Abstract: A method of making an ignition device and center wire assembly that includes first, second and third electrode members, a conductive seal, and a noise suppressing seal. The method locates the first electrode member at an axial end of the center wire assembly near a spark gap and the third electrode member at an axial end of the center wire assembly such that it receives an electrical ignition pulse and a second electrode member between the first and third electrode members. Furthermore, the method locates the conductive seal between the first and second electrode members and the noise suppressing seal between the second and third electrode members.

Abstract: A spark plug is provided which is constructed to ensure a higher degree of air-tightness. The spark plug includes a cylindrical metal housing within which an insulation porcelain is disposed. The housing has a hexagon head formed on an outer wall thereof and an annular chamber defined between itself and the insulation porcelain within which a sealing powder is disposed. The housing has an annular extension formed on the hexagon head. The annular extension is crimped inward to compress the sealing powder to enhance the air-tightness between the housing and the insulation porcelain. The annular extension has featured dimensions in order to ensure a desired degree of the air-tightness.

Abstract: A spark plug having a center electrode assembly that includes a center electrode and precious metal insert that is both mechanically interlocked and welded to the center electrode in a manner that permits trapped gases to escape from between the two components. Also disclosed is a method for manufacturing the same. During assembly, the precious metal insert is placed into a blind hole that extends axially into a lower end of the center electrode. Once in place, the center electrode is deformed around an enlarged head section of the insert to mechanically interlock the two components together. To further strengthen this attachment, the two components are welded together about their circumference. In one embodiment, the weld includes several interruptions that function as vapor vents for any gases that may be trapped. In other embodiments, a radially or an axially-extending vent hole is used in lieu of the weld interruptions.

Abstract: A spark plug comprising an insulator, on at least a part of a surface of the insulator being formed a marking layer and a glaze layer, wherein the marking layer is exposed on the surface of the insulator and has a composition as described herein.

Abstract: An optical sensor provides information about the burn of the fuel mixture in the combustion chamber of an internal combustion engine as well as the timing and waveform of the spark that ignites the fuel mixture in the combustion chamber. The optical sensor can be implemented as a stand-alone device, or incorporated into a spark plug.

Abstract: A spark plug center wire assembly that includes a noise suppressing conductive seal with improved isolation of the seal from the heat generated at the firing end of the spark plug. The center wire assembly includes a firing electrode, a conductive glass seal, an intermediate electrode, the noise suppressing glass seal, and a terminal electrode. By locating the firing electrode, conductive seal and intermediate electrode between the noise suppressing seal and the spark gap, the center wire assembly is able to utilize the noise suppression attributes of the suppressive seal, while distancing the seal from the high temperatures created during the combustion process. A method of manufacturing the same is also disclosed in which the two glass seals are formed by sequential firing operations.

Abstract: A method for manufacturing a spark plug which reduces the generation of spatters and the possibility of insufficient weld strength resulting from penetration depth insufficiency of a weld metal portion is disclosed. In accordance with the method, a chip joint face formation portion of a center electrode is formed from a heat-resistant alloy predominantly containing Fe or Ni. A noble metal chip is attached to a chip joint face of the chip joint face formation portion to thereby form a chip-attached assembly. A full-circled laser-beam weld metal portion is formed on the chip-attached assembly in such a manner as to intrude into the noble metal chip and into the chip joint face formation portion. A graded-index-type fiber optic cable is used as an optical transmission path extending between a laser beam generator and an optical emission section. A laser beam which is transmitted from the laser beam generator through the cable irradiates the chip-attached assembly while being condensed.

Abstract: In a spark plug for an internal combustion engine, an insulator is vided at its inside with a center electrode. A tubular housing is disposed to surround an outer periphery of the insulator. An annular space portion is provided between the housing and the outer periphery of the insulator. A powder filling is filled in the annular space portion so as to be formed as a filled portion therein. The powder filling is composed of a plurality of filling grains. 80 weight percent and over of the filling grains, before the powder filling is filled in the annular space, have a range from 100 to 1000 ?m in grain diameter, respectively.

Abstract: A high temperature material which consists of a chromium oxide forming iron alloy including: a) 12 to 28 wt % chromium, b) 0.01 to 0.4 wt % La, c) 0.2 to 1.0 wt % Mn, d) 0.05 to 0.4 wt % Ti, e) less than 0.2 wt % Si, f) less than 0.2 wt % Al, wherein, at temperatures of 700° C. to 950° C., the high temperature material is capable of forming a Mn Cr2O4 spinel phase. At a temperature of 700° C. to 950° on Mn, Cr2O4 the spinel phase formed protects a body, such as spark plug electrodes and other electrodes.

Abstract: A spark plug includes a ceramic component, whose surface is at least in part coated with a glaze, with the glaze containing 0.6% to 4% by weight of fluoride and 6% to 11.2% by weight of zinc oxide.

Abstract: An improved structure of a spark plug which provides higher durability of a joint of a noble metal chip to an electrode such as a center or a ground electrode. The joint is formed by laser welding. A fused portion made of materials of the noble metal chip and the electrode fused together by the laser welding is formed in the joint so that it may continue over at least half a circumference of a contact between the noble metal chip and the electrode without interfaces of welds, thereby enhancing the activity of the fused portion as a thermal stress absorber. A welding method is also provided.

Abstract: An ignition device, particularly a spark plug for internal combustion engines, permits improved corrosion protection. The ignition device includes an electrical connector and a tubular, metallic housing having a screw-in thread imprinted on it. At least one of the metallic components of the ignition device is provided at least partially with a protective coating made of a zinc/nickel alloy.

Abstract: Ir alloy firing tips are bonded on opposed surfaces of a center electrode and a ground electrode facing to a discharge gap. The configuration of a cross-sectional area of the Ir alloy firing tip taken along a plane perpendicular to the axis of the Ir alloy firing tip is out of round. In this cross-sectional area of this Ir alloy firing tip, when it is assumed that a circumscribed circle has a largest diameter A among virtual circles each contacting at least three portions of a visible outline of the cross-sectional area and an inscribed circle has a largest diameter B among inscribed circles each being coaxial with the circumscribed circle, a ratio of the diameter B to the diameter A (i.e., B/A) is equal to or larger than 0.8 and is less than 1.0.

Abstract: An electrode and spark plug for an internal combustion engine including an electrode of this type as a center electrode. The electrode includes an electrode base element made of a first material and an end section that is integrally joined to the electrode base element, with this end section including a first area that is integrally joined to the first material and is made of a platinum-containing material and including a second area that is integrally joined to the first area and is made of an iridium-containing and/or ruthenium-containing material. In a method for manufacturing an electrode of this type, a first recess is stamped in the electrode base element, a first preform is inserted into the first recess, the first preform is melted, thereby forming a first alloy, a second recess is stamped in an area of the first alloy, a second preform is inserted into the second recess, and the second preform is melted, thereby forming a second alloy.

Abstract: In a spark plug for an internal combustion engine oil is applied onto at least either the surface of an intermediate body portion of an insulator or the surface of an intermediate hole portion of a metallic shell, thereby forming an oil film. Since the oil film has a dielectric constant falling between those of the insulator and an ambient air layer, a great change in dielectric constant between the insulator and the ambient air layer is eased. Also, since the oil film is of liquid, the oil film smoothes a dent or protrusion or a fine defect such as crack present on the surface of the intermediate body portion of the insulator. Thus, electric field concentration is suppressed, thereby preventing dielectric breakdown caused by such a dent, protrusion or fine defect.

Abstract: An improved structure of a spark plug which provides higher durability and ignitability of a gaseous fuel. The spark plug consists of a center electrode, a ground electrode, a noble metal chip joined to a center electrode-opposed surface of the ground electrode by laser welding, and a fused portion that forms a weld of the noble metal chip and the ground electrode formed by materials of the ground electrode and the noble metal chip melted together. A sectional area of the noble metal chip traversing a length thereof is between 0.1 mm2 and 0.6 mm2. An unfused sectional area percentage that is a percentage of a sectional area of an unfused portion of a joined end of the noble metal chip within a range of a sectional area of the noble metal chip closest to the fused portion traversing the length of the noble metal chip is less than or equal to 50%.

Abstract: The present application is to provide a spark plug where a marking layer 2m under a glaze layer 2d can form a color stably, even if the Pb amount is decreased in the glaze layer. The glaze layer 2d is formed on an insulator 2 of the spark plug, and the marking layer 2m is formed under the glaze layer 2d. The glaze layer 2d contains, e.g., 1 to 25 mol % of a Zn component in terms of Zno and 5 mol % or lower, e.g., 1 mol % or lower of a Pb component in terms of PbO. On the other hand, the marking layer 2m is adjusted in kinds and amounts of metallic element components in such manners that a tint seen through the glaze layer 2d is 3 or lower in brightness specified by JIS:Z8721 as well as 3 or lower in chroma specified by JIS:Z8721, or 4 or lower in the brightness specified by JIS:Z8721 as well as 2 or lower in the chroma specified by JIS:Z8721.

Abstract: A spark plug 100 has a glaze layer 2d formed on a surface of an alumina based insulator 2 contains 1 mol % or less of a Pb component in terms of PbO. The glaze layer 2d comprises 35 to 55 mol % of a Si component in terms of SiO2; 15 to 35 mol % of a B component in terms of B2O3; 5 to 20 mol % of a Zn component in terms of ZnO; 0.5 to 20 mol % of a Ba component in terms of BaO; and 10 to 15 mol % in total of at least one alkaline metal component of Na, K and Li, in terms of Na2O, K2O and Li2O, respectively.

Abstract: An ignition device, in particular, a spark plug for Otto engines, includes an electric connection (11) and a tubular metal housing (13) with a screw-in thread (18) stamped on it. At least one of the metal components of the spark plug is provided with a paint coating that serves to protect the spark plug from corrosion.

Abstract: Reliability in connection between a chip and a base material (at least one of the central electrode and the ground electrode) of a spark plug is improved by forming a plurality of welding layers at connection between the chip and the base material in a distance increasing direction from the central electrode with overlap. With respect to section along the connection surface the sum of the sectional area of the first weld layer and the second weld layer at the overlap portion between the first and second weld layers is equal to or greater than 1.4 times the sectional are of the chip. A stress releasing layer of which linear expansion coefficient is between those of the chip and the base material may be provided between the chip and the base material for welding.

Abstract: A spark plug includes a shell on which a threaded shank having a thread and a tool attachment for installation in an internal combustion engine are situated, and an assembly shank of the shell running between the threaded shank and the tool attachment. The spark plug is dimensioned in such a way that the ratio of the sum of the threaded shank length and the assembly shank length to the sum of the assembly shank diameter and the thread diameter is between 0.95 and 1.55.

Abstract: A spark plug configured such that a metallic shell is joined to an insulator through crimping. The metallic shell is firmly joined to the insulator by means of a sufficient fastening force even when the diameter of the spark plug is reduced, to thereby enhance gastightness and vibration resistance. A method for manufacturing the spark plug is also disclosed.

Abstract: In a spark plug (100), at least one side face of the ground electrode (4) is made of an electrode base material comprising an Ni alloy containing 21-25% by mass of Cr, 1-2% by mass of Al, 7-20% by mass of Fe and 58-71% by mass of Ni. The noble metal wear resistant portion (32) is joined to the electrode base material via a welding portion (W). When the linear expansion coefficients at 800 K of the noble metal constituting the noble metal wear resistant portion (32) and the electrode base material are represented by &agr;1 and &agr;2, respectively, &Dgr;&agr;≡&agr;2−&agr;1 is adjusted to be 4.55×10−6/K or less. The outer diameter of the noble material wear resistant portion (32) is set from 0.6 mm to 1.5 mm.

Abstract: A spark plug is provided which consists of a center electrode retained within a metal shell and a ground electrode including a noble metal-made tip and a body joined to the metal shell. The noble metal-made tip is connected to the body through a fused portion that is a weld between the body and the noble metal-made tip. Portions of the noble metal-made tip and the fused portion closest to the tip of the center electrode are located within a range defined by a first line extending from the tip of the center electrode in a lateral direction of the center electrode and a second line extending from a portion of the center electrode closest to the ground electrode in a longitudinal direction of the center electrode so that they do not overlap with the tip of the center electrode both in the lateral and longitudinal directions of the center electrode.

Abstract: The seal between the insulator and the center electrode is to be improved in a spark plug for an internal combustion engine comprising a shell (12), an insulator (16) located in the shell and composed of a sintered ceramic material, as well as a center electrode (18) and a terminal stud (22) that have an electrically conductive connection with each other and are located in the insulator. For this purpose, it is provided that a cermet (28) abuts the center electrode, the ceramic phase of which is composed of the same or a similar material as the insulator, and the metallic phase of which is composed of a material having good electrical conductivity. Since the material properties of the cermet are similar to those of the insulator—the thermal expansion, in particular, is same—a particularly good seal is created between the cermet and insulating body.

Abstract: In a glow plug and a spark plug, the surface of a main metal shell is coated with a chromate film in which the quantity of trivalent chrome is 95 wt % or more of the contained chrome components and which has a thickness of 0.2 &mgr;m to 0.5 &mgr;m.

Abstract: A resistor-containing spark plug 100 has an alumina insulator 2 coated with a glaze layer 2d, the glaze layer 2d has a lead component content of 1 mol % or lower in terms of PbO and containing a silicon component, a boron component, a zinc and/or alkaline earth metal component, and an alkali metal component. The insulator has, in an axially central position thereof, a projection part protruding from the outer circumferential surface thereof and extending in a circumferential direction. That main body of the insulator which is located adjacent to the projection part on the rear side thereof, which is the side opposite to the front side facing the center electrode in the axial direction, has a base portion having a cylindrical outer circumference. The outer circumference of the base portion is covered with the glaze layer which, when examined by the method as provided for in JIS B 0601, gives a surface roughness curve having a maximum height Ry of 10 &mgr;m or smaller.

Abstract: In a spark plug, a complex chromate coat 42 that contains a chromium component and a phosphorus component as cationic components, at least 90 wt % of the chromium component being trivalent chromium and the phosphorus component being present in an amount of 1 to 15 wt % as calculated for PO4, is formed on the surface of the galvanized main metal shell 1 of a spark plug. If a silicon component is substituted for the phosphorus component, it may be present in an amount of 5 to 75 wt % as calculated for SiO2.

Abstract: A spark plug, which has an electrode, an electrode segment being provided at the one end segment of the electrode. The electrode segment has an alloy containing copper or an alloy containing platinum and rhodium.

Abstract: A spark plug comprising: a center electrode; a metal shell; and an alumina ceramic insulator disposed between the center electrode and the metal shell, wherein at least part of the surface of the insulator is covered with a glaze layer comprising oxides, the glaze layer comprising: 1 mol % or less of a Pb component in terms of PbO; 40 to 60 mol % of a Si component in terms of SiO2; 20 to 40 mol % of a B component in terms of B2O3; 0.5 to 25 mol % of a Zn component in terms of ZnO; 0.5 to 15 mol % in total of at least one of Ba and Sr components in terms of BaO and SrO, respectively; 2 to 12 mol % in total of at least one alkaline metal component of Na, K and Li, in terms of Na2O, K2O, and Li2O, respectively, wherein K is essential; and 0.

Abstract: A spark plug for an internal combustion engine includes a middle electrode which has an electrode base body (5) with an end face (51) oriented toward the combustion chamber, to which end face a precious metal platelet (8) is attached. An end section (15) of the electrode base body oriented toward the combustion chamber is formed in the shape of a truncated cone. The precious metal platelet (8) is likewise formed in the shape of a truncated cone and the diameter of the end face (52) of the electrode base body oriented toward the combustion chamber corresponds to the diameter of the end face (84) of the precious metal platelet oriented away from the combustion chamber. A method for producing middle electrodes for a spark plug of an internal combustion engine is also proposed.

Abstract: In a glow plug configured such that a metallic, tubular member having a heater fixedly provided therein is joined to a metallic shell, an external-thread portion is formed on the outer circumferential surface of the metallic shell so as to allow the glow plug to be screwed into a plug-mounting hole formed in an engine head. An annular protrusion is formed on the outer circumferential surface of the metallic, tubular member in such a manner as to protrude radially outward, to annularly extend in the circumferential direction, and to be located in the vicinity of a distal end of the metallic shell. A distally-facing end face of the annular protrusion abuts an annular seat face in the mounting hole, and the metallic, tubular member and the metallic shell are joined such that a distal end face of the metallic shell abuts a rearward-facing end face of the annular protrusion.

Abstract: A spark plug fabricating method and a spark plug fabricated by the same are provided. The spark plug is equipped with a piezoelectric sensor working to measure the pressure of combustion of fuel in an engine and required to apply a given preload to the piezoelectric sensor at all the time. The piezoelectric sensor is disposed within a holder and retained between the holder and a porcelain insulator. The fabrication method includes the steps of pressing the holder to apply a required preload to the piezoelectric sensor in a longitudinal direction of the porcelain insulator and joining the holder to a metal shell while maintaining the preload applied to the piezoelectric sensor as it is.

Abstract: A spark plug 100 is configured such that an insulator 2 is formed of alumina ceramic, and the diameter of a through-hole 6 is not greater than 4 mm as measured at a position where conductive seal materials 16 and 17 are disposed. The coefficient of linear expansion of the conductive seal materials 16 and 17 is adjusted to not greater than 6.5×10−6/° C.

Abstract: A method for manufacturing a starting element, in particular a sheathed-element glow plug, for the combustion process in an internal combustion engine having a ceramic element (1, 3) is proposed, which substantially improves the glazing of the ceramic element (1, 3). According to the present invention, this is achieved by a dry glaze (2) being applied on the ceramic element (1, 3).

Abstract: An earth electrode is formed on the brim surface of the plug insulator and on the outer surface of the middle portion of the plug insulator along the axial direction. The earth electrode connected with one side of the combustion pressure sensor is provided on a whole surface opposite to a combustion pressure signal electrode. The earth electrode works also a shield member for shielding the high frequency noise generated inside the insulator. A part of the outer side of the earth electrode is covered by an insulating layer for insulating the earth electrode from the combustion pressure signal electrode. The combustion pressure sensor held between the insulator brim and electrode brim is given a prescribed compression load by a metal cylindrical bolt which presses down the electrode brim of the toward the combustion pressure sensor.

Abstract: A pencil ignition coil assembly module (40) that has a frusto-conically tapered core (46) and encapsulation (280) surrounding the side of the core. Features (216, 230, 234) center the core to a bobbin 48. A retainer (240, 240A) captures the core within the bobbin.

Abstract: A spark plug has a central electrode, an insulator surrounding the central electrode and a metallic shell retaining therein the insulator and provided with no thread thereon. The spark plug is clearance fitted in a plug hole of a cylinder head, without being screwed into the plug hole, in such a manner that a front end portion of the metallic shell is accommodated in a front end section of the plug hole with a clearance therebetween provided with a sealant so as to transmit heat from the spark plug to the cylinder head. The clearance is preferably given by the following expression: 0.005≦D−d1≦0.05, where D is an inner diameter (mm) of the front end section and d1 is an outer diameter (mm) of the front end portion. By this, the spark plug can be easily attached to the cylinder head and attain improved heat resistance.

Abstract: A spark plug includes: a metal shell defining a front side having an outer periphery formed with a screw section which has a nominal size smaller than or equal to M12; a center electrode; a conductive seal layer; a terminal metal fitting fixed to the center electrode via the conductive seal layer; and an insulator formed with a through hole. The terminal metal fitting has a Vickers hardness in a range from 150-300 Hv. The terminal metal fitting includes: a front end section having an outer diameter, and embedded in the conductive seal layer, and a small diameter section disposed on a rear side of the front end section and having an outer diameter which is smaller than the outer diameter of the front end section. The through hole has an inner diameter different from the outer diameter of the small diameter section in a range from 1.0-1.4 mm.

Abstract: A spark plug includes a sparking electrode with a firing tip and a ground electrode. The ground electrode includes a toroidal member, having a convex outer surface, coupled to a support portion of a sleeve of the ground electrode. The toroidal member forms an annular curve disposed generally transverse to and having a radial center coinciding with a central axis of the insulator body, whereby each differential segment of the toroidal member radially thereabout is generally equidistant to the firing tip. The toroidal member is a closest portion of the ground electrode relative to the firing tip. At least a portion of the outer surface of the toroidal member opposing the firing tip has a radius of curvature of about that of the firing tip for providing a spark path of least from the firing tip to a point of contact on the opposing surface defined by the toroidal member.

Abstract: A spark plug includes a shell on which a threaded shank having a thread and a tool attachment for installation in an internal combustion engine are situated, and an assembly shank of the shell running between the threaded shank and the tool attachment. The spark plug is dimensioned in such a way that the ratio of the sum of the threaded shank length and the assembly shank length to the sum of the assembly shank diameter and the thread diameter is between 0.95 and 1.55.

Abstract: Process for producing a middle electrode with precious metal reinforcement, a middle electrode being used with an ignition tip which is tapered relative to the middle electrode body, such that a precious metal wire with a cross section which corresponds to the tapered ignition tip is welded flat onto the tapered ignition tip and such that this precious metal wire is cut off at the desired height, with a sharp edge.

Abstract: A plasma generating apparatus comprises a pair of electrodes consisting of an electrode connected to an AC power source and a grounded electrode. An inorganic dielectric substance containing barium titanate as a principal component is filled between the electrodes. It is possible to generate a stable and uniform glow discharge under the atmospheric pressure at low cost by applying a considerably low voltage between said electrodes.

Abstract: An ignition device, particularly a spark plug for internal combustion engines, permits improved corrosion protection. The ignition device includes an electrical connector and a tubular, metallic housing having a screw-in thread imprinted on it. At least one of the metallic components of the ignition device is provided at least partially with a protective coating made of a zinc/nickel alloy.

Abstract: In an ignition device for an internal combustion engine which is mounted in a cylinder head in a state where a spark plug and an ignition coil are integrated with each other, the plug side tube section is made of ceramics and internally accommodates a center electrode and the coil side tube section is made of ceramics, with one of a primary winding and a secondary winding being wound around the coil side tube section. The plug side tube section and the coil side tube section are constructed as separate bodies and then combined with each other. This shortens the overall lengths of both the tube sections, thus preventing the occurrence of cracks or bends at calcining and improving the dimension accuracy after the calcining.

Abstract: A ceramic sheathed-element glow plug is proposed in which a metallic tubular holder holds a ceramic U-shaped heating device in a cantilevered fashion at its combustion chamber side end and has a terminal stud for applying a voltage to the ceramic heating device on the end remote from the combustion chamber. At its end enclosed by the holder, the ceramic heating device has a segment of greatest diameter and is coated with an insulating layer which has recesses for an electrical contacting. One recess is provided at the end of the ceramic heating device remote from the combustion chamber and a second recess is provided on the external wall of the ceramic heating device. A for an electrically conductive sealing compound is provided between the external wall of the ceramic heating device and the internal wall of the holder.

Abstract: The spark plug body includes radially extending stops which limit the movement of the spark plug body in one direction with respect to an aperture through a around plane surface. The spark plug body further includes bosses radially extending from a section of reduced diameter wherein slots are formed between the radially extending bosses and a ring-shaped transverses floor which is positioned to be coplanar with the ground plane surface. The prongs of a ground fastener extend though the slots thereby securing the spark plug body with respect to the ground plane surface. Additionally, the ground fastener includes a spark gap portion which is positioned with respect to the tip of the spark plug thereby precisely forming a gap and forming the electrical connection between the spark gap and the ground plane surface.

Abstract: A spark plug having a tip composed of an iridium alloy essentially consisting of iridium is resistance welded through a relieving layer to a front end of a center electrode having an iron-based alloy and a facing portion of a ground electrode and wherein the material of the relieving layer has a coefficient of linear expansion between the iridium alloy and the iron-based alloy and has a Young's modulus of elasticity smaller than that of the two alloys.

Abstract: A spark plug includes: a central electrode; an insulator surrounding the central electrode radially; a metallic shell surrounding the insulator radially; and a ground electrode having a first end connected to the metallic shell and a second end defining a side face. The ground electrode is so bent that the side face of the second end faces the central electrode. The ground electrode contains: a nickel in a range from 58% to 71% by weight, a chromium in a range from 21% to 25% by weight, an iron in a range from 7% to 20% by weight, and an aluminum in a range from 1% to 2% by weight. The ground electrode has a Vickers hardness in a range from Hv 140 to Hv 220 through a Vickers hardness test specified in Japanese Industrial Standard Z2244. A load 9.8 N is applied to the ground electrode in the hardness test.

Abstract: In a spark plug, whose shell is provided with an eccentrically positioned, full-length, longitudinal bore designed to hold an insulating element, parts of the shell having varying wall thicknesses and a pressure measuring device being located in a part of greater wall thickness. In order to simplify connection with the ignition cable or coil, respectively, and to avoid breakage of the insulator, the spark plug insulator is configured as a multi-piece element and comprise at least an upper piece carrying the high voltage connector, a lower piece adjacent to the combustion chamber, and an insulating intermediate element of flexible material, which is placed between the upper and the lower piece of the insulator.