GB2164091A

GB2164091A - A spark plug for an internal combustion engine

Info

Publication number: GB2164091A
Application number: GB08422756A
Authority: GB
Inventors: Alan David Geraghty
Original assignee: Ford Motor Co
Current assignee: Ford Motor Co
Priority date: 1984-09-08
Filing date: 1984-09-08
Publication date: 1986-03-12
Also published as: GB8422756D0

Abstract

The spark plug has two electrodes (14, 16) which form a gap between them. The electrode (16) furthest into the combustion chamber has a hole (20) through it which is aligned with a bore (22) or other circular formation on the opposite electrode (14). The hole and the circular formation give better access of the fuel/air mixture to the spark and also allow the combusted fuel to move away from the plug after combustion. <IMAGE>

Description

SPECIFICATION Spark plug for an internal combustion engine This invention relates to a spark plug for an internal combustion engine.

According to the invention, there is provided a spark plug for an internal combustion engine having two electrodes which define a spark gap between them, one of the electrodes being, in use, further into the combustion chamber than the other electrode, said one electrode having a hole through it and said other electrode having a circular edge formation thereon and facing said one electrode, the hole and the edge formation being substantially coaxial.

With such an arrangement, the spark jumps from the edge of the hole to the circular edge formation. As ignition occurs it is thought that a cylindrical region ionises between the two electrodes around the edges of the hole and the circular formation, and this promotes efficient and complete combustion.

Preferably the common axis of the hole and the circular edge formation lies on the axis of the plug itself.

The circular edge formation may be the tip of a cylindrical electrode, but is preferably formed by a bore in the end face of said other electrode. When a bore of this type is used, it is thought to provide a small combustion chamber in itself. When combustion occurs, pressure builds up in the chamber formed by the bore and then provides a force to blow the combusting mixture out of the bore and through the hole in said one electrode. This promotes good mixing of the combusting mixture.

If the tip of a cylindrical electrode is used as the circular edge formation, it should be reduced in diameter compared with a conventional cylindrical electrode to ensure that the spark will jump to the edges of the hole in the said one electrode and not to the edges of the electrode itself.

The bore is preferably a blind bore.

The edges of the hole may be chamfered on the side facing away from the bore.

The invention will now be further described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a side view of a first embodiment of a spark plug tip in accordance with the invention; Figure 2 is a side view of a second embodiment of a spark plug tip in accordance with the invention; Figure 3 is an underneath view of the plug of Fig. 1; Figure 4 is an underneath view of the plug of Fig. 2; Figure 5 shows the plug tip of Fig. 1 with flow paths before ignition; and Figure 6 shows the plug tip of Fig. 1 with flow paths after ignition.

The plug shown in Fig. 1 has a threaded body 10, an insulator 12, a centre electrode 14 and a side electrode 16. As is conventional, the threaded body is screwed. into a bore in a cylinder head and, in use, a potential is applied between the electrodes 14 and 16 so that a spark jumps the gap between the electrodes.

A hole 20 is formed through the side electrode 16, and this side electrode will be further into the combustion chamber than the centre electrode 14. A blind bore 22 is formed in the end face of the centre electrode. If the hole 20 and the bore 22 are the same diameter, they may be easily formed in a single drilling operation. They may however be of different diameters. For example, the hole 20 may be up to 2.5 mm diameter. The bore 22 can be up to 2.5 mm in diameter and 2 mm deep.

A chamfer 24 is formed around the mouth of the hole 20, as shown.

If the hole 20 is small (up to 1.5 mm diameter), a standard sized side electrode may be used, as shown in Fig. 4. For larger holes, a modified side electrode with an enlarged, rounded end as shown in Fig. 3 can be used.

When the plug is in use and before ignition occurs, the fuel mixture which is being compressed into the top of the cylinder passes freely through the hole 20 and around the end of the centre electrode 14 as indicated by the arrows 26 in Fig. 5.

When ignition occurs, the resulting flame fronts 28 move out from the gap in radial directions, but also moves through the hole 20 as indicated in Fig. 6, to reach portions of the combustion chamber normally shielded by the electrode 16 and thus to help the achievement of complete combustion in the cylinder.

The presence of the hole 20 results in a noticeable improvement in fuel consumption due to three main factors: a) improved low speed driveability b) the idle speed can be reduced c) leaner fuel/air mixtures can be used Furthermore, the tendency of the plug to foul when cold is reduced, thus reducing misfiring.

1. A spark plug for an internal combustion engine having two electrodes which define a spark gap between them, one of the electrodes being, in use, further into the combustion chamber than the other electrode, said one electrode having a hole through it and said other electrode having a circular edge formation thereon and facing said one electrode, the hole and the edge formation being substantially coaxial.

2. A spark plug as claimed in Claim 1, wherein the common axis of the hole and the

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Spark plug for an internal combustion engine This invention relates to a spark plug for an internal combustion engine. According to the invention, there is provided a spark plug for an internal combustion engine having two electrodes which define a spark gap between them, one of the electrodes being, in use, further into the combustion chamber than the other electrode, said one electrode having a hole through it and said other electrode having a circular edge formation thereon and facing said one electrode, the hole and the edge formation being substantially coaxial. With such an arrangement, the spark jumps from the edge of the hole to the circular edge formation. As ignition occurs it is thought that a cylindrical region ionises between the two electrodes around the edges of the hole and the circular formation, and this promotes efficient and complete combustion. Preferably the common axis of the hole and the circular edge formation lies on the axis of the plug itself. The circular edge formation may be the tip of a cylindrical electrode, but is preferably formed by a bore in the end face of said other electrode. When a bore of this type is used, it is thought to provide a small combustion chamber in itself. When combustion occurs, pressure builds up in the chamber formed by the bore and then provides a force to blow the combusting mixture out of the bore and through the hole in said one electrode. This promotes good mixing of the combusting mixture. If the tip of a cylindrical electrode is used as the circular edge formation, it should be reduced in diameter compared with a conventional cylindrical electrode to ensure that the spark will jump to the edges of the hole in the said one electrode and not to the edges of the electrode itself. The bore is preferably a blind bore. The edges of the hole may be chamfered on the side facing away from the bore. The invention will now be further described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a side view of a first embodiment of a spark plug tip in accordance with the invention; Figure 2 is a side view of a second embodiment of a spark plug tip in accordance with the invention; Figure 3 is an underneath view of the plug of Fig. 1; Figure 4 is an underneath view of the plug of Fig. 2; Figure 5 shows the plug tip of Fig. 1 with flow paths before ignition; and Figure 6 shows the plug tip of Fig. 1 with flow paths after ignition. The plug shown in Fig. 1 has a threaded body 10, an insulator 12, a centre electrode 14 and a side electrode 16. As is conventional, the threaded body is screwed. into a bore in a cylinder head and, in use, a potential is applied between the electrodes 14 and 16 so that a spark jumps the gap between the electrodes. A hole 20 is formed through the side electrode 16, and this side electrode will be further into the combustion chamber than the centre electrode 14. A blind bore 22 is formed in the end face of the centre electrode. If the hole 20 and the bore 22 are the same diameter, they may be easily formed in a single drilling operation. They may however be of different diameters. For example, the hole 20 may be up to 2.5 mm diameter. The bore 22 can be up to 2.5 mm in diameter and 2 mm deep. A chamfer 24 is formed around the mouth of the hole 20, as shown. If the hole 20 is small (up to 1.5 mm diameter), a standard sized side electrode may be used, as shown in Fig. 4. For larger holes, a modified side electrode with an enlarged, rounded end as shown in Fig. 3 can be used. When the plug is in use and before ignition occurs, the fuel mixture which is being compressed into the top of the cylinder passes freely through the hole 20 and around the end of the centre electrode 14 as indicated by the arrows 26 in Fig. 5. When ignition occurs, the resulting flame fronts 28 move out from the gap in radial directions, but also moves through the hole 20 as indicated in Fig. 6, to reach portions of the combustion chamber normally shielded by the electrode 16 and thus to help the achievement of complete combustion in the cylinder. The presence of the hole 20 results in a noticeable improvement in fuel consumption due to three main factors: a) improved low speed driveability b) the idle speed can be reduced c) leaner fuel/air mixtures can be used Furthermore, the tendency of the plug to foul when cold is reduced, thus reducing misfiring. CLAIMS

2. A spark plug as claimed in Claim 1, wherein the common axis of the hole and the circular edge formation lies on the axis of the plug itself.

3. A spark plug as claimed in Claim 1 or Claim 2, wherein the circular edge formation is formed by a bore in the end face of said other electrode.

4. A spark plug as claimed in Claim 3, wherein the bore is a blind bore.

5. A spark plug as claimed in Claim 1 or Claim 2, wherein the circular edge formation is the tip of a cylindrical electrode.

6. A spark plug as claimed in any preceding claim, wherein the edges of the hole are chamfered on the side facing away from the circular edge formation.

7. A spark plug substantially as herein described with reference to the accompanying drawings.