EP1079487B1 - Bougie d'allumage pour moteurs à combustion interne - Google Patents

Bougie d'allumage pour moteurs à combustion interne Download PDF

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Publication number
EP1079487B1
EP1079487B1 EP20000118389 EP00118389A EP1079487B1 EP 1079487 B1 EP1079487 B1 EP 1079487B1 EP 20000118389 EP20000118389 EP 20000118389 EP 00118389 A EP00118389 A EP 00118389A EP 1079487 B1 EP1079487 B1 EP 1079487B1
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Prior art keywords
electrode
insulator
center electrode
discharge gap
earth
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Revoked
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EP20000118389
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German (de)
English (en)
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EP1079487A1 (fr
Inventor
Taiji Koyama
Ken Hanashi
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Denso Corp
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Denso Corp
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01T—SPARK GAPS; OVERVOLTAGE ARRESTERS USING SPARK GAPS; SPARKING PLUGS; CORONA DEVICES; GENERATING IONS TO BE INTRODUCED INTO NON-ENCLOSED GASES
    • H01T13/00—Sparking plugs
    • H01T13/52—Sparking plugs characterised by a discharge along a surface
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01T—SPARK GAPS; OVERVOLTAGE ARRESTERS USING SPARK GAPS; SPARKING PLUGS; CORONA DEVICES; GENERATING IONS TO BE INTRODUCED INTO NON-ENCLOSED GASES
    • H01T13/00—Sparking plugs
    • H01T13/02—Details
    • H01T13/14—Means for self-cleaning

Definitions

  • the present invention relates to a spark plug for an internal combustion engine, particularly, to an arrangement for preventing fuel-bridges from forming across a discharge gap of a spark plug.
  • An ordinary spark plug for an internal combustion engine is comprised of a center electrode, an insulator that covers and holds the circumference of the center electrode, and an earth electrode having one end fixed to a metal housing and the free end that forms a discharge gap between the same and the edge of the center electrode. A spark is generated across the discharge gap to ignite air-fuel mixture in an engine combustion chamber.
  • stratified fuel combustion system has been adopted to provide an environmentally suitable internal combustion engine of low fuel consumption.
  • JP-Y2-53-41629 and JP-A-47-19236 disclose self-cleaning spark plugs.
  • Each of the disclosed spark plugs (hereinafter referred to as the double-earth-electrode type spark plug) is comprised of a first earth electrode (main earth electrode), a first discharge gap formed by the first earth electrode, and a second earth electrode (auxiliary earth electrode) having a fixed end fixed to the metal housing and a free end forming a second discharge gap between the same and the side surface of the center electrode.
  • the second of the second earth electrode opposite the side surface of the center electrode is disposed at the outside of the outside diameter of the insulator.
  • JP-Y2-53-41629 normal spark discharges are generated across the first discharge gap, while the spark discharge is generated across the second discharge gap to burn away carbon deposites covering the insulator, thereby preventing the spark from discharging into the inside of the insulator as well as preventing the ignition performance from decreasing.
  • fuel such as gasoline remains in the first and second discharge gaps and forms a fuel-bridge. This causes engine misfires or ignition failure. Formation of the fuel-bridge is illustrated in Figs.10A - 10C.
  • J1 represents a center electrode
  • J2 is an insulator
  • J3 is a metal housing
  • J4 is a first earth electrode
  • J5 and J6 are, respectively, second earth electrodes.
  • Fuel is illustrated by hatched portions.
  • fuel-bridge j7 is formed in a first discharge gap (main gap) between first earth electrode J4 and center electrode J1 and fuel-bridge J8, is formed in a second discharge gap (auxiliary gap) between second earth electrodes J5, J6 and the center electrode. If both the gaps are sufficiently wide, the bridges J7, J8 are easily broken due to vehicle vibration or vibration caused by pressure change of combustion chambers. However, if the first discharge gap is excessively wide, discharge voltage has to be increased. If the second discharge gaps become excessively wider, sparks are not generated across the gap but generated along the surface of the insulator to reach the inside of the metal housing.
  • This kind of the fuel-bridge is often formed if fuel mixture becomes rich in case an internal combustion engine is started under a cold temperature.
  • the fuel-bridge is also formed in the stratified combustion engine that burns excessively rich fuel-air mixture.
  • GB 1 373 435 discloses a sparking plug comprising a first spark gap defined by a central electrode and at least one outer electrode.
  • the first spark gap includes a creeping spark gap and an air gap, in which sparks intermediate the central electrode and the outer electrode creep along an end surface of an insulator surrounding the central electrode.
  • the sparking plug known from GB 1 373 435 comprises a flashover spark gap defined by the central electrode and a further electrode, the flashover spark gap and the first spark gap being substantially in parallel.
  • an end face of the central electrode extends in a plane perpendicular to the axis of the central electrode, wherein the starting point for both the flashover spark and the creeping spark is on the end face of the central electrode.
  • an object of the invention is to prevent the fuel-bridges from forming at the first discharge gap and the second discharge gap of a double-earth-electrode type spark plug for an internal combustion engine, while maintaining sufficient ignition performance.
  • the invention has been made by discovery of the relationship between the second earth electrodes and the surface of the insulator opposite thereto and the relationship between the second earth electrodes and a side surface of the center electrode.
  • the fuel-bridges are prevented from forming at the first discharge gap and second discharge gap while normal ignition performance is maintained.
  • the surfaces facing each other are not flat but slightly curved. Therefore, the areas S1, S2 of flat surfaces approximately represent the facing surface areas.
  • the insulator's side surface has a projected area S2 to which a portion of the free end of the second earth electrode is normally projected, and the first discharge gap A, the outside diameter B, the cross-sectional area S1, the projected area S2, and the distance C are respectively determined so that a fuel-bridge is not formed at the first and second discharge gaps when the following test is conducted:
  • the performance of a spark plug is confirmed by a method for providing practically the same outside stress as the vibration applied to the spark plug.
  • the drop distance is equal to or less than 4 cm.
  • the distance C is equal to or longer than 0.3 mm or equal to or shorter than 1.2 mm.
  • the first discharge gap A is equal to or longer than 0.7 mm or equal to or shorter than 1.3 mm.
  • the distance C and the gap A are shorter than the shortest limits, the engine idling operation may become rough. On the other hand, if longer than the longest limits, the spark discharge cannot be generated, resulting in misfires.
  • the outside diameter B of the center electrode's edge is equal to or larger than 0.3 mm or equal to or less than 2.8 mm.
  • spark plug 100 has cylindrical metal housing 1, which is provided with fastening bolt 1a at the outer periphery to be fastened to an engine block.
  • Insulating member 2 which is made of such as aluminum ceramics (Al 2 O 3 ), is fixed to the inside of metal housing 1.
  • Insulator 2 has end portion 2a extending outward from metal housing 1.
  • end portion 2a has cylindrical edge portion 2b that has a smaller outside diameter than the other portion thereof.
  • Center electrode 3 is fixed to center hole 2c of insulator 2 and is held by metal housing 1 via insulator 2.
  • Center electrode 3 is a double-layered columnar member that is comprised of an internal member made of copper (Cu) or another heat conductive material and an external member made of nickel (Ni) alloy or another heat and corrosion resistant material.
  • the edge of center electrode 3 extends outward from end portion 2a of insulator 2.
  • base portion 3a of center electrode 3 has cylindrical edge portion 3b that is smaller in outside diameter than the other portions thereof.
  • the outer periphery of edge portion 3b is located inside of the inner periphery of edge portion 2b of insulator 2.
  • first earth electrode 4 and second earth electrodes 5 and 6 are fixed, by such as a welder, to an end of metal housing 1.
  • These first and second earth electrodes 4-6 are made of a nickel alloy.
  • the end (free end) of first earth electrode opposite to the end (fixed end) fixed to metal housing 1 is disposed opposite the top of edge portion 3b of center electrode 3, forming first discharge gap A between the same and the edge portion 3b.
  • second earth electrodes 5 and 6 opposite to the fixed ends fixed to metal housing 1 are disposed opposite side surfaces of edge portion 3b of center electrode 3, forming second discharge gap.
  • the free ends of second earth electrodes 5, 6 are disposed outside the diameter of the outer periphery of insulator's edge portion 2a by a distance C (shown in Fig. 4).
  • Dimensions A, B, C, S1 and S2, shown in Fig. 4, are specifically defined.
  • Dimension A is the width of first discharge gap
  • dimension B is the outside diameter of edge portion 3b of center electrode 3 (hereinafter referred to as the center electrode diameter).
  • Dimension C is a distance between second electrodes 5, 6 and the side surfaces of edge portion 2b of insulator 2 in the width direction (horizontal direction in Fig. 4) of second discharge gap.
  • Sectional area of the free end of second earth electrodes 5 and 6 in the direction perpendicular to the width direction of the discharge gap is assumed to be S1.
  • Sectional area S1 is the sectional area of the second earth electrodes 5 and 6 disposed at imaginary surface 900 (the surface perpendicular to the width direction of the second discharge gap) indicated by a one-dot chain line in Fig. 4A.
  • Portions of the free end surfaces of second earth electrodes 5, 6 and the side surfaces of edge portion 2b of center electrode 2 overlap each other in the axial direction to form confronting domain 901. In other words, portions of the free end's surfaces are projected on the side surface of edge portion 2b to form a projected surface (901).
  • sectional area S1 and projected surface area S2 are areas of rectangular surface.
  • the surfaces of insulator 2 and second earth electrodes 5 and 6 in confronting domain 901 are not flat but are slightly curved. However, they are approximated to flat surface areas S1 and S2.
  • fuel (high-octane gasoline) 910 of an internal combustion engine is put in a cold chamber (such as a beaker) of -25°C so that the temperature of fuel 910 becomes -25°C and the viscosity thereof increases to easily form fuel-bridges.
  • spark plug 100 is hung with a string 912 that is fixed to the end opposite earth electrodes 4-6. Then, earth electrodes 4-6 and the front end of metal housing 1 are dipped in fuel 910 and taken out from the same.
  • the fuel-bridges are formed at first discharge gap A between first earth electrode 4 and center electrode 3 and second discharge gaps between respective second earth electrodes 5, 6 and center electrode 3. These discharge gaps are short-circuited by fuel 910.
  • spark plug 100 is dropped by a predetermined distance H under natural conditions with the edge-side of center electrode 3 being down until it is stopped by string 912. Accordingly, the fuel-bridges at the discharge gaps can be broken due to a shock caused when spark plug is stopped. If a holding force of the fuel is large enough, the fuel-bridge remains at any of the discharge gaps. If the holding force is not large enough, the fuel-bridge cannot remain there.
  • the dropping height H was changed from 0 cm to 1cm, 2 cm, 3cm, 4 cm, and 5 cm.
  • the fuel holding forces of the second discharge gaps are tested while various dimensions including the cross-sectional area S1, projected surface area S2, and distance C are changed.
  • the following three different cross-sectional areas S1 of the second earth electrodes are tested: 1.44 mm 2 (0.8 mm ⁇ 0.8 mm), 2.64 mm 2 (1.2 mm ⁇ 2.2 mm), 4.16 mm 2 (1.6 mm ⁇ 2.6 mm).
  • the above distance C was changed to values between 0.3 mm and 1.2 mm in order to keep sufficient ignition performance of the second discharge gap. If distance C is equal to or less than 0 .3 mm, sparks are apt to be discharged across the second discharge gap rather than the first discharge gap A. This may cause a rough idling operation. On the other hand, if the distance C is longer than 1.2mm, it is difficult to generate the spark across the second discharge gap. This hinders the surface discharge and causes engine stall when carbon deposits form on the surface of spark plug 100.
  • a test sample is determined to be no good", if the fuel-bridge remains at the second gaps of the test sample after the dropping under natural condition. On the other hand, if the fuel-bridge does not remain at the second discharge gaps, the sample is determined to be " good”. If the test sample is determined to be " good” where the dropping height H is equal to or less than 4 cm, it is practically considered that the fuel-bridge is not formed. This was confirmed after various spark plugs having the different ratio S2/S1 and the different distance C were tested.
  • Fig. 7 is a graph of rectangular coordinates having x-axis indicating the above distance C and y-axis indicating the above ratio S2/S1.
  • pentagonal area R with diagonal hatching in other words, the area R (and lines) defined by straight lines connecting respective points P1 - P5 shows the area of the relationship between the distance C and areas S1 and S2 ("good" range of second discharge gap) where the above "good” result can be expected when the height H is equal to or less than 4 cm.
  • Range R is the range of the second discharge gap at least one "good” result is obtained. Most preferable range of the second discharge gap is the pentagonal range that is defined by straight lines connecting each of the points P1 - P3, P'4, P'5.
  • the fuel-bridge can be prevented from forming at the second discharge gaps. Moreover, since the above distance C is set to be equal to or longer than 0.3mm or equal to or shorter than 1.2 mm, good ignition performance at the second discharge gaps can be maintained.
  • the "good" range can be provided even if the ratio S2/S1 is 0, or the confronting domain 901 does not exist. In other words, it is also possible that the free end of second earth electrodes 5 and 6 and the side surfaces of edge portion of insulator 2 do not overlap each other (do not normally oppose to each other), as shown in Fig. 6A.
  • the above test on the fuel holding force was conducted while the first discharge gap A and the diameter of the center electrode (the diameter of the edge portion of the center electrode) were changed.
  • the holding force of the first discharge gap will be described hereafter.
  • the distance C and the ratio S2/S1 are set so that the dropping height H can be equal to or longer than 3 cm.
  • the first discharge gap A and the diameter of the center electrode 3 are variously changed.
  • first earth electrode 4 is 1.4 x 2.6 mm. This size corresponds to 1.4 mm in thickness D and to 2.6 mm in width E of first earth electrode 4 shown in Fig. 4A.
  • the first discharge gap A is changed variously between 0.7 mm and 1.3 mm. If the first discharge gap A is shorter than 0.7 mm, the idle operation of the engine may become rough. On the other hand, if the first discharge gap A is longer than 1.3 mm, the engine misfire may be caused frequently.
  • the center electrode diameter B is set between 0.3 mm and 2.8 mm, in view of practical use.
  • Fig. 8 shows the test result, which indicates relationship between the first discharge gap A and the center electrode diameter B.
  • the x-axis indicates the first discharge gap A (mm)
  • the y-axis indicates the diameter B (mm) of center electrode 3.
  • "Good” spark plugs respectively have the first air gaps A and diameters B in the range including solid line R1 and the right side of the solid line (hereinafter referred to as the good range of first discharge gap).
  • those of "No-good” spark plugs are plotted in the range at the left side of solid line R1. Accordingly, if the first discharge gap A and the diameter B are set so that B ⁇ 5A - 2.5 (mm), the fuel-bridge can be prevented from forming at the first discharge gap A.
  • first discharge gap A is set between 0.7 mm and 1.3 mm, sufficient ignition performance at the first discharge gap A can be maintained.
  • the free end of second earth electrodes 5 and 6 and the side surfaces of edge portion 2b of insulator 2 are parallel to each other.
  • a variation in which the free ends of the second earth electrodes incline within 30° in an angle ⁇ is also applicable. If the angle ⁇ is larger than 30°, edge K10 formed at the free ends of second earth electrodes 5 and 6 may project into the discharge gap. This increases wear of the earth electrodes. It is also possible that the angle ⁇ of one earth electrode is different from the other.
  • double-earth-electrode type spark plug according to the present embodiment has been made by setting respective dimensions to be optimum by the specific test method, which has not been noticed as means for preventing the fuel-bridge.
  • the number of the second earth electrodes can be one or three or more. If there are a plurality of earth electrodes and the second discharge gaps, it is not necessary that all the second earth electrodes have the same dimensions C, S1, and S2. The dimensions of each second electrode can be different as far as they are disposed in the same "good" range.
  • a spark plug for an internal combustion engine is comprised of a center electrode (3), a cylindrical insulator (2) holding the center electrode in a center hole thereof, a cylindrical metal housing (1) holding the insulator therein, a first earth electrode (4) having a free end disposed opposite the center electrode's edge to form a first discharge gap A, a second earth electrode (5, 6) having a free end disposed opposite the center electrode's side-surface to form a second discharge gap.
  • the free end of the second earth electrode has a cross-sectional area S1 at a portion normally opposite to the insulator's side surface.
  • the insulator's side surface has a projected area S2 to which the free end of the second earth electrode is normally projected.
  • the free end of the second earth electrode is disposed at a portion outside the outside diameter B of the center electrode's edge. There is the following relationship between the first discharge gap A and the outside diameter B: B ⁇ 5A - 2.5 (mm).

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  • Spark Plugs (AREA)

Claims (5)

  1. Une bougie d'allumage pour un moteur à combustion interne, comprenant :
    une électrode centrale (3) ayant une extrémité (3b) de l'électrode centrale et une surface latérale de l'électrode centrale;
    un isolateur cylindrique (2) ayant un trou central et une extrémité (2b) de l'isolateur, l'isolateur maintenant l'électrode centrale dans le trou central, et l'extrémité de l'isolateur ayant une surface latérale de l'isolateur;
    une enveloppe (1) en métal cylindrique maintenant l'isolateur à l'intérieur;
    une première électrode de masse (4) ayant une extrémité fixée qui est fixée à l'enveloppe et une extrémité libre disposée face à l'extrémité de l'électrode centrale pour former un premier espace de décharge A entre celle-ci et l'extrémité de l'électrode centrale;
    une deuxième électrode de masse (5, 6) ayant une extrémité fixée qui est fixée à l'enveloppe en métal et une extrémité libre disposée face à la surface latérale de l'électrode centrale, pour former un deuxième espace de décharge entre celle-ci et la surface latérale de l'électrode centrale, ladite extrémité libre ayant une aire de section droite S1 faisant face en direction normale à la surface latérale de l'isolateur; caractérisée en ce que
    la surface latérale de l'isolateur a une aire projetée S2 sur laquelle l'extrémité libre de la deuxième électrode de masse est projetée en direction normale,
    l'extrémité libre de la deuxième électrode de masse est disposée dans une partie située à l'extérieur du diamètre extérieur B de l'extrémité de l'électrode centrale,
    il y a la relation suivante entre le premier espace de décharge A et le diamètre extérieur B de l'extrémité de l'électrode centrale :
    B ≤ 5A - 2,5 (mm); et
    la distance C (mm) entre l'extrémité libre de la deuxième électrode de masse et la surface latérale de l'isolateur, et un rapport entre l'aire projetée S2 et l'aire de section droite S1 sont fixés dans une plage définie par des lignes reliant les points suivants, lorsque la distance C est portée sur l'axe x et ledit rapport est porté sur l'axe y : C , S ⁢ 2 / S ⁢ 1 = 0 , 3 , 0
    Figure imgb0038
     C , S ⁢ 2 / S ⁢ 1 = 1 , 2 , 0
    Figure imgb0039
     C , S ⁢ 2 / S ⁢ 1 = 1 , 2 , 1 , 0
    Figure imgb0040
     C , S ⁢ 2 / S ⁢ 1 = 0 , 8 , 1 , 0
    Figure imgb0041
     C , S ⁢ 2 / S ⁢ 1 = 0 , 3 , 0 , 5
    Figure imgb0042
  2. La bougie d'allumage selon la revendication 1, caractérisée en ce que
    ladite distance C et ledit rapport S2/S1 sont fixés dans une plage définie par des lignes reliant les points suivants : C , S ⁢ 2 / S ⁢ 1 = 0 , 3 , 0
    Figure imgb0043
     C , S ⁢ 2 / S ⁢ 1 = 1 , 2 , 0
    Figure imgb0044
     C , S ⁢ 2 / S ⁢ 1 = 1 , 2 , 1 , 0
    Figure imgb0045
     C , S ⁢ 2 / S ⁢ 1 = 1 , 0 , 1 , 0
    Figure imgb0046
     C , S ⁢ 2 / S ⁢ 1 = 0 , 3 , 0 , 3
    Figure imgb0047
  3. La bougie d'allumage pour un moteur à combustion interne selon la revendication 1, caractérisée en ce que
    ladite distance C est entre 0,3 mm et 1,2 mm.
  4. La bougie d'allumage pour un moteur à combustion interne selon la revendication 1, dans laquelle le premier espace de décharge A mesure entre 0,7 mm et 1,3 mm.
  5. La bougie d'allumage pour un moteur à combustion interne selon la revendication 1, dans laquelle le diamètre extérieur B est entre 0,3 mm et 2,8 mm.
EP20000118389 1999-08-25 2000-08-24 Bougie d'allumage pour moteurs à combustion interne Revoked EP1079487B1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
JP23886799 1999-08-25
JP23886799A JP3721877B2 (ja) 1999-08-25 1999-08-25 内燃機関用スパークプラグ

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EP1079487A1 EP1079487A1 (fr) 2001-02-28
EP1079487B1 true EP1079487B1 (fr) 2008-02-06

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2006114476A (ja) 2004-09-14 2006-04-27 Denso Corp 内燃機関用のスパークプラグ
EP1841028B1 (fr) 2006-03-29 2013-11-20 NGK Spark Plug Co., Ltd. Bougie d'allumage pour moteur à combustion interne
JP5870629B2 (ja) * 2011-11-02 2016-03-01 株式会社デンソー 内燃機関用のスパークプラグ及びその取付構造

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE2106893A1 (de) * 1971-02-13 1972-08-31 Bosch Gmbh Robert Kombinierte Hochspannungs Luft und Gleitfunken Zündkerze
JP3140006B2 (ja) * 1998-06-11 2001-03-05 日本特殊陶業株式会社 スパークプラグ

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EP1079487A1 (fr) 2001-02-28
JP2001068251A (ja) 2001-03-16
DE60037955T2 (de) 2009-03-19
DE60037955D1 (de) 2008-03-20

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