Classifications

• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
  • H05B3/00—Ohmic-resistance heating
  • H05B3/10—Heating elements characterised by the composition or nature of the materials or by the arrangement of the conductor
  • H05B3/12—Heating elements characterised by the composition or nature of the materials or by the arrangement of the conductor characterised by the composition or nature of the conductive material
  • H05B3/14—Heating elements characterised by the composition or nature of the materials or by the arrangement of the conductor characterised by the composition or nature of the conductive material the material being non-metallic
  • H05B3/141—Conductive ceramics, e.g. metal oxides, metal carbides, barium titanate, ferrites, zirconia, vitrous compounds
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
  • H05B3/00—Ohmic-resistance heating
  • H05B3/10—Heating elements characterised by the composition or nature of the materials or by the arrangement of the conductor
  • H05B3/12—Heating elements characterised by the composition or nature of the materials or by the arrangement of the conductor characterised by the composition or nature of the conductive material
  • H05B3/14—Heating elements characterised by the composition or nature of the materials or by the arrangement of the conductor characterised by the composition or nature of the conductive material the material being non-metallic
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
  • F23Q—IGNITION; EXTINGUISHING-DEVICES
  • F23Q7/00—Incandescent ignition; Igniters using electrically-produced heat, e.g. lighters for cigarettes; Electrically-heated glowing plugs
  • F23Q7/001—Glowing plugs for internal-combustion engines
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
  • F23Q—IGNITION; EXTINGUISHING-DEVICES
  • F23Q7/00—Incandescent ignition; Igniters using electrically-produced heat, e.g. lighters for cigarettes; Electrically-heated glowing plugs
  • F23Q7/001—Glowing plugs for internal-combustion engines
  • F23Q2007/004—Manufacturing or assembling methods
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
  • H05B2203/00—Aspects relating to Ohmic resistive heating covered by group H05B3/00
  • H05B2203/027—Heaters specially adapted for glow plug igniters

Definitions

• This invention relates to ceramic heater elements.
• this invention relates to ceramic heater elements, and methods of manufacture therefor, such as ceramic heaters used in high-temperature a glow plugs for diesel engines.
• Ceramic glow plugs having a multi-layered construction. Examples of such conventional glow plugs are described in United States Patent Nos. 4,742,209, 5,304,778 and 5,519,187.
• these glow plugs have a ceramic heater with a conductive core enclosed by insulative and resistive ceramic layers, respectively. The layers are separately cast and fitted together. The resulting green body is then sintered to form a ceramic heater.
• Such ceramic heaters suffer several drawbacks. Used in a glow plug, they experience cyclic heating and cooling, which results in high internal stresses at the interfacial junction between the ceramic layers, promoting eventual failure of the glow plugs. To reduce this failure rate, such ceramic heaters tend to be cycled at lower temperatures than would be optimal in a diesel engine.
• the internal stresses of a layered glow plug are mainly the result of differences in the coefficients of tliermal expansion between the differently composed layers.
• the different layers of the glow plug expand and contract at different rates. Further, residual stresses are the result of manufacture, particularly from uneven contraction in the cooling period which occurs below the plastic deformation state of the ceramic composition, and from non-uniform attachment between the layers.
• the present invention provides a ceramic heater element and a glow plug incorporating a novel heater element.
• the heater element has a base portion and a heater portion. Conductive, insulative and resistive layers extend through both the base and heater portions. An outer conductive layer is applied to the outside of the base portion to provide a highly conductive return path. This tends to limit the heating of the resistive layer in the base portion and results in better and more reliable heat concentration in the heater portion. A waterpro of non-conductive outer layer is provided over the outer surface of the heater element.
• the heater element can be assembled to form a glow plug for a diesel engine.
• the ceramic heater includes abase portion with a heater portion formed at one end.
• the heater portion has a lesser diameter than the base portion.
• the base portion and heater portion each having a conductive ceramic layer and a resistive ceramic layer, which are separated by an ins ⁇ lative ceramic layer except at a tip of the heater portion where they are electrically connected.
• the base portion further has an outer conductive ceramic layer in electrical contact with the resistive ceramic layer.
• a waterproof outer layer of non-electrically conductive ceramic extends over the base and the heater portions.
• An optional central conductive core can be included in this heater, which extends substantially the length of the base portion.
• a glow plug for a diesel engine employing the above-described heater element.
• the glow plug has a metallic housing, including a barrel and a tapered sleeve.
• a ceramic heater element having a base poition tapered to wedgingly fit within the sleeve, is mounted within the housing.
• the heater element has a heater portion formed at an end of the base portion.
• the heater portion has a lesser diameter than the base portion, and generally extends beyond the housing.
• the base portion and heater portion each having a conductive ceramic layer and a resistive ceramic layer, which are separated by an insulative ceramic layer except at a tip of the heater portion where they are electrically connected.
• the base portion further has an outer conductive ceramic layer in electrical contact with the resistive ceramic layer.
• a waterproof non-electrically conductive outer layer extends over the base and the heater portions.
• An optional central conductive core can be included in this heater, which extends substantially the length of the base portion.
• Figure 1 is a schematic cross sectional view of a ceramic heater element according to an embodiment of the present invention, sectioned along its longitudinal axis;
• Figure 2 is a schematic cross sectional view of the ceramic heater element according of Fig. 1, along the line A - A;
• Figure 3 is a schematic cross sectional view of the ceramic heater element according to Fig. 1, along the line B - B;
• Figure 4 is a cross section of a glow plug according to the present invention.
• Figure 5 is a cross section of a further embodiment of the heater element of the present invention.
• FIG. 1 A schematic view of a ceramic heater element according to a first embodiment of the present invention is shown in cross-section along its longitudinal axis in Fig. 1, and in cross-section along line A - A in Fig. 2.
• the heater element is not shown to scale and is generally designated at reference numeral 10.
• Element 10 consists of abase portion 20 and a heater portion 22.
• Base portion 20 and heater tip portion 22 form a generally cylindrical heater element that is thicker in diameter through base portion 20 and tapers to a thinner diameter heater portion 22.
• base portion 20 is typically sized to be received in a metal housing, including appropriate electrical contacts, to form a glow plug for a diesel engine. As described in U.S. Patent No.
• base portion 20 of heater element 10 can be so formed, but the present invention can be employed advantageously with any ceramic heater element, regardless of its particular shape and dimensions.
• heater portion 22 has a lesser diameter than base portion 20. This results in a higher resistance in heater portion 22, and, consequently, a higher heat output. Thus, heating of element 10 is ideally concentrated in heater portion 22.
• base portion 20 is formed of six layers of ceramic material. As is well known, the composition of the layers differs, particularly in the amount of conductive ceramic component such as MoSi 2 , such that the electrical conductivity of the different layers can be controlled. Beginning at the centre, base portion 20 consists of an inner electrically conductive core 24, an electrically conductive layer 26, an electrically insulative layer 28, an electrically resistive layer 30, an outer electrically conductive layer 32 and an outer insulative waterproof layer 38. Generally, base portion 20 also includes hole 34 that permits connection to an electrical lead (not shown) when element 10 is assembled as a glow plug. For the purposes of description, conductive layer 26 and resistive layer 30 are differentiated. However, as will be further- described below, these two layers have similar characteristics, and any heating ascribed to resistive layer 30 can be equally well accomplished in conductive layer 26.
• heater portion 22 is formed of four layers of ceramic material. Beginning again at the innermost layer, heater portion 22 consists of conductive layer 26, insulative layer 28, resistive layer 30 and an outer insulative waterproof layer 38. The distal end of heater portion 22 is formed into a tip 36 that forms an electrical connection between conductive layer 26 and resistive layer 30.
• the ceramic material forming the various layers is selected from the group comprising Si 3 N , Y 2 O 3 , silicon carbide, aluminum nitride, alumina, silica and zirconia. These non- conductive ceramic materials are then doped with one or more conductive components selected from the group comprising MoSi 2 , TiN, ZrN, TiCN and TiB 2 . The percent concentration of the conductive component, in conjunction with the layer thickness, determines the resulting conductivity of the ceramic material.
• a sintering additive from about 10 to about 0 percent by volume can also be included. The sintering additive includes yttrium, magnesia, calcium, hafnia and others of the Lanthanide group of elements.
• the conductive and non-conductive components are supplied as finely ground particles. Optimally, the particles can range in size from about 0.2 to about 0.8 microns.
• the finely ground components are mixed and suspended in a solvent, such as water, to form a slurry.
• a suitable defiocculant, such as ammonium polyacrylate. known commercially as DARVAN CTM can also be added.
• the non-conductive ceramic material is Si 3 N 4 and the conductive component is MoSi 2 .
• Inner core 24 can have 41 - 80 vol. % MoSi 2
• conductive layer 26 can have 30 - 45 vol. % MoSi 2
• insulative layer 28 and waterproof outer layer 38 can have 0 - 28 vol. % MoSi 25
• resistive layer 30 can have 30 - 45 vol. % MoSi 2
• outer layer 32 can have 41 - 80 vol. % MoSi,.
• heater element 10 can be formed of five layers, without a core. In this case, conductive la ⁇ 'er 26 also occupies the volume of conductive core 24.
• core 24 is presently believed to provide to heater element 10 is an improved conduction of electricity tlirough base portion 20 to concentrate heat development in heater portion
• heater element 10 can include a core that extends beyond the length of base portion 20. For example, for certain applications it can be desirable to have core 24 extend nearly to tip 36.
• Ceramic heater element 10 is preferably manufactured by slip casting, such as is described in U.S Patent Application No. 08/882,306, the contents of which are incorporated herein by reference. The method described therein is modified somewhat to incorporate the additional layers: inner core 24 and outer layer 32.
• An absorbent, tubular mold, open at both ends, is provided.
• the mold can be fabricated from plaster of Paris or any other suitable absorbent material.
• the mold is provided with a smaller inner diameter step to produce element
• successive layers of element 10 are added to the mold from the tip 36 end.
• the method commences by laying down outer waterproof insulative layer 38, then outer electrically conductive layer 32, and then forming resistive layer 30.
• insulative layer 28 is formed in the mold. It has been found, in a standard sized heater element, that insulative layer 28 needs to be at least 0.3 mm to provide an effective electrically insulative barrier between resistive layer 30 and conductive layer 26.
• conductive layer 26 is formed in a well known manner.
• Inner core 24 is then injected into the mold from the opposite end of the mold such that it extends substantially the length of base portion 20. Connecting hole 34 can be formed in inner core 24 at this time.
• tip 36 of the green body is reformed by, for example, applying low intensity vibrations from an ultrasonic wand to tip 36 before the green body is removed from the mold, The low intensity vibrations cause the particles at the tip to be blended into an electrically conductive tip joining the inner and outer volumes. Once the liquid phase has been substantially absorbed through the walls of the mold, the green body with a reformed tip is removed from the mold and allowed to air dry.
• the ceramic heater element 10 can be formed by commencing with resistive layer 30, and continuing as described above. Then prior to sintering the green bod ⁇ ', it is dipped into a conductive ceramic slurry to form outer layer 32. This results in very thin coating of conductive material that covers base portion 20. Next, the green body is dipped into an insulative ceramic body to form outer waterproof insulative layer. As is well known, the green ceramic body is then sintered and polished to produce element 10. Casting outer layer 32 is presently preferred, as greater control of the layer 32 thickness is achieved.
• element 10 can then be assembled to form a glow plug assembly 40, as described in the aforementioned U.S. Patent No. 5,880,432.
• Element 10 is inserted into a metallic housing 42 consistmg of a barrel 44 and a sleeve 46.
• Sleeve 46 is tapered to match the outer taper of base portion 20 such that element 10 is wedgingly held in place within housing 42.
• a conductive wire 48 is inserted into hole 34 of element 10. and element 10 and wire 48 are secured in place by filling barrel 44 with an epoxy, or other fixant suitable for operation in a corrosive, high temperature atmosphere. Barrel 44 is then sealed with connector cap 50.
• sleeve 46, and hence housing 42 is in electrical contact with ouler layer 32, while wire 48 is in electrical contact with inner core 24.
• an electrical potential is applied across housing 42 and conductive wire 48. This causes an electrical current to flow from conductive wire 48 tlirough conductive inner core 24 to conductive layer 26.
• the current then flows through resistive layer 30 at the exterior of heater portion 22, and returns along outer layer 32 to housing 42. As the current flows through resistive layer 30 in the region of heater portion 22, it heats heater portion 22 to a temperature sufficient for diesel fuel ignition.
• Experimental testing of element 10 has resulted in repeated cycling to heater temperatures in the range of 1500°C without failure of the element 24.
• the high conductivity of outer layer 32 results in little current flow tlirough the resistive layer 30 in the base portion 20, thus limiting the heating of the base portion, and improving the concentration of heat in the resistive layer 30 of heater portion 22.
• a ceramic heater element of the present invention is shown, and generally designated at reference numeral 60.
• This embodiment differs from the first embodiment in that it has no inner core. Instead conductive layer 26 fills the interior volume of element 10 and forms the inner core. Generally, this four layer ceramic heater element 60 relies on the conductive layer 26 to carry the electrical current to heater portion 22.
• the slightly less efficient resistivity of layer 26 results in slightly lower operating temperatures, typically in the range of 1300°C, but has the benefit of lowering the production costs of the ceramic heater elements.
• the ceramic heater element of the present invention has a number of advantages over the prior art.
• the four or five layer structure and and outer layer 32 result in a more efficient concentration of heat at heater portion 22, and enhances the stability and uniformity of the ceramic heater elements.
• the non-conductive waterproof outer layer 38 further enhances performance by protecting the heater element and minimizing the effects of atmospheric moisture on the electrical properties of the heater element. Consequently, this results in the manufacture of fewer rej ected pieces, thereby lowering production costs and increasing profit.
• the concentration of heat also results in a heater element that can be repeatedly cycled to approximately 1300 - 1500°C, which is a significant improvement over prior art ceramic heater elements which typically operate at 900 - 1100°C.

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• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Ceramic Engineering (AREA)
• Combustion & Propulsion (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Resistance Heating (AREA)
• Ceramic Capacitors (AREA)
• Production Of Multi-Layered Print Wiring Board (AREA)
• Ceramic Products (AREA)

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Citations (8)

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• 2000
  • 2000-10-06 JP JP2002507031A patent/JP4849765B2/ja not_active Expired - Lifetime
  • 2000-10-06 AU AU2000277653A patent/AU2000277653A1/en not_active Abandoned
  • 2000-10-06 CA CA002414687A patent/CA2414687C/en not_active Expired - Lifetime
  • 2000-10-06 WO PCT/CA2000/001147 patent/WO2002003759A1/en active IP Right Grant
  • 2000-10-06 AT AT00967456T patent/ATE270812T1/de not_active IP Right Cessation
  • 2000-10-06 EP EP00967456A patent/EP1300052B1/en not_active Expired - Lifetime
  • 2000-10-06 DE DE60012053T patent/DE60012053T2/de not_active Expired - Lifetime
  • 2000-10-06 KR KR1020027017286A patent/KR100750573B1/ko active IP Right Grant

Patent Citations (8)

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