EP1342889A1 - Exhaust system for a combustion engine with a catalytic converter - Google Patents

Abstract

An exhaust gas device comprises a catalytic exhaust gas converter with a housing (24), a catalyst body (60) held in the housing, and a feed pipe. A torsion producer is arranged in the feed pipe to expose a central flow path. The catalyst body has an inner region (64) and an outer region (66). The cell density of the flow channels in the inner region is more than in the outer region. Preferred Features: The inner region has the larger catalyst activity than the outer region. At least 40%, preferably 80% of the exhaust gas stream flows through the inner region of the catalyst body.

Description

The invention relates to an exhaust system for internal combustion engines, comprising a catalytic exhaust gas converter with a housing, a catalyst body supported in the housing, and a supply pipe.

Such exhaust systems with exhaust gas converter are known in many versions.

The invention is based on the technical problem of making an exhaust system of the type mentioned available, in which the exhaust gas converter has a better combination of fast light-off behavior and nevertheless good aging behavior compared to the previously usual.

To solve this problem, the exhaust system is characterized in that
that in the inlet pipe of the exhaust gas converter, a swirl generator is arranged, which leaves a central flow path free;
and that the catalyst body, viewed in the axial direction of view, has an inner area and an outer area, the cell density of the flow channels being greater in the inner area than in the outer area.

Catalyst bodies are particularly common in two technical designs: ceramic monolith having a large number of longitudinal flow channels, and metal catalyst bodies also having a large number of longitudinal flow channels, these flow channels being due to the mating of a corrugated sheet made with a flat sheet and spirally winding this pairing. Often they are called the Flow channels, when viewed in the axial direction, "cells", and the term "cell density" refers to the number of cells per unit area in the end view of the catalyst body. Thus, the indication of the cell density naturally also means an indication of the flow cross-section of each individual cell or of each individual flow channel, with the additional wall thickness entering between adjacent flow channels.

Catalytically active material is deposited on the walls of the flow channels. The standard technique is to apply a so-called washcoat as a liquid suspension, the washcoat in particular being a suspension of fine ceramic particles (typically aluminum oxide) in a suspension liquid. After drying the washcoat has a porous, strongly surface-enhancing coating on the walls of the flow channels. The actual catalyst particles, typically the noble metals platinum, palladium and rhodium in particular, are either finally deposited on the washcoat or applied in the form contained in the washcoat suspension.

The most important parameters of the exhaust gas flow of an internal combustion engine are its mass flow (for example in kg / s), its temperature and its flow velocity. 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 the temperature increases or decreases with the mass flow kept constant, the flow velocity increases or decreases due to the concomitant change in the density of the exhaust gas.

In the exhaust system according to the invention a swirl generator is arranged in the inlet pipe of the exhaust gas converter, which leaves a central flow path free. The swirl generator can be designed so that at a low portion of the occurring flow velocities (one could also say: "at a low portion of the occurring mass flows" or "at a low portion of the occurring exhaust gas temperatures", wherein the mutual The dependence of the mentioned parameters is to be considered) the exhaust gas predominantly or even almost completely flows only through the free central flow path in the inlet pipe and from there into the end face of the inner region. On the other hand, at higher flow velocities in an upper portion of the occurring flow velocities (one might say: "At higher mass flows" or "At higher exhaust gas temperatures", taking into account the interdependence of these parameters), a very substantial portion of the exhaust flow passes through the swirler and exits this as a swirl flow with considerable component in the circumferential direction. In the case of strong swirl flow, because of the toughness forces in the exhaust gas, a swirl is also imposed on the part of the exhaust gas flowing through the free central flow path. Due to the centrifugal forces present in the gas velvet swirl flow, the flow will, after leaving the feed pipe, flow predominantly or even almost completely outwards to the end face of the outer region of the catalyst body. At medium flow velocities or mass flows or exhaust gas temperatures, on the other hand, both the inner region and the outer region of the catalyst body are flowed through.

This flow behavior of the catalyst body is combined in the invention with the measure to provide a higher cell density in an inner region of the catalyst body than in an outer region of the catalyst body. The higher cell density goes hand in hand with a larger, catalytically active surface, so that catalytic exhaust conversion is inherently more perfect in the interior of the catalyst body than in the exterior (albeit at the cost of higher flow resistance and a higher production price due to greater amount of noble metal).

As a "start-up" of a catalyst body, the achievement of an operating point is referred to, in which the conversion of the exhaust components to be converted is widely used. For starting, it is primarily necessary to achieve the light-off temperature. The light-off temperature can be influenced by the choice of parameters associated with the washcoat, see more detailed below. Of particular influence is the number of so-called catalytically "active centers" of the coating of the flow channels. In the case of the larger cell density according to the invention, both indoors and out, there is, in principle, a larger number of active centers compared to the situation without increasing the cell density.

All in all, the invention, in its first aspect, provides an exhaust system in which the exhaust gas converter is preferably flowed in its interior, when the flow rate of the exhaust gas in a low portion of the occurring flow velocities is (particularly typical: idling, but also with operation low speeds, especially at not widely opened throttle). The interior region of the catalyst body which is primarily flowed through heats up much faster than if the entire catalyst body had to be heated. The light-off temperature is reached more quickly indoors. The larger cell density favors the exhaust gas conversion in this "warming-up state" of the exhaust system. In particular, the behavior after a cold start of the internal combustion engine is significantly improved.

If, on the other hand, a flow velocity prevails in an upper subarea of the occurring flow velocities (especially typical: higher rotational speeds, especially if the throttle valve is wide open and / or higher exhaust gas temperatures prevail when the engine is warm), the exterior of the catalyst body is primarily flown. Because of the smaller cell density and the larger inflow face, the flow through the catalyst body runs with less pressure loss. The internal heating of the catalyst body by exothermic reactions is distributed over a larger volume.

According to a second aspect of the invention, the above-mentioned technical problem is solved in that the exhaust system of the type mentioned
characterized
that in the inlet pipe, a swirl generator is arranged, which leaves a central flow path free;
and that the catalyst body, viewed in the axial direction of view, has an inner area and an outer area, the inner area being designed with greater catalyst activity than the outer area.

With regard to the function of the swirl generator, what has been stated above in connection with the first aspect of the invention also applies to the second aspect of the invention. The greater catalyst activity in the inner region means that in the described states with primary throughflow of the inner region, the exhaust gas conversion is favored, compared to the situation without increasing the catalyst activity. In the situation of the primary flow of the outside area, the interior area is spared.

It is emphasized that the measure "wherein the interior area with greater catalyst activity than the outside area" can be realized as a preferred feature also in the first aspect of the invention, so that one works both with increased cell density and with greater catalyst activity indoors. Although it is preferable that, in this case, the inner area of larger cell density is geometrically identical with the inner area of larger catalyst activity (as well as the outer area), it should be understood that basically, the inner area of greater cell density may be formed smaller or larger face than the interior with greater catalyst activity (as well as the exterior).

The invention is not limited to the fact that the catalyst body in only two sub-areas, as they have been described as indoor and outdoor, has. Embodiments are also possible in which it is possible to distinguish more than two subregions which differ with regard to cell density and / or catalyst activity.

In general, it is formed so that the end face of the inner region is aligned with the free central flow path of the inlet pipe. This does not necessarily mean that the longitudinal center axis of the inner region coincides with the longitudinal central axis of the entire catalyst body, as further down will become clearer. As a rule, but not necessarily, the housing of the exhaust gas converter has an extension section adjoining the local end of the inlet pipe, so that the total inlet end face of the catalyst body is significantly larger than the flow cross section of the inlet pipe at its end. In many cases, the catalyst bodies require such a larger upstream end. In addition, the extension of the flow cross section for the formation of the vortex flow described above is favorable.

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

Preferably, the exhaust gas converter is configured such that at least 80%, more preferably at least 90%, of the incoming exhaust stream flow through the exterior of the catalyst body when the exhaust stream has a flow rate in an upper portion of the range of flow rates encountered in operation in the exhaust system. Said upper subregion comprises preferably 80 to 100%, particularly preferably 70 to 100%, of the total range of the flow velocities occurring. As for the area size of the end face of the inside portion of the catalyst body, it is preferable that this area size be in the range starting with the cross-sectional area of the free central flow path up to the total flow area of the downstream end of the feed pipe. But it is also possible to make the end face of the interior even larger.

Preferably, the swirl generator is attached with its outer side to the inside of the inlet pipe, 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 possibilities for the concrete technical realization of the swirl generator. In a first preferred way, the swirl generator has an annular ring of vanes. According to a second preferred possibility, the swirl generator has at least one helically along the inlet pipe extending flow guide; the expression "along the inlet pipe" is not intended to mean "along the entire inlet pipe", but merely to reproduce the longitudinal orientation of the flow-guiding element.

Functionally, it is important in the case of the swirl generator provided according to the invention that virtually no or only little swirl is produced at relatively low flow velocities of the exhaust gas (or mass flows or temperatures), while at relatively high flow velocities (or mass flows or temperatures) much Twist is generated. It can be designed for virtually complete "flow switching", ie below a first threshold value of the flow rate practically 100% for the flow of the interior and virtually 0% for the flow of the outside, and above a second threshold value of the flow rate practically 0% to the flow of the interior and practically 100% to the flow of the outdoor area. Alternatively, however, one can make the design with less 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 flow of the outdoor area.

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

• 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 guide vanes or the flow guide elements has a considerable influence on the uniformity of the generated centrifugal field. A larger number causes a uniform centrifugal field. On the other hand, the pressure loss of the swirl generator increases with the number.

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

The angle of attack of the guide vanes or of the flow guide element has a particularly great influence on the strength of the generated twist. Strongly fitted guide vanes lead, e.g. even at average flow velocities to such a strong swirl that the part of the exhaust gas flow to the flow of the inner region of the catalyst body is very small. At particularly high centrifugal forces of the swirl flow, the pressure in the core region of the flow, i. through the free central flow path, so small that an outflow to the inner region 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 of the flow-guiding element, in particular in relation to the total diameter of the feed pipe, has a particular influence on the proportion of the flow which is to flow to the inner region of the catalyst body at low flow velocities. With a relatively small height of the guide vanes or the flow guide element and thus a large diameter of the free central flow path, a larger part of the flow will flow to the inner region of the catalyst body.

In the case of the axial length of the guide vanes or of the flow-guiding element, the tendency is generally such that, with a greater length, a stronger twist is also produced in the free central flow path. As the length increases, the pressure loss of the swirl generator increases. Along the swirl generator increasing angle of attack of the guide vanes or of the flow guide and along the swirl generator increasing height of the guide vanes or the Strömungsleitelements reduce the pressure loss of the exhaust gas converter in comparison to swirl generators without these measures.

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

The vanes may or may not warp (= angle of attack that changes as you move along the radius).

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

Preferably, the area-related cell density in the interior area is at least 1.2 times the cell density in the outer area, particularly preferably at least 1.5 times, and very particularly preferably at least 1.7 times. This is an optimal compromise between improving conversion, especially when warming up the internal combustion engine, on the one hand, and avoiding undue increase in flow resistance and production costs due to larger precious metal consumption, on the other hand.

Preferably, a larger noble metal loading is provided for the greater catalyst activity in the interior of the catalyst body, more preferably at least 20% greater precious metal loading, and most preferably at least 30% greater noble metal loading than in the exterior. This is an optimal compromise between increased conversion of exhaust gas indoors, on the one hand, and limiting the increase in production costs through higher use of precious metals, on the other hand.

Preferably, a finer noble metal dispersion is provided for the larger catalyst activity in the interior of the catalyst body, particularly preferably at least 20% finer noble metal dispersion and most preferably at least 30% finer noble metal dispersion than in the outer area. This is about a good compromise between good exhaust gas 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 due to sintering of the active centers at high exhaust gas temperatures.

Preferably, for the greater catalyst activity in the interior of the catalyst body, a different noble metal composition is provided as in the outer area. 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 the lowest possible noble metal compositions and aging resistance, on the other hand.

The concrete technical possibilities mentioned in the preceding paragraphs for increasing the catalyst activity in the interior of the catalyst body in comparison to its outside area all lead to a decrease in the light-off temperature of the interior area compared to a situation without an increase in the catalyst activity and even after a certain aging of the catalyst Catalyst body (which is usually accompanied by an increase in the light-off temperature) still sufficient reserves for the proper functioning of the exhaust gas conversion exist. The disadvantages associated with increasing the catalyst activity, such as increasing the production costs and increasing the susceptibility to aging, are limited by the fact that at higher load conditions of the internal combustion engine, the interior region of the catalyst body is substantially no longer flowed through or at least reduced.

Preferably, the interior of the catalyst body is only on a partial length Namely, in the case of the embodiments, it may be more favorable to make the inside area larger in its cross-section than one would have to do with greater catalyst activity using its entire length, and instead to carry out only a partial length of the interior area with greater catalyst activity. A particularly suitable method for applying the washcoat over a partial length of the inner region is to place the catalyst body on top of a pipe section and to feed the suspension from below through the pipe until it has reached a certain height in the interior of the catalyst body. Subsequently, the excess suspension is blown down. This manufacturing method is an invention, and it is expressly emphasized that this invention is also independent of the other exhaust system features according to the first aspect and second aspect of the invention described above.

The coating of the catalyst body with the washcoat suspension can be carried out successively in a dipping operation with subsequent blowing or in several dipping operations with subsequent blowing, wherein in the latter case the coating is built up in several steps. In the interior region of the catalyst body, it is possible either to apply one or more washcoat layers, in particular to produce the greater catalyst activity, based on a washcoat, similar to the washcoat applied externally. Alternatively, it is possible to coat the interior and the exterior separately in separate coating runs. Again, you can work for indoor use with an attached feed tube and the coating of the outdoor area with a cover of the front side of the interior.

The inlet pipe preferably has a circular cross-section in the interest of effective generation of the swirling flow. A circular cross-section is also preferred for the exhaust converter housing as a whole, because this provides the best flow conditions for a spiral flow. 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 common. As with mufflers, the lower overall height in the exhaust gas converter is to be emphasized as an advantage compared to a cross-sectionally identical exhaust gas converter with a circular cross section.

There are embodiments in which it is favorable to arrange the longitudinal center axis of the inner region of the catalyst body offset with respect to the longitudinal center axis of the overall catalyst body. Typical examples include non-central positioning of the inlet pipe and oblique opening of the inlet pipe into the housing. The end face of the inner region of the catalyst body should be positioned such that the exhaust gas flow flowing through the free central flow path or the part of the exhaust gas flow not detected by the swirl flow impinges on the catalyst body within the end face of the inner region.

There is the possibility of targeted for the interior or specifically for the exterior of the catalyst body, i. in front of the front end face, in the catalyst body or behind the rear end face, to provide a targeted increase in the flow resistance training, in particular in the form of a local constriction of the flow cross-section or in the form of local flow brakes. A targeted increase in the flow resistance for the interior training favors a flow towards the outer region of the catalyst body (as is the case in principle in the measure "greater cell density in the interior" the case) and vice versa. Targeted flow resistance enhancing designs are a highly effective means to achieve virtually perfect switching acuity at the swirler / free central flow path, in which case more freedom has been gained in designing the swirler.

It is possible to position an inner tube piece in front of the front side of the inner area of the catalyst body, which preferably has substantially the same diameter as the inner area. The inner tube piece favors inflow to the interior at low flow rates.

When in the present application, the flow rate and temperature of the flowing through the inlet pipe exhaust gas flow is spoken, a flow cross section is considered in front of the swirl generator. Since flow velocity and temperature are not constant across the cross section, averaged values are meant across the cross section. In view of the exhaust gas pulsations, temporally averaged values are meant for suitable short time intervals. Overall, one could alternatively consider the mass flow, in particular because the cross-sectional averaging is not required here. Constant exhaust gas temperature considered, the average flow velocity is directly related to the mass flow. Constant mass flow considered, the average flow rate is directly related to the exhaust gas temperature. Instead of using the term "flow velocity", the statements in the present application could also be linked to the term "temperature-normalized mass flow".

It is expressly stated that the subject matter of the invention, in the most general terms, is the following:

Exhaust system for internal combustion engines, comprising a catalytic exhaust gas converter with a housing, a catalyst body supported in the housing, and a supply pipe,
characterized,
that in the inlet pipe, a swirl generator is arranged, which leaves a central flow path free;
and that in the catalyst body, a parameter affecting catalyst efficiency varies across the direction of the flow path.

The above-described features "cell density of the flow channels in the interior of the catalyst body greater than in the exterior" and "interior with greater catalyst activity than the exterior" represent more specific cases of the feature "a parameter affecting the catalyst efficiency varying across the direction of the flow path".

It is emphasized that not only the previously mentioned exhaust system is the subject of the invention, but also the mentioned exhaust gas converter, both in accordance with the first aspect of the invention and according to the second aspect of the invention, is an object of the invention per se. All disclosed preferred embodiments not only apply to the exhaust system as a whole, but also for their part "exhaust gas converter" embodying the invention.

From the document WO 00/12879 a catalytic exhaust gas converter with an associated inlet pipe is known, in which a swirl generator, which leaves a central flow path through the inlet pipe, is arranged. There, however, the training is such that a uniform flow to the front end side 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 shows in a longitudinal section analogous to FIG. 2 a fifth embodiment of an exhaust gas converter; FIG.
• Fig. 13 shows a part of an exhaust gas converter in longitudinal section, wherein a swirl generator alternative embodiment is provided.

In Fig. 1, an exhaust system 2 for an internal combustion engine of a vehicle is shown with its essential components. Advancing from the upstream end to the downstream end, there are the following components: manifold 4, which is screwed to the cylinder head of the internal combustion engine and merges the exhaust gases from the cylinders of the internal combustion engine in a common pipe section 6; catalytic exhaust gas converter 12; Middle silencer 14; Pipe section 16, which leads around the rear axle of the motor vehicle; End silencer 18.

2, an inventive exhaust gas converter 12 is shown. It can be seen a feed pipe 22 having a circular cross-section, a housing 24 having a cone-shaped extension portion 24a, a peripheral wall 24b and a conical tapered portion 24c, and a drain pipe 26 having a circular cross-section. Shortly before the right in Fig. 2 end of the inlet pipe 22, where it merges into the extension portion 24 a, a swirl generator 40 is arranged in the inlet pipe 22.

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

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

Two different flow states of the exhaust gas converter 8 will be illustrated with reference to FIGS. 2 and 4.

An exhaust gas stream flowing through the exhaust system 2 during operation of the internal combustion engine is drawn with arrows 80 as far as the inlet pipe 22 before the swirl generator 40 is concerned. The exhaust gas stream 80 there has a certain mass flow at a certain operating state of the internal combustion engine, a specific flow rate (averaged over the flow cross-section) and a temperature (averaged over the flow cross-section).

At flow rates that are in a lower portion of the range of flow rates occurring during operation of the exhaust system 2, the presence of the swirl generator has little effect on the flow. The swirl generator 40 represents a flow resistance, so that the flow passes predominantly through the central flow path 50. In addition, the flow-mechanical influence of the vanes 46 on the flow is relatively low, because the vanes 46 are designed for flow control at higher flow rates. As a result of the described conditions, the flow leaving the section where the swirl generator 40 is located flows almost 100% into the end face 70 of the inner region 64. A small part of the incoming exhaust gas stream 60 flows into the end face 72 of the outer region 66 at a low flow velocity. All of these relationships are illustrated in FIG. 2 with arrows, which are presented as an illustration of the flow rate or as an illustration of the mass flow.

Conversely, if the flow rate of the exhaust gas flow 80 is in an upper portion of the range of flow rates encountered in operation in the exhaust manifold 2, the swirl generator 40 is operative (especially since the incoming exhaust gas flow 80 is less likely to flow into the central flow path 50 almost entirely, because a strong nozzle-like acceleration would have to take place); the swirl flow impressed when flowing through the swirl generator 40 exerts centrifugal forces on the flow, as a result of which the flow in the area of the expansion section 24a goes radially outward. In the region of the swirl generator 40 and in the region between the swirl generator 40 and the upstream side 70 of the inner region 64, the outer swirl flow exerts toughness forces on the part of the exhaust gas stream 80 flowing through the central flow path 50 and largely impresses on this part of the exhaust gas flow also a peripheral component of the flow velocity , As a result, it can be seen that at high flow velocities, a far greater portion of the total exhaust stream 80, with a suitable design even a near 100% portion of the exhaust stream 80, flows to the face 72 of the outer region 66. All of these relationships are illustrated in FIG. 4.

Between the two described extremes, there is a middle range of flow rates at which a first appreciable portion of the total exhaust stream 80 flows through the interior region 64 and a second, appreciable portion of the total exhaust stream flows through the exterior region 66.

FIG. 5 shows that the inner region 64 has a considerably greater cell density than the outer region 66. The individual cells are designated by 82. In addition, it can be seen in Fig. 5, the possibility of execution that the inner region 64 has a circular cross section, the entire catalyst body 60 has a circular cross section and the outer region 66 has an annular cross section.

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

By means of Fig. 7, the modification is illustrated that the inner region 64 has a square cross-section. A square cross-section can be exploited more perfectly with square-sectioned cells 82.

In Fig. 8 is shown in front view of the end face 84 and in cross section of a second embodiment of an exhaust gas converter 8 and a catalyst body 60; that one can run the flow channels 62 of the catalyst body 60 in the interior region 64 with increased catalyst activity, illustrated by darker coloring. This may be higher noble metal loading, finer precious metal dispersion, other noble metal composition, or several of these measures. In the illustrated embodiment, the cell density in the inner region 64 is equal to the cell density in the outer region 66. However, one could also, as in the first embodiment, work with a higher cell density in the inner region 64.

In FIG. 8, there are circular cross sections as in FIG. 5. In FIG. 9, the modification is drawn that the total catalyst body 60 is substantially 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.

FIG. 12 shows a fifth embodiment in which the inner region 64 of the catalyst body 60 is embodied only in an upstream partial length 86 with increased catalyst activity. 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 is realized by a helically extending flow guide 88 instead of vanes 46. The flow guide 88 has a radial height 48. Instead of providing only a helical flow guide 88 (which should be at least 360 ° long), as shown in FIG start offset by 180 ° (or 90 °, 72 °, etc.). The flow-mechanical effect of the flow-guiding element 88 is analogous to the effect which has been described above in connection with the guide vanes 46. The flow guide 88 is welded with its outer edge on the inside of the inlet pipe 22.

Claims (20)

Exhaust system for internal combustion engines, comprising a catalytic exhaust gas converter with a housing, a catalyst body supported in the housing, and a supply pipe,
characterized,
that in the inlet pipe, a swirl generator is arranged, which leaves a central flow path free;
and that the catalyst body, viewed in the axial direction of view, has an inner area and an outer area, the cell density of the flow channels being greater in the inner area than in the outer area. Exhaust system according to claim 1,
characterized in that the interior is designed with greater catalyst activity than the exterior. Exhaust system for internal combustion engines, comprising a catalytic exhaust gas converter with a housing, a catalyst body supported in the housing, and a supply pipe,
characterized,
that in the inlet pipe, a swirl generator is arranged, which leaves a central flow path free;
and that the catalyst body, viewed in the axial direction of view, has an inner area and an outer area, the inner area being designed with greater catalyst activity than the outer area. Exhaust system according to one of claims 1 to 3,
characterized in that the exhaust gas converter is arranged so that at least 40% of the inflowing exhaust gas flow through the interior of the catalyst body, when the exhaust gas flow has a flow rate in a lower portion of the occurring during operation of the exhaust system range of flow velocities. Exhaust system according to one of claims 1 to 4,
characterized in that the exhaust gas converter is arranged so that at least 80% of the incoming exhaust gas flow through the outer region of the catalyst body, when the exhaust gas flow has a flow rate in an upper portion of the occurring during operation in the exhaust system range of flow velocities. Exhaust system according to one of claims 1 to 5,
characterized in that the inner portion of the catalyst body has an end surface sized in the range from the cross section of the free central flow path to the cross section of the downstream end of the inlet tube. Exhaust system according to one of claims 1 to 6,
characterized in that the swirl generator is mounted in the feed pipe, preferably welded. Exhaust system according to one of claims 1 to 6,
characterized in that the swirl generator has been made integral with the feed tube. Exhaust system according to one of claims 1 to 8,
characterized in that the swirl generator comprises an annular ring of vanes. Exhaust system according to one of claims 1 to 8,
characterized in that the swirl generator has at least one helically along the inlet pipe extending flow guide. Exhaust system according to claim 9 or 10,
characterized in that the angle of attack of the guide vanes or of the flow guide increases along the inlet pipe. Exhaust system according to one of claims 9 to 11,
characterized in that the radial height of the guide vanes or the Strömungsleitelements increases along the inlet pipe. Exhaust system according to one of claims 1 to 12,
characterized in that the inner region of the catalyst body has an end face occupying at most 20% of the total end face of the catalyst body. Exhaust system according to one of claims 1, 2, 4 to 13,
characterized in that the area-related cell density in the interior is at least twice as large as in the outdoor area. Exhaust system according to one of claims 2 to 14,
characterized in that for the larger catalyst activity in the interior of the catalyst body, a larger precious metal loading is provided, preferably at least 20% larger precious metal loading than in the outer area. Exhaust system according to one of claims 2 to 15,
characterized in that a finer noble metal dispersion is provided for the larger catalyst activity in the interior of the catalyst body, preferably at least 20% finer noble metal dispersion than in the outer area. Exhaust system according to one of claims 2 to 16,
characterized in that for the larger catalyst activity in the interior of the catalyst body, a different precious metal composition is provided as in the outer area. Exhaust system according to one of claims 2 to 17,
characterized in that the inner region of the catalyst body is designed only on a partial length with greater catalyst activity than the outer region. Exhaust system according to one of claims 1 to 18,
characterized in that the exhaust gas converter has a substantially elliptical cross section. Exhaust system according to one of claims 1 to 19,
characterized in that the longitudinal central axis of the inner region of the catalyst body is offset with respect to the longitudinal central axis of the catalyst body.

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