GB2332021A

GB2332021A - An iridium coated electrode for an igniter device

Info

Publication number: GB2332021A
Application number: GB9725731A
Authority: GB
Inventors: Michael Charles Lyons
Original assignee: FLASHPOINT INTERNATIONAL LIMIT; FLASHPOINT SPARK PLUGS Ltd
Current assignee: FLASHPOINT INTERNATIONAL LIMIT; FLASHPOINT SPARK PLUGS Ltd
Priority date: 1997-12-04
Filing date: 1997-12-04
Publication date: 1999-06-09
Also published as: GB9725731D0

Abstract

An igniter device comprises a metallic body 2, a ceramic insulator 4, a central electrode 5 and an earth electrode 7; at least one of the electrodes having a coating of iridium 8 to increase the electrode's corrosion and erosion resistance. The coating 8 may be either pure iridium metal or an iridium alloy and may be deposited by electrostatic powder coating. The electrode may have a copper core surrounded by a nickel chromium layer which is then coated in the iridium. The igniter may be used for a variety of applications eg a spark plug in a petrol engine, a glow plug in a diesel engine, an igniter in an oven, a boiler etc.

Description

1 IGNITER DEVICE 2332021 The invention relates to long life electrodes for

use in igniter devices, eg heater plugs, glow plugs, igniters, spark plugs, overhead earth wires and side wires for use in industrial, domestic and automotive applications such as ovens, boilers, incinerators, petrol engines, diesel engines or aircraft engines.

These known igniter devices are of the type which comprise a ceramic insulator, by which an electrode is supported and an earth wire; a spark discharge gap is formed between the insulated electrode and the earth wire. Such igniter devices are used to ignite fuel in automobile petrol and diesel engines, aircraft engines, central heating boilers, incinerators, ovens and in many other applications.

Due to the high temperatures and the effect of carbon deposits, the components of these devices erode, with the result that the spark discharge gap has to be adjusted frequently and eventually the device has to be replaced completely. Platinum-iridium alloys have been used for the electrodes in spark plugs for some applications as these are very resistant to fouling, however such alloys are very expensive and such spark plugs are therefore not suitable for general use.

The object of the invention is to provide an igniter device that is resistant to corrosion but that is relatively inexpensive to manufacture and is suitable for general industrial, domestic or automotive use.

1- 2 1 In one aspect, the invention provides an igniter device suitable for use in igniting fuel comprising an insulator resistant to high temperatures, an electrode supported by the insulator and an earth conductor, wherein the electrode comprises an electrode base material, the earth conductor comprises an earth conductor base material and a coating comprising iridium is deposited on the surface of the base material of at least one of the electrode and the earth conductor.

The insulator must be resistant to temperatures likely to be encountered in 10 use and is conveniently a ceramic insulator.

Preferably the base material comprises a nickel/chromium alloy or other electrically conductive material generally used for such electrodes or earth conductors, eg wire.

Preferably the iridium coating comprises iridium metal. Alternatively the coating may comprise an iridium alloy.

Preferably both the electrode and the earth conductor are coated with the iridium coating.

Preferably the iridium coating is deposited by electrostatic powder coating. Alternatively the iridium coating may be deposited by any suitable process.

Advantageously, especially for spark plugs, the electrode may be formed with a core of copper metal, coated with a base material such as nickel/chromium and an iridium coating.

i 3 Advantageously the electrodes and earthwires may be formed by coating a nickel/chrornium alloy base material or nickel and/or steel or any suitable base metal with an iridium coating.

In another aspect, the invention provides an electrode suitable for use in an igniter in accordance with the invention comprising a base material and a coating comprising iridium deposited on the base material.

The invention will now be described, by way of example only, by 10 reference to the accompanying drawings, of which:

Figure 1 shows, in side view, an automobile spark plug in one embodiment of the invention; Figure 2 shows, in side view, a domestic boiler igniter in a further 15 embodiment of the invention; and Figure 3 shows, in cross section, an end portion part broken away of a spark plug showing one embodiment of an electrode embodying the invention.

As shown in Figure 1, an igniter device in accordance with one embodiment of the invention comprises a spark plug 1. The spark plug 1 comprises a metallic body 2 having a screw thread 3 for fitting into the spark plug recess of an engine (not shown). A ceramic insulator 4 is mounted on the end of the body 2 and an electrode 5 is mounted on the insulator 4. The electrode 5 comprises a nickel/chromium base coated with iridium 6.

4 An earthwire 7 is attached to the body 2.

comprises a nickel/chromium base coated with iridium 8.

The earthwire similarly Before assembly of the spark plug 1, the electrode 5 and earthwire 7 are prepared by pretreating the bases electrostatically coating the bases with iridium powder. There is thus formed an iridium coating 6, 8 on the electrode 5 and the eathwire 7.

An alternative embodiment of the invention is shown in Figure 2. In this 10 embodiment the igniter device comprises a domestic boiler igniter 20, for use in, for example, a central heating boiler (not shown). As in Figure 1, the device comprises a body 22 with a ceramic insulator 24 mounted on the end of the body 22. An electrode 25 comprising a metallic base coated with iridium 26 is bonded to the insulator 24 and an earthwire 27 comprising a metallic base coated with iridium 26 is mounted on the body 22 of the igniter 20.

Figure 3 shows in cross section an end portion of a spark plug part broken away showing one embodiment of an electrode 35 of an igniter device according to the invention. The electrode 35 comprises a core of copper metal which is welded to a base layer 31 of nickel/chromium alloy. A coating 33 of iridium is formed on the base layer 31 by electrostatically coating the base layer 31 with iridium metal powder. The core is welded to the base layer 31 subsequent to the formation of the iridium coating.

The earth electrode 7 is also provided with a coating 33 of iridium.

The igniter device according to the invention has the advantages over igniter devices according to the prior art in that it is very resistant to fouling and greatly extends the life of the device without substantially increasing the cost of manufacture.

To obtain the best performance of such igniter devices it is advantageous to install the device at a point which is located as near as possible to the source of fuel entering the combustion chamber. This results in the devices being installed in positions that are difficult to access for servicing or replacement. The devices according to the invention have the advantage that once fitted, they will remain installed for the life of the equipment and, under normal circumstances, they will not require replacing or adjusting. This provides benefits in reduced maintenance time and costs while giving an operational performance throughout the life of the equipment to which it is fitted that is of the same standard as for prior art igniter devices.

1 6

Claims

1. An igniter device suitable for use in igniting fuel comprising an insulator resistant to high temperatures, an electrode supported by the insulator and an earth conductor, wherein the electrode comprises an electrode base material, the earth conductor comprises an earth conductor base material and a coating comprising iridium is deposited on the surface of the base material of at least one of the electrode and the earth conductor.

2. An igniter device according to claim 1 wherein the base material comprises a nickel/chromium alloy or other material generally used for such electrodes or earth wires.

3. An igniter discharge device according to claim 1 or claim 2 wherein the iridium coating comprises iridium metal.

4. An igniter discharge device according to claim 1 or claim 2 wherein 20 the coating comprises an iridium alloy.

5. An igniter discharge device according to any one of the preceding claims wherein both the electrode and the earthwire are coated with the iridium coating.

6. An igniter device according to any one of the preceding claims wherein the iridium coating is deposited by electrostatic powder coating.

7 7. An igniter device according to any one of the preceding claims wherein the electrode is formed with a core of copper metal, a coating of base material and an iridium coating.

8. An igniter device according to claim 7 wherein the electrode is formed by coating a nickellchromium alloy base material with an iridium coating and welding a copper core to the electrode.

9. An igniter device as hereinbefore described with reference to 10 Figure 1 of the accompanying drawings.

10. An igniter device as hereinbefore described with reference to Figure 2 of the accompanying drawings.

11. An electrode suitable for use in an igniter device according to any one of the preceding claims comprising an electrically conductive base material and a coating comprising iridium deposited on the base material.