WO1998053540A1 - Bougie d'allumage - Google Patents

Bougie d'allumage Download PDF

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Publication number
WO1998053540A1
WO1998053540A1 PCT/GB1998/001434 GB9801434W WO9853540A1 WO 1998053540 A1 WO1998053540 A1 WO 1998053540A1 GB 9801434 W GB9801434 W GB 9801434W WO 9853540 A1 WO9853540 A1 WO 9853540A1
Authority
WO
WIPO (PCT)
Prior art keywords
spark
spark plug
cathode
plug according
ground electrode
Prior art date
Application number
PCT/GB1998/001434
Other languages
English (en)
Inventor
Joseph Gibson Dawson
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 GBGB9710085.3A external-priority patent/GB9710085D0/en
Application filed by Dawson Royalties Ltd. filed Critical Dawson Royalties Ltd.
Priority to JP55011098A priority Critical patent/JP2001525982A/ja
Priority to AU74430/98A priority patent/AU7443098A/en
Priority to EP98921648A priority patent/EP0983621A1/fr
Publication of WO1998053540A1 publication Critical patent/WO1998053540A1/fr

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
    • H01T13/32—Sparking plugs characterised by features of the electrodes or insulation characterised by features of the earthed electrode

Definitions

  • the present invention relates to spark plugs for internal combustion engines.
  • the spark plug is almost as old as the internal combustion engine itself and over the past decades many attempts have been made to modify and improve the performance of the spark plug so as to achieve a corresponding improvement in the performance of the engine.
  • improved performance has many facets and may include obtaining more power from the engine by improved combustion of the fuel; easier starting from cold; improved performance with regard to reducing misfires of the engine under operating conditions; and, improved performance with regard to the reduction of levels of harmful emissions, to name but a few.
  • spark plug manufacturers have mainly concentrated upon the fundamental design and quality improvements to the spark plug per se. Even some of these so-called improvements to the spark plug have imported features such as, for example, air gaps, resistors and capacitance's as integral features into the spark plug construction as exemplified inter alia in US 4,613,789.
  • spark plugs in use today are not precision components in the sense that their primary purpose, i.e. to produce a spark having consistent characteristics with respect to timing, spatial position, heat content, kernel shape and duration is not achieved. Spark plugs in use today still produce a spark within a relatively very broad spectrum. In order to produce a spark, it is necessary for the potential across the electrodes to ionise the intervening gas charge, and the provision of multiple ground electrodes makes the production of a repeatable spark more difficult in that in theory the spark could form between the centre electrode and any one or more of the ground electrodes.
  • the time to fire is very short, but when considered in precise terms and paying due regard to the need for a modern engine to fire at a precise instant at a predetermined position of the piston before top dead centre, the time required for the plug to find a position where ionisation of the fuel charge can occur between the electrodes and to create ionisation is critical and can have a significant effect on the engine performance. Therefore, an ignition system which has to "decide" between two, three or four ground electrodes before firing the spark cannot be said to be precise. Similarly, the provision of a plurality of ground electrodes means that the spark position can vary greatly from one spark to the next.
  • the spark energy and duration is limited by the use of the standard ignition coils used in induction based ignition systems. Such coils have been designed to produce sufficient energy and spark duration to ensure ignition under most engine circumstances.
  • the amount of energy must be limited by consideration of radio frequency interference (RFI) and the ability to charge the coil especially at high RPM.
  • the spark gap distance is also limited by restrictions on RFI and the possibility of misfire, especially at low RPM. If possible, given the specification of standard coil ignition systems, it would be desirable to make the following improvements:
  • the primary object of the present invention therefore, is to provide a spark plug working to the theorectical and industrially adopted conclusions of Rudolph Maly, who states in his publication "Spark Ignition: Its Physics and Effects on the Internal Combustion process", Maly. R. , Chapter 3, that "of the total electrical energy supplied to the spark, only that fraction contained within the outer surface layer of the plasma is available for initiating the flame propagation process".
  • the energy density and temperature gradient in this layer depend on the discharge mode. Highest energy densities and temperature gradients are achieved if the ignition energy is supplied in the shortest time interval.
  • a spark plug for an internal combustion engine including at least a cathode and an anode ground electrode between which a spark is formed wherein the part of the ground electrode on which the spark impinges is in the form of at least one low area projection as hereinbelow defined.
  • the low area projection working part of the one electrode may be in the form of a spike or a pointed end opposite the face of the other electrode at a predetermined distance therefrom.
  • a spark plug for an internal combustion engine including at least a cathode and an anode ground electrode between which a spark is formed wherein one electrode has an end facing the other electrode and which end has a recessed form.
  • spark plugs have a central electrode, generally concentric with the plug body and at least one ground electrode fixed to a metal body member, the ends of the two electrodes defining a gap therebetween.
  • the central electrode is generally referred to as the cathode and the ground electrode as the anode; this refers to vehicles having negative earth systems and for positive earth systems the polarity of the central and ground electrodes may be reversed. Thus, it is the geometrical relationship between the electrodes which is of primary importance rather than their strict polarity.
  • the centre electrode will be referred to as the cathode and the ground electrode as the anode hereinafter, though it should be remembered that their strict polarity may be reversed and which is intended to be covered by the spark plug of the present invention.
  • the spark plug according to the present invention comprises a cathode having a recessed end formation and a ground electrode having at least one low area projection generally pointed end on which the spark focuses such as the one electrode according to the spark plug of the first aspect of the present invention.
  • the recess at the end of the cathode is of spherical curvature.
  • the form of the recess portion may be rounded, hyperbolic, parabolic, conical, frusto-conical or may be of a generally cylindrical recessed form.
  • the form of the concave portion is a bowl of a spherical curvature.
  • the recess is not hemi-spherical in shape but has a larger radius of curvature wherein the centre of curvature lies outside of the electrode recess.
  • the low area projection or end of the anode ground electrode may coincide with the centre of curvature of the spherically dished cathode end, i.e. geometrically focused.
  • the gap between the anode point and the cathode end may be in the region from about 0.35mm to about 0.9mm. Spark plug gaps of up to about 1.5mm may be used with benefit in the electrode geometry according to the spark plug of the present invention as the focusing effect reduces the voltage required from the coil to initiate the spark and effectively accelerates the spark breakover voltage.
  • the rim or edge of the recess is not sharply defined but has a smoothly curved form.
  • spark plugs according to the present invention provide performance increases which are totally unexpected.
  • one electrode has a recess of spherical curvature with a centre of curvature lying at a point which allows a gap of up to about 1.5mm to be employed utilising an electrode having a point lying at the centre of curvature
  • an electrode projection tip lying anywhere within a sphere of about 30% of the recess radius of curvature and centred on the centre of curvature of the recess will achieve a large proportion of the benefits of the optimum electrode arrangement.
  • focusing of the spark is not to be construed in strictly geometric terms but is to be understood as meaning a spark which extends between a relatively large area recess in an electrode and impinges onto a relatively much lower area tip of a projection on the opposing electrode.
  • spark plugs tend to erode away the outer edges of the centre electrode during use causing the spark to become more diffuse and eventually leading to misfires. It has been found that with spark plugs according to the present invention, the focusing geometry of the electrodes appears to be self-preserving. To illustrate this fact, spark plugs with centre electrodes have been made where the recess in the end was of non-spherical curvature, e.g. frusto-conical . It has been found that operation of the spark plug over time has resulted in the frusto-conical form of the recess being eroded away to a spherical curvature having a centre of curvature coincident with the tip of the opposing electrode.
  • non-spherical curvature e.g. frusto-conical
  • spark plugs according to the present invention that a spark will be formed for coil voltages at least 20% lower than for a conventional spark plug at double the nominal gap. For the same coil voltage, a comparatively much larger gap may be employed than with a conventional plug. In this instance a bigger more energetic spark is produced.
  • the gap between the anode 20 and cathode 16 is denoted by “G 1 " and the diameter of the cathode by “2R".
  • the gap G' is typically about 0.65mm and the diameter 2R about 2.5mm to 2.8mm.
  • the gap "G" between the end of the anode 60 and the edges of the recess is also about
  • the distance "D" from the recess edges to the base thereof of the cathode 46 which may for example also be about 0.65mm thus, giving a total gap of about 1.3mm.
  • (G+D) of spark plugs according to the present invention may be double the conventional gap G' and at the same time reduce the breakover voltage required for a conventional spark plug as described with reference to
  • the breakover voltage can still be up to 20% less than that required for a conventional spark plug.
  • the depth of the bowl D is the depth of the bowl D:
  • Figure 11 shows a graph where the interrelationship between bowl depth, D, and nominal gap, G, are given for spherical curvature of the bowl for a perfectly focused spark and a radius R of the cathode of 1.25 mm.
  • the gap may be larger and/or the coil voltage lower with spark plugs according to the present invention
  • the quantity of energy contained in the spark is between 100 to 150% greater and spark path length increased by 100%.
  • the desirable criteria expressed in the above quotations of Maly and Bosch are fulfilled by the spark plugs of the present invention leading to improved engine operating characteristics.
  • the spark in the spark plug according to the present invention forms more quickly due to the lower voltage required, i.e. there is less wait due to a shortened voltage rise-time and spark formation is accelerated.
  • there is greatly increased energy in the spark as noted above.
  • spark plugs according to the present invention will fire about lO ⁇ s earlier than a conventional spark plug due to the lower voltage required under given conditions. At 3000 rev/min this equates to firing at about 0.2° of a revolution earlier and hence
  • spark plugs according to the present invention form an enhanced spark at lower coil voltages, they also appear to empty the coil of more of its stored energy thus increasing the spark duration and further tending to ensure more complete combustion of the fuel/air charge.
  • the spark plug according to the present invention appears to focus the spark energy from the cathode recess onto the anode and produces a generally conical spark extending substantially over the whole area of the end of the cathode.
  • a spark of greatly increased heat and intensity has been found to form compared with the sparks generated by conventional spark plugs.
  • the spark plug of the present invention forms a spark in precisely the same position each time thus allowing an engine designer certainty in factors relating to the point at which fuel combustion is initiated.
  • the spark plug of the present invention contrary to the prior art, seeks to maximise the area difference between the two electrodes, whereas prior art spark plugs appear to either reduce the central electrode to virtually a pin or to provide multiple ground electrodes of apparently ever increasing total area.
  • the diameter of the central cathode electrode is desirably between 2.5mm and 3.5mm.
  • Cathode diameters of about 3mm compared with about 2.5mm which is a commonly used diameter in conventional spark plugs appears to improve the performance of the spark plug of the present invention yet further in terms of further increased spark temperature and energy content for example.
  • the end thereof may be in the form of an insert to the spark plug wherein the end of the cathode is in the form of a flanged head having the recessed form therein.
  • spark produced by the spark plug of the present invention is of a different nature from the spark produced by conventional spark plugs is evidenced by a noticeable directional thrust which is associated with the spark. It has been found that combustible particles introduced into the spark are actually accelerated and ejected by the spark in a direction consistent with the spark direction. It is believed that this effect is due to the focusing and consequent "concentration" of the electron flow forming the spark from the cathode to the anode. The evident focusing of the spark from the cathode recess onto the anode appears to be analogous to the focusing of a light beam by a lens onto a point giving greatly increased effect in terms of energy and temperature.
  • a significant advantage of the spark plug of the present invention is that manufacturing costs for many of the embodiments may be largely the same as with conventional single cathode and anode spark plugs since the manufacturing technology involved is essentially the same and also in that there may be few if any additional components to the spark plug of the present invention.
  • the anode or ground electrode of the present invention may comprise one or more suitably formed flat metal bars as with conventional spark plugs but with the addition or formation of a pointed end or projection which may be integrally formed therewith or added thereto. It is preferred that the anode having the pointed end is formed of a single piece of metal which is, for example, welded to the spark plugs metal body such that the pointed end faces the recess in the central electrode. It is possible to provide an anode having a spike fixed thereto but it has been found that such constructions tend to be less reliable and the thermal discontinuity in the joint region leads to overheating. However, if a joint may be made reliably such constructions could be used.
  • the materials from which the cathode and anode may be made are well known to those skilled in the spark plug art and may include alloys of iron, nickel, chromium, molybdenum, iridium for example.
  • a further unexpected characteristic of spark plugs according to the present invention is an apparent self- cleaning or self-forming ability. It has been found that where a cathode bowl has been formed imperfectly and has, for example, pips or lumps of unwanted metal remaining thereon, during operation this unwanted material is removed by the action of the spark and results in a spherical curvature, free of imperfections.
  • spark plugs according to the present invention emit far less RFI than conventional spark plugs. This reduction is due to the ability of spark plugs according to the present invention to produce more powerful sparks at reduced peak coil voltages of, for example, about 20% and since RFI is at least partially dependent upon the peak coil voltage there is a consequent reduction. Thus, less shielding is necessary and/or performance of items such as radios is enhanced.
  • a spark plug construction having a pointed central electrode and a recess formed in the ground electrode may also be formed and which falls within the scope of the present invention.
  • Figures 1 to 3 show views of part of a prior art spark plug; a schematic illustration of the electric field searching for a discharge path; and, one example of a conventional spark discharge current, respectively;
  • Figure 4 shows a perspective view of part of a first embodiment of a spark plug according to the present invention
  • FIGS. 5A to 5C show some alternative ground electrode formations
  • Figure 6 shows part of a further embodiment having a modified form of central electrode
  • Figure 7 shows another embodiment having a modified form of ground electrode
  • Figure 8 shows the cathode and anode portion of a spark plug according to the first aspect of the present invention
  • Figure 9 shows a schematic view of the electrode portion of a conventional spark plug
  • Figure 10 shows a comparative view to that of Fig. 9 but of a spark plug according to the present invention and including information for calculating spark plug parameters from its dimensions;
  • Figure 11 shows a graph of nominal gap G vs bowl depth for a focused spark
  • Figure 12 which shows an example of a spark plug according to the present invention having a recess formed in the ground electrode.
  • FIG 4 part of a prior art spark plug is indicated generally at 10 and includes a body 12 having a threaded portion 14 for screwing into an engine cylinder head (not shown) , a central cathode electrode 16 having an insulator 18 therearound and a ground anode electrode 20.
  • the cathode 16 generally has a flat end face 22 which is in opposition to a flat face 24 on the anode 20.
  • the initially flat face 22 becomes slightly rounded.
  • the electrodes 20 and 16 must determine whereabouts initial ionisation is occurring between the electrodes and potentially, following ionisation a spark can occur at any position indicated by the arrows 30 in Figure 2.
  • the spark is rarely formed over the entire area between the electrodes as indicated at 32 in Figure 3 but usually occurs at one relatively small area as indicated at 28 in Figure 1 and furthermore, the spark seldom occurs consistently in the same position. Where the spark does occur over most of the opposing area between the electrodes as indicated at 32, it tends to be a distributed bow-shaped in the manner shown in Figure 3 causing the energy contained to be somewhat dissipated over a larger volume.
  • Figure 1 shows a feature where the ground electrode 50 has an undercut relief 322 so as to obviate any spark generation between the recess rim and the body of the ground electrode.
  • FIG 4 shows a portion of a spark plug 40 according to the present invention.
  • the spark plug according to the present invention includes a body portion having a threaded portion 44 for screwing into a cylinder head (not shown) , a central cathode electrode 46 insulated from the body portion by a ceramic insulator 48 and a ground anode 50.
  • the cathode is ultimately connected to a coil (not shown) to supply a high voltage and the anode 50 is connected to ground via the engine cylinder head (not shown) .
  • the shape of the end of the cathode 46 has a recess 56 in the form of a spherical curvature and the anode 50 has an integrally formed pin 60 having a tip 62, the tip 62 being in a position which coincides with the centre of curvature of the cathode end recess 56.
  • the spark formed by the spark plug of the present invention and indicated by the lines 66 extends substantially over the whole of the surface area of the recess 56 and to the tip 62 of the anode pin 50 in a generally conical form. The spark always extends between the cathode end and the tip 62 and thus always occurs in the same predictable position.
  • the spark temperature has been measured using an International Pyrometer Company Ltd.
  • each ground electrode 100 includes a pin or spike 102 having a pointed or low area tip 104.
  • FIG. 6 shows part of a spark plug having a modified form of central electrode 110.
  • the electrode comprises an internal conductor portion 112 having a cylindrical blind bore in the end and a further portion having a shank which is screwed or welded into the bore of the portion
  • the cathode 110 to have a recessed end portion 120 which is of greater diameter than would otherwise be the case.
  • the recessed end portion 120 also has a circumferential flanged rim 122 which sits over the end of the insulator 124. Thus a spark 126 is formed between the bowl 128 and the ground electrode spike 130.
  • Figure 7 shows another modified form of spark plug according to the present invention wherein the ground electrode 140 is formed with a pointed end 142.
  • FIG 8 shows the cathode 240 and anode 242 portion of a spark plug according to the first aspect of the present invention.
  • the cathode has a substantially flat face 244 as with cathodes of prior art spark plugs but, the anode 242 has a low area projection 246 on which the spark 248 impinges from the cathode face 244.
  • the spark is consistently formed in a predictable position and the temperature is greatly increased compared with conventional spark plugs as exemplified by the construction shown with reference to Figures 1 to 3.
  • Figure 12 shows a centre electrode 330 having a pointed end 332 and a ground electrode 334 having a recess 336 formed therein.
  • Spark plugs having the configuration shown in Figure 4 and having a gap of 1mm between the electrodes and a conventional commercially available plug as described with reference to Figures 1 to 3 and having a gap of 0.7mm were both connected to a common coil and shared a common ground connection.
  • the spark may be expected to form on one plug before the other, i.e. the plug having the lower spark break-over voltage.
  • the result of this test was that the plug according to the present invention consistently sparked first and as the gap on the plug according to the present invention was gradually increased, the conventional plug did not spark first until the gap on the inventive plug reached 1.2 to 1.25mm.
  • a spark plug according to the present invention gapped at 0.7mm and requiring 20% less voltage than a conventional plug at double the gap produces a spark which is 100% bigger in volume.
  • the spark size is about 250% bigger than that of a conventional spark plug.
  • the spark size can be increased to 300% and, in some cases where the cathode bowl diameter is increased to about 3.5mm and the anode focal point is made very sharp, increases to 500% of the size of a conventional spark may be achieved at the same voltage. If the gap of a conventional spark plug is increased, the energy content thereof tends to fall and can even be extinguished by turbulent fuel/air charges.
  • the focused spark produced by spark plugs according to the present invention are better able to deal with lean fuel/air ratios and, in a normal engine at stoichiometric fuel/air ratio, it can better buffer and protect catalytic converters against poisoning by incomplete or erratic combustion.

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Abstract

L'invention concerne une bougie d'allumage destinée à équiper un moteur à combustion interne. Cette bougie comprend au moins une électrode de terre à la cathode et une électrode de terre à l'anode, entre lesquelles se forme une étincelle. La partie de l'électrode de terre que vient heurter l'étincelle se présente sous la forme d'au moins une projection de zone de première vitesse, telle qu'un crampon, et une extrémité de la cathode jouxtant l'électrode de terre peut présenter une forme en creux.
PCT/GB1998/001434 1997-05-20 1998-05-19 Bougie d'allumage WO1998053540A1 (fr)

Priority Applications (3)

Application Number Priority Date Filing Date Title
JP55011098A JP2001525982A (ja) 1997-05-20 1998-05-19 スパークプラグ
AU74430/98A AU7443098A (en) 1997-05-20 1998-05-19 Spark plug
EP98921648A EP0983621A1 (fr) 1997-05-20 1998-05-19 Bougie d'allumage

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
GBGB9710085.3A GB9710085D0 (en) 1997-05-20 1997-05-20 Spark plug
GB9715035A GB9715035D0 (en) 1997-05-20 1997-07-17 Spark plug
GB9715035.3 1997-07-17
GB9710085.3 1997-07-17

Publications (1)

Publication Number Publication Date
WO1998053540A1 true WO1998053540A1 (fr) 1998-11-26

Family

ID=26311554

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/GB1998/001434 WO1998053540A1 (fr) 1997-05-20 1998-05-19 Bougie d'allumage

Country Status (4)

Country Link
EP (1) EP0983621A1 (fr)
JP (1) JP2001525982A (fr)
AU (1) AU7443098A (fr)
WO (1) WO1998053540A1 (fr)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP2131461A1 (fr) * 2007-03-29 2009-12-09 NGK Spark Plug Co., Ltd. Bougie d'allumage et son procédé de fabrication
CN103746292A (zh) * 2013-12-25 2014-04-23 柳州正菱集团有限公司 火花塞

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102012208069A1 (de) * 2012-05-15 2013-11-21 Man Diesel & Turbo Se Zündkerze für eine Brennkraftmaschine

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR406568A (fr) * 1908-09-05 1910-02-02 Archibald Montgomery Low Perfectionnements apportés aux dispositifs d'allumage électrique
GB152909A (en) * 1920-01-26 1920-10-28 Howard Edgar Holloway Improvements in sparking plugs for internal combustion engines
US1512319A (en) * 1922-07-22 1924-10-21 Henry W Stuver Spark plug
US5373214A (en) * 1992-06-12 1994-12-13 Mccready; David F. Spark plug and electrode arrangement therefor

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR406568A (fr) * 1908-09-05 1910-02-02 Archibald Montgomery Low Perfectionnements apportés aux dispositifs d'allumage électrique
GB152909A (en) * 1920-01-26 1920-10-28 Howard Edgar Holloway Improvements in sparking plugs for internal combustion engines
US1512319A (en) * 1922-07-22 1924-10-21 Henry W Stuver Spark plug
US5373214A (en) * 1992-06-12 1994-12-13 Mccready; David F. Spark plug and electrode arrangement therefor

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP2131461A1 (fr) * 2007-03-29 2009-12-09 NGK Spark Plug Co., Ltd. Bougie d'allumage et son procédé de fabrication
EP2131461A4 (fr) * 2007-03-29 2013-03-20 Ngk Spark Plug Co Bougie d'allumage et son procédé de fabrication
CN103746292A (zh) * 2013-12-25 2014-04-23 柳州正菱集团有限公司 火花塞

Also Published As

Publication number Publication date
EP0983621A1 (fr) 2000-03-08
JP2001525982A (ja) 2001-12-11
AU7443098A (en) 1998-12-11

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