A spark plug, particularly for supercharged and racing engines

Abstract

 The head portion (4a) of the central electrode (4) is disc-shaped and has an extent such that its lateral surface is substantially flush with the lateral surface of the adjacent end portion (3a) of the insulator (3).
The end portion (3a) of the insulator (3) is protected from erosion by the spark and from the effect of the combustion flame.

Description

[0001] The present invention relates to a spark plug, particularly a plug for supercharged (turbocharged) and racing engines.

[0002] More specifically, the subject of the invention is a spark plug comprising:
an outer tubular metal body,
an insulating element disposed in the body and having an end which projects axially beyond the end of the body facing the combustion chamber in use,
a central electrode which extends through the insulating element and has a substantially disc-shaped end head projecting axially beyond the end of the insulating element, and
a plurality of earth electrodes connected to the end of the body and extending towards the end of the central electrode which projects from the insulator.

[0003] The spark plug according to the invention is characterised in that the extent of the head portion of the central electrode is such that its lateral surface is substantially flush with the lateral surface of the end portion of the insulator.

[0004] By virtue of this characteristic, the head portion of the central electrode constitutes a protective shield for the end portion of the insulator, reducing the erosion of the insulator by the spark and at the same time protecting the insulator from the combustion flame.

[0005] Further characteristics and advantages of the invention will become clear from the detailed description which follows, with reference to the appended drawings provided by way of non-limiting example, in which:

Figure 1 is a perspective view of a spark plug according to the invention, and

Figure 2 is a partial axial section of an end portion of the plug of Figure 1, on an enlarged scale.

[0006] In Figure 1, a spark plug according to the invention for an internal combustion engine is generally indicated 1. The plug includes, in known manner, a tubular metal body 2 one end of which is threaded externally.

[0007] An element 3 of electrically-insulating material, typically a ceramic material, is disposed in the body 2 in known manner. An end portion 3a of this element projects axially beyond the end of the metal body 2 which faces the combustion chamber in use.

[0008] A central electrode 4 extends through the insulating element 3 and in turn projects axially beyond the end 3a of the insulating element 3.

[0009] The central electrode 4 is connected, in known manner, not shown, to a high-tension terminal, indicated 5 in Figure 1, projecting from the other end of the insulating element 3.

[0010] An end edge 2a of the metal body 2 is upset onto an annular metal element, indicated 6 (Figure 2). The annular element 6 may be made, for example, of a nickel-, platinum- or copper-based alloy.

[0011] The annular element 6 has a plurality of integral appendages 7 which extend from its inner edge towards the end portion 3a of the insulator in equiangularly-­spaced positions. These appendages constitute the earth electrodes of the plug.

[0012] As can be seen in Figure 2 in particular, the central electrode 4 has a substantially disc-shaped end head 4a whose radial extent is such that its lateral surface is substantially flush with the lateral surface of the end portion 3a of the insulating element 3.

[0013] By virtue of this conformation of the head portion of the central electrode, the portion 3a of the insulating element is protected from the flame which develops during combustion and, moreover, is less susceptible to erosion by the spark.

[0014] In short, these characteristics mean that the plug operates better and has a longer life.

[0015] In particular, the plug thus formed is suitable for use even in supercharged and racing engines.

Claims

1. A spark plug (1), comprising:
an outer tubular metal body (2),
an insulating element (3) disposed in the body (2) and having an end (3a) which projects axially beyond the end of the body (2) facing the combustion chamber in use,
a central electrode (4) which extends through the insulating element (3) and has a substantially disc-shaped end head (4a) projecting axially beyond the end (3a) of the insulating element (3), and
a plurality of earth electrodes (7) connected to the end of the body (2) and extending towards the end (4a) of the central electrode (4) which projects from the insulator (3),
characterised in that the extent of the head portion (4a) of the central electrode (4) is such that its lateral surface is substantially flush with the lateral surface of the end portion (3a) of the element (3) of insulating material.

Drawing