GB2574032A

GB2574032A - Annular seal for spark plug or the like

Info

Publication number: GB2574032A
Application number: GB1808475.6A
Authority: GB
Inventors: Guisasola Inigo
Original assignee: Caterpillar Energy Solutions GmbH
Current assignee: Caterpillar Energy Solutions GmbH
Priority date: 2018-05-23
Filing date: 2018-05-23
Publication date: 2019-11-27
Anticipated expiration: 2038-05-23
Also published as: GB201808475D0; DE102019112957A1; GB2574032B

Abstract

An annular seal for a threaded body (41 in Figure 10), such as a spark plug (40 in Figure 10) is provided. The seal assembly 1 comprises annular, first and second seal elements 10, 20, each seal element having annular, first 12, 22 and second 13, 23 sealing surfaces. The seal elements 10, 20 are arranged coaxially with their first sealing surfaces 12, 22 in abutment to define an interface 2 forming an angle θ with the central axis X of the assembly. The seal elements 10, 20 are then compressed axially at their second sealing surfaces 13, 23 to cause relative axial and radial displacement ∆a, ∆r between the first sealing surfaces 12, 22. The radial displacement ∆r generates a hoop stress Hc, Ht causing elastic deformation in one or both seal elements. A method of forming such a seal, and an assembly comprising such a seal are also disclosed.

Description

Technical field

This disclosure relates to seals and particularly although not exclusively to seals for use in sealing a threaded body such as a spark plug or glow plug against a mounting surface of an internal combustion engine.

Background

Annular seals or gaskets for spark plugs are generally required to act in compression between axially opposed faces of the spark plug and cylinder head. Generally such seals are made from metal so as to deform elastically to compensate for settling movement or unevenness while maintaining a pressure tight seal over the operating temperature range of the engine.

Such seals may be damaged by plastic deformation resulting from the application of excessive heat or excessive axial force in use.

Seals of the above mentioned type often have a generally S-shaped cross-section, for example, as taught by US 9,181,918 B2.

However, the curved surfaces may provide only small contact areas and hence only limited heat transmission between the spark plug and the cylinder head. Better heat transmission is desirable to cool the spark plug and the seal in use and may extend the useful life of either or both components.

Summary

Accordingly, in its various aspects the present disclosure provides a seal and a method of forming a seal, as defined in the claims.

The seal comprises first and second annular seal elements, each seal element having first and second annular sealing surfaces. The seal is formed by assembling the seal elements together to form an assembly defining an aperture extending along an axis X through both of the seal elements, wherein the first sealing surfaces are arranged in opposed abutting relation at an annular interface, and the second sealing surfaces define outer, oppositely and outwardly facing surfaces of the assembly. A compressive force F is then applied to the second sealing surfaces in opposed directions of the axis X to compress the seal elements axially together.

When considered in a plane P containing the axis X, a straight line collinear with or tangent to each of the first sealing surfaces at the interface intersects the axis X at an acute angle Θ which is selected to cause relative axial (Aa) and radial (Ar) displacement between the first sealing surfaces at the interface responsive to the compressive force F. At least one of the seal elements is elastically extensible or compressible responsive to a hoop stress (Ht, He) generated by the relative radial displacement Ar.

Brief Description of the Drawings

Further features and advantages will be appreciated from the illustrative embodiments which will now be described, purely by way of example and without limitation to the scope of the claims, and with reference to the accompanying drawings, in which: Figs. 1 -12 show a first embodiment wherein:

Figs. 1 and 2 are respectively a top view and a bottom view of a first seal element;

Figs. 3 and 4 are respectively a top view and a bottom view of a second seal element;

Fig. 5 is a section at A - A (Fig. 1) through the first seal element;

Fig. 6 is a section at B - B (Fig. 3) through the second seal element;

Fig. 7 is a side view of the first and second seal elements assembled together;

Fig. 8 is a section at A - A and B - B through the assembly of Fig. 7, taken in a common plane P containing the axis X;

Fig. 9 is a top view of the assembly of Fig. 7 illustrating the hoop stresses generated in the first and second seal elements by axial compression of the assembly;

Fig. 10 shows the seal assembly of Fig. 7 in use to form a seal between a spark plug and the cylinder head of an internal combustion engine; and

Figs. 11 and 12 show part of the assembly of Fig. 10, respectively before and after axial compression of the seal; and

Fig. 13 shows another seal assembly according to a second embodiment.

Reference numerals and characters appearing in more than one of the figures indicate the same or corresponding elements in each of them.

Detailed Description

Referring to Figs. 1 - 6, a first seal or seal assembly 1 comprises a first seal element 10 and a second seal element 20. Each seal element is annular and defines a central aperture 11, 21 which extends along a central axis X.

In this specification, the terms axially and radially are to be construed by reference to the central axis X, and annular means in the form of a ring surrounding the central aperture, irrespective of whether the ring is circular or noncircular. Conveniently however, each seal element 10, 20 may be generally circular so that most or, as exemplified by the illustrated embodiment, all of its surfaces including the first and second sealing surfaces are surfaces of revolution, and the seal element comprises or consists of a solid of revolution, about its central axis X.

Each seal element 10, 20 defines an annular, first sealing surface 12, 22 and an annular, second sealing surface 13, 23.

In use, the first and second seal elements 10, 20 are assembled together coaxially to form an assembly 1 defining an aperture 11, 21 extending along the central axis X through both of the seal elements, as shown in Figs. 7 and 8.

In the assembled condition, the first sealing surfaces 12, 22 are arranged in opposed abutting relation at an annular interface 2 which is defined by the mutually abutting portions of the first sealing surfaces 12, 22.

Figs. 10 -12 show how the seal assembly 1 may be used to install a threaded body 40 such as a spark plug or glow plug via a threaded aperture 41 into a combustion chamber 42 of an internal combustion engine 43. The threaded body is arranged to pass through the central aperture 11, 21 of the seal assembly 1 so that the second sealing surfaces 13, 23 bear respectively against a sealing surface 44 of the threaded body and an opposed sealing surface 45 of the engine, which may form for example part of a cylinder head or engine block. In the illustrated example, the threaded body 40 is advanced in the direction of the arrow in Fig. 12 by screwing it into the aperture 41 to apply a compressive force F to the seal assembly 1.

Referring particularly to Fig. 8 and Fig. 12, when considered in a plane P containing the axis as shown, it can be seen that a straight line 2' collinear with or tangent to each of the first sealing surfaces 12, 22 at the interface 2 intersects the axis X at an acute angle Θ.

The angle Θ is selected to cause relative axial displacement Aa and relative radial displacement Ar between the first sealing surfaces 12, 22 at the interface 2 when the compressive force F is applied to the second sealing surfaces 13, 23 in opposed directions of the axis X as shown to compress the seal elements 10, 20 axially together. By relative displacement is meant movement of the first sealing surfaces 12, 22 relative to one another.

The angle θ may be selected according to the coefficient of friction and other parameters defined by the selected material and other geometric parameters of the seal elements in accordance with design principles well known in the art to obtain the desired relationship between applied stress and strain.

Referring also to Fig. 9, the relative radial displacement Ar between the first sealing surfaces 12, 22 generates a tensile hoop stress Ht in the radially outermost, first seal element 10, which is reacted by a compressive hoop stress He in the radially innermost, second seal element 20. At least one of the first and second seal elements 10, 20 is arranged (inter alia, by suitable selection of the seal material) to be elastically extensible or compressible responsive to the hoop stress Ht or He which in turn permits the relative radial displacement Ar.

The balanced elastic forces energise the seal assembly to urge the second sealing surfaces 13, 23 resiliently axially outwardly and apart against the opposed surfaces 44, 45 of the use environment, and to urge the first sealing surfaces 12, 22 resiliently and 15 radially together. The seal assembly may thus move to accommodate movement in the use environment while maintaining a sealing force across the interface 2 and axially between the opposed surfaces 44, 45, which also permits effective thermal conduction through the seal assembly between the opposed surfaces 44,45 via the first and second seal elements 10, 20 and via the interface 2.

Either or both of the first and second seal elements 10, 20 may be arranged to react the hoop stress Ht or He by circumferential elastic deformation.

For example, the first sealing surface 12 of the first seal element 10 may be arrranged to 25 be displaced radially outwardly with respect to the axis X relative to the first sealing surface 22 of the second seal element 20 when the compressive force F is applied to compress the seal elements 10, 20 axially together. Thus, the first seal element 10 may be elastically extensible responsive to the tensile hoop stress Ht generated by the outward relative radial displacement Ar of the first sealing surface 12 relative to the first 30 sealing surface 22.

Advantageously, the first seal element 10 may be arranged to withstand the resulting tensile hoop stress Ht in normal use when it is radially outwardly unsupported, as shown in the example of Fig. 12 where the first seal element 10 is free to move radially outwardly away from the axis X. In this way the seal assembly can be arranged in a recess without relying on the radially inwardly facing wall of the recess to confine its radial expansion, so that it can easily be removed from the recess when required.

Similarly, the second seal element 20 may be arranged to withstand the compressive hoop stress He without contacting the threaded body 40 with its radially inner surface 10 which defines its central aperture 11.

The seal assembly may be installed and removed over the threaded body 40 or, (not shown), may be captive on the threaded body in the manner of a conventional gasket or sealing ring as used in spark plugs and the like.

Referring again to Figs. 10 -12, it can be seen that the second sealing surfaces 13, 23 define outer, oppositely and outwardly facing surfaces of the assembly 1 which are oriented to react the compressive force F which, in use, is applied to the second sealing surfaces 13, 23 in opposed directions of the axis X to compress the seal elements 10, 20 20 axially together from the rest position of Fig. 11 to the axially compressed, use position of Fig. 12.

Conveniently, and as exemplified by the illustrated embodiment, the second sealing surfaces 13, 23 may define axial end faces or extremities of the assembly 1.

Either or each of the second sealing surfaces 13, 23 may extend in a flat plane normal to the axis X and/or, when considered in a plane P containing the axis X, along a straight line normal to the axis X. The assembly 1 may thus be arranged between opposed, flat surfaces normal to the direction of axial compression as illustrated in Figs. 10 -12.

In alternative embodiments, either or both of the second sealing surfaces 13, 23 may be inclined or curved relative to the axis X so as to contact a correspondingly shaped surface in its intended use position.

Preferably, each of the second sealing surfaces 13, 23 extends over a relatively large surface area so as to provide effective heat transfer through the seal assembly 1 between the axially opposed surfaces 44,45 of an engine and a spark plug or other threaded body 40, or of any other use environment which maintain the seal assembly in compression.

Referring particularly to Fig. 8, in the illustrated embodiment, when considered in a plane P containing the axis X, each of the second sealing surfaces 13, 23 is normal (i.e. perpendicular) to the axis X with a radial width respectively R1 and R2, while the assembly 1 has a total radial width R3 between its inner and outer diameters on each 15 side of the axis X. In order to provide a compact seal assembly with good heat transfer capability, when the total radial width R3 is measured in normal use in an axially compressed condition of the seal assembly as illustrated for example in Fig. 12, the radial width Rl, R2 of each of the second sealing surfaces 13, 23 may be not less than 0.4-R3, further advantageously not less than 0.5-R3.

When considered in a plane P containing the axis X, either or both of the first sealing surfaces 12, 22 may extend along a straight or curved line which may define a common line of their respective, mutually abutting portions at the interface 2, so that the interface 2 may extend along a straight or curved line in the plane P.

Thus, as exemplified by the illustrated embodiment, each of the first sealing surfaces 12, may extend in the longitudinal section plane P along a straight line which defines relative to the axis X (represented in Figs. 5 and 6 by a parallel line X') the acute angle Θ of the interface 2.

Referring again to Fig. 8, in the illustrated embodiment, the interface 2 extends in the plane P containing the axis X along a straight line having a length L2.

The assembly 1 has a maximum axial length LI, which as in the illustrated example may be defined between the parallel planes of the second sealing surfaces 13, 23. It can be seen that the axial length LI is reduced in the energised, use position of Fig. 12 compared with the unenergised, rest position of Fig. 11.

In order to provide good heat transfer capability in a seal assembly 1 of given axial length LI, when the lengths LI and L2 are measured in normal use in an axially compressed condition of the assembly, for example as shown in Fig. 12, the common line defining the interface 2 may have a length L2, wherein L2 > 0.3-L1. (In this case, if the common line is not straight, then the length L2 should be measured to follow its curvature.)

Each of the first and second seal elements 10, 20 may be made from (e.g . may comprise or may consist substantially of) a metal or a metal alloy or any other suitable material or materials, which may be selected for suitable elasticity, thermal conductivity and other characteristics as known in the art according to the intended application.

A metal or metal alloy may be suitable for many applications such as sealing spark plugs and other threaded bodies for installation in a combustion chamber.

Where the first and second seal elements are made from a metal or metal alloy or other suitable material, thermal conductivity and mechanical strength may be further improved by arranging for each of the first and second seal elements 10, 20 to be of monolithic construction - which is to say, when considered in a plane P containing the axis X, each of the first and second seal elements 10, 20 defines a cross-section bounded by a boundary having no inflections.

This can be seen in the illustrated embodiment of Figs. 1 -12 where both seal elements 10, 20 are of monolithic construction.

By way of illustrating the point, Fig. 13 shows a section in a plane P containing the axis X through a similar assembly in an alternative embodiment comprising a first seal element 110 and a second seal element 120. The first seal element 110 is of monolithic construction, defining in section a boundary 101 without inflections (points where curvature changes from convex to concave) - which is to say, a continuous boundary which is outwardly protuberant with an absence of inwardly pointing regions or concavities. The second seal element 120 is not quite monolithic, defining in section a boundary 101 with inflections defining small concavities 102 in its boundary.

Of course, good mechanical strength (particularly resistance to axial compression) and thermal conductivity can still be obtained where any such concavities are only small relative to the overall size of the section.

Thus in the example of Fig. 13 it can be seen that when considered in a plane P containing the axis X, each of the first and second seal elements 110,120 defines a cross-section having a cross-sectional area, and at least 80% of the cross-sectional area of each respective cross-section may be contained within an imaginary boundary 103 lying entirely within the respective cross-section and having no inflections.

The boundary 103 of the second seal element 120 is defined a small distance inwardly from the boundary 101 representing the outer surface of the section. The large majority of the section is free from concavities and so the second seal element 120 is substantially monolithic.

In summary, a seal assembly 1 comprises annular, first and second seal elements 10, 20, each seal element having annular, first and second sealing surfaces 12, 22,13, 23. The seal elements are arranged coaxially with their first sealing surfaces 12, 22 in abutment to define an interface 2 forming an angle θ with the central axis X of the assembly, and then compressed axially at their second sealing surfaces 13, 23 to cause relative axial and radial displacement Aa, Ar between the first sealing surfaces 12, 22. The radial displacement Ar generates a hoop stress He, Ht causing elastic deformation in one or both seal elements 10, 20.

The first and second seal elements may be configured so that, as illustrated, the first seal element 10 has an internal and external diameter larger than the respective internal and external diameter of the second seal element 20 so that the second seal element fits partially or substantially inside the first seal element with the interface 2 forming for example a partially conical surface of revolution between them. The radially inner and outer surfaces of the assembly (comprising the radially outer surface 14 of the first, larger seal element 10 and the radially inner surface 24 of the second, smaller seal element 20) may be cylindrical surfaces of revolution about the axis X as shown, so that the assembly fits neatly around a cylindrical threaded body and/or into a cylindrical recess. However, other configurations may be adopted to suit a particular use situation.

In alternative embodiments, one of the first sealing surfaces could extend along a straight line and the other along a curved line, or both could extend with common curvature (selected to define the desired relationship between axial displacement and radial and hoop stresses) to define a curved interface.

Industrial applicability

The novel seal assembly may be used as a seal or gasket in static (i.e. non-rotating) applications in place of known elastically compressible seal assembles of S or other configuration to provide effective heat transfer between axially opposed sealing surfaces, for example, of an engine and a spark plug, glow plug, fuel injector, sensor or other threaded body installed into a combustion chamber via a threaded aperture in the engine, prolongiing the life of the seal assembly and associated components.

The seal assembly can be used in situations where the seal elements are radially unconfined so that it can easily be removed with the threaded body, even when installed in a recess, without binding on the walls of the recess.

Thermal conductivity between the sealing surfaces can be improved by selecting the relative dimensions of the seal elements such that L2 > 0.3-L1 for good conduction between the first and second seal elements, and/or such that R1 > 0.4-R3 and R2 > 0.4-R3, preferably R1 > 0.5-R3 and R2 > 0.5-R3 for good conduction between each of the seal elements and the respective sealing surface of the engine, threaded body or other use environment, and further by arranging for each seal element to have a substantially monolithic construction as discussed above, and most preferably by providing all of these features in combination.

A relatively monolithic construction may also provide better resistance to crushing and so ensure that the seal assembly is less susceptible to damage by axial compressive forces when compared with an S shaped or other folded configuration as known in the art.

In order to maximise resistance to axial compression, the first and second seal elements 10, 20 may further be configured (inter alia, by selecting a suitable interface angle Θ) such that the first and second seal elements 10, 20 may be axially compressed without permanent deformation (i.e. to remain within their elastic limits) to reduce their combined axial length LI to a value equal to the overall axial length (in plane P) of only one of the first and second seal elements 10 or 20.

In this case, the axially longer seal element or, if both seal elements are of equal axial length, each seal element may define a solid body which extends unbroken when considered in a straight line in the axial direction between its second sealing surface 13, 23 and an axially opposite, outwardly facing surface 15, 25 of the respective seal element, so that the solid body is placed in compression between the opposed surfaces 44, 45 of the use environment acting against surfaces 13 and 15 or against surfaces 23 and 25 when both seal elements are maximally elastically strained. The opposite surface 15 or 25 may be of smaller radial width than the respective second sealing surface 13 or 23, as shown.

In this way, the monolithic body of the axially longer one, or (if of equal axial length) each, of the first and second seal elements 10, 20 may act in compression between the opposed sealing surfaces of the use environment to resist an excessive axial compressive force F without further increasing the tensile or compressive hoop stress Ht, He in either element, so that the assembly 1 can return resiliently to a functional (i.e. resiliently axially outwardly biased) state when the excessive compressive force is relieved.

Many further adaptations may be made within the scope of the claims.

In the claims, reference numerals and characters are provided in parentheses purely for ease of reference, and should not be construed as limiting features.

Claims

1. A seal (1) comprising an annular first seal element (10) and an annular second

5 seal element (20), each seal element having an annular first sealing surface (12, 22) and an annular second sealing surface (13, 23);

the seal elements being configured such that, when assembled together to form an assembly (1) defining an aperture (11, 21) extending along an axis (X) through both of the seal elements:

10 the first sealing surfaces (12, 22) are arranged in opposed abutting relation at an annular interface (2) wherein, when considered in a plane (P) containing the axis, a straight line (2') collinear with or tangent to each of the first sealing surfaces at the interface intersects the axis (X) at an acute angle Θ, and the second sealing surfaces (13,23) define outer, oppositely and outwardly

15 facing surfaces of the assembly (1); wherein the angle θ is selected to cause relative axial (Aa) and radial (Ar) displacement between the first sealing surfaces (12, 22) at the interface (2) when a compressive force (F) is applied to the second sealing surfaces (13, 23) in opposed directions of the axis (X) to compress the seal elements (10, 20) axially together; and

20 at least one of the seal elements (10, 20) is elastically extensible or compressible responsive to a hoop stress (Ht, He) generated by said relative radial displacement (Ar).

2. A seal according to claim 1, wherein the first sealing surface (12) of the first seal element (10) is arranged to be displaced radially outwardly with respect to the axis (X)

25 relative to the first sealing surface (22) of the second seal element (20) when the compressive force (F) is applied to compress the seal elements axially together; and the first seal element (10) is elastically extensible responsive to a tensile hoop stress (Ht) generated by said outward relative radial displacement (Ar); and the first seal element (10) is arranged to withstand said tensile hoop stress (Ht)

30 in normal use when radially outwardly unsupported.

3. A seal according to claim 1, wherein mutually abutting portions of the first sealing surfaces (12, 22) at the interface (2) extend along a common line in a plane (P) containing the axis (X).

4. A seal according to claim 3, wherein, in normal use in an axially compressed condition of the assembly (1), when considered in the plane (P) containing the axis (X), the assembly (1) has a maximum axial length LI, and the common line has a length L2, wherein L2 > 0.3L1.

5. A seal according to claim 1 wherein, when considered in a plane (P) containing the axis (X), each of the first and second seal elements (10, 20) defines a cross-section bounded by a boundary (101) having no inflections.

15

6. A seal according to claim 1 wherein, when considered in a plane (P) containing the axis (X), each of the first and second seal elements (10, 20) defines a cross-section having a cross-sectional area, and at least 80% of the cross-sectional area of each respective cross-section may be contained within a boundary (103) lying entirely within the respective cross-section and having no inflections.

7. A seal according to claim 1, wherein when considered in a plane (P) containing the axis (X), at least one of the second sealing surfaces (13, 23) extends along a straight line normal to the axis (X).

25

8. A seal according to claim 1, wherein each of the first and second seal elements (10, 20) is made from a metal or metal alloy.

9. An assembly comprising a threaded body (40) for sealing installation via a threaded aperture (41) into a combustion chamber (42) of an internal combustion

30 engine (43), and a seal (1) according to claim 1, the second sealing surfaces (13, 23) being arranged in use to bear respectively against a sealing surface (44) of the threaded body (40) and an opposed sealing surface (45) of the engine (43).

10. A method of forming a seal (1), comprising:

providing an annular first seal element (10) and an annular second seal element (20), each seal element having an annular first sealing surface (12, 22) and an annular second sealing surface (13, 23);

assembling together the first and second seal elements to form an assembly (1) defining an aperture (11, 21) extending along an axis (X) through both of the seal elements (10, 20), wherein:

the first sealing surfaces (12, 22) are arranged in opposed abutting relation at an annular interface (2) wherein, when considered in a plane (P) containing the axis (X), a straight line (2') collinear with or tangent to each of the first sealing surfaces (12, 22) at the interface (2) intersects the axis (X) at an acute angle Θ, and the second sealing surfaces (13, 23) define outer, oppositely and outwardly facing surfaces of the assembly (1);

applying a compressive force (F) to the second sealing surfaces (13, 23) in opposed directions of the axis (X) to compress the seal elements (10, 20) axially together;

causing, by said compressive force (F), relative axial (Aa) and radial (Ar) displacement between the first sealing surfaces (12, 22) at the interface (2);

generating, by said relative radial displacement (Ar), a hoop stress (Ht, He) in at least one of the seal elements (10, 20); and causing, responsive to said hoop stress (Ht, He), elastic extension or compression of said at least one of the seal elements (10, 20).