fox example, a so-called sezni-cxeepin.g-dzschaxge type spaxJ~ plug ixzcludes a center electrode, az~ insulator surrounding the center electrode and, a ground electrode disposed such that a firing surface of a front end thereof faces a aide surface of the center electrode, wherein the front end portion of the insulator is positioned so as to be inserted between the center electrode and the fiz-ing surface of the ground electrode (that is, a spark discharge gap). Whew creeping discharge za released, aerial discharge occurs only in a gap between the gxou~a.d electrode firing surface and an insulator surface, while discharge sparks leap along the surface of the front end of the insulator. In such a 5emi-creeping-discharge type spark plug, since as shaven in FICI. 6(b), sparks S creeping the surface of the insulator 2 aze frequently generated, there is a case where the surface of the insulator 2 made of aluzn,ina or the like is partly eroded off_ The dusts J generated due to the erosion of the insulator 2 are, in a case, deposited in a clearance K betwreen the center electrode 3 and an inner surface of an insulator through-hole 2d together with a reaction product from the electrodes due to the discharge.
Since the dusts J absorb a sulfur constituent in a busnizxg gas with ease, the suJ_fur constituent is coz~ce~atxated zz~ the dusts deposited in the clearance K.
thereby eventually leading to damage by melting on the external surface of the center electrode 3.
It is accordingly an object of the present invention is to provide a spark plug hard to suffer electrode consumption through a reaction with a sulfur constituent or other inconveniences even in a working environment in which contact with the sulfur constituent at a high concentration can arise and thereby, capable of ensuring a sufficiently long lifetime of an electrode even when being employed in a direct-injection type engine or the like and i5 an internal combustion engine adopting the spark plug.
SUMMARY OF THE INVENTION
In order to solve the above described problem, a first aspect of the pre9ent invention is directed to a spark plug includes= a center electrode an insulator provided outside the center electrode; a cylindrical metallic shell further pxovided outside the insulator; and a ground electrode, a base end of which. is joiuaed with a surface of one end of the metallic shell and ~.
distal end of which is bent towazd the cez~ter electrode to Porxa a spark discharge gap therebetween, wherein when a side of the spark plug in which the spark discharge gap is formed in an axial direction of the center electrode is a front side thereof by definition, a distance along the axial direction from the surface of one end of the metallic shell to the outermost point of a front end portion of the ground electrode is 6 mm or more arid at least a surface layer portion of the ground electrode is made from a sulfur corxocion resistant metal.
When the distance "a" along the axial direction ~xom. the surface of oz~e end of the zaetaJ_Lic shell to the outerzx~ost point of a front end portion of the ground electrode exceeds 6 ~oo,za, temperature of the found electrode rises in a combustion chamber with extreme ease therefore, an adverse influence of sulfur corrosion is apt to act on the ground electrode very easily when the electrode is attacked by a sulfur constituent in the fuel. Vfxth a surface Iayer portion of the ground electrode made from a sulfur corrosion resistant metal, however, corrosion caused by a reaction with a sulfur constituent is alleviated even when the attack of the sulfur constituent arises and a long lifetime of the ground electrode of a spark plug can be ensured even in an environment under which the ground electrode has a chance to be put into contact with a high concentration sulfur constituent. It should be noted that in the above described first aspect, the effect is especially greatly exezted when the distance "a" exceeds 7.5 mm.
A construction of the above described first aspect is applicable to both of a so-called parallel type spark plug in which a side surface of one D ound electrode face9 a front end surface of a center electrode and a so-called multi-electrode type spark plug in which front end surfaces of a plurality of ground electxodec surrounding a center electzode ~ace a tide surface of the center electxode_ Of the two types, in the parallel type sparlt plug, the -round electrode inevitably protrudes ixato a combustion chazr~bez beyond the front end of the center electrvde~ therefore, temperature of the ground electrode is easier to rise. with the result that the effect of applicatiorx of the first aspect construction of the present invention is especially greatly exerted.
A second aspect of the present invention is directed to a sp~.rk plug includes'- a center electrode: an insulator provided outside the center electrode: a cylindrical metallic shell further provided outside the zx~sulator~
~.ad a ground electrode, a base end of which is joined with a suz~~ace o~ one s ex~.d of the ~oaetallac shell azxd a distal end of whzch faces the center electrode to ~ozxn a spank discharge gap thezebetween, wherein a difference d - D1 between an outer diameter D 1 of the center electrode and an inner diameter d of a through-hole of the insulator in which the center electrode is inserted is ensured to be 0_07 mm or more and at least a surface layer portion of the l0 center electrode is made from a sulfur corrosion resistant metal.
When the center electrode is subjected to sulfur corrosion, a corrosion product in the fornn of powder is, in a case, deposited as dusts in a clearance between an outer surface of the center electrode and an inner surface of the through-hole of the insulator. The above described difference d - D1 is a parameter reflecting a magnitude oP the clearance. When a magnitude of the clearance is small, generated dusts deposit in the clearance with a high density; for example, when a cold-hot cycle is repeated, an inconvenience can also tabe place since a difference in thermal expansion between the center electrode and the insulator causes cracking in the insulator_ With at least the surface layer portion of the center electrode made from a sulfur corrosion resistant metal, however, generation of dusts in company with sulfiir cozxocion is suppressed: thereby suppressing the very phezaoxnenon that the dusts fall down into the clearance. NZoxeovex, with the parameter d - D1 ensured to be 0.07 mm or more. high density 26 packing of the dusts in the clearar~ce, i~ the dusts fall down into the clearance, is suppressed therefore, cracking or the like in the insulator becomes harder to occur even when a cold-hot cycle is repeated. However, when the parameter d - D1 is larger than 0.2 mm, hest resistivity of the center electrode is reduced or eccentric positioning of the center electrode in assembly is easy to take place; therefore, the parameter d - D1 is preferably 0.2 mm or less and more preferably in the range of 0_07 to 0.15 z~axz~. '_fhis second aspect construction can be combined with the fizst aspect construction. In the case of the co~oabination, at least the surface layer poztion of the gzound electzvde is also made from the sulfux corrosion resistant metah therefore, the sulfur corrosion of the ground electrode can be effectively prevented or suppressed_ The second aspect of the present invention has a construction applicable to a creeping-discharge type spark plug, that is a spark plug in which an insulator is disposed outside of a center electrode while a surface of a front end of the center electrode is exposed so as to be flush with a suzface of a front end of the insulator, and a positional relation between the front ends of the insulator and the center electrode is deterncxi.ned such that 16 not only can a spark discharge gap be formed between the ground electrode and a portion including the front end of the center electrode, but creeping spark discharge along a surface of a portion including the front end of the insulator can also be effected in the spark discharge gap. In this case, dust generated due to the erosion of the insulator fall down into a clearancE as described above therefore, cracking in the insulator or the like, when a cold-hot cycle is repeated, can be more e$ectively auppxessed by coatrolli_ng the parameter d - D1 within the above described range. Furthex, z ~rolume of the dust gez~erated due to the erosion of the insulator ixxczeases absorbing a sulfur constituent. but when the param.etex' d - Dl is controlled within the abo~re desexibed range, no worry about generation of cracking or the like arises. On the other hand, since dusts have a function to absorb and concentrstte the sulfur constituent, a surface of the center electrode exposed to the clearance is further apt to suffer aulfux corroaion_ Accordingly, when an outer surface portion of the center electrode is at least made from a sulfur corrosion resistant metal, it is more effective for prevez~.tion of sulfur corrosion.
It chould be noted that the ground electrode or tk~e center electzode s may be made from a sulfur corrosion resistazxt ~oaetal i~a the entizety thereof ox alternatively, only a surface layer portion which is attacked by corrosion can be made from a aul.fur corrosion resistant metal. In the latter case, for example, a heat conduction accelerating material section whose maize constituent is at least one of copper and nicbel is formed in each of the bulks IO of the ground electrode and the metallic shell, and heat dissipation during actual use of a spark plug is promoted, thereby enabling further improvement of a lifetime of an electrode.
As a sulfur corrosion resistant metal, to be concrete, there can be employed an iron-based alloy eantaining iron as a main constituent and at t5 least one of chromxunn and cobalt in total content of 10 mass % or more.
Iron is basically zxxuch more excellent in sulfur corrosion resistivity than nickel and e~fectivelry contributes to improvement on electrode lifetime in the presence of sulfur, which is the object of the present invention. The reason is speculated to be as follows: That is, according to the Ni-S binary phase 20 diagram, an outectic with a sulfur compound (~TisSa~ is formed on the nickel side and an eutectic temperature is e~ctremely as low as about 630°C>
therefore, not only does a reaction between sulfur and nickel cozxetituezxts progress rapidly, but melting damage also occurs with ease due to reduction in melting point. In contrast to this> according to the Fe-S biuaxy phase 25 diagram, an eutectic with a sulfizr compound (FeS) is Formed on the iron side, whereas an eutectic terr~perature is as high as near 1000°C~
therefore, not only is a reaction with sulfur cons7picuously su~pQressed, but melting damage is harder to occur due to a high melting point of a sulfur compound, a if the compound arises.
HowevEr, iron-based alloys ti.e., alloys whose main component is iron are generally poor in oxidation resistivity~ therefore, at least one of chromium and cobalt is compounded in total content of 10 mass % or m.oxe co a~ to ensure sufficient oxidation resistivity even at a high tempexatu7ce_ Chromium and cobalt can be compounded at LO mass % oz more singly or in cozubination_ Zt should be noted that the term "main constituent" in the present specification means a component with the highest mass content.
In the above described iron alloy, when a content of chromium or cobalt is excessively high, embrittlement of the alloy may occur and therefore, machinability thereof may be reduced, with the result that, for example, machining iota a desired electrode shape may be, in a case, difficult: therefore, a total content thereof is set to 30 mass % or less and desirably 27 mass °~° of less.
It should be noted that when an iron-based alloy is adopted as a sulfur corrosion resistant metal, a case might arise in which a sulfur corrosion resistivity is degraded by a xeactxozi between nickel and sulfur if nickel is much contained_ Nickel, however, has an effect increasing oxidation resistivity of iron as well therefore, the metal can be compounded in a range where the sulfur corrosion resistivity is not degz~aded. In this case, a content o~ xxickel is set to 30 mass % or less and desirably 25 mass % or less_ Fuzther, to the above described ixon-based alloy, aluminum is effectively added in. order to improve oxidation. resistivity at bagh temperature. A content of aluminum is preferab),y in the range of. for example, 2 to 5 mass °~b. When a content of aluminum exceeds S mass %.
embrittlement of the alloy may occur and therefore, reduction in machinability thereof may be effected therefore, for example, a case may arise where machining into a desired shape of an electrode becomes hard, while when less than 2 mass %, the effect to improve oxidation resistivity comes to be not conspicuous. A content of alun~.inum is desirably in the range of 2 to d mats %.
For example, when chromium and cobalt axe simultaneously added, a~a iron-based alloy more e~zcellent x~o. oxidation resistivity can be obtained.
In this case, the iron-based alloy preferably contains I5 to 25 mass chromium and 2 to 5 mass % aluminum. When a content of chromium exceeds 25 mass 36 or a content of aluminum exceeds S mass %, embrittlement of the alloy may occur and therefore, reduction in z~nachinability may be effected, wherein, for example, a case may arise where machining into a desired electrode shape becomes hard. On the other hand, when a content of chromium is 15 mass % or less or a content of aluminum is 2 mass % or less, a case may arise where oxidation resistivity at high temperature is not sufficiently ensured. Desirably, the iron-based alloy contains 16 to 19 mass % chromium and 2 to 4 mass % aluminum. Further, as such an irvn-based alley, for example. an electrical heating alloy can be ezxaployed, which contains 15 to 25 mass % chromium, 2 to 6 mass °Y
aluminum and the balance being iron and inevitable impurities.
On the other hand, also in a nickel-based alloy containing nickel as a main constituent, resistirrity to sulfur corrosion is conspicuously improved by compounding chromium in content of 25 mass % or more and such a nzckel-based alloy can be adopted as sulfur corrosion resistant nxetal, being referred to as in the present inveratioz~._ Sauace nickel is inherently excellent 2s in high temperature o~dation resistivity and in addition to this, the high temperature oxidation resistivity is further i.zn~pzoved in the presence of chxomium~ by using the nickel-based alloy, not only is sulfur corrosion rosistivity improved, but a long lifetime of a spark plug can be en.;ured even under a severe working envirorxment_ When a nickel-based alloy is used, a content of chromium is desirably 30 mass % or more_ Furthex, a coz~positi.oxz may be adopted which contains, for example, 1 to 3 mass % aluxaix~uxn and, for example, 3 to 20 mass % iron for ensuring high temperature strength 5 az~d high tem.pexature oxidation xesisti.vity_ As such a nickel based alloy, there can be used a heat resistant nickel-based alloy having chromium in content of 25 mass % or more.
Next, by using a spark plug of the present invention, an internal combustion engine can be constructed in which a combustion chamber is 10 formed in a cylinder head and not only can a spark plug be mounted on the cylinder head such that a spark discharge gap is positioned in the combustion chamber, but a fuel injection system for injecting a fuel direct into the combustion chamber is also provided. By applying a spark plug of the present invention to such a dizect-injection type internal combustion engine, sulfur corrosion on electrodes of a spark plug to take place due tv fuel injection can be prevented with extreme effectiveness, thereby enabling frequency of exchanges to decrease.
Further, an internal combustion engi-ne can also be constructed in which a spsrk plug relating to the second aspect of the present invention of a creeping discharge type (a spark plug in which at least the surface layer portion of the center electrode is made from the sulfur corrosion resistant ~oo.etal) is ~aaounted such that the combustion chamber is fozzxxed in the cylinder head and the spaxk discharge gap is positioned i.n the combustion chamber. The center electrode is harder to be affected by sulfur corrosion even when dusts generated due to the erosion of the insulator are deposited in the clearance between an outer surface of the center electrode of the 9psrk plug and an izxner surface of the through-hale of the insulator, and a sulfur constituent is concentrated in the deposited dusts thereby ensuring a lI
longEr Lifetime of a spark plug and enabling frequency of exchanges o~ spark plugs to decrease.
BRIEF DESCRIPTION OF TITS DR.A.WINGS
FIG. 1 is a longitudinal sectional view showing a spark plug of a first example of the present invention and an enlarged sectional view including a partial front view showing a main part of the spark plug;
FIG. 2 is an enlarged sectional view of a main part showing a first modification of the first example of the spark plug of FIG. 1;
FIG. 3 is an enlarged sectional view of a main part showing a second modification of the first example of the spark plug of FIG. l~
FIG. 4 is a front view showing a spark plug of a second example of the present invention;
FIG. 5 is a sectional view of a main part of FIG_ 4;
FIGS. 8(a) and 6(b) are sectional views illustrating an action of the spark plug of FIG. 4 in compazison with an comparative example;
FIG. 7 is a simplified sectional view of a direct-injection type gasoline engine on which the spark plug of FIG. 1 is mounted FIG_ 8 is a simplified sectional view of a gssoline engine on which the spsxrk plu$ of FIG. 4 is mounted>
FIGS- 9(a) to 9(d) are magnified photographs showing sectional views of ground electzodes after a test oaf test pieces of zuaterials nwoabered 1 to 4 (inventive electrodes) used in a first experiment 26 FIGS. 10(a) to 7.0(c) are magnified photographs showing sectional views of ground electrodes after a test of test pieces of materials nuna,bexed to 7 (outside of the scope of the inventions used in the first experiment; and FIGs. lI(a) and 11(b) are photobraphs showing outer appearances of peripherals of spark discharge gaps o~ an example and a comparative example, respectively, after a test in a second e;cperiment.
PREFERRED EMBODIEMNTS OF THE INVENTION
Descz-iption will be given of ezabod~i.~oaen.ts o~ the present invention below with zefere~ace to exazaples shown in the accompanying drawings.
(First Example) l0 A spark plug 100 shown in FIG. l, as an example of the present invention, has a construction of a so-called parallel electrode type spark plug and includes: a cylindrical metallic shell 1; an insulator 2 fittingly inserted into the interior of the metallic shell I such that a front end portion 21 thereof protrudes from the metallic shell 1i a center electrode 3 provided in the interior of the insulator 2 such that a high melting point metal firing section ~1 formed at a front end thereof is protruded from the insulator 2; a ground electrode 4. one end of which joined with the metallic shell 1 by means of welding or the like, the ether of end of which is bent sideways such that a side surface of the ground electrode 4 faces the front end of the center electrode 8. A distsnce "a" measured from a surface of one end of the metallic shell 1 to the outermost point of a front end portion of the gxound electrode 4 along an axial direction O of the center electrode 3 is 6 u~m or zaoze ox ?_5 mm or more.
The high welting zaetal ~Zxiuag section 31 is made &oxaa a metal containing at least one selected from the group consisting of Ir. Pt. Rh. W.
Re and Ru, fox example Ir, as a main component. or a composite material containing the metal as a main constituent. Fuxther, a Pt-based metal firing section 32 fscing the high melting metal firing section 31 is formed on the J.3 ground electrode 4 and a gap between the high zzxelting point metal firing section 31 and the Pt-based metal firing section 32 works as the spaxl~
discharge gap g.
The insulator 2 is made from a ceramic sintered body, fox example Of ~nmi a, aluminum nitride or the like, and has, il~. the interior thereof. a through-hole 6 for fitti~agly inserting the centez electrode 3, extending along an axial direction thereof. Further, the metallic shell 1 has a cylindrical shape and is zxxade from. a metal such as low carbon steel or the like and not only serves as a housing for the spark plug 100, but also has a threaded l0 portion '7 for mounting the spark plug 100 on the cylinder head 53 (FIG_ 7), which is formed on an outer surface thereof.
At least surface layer portions of the center electrode 3 and the ground electrode 4 are formed from a sulfur corrosion resistant metal described above. Concrete examples of iron-based alloys preferably usable in m the present invention as a sulfur corrosion resistant metal are exemplified as follows:
*FCHW1 (JZS C 2520 Electrical heating iron chromium alloy Class No. 1) main composition containing 23 to 26 mass °i6 Cr~ 4 to 6 mass °r6 Ah and the balance o~ Fe, and traces of additive elements or inevitable impurities, and 20 '~FCHW2 (JIS C 2620 Electrical heating iron chromium alloy Class No. 2) main composition containixzg I7 to 21 mass % Cr~ 2 to ~1 mass % Ah and the balance of Fe, and traces of additive elements or inevitable xxnpurities_ .
Further, concrete examples of a nickel-based alloy preferably usable in the present invention as a sulfur cozzosion x'esistant metal are 25 exemplified as follows:
* II~CONEL s9o maze composition containing 30 mass °r~ Cr~ 9.5 mass % Fe~ arxd the balance of Ni, and traces of additive elements or inevitable impurities.
1~
* Haatelloy G80 main composition containing 29.5 mass % Cr~ 2.0 mass % Co; 5.5 mass Mo: 2.5 mass % W: 15.0 mass % Fe~ and the balance of Ni, and traces of additive elements or inevitable impurities.
In this example, a heat cozxduction accelerating mate~rzal secti.ox~ He made from copper or a copper alloy is formed zn the ixatexior of the center electrode 3 along an axial direction thereof axed the rest including the electrode surface layer portion is a sulfur corrosion resistant metal section 3d. The ground electrode 4 is made from a sulfur corrosioxi resistant metal l0 in the entirety. It should he noted that a similar heat conduction accelerating material section 4c can also be formed in the bulk of the ground electrode 4 as shown in FIG_ 2. Further, contrary to those cases, the heat conduction accelerating material section 3c and 4c can be omitted in a working environment where temperature rise of the electzodes is not so much of a problem.
Moreover, as shown in FIG. 3, a modification is allowed that the fi-ring sections 31 and 32 are ozuztted az~d a spark gap g is formed between a side surface of the ground electrode 4 and the front end surface of the cezxtez electrode ~_ FIG. ? shows an example of a direct-injection type engine (an internal combustion engine) with the Spark plug 100 mounted thereon. In the dixect-injection type engine 40, the spark plug 100 is screwed with the threaded portion 7 to fasten into a plug hole 53a formed in a cylinder head 58. By doing so, the spark plug 1.00 is mou~ated such that a spark discharge gap g is positioned in a combustion chamber 52 and a front end portion thereof protrudes into the chamber_ On the othez hand. a jet nozzle 50 jetting a fuel F in a mist directly into the combustion chamber 52 with a fuel injection pump 54 is mounted on the cylinder head o2. The jetted fuel F is Fprayed directly over the front end section of the spark plug 100_ When the direct-injection type engi.~ne 40 is activated, the front end section of the spark plug 100, including the ground electrode 4 and the center electrode 3, is heated to a higb. temperature by combustion of the ~uel 5 F. EspecialJy> the ~cound electrode 4 protzudxng from the ane end surface of the metallic shell 1 by a distance "a" as large as 6 mm or more is heated to a considerably high temperature and in this condition, the ground electrode 4 is kept exposed repeatedly to a jetted mist of the fuel F containing sulfur.
The grouxxd electrode 4 and the center electrode 3 are, however, made from 10 the above described sul~ux corrosion resistant metal; therefore, no inconvenience such as increase in the spark discharge gap g or melting damage is hard to occur even if there arises an attack by a sulfur constituent. It should be noted that when the center electrode H side does not have so much of rise in tez~apezature and therefore, sulfur corrosion 1~ thereof is not problematic either, only the center electrode 3 may be made from a common electrode metal such as INCONEL 600, which is not a sulfur corrosion resistant metal.
(Second Example) The spark plug 200 shown in FIC_ 4 ig constructed as a so-called semi-creeping- discharge type spark plug rind includes= a cylindrical metallic shell 1: an insulator 2 fittimgly inserted in the zzxetalLic shell 1 with a front end portion thereof protruding from the metal mezr~ber~ a center electrode ~
provided in the insulator 2; a plurality of gzou~ad electrodes 4 disposed such that base ends thereof are joined with the metallic shell 1, intermediate portions thereof surround the front end portion o~ the insulator 2, and front ends thereof face a side surface of the center electrode 3_ The insulator 2 is made from a cersmic sintered body such as alun~i.na or sluminum nitride and has, in the inberior thereof, a hole Section (a thxough-hole) 2d for fittingly inserting the center electrode 3, formed along an axial direction of the insulator 2. Further, the metallic shell 1 is made from lover carbon steel in a cylindrical shape and serves as a housing of the spark plug_ Further, a threaded portion 7 ~ox mountiz~.g the spark plug 200 on the cy~uader head is formed on an outer surface of the metallic shell 1 as showb. in FIG_ 4_ '~vo of the ground electrodes ~ axe, as shown in FZGs. ~ aza.d 5, provided on both sides of the center electrode 3 one on. each side (that is. one kind of multi-electrode type spark plug) and are bent inward such that front end surfaces 4a thereof face a side surface of the center electrode 3 in parallel thereto with the insulator 2 interposed therebetween, while the base ends of the ground electrodes 4 are fixed to the metallic shell J. into one body by welding or the like means. A front end portion of the insulator 2 is located so as to be inserted between the side surface of the center electrode 3 and the front end surfaces 4a of the ground electrodes 4.
The center electrode 3 and the ground electrodes 4 in this example are made from the sulfur corrosion resistant metal in the entirety thereof. It should be noted that the above described heat conduction accelerating material section can be inserted in each of the bulks of the center electrode and the ground electrode 4 for improvement on heat dissipation according to a necessity.
Description will be given of a function of the spark plug 200 below:
The spark plug 200 is, as shown in FIG. $, mounted on a gasoline engine (an internal coz~abusti.ozx engine) 41 by a threaded portion 7 thereof and works as an ignition source for a mixed gas supplied into the combustion ebaxnber 52_ Fox example, a high discharge voltage is applied across the center electrode 3 and the ground electrodes 4 so as to have a negative potential and a positive potential, respectively, and thereby, sparks S are, as shown in FIG.
6(a), generated betwoen the froxxt end surfaces 4a of the ground electrodes 4 snd the center electrode 3, thereby setting fire to a mixed gas. The sparks S
are propagated on routes along a surface of the front end portion of the insulator 2.
When the internal combustion engine dl is operated at a prescribed or higher speed, or under a prescribed or higher load, the surface of the front e~.d portxoz~ o~ the insulator 2 is øxaduaJJ,y ezoded i.n company with spark discharge_ Moreover, ions are driven by an electric field (a potential gradient) formed between the electrodes 3 and 4 to impinge on surfaces o~
the electrodes 3 and 4 to sputter a metal constituent of the electrodes, which, in a case, produces a reaction product by oxidation thereof. As a result, removed stock of the insulator or a reaction product concurrently formed flies off in the form of dusts J to settle into a clearance K between an outer surface of the center electrode 3 and an inner surface of the through-hole 2d as deposits. The dusts J come to be in contact with the outer surface of the center electrode 3, while absorbing a sulfur constituent included in the fuel to a higher concentration, but since the center electrode 3 is made from a sulfur corrosion resistant metal. corrosion or melting damage of the center electrode 3 can be hard to occur.
Here, a difference d - D1 between an outer diameter D1 of the center electrode 3 and an inner diameter d of the through-hole 2d through which the center electrode 3 penetrates is ensured to be 0.07 mm or more. 'When the front end portion of the center electrode 3 is smaller in diameter than the base ex~d portion 3c thereof, a difference d - D1 between the outer diameter D1 of the base exi.d portzon 3c and the in~aer di.ax~aeter d of the thzough hole 2d is only required to be ensured 0.07 mm or more. When the clearance K is small in magnitude, the dusts J generated are, as shown in FIG. 6(b), deposited and packed in the clearance K at a high density, r~rhich can, in a case, cruse arx inconvEnience such as to produce cracks C in the 1~
insulator 2, for example, in repetitions of the cold-hot cycle. By ensuring the difference d - D 1 to be 0.0? mxn or more, however, the dusts ~1 have a lizxxitation in high density packing in the clearance K, whereby cracki.~ag or the like is hard to occur even in repetitions of a cold-hot cycle.
Further, in the spark plug 200, poztiozts i.ucluding parts of firing surfaces of the gxou~ad electrode ~ and/or the center electrode 3 can be each transformed into a consumption resistant section made from a metal containing at least one selected from the group consisting of Ir, Pt, Rh, W, Re and Ru, as a main component, or alternatively from a composite material containing the metal as a main constituent. For instance, in an example shown in FIG. 5, the spark plug 200 has a construction in which a band-like consumption resistant section 31 is formed in the outer peripheral portion of the front end surface of the center electrode 3. To be concrete, a material of the consumption resistant section ~1 in use can be a Pt-Ni alloy, far example 16 an alloy containing Pt as a main component and 15 mass % or more Ni_ A gasoline engiz~.e 41 of FIG. 8 adopts a construction in which a fuel is atomized and mixed with intake air through a carburetor not shown by a negative pressure created in a cylinder expansion, whereas the engine 41 xnay also be of a direct-injection type, similar to FIG. ?. In tk~ia csse, since a fuel is sprayed direct onto the electrodes 2 and 4 in additioz~ to croncentration of a sulfur constituent in the dubts d, the electrodes 3 and 4 are exposed to a very severe environment considering from the viewpoint of sulfur corroeion_ However, the electrodes 3 azzd 4 axe ncaade :6rom. a suJ.fuz coxrosi~on resistant metal therefore, corrosion is hard to advance even in such an environment, 26 thereby enabling a longer lifetime of the spark plug 200.
Also in this construction, a distance "a" from the one end surface of the metallic shell 1 to the outermost point of a front end portion of the ground electrodes 4 can be 6 mm or more. In this case, ovhile a temperature . x9 of the ground electrode 4 rises more conspicuously, sulfur corrosion can be effectively suppressed by forming at least a surface layer portion of the ground electrodes 4 with a sulfur corrosion resistant metal.
Experiments The following experiments below were co~aducted ix~ oxder to confirm the effect of the present invention_ (First Experiment) x0 First of all, wires (of a rectangle of 1.5 mm x 2_8 mm in section) made of vazious kinds of alloy were prepared as base materials of the ground electzode, which is one of main parts of the spark plug of FIG_ 1_ The wires were each cut into pieces of 20 mm in length to form test pieces_ .Alloy compositions of wires used in the first experiment are shown in Table 1.
I
c~ ~ U
('~ ~ U
v ~ v ~ O O O
rC"~Ci~ Jn ~ T~ r1 r1 I p ~ ~-.--aH 1--~a O O p C
r~
JG"~O O ..r O
~ ~
z Z
U U ~
~, a~
c~
C~..LL ,-, ~--, .~ -;
~., ~C
..., tt~ o N N i.n -i ,-1 I I O O O
V V
0 o um .n o0 _ _ I I O O O
Ca Cl7 p ....O O O 1 '~' y' ~ ICJ C~'JCTj I I O ~
~
U
p ..-.
Q O O O O tl~ O O U b I
~
U ~n a~ cfl C u~ c~
p c~ ~ ,~ m .-a N cw7 ~
U rn .
~
p G I I I ~ ~ ~ N c~
I .~
' U
,~ ~ _.
cc5 .-, .~ ...~W p r-, --, '-d .f~ 'z'~
U c~ :~ c~
4~ t=. ~ ~ ~ G~ ca C' ~. '-.--,I ,-s #
"~ N n'7 d' l~7 Cfl h Next, 9 parts by wt sodium sulfate and 1 part by ~srt sodium chloxide were compounded and a mixture is heated at 900°C using a heater into a molten salt bath_ The test pieces were immersed in the moltex~ salt bath as a su1~uac coxxosioza test bath for 10 hr and then take~a out ~6cona the bath, followed by cleaning the test pieces with distilled water and then drying the test pieces. Thereafter, the test pieces (of the ground electrode) were each cut along a cross section perpendicular to the axial direction thereof and the cut pieces were further polished to observe czoss sections under an optical microscope. yIicrophotographs of observed images are shown in FIG2. 9(~ to l0 9(d) and IO(a) to 10(c). FIGs. 9(a) to 9(d) are microphotographs of ground electrodes made of alloys having desirable compositions of sulfur corrosion resistant metals, and correspond to respective materials numbered 1 to 4 in Table 1. Neither corrosion nor melting damage is observed in each photograph and it is understood that electrode surface layer portions were 1~ mainta_i_ned in good conditions. After the corrosion test, surface portions of the test pieces (of ground electrodes) were further investigated using an electron probe micro-analyzer (EPMA) to obtain distributions of a sulfur constituent, rwith the result that almost no sulfur constituent was detected in each test piece. That is, it was found that almost no advance in corrosion 20 by sulfur took place vn each test piece_ On the other hand, FZGs. 10(a) to 10(c) are microphotographs of test pieces from alloys having a Chemical composition outside the desirable ran.~e described above as ground electrode raaterzals and the test pieces correspond to respective materials numbered 5 to ? in Table 1. Cvnspicuvus 2s corrosions or melting damage are observed in electrode surface layer portions of the test pieces. After the corrosion test, suxface portions of the test pieces were further investifatcd using an. electron probe micro-analyaer (EPNIA) to obtain dic~tributions of a sulfur constituent, with the result that 2.'~.
much of a sulfur constituent was detected in each text piece, leading to understanding that the corrosion and melting damage observed on. the microphotographs were caused by sulfur corrosion.
(Seco~ad Expexaxaent) The following exper.~oaent was conducted on the spark plug shown in FIG. 1 in order to confirm the effect of the first aspect of the present invention. As a material of the center electrode, a material 2 of Table 1 (FCHW-2~ example) and a material 5 of Table 1 (INCONEL 600 comparative example) were adopted. Not only was a value of an initial spark discharge gap g adjusted in the range of 0.8 to l.5mm, but also a length of the ground electrode 4 was varied to adjust the distance "a" of FIG_ 1 to obtain various values in the range of 6 to 8 mm_ The spark plugs were mounted on a direct-injection type 6-cylinder gasoline engine with a cylinder volume of 2000cc and an engine oil having a sulfur constituent in content of 1 mass % was used. The engine was operated for a continuous 100 hr at a revolution speed of 5500 rpm with a full-vpen throttle valve before testing sulfur corrosion. After the operation of the engine for the 100 hr, sulfur corrosion produced on the ground electrode portion of each tested spark plug was observed with the naked eye, Evaluation. results were indicated as follows: ~,vhen almost no sulfur corrosion arises, it is given "very good'' with a xaark of O> when. although some sulfur corrosion arnses, no trouble was encountered in operation, it is given " good" with a m.axk of O, azzd when sulfur corrosion is great and troubles such as misfire frequently occur, it is given "bad" with a mark of X. The results are shown in Table 2_ From the results in Table 2, it is found that the comparative examples suffer Sulfur corrosion, and inconvenience due to sulfur corrosion is very much severe ix~. the cozuxparative e~camples when the distance "a"
exceeds 7.5 mm, while in the examples no sulfur corrosion occurs at all even when the distance increases up to the order of 8 mm_ FIGs_ 11(a) and 11(b) chov~r a:fter-test outer appearances of a comparative example azxd ate.
example of this invention, respectively_ VVb.ile the comparative example receives co~aspicuous da~oaage to the ground electrode due to sulfur corrosion. the example of the invention is influenced a little by sulfur corrosion and maintains a good outer appearance.
(Third Experiment) The following experiment was conducted on a spark plug of the same type as the first experiment in order to confirm the effect of the second aspect of the present invention. First of all, both of ground electrodes 4 and center electrode 3 were prepared with the material 2 of Table 1 (FCHW-2~
example) and a value of the distance "a" of each was set to 8 mm.
Furthermore, an outer diameter D 1 of each of the center electrode 3 was fixed at 2.60 mm, while an inner diameter d of the through-hole 6 of an insulator 2 was adjusted to various values in the range of 2.65 to 2.6~ mm such that the difference d -DI assume various values in the range of 0.05 to 24 0.08 mm_ Thus prepared spsrk plugs esch were mounted on a direct-injection type 6-cylinder gasoline engine to perform, as eold-hot cycle test, 3000 time repetitions of an operating cycle including operatiox~ for 1 min with a full-open throttle valve at an engine revolutiozx speed o~ 5500 rpm, followed by idling for 1 mix~_ The ~aumber hT o:f test spark plugs ix~
the 2s same condition is 5. Evaluation results were indicated as fellows= when no cracking occurs in the insulators of test spark plugs after test, it is given "good" arid when cracking occurs even in one of the insulators of test spark plugs, it i9 given 'dad"_ The results are shown in Table 2.
As seen from the results, it is found that by adjusting the difference d - D 1 to be 0.07 mm or more, generation of cracl~n.g can be effectively prevente d from occurring.
Tab 1 a 2 FCHW-2 I NCOl~iEL 6 O ~1 O D
7. 5 0 x Tab 1 a 3 c~
r- c~-~w-0. 0 5 X
0. 0 6 x 0. 0 7 0. 0 8 ~ O
Claims (18)
1. A spark plug comprising: a center electrode: an insulator provided outside said center electrode a cylindrical metallic shell further provided outside said insulator and a ground electrode, a base end of which is joined with a surface of one end of said metallic shell and a distal end of which is bent toward said center electrode to form a spark discharge gap therebetween, wherein when a side of said spark plug in which said spark discharge gap is formed in an axial direction of said center electrode is a front side thereof by definition, a distance along the axial direction from the surface of one end of said metallic shell to the outermost point of a front end portion of said ground electrode is 6 mm or more and at least a surface layer portion of said ground electrode is made from a sulfur corrosion resistant metal.
2. A spark plug according to claim 1, wherein said sulfur corrosion resistant metal is an iron-based alloy containing iron as a component and at least one of chromium and cobalt in total content of 10 mass % or more.
3. A speak plug according to claim 2, wherein a content of nickel in said iron-based alloy is 30 mass % or less.
4. A speak plug according to claim 2, wherein sand iron-based alloy contains aluminum.
5. A spark plug according to claim 4, wherein said iron-based alloy contains: 15 to 25 mass % chromium; and 2 to 5 mass % aluminum.
6. A spark plug according to claim 1, wherein said sulfur corrosion resistant metal contains iron as a main constituent: 30 mass % or less nickel; 15 to 25 mass % chromium: and 2 to 5 mass % aluminum.
7. A spark plug according to claim 1, wherein said sulfur corrosion resistant metal is a nickel-based alloy containing: nickel as a main component and 25 mass % or more chromium.
8. A spark plug according to claim 1, wherein in the bulk of at least one of said ground electrode and said metallic shell, a heat conduction accelerating material section whose main component is at least one of copper and nickel is formed.
9. A spark plug comprising: a center electrode an insulator provided outside said center electrode a cylindrical metallic shell further provided outside said insulator; and a ground electrode, a base end of which is joined with a surface of one end of said metallic shell and a distal end of which faces said center electrode to form a spark discharge gap therebetween, wherein a difference d ~ D1 between an outer diameter D1 of said center electrode and an inner diameter d of a through-hole in said insulator through which said center electrode penetrates is ensured to be 0.07 mm or more and at least a surface layer portion of said center electrode is made from a sulfur corrosion resistant metal.
10. A spark plug according to claim 9, wherein a base end of said ground electrode is joined with a surface of one end surface of said metallic shell and a distal end thereof is bent toward said center electrode to form a spark discharge gap therebetween, wherein whew, a side of said spark plug in which said spark discharge gap is formed in an axial direction of said center electrode its a front side thereof by definition, a distance along the axial direction from the surface of one end of said metallic shell to the outermost point of a front end portion of said ground electrode is 6 mm or more and at least a surface layer portion of said ground electrode is made of a sulfur corrosion resistant metal.
11. A spark plug according to claim 9, wherein said insulator is disposed outside of said center electrode while a surface of a front end of said center electrode is exposed so as to be flush with a surface of a front end of said insulator, and a positional relation between the front ends of said insulator and said center electrode is determined such that not only can a spark discharge gap be formed between said ground electrode and a portion including the front end of said center electrode, but creeping spark discharge along a surface of a portion including the front end of said insulator can also be effected in said spark discharge gap.
12. A spark plug according to claim 9, wherein. said sulfur corrosion resistant metal is an iron-based alloy containing: iron as a main component and at least one of chromium and cobalt in total content of 10 mass % or more.
13. A spark plug according to claim 12, wherein a content of nickel in said iron-based alloy is 80 mass % or less.
14. A spark plug according to claim 12, wherein said iron-based alloy contains aluminum.
15. A spark plug according to claim 14, wherein said iron-based alloy contains: 15 to 25 mass % chromium and 2 to 5 mass % aluminum.
16. A spark plug according to claim 9, wherein said sulfur consisting resistant metal is a nickel-based alloy containing nickel as a main component; and 25 mass % or more chromium.
17. A spark plug according to claim 9. wherein said sulfur corrosion resistant metal contains: iron as a main constituent 30 mass % or less nickel 15 to 25 mass % chromium and 2 to 5 mass % aluminum.
18. A spark plug according to claim 9, wherein in the bulk of at least one of said ground electrode and said metallic shell, a heat conduction accelerating material section whose main component is at least one of copper and nickel is formed.
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP27040799 | 1999-09-24 | ||
| JP11-270407 | 1999-09-24 | ||
| JP2000282385A JP2001160474A (en) | 1999-09-24 | 2000-09-18 | Spark plug |
| JP2000-282385 | 2000-09-18 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2320415A1 true CA2320415A1 (en) | 2001-03-24 |
Family
ID=26549209
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2320415 Abandoned CA2320415A1 (en) | 1999-09-24 | 2000-09-22 | Spark plug |
Country Status (2)
| Country | Link |
|---|---|
| JP (1) | JP2001160474A (en) |
| CA (1) | CA2320415A1 (en) |
Cited By (12)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US7615914B2 (en) * | 2001-06-05 | 2009-11-10 | Ge Jenbacher Gmbh & Co Ohg | Spark plug of an internal combustion engine |
| US8461750B2 (en) | 2009-09-11 | 2013-06-11 | Woodward, Inc. | Pre-chamber spark plug and electrodes therefor |
| US8839762B1 (en) | 2013-06-10 | 2014-09-23 | Woodward, Inc. | Multi-chamber igniter |
| US9172217B2 (en) | 2010-11-23 | 2015-10-27 | Woodward, Inc. | Pre-chamber spark plug with tubular electrode and method of manufacturing same |
| US9476347B2 (en) | 2010-11-23 | 2016-10-25 | Woodward, Inc. | Controlled spark ignited flame kernel flow in fuel-fed prechambers |
| US9653886B2 (en) | 2015-03-20 | 2017-05-16 | Woodward, Inc. | Cap shielded ignition system |
| US9765682B2 (en) | 2013-06-10 | 2017-09-19 | Woodward, Inc. | Multi-chamber igniter |
| US9840963B2 (en) | 2015-03-20 | 2017-12-12 | Woodward, Inc. | Parallel prechamber ignition system |
| US9856848B2 (en) | 2013-01-08 | 2018-01-02 | Woodward, Inc. | Quiescent chamber hot gas igniter |
| US9890689B2 (en) | 2015-10-29 | 2018-02-13 | Woodward, Inc. | Gaseous fuel combustion |
| US9893497B2 (en) | 2010-11-23 | 2018-02-13 | Woodward, Inc. | Controlled spark ignited flame kernel flow |
| US11777282B2 (en) | 2019-09-06 | 2023-10-03 | Federal-Mogul Ignition Llc | Electrode material for a spark plug |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP4933106B2 (en) * | 2005-03-23 | 2012-05-16 | 日本特殊陶業株式会社 | Spark plug and internal combustion engine equipped with the spark plug |
| JP2008123989A (en) * | 2006-10-18 | 2008-05-29 | Denso Corp | Spark plug for internal combustion engine |
| JP4965492B2 (en) * | 2008-03-28 | 2012-07-04 | 日本特殊陶業株式会社 | Internal combustion engine |
| JP4875016B2 (en) * | 2008-03-28 | 2012-02-15 | 日本特殊陶業株式会社 | Internal combustion engine |
-
2000
- 2000-09-18 JP JP2000282385A patent/JP2001160474A/en active Pending
- 2000-09-22 CA CA 2320415 patent/CA2320415A1/en not_active Abandoned
Cited By (17)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US7615914B2 (en) * | 2001-06-05 | 2009-11-10 | Ge Jenbacher Gmbh & Co Ohg | Spark plug of an internal combustion engine |
| US8461750B2 (en) | 2009-09-11 | 2013-06-11 | Woodward, Inc. | Pre-chamber spark plug and electrodes therefor |
| US8657641B2 (en) | 2009-09-11 | 2014-02-25 | Woodward Inc. | Method for forming an electrode for a spark plug |
| US9893497B2 (en) | 2010-11-23 | 2018-02-13 | Woodward, Inc. | Controlled spark ignited flame kernel flow |
| US9172217B2 (en) | 2010-11-23 | 2015-10-27 | Woodward, Inc. | Pre-chamber spark plug with tubular electrode and method of manufacturing same |
| US9476347B2 (en) | 2010-11-23 | 2016-10-25 | Woodward, Inc. | Controlled spark ignited flame kernel flow in fuel-fed prechambers |
| US11674494B2 (en) | 2010-11-23 | 2023-06-13 | Woodward, Inc. | Pre-chamber spark plug with tubular electrode and method of manufacturing same |
| US10907532B2 (en) | 2010-11-23 | 2021-02-02 | Woodward. Inc. | Controlled spark ignited flame kernel flow in fuel-fed prechambers |
| US10054102B2 (en) | 2013-01-08 | 2018-08-21 | Woodward, Inc. | Quiescent chamber hot gas igniter |
| US9856848B2 (en) | 2013-01-08 | 2018-01-02 | Woodward, Inc. | Quiescent chamber hot gas igniter |
| US8839762B1 (en) | 2013-06-10 | 2014-09-23 | Woodward, Inc. | Multi-chamber igniter |
| US9765682B2 (en) | 2013-06-10 | 2017-09-19 | Woodward, Inc. | Multi-chamber igniter |
| US9840963B2 (en) | 2015-03-20 | 2017-12-12 | Woodward, Inc. | Parallel prechamber ignition system |
| US9843165B2 (en) | 2015-03-20 | 2017-12-12 | Woodward, Inc. | Cap shielded ignition system |
| US9653886B2 (en) | 2015-03-20 | 2017-05-16 | Woodward, Inc. | Cap shielded ignition system |
| US9890689B2 (en) | 2015-10-29 | 2018-02-13 | Woodward, Inc. | Gaseous fuel combustion |
| US11777282B2 (en) | 2019-09-06 | 2023-10-03 | Federal-Mogul Ignition Llc | Electrode material for a spark plug |
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| JP2001160474A (en) | 2001-06-12 |
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