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WO1999031775A1 - Bougie d'allumage - Google Patents

Bougie d'allumage Download PDF

Info

Publication number
WO1999031775A1
WO1999031775A1 PCT/GB1998/003649 GB9803649W WO9931775A1 WO 1999031775 A1 WO1999031775 A1 WO 1999031775A1 GB 9803649 W GB9803649 W GB 9803649W WO 9931775 A1 WO9931775 A1 WO 9931775A1
Authority
WO
WIPO (PCT)
Prior art keywords
spark plug
bridging member
electrode
plug according
centre
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
PCT/GB1998/003649
Other languages
English (en)
Inventor
Joseph Gibson Dawson
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Dawson Royalties Ltd
Original Assignee
Dawson Royalties Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from GBGB9726591.2A external-priority patent/GB9726591D0/en
Application filed by Dawson Royalties Ltd filed Critical Dawson Royalties Ltd
Priority to GB0012762A priority Critical patent/GB2346933A/en
Priority to AU14945/99A priority patent/AU1494599A/en
Publication of WO1999031775A1 publication Critical patent/WO1999031775A1/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

Links

Classifications

    • 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
    • H01T13/20—Sparking plugs characterised by features of the electrodes or insulation

Definitions

  • the present invention relates to spark plugs for internal combustion engines.
  • Conventional spark plugs in use at the present time typically have a life expectancy of about 12,000 to 18,000 miles before they need to be replaced.
  • Major contributing factors to the gradual deterioration of a spark plug include: the direction and intensity of the spark leading to electrode erosion; temperature differential between the hotter central electrode and the cooler ground electrode due to poor heat transfer from the central electrode; limits on the life of the electrode materials; the size of the spark gap; and, corrosion due to acids formed during combustion.
  • the centre electrode is constantly under the greatest stress.
  • the centre electrode works harder than the ground electrode and functions as the cathode emitter to form a spark.
  • the central electrode is unable to dissipate heat efficiently due to being surrounded along its length by a ceramic insulator and being connected to a plastics material insulated high tension (HT) lead having a carbon trace core conductor.
  • HT plastics material insulated high tension
  • a new spark plug starts with a sharp edged flat surface on the centre electrode and a corresponding flat surface on the ground electrode, there being a gap in the region of 0.028" to about 0.060" depending upon the engine builders specification and application.
  • Heat and spark erosion are the two factors which most affect spark plug longevity. Heat is produced in two forms: initially the heat and intensity of the spark itself as it crosses the gap; and, the heat of combustion itself.
  • the formation of the spark can raise the temperature of the centre electrode far higher than that of the ground electrode which is on the "cool side" of the spark and has the benefit of being firmly attached to the metal shell of the spark plug body which itself is in good thermal contact with the cooled engine cylinder head so that heat may be readily dissipated.
  • the central electrode is surrounded by a ceramic insulator, is carrying 50 millijoules, transmits from 5 to 25 KV, has an air gap at one end and is connected at its outer end to a poorly conducting HT lead. Thus, if the centre electrode becomes too hot, erosion due to the spark and increasing breakover voltage will be rapid.
  • US-A-4 939 409 describes a spark plug having a surface discharge member bridging the gap to the ground electrode.
  • the surface discharge member comprises an alumina body having conductive surface coatings of a sintered mixture of alumina and from 60 to 85 wt% platinum at each end where the body is in contact with the centre and ground electrodes respectively and, a non- conductive surface film of alumina and from 10 to 40 wt% platinum in between the two conductive surface coatings.
  • the surface discharge member itself is expensive to manufacture and the remaining structure of the spark plug and the manufacturing process to make the spark plug appear to place this spark plug outside the scope of an economic device which could be used in ordinary vehicles.
  • a spark plug for an internal combustion engine including two electrodes, the electrodes comprising a central electrode and a ground electrode, there being a gap between the two electrodes and wherein the gap between the central and ground electrodes is bridged by a member made of a monolithic, electrically insulating material .
  • the gap between the centre electrode and the ground electrode is bridged by a bridging member made of a monolithic material which is electrically insulating under "normal" ambient conditions but is preferably a good thermal conductor.
  • a bridging member is used to denote any configuration or cross-section of member which bridges or connects the two electrodes.
  • the material should be electrically insulating to 25 Mega Volts per metre.
  • Examples of materials fulfilling these conditions are aluminium nitride and silicon nitride.
  • Aluminium nitride is a ceramic and is used in high temperature resistors, has heat conduction properties more akin to metals than ceramics yet is a strong engineering ceramic having excellent electrical insulating properties at high temperatures.
  • Silicon nitride has good thermal shock resistance and is also a strong engineering ceramic.
  • Other potential materials may include electrically insulating reaction bonded silicon carbide and beryllium oxide for example.
  • the bridging member may be allowed to 'float' in and be located and retained by recesses in the centre electrode and possibly also in the ground electrode.
  • the bridging member in the form of a rod of silicon nitride or aluminium nitride is fixed between the two electrodes across the gap therebetween.
  • the rod may be fixed at one end into the centre electrode and at the other into the ground electrode.
  • the recess in the centre electrode may have a depth substantially the same or slightly greater than the axial length of the bridging member.
  • the end of the bridging member in contact with the ground electrode may have a substantially conical or pointed end, the spark formed in this embodiment being analogous with the conical, focused spark formed in the spark plug described in our co- pending International patent application number PCT/GB98/01434.
  • spark plugs of the present invention are easily able to provide spark gaps of 2mm at breakover voltages much less than are currently employed with conventional spark plugs which is a very considerable advantage of the present invention.
  • the rod is able to expand or contract as temperature dictates due to the relatively little resistance thereto by the hot ground electrode which is able to deform slightly.
  • the rod may be fixed to the centre or ground electrode only, as described above, and the remote end left to move within a bore provided in the other electrode.
  • the rod conducts heat away from the centre electrode to the ground electrode preventing excessive heating thereof.
  • the nature of the spark has been altered due to the rod providing a path therefor which has resulted in greatly reduced erosion of the electrodes.
  • breakover voltage is reduced due to the presence of the bridging rod thus reducing stress on the coil and allowing the use of a larger "gap" if desired and which is beneficial for fuel combustion.
  • Figure 1 shows a part-sectioned side elevation of part of a spark plug according to a first embodiment of the present invention
  • Figure 2 shows a monolithic bridging member as used in the embodiment of Figure 1;
  • Figure 3 shows a partially sectioned view similar to Figure 1 of a second embodiment of a spark plug according to the present invention.
  • FIG 4 which shows a perspective view of a bridging member for the embodiment shown in Figure 3.
  • FIG 1 shows a part-sectioned portion of a spark plug 10 according to the present invention.
  • the spark plug comprises a metal body 12 having a screw threaded portion 14 for fixing the spark plug into the cylinder head (not shown) for example of an associated internal combustion engine (not shown) ; a ceramic insulator 16; a centre electrode 18 within the insulator 16; a ground electrode 20 fixed to the body 12; and, a gap bridging member 22 in the form of a cylindrical rod (also shown alone in Figure 2).
  • the centre electrode 18 extends through the spark plug 10 surrounded by the insulator 16 and has at one end a recess 24 to accept one end 26 of the bridging member 22 and a terminal (not shown) at its remote end for connecting to a high voltage source.
  • the ground electrode 20 is made of metal, welded at one end 30 to the threaded portion 14 and has a recess 32 for the other end 34 of the bridging member 22.
  • the bridging member 22 is made of silicon nitride (e.g. Nitrasil- trade name).
  • the gap 40 between the centre 18 and ground 20 electrodes is bridged by the member 22.
  • the member 22 is of high electrical resistance but has good thermal conductivity and enables a spark to form by initially tracking across the surface of the bridging member which then allows a spark ⁇ body' to spread out over the opposing faces of the centre and ground electrodes to establish a substantial spark volume to ignite the fuel charge.
  • a "gap" 40 of about 0.7mm with the bridging member 22 bridging thereacross has substantially the same breakover voltage as an air gap of about 0.125mm therefore, as mentioned above larger electrode separation gaps and consequently larger sparks may be employed at one third to one half of the breakover voltage required by conventional spark plugs.
  • the member 22 conducts heat away from the centre electrode 18 to the ground electrode 20 and thence to the cylinder head (not shown) to be dissipated thus reducing the thermal stress on the electrode 18.
  • the bridging member 22 may be a 'floating' or interference fit in the recesses 24 and 32 and not fixed.
  • the ground electrode recess 32 may be provided with a channel (not shown) extending to the side edge of the electrode to allow the ground electrode to be twisted so as to locate the member 22.
  • the material of the bridging member 22 may be loaded with conductive particulate material to vary and control the resistance thereof.
  • FIGs 3 and 4 show a second embodiment of a spark plug according to the present invention wherein the central electrode 18 has a recess 50 of a depth sufficient to accommodate the entire length of the bridging member 52 (shown in more detail in Figure 4) .
  • This enables the gap 40 between the flat face 56 of the centre electrode 18 and the opposing face 58 of the ground electrode 20 to be set accurately without danger of damaging the bridging member.
  • the spark plug is merely inverted to allow the member 52 to slide inside the recess 50. Once the gap 40 is set, the plug is merely held in a generally upright position to enable the member 52 to slide out of the recess and contact the face 58 of the ground electrode.
  • the end of the bridging member 52 in contact with the ground electrode 20 is in the form of a cone 60 having a pointed end 62.
  • the shape of the spark is at least partially conical as indicated by the dashed lines 64, the spark 64 being formed over the surface of that portion of the bridging member which projects from the recess 50.
  • the breakover voltage is reduced to about 16% of the normal voltage.
  • the size of the bridging members 22, 52 in both the embodiments shown in Figures 2 and 4 is about 3mm in length and about 1mm in diameter.
  • spark duration is increased due to the breakover voltage being so dramatically reduced leading to improved combustion of the fuel charge. Spark duration increases by about 12 to 16%.

Landscapes

  • Spark Plugs (AREA)

Abstract

Bougie d'allumage conçue pour un moteur à combustion interne et comprenant deux électrodes comportant une électrode centrale et une électrode de terre, ces deux électrodes présentant un écartement ponté par un élément de liaison en matériau monolithique isolant électriquement.
PCT/GB1998/003649 1997-12-17 1998-12-07 Bougie d'allumage Ceased WO1999031775A1 (fr)

Priority Applications (2)

Application Number Priority Date Filing Date Title
GB0012762A GB2346933A (en) 1997-12-17 1998-12-07 Spark plug
AU14945/99A AU1494599A (en) 1997-12-17 1998-12-07 Spark plug

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
GBGB9726591.2A GB9726591D0 (en) 1997-12-17 1997-12-17 Spark plug
GB9726591.2 1997-12-17
GBGB9815236.6A GB9815236D0 (en) 1997-12-17 1998-07-15 Spark plug
GB9815236.6 1998-07-15

Publications (1)

Publication Number Publication Date
WO1999031775A1 true WO1999031775A1 (fr) 1999-06-24

Family

ID=26312785

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/GB1998/003649 Ceased WO1999031775A1 (fr) 1997-12-17 1998-12-07 Bougie d'allumage

Country Status (3)

Country Link
AU (1) AU1494599A (fr)
GB (1) GB2346933A (fr)
WO (1) WO1999031775A1 (fr)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1553671A1 (fr) * 2004-01-05 2005-07-13 Ford Global Technologies, LLC, A subsidary of Ford Motor Company Bougie d'allumage
JP2013254670A (ja) * 2012-06-08 2013-12-19 Ngk Spark Plug Co Ltd スパークプラグ
AT525737A4 (de) * 2022-06-28 2023-07-15 Lec Gmbh Zündkerze

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2548170A (en) * 1948-12-30 1951-04-10 Pure Oil Co Spark plug
DE883817C (de) * 1941-11-28 1953-07-20 Nienburger Metallwarenfabrik A Gleitfunkenzuendkerze
US4939409A (en) * 1986-06-12 1990-07-03 Robert Bosch Gmbh Spark plug with a surface discharge section

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE883817C (de) * 1941-11-28 1953-07-20 Nienburger Metallwarenfabrik A Gleitfunkenzuendkerze
US2548170A (en) * 1948-12-30 1951-04-10 Pure Oil Co Spark plug
US4939409A (en) * 1986-06-12 1990-07-03 Robert Bosch Gmbh Spark plug with a surface discharge section

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1553671A1 (fr) * 2004-01-05 2005-07-13 Ford Global Technologies, LLC, A subsidary of Ford Motor Company Bougie d'allumage
JP2013254670A (ja) * 2012-06-08 2013-12-19 Ngk Spark Plug Co Ltd スパークプラグ
AT525737A4 (de) * 2022-06-28 2023-07-15 Lec Gmbh Zündkerze
AT525737B1 (de) * 2022-06-28 2023-07-15 Lec Gmbh Zündkerze

Also Published As

Publication number Publication date
GB2346933A (en) 2000-08-23
GB0012762D0 (en) 2000-07-19
AU1494599A (en) 1999-07-05

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