EP0376147A1 - Zündkerzen für Verbrennungsmotoren - Google Patents

Zündkerzen für Verbrennungsmotoren Download PDF

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Publication number
EP0376147A1
EP0376147A1 EP89123574A EP89123574A EP0376147A1 EP 0376147 A1 EP0376147 A1 EP 0376147A1 EP 89123574 A EP89123574 A EP 89123574A EP 89123574 A EP89123574 A EP 89123574A EP 0376147 A1 EP0376147 A1 EP 0376147A1
Authority
EP
European Patent Office
Prior art keywords
center electrode
insulator
diameter
inside bore
spark plug
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.)
Granted
Application number
EP89123574A
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English (en)
French (fr)
Other versions
EP0376147B1 (de
Inventor
Yasuyuki Sato
Hiroyuki Murai
Kozo Takamura
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.)
Offta Al Pubco Licza Uso Non Esclusivoffta Di
Original Assignee
NipponDenso Co Ltd
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Filing date
Publication date
Application filed by NipponDenso Co Ltd filed Critical NipponDenso Co Ltd
Publication of EP0376147A1 publication Critical patent/EP0376147A1/de
Application granted granted Critical
Publication of EP0376147B1 publication Critical patent/EP0376147B1/de
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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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
    • 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

  • a special spark plug for internal-combustion engines is disclosed in Japanese Patent Publication No. 58-40831.
  • This spark plug is designed such that a spark jumps across a first spark-plug gap under a normal operating condition when no carbon residue is present over the end of the insulator nose and the inside bore wall surface are stained with soot and carbon deposits.This spark reaching the second gap burns off carbon deposits covering the inside bore wall surface, recovering the normal surface condition for sparking.
  • the second gap of the above- described conventional spark plug for the internal-combustion chamber is provided on the wall surface side of the combustion chamber relative to the first gap, the core of flame produced by a spark across the second gap can not easily contact the mixture.
  • the second gap is smaller in size than the first gap, and therefore the flame core can not grow larger. Consequently, there occurs the problem that a spark generated across the second gap results in unreliable ignition of the air-fuel mixture.
  • This spark plug for the internal-engine is designed to ionize the ambient atmosphere by capacity discharge, and to burn off carbon deposits in the inside bore of the insulator by utilizing induction discharge generated within the most ionized area of the range of ionization.
  • this spark plug for the internal-combustion engine because the small-diameter portion of the center electrode projects out of the inside bore of the insulator over the end of the insulator nose, a larger flame core can be produced by the gap, thereby enabling an improvement in the ignition of the air-fuel mixture.
  • spark plugs for internal-combustion engines in particular directly determine the engine operation performance, it can well be expected that much stricter requirements will be imposed for the manufacture of spark plugs having an improved carbon burn-off effect.
  • Spark discharge produced across the electrode gap of a spark plug 1 may be divided into two types: capacitive discharge which breaks insulation between the electrodes and induction discharge which subsequently takes place along the range of lowered insulation through the ionization of the ambient atmosphere.
  • Fig. 3 is a schematic diagram for observing the state of the spark plug used in an air-cooled, four cycle, 230 cc single-cylinder engine running at the speed of 1500 rpm at idle in which a crystal was embedded in a part where the spark plug discharge could be observed.
  • the state of the spark plug producing the inductive discharge is shown, partly enclosed by oblique lines indicating the induction discharge.
  • the present inventor et al found that, in the case of the capacity discharge, a spark plug with a center electrode 3 of an extremely small diameter d, much smaller than ordinary types, produced a spark at the end of the center electrode 3 as in normal diameter size plugs and that, in the case of the induction discharge, the spark jumped from at the side of the end area of the center electrode 3.
  • the present inventor et al therefore, noticed the reliable and remarkable burn-off of carbon deposits from the insulator of the spark plug by utilizing the induction discharge generated at the side of the end area of the center electrode 3.
  • the spark plug 1 for the internal-combustion engine includes a cylindrical insulator 2 having an inside bore 23 in the axial direction; a center electrode 3 inserted in the inside bore and held in the insulator 2 with its end projecting out of the inside bore 23; a ground electrode 4 forming a gap between the same and the end of the center electrode 3; and a housing holding the ground electrode 4, and fixed on the outer periphery of the insulator2.
  • This spark plug 1 satisfies the following relation:
  • the center electrode 3 projecting out of the cylindrical space 6 has a tapered portion at the end; d indicates the largest diameter at the tapered portion of the center electrode 3.
  • Fig. 4 shows a spark plug 1 slightly covered with carbon residue, with which the capacity discharge and induction discharge take place.
  • Figs. 5 to 9 show the lapse of discharge time and principal cleaning mechanism in the spark plug 1 heavily covered with carbon deposits.
  • Fig. 10 shows the state of the spark plug 1 after the finish of the first discharge.
  • a full line with an arrow indicates the capacity discharge; and area enclosed with oblique lines is the induction discharge; a waveform area is a pilot discharge which accelerates the cleaning action; and a dotted area represents an ionized area.
  • Fig. 4 to 10 are schematic diagrams for the observation of the capacity discharge and the induction discharge in an internal-combustion engine using spark plugs with a crystal glass embedded in a part where spark plug discharge can be observed, and an analysis of a result of the observation.
  • Fig. 11 is a schematic diagram of the capacity discharge and induction discharge waveforms.
  • the spark plug 1 is likely to be covered with carbon 100 over the nose of the insulator 2 and the wall surface of the inside bore 23 when very rich air-fuel mixture is used.
  • a capacity discharge is generated from the edge of the center electrode 3 when a high voltage is applied to the center electrode 3.
  • the induction discharge is generated in the ionization range of ambient atmosphere which has been ionized by the capacity discharge. Since the capacity discharge takes place across the electrode gap formed between the end of the center electrode 3 and the ground electrode 4, the induction discharge also is generally thought to be generated across this gap, but the ionization range presented by the capacity discharge spreads as far as the area in which the side of the center electrode 3 also can be ionized.
  • the induction discharge is occurring from the side of the center electrode 3 into the gap, thereby burning off carbon 100 deposits from the insulator exposed to the induction discharge (hereinafter referred to as the side discharge).
  • Fig. 5 is a schematic diagram showing the condition in which the electrostatic capacity C and the leakage resistance R are applied in parallel between the insulator 2 surface and the housing due to the presence of a high-resistance conductive layer carbon.
  • the leakage current flows from the center electrode 3 to the housing 5 through the leakage resistance on the insulator surface 2, and also a charge current flows to charge between the center electrode 3 and the inner wall of the inside bore 23 and between the insulator 2 surface and the housing 5.
  • a technological idea of the ionization of the cylindrical space 6 is based on the action of the third electrode at the three-core gap, that is, the pilot discharge that accelerates ionization in the gap.
  • the cylindrical space 6 is provided to facilitate ionization by utilizing carbon residue which a gradually deposited, as the third electrode.
  • This action is continuously effected during a period of time when the voltage being applied reaches a voltage great enough to generate the capacity discharge to break insulation at the gap shown at (2) of Fig. 11, keeping on the expansion of the ionization range 120 in the vicinity of the cylindrical space 6 as shown in Fig. 7.
  • the capacity discharge takes place across the gap from the end of the center electrode 3 as shown in Fig. 8 the instant the voltage applied has reached a value at which there occurs the capacity discharge which breaks insulation at the electrode gap shown at (2) of Fig. 11.
  • the capacity discharge has spread wide enough to include the side of the center electrode 3 within the ionization range, and therefore the side discharge will occur into the gap from the side of the center electrode 3 immediately after the generation of the capacity discharge, thereby burning off carbont00 deposits from the insulator portion exposed to the side discharge.
  • the side discharge blows out into the gap from a wide area including the cylindrical space 6 and the end and side surfaces of the center electrode 3 as shown in Fig. 9.
  • This side discharge continues during the continuous discharge time (3) shown in Fig. 11. Accordingly the carbon deposits on the wall surface of the inside bore forming the cylindrical space 6 between the inside bore 23 and the outer periphery of the center electrode 3 and on the nose of the insulator 2 can be burned off.
  • the pilot discharge occurs and the side discharge shown in Fig. 9 is produced in other areas such as soft in Fig. 10 covered with carbon 100 residue of the inner wall of the inside bore of the insulator 2 than the cleaned portion, thus gradually burning off the carbon 100 residue on the wall surface of the inside bore 23 and the insulator nose.
  • the burn-off of carbon deposits of the insulator 2 can be effected by two kinds of discharges: the side discharge alone and the side discharge combined with the ionization range produced by the pilot discharge.
  • Fig. 1 shows a major portion of the spark plug for internal-combustion engines according to this invention
  • Fig. 2 shows a spark plug for internal-combustion engines adopting this invention.
  • Numeral 1 denotes the spark plug for internal-combustion engines.
  • the spark plug 1 has a cylindrical insulator 2, a center electrode 3 held in the insulator 2, a ground electrode 4 forming a gap G between the same and the tip face 31 of the center electrode 3, and a metallic housing 5 holding the ground electrode 4.
  • the insulator 2 has an axial inside bore 23 opening at the top end 21 and the bottom end 22.
  • the center electrode 3 is inserted, in the inside bore 23 of a nose section 24 of this insulator 2 which projects into the combustion chamber of the internal-combustion engine.
  • the center electrode 3 is inserted in the inside bore 23 with its tip face 31 projecting out of the inside bore 23 and held in the nose 24 of the insulator 2.
  • the top end portion above the edge section 32 of this center electrode 3 is a small-diameter portion 33 which is smaller in diameter than the inner diameter of the inside bore 23.
  • This small-diameter portion 33 includes an inserted portion 34 positioned within the inside bore 23 and an projecting portion 35 projecting out of the inside bore 23.
  • the ground electrode 4 is disposed opposite to the tip face 31 of the center electrode 3.
  • the housing 5 is provided with a screw mounting section 51 on the outer periphery with the ground electrode 4 connected to the end thereof. Also this housing 5 is secured on the outer periphery of the insulator 2.
  • the spark plug also includes a resistor 71 for the suppression of radio wave noise, numeral 72 indicates an inductive layer of glass 72, a terminal stud 73, a terminal 74.
  • the air-fuel mixture is flowing in the engine combustion chamber.
  • the vicinity of the center electrode itself becomes an obstacle for the flow of the mixture, increasing the turbulent component of the flow. Therefore, it is postulated that the side discharge is generated by the ionization range flowing from the tip of the center electrode.
  • the present inventor et al therefore, noticed the burn-off of carbon deposits on the side of the tip of the center electrode through the utilization of this side discharge.
  • Fig. 12 shows the diameter d of center electrode on the horizontal axis and the frequence of generation of the side discharge on the vertical axis.
  • Fig. 13 is a schematic presentation showing the side discharge generated in the experiments conducted in Fig. 12.
  • the side discharge generation frequency in spark plugs in conventional use, suddenly increases below 2.0mm when the diameter (d) of the center electrode projecting out of the insulator nose is decreased from 2.5mm, and begins to increase largely at the diameter (d) of below 1.5mm.
  • the ionization range becomes hard to flow due to the turbulent component of the flow. From this, it is presumed that the side discharge generation frequency remarkably decreased.
  • Fig. 14 shows the diameter d of the center electrode plotted on the horizontal axis and the carbon burn-off length F plotted on the vertical axis.
  • Fig. 15 shows a spark plug used in the experiment performed in Fig. 14, in which F denotes the carbon burn-off length.
  • the high side discharge generation frequency (over 50 ) is when 0.6 mm ⁇ d ⁇ 1.6 mm.
  • the long carbon burn-off length F (over 0.8 mm) is when 0.5 mm ⁇ d ⁇ 1.55 mm. Therefore, a higher side discharge generation frequency and a longer carbon burn-off length F will occur when 0.60 mm ⁇ d ⁇ 1.55 mm.
  • the present inventor et al have found that the generation of the side discharge varies with the diameter d of the center electrode, and the carbon burn-off length also varies with the diameter d of the center electrode. It is, therefore, necessary to select the center electrode diameter within a range of high side discharge generation frequency and long carbon burn-off length F, that is, 0.60 mm d d ⁇ 1.55 mm obtained from the result of experiments. Furthermore, since it is 0.8 mm S d 1.4 mm at 70% of the side discharge generation frequency and 0.8 mm ⁇ d ⁇ 1.2 mm at 1.2 mm of the carbon burn-off length F, the optimum value of the diameter d may be said to be 0.8 mm ⁇ d 1.2 mm.
  • Fig. 16 shows the length l of the center electrode plotted on the horizontal axis and the spark voltage between the center electrode and the ground electrode plotted on the vertical axis
  • the plug gap G between the tip of the center electrode and the ground electrode in the 4- gauge atmospheric air was set to 1.1 mm.
  • Fig. 17 shows the length t of the center electrode plotted on the horizontal axis and the air-fuel ratio (A/F) at the ignition limit at idle which is an index expressing the ignition performance, plotted on the vertical axis.
  • A/F air-fuel ratio
  • a four-cycle, 1600 cc, water-cooled four-cylinder engine was used. While this engine was running at idle, the air-fuel mixture was leaned out to provide an air-fuel ratio (ignition limit air-fuel ratio) suitable for the stabilization of combustion.
  • Fig. 18 shows the dimensions of the spark plug used in the experiments in Fig. 16 and 17.
  • Fig. 18 the spark voltage is lower and the ignition performance is less affected than those in Figs. 16 and 17 because 0 mm ⁇ l.
  • the spark plug is subjected to gradual consumption of the tip of the center electrode, thus resulting in a gradually decreased length of the center electrode.
  • This consumption of the tip of the center electrode of this spark plug has been empirically confirmed to reach a maximum 0.2 mm at the end of its service life. Therefore, an optimum length of the center electrode is 0.2 mm ⁇ l to ensure low spark voltage and little influence on the ignition performance until the end of the service life.
  • spark plugs Type W16EX-U 11 the applicant manufactured as typical examples of spark plugs most adopted in general, showed an evaluation result of 1 M ⁇ at eight cycles. Accordingly, it can be clarified that a desired effect can not be obtained under the eight cycles.
  • Fig. 21 shows the diameter d of the center electrode plotted on the horizontal axis and the effect of resistance to fouling plotted
  • Figs. 20 to 25 demonstrate that the desirable range of effect of resistance to fouling relative to the length of the center electrode is 0.2 mm ⁇ l ⁇ 1.1 mm, and that the center electrode length t varies with the center electrode diameter d.
  • Fig. 27 indicates the depth L of the cylindrical space plotted on the horizontal axis and the effect of resistance to fouling plotted on the vertical axis.
  • the effect of resistance to fouling exceeds 40 (cycles/1M ⁇ ) when the depth of the cylindrical space is 0.2 mm ⁇ L ⁇ 1.0 mm.
  • the spark plug disclosed in this invention should be free from the influence of the depth L of the cylindrical space relative to the effect of resistance to fouling.
  • Figs. 20 to 25 also show that the center electrode length t, the center electrode diameter d and the inner diameter D of the inside bore are correlated with one another.
  • Fig. 28 shows that the effect of resistance to fouling provided through the effective combination of the side discharge of the center electrode and ionization of the cylindrical space is within a desirable range relative to the combination of the center electrode length l, the center electrode diameter D of the inside bore.
  • the center electrode diameter of the present invention is between 0.60 mm ⁇ d 1.55 mm. Particularly when 0.8 mm ⁇ d 1.20 mm,the side discharge is generated at a high probability and the carbon burn-off length is prolonged, thereby improving the resistance to fouling. That is, the same result as that of the experiments in Fig. 12 to 14 could be obtained. In this result, d ⁇ 0.60 mm and d> 1.55 mm are not included in the desirable range probably because any effect to be obtained by the ionization range within the cylindrical space is not obtainable due to a low side discharge generation frequency and short carbon burn-off length.
  • desirable center electrode length is 0.2 mm ⁇ l ⁇ 1.1 mm. Furthermore, as is clear from Fig. 14, particularly when 0.2 mm ⁇ l ⁇ 0.7mm, the side discharge can be generated exactly from the cylindrical space, thereby enabling an improvement in the carbon burn-off effect.
  • l ⁇ 0.2mm is not included within the desirable range for the following reason. As seen from the result of experiments shown in Figs. 16 and 17, the spark voltage is high and the ignition performance is not within the desirable range, which have an effect on the life of the center electrode. Reversely, l>1.1 mm is not included in the desirable range because of a greater distance from the tip of the center electrode to the tip of the insulator nose and a lower effect of resistance to fouling by the side discharge than the result of experiments in Figs. 20 to 25.
  • the optimum range of the inner diameter of the inside bore satisfies D ⁇ 1.1 dmm + (l/2) mm + 0.2 mm and D ⁇ 0.9 dmm - (l/2) mm + 1.6 mm.
  • D ⁇ 1.1 dmm + (t/2) mm + 0.2 mm is not included within the desirable range because it is presumable that when the cylindrical space is narrower than the optimum size from which a cleaning effect can be expected, the heat energy of the induction discharge is restricted from expanding by the cooling action of the insulator and the center electrode, and therefore fails in effectively burning off carbon soot.
  • Fig. 29 shows a variation of Fig.1.
  • a taper section 37 is provided between the small-diameter portion 33 and the large-diameter portion 36 of the center electrode 3.
  • This intermediate portion 38 has an diameter which is intermediate between the small-and large-diameter portions.
  • the side discharge is generated at the tip side surface of the small-diameter portion 33 similar to that shown in Fig.1.
  • Fig. 31 shows a variation of Fig. 30.
  • a tapered section 39a is provided between the small-diameter portion 33 and the intermediate portion 38 of the center electrode 3, and further a tapered section 39b is provided between the intermediate portion 38 and the large-diameter portion 36.
  • the side discharge is generated from the tip side surface of the small-diameter portion similarly to that shown in Fig. 1.
  • Fig. 32 shows another variation of Fig. 1.
  • d denotes the diameter of the center electrode 3 at the portion 36a held in the nose 24 of the insulator 2.
  • This embodiment also includes a pocket 25, at the tip section of the insulator 2 forming the cylindrical space 6 between the outer periphery of the center electrode 3 and the wall surface of the inside bore 23. The side discharge is generated in the pocket 25 and at the tip side surface of the center electrode 3 which projects out of the pocket 25.
  • Fig. 33 shows another embodiment, being another variation of Fig. 1.
  • the tapered section 31a is provided at the end of the small-diameter portion 33 of the center electrode 3, Also, in this example, d represents the diameter of the large-diameter portion 31 b which is of the largest diameter of the tapered section 31a.
  • the side discharge is generated from the tip side surface of the small-diameter 33 similarly to that in Fig. 1.
  • the spark plug is provided with a resistor for the suppression of radio wave noise.
  • a resistor for the suppression of radio wave noise it is not necessary required to provide the spark plug with this resistor for radio wave noise suppression.
  • the spark plug for internal-combustion engines of this invention has the following effect.
  • the use of a center electrode of decreased diameter can burn off carbon deposit on the tip of the insulator with the side discharge generated thereat. Furthermore, carbon deposit on the tip of the insulator nose and the wall surface of the inside bore can be burnt off by the combination of the ionization range produced by the pilot discharge in the cylindrical space and the side discharge, thereby remarkably, improving the effect of resistance to fouling.
  • a spark plug for an automotive internal combustion engine providing improved ignition even when carbon is deposited on the insulator of the ' plug.
  • a rich fuel-air ratio causes carbon to be deposited on spark plug insulators, thereby decreasing its effective insulation.
  • By limiting the geometrical dimension of the plug's center electrode the problem of carbon build-up is overcome.
  • the sizes of these elements have certain allowable ranges that enhance the igniting effect of the plug.

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EP19890123574 1988-12-29 1989-12-20 Zündkerzen für Verbrennungsmotoren Expired - Lifetime EP0376147B1 (de)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
JP332010/88 1988-12-29
JP63332010A JP2805781B2 (ja) 1988-12-29 1988-12-29 内燃機関用スパークプラグ

Publications (2)

Publication Number Publication Date
EP0376147A1 true EP0376147A1 (de) 1990-07-04
EP0376147B1 EP0376147B1 (de) 1994-08-17

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EP19890123574 Expired - Lifetime EP0376147B1 (de) 1988-12-29 1989-12-20 Zündkerzen für Verbrennungsmotoren

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EP (1) EP0376147B1 (de)
JP (1) JP2805781B2 (de)
DE (1) DE68917573T2 (de)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0803950A1 (de) * 1996-04-25 1997-10-29 NGK Spark Plug Co. Ltd. Zündkerze für einen Verbrennungsmotor
DE19950922A1 (de) * 1999-10-21 2001-04-26 Beru Ag Zündkerze

Families Citing this family (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP3272615B2 (ja) 1995-11-16 2002-04-08 日本特殊陶業株式会社 内燃機関のスパークプラグ
JP2004006250A (ja) 2002-04-10 2004-01-08 Denso Corp 内燃機関用スパークプラグ
JP6041824B2 (ja) * 2014-03-22 2016-12-14 日本特殊陶業株式会社 スパークプラグ、および、点火システム
DE102016223404A1 (de) * 2016-11-25 2018-05-30 Robert Bosch Gmbh Zündkerze

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE2215276A1 (de) * 1972-03-29 1973-10-31 Daimler Benz Ag Zuendkerze fuer brennkraftmaschinen
US4211952A (en) * 1977-04-07 1980-07-08 Nippon Soken, Inc. Spark plug
EP0287080A1 (de) * 1987-04-16 1988-10-19 Nippondenso Co., Ltd. Zündkerze für Verbrennungsmotor

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS5910549B2 (ja) * 1977-04-11 1984-03-09 株式会社日本自動車部品総合研究所 点火プラグ

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE2215276A1 (de) * 1972-03-29 1973-10-31 Daimler Benz Ag Zuendkerze fuer brennkraftmaschinen
US4211952A (en) * 1977-04-07 1980-07-08 Nippon Soken, Inc. Spark plug
EP0287080A1 (de) * 1987-04-16 1988-10-19 Nippondenso Co., Ltd. Zündkerze für Verbrennungsmotor

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0803950A1 (de) * 1996-04-25 1997-10-29 NGK Spark Plug Co. Ltd. Zündkerze für einen Verbrennungsmotor
US5877584A (en) * 1996-04-25 1999-03-02 Ngk Spark Plug Co., Ltd. Spark plug for an internal combustion engine
DE19950922A1 (de) * 1999-10-21 2001-04-26 Beru Ag Zündkerze

Also Published As

Publication number Publication date
JPH02181383A (ja) 1990-07-16
JP2805781B2 (ja) 1998-09-30
DE68917573T2 (de) 1994-12-15
EP0376147B1 (de) 1994-08-17
DE68917573D1 (de) 1994-09-22

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