Patent Application
20150017073
The invention relates to an exhaust-gas cleaning device as well as to an exhaust-gas system comprising such a device, especially for internal combustion engines.
The state of the art discloses exhaust-gas cleaning devices in which, upstream from an exhaust-gas converter, the exhaust-gas path is divided by an inner tube into a central flow path and a peripheral flow path (e.g. German patent application DE 103 50 516 A). One of these parallel flow paths, especially the peripheral flow path, can contain an exhaust-gas catalyst. Suitable actuators serve to convey the exhaust-gas stream via the peripheral flow path through the annular exhaust-gas cleaning means or else to bypass the latter via the central flow path. Such an arrangement is known, for example, in conjunction with a downstream three-way catalyst upstream from which there is an adsorber for hydrocarbons (HC adsorber) in one of the parallel flow paths. As long as the main catalyst has not yet reached its operating temperature after the engine has been started, the exhaust-gas stream is conveyed via the peripheral HC adsorber that temporarily stores the hydrocarbons that are present in the exhaust gas. As soon as the downstream catalyst has reached its operating temperature, the exhaust-gas stream is conveyed via the central flow path so as to bypass the HC adsorber and to heat it up. Once the HC adsorber has reached its desorption temperature, the exhaust gas is once again conveyed partially or completely through the HC adsorber in order to discharge the released hydrocarbons and to transport them into the main catalyst, where they are catalytically converted. This arrangement permits a very good reduction of HC start-up emissions. However, the production of an annular catalyst support is relatively complicated.
German patent application DE 26 27 596 A describes a holder for a catalyst support in a catalyst housing, whereby, along the circumference of the front faces of the catalyst support, a sealing ring is placed onto each support where it widens conically towards the housing and is in contact with it.
The present invention is based on the objective of putting forward an exhaust-gas cleaning device which entails the possibility of exhaust-gas lines that can be connected in parallel and which has a simpler design than prior-art devices such as those known, for example, from German patent application DE 103 50 516 A.
The exhaust-gas cleaning device according to the invention comprises the following:
The presence of the sealing means hinders or even completely prevents the cross flow of the exhaust gas stream between the flow paths upstream from the support. Consequently, the at least two parallel flow paths upstream from the exhaust-gas cleaning component are separated from each other up to the front face of their support on the inlet side. In this manner, exhaust gas can be systematically fed to certain zones of the support, whereas exhaust gas does not flow through other areas.
When two or more flow paths are sealed off from each other, especially the high temperatures that occur as well as the large temperature differences that occur as a function of the operating point have to be taken into consideration. In particular, the temperature differences lead to significant thermal expansions of the various components. For this reason, it is not permitted for the downstream end of the separating element of the parallel flow paths to come into direct contact with the front face of the support since this could subject the components to high stresses or could even damage them.
In a preferred embodiment of the invention, the at least one sealing means comprises a groove which is created in the support and into which the downstream end of the separating element and/or another sealing means (that is attached to the separating element) of the above-mentioned type extends. Owing to the above-mentioned thermal expansions of the components, the downstream end of the separating element preferably ends at a certain distance, that is to say, without making contact with the groove bed. The configuration of the sealing means in the form of a groove in the support functions in the manner of a labyrinth seal (also called a gap seal) in which the cross flow of the exhaust gas stream is reduced between the flow paths by means of deflections and a lengthening of the flow path in the gap that is to be sealed as well as by means of the formation of baffles.
According to another embodiment of the invention, the at least one sealing means comprises a sealing element that is attached to the downstream end of the support and that is elastically in contact with the front face of the support or—in case a groove has been created into the support—with the groove (the groove bed). Here, within the scope of the present invention, the term “elastically in contact” refers to a reversible yieldingness of the sealing element in the axial direction, thereby taking into consideration the thermal expansions of the components, which can be expected during the operation of the exhaust-gas cleaning device. Preferably, the axially elastic yieldingness of the sealing element is selected in such a way that there is still contact between the sealing element and the support, even at the maximum temperature-induced distance that is to be expected between the separating element and the support.
According to a first embodiment, such a sealing element comprises a brush element having several brushes that are in contact with the front face of the support or, if applicable, with the groove (especially the groove bed) of the support. Here, the brushes can be configured as metal wires that are made, for example, of stainless steel, nickel or a nickel alloy. The number and density of the brushes should be selected in such a way that a sufficient sealing effect between the flow paths is achieved.
In an alternative embodiment, the sealing element comprises a spring plate having a plurality of slots that run diagonally in the axial direction (that is to say, in the flow direction of the exhaust gas), in other words, at a slanted angle relative to the axial direction. The lamellar structure of the spring plate created by the slots ensures a certain amount of elasticity in the axial direction and thus a sealing effect, even at different temperatures and expansions of the components. The spring plate is preferably made of a heat-resistant and corrosion-resistant material, for example, stainless steel, nickel or a nickel alloy. In another configuration, the sealing element also encompasses a sealing mat that surrounds the spring plate, at least on one side. In this manner, the cross flow is reduced even further by the slots of the spring plate and a mechanical damping effect is achieved. Especially ceramic fibers and glass fibers are options as materials for the sealing mat.
The division of the flow path upstream from the exhaust-gas cleaning component can be implemented with various geometries. According to a first embodiment, the separating element is configured as an inner tube, for instance, with a round or oval cross section, and it is arranged on the inside of the housing, preferably coaxially. It is likewise conceivable for two or more inner tubes having different diameters to be arranged concentrically so that, during operation, the streams flow over the exhaust-gas cleaning component in the form of several separate ring zones. In an alternative embodiment, the separating element is configured as a partition that passes through the housing radially (centrally or off-center) and that can have a planar or any other desired contoured shape. For example, a planar partition that passes through the housing centrally can be provided, so that the exhaust-gas path is divided into two flow paths in the form of semi-circles or semi-ellipses. By the same token, several partitions running in parallel can be provided, or else several intersecting partitions that divide the flow path into circular segments. Fundamentally, the term “parallel flow paths” as used within the scope of the present invention is not to be construed in the strict geometric sense, but rather, from a fluid mechanics perspective, in the sense of a flow that can take place through such paths selectively.
According to a preferred embodiment of the invention, in the area of an axial projection of the separating element onto the support, the support of the exhaust-gas cleaning component has a zone that is essentially flow-impermeable. In this context, the term “axial projection of the separating element” refers to the imaginary connection surface of the separating element when the latter is fictively lengthened in the flow direction of the exhaust gas and would thus touch the front face of the support. The axial projection of the separating element on the support corresponds, in a manner of speaking, to the “slipstream” of the separating element. Owing to the presence of the flow-impermeable zone, the sealing effect of the device is reduced even further as far as a cross flow of the exhaust gas between the parallel flow paths is concerned. Such a flow-impermeable zone can be implemented, for example, in that the support has a plurality of flow channels running axially which, in the area of the flow-impermeable zone, are either absent or closed off on the inlet side.
In a preferred embodiment of the invention, the exhaust-gas cleaning component has at least two zones in the radial direction with different functionalities, whereby these zones correspond to the at least two upstream flow paths, that is to say, they are essentially flush with them. In this manner, the exhaust-gas stream can be selectively and systematically guided to certain zones of the exhaust-gas cleaning component in order to utilize these functionalities in a targeted manner. In particular, the zones of the exhaust-gas cleaning components can have the functionality of an exhaust-gas catalyst, for instance, an oxidation catalyst, a reduction catalyst or a three-way catalyst, an adsorber, for instance, an HC adsorber or an NOx adsorber, or else a particle filter. Such functionalities can be implemented in a familiar manner by means of suitable coatings and/or by means of the geometric configurations of the flow channels. Optionally, the zones of the exhaust-gas cleaning component can also encompass a function-free zone through which the exhaust gas is merely conducted without any catalytic functions or retention functions coming to the fore.
In a special embodiment, the first zone has the functionality of an HC adsorber while a second zone has the functionality of a three-way catalyst, or else it is function-free. In this embodiment, the HC adsorber zone serves to retain hydrocarbons after a cold start of the internal combustion engine. As soon as an upstream pre-catalyst or the actual three-way catalyst of the second zone has reached its operating temperature, at least in certain areas, the exhaust-gas stream is switched over to pass through the second zone while bypassing the HC adsorber zone. Then, when a downstream three-way catalyst or oxidation catalyst has also reached its operating temperature, the exhaust-gas stream is once again diverted to the first zone via the HC adsorber, so that the hydrocarbons are desorbed and then converted in the downstream catalyst.
According to another aspect, the invention relates to an exhaust-gas system, especially for an internal combustion engine, that comprises an exhaust-gas cleaning device according to the invention. In an advantageous manner, this exhaust-gas system can be part of a motor vehicle.
Other advantageous embodiments of the invention are the subject matter of the other subordinate claims.
The invention will be explained below on the basis of embodiments. The following is shown:
First of all,
The exhaust-gas cleaning device 10 shown in
In the housing 14, there is an exhaust-gas cleaning component 16 that is affixed in the axial direction, in other words, in the flow direction of the exhaust gas 12, by two cross-section constrictions 18 (narrowed sections). Additional fixation and impact damping of the exhaust-gas cleaning component 16 can be attained in a known manner by surrounding them radially with a mat (not shown here), especially with a so-called intumescent mat.
The exhaust-gas cleaning component 16 comprises a support 20 having a front face 22 on the inlet side as well as a front face 24 on the outlet side. The support 20 has a plurality of flow channels that pass through the support in the axial direction. For instance, the support 20 can be configured as a monolith made of a ceramic material. As an alternative, it is likewise possible to use supports that are made of a rolled metal plate. The walls of the flow channels can have a coating (so-called washcoat) which gives the exhaust-gas cleaning component 16 its desired functionality. For example, the coating can comprise a catalytically active component, especially a noble metal, or else a storage component for the reversible storage of certain exhaust-gas components. By the same token, the support 20 can have a particle-retention function, thanks to a suitable design of the flow channels.
Inside the housing 14, upstream from the exhaust-gas cleaning component 16, there is a separating element 26 that divides the flow path of the exhaust gas into two parallel flow paths. In the example at hand, the separating element is configured as an inner tube 26 that divides the exhaust-gas path into a central flow path 28 and an annular, peripheral flow path 30. The exhaust-gas cleaning device 10 also encompasses means (not shown here) with which the exhaust-gas stream can be selectively guided into the first flow path 28 or into the second flow path 30. Optionally, these means can also be configured to be continuously adjustable so that any desired division of the exhaust-gas stream into the two flow paths 28, 30 is possible. For instance, these baffles can have an adjustable flap that is arranged at an inlet area of the inner tube 26. An example of a suitable arrangement is described in German patent application DE 10 350 516 A1. In the position shown in
Depending on the selection of the flow path 28 or 30, the exhaust gas enters different zones of the support 20, namely, a first zone 32 comprising a central area of the support 20 that corresponds to the first flow path 28, or else a second zone 34 having an annular geometry corresponding to the second flow path 30.
The various zones 32, 34 of the exhaust-gas cleaning component 16 can have different functionalities in terms of their coating and/or the geometric design of their flow channels. In a special embodiment, for example, the peripheral annular zone 34 can have an HC adsorber coating so that, up to a certain temperature limit, hydrocarbons are reversibly adsorbed. At the same time, the central zone 32 can be function-free, that is to say, not have any coating, or else it can have a three-way catalytic coating. By the same token, the diameter and cell densities of the flow channels of the various zones 32, 34 can be selected so as to differ. For instance, as shown here, the flow channels of the peripheral zone 34 can be configured so as to be smaller and to have a larger number of cells than the central zone 32. Owing to the smaller diameter and the greater cell density, a high specific surface area and thus a higher efficiency are achieved for the catalytic coating.
In the example shown, the support 20 has a flow-impermeable zone 36 which is characterized in that, in this area, there are no flow channels in the support 20 or else these flow channels are closed on the inlet side. The arrangement of the flow-impermeable zone 36 matches an axial projection of the inner tube 26 on the support 20 or, to put it in other words, it corresponds to the “slipstream” of the separating element 26. Together with the sealing means that are still to be elaborated on, the flow-impermeable zone 36 ensures a reduction of the cross flow of the exhaust-gas stream 12 between the flow paths 28 and 30.
According to the invention, in the area of the front face 22 of the support 20 on the inlet side and/or in the area of the downstream end of the separating element 26, there are sealing means 38 that counter the cross flow of the exhaust gas between the parallel flow paths 28 and 30. In the present example shown in
Thanks to the sealing means 38, a systematic flow towards the zones 32 and 34 can be achieved while largely avoiding leakage flows. At the same time, the elastic configuration of the sealing means 38 avoids a direct contact between the separating element 28 and the front face 22 of the support 20. This prevents thermal stresses between these components as well as damage to them.
An exhaust-gas cleaning device according to a second embodiment of the invention is explained on the basis of
Diverging from the embodiment shown in
Corresponding to the straight configuration of the partition 40, the brush element 38 likewise has a straight shape. Aside from that, the brush element 38 can be configured as described in
A third embodiment of the exhaust-gas cleaning device according to the present invention will be explained on the basis of
Similarly to the first embodiment according to
The spring plate 42 shown in greater detail in a single view in
An exhaust-gas cleaning device 10 according to a fourth embodiment of the invention is explained with reference to
As can be seen in
A fifth embodiment of the invention is shown in
A sixth embodiment of the exhaust-gas cleaning device 10 according to the invention is shown in
A seventh embodiment of the exhaust-gas cleaning device 10 according to the invention is shown in
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2012 017 178.1 | Mar 2012 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2013/052547 | 2/8/2013 | WO | 00 |
