EP0472009B1 - Exhaust gas purifying device with two exhaust gas treatment bodies one behind the other - Google Patents

Description

The invention relates to a device for cleaning internal combustion engine exhaust gases, in which at least two spaced-apart exhaust gas treatment bodies are held one behind the other in a housing in the longitudinal direction and in which a wire mesh is provided which is placed in the mutually facing end regions of the two exhaust gas treatment bodies around their peripheral surfaces and bridging their distance.

Such devices with ceramic monoliths, which are provided with a catalytically active coating, are known as exhaust gas treatment bodies. Compared to exhaust gas cleaning devices with only one exhaust gas treatment body, they are characterized in particular by the fact that two exhaust gas treatment bodies arranged one behind the other are easier to manufacture and cheaper than a correspondingly longer exhaust gas treatment body and that the cleaning effect is better because behind the first exhaust gas treatment body the partially cleaned exhaust gas is new across the flow cross section mixes before flowing through the second exhaust treatment body.

In exhaust gas purification devices with a tandem arrangement of the exhaust gas treatment bodies, the problem is how to best bridge the distance between the two exhaust gas treatment bodies from the point of view of avoiding at least a substantial flow around the outside Exhaust treatment body and ensuring reliable positioning of the exhaust treatment body in the housing. So far, it has been considered necessary to provide a spacer ring made of sheet metal or rigid ceramic material in the space between the two exhaust gas treatment bodies. Such solutions are comparatively complex, in particular also because of the need to keep the intermediate rings in the correct position during assembly of the exhaust gas cleaning device (combination of the exhaust gas treatment bodies and the housing).

DE-A-38 35 841 results in an arrangement in which the holding of two exhaust gas treatment bodies arranged one behind the other is carried out by a wire mesh that is placed in the facing end regions of the two exhaust gas treatment bodies around their surface and bridges their distance. A similar arrangement is also shown in EP-A-0 415 101, in which a wire mesh mat is arranged as a shielding ring in the bridging area. Both arrangements are wire mesh arrangements without a recognizable thread course. They are used to hold the exhaust gas treatment body and are covered by another mat, e.g. a swelling mat, pressed on or are so thick that they fill the space between the housing and the exhaust gas treatment body. These mats are complex and do not provide adequate outflow protection (barrier effect).

The invention has for its object to provide a generic exhaust gas purification device with a bridging wire mesh in the space between the two exhaust gas treatment bodies, the low cost and a barrier effect against outflow of exhaust gas from the space between the two exhaust gas treatment bodies advantageously combines.

To achieve this object, the device according to the invention is characterized by the features of claim 1 or alternatively of claim 2.

Since this wire mesh is wrapped around the end regions of the two exhaust gas treatment bodies, the assembly of the device is completely free of complications. The expression "cleaning of internal combustion engine exhaust gases" primarily means the catalytic conversion of the pollutant gases CO, NO _x and hydrocarbons into the harmless exhaust gas components CO₂, H₂O and N and / or the removal of particles, often simply called "soot particles", from diesel engine exhaust gases. Accordingly, “exhaust gas treatment body” primarily means ceramic or metallic bodies provided with a catalytically active coating and / or particle filter bodies, which can consist of metallic or ceramic material. Particle filters are also known to consist of several filter elements, which together form the filter in their arrangement; Such arrangements are also included in the term "exhaust gas treatment body". It is understood that the exhaust gas treatment bodies are designed so that the exhaust gas can flow through them.

In most cases, the wire mesh is in a single layer, usually with some overlap at the peripheral end portions around the peripheral end portions of the two exhaust treatment bodies laid around. However, it is pointed out that the scope of the invention also includes designs in which the wire mesh is laid around essentially twice or even more often. The expression "circumferential surfaces" does not mean that the exhaust gas treatment bodies have to be circular in cross section. "Circumference" is only intended to denote that part of the surface of the exhaust gas treatment body in question that is not the entry end face and not the exit end face. Preferred cross-sectional shapes of the exhaust gas treatment bodies are circular, oval, elliptical, rounded with a square, rounded with a triangle. Because of the largely rationalization effect, embodiments of the device according to the invention are preferred in which there is no other distance bridging ring between the edge regions of the mutually facing end faces of the two exhaust gas treatment bodies.

• 1. Drahtgewebe, bei denen die Kette aus vergleichsweise dickeren Drähten und der Schuß aus vergleichsweise dünneren Drähten besteht. Diese Art von Drahtgeweben wird vorzugsweise so eingebaut, daß die dickeren Drähte im wesentlichen in der Längsrichtung der Abgasbehandlungskörper und die dünneren Drähte im wesentlichen in Umfangsrichtung der Abgasbehandlungskörper verlaufen.
• 2. Drahtgewebe, bei denen Kette und Schuß, bestehend aus gleichdicken Drähten oder aus unterschiedlich dicken Drähten, nach Art eines Leinengewebes verwebt sind. In diesem Fall wird das Drahtgewebe vorzugsweise so eingesetzt, daß die Drähte der Kette und die Drähte des Schusses schräg zur Längsrichtung des Abgasbehandlungskörpers verlaufen.

Among a large number of possible, usable wire meshes, two are particularly preferred:

• 1. Wire mesh in which the warp consists of comparatively thicker wires and the weft consists of comparatively thinner wires. This type of wire mesh is preferably installed so that the thicker wires run substantially in the longitudinal direction of the exhaust gas treatment body and the thinner wires substantially in the circumferential direction of the exhaust gas treatment body.
• 2. Wire mesh in which the warp and weft, consisting of wires of the same thickness or of wires of different thickness, are woven in the manner of a linen fabric. In this case, the wire mesh is preferably used so that the wires of the chain and the wires of the weft run obliquely to the longitudinal direction of the exhaust gas treatment body.

Wire mesh is naturally not gas-tight. Nevertheless, the wire mesh laid around provides a certain flow barrier for the exhaust gas against flowing out of the distance area between the two exhaust gas treatment bodies For higher requirements, however, it can be favorable to provide one or more layers of a ceramic fiber fabric or a glass fiber fabric around the wire mesh. It is advantageous if the last-mentioned fabric is at least a little longer in the longitudinal direction than the wire fabric, so that the two end edges of the wire fabric are covered.

In a further development of the invention, it is preferred that the two exhaust gas treatment bodies are held in the housing by means of a mounting mat which also bridges their distance and overlaps the wire mesh. The arrangement of exhaust gas treatment bodies, the wire-bridging wire mesh lying around and the mounting mat lying over it can be combined with the housing in a simple and efficient manner to assemble the device. The mounting mat forms a continuous heat insulation layer between the exhaust gas treatment bodies or the exhaust gas-flowed space of the device and the housing, so that the exhaust gas treatment bodies desirably quickly reach and maintain their operating temperature and that the exterior of the housing does not desirably become excessively hot. The term “superimposed” should not necessarily mean that they lie directly on top of one another, rather one or more intermediate layers may still be present between the exhaust gas treatment bodies and the wire mesh on the one hand and the mounting mat on the other hand. It is even particularly preferred if, in particular, a ceramic fiber fabric or a glass fiber fabric is laid around on the inside of the mounting mat. In addition to the advantage of protecting the mounting mat from stronger exposure to exhaust gas, there is the further significant advantage that relative sliding movements between the housing with mounting mat on the one hand and the arrangement of exhaust gas treatment bodies and wire mesh on the other hand are easier; this is of particular importance for the behavior of the device under temperature changes between operating temperature and non-operating temperature. The housing is usually made of sheet metal and therefore expands quite considerably at the comparatively high operating temperature the exhaust gas treatment bodies, especially if they are made of ceramic, practically do not stretch when the temperature rises.

The state that the wire mesh assumes in the space between the two exhaust gas treatment bodies after the assembly of the device depends primarily on the resistance to deformation of the wire mesh and on the pressure that the mounting mat, which is normally compressed between the housing and the exhaust gas treatment bodies, depends on from the outside exercises the wire mesh. In a first option (high resistance to deformation of the wire mesh, relatively low pressure exerted by the mounting mat) there is practically no inward pushing of the wire mesh in the spacing area; the exhaust gas treatment bodies and the wire mesh are held by the "pre-tensioning" of the mounting mat against longitudinal displacement relative to the housing, with the exception of the relative movement described above in the case of thermal expansions and thermal contractions. In a second possibility (pressure exerted by the mounting mat so large that the wire mesh is slightly deformed inward in the spacing area), the wire mesh assumes a position in the assembled state in which it is pressed a little inward in the spacing space, so that this results in a certain amount positive, additional fixation of the distance between the two exhaust gas treatment bodies arises. Incidents are possible, in particular the formation of a small step of the wire mesh at the transition from the peripheral surface of the exhaust gas treatment body in question to the spacing area.

It is preferred to hold the two exhaust gas treatment bodies in the housing by means of a so-called inflation mat. Inflatable mats, which are known per se, consist essentially of ceramic fibers with mica embedding. As a result of the mica deposits, the inflatable mat tends to expand as the temperature rises, as a result of which the exhaust gas treatment body is held particularly securely even at higher temperatures of the device. It is pointed out that the inflatable mat does not necessarily extend over the length of the two exhaust gas treatment bodies, including the spacing area must, but can be divided into several inflatable mats, in particular one inflatable mat per exhaust gas treatment body. However, it is particularly preferred if the inflatable mat extends in the longitudinal direction, as described above in connection with the mounting mat.

According to a preferred embodiment of the invention, it is provided that the housing in front of the exhaust gas treatment bodies has a first transition area that widens in the flow direction and behind the exhaust gas treatment bodies has a second transition area that narrows in the flow direction; that an inner housing part is provided in the transition region, which ends close to the adjacent exhaust gas treatment body; and that an insulating mat is arranged in a circumferential space between the respective housing part and the housing. In this way, the housing, including the transition regions, is insulated from the gas-flowed space throughout. The insulating mats can each bridge the gap between the inner housing part and the adjacent exhaust gas treatment body, and the respective insulating mat can be protected on the inside in the gap area by a ceramic fiber fabric or by a glass fiber fabric. It is particularly preferred if the ceramic fiber fabric or the glass fiber fabric passes from the first gap area over the first exhaust gas treatment body, the metal fabric for the distance between the exhaust gas treatment bodies and the second exhaust gas treatment body up to the second gap area.

The longitudinal direction of the device, which has been mentioned several times in the preceding description, generally coincides at least essentially with the general gas flow direction in the device.

In absolute terms, the wires of the wire mesh are preferably very thin and in most cases lie in a diameter range from 0.04 to 0.6 mm. The larger wire thicknesses are particularly suitable for those wire fabrics which are woven from thicker and thinner wires and are used in such a way that the thicker wires run essentially in the longitudinal direction of the device.

Fig. 1

einen Längsschnitt durch die Längsachse einer Abgasreinigungsvorrichtung, wobei in der oberen Hälfte der Fig. 1 und in der unteren Hälfte der Fig. 1 unterschiedliche Ausführungsvarianten dargestellt sind;

Fig. 2

einen Teil-Querschnitt längs II-II in Fig. 1, wobei wiederum in der oberen Zeichnungshälfte und in der unteren Zeichnungshälfte unterschiedliche Ausführungsformen dargestellt sind.

The invention and refinements of the invention are explained in more detail below with reference to exemplary embodiments illustrated in the drawings. It shows:

Fig. 1

a longitudinal section through the longitudinal axis of an exhaust gas purification device, different variants being shown in the upper half of FIG. 1 and in the lower half of FIG. 1;

Fig. 2

a partial cross section along II-II in Fig. 1, again different embodiments are shown in the upper half of the drawing and in the lower half of the drawing.

The illustrated exhaust gas purification device 2 has a housing 4 made of sheet steel, which is essentially cylindrical in the central region and is substantially frustoconical in shape on the right and left in FIG. 1. Seen in cross section, the housing 4 consists of two half-shells each with two outwardly bent longitudinal edges 6, which are welded to the longitudinal seam 8 when the device 2 is assembled. The two essentially frustoconical areas are called first transition area 10 (left in FIG. 1) and second transition area 12 (right in FIG. 1).

An inner housing part 14 is provided in the transition regions 10 and 12, which is welded to the housing 4 at the inlet end or at the outlet end of the device 2 and ends at the other end close to an adjacent exhaust gas treatment body 16. With the exception of the respective area where the inner housing part 14 is welded to the housing 4, there is a circumferential spacing space between the inner housing part 14 and the housing 4. An insulating mat 18 is arranged in each of these spacing spaces. The insulating mat extends in each case over the gap area 20 between the relevant inner housing part 14 and the relevant exhaust gas treatment body 16 and surrounds a part of the inlet-side or outlet-side peripheral surface of the relevant exhaust gas treatment body 16.

The two exhaust gas treatment bodies 16 are held in the housing 4 at a mutual spacing 22 by means of a swelling mat 24 which is passed around between the two insulating mats 18. To better fix the position of the two insulating mats 18 and the inflatable mat 24, the housing 4 has various circumferential beads. The inner housing parts 14 also have a circumferential bead in their end regions closer to the exhaust gas treatment bodies 16.

Around the circumferential surfaces of the two exhaust gas treatment bodies 16, a wire mesh 26 is placed in their mutually facing end regions, which bridges the distance region 22 between the two exhaust gas treatment bodies 16. For a clearer illustration, the exhaust gas treatment bodies are drawn uncut. It can be seen in the more central area of the device how the wire mesh 26 bridges the spacing area between the two exhaust gas treatment bodies 16, and further up or down in FIG. 1 it can be seen how the wire mesh 26 covers a part of the peripheral surface of the exhaust gas treatment body 16 in question.

The variant above in FIG. 1 is a wire mesh that is woven from thicker wires running in the longitudinal direction of the device 2 and from thinner wires running in the circumferential direction. Such a wire mesh is well bendable parallel to the thicker wires, so that it can be easily laid around the exhaust gas treatment body 16. The thicker wires running in the longitudinal direction result in a relatively high resistance to deformation against deformation from the cylindrical surface of the wire mesh 26 lying around, particularly inwards. Therefore, the upper wire mesh 26 is drawn in such a way that, without being pressed inwards in the spacing area 22, it passes from left-front to right-back in a substantially cylindrical shape. Deviating from the embodiment shown in Fig. Above, however, it can be such that the pressure of the inflatable mat 24 is chosen so large that the wire mesh 26 above in Fig. 1 on the facing end edges of the two exhaust gas treatment body 16 a little bit quasi gradually is pressed inside.

The wire mesh 26 shown at the bottom in FIG. 1 is a wire mesh in which the wires are woven together in the manner of a linen fabric, with warp and weft having the same wire thickness but also a slightly different wire thickness. The wires all run at approximately 45 ° to the longitudinal direction or gas flow direction of the device 2. This wire mesh 26 has a lower resistance to deformation, so that in the spacing area 22 there is a slight deformation of the wire mesh 26 towards the inside in longitudinal section. This deformation results in a certain, additional positional fixation of the exhaust gas treatment body 16 and keeps the exhaust gas flow flowing through the distance region 22 to a certain extent away from the edge region of the inlet end face on the left in FIG. 1 of the exhaust gas treatment body 16 on the right in FIG. 1.

In FIG. 1 above, a ceramic fiber fabric or a glass fiber fabric 28 is also drawn in, which is wrapped around the arrangement of the two exhaust gas treatment bodies 16 and the wire mesh 26 and in FIG. 1 on the left and in FIG. 1 on the right over the gap area 20 to a piece extends on the peripheral surface of the relevant inner housing part 14. The inflatable mat 24 or the respective insulating mat 18 is placed around this fabric 28.

In Fig. 1 below, a variant is drawn in which two ceramic fiber fabrics or glass fiber fabrics 28 are laid around in an analogous position, but only to cover the relevant gap area 20 and the joint area between the relevant insulating mat 18 and the expanding mat 24, and not continuously therebetween. It is understood that the wire mesh 26 drawn at the top in FIG. 1 can be combined with the fabrics 28 drawn at the bottom in FIG. 1 and vice versa.

In Fig. 2 you can again see the structure of the device 2 with from the inside to the outside exhaust gas treatment body 16, wire mesh 26, optionally ceramic fiber or glass fiber fabric 28, inflatable mat 24, housing 4. In Fig. 2 above you can see that the upper wire mesh 26 in a special weave is woven in which the weft wires 30 on one side each along two chain wires 32 before they go over to the other flat side of the wire mesh 26. An example of this special weave is the so-called twill weave.

It goes without saying that the wire mesh has a sufficiently high temperature resistance to withstand the temperatures that occur in internal combustion engine exhaust gases. A particularly preferred material for the wires of the wire mesh 26 is stainless steel. In the illustrated exemplary embodiments, the wire mesh 26, the ceramic fiber mesh or glass fiber mesh 28, the insulating mat 18 and the inflatable mat 24 are each provided essentially in one layer (essentially with a butt joint or with a small circumferential overlap). However, you can also work in multiple layers.

It is pointed out that instead of the provision of two insulating mats 18 and an inflatable mat 24, it is also possible to work with a continuous support mat, either made of inflatable mat material or of ceramic fiber material or of glass fiber material. Other materials, in particular wire mesh, are also possible for the mats 18 and 24. The fabric 28 facilitates sliding movements between the exhaust gas treatment bodies 16 and the housing 4 as a result of thermal expansions or thermal contractions. In addition, the fabric 28 prevents attacks of the pulsating, hot gas on the mats 18 and 24. The direction of exhaust gas flow through the device 2 is indicated by the arrow 34.

Claims (9)

1. Device for cleaning internal combustion engine exhaust gases, in which there are mounted in a housing (4) one behind the other in the longitudinal direction (34) at least two spaced exhaust gas treatment bodies (16) and in which there is provided a wire woven material (26) which, in the mutually facing end regions of the two exhaust gas treatment bodies (16), is laid around the peripheral surfaces thereof and bridges over the spacing (22) thereof, characterized in that the wire woven material (26) has thicker wires (30) running substantially in the longitudinal direction (34), and thinner wires (32) running substantially in the peripheral direction.
2. Device for cleaning internal combustion engine exhaust gases, in which there are mounted in a housing (4) one behind the other in the longitudinal direction (34) at least two spaced exhaust gas treatment bodies (16) and in which there is provided a wire woven material (26) which, in the mutually facing end regions of the two exhaust gas bodies (116), is laid around the peripheral surfaces thereof and bridges over the spacing (22) thereof, characterized in that the wire woven material (26) has wires which are woven in the manner of a linen fabric, and in that the wires run obliquely with respect to the longitudinal direction (34).
3. Device according to Claim 1 or 2, characterized in that there is arranged in the free space between the two exhaust gas treatment bodies (16) a spacing-bridging ring.
4. Device according to one of Claims 1 to 3, characterized in that there is laid around the wire woven material (26) a ceramic fibre woven material (28) or a glass fibre woven material (28) which in the longitudinal direction (34) is longer than the wire woven material (26).
5. Device according to one of Claims 1 to 3, characterized in that the two exhaust gas treatment bodies (16) are mounted in the housing (4) by means of a mounting mat (24) which also bridges over the spacing (22) thereof and lies on top of the wire woven material (26).
6. Device according to Claim 5, characterized in that the wire woven material (26) in the region of the spacing (22) between the two treatment bodies (16) is pressed inwards somewhat by the mounting mat (26).
7. Device according to one of Claims 1 to 5, characterized in that the mounting mat (24) comprises a swelling mat.
8. Device according to one of Claims 1 to 6, characterized in that the housing (4) has upstream of the exhaust gas treatment bodies (16) a first transition region (10) which widens in the direction of flow (34), and has downstream of the exhaust gas treatment bodies (16) a second transition region (12) which tapers in the direction of flow; in that there is provided in the transition regions (10, 12) in each case an internal housing part (14) which terminates just before the adjacent exhaust gas treatment body (16); and in that an insulating mat (18) is arranged in a peripheral spacing area between the respective internal housing part (14) and the housing (4).
9. Device according to Claim 8, characterized in that the insulating mats (18) in each case bridge over the gap (20) between the internal housing part (14) and the adjacent exhaust gas treatment body (16), and in that in the gap region (20) the respective insulating mat (18) is protected on the inside by means of a ceramic fibre woven material (28) or a glass fibre woven material (28).

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