Electric lamp and discharge devices – Spark plugs – Particular electrode structure or spacing
Patent
1996-10-22
1998-06-02
Chilcot, Richard
Electric lamp and discharge devices
Spark plugs
Particular electrode structure or spacing
313142, 313123, 313139, H01T 1320
Patent
active
057605343
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE ART
STATE OF THE ART
One of the problems of combustion engines is achieving the correct timing of the ignition of the fuel-air mixture which is directed to the combustion chamber or chambers and, that the spark is effective to ignite the fuel-air mixture. If the ignition is too slow or ineffective, fuel consumption and, hence, pollution increases and engine efficiency decreases.
Conventional spark plugs consist of a cylindrical ceramic insulator sealed in a steel body to form a gasproof device. One end of the steel body device is threaded to enable the spark plug to be inserted into the engine block. A central electrode is axially inserted into the ceramic insulator. A metal bolt, sealing the central electrode within the body of the insulator, serves as a high voltage input terminal. A ground electrode is positioned above the central electrode, electrically and mechanically coupled to the steel body. Both the central and ground electrodes operate in the engine combustion chamber.
Such a spark plug has a spark discharge on a small concentrated surface of the electrodes which causes erosion of the central electrode and, therefore, reduces the useful life of the plug.
Other types of spark plugs have multiple ground electrodes, for example, two or three electrodes. These electrodes are welded to the body of the plug. The ends of the electrodes are bent towards the central electrode. The ground electrode may also be formed as a single piece with plugs representing the active parts. However, even these types of spark plugs have a reduced life span due to wear and are also difficult and expensive to manufacture.
More effective and faster ignition of the fuel-air mixture and subsequently, more reliable engine operation can be achieved by spark plugs having a multispark discharge. In these types of spark plugs, as shown in FIG. 1, there is generally an arrangement of up to three auxiliary ring-shaped electrodes 22. These create a number of sequential spark gaps. The auxiliary electrodes are located between the central electrode 23 and ground electrode 21 around an end part of the ceramic insulator 20. The specially separated multispark discharges can then occur at the point of the highest concentration of the inflammable mixture. Therefore, these types of plugs are capable of igniting and burning very weak mixtures.
A spark plug of this type is described under U.S. Pat. No. 1,465,582. The central electrode is provided with a metal roof-shaped cup. The metal ring shape auxiliary electrodes, formed on the circular section, are elastically fitted into ceramic insulator grooves. The edge of the plug body has a rim which is bent towards the insulator. This spark plug has many disadvantages. During-shaped engine operation, at temperatures of 600.degree. C. to 700.degree. C., the metal ring-shaped electrodes lose their mechanical pre-stress. Owing to insufficient heat removal from the ring-shaped to the ceramic insulator, the ring-shaped electrodes overheat, wear out quickly and may burn up when overloaded. The roof-shaped cup of the central electrode of this type of spark plug is also overheated during-shaped engine operation. This is because the cup is not sufficiently thermally coupled to the insulator. The cross section of cup is inadequate for its heat absorption surface. The overheated cup and ring-shaped electrodes, therefore, increase the risk of self-ignition. Moreover, the steel rim can become dirty and may short-circuit the spark gap.
Another type of spark plug, using an auxiliary ring-shaped electrode, is described in UK Patent No. 2,094,833. Both the central electrode and auxiliary electrode are built into the plug body. The disadvantage of this system is that it is not possible to install the top of the ceramic insulator (i.e. the spark gap) into the best position within the combustion chamber. For the above reasons, use of these spark plugs has not been extended in practice.
BACKGROUND OF THE INVENTION
The arrangement of the spark plug under this invention considerably overcomes the disa
REFERENCES:
patent: 1461405 (1923-07-01), Solomon
patent: 1465582 (1923-08-01), Leager et al.
patent: 1621581 (1927-03-01), Clark
Bednar Jan
Safrata Josef
Brisk Tabor, a.s.
Chilcot Richard
Patel Harshad
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