Exhaust gas aftertreatment component with an HC adsorber function and exhaust gas system including such an exhaust gas aftertreatment component

Abstract

An exhaust gas aftertreatment component includes a ceramic carrier body with a plurality of axial flow channels, wherein the carrier body has an inner region and an outer region, which radially surrounds the inner region. A cell density of the carrier body is smaller in the inner region than a cell density in the outer region. At least the outer region of the carrier body has a coaling, wherein the coating of the outer region has an HC adsorber function for a reversible adsorption of unburnt hydrocarbons. An exhaust gas system, which is equipped with such an exhaust gas aftertreatment component, and a vehicle, which has such an exhaust gas system are also provided.

Claims

1. An exhaust gas aftertreatment component comprising: a ceramic carrier body with a plurality of axial flow channels, said carrier body being a one-piece carrier body, said carrier body having an inner region and an outer region, said outer region radially surrounding said inner region; said carrier body having a cell density in said inner region and having a cell density in said outer region, said cell density in said inner region of said carrier body being smaller than said cell density in said outer region of said carrier body, wherein a ratio of said cell density in said outer region to said cell density in said inner region is an integer selected from the group consisting of 6, 8, 9, and 12; at least said outer region of said carrier body having a coating, said coating of said outer region having an HC adsorber function for a reversible adsorption of unburnt hydrocarbons; and said outer region being configured as a wall-flow filter such that said outer region further has a particulate filter function.

2. The exhaust gas aftertreatment component according to claim 1, wherein said inner region has no coating.

3. The exhaust gas aftertreatment component according to claim 1, wherein said inner region has a coating with a catalytic function.

4. The exhaust gas aftertreatment component according to claim 1, wherein said inner region has a coating with a three-way catalytic function.

5. The exhaust gas aftertreatment component according to claim 1, wherein said cell density in said inner region is in a range from 100 to 225 cells per square inch.

6. The exhaust gas aftertreatment component according to claim 1, wherein said cell density in said inner region is in a range from 150 to 200 cells per square inch.

7. The exhaust gas aftertreatment component according to claim 1, further including an adjusting device, said adjusting device selectively routing an exhaust gas flow into at least one of said inner region and said outer region of said carrier body, said adjusting device including an adjustable flap and an inner pipe, said adjustable flap being disposed in said inner pipe, said inner pipe having a downstream end, said downstream end of said inner pipe adjoining said carrier body, and said inner pipe being formed with a plurality of passage openings.

8. An exhaust gas system for an internal combustion engine, the exhaust gas system comprising: an exhaust gas aftertreatment component including a ceramic carrier body with a plurality of axial flow channels, said carrier body being a one-piece carrier body, said carrier body having an inner region and an outer region, said outer region radially surrounding said inner region; said carrier body having a cell density in said inner region and having a cell density in said outer region, said cell density in said inner region of said carrier body being smaller than said cell density in said outer region of said carrier body, wherein a ratio of said cell density in said outer region to said cell density in said inner region is an integer selected from the group consisting of 6, 8, 9, and 12; at least said outer region of said carrier body having a coating, said coating of said outer region having an HC adsorber function for a reversible adsorption of unburnt hydrocarbons; and said outer region being configured as a wall-flow filter such that said outer region further has a particulate filter function.

9. The exhaust gas system according to claim 8, further including a precatalytic converter connected in an exhaust gas flow direction upstream of said exhaust gas aftertreatment component.

10. The exhaust gas system according to claim 9, wherein said precatalytic converter is a three-way catalytic converter.

11. The exhaust gas system according to claim 8, further including a main catalytic converter connected in an exhaust gas flow direction downstream of said exhaust gas aftertreatment component.

12. The exhaust gas system according to claim 11, wherein said main catalytic converter is a three-way catalytic converter.

13. A vehicle comprising: an internal combustion engine; an exhaust gas system connected to said internal combustion engine, said exhaust gas system including an exhaust gas aftertreatment component; said exhaust gas aftertreatment component including a ceramic carrier body with a plurality of axial flow channels, said carrier body being a one-piece carrier body, said carrier body having an inner region and an outer region, said outer region radially surrounding said inner region; said carrier body having a cell density in said inner region and having a cell density in said outer region, said cell density in said inner region of said carrier body being smaller than said cell density in said outer region of said carrier body, wherein a ratio of said cell density in said outer region to said cell density in said inner region is an integer selected from the group consisting of 6, 8, 9, and 12; at least said outer region of said carrier body having a coating, said coating of said outer region having an HC adsorber function for a reversible adsorption of unburnt hydrocarbons; and said outer region being configured as a wall-flow filter such that said outer region further has a particulate filter function.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic view of an exhaust gas system according to the present invention;

(2) FIG. 2 is a diagrammatic longitudinal sectional view of an inventive exhaust gas aftertreatment component of the exhaust gas system of FIG. 1 according to a first embodiment of the invention;

(3) FIG. 3 is a diagrammatic longitudinal sectional view of an inventive exhaust gas aftertreatment component of the exhaust gas system of FIG. 1 according to a second embodiment of the invention; and

(4) FIG. 4 is a diagrammatic cross-sectional view of an exhaust gas aftertreatment component according to FIG. 2 or FIG. 3.

DETAILED DESCRIPTION OF THE INVENTION

(5) Referring now to the figures of the drawings in detail and first, particularly, to FIG. 1 thereof, there is shown an overall view of an exhaust gas system 10 according to the invention of a vehicle. The vehicle is only schematically indicated by a dashed line.

(6) The exhaust gas of an internal combustion engine 12, such as an Otto cycle engine, exits through exhaust gas outlets of its cylinders 14 first into an exhaust gas manifold. At a position close to the engine, in particular directly adjacent to the exhaust gas manifold, a small-volume precatalytic converter 16 can be disposed, that performs the function of a primary catalytic converter by getting warm very quickly after a cold start of the internal combustion engine and taking over the main conversion performance after its light-off after an engine start until there is a light-off of a converter that is connected downstream. Depending on the type of the internal combustion engine, the precatalytic converter can be an oxidation catalytic converter or a three-way catalytic converter. The precatalytic converter 16 is connected to an exhaust gas pipe 18 via, for example, a flange connection.

(7) In a position close to the engine, upstream of the precatalytic converter 16, a first lambda sensor 20 is disposed, which measures an oxygen content of the raw exhaust gas of the engine and serves in a known manner for controlling the air-fuel mixture of the engine. Further, a second lambda sensor 22 can be provided downstream of the precatalytic converter 16. The second lambda sensor 22 can perform different functions. For example, it can serve for the diagnosis of the precatalytic converter 16, the calibration of the sensors with respect to one another and/or the mixture control.

(8) A catalytic converter unit 24 is also installed in the exhaust gas pipe 18, wherein the catalytic converter unit 24 includes an exhaust gas aftertreatment component 26 according to the invention 26 and will be explained in detail with reference to FIGS. 2 to 4.

(9) As can be seen in FIGS. 2 and 3, the catalytic converter unit 24 has in the present example a common catalytic converter housing 28, in which the exhaust gas aftertreatment component 26 is mounted in a shock-absorbing manner, for example in a so-called expanding mat, specifically an intumescent mat.

(10) The exhaust gas aftertreatment component 26 has a carrier body 30, which is manufactured in one piece from a ceramic material and has in longitudinal direction (see exhaust gas arrow) a plurality of flow channels 32, which are formed between thin ceramic walls. The known ceramic materials that are common for exhaust gas components are suitable. The carrier body 30 has an inner region 34 as well as an outer region 36 surrounding the inner region 34 along its radial periphery (perimeter). The inner region and the outer region differ in their cell density wherein that of the outer region 36 is larger than that of the inner region 34, preferably by a factor of four, Preferably, the (lower) cell density of the inner region is in the range of 100 to 225 cpsi (cells per square inch), so that in this case a cell density for the outer region of 400 to 900 cpsi results,

(11) As is in particular apparent from the cross-sectional view of the exhaust gas aftertreatment component 26 in FIG. 4, the inner region 34 and the outer region 36 may have an essentially round or ring-shaped cross-sectional shape, although other shapes, such as elliptical shapes are possible. In fact, due to factors related to production there will often not be a smooth, but a step-shaped boundary surface running between the inner region and the outer region, wherein the boundary surface follows the dimensions of the flow channels 32. Furthermore, the inner region 34 can be disposed centrally (coaxial) or in a decentralized manner with respect to the outer region 36.

(12) At least the flow channels 32, that is their cell walls, of the outer region 36 have a coating with an HC adsorber function. This is typically a zeolite coating, which is capable of binding unburnt hydrocarbons HC by adsorption and/or by chemisorption and desorbs them again at increased temperatures. Such coatings are applied in a known manner as a suspension (washcoat) of fine ceramic particles, such as aluminum oxide. Suitable HC adsorbers are known to a person of skill in the art and require no further explanation.

(13) Furthermore, in accordance with a particularly preferred embodiment, the outer region 36 is provided with a particulate filter function 36. This filter function is preferably achieved by flow channels 32 which are alternately closed in the flow direction. In this case, the term alternately means that a part of the flow channels 32 are closed on the inlet side and the other part, namely the channels 32 that are adjacent to the flow channels 32 that are closed on the inlet side, are closed on the outlet side. In this way, the exhaust gas entering into the flow channel that is closed on the outlet side is forced to pass through the cell walls, in order to get into an adjacent flow channel 32 that is dosed on the inlet side. When penetrating the cell wall, particles are held back. The structure of these wall filters is in principle known.

(14) The inner region 34 also has a coating, such as a zeolite coating, which is furthermore equipped with an exhaust gas aftertreatment functionality, in particular with a catalytic function, in the present example with the function of a three-way catalytic converter.

(15) For this purpose, suitable catalytically active noble metal particles adhere in and/or on the zeolite coating in a very fine dispersion.

(16) The inner region 34 may in principle however also be formed without a coating, so that the inner region itself has no exhaust gas aftertreatment functionality. In this case, the inner region 34 only serves the purpose of facilitating a bypass line for bypassing the HC adsorber of the outer region 36 and of stabilizing the carrier body 30.

(17) As can be seen in FIG. 2, a concentric inner pipe 38 is disposed in an input-side section of the catalytic converter housing 28, so that the exhaust gas path splits in this section into two parallel exhaust gas lines, namely, an inner main line 40, and a ring-shaped side line 42 enclosing the main line 40. With its downstream end, the inner pipe 38 adjoins the carrier body 30 of the exhaust gas aftertreatment component 26 according to the invention, in particular such that the main line 40 joins up to the inner region 34 and the side line to the outer region 36. The inner pipe 38 has a plurality of passage openings 44, which allow the exhaust gas to flow therethrough.

(18) The catalytic converter unit 24 further includes an adjusting device 46 for selectively diverting the exhaust gas flow into the main line 40 and/or the side line 42. The adjusting device 46 is in the present example embodied as a flap which is pivotably mounted on a shaft, wherein the flap is disposed in the inner pipe 38 and can be moved between an open position and a closed position by a suitable actuator 48. In the closed position, the flap closes the access into the inner region 34 of the exhaust gas aftertreatment component 26 so that the exhaust gas flow flows through the openings 44 of the inner pipe 38 into the side line 42 and is thus guided into the outer region 36 and across the HC adsorber. In the open position, in contrast, both the main line 40 and the side line 42 are open. Due to the lower flow resistance in the inner region 34 of the component 26, at least the main portion of the exhaust gas flow flows through the inner region 34 and through the exhaust gas catalytic converter provided there. Preferably, the adjusting device 46 is furthermore controllable to be in intermediate positions, so that the exhaust gas flow can be guided proportionately into the main line 40 and the side line 42. Of course, the device for selectively directing the exhaust gas into the regions 34 and 36 of the component 26 can also be configured in a manner that is different from the device shown here by way of example.

(19) Downstream of the exhaust gas aftertreatment component 26, the exhaust gas flows into a common exhaust gas line 50, where a main catalytic converter 52 is disposed, which has in particular a three-way catalytic coating and thus serves for the conversion of unburnt hydrocarbons HC, carbon monoxide CO and nitrogen oxides NO.sub.X.

(20) For controlling the adjusting device 46 and thus for guiding the exhaust gas flow across the HC adsorber of the outer region 36 and/or across the exhaust gas catalytic converter of the inner region 34, temperature sensors 54, 56 can be disposed at the positions designated by reference numerals 54 and 56 in FIG. 2, that is upstream and downstream of the exhaust gas aftertreatment component 26. The sensors 54, 56 measure the exhaust gas temperature and therefore allow drawing conclusions about the temperatures of the HC adsorber in the outer region 36 or, respectively, of the main catalytic converter 52. It is also conceivable to install the temperature sensors directly in the respective components.

(21) The embodiment of the catalytic converter unit 24 shown in FIG. 3 differs from that according to FIG. 2 only by a longer configuration of the inner pipe 38, which in this case projects axially beyond the inlet nozzle of the housing 28. The inner pipe 38 can be connected, for example by a weldseam with the front edge of the inlet nozzle. The embodiment illustrated here has advantages mainly related to the manufacturing technique when compared to that of FIG. 2.

(22) The exhaust gas system 10 shown in FIGS. 1 to 3 exhibits the following function.

(23) After a cold start of the internal combustion engine 12, when the catalytic converters 16 and 52 and, if applicable, the catalytic converter provided in the inner region 34 of the component 26 do not yet have their operating temperature, the adjusting device 46 in front of the inner region 34 of the component 26 is initially dosed, so that the entire exhaust gas flow flows through the HC adsorber of the outer region 36. It stores the hydrocarbons contained in the exhaust gas, that pass the precatalytic converter 16, which is not ready for operation, unconverted in the first few seconds after the engine start. The size of the adsorber is dimensioned in a manner so that the hydrocarbons can be completely stored so long until the precatalytic converter 16 has reached its light-off temperature and takes over their conversion.

(24) When the precatalytic converter 16 has reached this temperature, which can be identified by a modeling or by the temperature sensor 54, the adjusting device 46 is opened so that the hot exhaust gas flows across the exhaust gas catalytic converter provided in the inner region 34 of the exhaust gas aftertreatment component 26 and heats it. As soon as the exhaust gas catalytic converter of the inner region 34 reaches its light-off temperature, its further warming is accelerated due to the exothermic property of the conversion reactions. The exhaust gas that has thus already been heated furthermore flows into the main catalytic converter 52 and leads to its heating.

(25) If, through the use of the temperature sensor 56, it is detected that also the main catalytic converter 52 has reached its light-off temperature, the adjusting device 46 is again partially or completely closed, so that the entire or, respectively, a given portion of the exhaust gas flow is guided across the HC adsorber and heats it up. Once the HO adsorber has reached its desorption temperature, the stored hydrocarbons are set free and flow into the common exhaust gas line 50 and into the main catalytic converter 52, where they are converted to CO.sub.2 and H.sub.2O.

(26) Altogether, the heating of the downstream-connected main catalytic converter 52 and its light-off after a cold start are significantly accelerated by the placement of the exhaust gas catalytic converter in the inner region 34.

(27) The volumes and/or the noble metal loadings of the exhaust gas catalytic converter of the inner region 34 and of the main catalytic converter 52, andif providedof the precatalytic converter 16 are configured such that the sum of their conversion performances in the entire operating characteristic map of the engine achieves a predetermined, sufficient and high total conversion performance. This means that even in corresponding high speed phases of the driving cycle, the limited exhaust gas components must be converted at least according to the specifications. The main catalytic converter 52 must furthermore be capable of converting the desorbed hydrocarbons in the desorption phase of the HC adsorber. In contrast to an analog system, in which no exhaust gas catalytic converter is provided in the inner region 34, this allows the main catalytic converter 52 to be dimensioned smaller, because the exhaust gas catalytic converter in the inner region 34 provides an additional surface area having a catalytic activity. In an extreme case, if the precatalytic converter 16 and the inner region catalytic converter 34 together provide a sufficient conversion performance in the driving cycle, the main catalytic converter 52 may be dimensioned so that it only converts the hydrocarbons released in the desorption phase. In this case, even a pure oxidation function of the main catalytic converter 52 may be sufficient.

LIST OF REFERENCE CHARACTERS

(28) 10 exhaust gas system

(29) 12 internal combustion engine

(30) 14 cylinder

(31) 16 precatalytic converter

(32) 18 exhaust gas pipe

(33) 20 first lambda sensor

(34) 22 second lambda sensor

(35) 24 catalytic converter unit

(36) 26 exhaust gas aftertreatment component

(37) 28 catalytic converter housing

(38) 30 carrier body

(39) 32 flow channels

(40) 34 inner region

(41) 36 outer region

(42) 38 inner pipe

(43) 40 main line

(44) 42 side line

(45) 44 openings

(46) 46 adjusting device

(47) 48 actuator

(48) 50 common exhaust gas line

(49) 52 main catalytic converter

(50) 54 temperature sensor

(51) 56 temperature sensor