GB2268695A - Catalytic converter mesh seals - Google Patents

Abstract

A continuous, substantially uniform annular wire mesh ring seal 20 for a catalytic converter, is formed by rolling a knitted wire mesh sleeve upon itself in a direction substantially parallel to the longitudinal axis of the sleeve. The annular wire mesh ring seal 20 has a substantially cylindrical cross-section comprised of spirally-wound layers of wire mesh, in which adjacent wire portions 40, 42 in contact with one another are securely anchored to one another, for example by welding as at points 38, 50 as to produce a resilient annular wire mesh ring seal 20 having a substantially stable dimensional configuration during usage as a wire mesh seal in a catalytic converter. <IMAGE>

Description

CATALYTIC CONVERTER MESH SEALS This invention relates to catalytic converters for use in the treatment of exhaust gases produced from internal combustion engines, such as internal combustion engines used in motor vehicles.

In particular it relates to catalytic converter mesh seals used in such catalytic converters.

A catalytic converter for use in the treatment of exhaust gases produced from an internal combustion engine of a motor vehicle customarily comprises a catalytically-active material, such as platinum, palladium, rhodium, or mixtures thereof, which is finely distributed upon an inert support material so as to provide as large a contact area as possible to the exhaust gases to be treated. One common form of the support material is a porous honeycomb-type monolithic structure of ceramic material having a plurality of passages formed therethrough from one end to another, the monolithic structure having a circular or oval cross-section.The catalyticallyactive material is deposited on the walls of the through passages of the monolithic structure, and the monolithic structure is encased within a metal housing connected into the exhaust system of the motor vehicle so that the exhaust gases produced from the engine of the motor vehicle all pass through the passages in the monolithic structure for treatment before those gases are released into the atmosphere.

It is essential in catalytic converters utilising a porous monolithic structure that the monolithic structure shall be retained within the metal housing in such a way as to avoid any risk of any untreated exhaust gases by-passing the monolithic structure and issuing into the atmosphere.

Consequently it is customary to surround the outer periphery of the monolithic structure with some form of sealing means to prevent any by-pass of untreated exhaust gases between the outer periphery of the monolithic structure and the interior surface of the metal housing. Such a sealing means needs to be of a resilient nature, in order to cushion any shocks or vibration transmitted from the metal housing to the monolithic structure as a result of the operation of the engine of the motor vehicle and/or the motion of the motor vehicle, since the monolithic structure is formed of frangible ceramic material.Moreover, the sealing means also needs to be formed from a heat-resistant and heat-expandable material in order to resist the temperatures of the hot exhaust gases passing through the converter and to compensate for the differences in thermal expansion between the monolithic structure and the metal housing.

A sealing means that has been shown to be remarkably effective for this purpose is a peripheral wrapping mat of resilient heat-expandable intumescent material sandwiched between the monolithic structure and the metal housing, with each exposed end of the mat being in contact with a wire mesh seal woven from a fine gauge metal wire, such as stainless steel wire.

The wire mesh seal acts both as part of the overall sealing means and as a means of preventing the hot exhaust gases from coming into direct contact with the exposed end of the wrapping mat and eroding that mat.

It will be understood, therefore, that such a wire mesh seal should be manufactured in such a fashion as ensure that it will not become loose or misplaced relative to the end of the wrapping mat with which it is in contact.

A wire mesh seal that is in current use in catalytic converters is termed a "lap and smash" wire mesh seal, and which is produced by firstly knitting a cylindrical sleeve approximately 25 mm in diameter from fine gauge steel wire of approximately 0.152 mm in diameter; flattening said sleeve into a substantially flat, rectangular shape; rolling said flat shape spirally into a cylindrical shape having a longitudinal axis which is parallel to the longitudinal axis of the flat, rectangular shape; pulling the cylindrical shape through a cylindrical die in order to stretch the woven material and to form the cylindrical shape into a cylindrical shape of predetermined diameter; cutting the formed cylindrical shape into a predetermined length; forming said predetermined length into a circle; and then spot-welding the free ends of said predetermined length together in order to produce the finished "lap and smash" wire mesh seal.

Wire mesh seals can also be produced more directly by knitting the fine gauge steel wire into a cylindrical sleeve having a diameter of approximately 115 mm, which cylindrical sleeve is cut to length and rolled up from each end to produce an annular wire mesh structure comprising two annular rings in contact with one another, each having a layered circular cross-section. This annular wire mesh structure is then placed into an annular die set of the correct dimension and compressed to size in order to form the desired wire mesh seal.Unfortunately, although such seals have the advantage that they are continuous in construction and do not require to be spot-welded in order to produce the finished wire mesh seal, it is difficult to remove the tendency for such continuous seals to stretch and loosen around the monolithic structure of the catalytic converter during the use of the converter.

A catalytic converter wire mesh seal according to the present invention comprises a continuous, substantially uniform annular wire mesh ring seal formed by rolling a knitted wire mesh sleeve upon itself in a direction substantially parallel to the longitudinal axis of the sleeve, said annular wire mesh ring seal having a substantially cylindrical cross-section comprised of spirally-wound layers of wire mesh, in which annular wire mesh ring seal, adjacent wire portions in contact with one another are securely anchored to one another, so as to produce a resilient annular wire mesh ring seal having a substantially stable dimensional configuration during usage as a wire mesh seal.By the term "a substantially stable dimensional configuration", we mean that the annular wire mesh ring seal retains sufficient resilience during usage as a seal between a monolithic structure and a metal housing surrounding said structure, so as to function satisfactorily as a seal during thermal expansion and contraction of said monolithic structure relative to said metal housing, without stretching and loosening on the monolithic structure.

Preferably the adjacent wire portions in contact with one another are securely anchored to one another by projection welding of those adjacent wire portions to one another at the contact points thereof.

In a preferred embodiment of the present invention, in which projection welding is used to secure the adjacent wire portions to one another at the contact points thereof, the thickness of the wire used to form the mesh ring ranges from 0.1 mm to 0.2 mm, the mesh ring is subjected to a welding contact pressure of 10 to 20 N, and projection welding of the adjacent wire portions to one another at the contact points thereof is achieved by applying a weld current of 3,000 to 7,000 amps for a period of 0.1 to 0.5 seconds.

A method of producing a catalytic converter wire mesh seal according to the present invention comprises the steps of knitting a sleeve of wire mesh of a first predetermined diameter from fine gauge wire; cutting said wire mesh sleeve to a predetermined length; rolling said predetermined length of wire mesh sleeve upon itself in a direction substantially parallel to the longitudinal axis of the sleeve, so as to form an annular wire mesh structure comprising at least one annular wire mesh ring having a substantially cylindrical cross-section comprised of a spirally-wound layer of wire mesh; placing said annular wire mesh structure into a die set having a second predetermined, larger, diameter and compressing and stretching said annular wire mesh structure to form a pre-stretched annular wire mesh ring of said second predetermined diameter; placing the pre-stretched annular wire mesh ring between two plate electrodes of a projection welding assembly, and clamping the pre-stretched annular wire mesh ring in position between said plate electrodes with a predetermined welding contact pressure; and then subjecting said pre-stretched annular wire mesh ring to a predetermined welding current for a predetermined brief welding time just sufficient to weld together adjacent wire portions in the pre-stretched annular wire mesh ring that are in contact with one another.

Preferably, in this method of producing a catalytic converter wire mesh seal according to the present invention, the fine gauge wire has a thickness ranging from 0.1 mm to 0.2 mm; the wire mesh sleeve is knitted on a cylindrical knitting machine employing from 50 to 65 needles per row of mesh, for example, 58 needles per row of mesh, with each row of mesh being approximately 4.5 mm wide; the first predetermined diameter of the wire mesh sleeve is approximately 115 mm; the predetermined length of the wire mesh sleeve is 250 mm; the wire mesh seal is rolled upon itself by starting the rolling from both ends simultaneously so as to produce an annular wire mesh structure comprising two annular wire mesh rings, each having a substantially cylindrical cross-section comprised of a spirally-wound layer of wire mesh, in contact with one another; the second predetermined diameter of the die set is approximately 130 mm; the predetermined welding contact pressure ranges from 10 to 20 N; the predetermined welding current ranges from 3,000 to 7,000 amps; and the brief welding period ranges from 0.1 to 0.5 seconds. It should be understood, of course, that the specific dimensional figures quoted above are in respect of a wire mesh seal for a specific size of catalytic converter, and that these specific dimensional figures would be different for a wire mesh seal designed to fit a larger or smaller size of catalytic converter.

The invention and how it may be performed are hereinafter particularly described with reference to the accompanying drawings, in which: Figure 1 shows an exploded, isometric view of a catalytic converter containing catalytic converter wire mesh seals according to the present invention; Figure 2 is an enlarged isometric view of a monolithic structure and catalytic converter wire mesh seals from the converter shown in Figure 1; Figure 3 is a plan view of one of the catalytic converter wire mesh seals shown in Figure 2, when removed from the monolithic structure; Figure 4 is an enlarged cross-sectional view of the catalytic converter wire mesh seal shown in Figure 3, taken on the line 4 - 4' of Figure 3; Figure 5 is an enlarged view of the portion of Figure 4 shown within the dashed circle A of Figure 4;; Figure 6 is a schematic view of a portion of a wire mesh sleeve used to make the catalytic converter wire mesh seal shown in Figures 3 to 5; Figure 7 is a schematic view of a wire mesh structure formed from the wire mesh sleeve partially illustrated in Figure 6; Figure 8 is a partial, cross-sectional view of an annular die set used to stretch and compress the wire mesh structure shown in Figure 7 into a pre-stretched annular wire mesh seal; and Figure 9 is a schematic view of a portion of a projection welding apparatus for forming the catalytic converter wire mesh seal shown in Figures 3 to 5 from the pre-stretched annular wire mesh seal produced in the annular die set shown in Figure 8.

Figure 1 shows an exploded, isometric view of a catalytic converter 10 comprising two porous honeycomb-type monolithic structures 12, 14 of ceramic material, each having a plurality of passages 16 formed therethrough from one end to another, and having an oval cross-section. Each of the porous honeycomb-type monolithic structures 12, 14 is wrapped in a peripheral wrapping mat 18 of resilient heat-expandable intumescent material, with each exposed end of the mat being in contact with a wire mesh seal 20 according to the present invention, woven from a fine gauge metal wire, such as stainless steel wire. The monolithic structures 12 and 14 are encased within a metal housing which comprises an upper shaped sheet metal shell 22 and a lower shaped sheet metal shell 24.Each of the shells 22 and 24 have integrally-formed funnel portions 26,27 and 28,29, respectively at opposite ends thereof, a series of re-inforcing ridges 30 formed on a main body portion 32 of the shell, and integral side flanges 34,35 and 36,37, respectively, which mate with one another to encase the monolithic structures 12 and 14 within the metal housing formed by the metal shells 22 and 24. The peripheral wrapping mat 18 of resilient heat-expandable intumescent material is sandwiched between the monolithic structures 12 and 14 and the metal shells 22 and 24 forming the metal housing, and forms a heat-resistant sealing means therebetween.The funnel portions 26 and 28 co-operate with each other to form an inlet for hot exhaust gases when the catalytic converter 10 is installed in an exhaust system of a motor vehicle (not shown), and the funnel portions 27 and 29 co-operate with each other to form an outlet for treated exhaust gases leaving the converter 10. Each wire mesh seal 20 acts both as part of the overall sealing means between the monolithic structures 12 and 14 and the metal shells 22 and 24 forming the metal housing, and as a means of preventing the hot exhaust gases from coming into direct contact with the exposed end of the wrapping mat 18 and eroding that mat 18.

Figure 2 shows an enlarged isometric view of the monolithic structure 12 and two of the catalytic converter wire mesh seals 20 from the catalytic converter 10 shown in Figure 1, illustrating more clearly how the peripheral wrapping mat 18 of resilient heat-expandable intumescent material is wrapped around substantially the whole of the outer curved portion of the monolithic structure 12, and how the ends of the peripheral wrapping mat 18 of resilient heat-expandable intumescent material are covered by being in contact with the respective wire mesh seals 20.

The catalytic converter wire mesh seal 20 of the invention is shown in more detail in Figures 3 to 5 of the accompanying drawings. As can be seen in Figures 3 to 5, the wire mesh seal 20 is essentially a continuous annular, resilient wire mesh ring formed from a continuous knitted mesh of fine gauge wire rolled upon itself to form a spirally-wound wire mesh structure in the form of a pre-stretched annular wire mesh ring in which adjacent strands of wire are anchored to one another, as by welding, so as to stabilise the dimensional configuration of the wire mesh seal 20 against any tendency to stretch and to loosen from the respective monolithic structure 12,14 during the operation of the catalytic converter 10. As can best be seen in Figure 5, contact points 38 between adjacent strands 40,42 of wire in the wire mesh seal 20 are subjected to projection welding conditions such that the adjacent strands 40,42 of wire become welded to one another at those contact points 38 so as to effectively lock the adjacent strands 40,42 to one another in the wire mesh seal 20, and thus prevent any tendency for the wire mesh seal to stretch and loosen due to relative movement occurring in the knitted wire mesh between the adjacent strands 40 and 42.

Turning now to a preferred method for making the catalytic converter wire mesh seals of the invention, the steps involved are illustrated in Figures 6 to 9 of the accompanying drawings. Firstly, as shown in Figure 6, a wire mesh sleeve 44 is knitted from a fine gauge metal wire having a thickness within the range of 0.1 mm to 0.2mm, preferably a thickness of 0.152 mm. As is shown schematically in Figure 6, the wire mesh forming the sleeve 44 is comprised of adjacent strands 40 and 42 interlaced with one another to form knitted rows of mesh, each of which knitted rows are approximately 4.5 mm wide. The wire mesh sleeve 44 is continuously knitted on a circular knitting machine (not shown) employing 58 needles per row, and is knitted to a diameter d1 which is approximately 115 mm.A predetermined length of the continuous wire mesh sleeve 44, such as 250 mm, is then cut off to make each catalytic converter wire mesh seal 20. This predetermined length of wire mesh sleeve 44 is rolled upon itself in a direction substantially parallel to the longitudinal axis of the sleeve 44, by starting the rolling from both ends simultaneously so as to produce an annular wire mesh structure 46 comprising two annular wire mesh rings 48,50, each having a substantially cylindrical cross-section comprised of a spirally-wound layer of wire mesh, in contact with one another, as shown in Figure 7.

The annular wire mesh structure 46 is now placed in an annular die set 52 having relatively movable pressing members 54, 56 and 58. A cross-sectional view of a portion of the annular die set 52 is shown in Figure 8. The annular wire mesh structure 46 undergoes both stretching and compression as a result of the relative movement of the pressing members 54, 56 and 58, so as to produce a pre-stretched annular wire mesh ring 60 of a predetermined diameter d2 such as, for example, 130 mm.

This pre-stretched annular wire mesh ring 60 is now placed between spaced, relatively movable electrode plates 62 and 64 of a projection welding apparatus 66, a portion of which is illustrated in cross-section in Figure 9 of the drawings. The electrode plates 62 and 64 are then moved towards one another so as to clamp the pre-stretched annular wire mesh ring 60 therebetween with a welding contact pressure which ranges from 10 to 20 N. A welding current which ranges from 3,000 to 7,000 amps is then passed through the pre-stretched annular wire mesh ring 60 from electrode plate 62 to electrode plate 64 for a period of time just sufficient to weld together said adjacent wire portions 40,42 in the pre-stretched annular wire mesh ring 60 that are in contact with one another. A suitable period of time ranges from 0.1 to 0.5 seconds.

The catalytic converter wire mesh seal of the invention represents a marked improvement over both the known "lap and smash" seals and the continuous annular wire mesh seals referred to earlier in this application. The catalytic converter wire mesh seal of the invention has the advantage over the "lap and smash" seal in that it possesses a uniform shape and produces a uniform seal around a monolithic structure on which it is placed, and in that it is cheaper and easier to make. The catalytic converter wire mesh seal of the invention has the advantage over the continuous annular wire mesh seal referred to earlier in that it does not suffer from the tendency to stretch and loosen around a monolithic structure on which it is placed, during the operating conditions experienced by that monolithic structure in a catalytic converter.

Claims (13)

Claims:

1. A catalytic converter wire mesh seal comprising a continuous, substantially uniform annular wire mesh ring seal formed by rolling a knitted wire mesh sleeve upon itself in a direction substantially parallel to the longitudinal axis of the sleeve, said annular wire mesh ring seal having a substantially cylindrical cross-section comprised of spirally-wound layers of wire mesh, in which annular wire mesh ring seal, adjacent wire portions in contact with one another are securely anchored to one another, so as to produce a resilient annular wire mesh ring seal having a substantially stable dimensional configuration during usage as a wire mesh seal.

2. A catalytic converter wire mesh seal according to claim 1, in which the adjacent wire portions in contact with one another are securely anchored to one another by projection welding of those adjacent wire portions to one another at the contact points thereof.

3. A catalytic converter wire mesh seal according to claim 1 or 2, in which the thickness of the wire used to form the mesh ring ranges from 0.1 mm to 0.2 mm.

4. A catalytic converter wire mesh seal according to claim 3, in which the thickness of the wire used to form the mesh ring is 0.152 mm.

5. A method of producing a catalytic converter wire mesh seal according to claim 1, which method comprises the steps of knitting a sleeve of wire mesh of a first predetermined diameter from fine gauge wire; cutting said wire mesh sleeve to a predetermined length; rolling said predetermined length of wire mesh sleeve upon itself in a direction substantially parallel to the longitudinal axis of the sleeve, so as to form an annular wire mesh structure comprising at least one annular wire mesh ring having a substantially cylindrical cross-section comprised of a spirally-wound layer of wire mesh; placing said annular wire mesh structure into a die set having a second predetermined, larger, diameter and compressing and stretching said annular wire mesh structure to form a pre-stretched annular wire mesh ring of said second predetermined diameter; placing the pre-stretched annular wire mesh ring between two plate electrodes of a projection welding assembly, and clamping the pre-stretched annular wire mesh ring in position between said plate electrodes with a predetermined welding contact pressure; and then subjecting said pre-stretched annular wire mesh ring to a predetermined welding current for a predetermined brief welding time just sufficient to weld together adjacent wire portions in the pre-stretched annular wire mesh ring that are in contact with one another.

6. A method of producing a catalytic converter wire mesh seal according to claim 5, in which the fine gauge wire has a thickness ranging from 0.1 mm to 0.2 mm.

7. A method of producing a catalytic converter wire mesh seal according to claim 5 or 6, in which the wire mesh sleeve is knitted on a cylindrical knitting machine employing 58 needles per row of mesh, with each row of mesh being approximately 4.5 mm wide.

8. A method of producing a catalytic converter wire mesh seal according to claim 5, 6 or 7, in which the first predetermined diameter of the wire mesh sleeve is approximately 115 mm; the predetermined length of the wire mesh sleeve is 250 mm; and the second predetermined diameter of the die set is approximately 130 mm.

9. A method of producing a catalytic converter wire mesh seal according to any one of claims 5 to 8, in which the wire mesh seal is rolled upon itself by starting the rolling from both ends simultaneously so as to produce an annular wire mesh structure comprising two annular wire mesh rings, each having a substantially cylindrical cross-section comprised of a spirally-wound layer of wire mesh, in contact with one another.

10. A method of producing a catalytic converter wire mesh seal according to any one of claims 5 to 9, in which the predetermined welding contact pressure ranges from 10 to 20 N; the predetermined welding current ranges from 3,000 to 7,000 amps; and the brief welding period ranges from 0.1 to 0.5 seconds.

11. A catalytic converter wire mesh seal substantially as hereinbefore particularly described with reference to Figures 1 to 5 of the accompanying drawings.

12. A method of producing a catalytic converter wire mesh seal substantially as hereinbefore particularly described with reference to Figures 6 to 9 of the accompanying drawings.

13. A catalytic converter containing at least one catalytic converter wire mesh seal according to claim 1.