GB2179397A - Spark plug - Google Patents

Abstract

The spark plug has a body 16 formed with a nut 18 by means of which the plug may be turned to screw the plug into and out of a cylinder head. To reduce the size of the plug and the size of the bore required to accommodate it, the nut 18 has more than the usual six sides, being preferably constructed as a double hexagon with twelve sides and twelve corners. <IMAGE>

Description

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

Positioning a spark plug in a cylinder head for thermo-dynamic efficiency often entails placing the plug in an inaccessible location.

Thus the plug is often to be found deep in an narrow bore in the cylinder head. The bore must be large enough to accept a socket spanner for permitting insertion and removal of the spark plug and it is desirable to minimise the size of the bore for the spark plug.

However, conventional spark plugs which have hexagonal nuts require a high stress to be applied at each corner during their removal and for this reason both the nut on the plug and the wall thickness of the socket spanner must be large so as to withstand these stresses. Thus, a conventional spark plug necessitates a relatively large bore in the cylinder head.

With a view to mitigating the foregoing disadvantage, the present invention provides a spark plug having a body formed with a nut by means of which the plug may be turned to screw the plug into and out of a cylinder head, wherein the nut has more than six sides.

Preferably, the nut is in the form 6f a double hexagon having twelve sides and twelve corners.

Because the socket spanner for removing the plug may now grip twelve corners rather than six, the stress at each corner is reduced thereby permitting the spanner to have a reduced wall thickness. Consequently, the size of the plug and the clearance required between the spark plug and the bore may be reduced so as to permit the bore to be of smaller diameter.

The invention will now be described further, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a longitudinal section through a spark plug, and Figure 2 is a plan view showing the shape of the nut on the body of the spark plug.

The plug in the drawings comprises a central electrode 10 fitted with a screw-on cap 12 and located within an insulator 14. The insulator 14 is located within a metal body 16 which is formed about the insulator 14 and is sealed relative to the insulator 14 in a suitable manner. The body 16 has three main portion namely a nut 18, a screw-threaded portion 20 and an earth electrode portion 22 which defines with the central electrode 10 the spark gap 24. Apart from the nut and the size of the spark plug, the construction of the plug is generally conventional and need not therefore be described in greater detail.

The nut of a conventional spark plug is hexagonal. By contrast, as shown in Fig. 2, the nut 18 of the spark plug body 16 in the present invention has twelve sides and twelve corners, being in the form of a double hexagon, that is to say a hexagon rotated through thirty degrees and superimposed on itself.

When gripped by a correspondingly shaped socket spanner, the stress exerted on each corner of the spanner and the spark plug is reduced, in effect halved. Therefore, the plug may be of reduced size and the wall thickness of the socket spanner may be reduced.

In this way, the invention can be seen to permit the spark plug to be located within a smaller diameter bore, for a plug of any given insulator outer diameter.

1. A spark plug having a body formed with a nut by means of which the plug may be turned to screw the plug into and out of a cylinder head, wherein the nut has more than six sides.

2. A spark plug as claimed in claim 1, wherein the nut is in the form of a double hexagon, having twelve sides and twelve corners.

3. A spark plug constructed substantially as herein described with reference to and as illustrated in the accompanying drawings.

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

Claims (3)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Spark plug The present invention relates to a spark plug. Positioning a spark plug in a cylinder head for thermo-dynamic efficiency often entails placing the plug in an inaccessible location. Thus the plug is often to be found deep in an narrow bore in the cylinder head. The bore must be large enough to accept a socket spanner for permitting insertion and removal of the spark plug and it is desirable to minimise the size of the bore for the spark plug. However, conventional spark plugs which have hexagonal nuts require a high stress to be applied at each corner during their removal and for this reason both the nut on the plug and the wall thickness of the socket spanner must be large so as to withstand these stresses. Thus, a conventional spark plug necessitates a relatively large bore in the cylinder head. With a view to mitigating the foregoing disadvantage, the present invention provides a spark plug having a body formed with a nut by means of which the plug may be turned to screw the plug into and out of a cylinder head, wherein the nut has more than six sides. Preferably, the nut is in the form 6f a double hexagon having twelve sides and twelve corners. Because the socket spanner for removing the plug may now grip twelve corners rather than six, the stress at each corner is reduced thereby permitting the spanner to have a reduced wall thickness. Consequently, the size of the plug and the clearance required between the spark plug and the bore may be reduced so as to permit the bore to be of smaller diameter. The invention will now be described further, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a longitudinal section through a spark plug, and Figure 2 is a plan view showing the shape of the nut on the body of the spark plug. The plug in the drawings comprises a central electrode 10 fitted with a screw-on cap 12 and located within an insulator 14. The insulator 14 is located within a metal body 16 which is formed about the insulator 14 and is sealed relative to the insulator 14 in a suitable manner. The body 16 has three main portion namely a nut 18, a screw-threaded portion 20 and an earth electrode portion 22 which defines with the central electrode 10 the spark gap 24. Apart from the nut and the size of the spark plug, the construction of the plug is generally conventional and need not therefore be described in greater detail. The nut of a conventional spark plug is hexagonal. By contrast, as shown in Fig. 2, the nut 18 of the spark plug body 16 in the present invention has twelve sides and twelve corners, being in the form of a double hexagon, that is to say a hexagon rotated through thirty degrees and superimposed on itself. When gripped by a correspondingly shaped socket spanner, the stress exerted on each corner of the spanner and the spark plug is reduced, in effect halved. Therefore, the plug may be of reduced size and the wall thickness of the socket spanner may be reduced. In this way, the invention can be seen to permit the spark plug to be located within a smaller diameter bore, for a plug of any given insulator outer diameter. CLAIMS

1. A spark plug having a body formed with a nut by means of which the plug may be turned to screw the plug into and out of a cylinder head, wherein the nut has more than six sides.

2. A spark plug as claimed in claim 1, wherein the nut is in the form of a double hexagon, having twelve sides and twelve corners.

3. A spark plug constructed substantially as herein described with reference to and as illustrated in the accompanying drawings.