NZ247906A - Spark plug with toroidal electrode - Google Patents

Description

24 7 9 Priority Daio{s): Compiets Specification Filed: ...lJo:.As?.:3.3.. Class: Publication Date: P.O. Journal No: Patents Form No. 5 NEW ZEALAND PATENTS ACT 1953 COMPLETE SPECIFICATION SPARKING PLUG I JAN BEDNAR, a citizen of The Czech Republic of Tyrsova 228, Chynov, The Czech Republic hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement: (followed by page la 247906 -la- The invention relates to a spark plug for use in an internal combustion engine. More particularly, but not exclusively, the invention relates to a spark plug for use in an internal combustion engine running with a lean mixture of fuel.

Known spark plugs may consist of a metal case fitted at one end with a thread for attaching or screwing the spark plug to the cylinder head of an internal combustion engine.

This known spark plug may further comprise a cylindrically shaped insulated part, which is axially inserted into the metal case and serves to insulate the plug from high voltages. A cylindrically shaped central electrode is inserted axially in the insulator, and a terminal pin is provided to conduct a high voltage to the central electrode. The terminal pin is generally located in the insvxlator and provided with a seal to secure the connection between the central electrode and the terminal pin. The metal case of the spark plug is connected to the ground electrode, which is led out into the combustion chamber of the engine and its active part is placed above the central electrode.

Other known spark plugs are limited by their construction by having a simple ground electrode to discharge the spark in only one place. These known plugs are unsuitable for engines running with very lean mixtures of fuel. Furthermore, the use of these spark plugs may adversely affect combustion in the engine, resulting in inefficient running of the engine. The inefficient combustion of the lean mixture is also the result of the position of the spark gap in the plug, which may be shifted out of reach of the edge of the case, resulting in igniting the mixture only at the wall of the combustion chamber. (followel b^./p^g^i'.S 247906 The spark discharge in this type of plug construction is concentrated in the small area of the central and ground electrodes. The consequence of this arrangement is a decrease in the size of the central electrode, which has an adverse affect on the working life of the spark plug.

Another known spark plug may have multiple ground electrodes welded to the end of the thread of the metal case of the spark plug. The end of each ground electrode is bent over towards the central electrode, where a gap corresponding to the spark-over distance for the given type of spark plug and engine is between the central electrode and each ground electrode.

Another known type of spark plug uses a ground electrode built from one piece of conductive material with projections which are pressed into the end of the thread-part of the metal case, and with each projection representing the active part of the ground electrode.

These known constructions, however, have no direct effect in prolonging the normal working life of spark plugs. Furthermore, when the insulation tip or the edges of the spark gap are contaminated with conductive deposits, the efficient working of the spark plug is affected adversely. This result can not be changed by adding ground electrodes. Moreover, the production of spark plugs wj.th a greater number of ground electrodes results in greater technological demands.

European patent number 430899 partially overcomes the problem of the limited working life of spark plugs. This patent discloses a spark plug comprising a central electrode with an outer end shaped as a low cylinder. The circular ground electrode generally has four projections pressed into the end of the thread-part of the metal case of the spark plug. The projections are bent toward the edge of the central electrode, whereby a spark gap is formed between the end of the projections ar 1 '1 247906 edge of the central electrode. The working life of the spark plug is extended by increasing the dimensions of the lower edge of the central electrode.

Another method of extending the working life of a spark plug is with a construction disclosed in German patent No. 3,816,968. In this patent, a spark plug has a cavity in the shape of a cone to one side of the central electrode which is itself located within the insulator. This cavity is broadened towards the outer end of the spark plug. The conical cavity is at its open end terminated by the ground electrode in the form of an annulus. A central electrode is located along the whole length of the central axis of the cavity. This spark plug, when compared with other described constructions, overcomes the requirement for a plug to have a low voltage spark discharge. However, the disadvantages mentioned above remain.

It is an object of the invention to overcome at least some of the abovementioned disadvantages, or at least to provide the public with a useful choice.

According to one aspect of the invention there is provided a spark plug for an internal combustion engine comprising: a metal case having a threaded portion for fixing the spark plug into a cylinder head of the combustion engine; an insulator mounted within the metal case having an end portion extending longitudinally from the metal case; a central electrode provided within the insulator; and a terminal pin provided within the insulator for supplying a high voltage to the central electrode, an end of the central electrode and an edge of the metal case defining a spark gap, wherein at least two toroidal auxiliary electrodes are provided along the periphery of the end portion of the insulator.

Preferably a ground electrode of annular shape is provided about the inner periphery of the metal casi >i. i >i i ■ * ttz. PATWfr omce 13 SEP 1995 24790 Preferably the central electrode is provided with a disc-shaped head axially extending from the end portion of the insulator.

The invention will now be described by way of example with reference to the accompanying drawings in which: Figures 1 and 2: show partial cross-sectional views of a spark plug not in accordance with the present invention with and without a ground electrode.

Figures 3 and 4 show partial cross-sectional views of a spark plug according to first and second embodiments of the invention comprising two auxiliary electrodes being shown with and without a ground electrode.

Figures 5 and 6 show partial cross-sectional views of a spark plug not in accordance with the present invention. These views show the disc-shaped head with and without a ground electrode.

Figure 7: shows a partial cross-sectional view of a spark plug according to a third embodiment of the invention with two auxiliary electrodes and a disc-shaped head.

Referring to figure 1, a spark plug without a ground electrode is shown. The spark plug consists of a metal case 1 provided with a thread 10. An insulator 2 is provided co-axially within the metal case around a terminal pin 6, a special seal 7 and a central electrode 3. The central electrode 3 is connected by the special seal 7 to the terminal pin 6 to allow for the conduction of high voltages through the spark plug. The insulator 2 axially f?„z. patwi" ] SEP 1995 ! 247906 extends from the metal case 1 adjacent the central electrode 3 or by an end portion 2a.

The insulator 2 is provided with an end portion 2b at the opposite end of the spark plug from the end portion 2a. The end portion 2a of the insulator 2 is provided around its periphery with one toroidal auxiliary electrode 8. The electrical discharges takes place between the central electrode 3 through the toroidal auxiliary electrode 8 and the inner edge 5 of the metal case 1.

Referring to figure 2, a spark plug provided with a ground electrode 4 is shown. The ground electrode is received into the metal case 1. The threaded part 9 of the metal case 1 is screwed into the combustion chamber during use.

Referring to figures 3 and 4, a spark plug according to first and second embodiments of the invention are shown. The central electrode 3 and two auxiliary electrodes 8 are constructed as shown to form a spark gap between the auxiliary electrodes 8 and the inner edge 5 of the metal case 1. A slipping discharge may take place between the lower auxiliary electrode 8 and the ground electrode 4 resulting in a discharge through the air.

Referring to figures 5, 6 and 7, various types of spark plugs with a disc-shaped head 11 are shown. The outside diameter of the disc-shaped head 11 of the central electrode 3 is formed to correspond with the outside diameter of the end portion 2a of the insulator 2.

The spark plug in figure 7 constitutes a third embodiment of the present invention. The demanding requirements of high voltage can be regulated by adapting the auxiliary electrodes 8 to a predetermined width to provide an adequate gap for discharging the high voltages through the spark plug. 247906 In the spark plug of the invention, due to the auxiliary-electrodes, two or more spark-discharges occur simultaneously at the tip of the insulator. The auxiliary electrodes are spaced from each other so that spark discharges generally occur in the places with the highest concentration of fuel. This effect substantially increases the probability of an even ignition of a very lean mixture, resulting in good combustion. If one of the spark gaps is contaminated and a spark plug fails to function properly, the spark discharge may take place on one of the further spark gaps between the auxiliary electrodes.

Tests have shown that using the spark plug of the invention increases engine power and range. The life of a spark plug according to the invention is typically about two to three times as long as a conventional spark plug due to the fact that discharge takes place along the whole periphery of the central, auxiliary and ground electrode. The spark plug of the invention functions in a similar manner to a spark plug having multiple ground electrodes in which discharge can take place, although at a much greater number of places. The spark plug of the invention is simple to manufacture if the ground electrode is either not required, especially for applications with low heat stress, or is of simple shape and construction. A major advantage of the invention is the wide range of temperatures over which the spark plug can be used for a very wide range of heat ?oads. Further, the spark plug of the invention has the advantage of shifting the tip of the insulator towards the centre of the combustion chamber.

It will be appreciated that the spark plug according to the invention may be utilised for all types of spark-ignition engines, particularly engines which run on a lean mixture of fuel.

Although this invention has been described by way of example it is to be appreciated that modifications may be made thereto without departing from the scope of the invention as defined in the appended claims.

NXftynarromce 13 SEP 1995 f'Cciv™2

Claims (4)

-8- WHAT I CLAIM IS:

1. A spark plug for an internal combustion engine comprising: a metal case having a threaded portion for fixing the spark plug into a cylinder head of the combustion engine; an insulator mounted within the metal case having an end portion extending longitudinally from the metal case; •a central electrode provided within the insulator; and a terminal pin provided within the insulator for supplying a high voltage to the central electrode, an end of the central electrode and an edge of the metal case defining a spark gap, wherein at least two toroidal auxiliary electrodes are provided along the periphery of the end portion of the insulator.

2. A spark plug according to claim 1 wherein a ground electrode of annular shape is provided about the inner periphery of the metal case.

3. A spark plug according to claim 1 or claim 2 wherein the central electrode is provided with a disc-shaped head axially extending from the end portion of the insulator.

4. A spark plug substantially as herein described with reference to any one of figures 3, 4 and 7 of the accompanying drawings. es/specs/201586