GB2248879A

GB2248879A - Spark plug assembly

Info

Publication number: GB2248879A
Application number: GB9022164A
Authority: GB
Inventors: Andre Demeuter; Michael Lenk
Original assignee: Champion Spark Plug Europe SA
Current assignee: Champion Spark Plug Europe SA
Priority date: 1990-10-11
Filing date: 1990-10-11
Publication date: 1992-04-22
Also published as: GB9022164D0; CA2052975A1; EP0480670A1; JPH0696836A

Description

224337' 1 SPARK PLUGS WITH UNIVERSAL COMPONENTS The present invention

relates to a spark plug comprising a central electrode, an insulator surrounding the central electrode, an outer shell and at least one ground electrode arranged to form a spark gap with an end of the central electrode protruding from the insulator, a portion of the shell being separated from the insulator by a substantially annular space extending along a predetermined length of the insulator and being open towards the spark gap. The present invention also relates to a method of manufacturing spark plugs of this type and a range of such spark plugs.

Spark plugs such as defined above have no particular features with respect to conventional spark plugs and are, for example, disclosed in US patents 4,568,855 - 4,742,265 - 4,771,210 - 4,795,944 4.810,929 and 4,814, 665. Such or similar spark plugs are well known through many other prior art patents and need not be described for the purpose of the present invention.

Since one aspect of the present application relates to a spark plug range it will firstly be explained what, in the present application, is meant by the term "range". The different types of spark plugs produced by a spark plug manufacturingcompany are generally subdivided into ranges and sub-ranges, the criteria for the subdivision being principally one or more common characteristics of one or more of the components of the spark plugs.

For example, if the criteria for the subdivision into ranges is the size and the length of the thread as well as the size of the hexagon of the spark plug shell a manufacturing company may be forced to produce as many as 20 ranges of spark plugs. This is indeed a necessity for said company since the size and the length of the thread as well as the size of the hexagon of the spark plug shell depends on the configuration of the engines which are to be provided with the spark plugs manufactured and sold. More precisely, the size and the length of the thread as well as the size of the hexagon of the spark plug shell depends in fact on the configuration of the cylinder heads of said engines and one type of cylinder head can be used on different engines.

In the present application the term "range" is to be understood as defined in the above example. i.e. a range is a series of spark plugs wherein the size and the length of the thread as well as the size of the hexagon of the spark plug shell is the same for all the plugs. A thus defined range may include as many as 50 different spark plugs, the differences between said plugs being constructional differences other than those defining the ranges. Thus there can be as many as 20 (ranges) x 50 (plugs per range) 1,000 different plugs.

The for example 20 spark plug ranges.of which each includes for example 50 types of plugs are generally further subdivided into sub-ranges, the criteria for the sub-ranges being said constructional differences other than those defining the ranges and which could for example be (a) plug shell with one ground electrode, (b) plug shell with two ground electrodes, (c) multi-metal central electrode, etc. There can be as many as 10 sub-ranges in one range. Each of the sub-ranges comprises a series of spark plugs which differ one from the other by characteristics defining more precisely for example (a) the single ground electrode, (b) the dual ground electrodes, (c)the multi-metal central electrode, etc.

All the spark plugs of one range, i.e. all the spark plugs of the subranges of said range, can be further characterised by the relative axial position of the insulator with respect to the shell of the spark plug, i. e. there could for example be a large (deep), a medium, or a small annular space between the insulator and the plug shell.

As well known by the man of the art heat rating of conventional plugs is mainly determined by where in the heat transfer path away from the spark gap the insulator first makes intimate contact with the shell. Thus variation of the depth of the annular space between the insulator and the plug shell defines -a series of plugs of the same sub-range having different heat ratings. In other words, each of the spark plugs of such a sub-range can be designed in such a way that it works best within a certain heat range, heat range which is imposed by the type of engine said spark plug is to be used in. The spark plugs designed for working at extreme heat ranges are generally known under the designation "cold plugs" and "hot plugs", the cold plugs being generally used in high specific power output (high performance) engines and the hot plugs in low specific power output engines. In the prior art the aforementioned depth variation of said annular space has been achieved using differently constructed shells and insulators for a given plug range.

It should be mentioned here that the majority of commonly available spark plugs have a fixed heat rating which is mainly determined by the depth of the annular space referred to above. However, the prior art also includes so-called "selfadjusting" spark plugs which are intended to exhibit the characteristics of a "hot" plug at lower working temperatures and the characteristics of a "cold" plug at higher working temperatures. Several examples of self-adjusting spark plugs are illustrated in US patents 3612931 and 3743877. These plugs include a thermal shunt positioned in the annular space between the insulator and the shell. The shunt may be bonded to the insulator or the shell. At lower working temperatures a thermal gap is present between the shunt and the shell or insulator so that it has no effect on the transfer of heat in the region of the insulator nose. The dimensions of the shunt are chosen such that it expands to provide a heat transfer path between the insulator and the shell at or above a predetermined design temperature so that the spark plug then behaves as a "cold" plug.

The present invention is concerned with spark plugs having fixed heat ratings.

A very important cost factor in prior art spark plug ranges is the fact that for each type of plug of the range a different insulator had to'be designed, manufactured and stocked and it would therefore be desirable to provide a spark plug range in which this cost factor is substantially reduced.

- 5 The present invention provides a spark plug of the type defined hereinabove in which a portion of the insulator is separated from the shell by a substantially annular space extending along a predetermined portion of the insulator and being open towards the spark gap, and in which a portion of the annular space is filled with a heat conducting material arranged to make intimate contact with the insulator and the shell under all operating conditions of the spark plug.

The portion of the annular space remaining open to the spark gap with the heat conducting material in place determines the heat rating of the spark plug.

Thus, a spark plug range according to the invention may comprise several spark plugs having identical insulators, central electrodes, shells and ground electrodes, with different portions of the annular space being filled with heat conducting material so that different spark plugs in the range have different heat ratings.

The method of manufacturing spark plugs according to this invention comprises filling a portion of the annular space between the insulator and the shell with a heat conducting material so that it makes intimate contact with the insulator and the shell.

An embodiment of the invention will now be described by way of example only and with reference to the accompanying drawings in which:

Figures 1(a) and 1(b) illustrate two prior art spark plugs in vertical cross section having different heat ratings;

Figures 2(a) and 2(b) illustrate schematically the method of manufacturing spark plugs according to this invention; Figures 3(a) and (b) and (c) show partial vertical cross sections of three spark plugs having different heat ratings resulting from the method illustrated in figure 2; and Figure 4 is a further view of the spark plug of figure 3(a) after the ground electrode has been bent to its final position.

Referring firstly t6 figures 1(a) and (b), a conventional spark plug comprises a central electrode 1, and insulator 2 surrounding the central electrode 1, and an outer shell 3, made from electrically conductive material. Attached to the outer shell is a ground electrode 4 arranged to form a spark gap 5 with an end 6 of the central electrode 1 protruding from the insulator 2.

In each of the spark plugs shown in figures 1(a) and (b) the insulator and shell are shaped so as to provide an annular space therebetween extending along a portion of the insulator and open towards the spark gap. This space is indicated as 7(a) and 7(b) in figures 1(a) and 1(b) respectively. The depth X of the annular space of the spark plug of figure 1(a) is less than that V of the spark plug of figure 1(b). Thus, in the spark plug of figure 1(b) heat may be conducted away from the electrodes relatively quickly as compared to the plug of figure 1(b). In other words figure 1(a) shows a "cold" plug whilst figure 1(b) shows a "hot" plug.

It will be noted that the insulators and shells are constructed differently in the two illustrated spark plugs in order to produce annular spaces 7(a), 7(b) of different dimensions. In particular, the insulators 2 each have a flange 8 which rests on a seat 9 on the shells 3. The position of the flange and seat with respect to the ends of the insulators and shells respectively is different in the two spark plugs.

A method of manufacturing spark plugs according to the present invention will now be described in detail with reference to figure 2. Firstly, a spark plug comprising a central electrode 11, an insulator 12. a shell 13 and a ground electrode 14 is assembled according to any suitable method. This may be a conventional method or the novel method of assembly described in our copending application filed simultaneously herewith entitled "Spark plug and method for making it". The end portion of the resulting spark plug including the ground electrode is illustrated in figure 2(a). It will be noted that the ground electrode 14 is in a straight position leaving clear the open end of the annular space 17 between the insulator 12 and the shell 13. The depth Y of the annular space corresponds to that of a "hot" plug, i.e. it is relatively large. The side walls of the annular space, defined by the inner surface of the shell and the outer surface of the insulator, are preferably straight, i. e. without any stepped portion.

Having thus assembled a spark plug, a quantity of heat conducting material is inserted in the annular space 17. This may be in the form of powered metal, fed from a hopper 21 or a metal cylinder 22 or helical spring 23 shaped to fit in the annular space 17, as shown in figure 2(a) or a combination of the above. The metal of the powder, spring or sleeve may, for example be copper. Figure 2(b) illustrates a portion of the assembled spark plug after insertion of the heat conducting material 24. The shading in figure 2(b) is intended to indicate that the material, be it powder or solid metal, is loosely located in the annular space 17.

The material is then subject to a process whereby it is compressed and caused to make intimate contact with the inner surface of the shell 13 and the outer surface of the insulator 12. This may be achieved using a stamp 25, illustrated in figure 2(b), shaped so as to enter the open end of the annular space 17 and compress the heat conducting material 24 without deforming the insulator 12 or the shell 13. Stamping processes of this type are well known in the art and will not be described in detail herein. The heat conducting material 24 can be compressed in such a way that it becomes bonded to itself (in the case of powder or a spring) and to the insulator 12 and shell 13.

Figure 3 illustrates three spark plugs which have been subjected to the process steps illustrated in figure 2. The three plugs are identical in the regions shown and differ only by the depth Z, Z; V' of heat conducting material 24 which has been inserted in the annular space 17. It will be understood that the result is three spark plugs having different heating ratings ranging from "cold" in figure 3(a) to "hot" in figure 3(c). The three plugs illustrated in figure 3 are each filled with heat conducting material along a given portion of the length of the annular space 17 extending from its closed end towards its open end, that given portion being different in each plug whereby each plug has a different heat rating. The intimate contact between the heat conducting - 9 material and the shell and the insulator provides a thermal transfer path for conducting heat away from the spark gap. The heat conducting material should desirably be in intimate contact with the shell and the insulator over the entire facing surfaces of the material 24, shell 13 and insulator 12. A range of spark plugs according to this invention could of course also include a spark plug having no filling in the annular space 17, being at the "hot" end of the range.

After insertion and compression of the heat conducting material 25, the ground electrode is bent into place to form a spark gap 15 with the protruding end 16 of the central electrodes 11. Figure 4 illustrates the spark plug of figure 3(a) after this final step has been completed.

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Claims

CLAIMS:

A method of manufacturing spark plugs having a central electrode (11), an insulator (12) surrounding the central electrode, an outer shell (13) and at least one ground electrode (14) arranged to form a spark gap (15) with an end (16) of the central electrode protruding from the insulator (12), the method comprising providing a substantially annular space (17) between the shell (13) and the insulator (12) extending along a predetermined length (Y) of the insulator (12) and open towards the spark gap (15) and characterised by the step of filling a portion of the space (17) with a heat conducting material (24) so that it makes intimate contact with the insulator (12) and the central electrode (11).
2. A method as claimed in claim 1 in which heat conducting material (24) is inserted in the annular space (17) in the form of a tube (22).
3. A method as claimed in claim 1 or 2 in which heat conducting material (24) is inserted in the annular space (17) in the form of a powder (20).
4. A method as claimed in claim 1, 2 or 3 in which heat conducting material (24) is inserted in the annular space (17) in the form of a helical spring (23).
5. A method as claimed in any preceding claim in which the filling step comprises compressing the heat conducting material (24) into the annular spce (17).

11
6. A spark plug comprising a central electrode (11), an insulator (12) surrounding the central electrode, an outer shell (13) and at least one ground electrode (14) arranged to form a spark gap (15) with an end (16) of the central electrode (11) protruding from the insulator (12), a portion of the insulator being separated from the shell by a substantially annular space (17) extending along a predetermined length (Y) of the insulator (12) and being open towards the spark gap (15), characterised in that a portion of the annular space (17) is filled with a heat conducting material (24) arranged to make intimate contact with the insulator (12) and the shell (13) under all operating conditions of the spark plug.
7. A spark plug as claimed in claim 6 in which the heat conducting material (24) comprises a powder (20).
8. A spark plug as claimed in claim 6 or 7 in which the heat conducting material (24) comprises a cylinder.
9. A spark plug as claimed in claim 6, 7 or 8 in which the heat conducting material comprises a helical spring.
10. A spark plug as claimed in any of claims 6 to 9 in which the heat conducting material (24) is a metal.
11. A spark plug as claimed in any of claims 6 to 10 in which the heat conducting material (24)) is copper.

1 1
12. A spark plug range in which each spark plug comprises a central electrode (11), an insulator (12) surrounding the central electrode (11), an outer shell (1 3) and at least one ground electrode (14) arranged to form a spark gap (15) with an end (16) of the central electrode (11) protruding from the insulator (12), a portion of the insulator (12) being separated from the shell (13) by a substantially annular space (17) extending along a predetermined portion of the insulator (12) and being open towards the spark gap (1 5), characterised in that in at least one of the spark plugs of the range a portion of the annular space (17) is filled with a heat conducting material (24) and in at least one other spark plug of the range a different portion of the annular space (17) is filled with heat conducting material (24), the heat conducting material (24) in said spark plugs being arranged to make intimate contact with the shell (13) and the insulator (12) under all operating conditions of the spark plug.
13. A spark plug range as claimed in claim 9 including at least one spark plug whose annular space is not filled with any heat conducting material.
14. A method of manufacturing spark plugs substantially as hereinbefore described with reference to figures 2 to 4 of the accompanying drawings.
15. A spark plug substantially as hereinbefore described with reference to figures 2 to 4 of the accompanying drawings.
16. A spark plug range substantially as hereinbefore described with reference to figures 2 to 4 of the accompanying drawings.