GB2202274A

GB2202274A - I.C. engine spark plug fitment

Info

Publication number: GB2202274A
Application number: GB08706696A
Authority: GB
Inventors: Bruce Graham Westmoreland
Original assignee: Westmoreland & Co Ltd
Current assignee: Westmoreland & Co Ltd
Priority date: 1987-03-20
Filing date: 1987-03-20
Publication date: 1988-09-21
Also published as: GB8706696D0

Abstract

The engine compression ratio is reduced by inserting an adaptor 10 into the normal spark plug opening in the combustion chamber wall 14. The adaptor comprises an externally threaded tubular mounting portion 16 which is screwed fully into the normal threaded opening in the wall and forms a chamber 24 as an extension to the combustion chamber. A spark plug 12 is screwed into an internal threaded bore 28 of the adaptor for its electrodes 30 to be positioned within the extension chamber 24. <IMAGE>

Description

SPARK PLUG FITMENT In the operation of internal combustion engines with spark ignition, problems of pre-ignition (commonly known as "pinking") can arise from the use of too low a grade of fuel (i.e. too low an octane rating) to suit the compression ratio of the engine; since the lower fuel grades are cheaper to buy, there is an incentive to run an engine on as low a grade as possible, but one is limited by the onset of pinking at a certain grade level. Furthermore, pinking problems can also arise with the introduction of lead-free petrol.

Pinking problems could generally be alleviated by reducing the compression ratio of the engine, albeit usually with some loss of power and efficiency.

However, production engines do not normally have any ready facility for adjusting the compression ratio, and it would -normally mean, for example, altering or exchanging the cylinder head to increase the cylinder volume.

It is an object of the present invention to provide a ready facility for the compression ratio of an internal combustion engine to be varied, for example to permit the use of lower fuel grades, or for any other reason to militate against the onset of pinking.

The invention provides in one of its aspects an internal combustion engine in which a spark plug fitment is secured in an aperture extending through a combustion chamber wall for ignition of fuel in the combustion chamber in running the engine, the fitment forming an extension chamber within the aperture and in communication with the combustion chamber, and comprising spark inducing means arranged to produce an ignition spark within the extension chamber in running the engine.

Conveniently a tubular chamber-forming portion of the fitment may be externally screw-threaded for threaded engagement in the chamber wall, and may be so threaded and generally dimensioned as to be directly interchangeable in the aperture with a standard spark plug (i.e. meeting recognised British and/or other national and/or international standards).

The fitment may be in two separable parts comprising a tubular adaptor for securement in the chamber wall and a standard spark plug received into an outer end of the adaptor and extending axially through the adaptor, its electrodes forming the spark inducing means. To that end the adaptor may be formed with a suitably screw-threaded bore to receive a threaded body of the plug, and part at least of that bore may be within that portion of the adaptor arranged to be received within the aperture in the chamber wall. For example, the inner end portion of the adaptor may be externally screw-threaded for interchangeability with a standard 18 mm spark plug in the combustion chamber wall, and be internally threaded to receive a standard 14 mm spark plug.

In another of its aspects the invention provides a spark plug fitment for use in an engine as set out in the last preceding paragraph but two, the fitment comprising a mounting portion adapted to be secured within an aperture in a combustion chamber wall and forming an extension chamber, and the fitment comprising spark inducing means arranged to produce an ignition spark within the extension chamber in use.

In yet another of its aspects the invention provides a tubular adaptor suitable for use in combination with a spark plug to form a fitment for an engine as set out in the last preceding paragraph but three, the adaptor comprising an externally screw-threaded mounting portion for threaded engagement in an aperture in a combustion chamber wall to form an extension chamber and the adaptor having a screw-threaded bore arranged to receive a threaded portion of a spark plug of lesser diameter than the mounting portion, the threaded bore extending through the adaptor to the extension chamber.

There now follows a detailed description, to be read with reference to the accompanying drawing, of an adaptor and its use in combination with a spark plug in an internal combustion engine.

The accompanying drawing shows, partially in axial cross-section, an adaptor and a spark plug in combination forming a fitment secured in a combustion chamber wall.

To create a small increase in the volume of a combustion chamber of a spark-ignition internal combustion engine, a spark plug fitment comprising in combination an adaptor 10 and a spark plug 12 is secured in a threaded aperture extending through the combustion chamber wall 14, in place. of a spark plug previously installed.

The adaptor 10 is of a straight tubular form, but externally is similar to inner end portions of a standard spark plug for which it is substituted; it comprises an externally screw-threaded mounting portion 16 which has the same thread form as the replaced plug, for mounting in the combustion chamber wall 14, and a head portion 18 which comprises a hexagonal outer end portion 20 of substantially the same form as that of the replaced plug. The similarity between the outer form of the adaptor and that of a standard plug ensures that the adaptor can readily be introduced in place of a plug and secured with the usual tools. In the manner of a spark plug, the adaptor may be screwed into the wall 14 until a copper sealing washer 22 is firmly trapped between the wall and an annular shoulder presented by the head portion 18.

The adaptor is axially board out at each end, at an inner end to form an extension chamber 24 wholly within the mounting portion 16, and at an outer end to form a plug-accommodating chamber 26 wholly within the head portion 18. Extending axially from one chamber to the other is a screw-threaded bore 28. The bore 28 has a thread form compatible with that of the standard spark plug 12 of the fitment, which is of a size smaller than that which the adaptor replaces; for example, if the mounting portion 16 is for an 18 mm diameter plug the bore 28 may be for a 14 mm diameter plug.

The fitment is completed by introducing the spark plug 12, of the appropriate size, through the outer end chamber 26 and securing it in the bore 28. The spark-producing electrodes 30 of the plug so become accommodated within the chamber 24, which forms an extension of the combustion chamber within the aperture in the combustion chamber wall 14 when the fitment is secured in the wall.

Claims

1. An internal combustion engine in which a spark plug fitment is secured in an aperture extending through a combustion chamber wall for ignition of fuel in the combustion chamber in running the engine, the fitment forming an extension chamber within the aperture and in communication with the combustion chamber, and comprising spark inducing means arranged to produce an ignition spark within the extension chamber'in running the engine.

2. An engine according to claim 1 in which the aperture in the chamber wall comprises a screw-threaded bore and the fitment comprises an externally screw-threaded mounting portion which forms the extension chamber and is inserted fully to that end of said bore adjacent to the combustion chamber.

3. An engine according to either of claims 1 and 2 in which the fitment comprises a tubular adaptor secured in the aperture in the chamber wall and a spark plug secured in the adaptor, the spark plug comprising electrodes which form the spark inducing means within the extension chamber formed by the adaptor.

4. An engine according to claim 3 in which the adaptor is formed internally with a screw-threaded bore to receive an externally threaded body portion of the spark plug.

5. A spark plug fitment suitable for use in forming an engine- according to claim 1, the fitment comprising a mounting portion which is adapted to be secured within an aperture in a combustion chamber wall and forms an extension chamber and comprising alse spark inducing means arranged to produce an ignition spark within the extension chamber in use of the fitment in running the engine.

6. A fitment according to claim 5 in which the mounting portion is externally screw-threaded for threaded engagement in a screw-threaded bore of the aperture in the combustion chamber wall.

7. A fitment according to either of claims 5 and 6 comprising a tubular adaptor which comprises said mounting portion and comprising a spark plug secured in the adaptor, the spark plug comprising electrodes which form the spark inducing means within the extension chamber.

8. A fitment according to claim 7 in which the adaptor is formed internally with a screw-threaded bore to receive an externally threaded body portion of the spark plug.

9. A tubular adaptor suitable for use in combination with a spark plug to form a fitment according to claim 5, the adaptor comprising an externally screw-threaded mounting portion for threaded engagement in an aperture in a combustion chamber wall to form an extension chamber and the adaptor having a screw-threaded bore arranged to receive a threaded portion of a spark plug of lesser diameter than the mounting portion, the threaded bore extending through the adaptor to the extension chamber.

10. A spark plug fitment substantially as hereinbefore described with reference to the accompanying drawings.

11. An adaptor -substantially as hereinbefore described with reference to the accompanying drawings.