GB2032516A

GB2032516A - Sparking plug

Info

Publication number: GB2032516A
Application number: GB7848402A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1978-10-25
Filing date: 1978-12-13
Publication date: 1980-05-08
Also published as: DE2854251A1; IT7947549A0; FR2440100A1; NL7900091A

Abstract

A sparking plug comprises a disc- shaped earth electrode (8) having a central aperture into which the end of a central electrode (7) extends, leaving a gap (9) between the electrodes across which sparking occurs in a radial direction. The innermost edge of the earth electrode (8) may be circular as shown, or shaped so as to produce tongues which extend towards the central electrode (7). <IMAGE>

Description

SPECIFICATION Sparking plug with circular earth electrode In the known type of sparking plug the earth electrode is a metal strip bent inwardly beneath the central electrode with a certain gap, the size of which is calculated according to the fuel mixture, across which sparking occurs. Since the metal strip electrode has a relatively small tip it is readily coated with carbon ash and other dust which can interfere with regular sparking of the sparking plug after a certain period of sparking and must be eliminated for efficient further use. In addition, the limited size of the strip results in poor heat emission from the electrode, producing temperature rises which might affect regular sparking of the sparking plug.

In the present invention, the sparking plug has a disc-shaped earth electrode around the end of the central electrode which extends into an aperture in the disc-shaped electrode so that there is an annular gap between the central electrode and the earth electrode across which sparking occurs. The inner edge of the earth electrode may be shaped so as to adjust the nature or size of the gap and to increase the area of the earth electrode onto which a spark will be attracted.

Thus, according to this invention there is provided a sparking plug having, a central electrode extending longitudinally through the plug and an earth electrode, the earth electrode defining a central aperture into which the central electrode extends.

Preferably the aperture of the earth electrode is shaped so as to provide one or more tongues which extend inwardly towards the central electrode further than the sections of the innermost edge which interconnect these portions.

The relatively larger area of disc-shaped earth electrode makes carbon deposits more thinly distributed over the electrode surface so that the electrical resistance to sparking rises only slowly, enabling the sparking plug to maintain regular sparking over a much longer period. Furthermore, larger size of the earth electrode facilitates the emission of heat so that the temperature of the earth electrode as held constant thereby encouraging regular sparking of the plug.

An embodiment of the invention will now be described with reference to the accompanying drawings wherein, Fig. 1 is a side elevation partly in cross-section of a sparking plug with a plan view of its lowermost surface as seen from below and Figs. 2 and 3 show plan views of the lower most surface of a sparking plug having modified earth electrodes.

As seen in Fig. 1 , the sparking plug has a body portion, a screw-threaded portion 6, with a washer 10 and a central electrode 7 which extends through the plug and beyond the end of the screw-threaded portion. The body portion comprises a screw cap 1, ceramic insulation 2, hexagonal nut 4 and metal body 5, all essentially as found in a conventional sparking plug.

The earth electrode is the disc-shaped element 8 which is secured to the end of the screwthreaded portion 6 and which has a central aperture into which extends the central electrode 7 so that it is surrounded by a gap 9. The.disc- shaped element 8 is in electrical contact with the screw-threaded portion 6 so that, on sparking, current created can pass through the screwthreaded portion 6 and metal body 5 of the plug to the engine block and ultimately to earth.

The spark gap 9 provides an adequate volume for a proper interchange of fuel/gas mixture before ignition.

Fig. 2 shows a modified earth electrode in which the inner most edge of the disc-shaped element 8 is shaped so as to provide three tongues 12 which extend inwardly towards the central electrode 7 further than the interconnecting sections of the innermost edge.

Qn sparking, the current takes the path of least electrical resistance and in this case the spark will cross from the central electrode 7 to a nearest part of the earth electrode 8 which is the inner most end of any of the tongues 12.

Fig. 3 shows an earth electrode which is similarly modified to produce four tongues 13.

With a conventional strip-shaped earth electrode'the end of the electrode which is axially spaced from the central electrode, and to which the spark will cross, is small and therefore quickly coated with carbon, making its electrical resistance much higher and therefore preventing regular sparking; this problem is avoided in the sparking plug described, in which sparking occurs radially. Furthermore, the relatively larger surface area of the disc-shaped earth elecrode will allow better dissipation of the heat formed in the electrode due to sparking so that any effect that a temperature rise in the electrode might have on the regularity and efficiency of the sparking is reduced.

1. A sparking plug having, a central electrode extending longitudinally through the plug and an earth electrode, the earth electrode defining a central aperture into which the central electrode extends.

2. A sparking plug according to claim 1 wherein the earth electrode is a disc-like element secured at one end of a body of the plug.

3. A sparking plug according to claim 1 or claim 2 wherein the aperture of the earth electrode is shaped so as to provide one or more tongues

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Sparking plug with circular earth electrode In the known type of sparking plug the earth electrode is a metal strip bent inwardly beneath the central electrode with a certain gap, the size of which is calculated according to the fuel mixture, across which sparking occurs. Since the metal strip electrode has a relatively small tip it is readily coated with carbon ash and other dust which can interfere with regular sparking of the sparking plug after a certain period of sparking and must be eliminated for efficient further use. In addition, the limited size of the strip results in poor heat emission from the electrode, producing temperature rises which might affect regular sparking of the sparking plug. In the present invention, the sparking plug has a disc-shaped earth electrode around the end of the central electrode which extends into an aperture in the disc-shaped electrode so that there is an annular gap between the central electrode and the earth electrode across which sparking occurs. The inner edge of the earth electrode may be shaped so as to adjust the nature or size of the gap and to increase the area of the earth electrode onto which a spark will be attracted. Thus, according to this invention there is provided a sparking plug having, a central electrode extending longitudinally through the plug and an earth electrode, the earth electrode defining a central aperture into which the central electrode extends. Preferably the aperture of the earth electrode is shaped so as to provide one or more tongues which extend inwardly towards the central electrode further than the sections of the innermost edge which interconnect these portions. The relatively larger area of disc-shaped earth electrode makes carbon deposits more thinly distributed over the electrode surface so that the electrical resistance to sparking rises only slowly, enabling the sparking plug to maintain regular sparking over a much longer period. Furthermore, larger size of the earth electrode facilitates the emission of heat so that the temperature of the earth electrode as held constant thereby encouraging regular sparking of the plug. An embodiment of the invention will now be described with reference to the accompanying drawings wherein, Fig. 1 is a side elevation partly in cross-section of a sparking plug with a plan view of its lowermost surface as seen from below and Figs. 2 and 3 show plan views of the lower most surface of a sparking plug having modified earth electrodes. As seen in Fig. 1 , the sparking plug has a body portion, a screw-threaded portion 6, with a washer 10 and a central electrode 7 which extends through the plug and beyond the end of the screw-threaded portion. The body portion comprises a screw cap 1, ceramic insulation 2, hexagonal nut 4 and metal body 5, all essentially as found in a conventional sparking plug. The earth electrode is the disc-shaped element 8 which is secured to the end of the screwthreaded portion 6 and which has a central aperture into which extends the central electrode 7 so that it is surrounded by a gap 9. The.disc- shaped element 8 is in electrical contact with the screw-threaded portion 6 so that, on sparking, current created can pass through the screwthreaded portion 6 and metal body 5 of the plug to the engine block and ultimately to earth. The spark gap 9 provides an adequate volume for a proper interchange of fuel/gas mixture before ignition. Fig. 2 shows a modified earth electrode in which the inner most edge of the disc-shaped element 8 is shaped so as to provide three tongues 12 which extend inwardly towards the central electrode 7 further than the interconnecting sections of the innermost edge. Qn sparking, the current takes the path of least electrical resistance and in this case the spark will cross from the central electrode 7 to a nearest part of the earth electrode 8 which is the inner most end of any of the tongues 12. Fig. 3 shows an earth electrode which is similarly modified to produce four tongues 13. With a conventional strip-shaped earth electrode'the end of the electrode which is axially spaced from the central electrode, and to which the spark will cross, is small and therefore quickly coated with carbon, making its electrical resistance much higher and therefore preventing regular sparking; this problem is avoided in the sparking plug described, in which sparking occurs radially. Furthermore, the relatively larger surface area of the disc-shaped earth elecrode will allow better dissipation of the heat formed in the electrode due to sparking so that any effect that a temperature rise in the electrode might have on the regularity and efficiency of the sparking is reduced. CLAIMS

3. A sparking plug according to claim 1 or claim 2 wherein the aperture of the earth electrode is shaped so as to provide one or more tongues which extend inwardly towards the central electrode further than the sections of the innermost edge which interconnects these portions.

4. A sparking plug essentially as herein described with reference to and as illustrated in the accompanying drawings.