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
  • H01T13/50—Sparking plugs having means for ionisation of gap
• • 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

Definitions

• the present invention relates, in general, radiofrequency plasma candles. More particularly, the invention relates to a spark plug, referred to as a radiofrequency plasma, intended to equip a combustion chamber of an internal combustion engine, and comprising:
• annular base of main axis D formed in a first conducting material and having first and second ends, and an extreme circular surface having a principal axis of symmetry D located at the first end of the base; a central electrode formed in a second conductive material, extending along the main axis D and having an inner portion disposed within said annular base and an outer portion disposed outside said annular base, to a larger extent; near the first extremity of the base of the second; an electrically insulating piece of annular shape extending at least around the inner portion of the central electrode so as to be interposed between the base and the electrode, this insulating part covering only a part of the outer portion of the central electrode so that the portion of the outer portion not covered is in contact with a gas mixture surrounding the candle.
• the ignition of gasoline internal combustion engines consisting of initiating the combustion of an air-fuel mixture in a combustion chamber of said engine, is relatively well controlled in current engines.
• the car manufacturers have developed spark ignition engines capable of operating with poor carbide mixtures, that is to say having an excess of air relative to the amount of fuel injected.
• Ignition of a fuel-poor mixture is, however, difficult to control. For this, and in order to increase the probability of successful ignition, it is necessary to have more fuel-rich mixtures around the candle at the moment the spark occurs.
• Such candles are described in particular in patent applications FR97-14799, FR99-09473 and FR00-13821. Such candles generate sparks of large sizes from reduced potential differences.
• the surface spark plugs have a dielectric (insulating part) separating the electrodes (one electrode being the annular base and the other electrode being the central electrode) in the zone where the distance separating them is the lowest; the sparks formed between the electrodes are thus guided on the surface of the dielectric.
• These candles amplify the inter-electrode field on the surface of the dielectric.
• the elementary capacities are progressively formed by the dielectric and an underlying electrode.
• the candles generate a spark propagating along the surface of the insulator in areas where the electric field in the air / gas mixture is the strongest.
• the present invention therefore aims to provide a spark plug which when assembled in a combustion chamber increases the probability of ignition of the mixture surrounding the candle.
• the spark plug of the invention which is also in accordance with the generic definition given in the preamble defined above, is essentially characterized in that the insulating piece has an annular shoulder concealing the entire circular end surface of the base relative to the uncoated portion of the electrode.
• the central electrode (following a path passing to the surface of the insulating part) is particularly important since it is greater than the minimum dimension of the extreme circular surface (ie the diameter of this circular surface); - And secondly the central electrode and the base are separated by the insulating part and are not in relation to one another.
• the spark plug according to the invention when the spark plug according to the invention is assembled in a vehicle combustion chamber, with the part of the central electrode not covered by the insulator, arranged inside the chamber, and with the base assembled in the thickness of the chamber wall, no electric arc can occur between the base and the central electrode. Indeed access to the base from the uncoated portion of the central electrode is prevented by the presence of 1 'insulator.
• the spark plug according to the invention when subjected to a radio frequency excitation, ie an alternating voltage between the base and the central electrode (for example said alternating voltage being greater than 5kV and having a frequency higher than 1 MHz) forms a branched plasma near the central electrode and not an electric arc. It is understood that this given voltage and frequency is suitable for creating a plasma in a gaseous mixture having a molar density greater than 5 * 10 -2 mol / L.
• plasma or branched plasma refers to the simultaneous generation of at least several lines or ionization paths in a given gaseous volume, their branches being moreover omnidirectional.
• volume plasma involves heating up the entire volume in which it is to be generated
• the branched plasma only requires the heating in the path of the sparks formed.
• the energy required for a branched plasma is significantly less than that required by a volume plasma.
• the branched plasma generated by the candle according to the invention is generated at a distance from the insulating part, towards the walls of the chamber which are opposite the central electrode, which makes it possible to reduce the probability of generation of an arc with the base and allows correlatively reduce the wear of the electrodes.
• the plasma has the advantage of having a large number of ionization paths or sparks in a large volume of gas located around the central electrode which increases the probability of ignition of the mixture containing oxidant.
• a difference between an electric arc and a branched plasma is that: the arc consists of a single chain of ionized gas molecules extending directly between the electrodes and allows electrons to be transferred from one electrode to the other to reduce the difference in electrical potential existing between these electrodes energized while; the plasma produced according to the invention is a set of multiple chains of ionized molecules of gas extending disorderedly around the exciter electrode and issuing from said electrode. These multiple chains can alternately transfer electrons between said electrode and the air located nearby and vice versa.
• the formation of a spark is initiated by the tearing out of the middle (gas mixture) of a few electrons subjected to a large electric field.
• electrons of an electrode are accelerated by the electrostatic forces generated between the electrodes and collide with the gaseous mixture containing air.
• the portion of the electrode that experiences the largest electrostatic field (usually an angle of one electrode or tip near the other electrode) is the starting point of the first avalanche.
• the molecules of the air are heated and release an electron and a photon ionizing in their turn other molecules of air.
• a chain reaction ionizes the air when applying a large voltage between electrodes separated by an insulator.
• the ionized air around the central electrode has a potential close to this central electrode and behaves as an extension of it.
• the electric field is amplified upstream of the front and promotes the creation of new avalanches.
• the phenomenon tends to self-maintain to create around the central electrode a conductive ionized gaseous mass in the direction of the walls of the chamber.
• the candle of the invention is put under AC voltage which makes it possible to vary the potential existing between the central electrode and the base / chamber, this potential being reversible. At each alternation of potential / polarity, the electrons are more and more accelerated in opposite directions.
• a polarization wave thus propagates oscillatoryly at the frequency of the excitation, recovering at each period the expenses deposited in the previous period. Each alternation then produces a propagation of the wave greater than the preceding one; it is thus possible with the candle of the invention thus fed to obtain relatively large spark amplitudes with voltages between electrode and relatively large cap.
• the radiofrequency excitation of such a candle makes it possible moreover by avoiding the arcs to suppress the breakdown voltage variations between successive cycles.
• the extreme circular surface of the base to bear against a complementary bearing surface of the shoulder of the insulating part.
• This feature makes it possible to eliminate the space between the insulating part and the base, so the heat associated with the presence of a flame triggered by the plasma can be dissipated to the base which prevents overheating of the ceramic.
• the insulating part has a minimum thickness located inside said base, and the shoulder of the insulating part has a shoulder thickness greater than or equal to half of said minimum thickness.
• This feature prevents the junction between the uncovered portion of the central electrode and therefore the air / ceramic / central electrode junction is too close to the base. If this part not covered with the electrode or more precisely this junction was too close to the base it could constitute a surface spark emission zone.
• the base, the electrically insulating part, and the electrode central are parts of revolution having as axis of common symmetry the main axis D.
• the relative positioning accuracy of the constituents of the candle with respect to a common axis of symmetry makes it possible to center the branched plasma around this axis D and the central electrode, which facilitates the location of the zone of the combustion chamber in which sparks occur.
• the annular base is in the form of a cylindrical tube comprising at the first end of the base an internal chamfer coming into contact with the extreme circular surface, this internal chamfer being in contact with a complementary chamfer formed on a portion of the insulating part.
• the inner chamfer has a cross section, in a plane parallel to the main axis D, of rounded shape. It is also possible to ensure that the annular shoulder has an end remote from the annular base at the outer periphery of which is formed a rounded peripheral chamfer, coaxial with the main axis D. This peripheral chamfer reduces or eliminates the presence of sharp angle, at the outer periphery of the annular piece, at the end of the annular shoulder.
• Figure 1 shows a candle described in the applications for French patents FR03-10766, FR03-10767, FR03-10768 filed by the Applicant and not yet published;
• Figures 2A, 2B and 2C show embodiments of the candle according to the invention.
• the candle 1 of Figure 1 is a candle developed by the applicant to be used as plasma generation candle. This candle is the subject of patent applications not yet published at the filing date of this application.
• This candle comprises a central cylindrical electrode 7 having an axis of symmetry D, a portion of which, said internal portion, is disposed inside and at a distance an annular base 3 which in the form of a cylindrical tube of axis D.
• An insulating piece of annular shape is also arranged partly inside the annular base, around the central electrode, so as to separate the base of the central electrode 7.
• the insulating part, the central electrode and the base 3 are parts of revolution oriented along the axis D.
• the central electrode 7 has an uncoated portion 16 that is not surrounded by the electrically insulating piece 10 and not surrounded by the base 3, this uncovered portion 16 being disposed inside the combustion chamber 2 of the engine.
• the base 3 has an outer circular surface in the form of a flat disk perforated at its center and having the axis of symmetry axis D and being arranged perpendicular to this axis D.
• the base 3 has a connection with the wall of the chamber 2 which is usually a thread of the base in a hole made through the wall.
• the base of the candle thus assembled with the wall of the chamber 2 is at iso electric potential with this wall, that is to say at an electric potential of mass.
• the central electrode When the central electrode is supplied with AC voltage centered around the ground potential, this voltage being of a frequency between 1 and 1 MHz, the electrons located near the tip 17 of the central electrode move either from the electrode to the walls of the chamber through the gaseous mixture surrounding the chamber, or the gas mixture to the electrode. In both cases, the electrical alternation is such that an electron does not have time to go from the central electrode to the wall of the chamber.
• the air can thus be ionized without there being a real electric discharge between the two electrical terminals constituted by the central electrode 7 and the wall of the chamber 2. This ionization creates a plasma located around the tip 17 of the central electrode which concentrates the electric charges in movement around a small volume of exchange.
• the candles of these figures have all the characteristics described for the candle with reference to Figure 1, but also have a shoulder 11 formed on the insulating part 10 and obscuring the outer circular surface 6 of the base 3.
• This shoulder 11 increases the distance, passing through the gaseous mixture, between the electrode and the base, thereby avoiding the creation of arcs between the central electrode 17 and the base 3.
• the shoulder of the insulating part 10 of Figure 2A is a shoulder having in longitudinal section right angles which can create concentrations of loads and mechanical stresses.
• the candles of Figures 2B and 2C have at the first end 4 of base 3, an inner bevel 13.
• the insulating part 10 has a complementary chamfer 14 coming into contact against the inner bevel 13. This important contact surface allows to evacuate the heat of the insulating part towards the base which prolongs the average life of the candle.
• the spark plug according to the invention of FIG. 2C has a rounded peripheral chamfer 15 formed on the annular shoulder 11, at the location of the shoulder which is the furthest axially distant from the base 3.
• This shoulder makes it possible to avoid a right angle at the shoulder, on the path passing through the gaseous mixture, between the tip 17 and the annular base 3. This rounding reduces the risk of creating an arc.
• the first and second conductive materials which are the respective materials of the central electrode and the base 3 are, according to a particular embodiment of the invention, identical to each other. These materials are metallic materials such as copper alloys. According to a particular embodiment of the invention, the end of the central electrode 7 may consist of a copper core surrounded by a nickel sheath.
• the insulation material is preferably a ceramic having a breakdown voltage greater than 20 Kv / mm.

Landscapes

• Spark Plugs (AREA)
• Ignition Installations For Internal Combustion Engines (AREA)
• Percussion Or Vibration Massage (AREA)
• Absorbent Articles And Supports Therefor (AREA)
• Plasma Technology (AREA)
• Coating By Spraying Or Casting (AREA)

Priority Applications (1)

Applications Claiming Priority (2)

Publications (2)

Family

ID=34951956

Family Applications (1)

Country Status (12)

Cited By (1)

Families Citing this family (20)

Family Cites Families (15)

• 2004
  • 2004-11-16 FR FR0412153A patent/FR2878086B1/fr not_active Expired - Fee Related
• 2005
  • 2005-10-27 CN CN2005800391080A patent/CN101057379B/zh not_active Expired - Fee Related
  • 2005-10-27 JP JP2007540687A patent/JP5062629B2/ja not_active Expired - Fee Related
  • 2005-10-27 WO PCT/FR2005/050909 patent/WO2006054009A1/fr not_active Ceased
  • 2005-10-27 PL PL05815563T patent/PL1815570T3/pl unknown
  • 2005-10-27 RU RU2007122515/06A patent/RU2352041C1/ru not_active IP Right Cessation
  • 2005-10-27 DE DE602005020345T patent/DE602005020345D1/de not_active Expired - Lifetime
  • 2005-10-27 KR KR1020077011716A patent/KR101110436B1/ko not_active Expired - Fee Related
  • 2005-10-27 AT AT05815563T patent/ATE463062T1/de not_active IP Right Cessation
  • 2005-10-27 EP EP05815563A patent/EP1815570B1/de not_active Expired - Lifetime
  • 2005-10-27 ES ES05815563T patent/ES2343362T3/es not_active Expired - Lifetime
  • 2005-10-27 US US11/719,403 patent/US7741761B2/en not_active Expired - Fee Related

Non-Patent Citations (1)

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