EP1342889B1 - Exhaust system for a combustion engine with a catalytic converter - Google Patents

Description

The invention relates to an exhaust system for internal combustion engines according to the preamble of claim 1.

Such exhaust systems with exhaust gas converter are e.g. from DE 35 36 315 A1. known.

The invention is based on the technical problem of an exhaust system of the initially type to make available, in which after a cold start of the engine a quickly reaching the light-off temperature in the Interior of the exhaust converter is possible.

To achieve this object, the exhaust system has the features in claim 1.

Catalyst bodies are very common in two technical versions: Ceramic monolith containing a large number of longitudinal flow channels and metal catalyst bodies, in which also a large number of longitudinal flow channels is present, these flow channels by the mating of a corrugated sheet with a flat sheet metal and spiral-like winding of this pairing are made. Often they are called the Flow channels, when viewed in the axial direction, "cells", and the term "cell density" denotes the number of cells per unit area in the front view of the Catalyst body. Thus, the indication of cell density naturally means as well an indication of the flow cross-section of each individual cell or each individual Flow channel, in addition, the wall thickness between adjacent Flow channels is received.

Catalytically active material is deposited on the walls of the flow channels. The standard technique is to use a so-called washcoat as a liquid suspension, the washcoat in particular a suspension of fine ceramic particles (typically aluminum oxide) in a suspension liquid is. After drying the washcoat has a porous, strong Surface-increasing coating on the walls of the flow channels. The actual catalyst particles, typically the precious metals in particular Platinum, palladium and rhodium, will either be final on the Washcoat deposited or applied in form contained in the washcoat suspension.

The most important parameters of the exhaust gas flow of an internal combustion engine are Mass flow (e.g., in kg / s), its temperature and flow rate. These parameters are not all independent. From a given Mass flow at a given temperature results in a (mean) flow velocity (at a considered flow cross-section). If at held constant mass flow increases or decreases the temperature increased because of the associated density change of the exhaust gas, the flow rate or humiliates.

In the exhaust system according to the invention is in the inlet pipe of the exhaust gas converter arranged a swirl generator, which leaves a central flow path. The swirl generator can be designed so that at a low range of the occurring flow velocities (one could also say: "at one low portion of the occurring mass flows "or" at a low sub-range of the occurring exhaust gas temperatures ", whereby the mutual Dependence of the mentioned parameters is to be considered) the exhaust gas predominantly or even almost completely only through the free central flow path flows in the inlet pipe and from there into the end face of the inner region. At higher flow rates in an upper portion of the occurring Flow velocities (one could also say: "At higher Mass flow "or" At higher exhaust gas temperatures ", wherein the mutual By contrast, the dependence of these parameters must be taken into account) very significant part of the exhaust stream the swirl generator and leaves this as Swirl flow with significant component in the circumferential direction. With strong swirl flow is due to the toughness forces in the exhaust also by the free central flow path flowing part of the exhaust gas imparted a twist. On The reason of the existing centrifugal forces in the Gasamt swirl flow is the Flow after leaving the inlet pipe predominantly or even almost completely outward to the end face of the outer portion of the catalyst body stream. - At medium flow velocities or mass flows or Exhaust gas temperatures, on the other hand, become both the interior and the exterior flows through the catalyst body.

As a "start" of a catalyst body is the achievement of an operating point in which the conversion of the exhaust components to be converted widely used. To start is primarily the achievement the light-off temperature required. The light-off temperature can be passed through Select parameters that are related to the washcoat, compare more detailed explanations below. Of particular influence is the number of so-called catalytically "active centers" of the coating of the flow channels. In the larger catalyst activity of the invention indoors Outside, in principle, there are a larger number of active ones Centers.

All in all, the invention provides an exhaust system, in which the exhaust gas converter preferably flows in its interior when the flow rate of the exhaust gas is in a low partial range the occurring flow velocities is (especially typical: Idling, but also operating at fairly low speeds, especially at not widely opened throttle). The primarily flowed through interior area The catalyst body heats up much faster than if the entire catalyst body would have to be heated. The light-off temperature is indoors reached faster. The greater catalyst activity favors the exhaust gas conversion in this "warm-up state" of the exhaust system. Especially the behavior after a cold start of the engine is significantly improved.

If, however, a flow velocity in an upper portion of the occurring flow velocities (especially typical: higher speeds, especially when the throttle is wide open and / or when higher exhaust gas temperatures prevail with a warm combustion engine) on the other hand, the outside area of the catalyst body is primarily flown on.

The greater catalyst activity in the interior leads to that in the described states with primary flow through the interior the exhaust gas conversion compared to the situation without increasing the catalyst activity, is favored. In the situation of the primary flow of the Outside, the interior is spared.

It is emphasized that one both with increased cell density as well as with greater catalyst activity in the Inrienbereich is working. Although it is preferred that, in this case, the interior with larger cell density geometric with the interior area with greater catalyst activity is identical (as is the outdoor area), it is noted that one Basically, it can also form so that the interior area with greater cell density a smaller or larger frontal area than the interior area with larger ones Catalyst activity has (as the outdoor area).

The invention is not limited to that of the catalyst body in only two Subareas, as they have been described as indoor and outdoor are, has. There are also possible versions, where more than can distinguish two sub-areas, which in terms of catalyst activity and, if necessary, differentiate cell density.

As a rule, one forms so that the end face of the inner area on the free central flow path of the inlet pipe is aligned. this means not mandatory that the longitudinal center axis of the inner region with the longitudinal central axis the total catalyst body coincides, as further down will become clearer. As a rule, but not necessarily, has the housing of the exhaust gas converter a subsequent to the local end of the inlet pipe Extension section, so that the total inflow face of the catalyst body is significantly larger than the flow cross-section of the inlet pipe at his The End. In many cases, the catalyst bodies require such a larger upstream end. In addition, the extension of the flow cross section for the Training the swirl flow described above favorable.

Preferably, the exhaust gas converter is designed so that at least 40%, especially preferably at least 50% and most preferably at least 60%, the incoming exhaust gas flow through the interior of the catalyst body flow when the exhaust stream has a flow rate in a lower Part of the range of flow rates occurring during operation in the exhaust system Has. Said lower portion preferably comprises 0 to 10%, more preferably 0 to 20%, and most preferably 0 to 30% of the total range of flow velocities occurring.

Preferably, the exhaust gas converter is designed so that at least 80%, especially preferably at least 90%, of the inflowing exhaust gas flow through the exterior of the catalyst body flow when the exhaust gas flow is a flow velocity in an upper portion of the operation in the exhaust system has occurring range of flow velocities. The named Upper portion preferably comprises 80 to 100%, more preferably 70 to 100% of the total range of flow velocities occurring. What the area size of the end face of the inner portion of the catalyst body When this area size is within the range, it is preferred that which starts with the cross-sectional area of the free central flow path up to the total flow area of the downstream end of the inlet pipe goes. But it is also possible, the end face of the inner area even greater do.

Preferably, the swirl generator with its outside on the inside of the Attached inlet tube, particularly preferably welded. That way is one outside flow around the swirl generator excluded. Alternatively, it is preferred that the swirl generator has been produced integrally with the feed pipe, in particular by casting or by high pressure forming.

There are a number of concrete technical realization of the swirl generator of possibilities. According to a first preferred option, the swirl generator an annular ring of vanes. After a second preferred Possibility, the swirl generator at least one helical longitudinally the inflow pipe extending flow guide on; the idiom "along the inlet pipe" should not mean "along the entire inlet pipe", but only the longitudinal orientation of the flow guide play.

Functionally it comes with the swirl generator provided according to the invention that at relatively low flow rates of the exhaust gas (or Mass flows or temperatures) virtually no or only little Spin is generated while at relatively high flow velocities (or Mass flows or temperatures) much swirl is generated. It can be practical full "flow switching" are designed so below one first threshold of flow rate is virtually 100% for the Inflow of the interior and practically 0% for the flow of the outside area, and above a second threshold flow rate practically 0% to the flow of the interior and practically 100% to the flow of the outdoor area. Alternatively, however, one can design with less make sharp flow switching, e.g. never less than 20% (preferably never less than 10%) to the flow of the interior or never less than 30% (preferably never less than 20%) to the outside flow.

In addition, one can determine by design of the swirl generator, when the Switching clearly starts and when the switching stops significantly.

• Anzahl der Leitschaufeln für den Umfang;
• Anzahl der wendelförmigen Strömungsleitelemente, die umfangsmäßig versetzt vorgesehen sind;
• Überlappung der Leitschaufeln in axialer Blickrichtung;
• Anstellwinkel der Leitschaufeln oder des wendelförmigen Strömungsleitelements ("Steigung");
• Höhe der Leitschaufeln oder des Strömungsleitelements und dadurch bestimmt der Durchmesser des freien zentralen Strömungswegs;
• Länge der Leitschaufeln bzw. des Strömungsleitelements in Axialrichtung;
• Position des Drallerzeugers in axialer Hinsicht in dem Zulaufrohr (axialer Abstand zum Ende des Zulaufrohrs oder axialer Überstand über das Ende des Zulaufrohrs hinaus);
• zunehmender Anstellwinkel der Leitschaufeln (d.h. gekrümmte Leitschaufeln) oder zunehmender Anstellwinkel des Strömungsleitelements (d.h. abnehmende Steigung) längs des Drallerzeugers;
• zunehmende Höhe der Leitschaufeln oder des Strömungsleitelements längs des Drallerzeugers;
• Durchmesser des Zulaufrohrs;
• Durchmesser bzw. Flächengröße der Stirnseite des Katalysatorkörpers;
• Winkel der Erweiterung bei dem Erweiterungsabschnitt;
• axialer Abstand zwischen dem Drallerzeuger und der Stirnseite des Katalysatorkörpers.

The following geometry parameters which influence the design are mentioned:

• Number of vanes for the circumference;
• Number of helical flow guide elements which are provided circumferentially offset;
• Overlap of the vanes in the axial direction;
• Angle of incidence of the vanes or helical flow guide ("pitch");
• Height of the vanes or the flow guide and thereby determines the diameter of the free central flow path;
• Length of the guide vanes or the flow guide in the axial direction;
• Position of the swirl generator in the axial direction in the feed pipe (axial distance to the end of the feed pipe or axial projection beyond the end of the feed pipe addition);
• increasing angle of attack of the vanes (ie, curved vanes) or increasing angle of incidence of the flow director (ie, decreasing pitch) along the swirler;
• increasing the height of the vanes or the flow guide along the swirl generator;
• Diameter of the inlet pipe;
• Diameter or area size of the end face of the catalyst body;
• Angle of extension at the extension section;
• axial distance between the swirl generator and the end face of the catalyst body.

The number of vanes or the flow guide has a considerable Influence on the uniformity of the generated centrifugal field. A bigger one Number causes a uniform centrifugal field. On the other hand, he takes Pressure loss of the swirl generator with the number of too.

If the swirl generator is designed with overlapping vanes, one has even at low flow velocities a tangible flow resistance in the swirl generator; the outflow is particularly pronounced only too the interior of the catalyst body. On the other hand, one has at high flow rates a relatively high flow resistance.

The angle of attack of the guide vanes or the flow guide has a special great influence on the strength of the generated twist. Strong employee Guide vanes guide e.g. even at medium flow velocities to one so strong swirl that the part of the exhaust gas flow to the inflow of the interior the catalyst body is very small. For particularly high centrifugal forces the swirl flow becomes the pressure in the core region of the flow, i. by the free central flow path, so small that an outflow to the interior of the catalyst body can be largely avoided. The angle of attack is measured relative to the axial direction of the inlet pipe.

The height of the guide vanes or the flow guide, especially in relation to the total diameter of the inlet pipe, has particular influence on the Proportion of flow at low flow rates to the interior to flow of the catalyst body. At relatively low height of the vanes or the flow guide and thus a large diameter the free central flow path becomes a larger part of the flow to the Flow inside the catalyst body.

In the axial length of the guide vanes or the flow guide is the Generally the tendency is that with a greater length a stronger twist also is generated in the free central flow path. With increasing length decreases the pressure loss of the swirl generator to. Increasing along the swirl generator Angle of the guide vanes or the flow guide and along the Swirl generator increasing height of the vanes and the flow guide reduce the pressure loss of the exhaust gas converter compared to swirl generators without these measures.

Also, the distance between the swirl generator and the end face of the inner area of the catalyst body has considerable influence. The larger this distance is, the more the flow of the outdoor area is favored.

The vanes may warp (= angle of attack as it progresses changing along the radius) or not.

Preferably, the inner region of the catalyst body has an end face, the occupies at most 20% of the total end face of the catalyst body, especially preferably at most 15% of the total end face and most preferably at most 10%. The percentage of the total face area chosen for a specific product is a compromise between the safest possible flow predominantly indoors only, especially when warming up the internal combustion engine, on the one hand, and the best possible protection of the interior at high load conditions of the internal combustion engine and / or high exhaust gas temperatures, on the other hand.

Preferably, the area-related cell density in the interior is at least 1.2 times the cell density outdoors, more preferably at least 1.5 times and most preferably at least 1.7 times. Here goes It is an optimal compromise between improvement of conversion in particular when warming up the internal combustion engine, on the one hand, and avoidance undue increase in drag and production costs due to larger precious metal consumption, on the other hand.

Preferably, for the greater catalyst activity in the interior of the catalyst body a larger precious metal loading provided, particularly preferred an at least 20% greater noble metal loading, and most preferably at least 30% greater precious metal loading than outdoors. Here goes it is an optimal compromise between increased internal exhaust gas conversion, on the one hand, and limiting the increase in production costs by higher use of precious metals, on the other hand.

Preferably, for the greater catalyst activity in the interior of the catalyst body a finer noble metal dispersion provided, particularly preferred an at least 20% finer noble metal dispersion, and most preferably at least 30% finer precious metal dispersion than outdoors. Here goes It is a good compromise between good exhaust conversion when warming up the internal combustion engine, on the one hand, and limiting the aging of the catalyst body. The finer the noble metal dispersion used, the greater the risk of aging by sintering the active centers at high exhaust gas temperatures.

Preferably, for the greater catalyst activity in the interior of the catalyst body another precious metal composition intended than outdoors. This is about a good compromise between exhaust conversion when warming up the internal combustion engine, on the one hand, and limiting production costs by choosing as inexpensive precious metal compositions as possible and aging resistance, on the other hand.

The specific technical issues addressed in the previous paragraphs Possibilities to increase the catalyst activity in the interior of the catalyst body Compared to its outdoor area, all lead to - compared with a situation without a catalyst activity increase, the light-off temperature of the interior decreases and that even after some aging of the catalyst body (which normally involves an increase in the light-off temperature there are still enough reserves for a proper There is a functioning of the exhaust gas conversion. The with the increase of the catalyst activity associated disadvantages, such as increase in production costs and increasing the susceptibility to aging are thereby limited, that at higher load conditions of the internal combustion engine, the interior of the Catalyst body substantially no longer flows through or at least reduced becomes.

Preferably, the interior of the catalyst body is only on a partial length with greater catalyst activity than the outdoor area. At one part the execution cases, it may be cheaper, the interior in his To make cross-section larger than it is using its entire length would have to do with greater catalyst activity, and instead only a partial length of the interior with greater catalyst activity. A special suitable method for applying the washcoat on a partial length of the inner area is that you put the catalyst body on top of a piece of pipe and feed the suspension from below through the tube until it has reached a certain height in the interior of the catalyst body. Subsequently the excess suspension is blown down.

The coating of the catalyst body with the washcoat suspension can in a dive with subsequent blowing or in several dives be carried out successively with subsequent blowing, wherein in the latter case, the coating is built up in several steps. at the interior of the catalyst body can be either based on a Washcoat similar to the outdoor applied Washcoat, one or several Washcoatlagen in particular for generating the larger catalyst activity muster. Alternatively, it is possible to use the indoor and outdoor areas to be coated separately in separate coating runs. Here too you can work for indoor use with an attached feed pipe and when coating the outside area with a cover of the front side of the Inside area.

The inlet pipe preferably has in the interest of effective generation of the swirling flow a circular cross-section. A circular cross section is also for the exhaust converter housing overall preferred because this is for a spiral Flow provides the best flow conditions. Alternatively, however a substantially elliptical configuration of the housing cross-section is preferred. A substantially elliptical cross-sectional configuration is with mufflers, which are mounted under the floor of motor vehicles, quite often encountered. As with mufflers is the lower the exhaust gas converter Height compared to a cross-sectionally identical exhaust gas converter with circular Emphasize cross section as an advantage.

There are embodiments in which it is favorable, the longitudinal central axis of the inner region of the catalyst body with respect to the longitudinal central axis of the overall catalyst body to arrange staggered. As typical examples are non-central positioning of the inlet pipe and inclined inlet of the inlet pipe called in the housing. The end face of the interior of the catalyst body should be positioned so that through the free central flow path flowing exhaust stream or not detected by the swirl flow Part of the exhaust gas flow within the end face of the inner region on the catalyst body meets.

There is the option of targeted for the interior or purposefully for the outdoor area of the catalyst body, i. in front of the front end, in the catalyst body or behind the rear end, a targeted flow resistance provide for increased training, in particular in the form of a local constriction the flow cross-section or in the form of local flow brakes. A specifically designed to increase the flow resistance for the interior training favors flow towards the exterior of the catalyst body (as in principle with the measure "larger cell density in the interior area" of the Case is) and vice versa. Targeted the flow resistance increasing training are an extremely effective way to achieve virtually perfect switching to achieve the swirl generator / free central flow path, where in this Case in the design of the swirl generator has gained more freedom.

It is possible to form an inner pipe piece in front of the front side of the inner portion of the catalyst body to be positioned, which are preferably substantially the same Diameter as the interior has. The inner pipe piece favors the inflow to the interior at low flow rates.

If in the present application of flow rate and temperature is spoken of the inflow through the inlet pipe exhaust stream is considered a flow cross section in front of the swirl generator. Because flow speed and temperature over the cross section are not constant, are over meant cross-sectional values. Given the exhaust pulsations are for temporally averaged values meant for suitable short time intervals. All in all one could alternatively consider the mass flow, in particular because here the Cross-section averaging is not required. Constant exhaust gas temperature considered, the average flow velocity depends directly on the mass flow together. Constant mass flow considered, the average flow rate depends directly together with the exhaust gas temperature. Instead of with The term "flow velocity" could be the statements in the present Registration also with the term "temperature standardized mass flow" link.

It is emphasized that not only the previously mentioned exhaust system subject The invention is, but also the mentioned exhaust gas converter is itself an object of the invention. All disclosed preferred training not only apply to the exhaust system as a whole, but also for their component embodying the invention "exhaust gas converter".

From the document WO 00/12879 is a catalytic exhaust gas converter with a associated inlet pipe known in which a swirl generator having a central Flow path through the inlet tube leaves free, is arranged. There, however, is the Training so that a uniform flow of the front end of the Catalyst body to be achieved.

Fig. 1 eine Abgasanlage in Seitenansicht, sozusagen einbaufertig zum Einbau von unten an ein Kraftfahrzeug mit Verbrennungsmotor;

Fig. 2 einen katalytischen Abgaskonverter im Längsschnitt;

Fig. 3 den Abgaskonverter von Fig. 2 in der geschnittenen Stirnansicht gemäß III-III in Fig. 2;

Fig. 4 den Abgaskonverter von Fig. 2, jedoch in einem anderen Durchströmungszustand, im Längsschnitt;

Fig. 5 einen Querschnitt des Abgaskonverters von Fig. 2 gemäß V-V in Fig. 2;

Fig. 6 in einem Querschnitt analog Fig. 5 einen abgewandelten Abgaskonverter;

Fig. 7 in einem Querschnitt analog Fig. 5 einen abgewandelten Abgaskonverter;

Fig. 8 in einem Querschnitt analog Fig. 5 eine zweite Ausführungsform eines Abgaskonverters;

Fig. 9 in einem Querschnitt analog Fig. 5 und Fig. 8 einen abgewandelten Abgaskonverter der zweiten Ausführungsform;

Fig. 10 in einem Querschnitt analog Fig. 2 eine dritte Ausführungsform eines Abgaskonverters;

Fig. 11 in einem Querschnitt analog Fig. 2 bzw. Fig. 10 eine vierte Ausführungsform eines Abgaskonverters;

Fig. 12 in einem Längsschnitt analog Fig. 2 eine fünfte Ausführungsform eines Abgaskonverters;

Fig. 13 einen Teil eines Abgaskonverters im Längsschnitt, wobei ein Drallerzeuger alternativer Ausführungsform vorgesehen ist.

The invention and preferred embodiments of the invention will be explained in more detail with reference to schematically diagrammatically illustrated embodiments. It shows:

Figure 1 is an exhaust system in side view, as it were ready for installation from below to a motor vehicle with internal combustion engine.

2 shows a catalytic exhaust gas converter in longitudinal section.

FIG. 3 shows the exhaust gas converter of FIG. 2 in the sectioned end view according to III-III in FIG. 2; FIG.

Fig. 4 shows the exhaust gas converter of Figure 2, but in another flow condition, in longitudinal section.

FIG. 5 shows a cross section of the exhaust gas converter of FIG. 2 according to VV in FIG. 2; FIG.

FIG. 6 is a cross-sectional view similar to FIG. 5 of a modified exhaust gas converter; FIG.

FIG. 7 shows a modified exhaust gas converter in a cross section analogous to FIG. 5; FIG.

FIG. 8 is a cross-sectional view similar to FIG. 5 of a second embodiment of an exhaust gas converter; FIG.

9 shows in a cross section analogous to FIG. 5 and FIG. 8 a modified exhaust gas converter of the second embodiment;

FIG. 10 is a cross-sectional view similar to FIG. 2 of a third embodiment of an exhaust gas converter; FIG.

FIG. 11 is a cross-sectional view similar to FIG. 2; FIG. 10 is a fourth embodiment of an exhaust gas converter;

FIG. 12 is a longitudinal sectional view similar to FIG. 2 of a fifth embodiment of an exhaust gas converter; FIG.

Fig. 13 shows a part of a Abgaskonverters in longitudinal section, wherein a swirl generator alternative embodiment is provided.

In Fig. 1 is an exhaust system 2 for an internal combustion engine of a vehicle represented with their most essential components. Progressing from the upstream End to the downstream end you have the following components: Manifold 4, which is screwed to the cylinder head of the internal combustion engine and the exhaust gases from the cylinders of the internal combustion engine in a common Pipe section 6 merges; catalytic exhaust gas converter 12; middle silencer 14; Pipe section 16, around the rear axle of the motor vehicle round lead; End silencer 18.

2, an inventive exhaust gas converter 12 is shown. One recognises an inlet tube 22 with a circular cross-section, a housing 24 with a cone-shaped Extension portion 24a, a peripheral wall 24b and a cone-shaped Rejuvenation section 24c, and a drain pipe 26 with circular Cross-section. Shortly before the right in Fig. 2 end of the inlet pipe 22, where it is in the Expansion section 24a passes, is in the inlet pipe 22, a swirl generator 40th arranged.

The swirl generator 40 consists of a circumferentially distributed ring of vanes 46, which is shown schematically in Fig. 2 as an inclined surface are and can be seen somewhat more clearly in Fig. 3. The vanes 46 are on its radially outer edge welded to the inside of the inlet pipe 22 and have a radial height 48, see Fig. 3. The vanes leave with their inner edges free a central flow path 50 whose diameter at the illustrated embodiment about 60% of the inner diameter of the Inlet pipe 22 is. In Fig. 2, the diameter of the central flow path indicated by two dotted lines 52.

In the housing 24, a catalyst body 60 is supported, e.g. as a ceramic monolith with a plurality of longitudinal flow channels through it 62 is constructed. The catalyst body 60 has an interior region 64 and a Outdoor area 66 on. The inner region 64 has a longitudinal center axis which coincides with the Longitudinal center axis 68 of the entire catalyst body 60 coincides. The interior 64 has in Fig. 2 left an end face 70 (= inflow side), and the outside area 66 has in Fig. 2 left an end face 72 (= inflow side). The area size the end face 70 of the inner region 64 is slightly larger than the cross section the free central flow path 50.

With reference to Figures 2 and 4, two different flow conditions the exhaust gas converter 8 illustrated.

A flowing during operation of the internal combustion engine through the exhaust system 2 Exhaust gas flow is, as far as the inlet pipe 22 before the swirl generator 40, with arrows 80 drawn. The local exhaust stream 80 has at a certain operating condition the internal combustion engine a certain mass flow, one of them resulting certain (averaged over the flow cross-section) flow rate and a temperature (averaged over the flow area).

At flow velocities that are in a lower subrange during operation the exhaust system 2 occurring range of flow rates are, the presence of the swirl generator has only a small influence on the Flow. The swirl generator 40 represents a flow resistance, so that the Flow predominantly through the central flow path 50 goes. Furthermore is the fluidic influence of the vanes 46 on the flow relatively low, because the vanes 46 on flow control at higher Flow rates are designed. As a result of the circumstances described which leaves the section where the swirl generator 40 is located Flow to almost 100% in the end face 70 of the interior 64. In the Front side 72 of the outer region 66 flows a small part of the inflowing exhaust gas flow 60 with low flow velocity. All these relationships are in Fig. 2 illustrates with arrows, which can be seen as an illustration of the flow rate or as an illustration of the mass flow can.

If, however, the flow rate of the exhaust stream 80 in a upper portion of the occurring during operation in the Abgasanalage 2 area of flow velocities, the swirl generator 40 is in function (especially the incoming exhaust gas stream 80 no longer so easily almost in the total central flow path 50 can flow, because a strong nozzle-like acceleration would have to take place); when flowing through the swirl generator 40th impinged swirl flow exerts centrifugal forces on the flow, causing the flow in the region of the extension section 24a goes radially outward. In the area of the swirl generator 40 and in the area between the swirl generator 40 and the upstream side 70 of the inner region 64 exerts the outer swirl flow toughness forces on the flowing through the central flow path 50 of the part Exhaust stream 80 and largely dominates this part of the exhaust stream and a Peripheral component of the flow velocity. As a result shows itself, that at high flow velocities a far more prevalent part the total exhaust stream 80, with a suitable design even close to 100% Part of the exhaust stream 80, to the end face 72 of the outer area 66th flows. All of these relationships are illustrated in FIG. 4.

Between the two extremes described there is a middle range of Flow rates at which a first, appreciable part of the total exhaust gas flow 80 flows through the inner region 64 and a second, appreciable part the total exhaust gas flow through the outer region 66 flows.

In Fig. 5 it can be seen that the inner region 64 has a considerably greater cell density when the outside area 66 has. The individual cells are designated by 82. Furthermore can be seen in Fig. 5, the possibility of execution that the interior 64th has a circular cross-section, the entire catalyst body 60 a circular Cross section and the outer region 66 has a circular cross-section Has.

By means of FIG. 6, the modification is illustrated in which the catalyst body 60 overall has a substantially elliptical cross-section. The interior 64 still has a circular cross-section.

By means of Fig. 7, the modification is illustrated that the inner region 64 a has square cross section. A square cross section is perfect exploit with square in cross-section cells 82.

In Fig. 8 is an end view of the end face 84 and in cross section of a second Embodiment of an exhaust converter 8 and a catalyst body 60 shown, that the flow channels 62 of the catalyst body 60 in the inner region 64 executed with increased catalyst activity, illustrated in the drawing by darker coloring. This may be higher precious metal loading, to finer precious metal dispersion to other precious metal composition or to act on several of these actions. In the illustrated embodiment the cell density in the inner area 64 is equal to the cell density in the outer area 66. But you could also, as in the first embodiment, with a higher cell density indoors 64 work.

FIG. 8 shows circular cross sections as in FIG. 5. In FIG. 9, the modification is drawn in that the total catalyst body 60 is essentially elliptical, analogous to FIG. 6.
FIG. 10 shows a third embodiment in which an inner area 64 with a greater cell density is placed eccentrically to the longitudinal central axis 68 of the catalyst body 60. In the fourth embodiment shown in FIG. 11, this is drawn analogously for an interior region 64 with increased catalyst activity.

In Fig. 12, a fifth embodiment is drawn, wherein the interior 64 of the catalyst body 60 only in an upstream partial length 86 with increased catalyst activity is carried out. In the illustrated embodiment the partial length is about 50% of the total length of the catalyst body 60th

In Fig. 13, an embodiment is shown in which the swirl generator 40 by a helically extending flow guide 88 instead of vanes 46 is realized. The flow guide 88 has a radial height 48th Instead only a helical flow guide 88 (which at least one 360 ° -Windung should be long), as drawn in Fig. 13, you can also provide two (or even more) flow guide 88, which by 180 ° (or. 90 °, 72 ° etc.) start offset. The fluidic effect of the flow guide 88 is analogous to the effect related above with the vanes 46 has been described. The flow guide 88 is welded with its outer edge on the inside of the inlet pipe 22.

Claims (19)

1. Exhaust system (2) for internal combustion engines, having a catalytic exhaust gas converter (12) with a housing (24), an inflow pipe (22) and a catalytic converter element (60), which is secured in the housing (24), wherein a swirl generator (40) which opens a central flow path (50) is arranged in the inflow pipe (22), and the catalytic converter element (60) comprises an internal region (64) with catalytically active flow ducts (62; 82) through which exhaust gas flows, and an external region (66) with catalytically active flow ducts (62; 82) through which exhaust gas flows, characterized in that the flow ducts (62) in the internal region (64) are embodied with higher catalytic converter activity than the flow ducts (62) in the external region (66).
2. Exhaust system according to Claim 1, characterized in that the cell density of the flow ducts is higher in the internal region (64) than in the external region (66).
3. Exhaust system according to Claim 1 or 2,
   characterized in that the exhaust gas converter (12) is configured in such a way that at least 40% of the inflowing stream of exhaust gas flows through the internal region of the catalytic converter element (60) if the stream of exhaust gas has a flow speed in a lower part of the range of flow speeds occurring during the operation of the exhaust system.
4. Exhaust system according to one of Claims 1 to 3, characterized in that the exhaust gas converter (12) is configured in such a way that at least 80% of the inflowing stream of exhaust gas flows through the external region of the catalytic converter element (60) if the stream of exhaust gas has a flow speed in an upper part of the range of flow speeds occurring during the operation of the exhaust system.
5. Exhaust system according to one of Claims 1 to 4, characterized in that the internal region (64) of the catalytic converter element has an end face which, according to its size, is in the range from the cross section of the free central flow path to the cross section of the downstream end of the inflow pipe (22).
6. Exhaust system according to one of Claims 1 to 5, characterized in that the swirl generator (40) is mounted on the inflow pipe (22), preferably welded to it.
7. Exhaust system according to one of Claims 1 to 5 characterized in that the swirl generator (40) has been manufactured integrally with the inflow pipe (22).
8. Exhaust system according to one of Claims 1 to 7 characterized in that the swirl generator (40) has an annular ring of guide vanes.
9. Exhaust system according to one of Claims 1 to 7 characterized in that the swirl generator (40) has at least one flow guiding element which runs in a helical shape along the inflow pipe (22).
10. Exhaust system according to Claim 8 or 9, characterized in that the incidence angle of the guide vanes or of the flow guiding element increases along the inflow pipe (22).
11. Exhaust system according to one of Claims 8 to 10, characterized in that the radial height of the guide vanes or of the flow guiding element increases along the inflow pipe (22).
12. Exhaust system according to one of Claims 1 to 11, characterized in that the internal region (64) of the catalytic converter element has an end face which at maximum takes up 20% of the overall end face of the catalytic converter element (60).
13. Exhaust system according to one of Claims 2 to 12, characterized in that the area-related cell density is at least twice as large in the internal region (64) as in the external region (66).
14. Exhaust system according to one of Claims 1 to 13, characterized in that a larger noble metal loading, preferably an at least 20% larger noble metal loading, is provided in the internal region (64) of the catalytic converter element than in the external region (66) for the higher catalytic converter activity.
15. Exhaust system according to one of Claims 1 to 14, characterized in that a finer dispersion of noble metal, preferably an at least 20% finer dispersion of noble metal, is provided in the internal region (64) of the catalytic converter element (60) than in the external region (66) for the higher catalytic converter activity.
16. Exhaust system according to one of Claims 1 to 15, characterized in that a different composition of noble metal is provided in the internal region (64) of the catalytic converter element than in the external region (66) for the higher catalytic converter activity.
17. Exhaust system according to one of Claims 1 to 16, characterized in that the internal region (64) of the catalytic converter element (60) is embodied with a higher catalytic converter activity than the external region (66) over only part of its length.
18. Exhaust system according to one of Claims 1 to 17, characterized in that the exhaust gas converter (12) has an essentially elliptical cross section.
19. Exhaust system according to one of Claims 1 to 18, characterized in that the longitudinal centre axis of the internal region (64) of the catalytic converter element (60) is offset with respect to the longitudinal centre axis of the catalytic converter element (60).

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