Electric heating – Heating devices – Resistive element: igniter type
Patent
1995-06-12
1997-07-08
Jeffery, John A.
Electric heating
Heating devices
Resistive element: igniter type
123145A, 361266, 428633, F23Q 700
Patent
active
056457421
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a glow plug with a heating rod consisting of an inner pole and a glow tube in which there is a heating element which is electrically connected to the inner pole.
A glow plug of this type which is known for example from published German Patent Application 41 33 338, can be made in the form of a rod glow plug and can be used as a starting aid for an air-compressing internal combustion engine.
Glow plugs are moreover used for ignition support in heaters.
The problem in conventional known glow plugs of this type is that they do not satisfy future requirements for a short heat-up time, or shortening of the heat-up time must be achieved at the cost of reducing the service life of the glow plug.
The problem underlying the invention therefore consists in devising a glow plug of the aforementioned type which has a short heat-up time without adversely affecting its service life.
This problem is solved according to the invention by providing the glow plug at least in the area of its tip with a coating of ceramic material.
The ceramic coating according to the invention acts as a surface protection of the glow tube so that its wall thickness can be greatly reduced. The resulting lower mass leads to the glow plug according to the invention having a short heat-up time, i.e. rapid heat-up, by which faster starting readiness can be achieved in diesel motor vehicles with engines which are equipped with these glow plugs. In this case the extremely fast heat-up time is achieved without adversely affecting the service life of the glow plug.
The version according to the invention furthermore has the advantage that scaling off of the material of the glow tube with the short heat-up times, longer afterglow and high temperatures is prevented, by which it becomes possible to use glow tubes of a material of lower costs. This cost savings moreover arises due to the fact that the glow tube can have smaller wall thicknesses.
The coating provided according to the invention furthermore satisfies the requirement which exists in heating devices that the glowing tip of the heating rod must be electrically insulated from the glow current.
Finally, relative mass freedom of the tip of the heating rod or the heating rod itself for two-pole glow plugs, for example when installed in a protective tube in heaters, is achieved.
Below, one especially preferred embodiment of the invention is detailed using the pertinent drawing.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a partial cross-sectional view of a glow plug in accordance with a preferred embodiment of the invention; and
FIG. 1A is an enlarged view of the encircled detail A of FIG. 1.
DETAILED DESCRIPTION OF THE INVENTION
The embodiment of the glow plug according to the invention shown in the drawing comprises a housing in which heating rod 1 is located which consists of inner pole 2 for connection to the electric power supply and glow tube 5 in which heating element 3 is located which is electrically connected to inner pole 2. Heating element 3 which can consist of a heating and control coil, of which the control coil is connected to inner pole 2, is embedded in MgO filler 4 in glow tube 5.
Glow tube 5 has at least on its tip, a coating 6, 7 of ceramic material which consists in the embodiment shown in the drawing of subsurface or adhesive layer 6 of NiCrAlY, especially of Ni 22Cr 10Al 1Y or similar material and actual ceramic cover layer 7 which consists preferably of yttrium-stabilized zirconium dioxide mixed with Ni Cr Al Y. The mixing ratio between the zirconium dioxide and the admixtures is between 10 and 80% for ZrO2, especially 50:50.
Adhesive layer 6 which is applied directly to glow tube 5 has a thickness between 10 and 50 microns, especially between 20 and 30 microns. Cover layer 7 is provided on adhesive layer 6.
In a design of this type glow tube 5 can consist of the alloys conventionally used to date, for example, Inconel 600 or 601, however with a low wall thickness over its entire length or on its tip or of another especially more cost-favorable
REFERENCES:
patent: 4055705 (1977-10-01), Stecura et al.
patent: 4217138 (1980-08-01), Ito
patent: 4485151 (1984-11-01), Stecura
Delesky Hans
Schmidt Gabriele
Schmidt Karl-Heinz
BERU Ruprecht GmbH & Co. KG
Jeffery John A.
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