GB2184484A

GB2184484A - Spark plugs

Info

Publication number: GB2184484A
Application number: GB08531547A
Authority: GB
Inventors: Joseph Gibson Dawson
Original assignee: Dawson Royalties Ltd
Current assignee: Dawson Royalties Ltd
Priority date: 1985-12-21
Filing date: 1985-12-21
Publication date: 1987-06-24
Also published as: GB8531547D0

Abstract

The spark plug comprises a first earthed electrode 5 and a second electrode 4 to which a high tension supply is connected. The tip of one of the electrodes defines a wedge, a surface of which faces the other electrode. When high tension is supplied to the gap defined between the electrodes two sparks 12, 13 are generated which bend outwards away from each other so as to produce a large spark surface. <IMAGE>

Description

SPECIFICATION Spark plug The present invention relates to a spark plug.

Conventional spark plugs comprise a metal body which in use is screwed into the cylinder head of an engine and supports an earth electrode, a ceramic insulator mounted on the metal body, and a high tension electrode extending through the ceramic insulator to terminate adjacent the earth electrode. A high tension supply is connected to the high tension electrode and a single spark is generated between thetipofthe high tension electrodeand the earth electrode.

The high tension electrode is generally ofcircular cross-section and its tip defines an end surface perpendicularto the axis ofthe electrode. The end surface of the electrode tip faces a surface of the electrode which is parallel thereto.

Various proposals have been made to increase the size, duration and number of sparks generated within an internal combustion engine in an attempt to improve the efficiency ofthe combustion process within such engines. There is however some reluctance on the part of the engine manufacturers to make major modifications to ignition systems and it would be highly advantageous ifthe quality ofthe spark generated by a spark plug could be improved by making a simple modification to the structure of conventional spark plugs It has now surprisingly been discovered that the qualityof a sparkgenerated bya simple two-electrode spark plug can be significantly improved by making relatively minor adjustments to the electrode geometry.

According to the present invention there is provided a spark plug comprising a first electrode which in use is earthed and a second electrodeto which in use a high tension supply is connected, the first and second electrodes defining spaced apart tips positioned such that an electrical discharge occurs between them when high tension is supplied to the second electrode, wherein the tip of one electrode defines a wedge a surface ofwhich faces the other electrode.

Where the high tension electrode is of circular cross-section its tip may comprise a firstflat surface extending perpendicular to the axis of the high tension electrode and a second flatsurface defining the wedge shape. The first and secondflatsurfaces meet along a straight line. When a high tension supply is connected to the high tension electrode two sparks are generated, one from each end ofthe said line, and the sparks are curved outwards away from each other. An effect is obtained which is similartothat which would be obtained if an extremely large spark of spherical cross-section could be generated.

The theoretical basis for the present invention has not yet been fully investigated and experimentation with various electrode geometries will be required before an optimum geometry can be realized. It does appear preferable howeverforthewedge-shaped electrode to have two planar surfaces meeting along a straight line.

Embodiments of the present invention will now be described, byway of example, with reference to the accomapnying drawings, in which: Figure I is a side view of a spark plug in accordance with the present invention; Figure2 is an enlarged view of the tip ofthe high tension electrode of the spark plug according to Figure 1; Figure 3 illustrates the formation of two sparks between the electrodes ofthe spark plug according toFigure1; Figure 4 illustrates the result of reducing the radial distance between the high tension electrode and earth electrode ofthe spark plug according to Figure 1; Figure 5is a side view of an electrode structure similartothatshown in Figures 1 to4; Figure 6is a view on the line 6-6 of Figure 5;; Figure 7 is a side view of an electrode structure which isa modification ofthatshown in Figure6; Figure 8is a view of Figure 7 on line 8-8; Figure9 is a side view of an electrode structure incorporating two earthed electrodes and a geometry similar in performance to that of Figure 7; Figures 10 and 11 are views on the lines 10-10 and 11-11 of Figure 9; Figure 12 is a side view of an alternative electrode structure to that of Figure 5; Figure 13 is a side view of another alternative electrode structure; Figure 14 illustrates a modification to the electrode structure of Figure 13; and Figure 15isa view on the lines 15-15 of Figure 14.

Referring to Figure 1 ,the illustrated spark plug comprises a metal body 1 defining a screwthreaded portion 2 which in use is screwed into a cylinder head (not shown). A ceramic insulator 3 extends through the spark plug body and supports an electrically insulated high tension electrode 4. An earth electrode 5 is mounted directly on the spark plug body so as to be electrically connected to the cylinder head of an engine to which the spark plug is fitted.

As more clearly shown in Figure 2,the high tension electrode 4 is of circular cross-section and defines a first end face 6 which is perpendicularto the axis of the electrode. The end of the electrode 4 is wedge-shaped as the result of the formation of a wedge surface 7. The surfaces 6 and 7 come together along line 8 extending between points 9 and 10. The lowermost portion of the edge of the surface 7 is indicated by reference numeral 11.

Referring now to Figure 3, when a high tension supply is connected to the electrode 4 sufficientto ionize the space between the electrodes 4 and 5 an electrical discharge is initiated. In the conventional electrode structures a single spark results but in the case ofthe illustrated structure two sparks result each extending from a respective one of points 9 and 10. The two sparks are indicated schematically by the lines 12 and 13. The two sparks bend outwards away from each other. The effect of this is to produce a very large spark surface which improves combustion of any fuel mixture in the gap between and the region around the electrodes 4 and 5.

Referring now to Figure 4, this illustrates the formation ofthree sparks as will occurwhen the spacing between the point 11 and the electrode 5 is relatively small. A spark represented by line 14 is generated in addition to the sparks 12 and 13 further increasing the effective surface area ofthe sparks.

It will be appreciated that the embodiment ofthe invention as illustrated in Figures 1,2,3 and 4 has the same geometry as that used in conventional spark plugs exceptforthe formation of the surface 7 (Figure 2). Thus a conventional spark plug can be converted to a geometry resulting in double spark generation simply by filing away a portion of a conventional spark plug. The efficiency ofthe spark generation process can in addition be improved by increasing the voltage and duration of the high tension pulses applied to the electrode 4 and the gap between the electrodes 4and 5 will of course be matched to the characteristics ofthe high tension supply.

Referring to Figures 5 and 6 the illustrated structure is similarto that ofthe arrangement of Figures 1 to 4. It will be noted that the axis 15 ofthe high tension electrode 4 is positioned to one side of the line 8 defined by the wedge-shaped tip ofthe electrode, a line (not shown) parallel to the axis 15 and through the line 8 extending along the surface 15 defined bythe earth electrode 5.

Referring to Figures 7 and 8, the illustrated structure is similarto that of Figures 5 and 6 except forthefactthattheaxis 15 is displaced relative to The end surface 16 ofthe earth electrode 5 so that a line 17 drawn from the line 8to the lowermostedge of the surface 16 is inclined to the axis 15.

Referring nowto Figures 9,10 and 11 ,the illustrated structure corresponds to that of Figures 7 and 8 exceptforthefactthattwo earth electrodes 5 are provided in a symmetrical arrangement on either side of a high tension electrode 4 defining two wedge surfaces 7. With this arrangement damage to one ofthe earth electrodes does not preventthe continued operation of the spark plug.

Referring to Figure 12 the illustrated arrangement shows an alternative shape forthe earth electrode 5 to that of previously described embodiments.

Figure 13 shows a further alternative shape forthe earth electrode 5.

Figures 14 and 15 illustrate a modification to the structure of the earth electrode as compared with the structure illustrated in Figure 13. Itwill be seen that the earth electrode of Figures 14and 1Ssupports projections 17 so as to increase the effective width of the earth electrode and thereby increasethe spacing between the two sparks generated from each end of the line 8 on the high tension electrode 4.

Claims

1. A spark plug comprising a first electrode which in use is earthed and a second electrode to which in use a high tension supply is connected,the first and second electrodes defining spaced apart tips positioned such that an electrical discharge occurs between them when high tension is supplied to the second electrode, wherein the tip of one electrode defines a wedge a surface of which faces the other electrode.

2. A spark plug according to claim 1, wherein the tip of the second electrode comprises a first flat surface extending perpendicularto the axis of the electrode and a secondflatsurface defining the wedge shape, the first and second flat surfaces meeting along a straight line.

3. A spark plug according to claim 2, wherein the second electrode extends along the spark plug axis, the first electrode extends from a point spaced to one side of the spark plug axis towards the spark plug axis, and a line perpendicularto the said surface of the wedge is inclined to the spark plug axis and lies in a plane which extends through the first and second electrodes.

4. A spark plug according to claim 3, wherein two said first electrodes are provided spaced apart on opposite sides ofthe spark plug axis, the second electrode defining two said surfaces each facing a respective first electrode.

5. A spark plug substantially as hereinbefore described with reference to Figures 1 to 4, Figures 5 and6, Figures7 and8, Figures9, 10and 11, Figure 12, Figure 13, or Figures 14 and 15 ofthe accompanying drawings.