Title of Invention

A HONEYCOMB BODY WITH CHANNELS

Abstract

The invention relates to a honeycomb body (1) comprising gas-permeable channels (2). The inner cross-section and number of said channels define a specific geometric surface area (GSA) of the honeycomb body, and they are at least partially separated from one another by separating walls (3). The material and thickness of said walls define a specific heat capacity with regard to the geometric unit area. The honeycomb body comprises an adsorption material provided especially for the adsorption of hydrocarbons. The specific geometric surface area (GSA) of the honeycomb body (1) is greater or equal to 37.5 m K/J [meter Kelvin/joule], preferably greater or equal to 40, especially greater than 60, said geometric surface area being divided by the specific heat capacity (cp) with regard to the area, measured at room temperature without adsorption material and eventual other coatings. The honeycomb body (1) can additionally comprise a catalytically active coating which works in an at least oxidative manner. The honeycomb body is preferably constructed of VKHHWPHWDOOD\HUVKDYLQJDWKLFNQHVVRIOHVVWKDQRUHTXDOWRPwith more than 450 cpsi, especially more than 540 cpsi. This dimensioning of a hydrocarbon trap can be used for the purification of motor vehicle exhaust gases in order to reduce the emission of pollutants during the cold-start phase.

Full Text

The present invention relates to a honeycomb body with channels. The present invention is a honeycomb body with absorber material, in particular for a so- called hydrocarbon trap (HC trap), preferably in the exhaust emission control system of a motor vehicle. As the emission control requirements which motor vehicles have to meet become increasingly more stringent worldwide, particular attention is being paid to cleaning the exhaust gas in the cold-starting phase of an internal combustion engine. The reason for this is that relatively large quantities of unburned hydrocarbons are present in the exhaust gas immediately after an internal combustion engine is started, while at the same time catalytic converters in the exhaust emission control system are not yet at a sufficiently high temperature for the catalytic conversion of these hydrocarbons. One solution for reducing the emission of hydrocarbons in particular during the cold-starting phase of an internal combustion engine, is the use of an HC trap. An HC trap is generally a honeycomb body with channels through which a gas can pass and which are separated at least partly from one another by separating walls, the honeycomb body being coated with an absorber material, preferably zeolite, which absorbs hydrocarbons at a low temperature and desorbs them again at a higher temperature. Typically, such HC traps are arranged upstream of a catalytic converter. An example of this is known, for example, from EP 0 582 971 Bl. EP 0 424 966 Al also describes such a system, the HC trap additionally being bridged at the end of the cold-starting phase by a bypass line in order to avoid overheating in continuos operation. What is said here may also be of significance in the case of adsorbers for other constituents of the exhaust gas, for example nitrogen oxides or water. All previous concepts for the construction and arrangement of an HC trap must allow for the fact that there has in the past been scarcely any adsorber materials which are durable on a long-term basis in the exhaust system of an internal combustion engine and at the same time have a desorption temperature which lies above the minimum temperature necessary for a catalytic conversion of hydrocarbons. For this reason, the previously known concepts assume that an HC trap should have a high specific thermal capacity, in particular a higher thermal capacity than a downstream catalytic reactor, in order that the catalytic reactor can heat up to the minimum temperature necessary for the catalytic reaction before the desorption in the HC trap begins. This concept is described in particular also by EP 0 582 971 Bl. In spite of this, the problem remains that the HC trap draws heat from the exhaust gas in the cold-starting phase and, as a result, in any event delays the time taken by a downstream catalytic converter to reach the minimum temperature necessary for the catalytic reaction, so that it is always difficult to find a compromise for dimensioning an HC trap and a downstream catalytic converter. The object of the present invention is to provide a honeycomb body with adsorber material, in particular for hydrocarbons, which permits improved cleaning of the exhaust gas of an internal combustion engine, in particular in the cold-starting phase. Serving to achieve this object, according to claim 1, is a honeycomb body with channels through which a gas can pass and the inner cross-sectional shape and number of which define a specific geometrical surface area (GSA), measured in m2/l, of the honeycomb body, and which are separated at least partly from one another by separating walls, the material and thickness of the separating walls defining a specific thermal capacity (cp) in relation to the geometrical surface area, measured in kJ/(K-m2) of the honeycomb body, the honeycomb body further having an adsorber material, in particular for hydrocarbons, and the specific geometrical surface area (GSA) of the honeycomb body divided by the surface-area-related specific thermal capacity (cp), measured at room temperature and without adsorber material and without any other coatings, further being greater than or equal to 37.5 m-K/J (meters-Kelvin/Joule), preferably greater than or equal to 40, in particular greater than or equal to 60. The thermal capacity of a material is dependent on the temperature of the material and, in the case of exhaust emission control systems, is often considered and specified for relatively high temperature ranges. For the function of an adsorber, in particular an HC trap, however, the temperature range below 350 °C is decisive, for which reason the figures specified in the present case are related to room temperature, that is 20 °C. The specific thermal capacity in the sense defined here is in this case the thermal capacity in relation to a unit of geometrical surface area of the honeycomb body, that is a value dependent on the wall thickness and porosity of the separating walls and material. Previous considerations assumed that an HC trap should not reach the desorption temperature, at which the desorption of . hydrocarbons begins, before a downstream catalytic converter has reached a minimum temperature necessary for the catalytic conversion. However, this consideration does not take into account the fact that, when the necessary minimum temperature is reached, the catalytic conversion brings about the complete conversion of all hydrocarbons very quickly, since, even if it reaches the necessary minimum temperature only at one point, a catalytic converter completely heats up further almost abruptly because of the exothermal reaction then taking place and, as it does so, catalytically converts all the hydrocarbons flowing onto it. By contrast with this, the desorption in an HC trap proceeds very slowly, so that even when the desorption temperature is reached and after it is exceeded, the stored hydrocarbon is released only gradually. By contrast with the technical teaching in the past, this realization, found after calculations and tests, leads to an HC trap with as low a thermal capacity as possible and as large a geometrical surface area as possible being preferred, a ratio between the specific geometrical surface area and surface-area-related specific thermal capacity, measured at room temperature and without adsorber material and without any other coatings, of greater than or equal to 4 0 m-K/J having been found to be favorable. Preferred even is a still greater ratio of greater than or equal to 60. In the case of such an arrangement, although the HC trap heats up relatively quickly in the exhaust gas flow during the cold-starting phase, and gradually begins the deaorption of hydrocarbons, a downstream catalytic converter can also heat up more quickly, and consequently reach its minimum temperature necessary for the catalytic reaction more quickly, because the HC trap draws increasingly less heat from the exhaust gas flow as it heats up more and more. This has the overall effect that hydrocarbons are converted already at a very early stage in the cold-starting phase and the emission of pollutants can be lowered. The solution according to the invention also has advantages for the dimensioning of an HC trap, since rapid kicking off of the catalytic reaction allows a smaller storage volume for the HC trap. A particularly advantageous aspect of the invention is obtained if the honeycomb body itself additionally has a catalytically active coating, which has at least an oxidizing effect. Then, as soon as the minimum temperature necessary for this is achieved, the desorbed hydrocarbons can be catalytically converted immediately on this coating. In this respect, tests show that the temperature of the honeycomb body rises immediately at the beginning of the conversion due to the exothermal reaction, whereby the desorption process and the conversion are speeded up. This is of advantage in particular if a motor vehicle is frequently operated over short distances, since the HC trap is very quickly fully regenerated again and ready for taking up hydrocarbons during the next cold start. In the dimensioning of a honeycomb body according to the invention, numerous factors play a role, inter alia the overall volume of the honeycomb body, the ratio of axial length and cross-sectional surface area and the placement in the exhaust system. Independently of this, however, it has been found that an increase in the specific geometrical surface area of the honeycomb body is generally favorable, which can mainly be achieved by increasing the number of channels per unit of cross-sectional surface area. Particularly favorable are therefore honeycomb bodies with over 360 channels per square inch (cpsi), preferably even over 450 cpsi and in particular over 540 cpsi. Likewise favorable for a honeycomb body according to the invention is to design the separating walls in such a way that they have as low a thermal capacity as possible, which can be achieved essentially by reducing the thickness of the separating walls. For honeycomb bodies comprising layers of sheet metal, therefore, a thickness of less than or equal to 40 µm, preferably less than or equal to 30 urn is used. For ceramic honeycomb bodies, by analogy, the use of so- called thin-wall ceramic is particularly favorable. A honeycomb body according to the invention is preferably used in an exhaust emission control system of a motor vehicle, to be precise in conjunction with a downstream three- way catalytic converter. Configuration of known exhaust emission control systems may also be of advantage of application of the honeycomb body according to the invention, in particular a bypass line which can be controlled in dependence on the operating state and/or electrical means of heating the honeycomb body or a downstream three-way catalytic converter. An exemplary embodiment of the invention is schematically represented in the accompanying drawing. The honeycomb body 1 according to the invention, serving as an HC trap, has channels 2, which are separated from one another by separating walls 3. Such a honeycomb body 1 may be arranged in particular in an exhaust system 5 of a motor vehicle, being arranged upstream of the three-way catalytic converter 4. In the cold-starting phase, the exhaust gas, becoming slowly hotter, initially flows through the honeycomb 1, with virtually all the hydrocarbons contained in the exhaust gas being absorbed by a coating for the adsorption of hydrocarbons, in particular a zeolite coating, on the separating walls 3. The exhaust gas subsequently flows through the three-way catalytic converter 4. On account of the favorable ratio, according to the invention, of the geometrical surface area and thermal capacity of the honeycomb body 1 per unit of surface area, the time period in which the honeycomb body 1 ie already desorbing hydrocarbons but the three-way catalytic converter 4 cannot yet convert them is very short. This is followed almost abruptly by a complete conversion of all the hydrocarbons contained and desorbed in the exhaust gas, so that altogether the emission of hydrocarbons is less than in the case of conventional systems. This process may be further assisted if the honeycomb body 1 additionally has a catalytically active coating, speeding up at least the oxidation. A honeycomb body according to the invention is suitable in particular for use in exhaust emission control systems of motor vehicles which are to meet the most stringent requirements for environmental compatibility. List of designations 1 honeycomb body 2 channels 3 separating walls 4 three-way catalytic converter 5 exhaust emission control system GSA specific geometrical surface area (square meters per liter) cp specific thermal capacity per geometrical surface area (kilojoules per square meter) WE CLAIM 1. A honeycomb body (1) with channels (2) through which a gas can pass and the inner corss-sectional shape and number of which define a specfic geometrical surface area (GSA) of the hoenycomb body, and which are separated at least partly from one another by separating walls (3) such as of ceramic, the material and thickness of which define a specific thermal capacity in relation to the unit of surface area, the honeycomb body having an adsorber material such as a zeolite coating, in particular for hydrocarbons, characterized in that the specific geomaterical surface area (GSA), measured in square meters per liter (m2/l) of the honeycomb body (1) divided by the surface-area-realted specific thermal capacity (cp), measured in kilojoules per kelvin per square meter [kJ.(Km2)], at room temperature and without adsorber material and without any other coatings, is greater than or equal to 37.5 maters-kelvin per Joule (mK/J), preferably greater than or equal to 40, in particular greater than or equal to 60. 2. The honeycomb body as claimed in claim 1, wherein the honeycomb body (1) has a catalytically active coating, which has at least an oxidizing effect. 3. The honeycomb body as claimed in claim 1 or 2, wherein the number of channels (2) per square inch (cpsi) is at least 360, prefereably over 450, in particular over 540. 4. The honeycomb body as claimed in one of the preceding claims, wherein the honeycomb body (1) is laminated or wound from layers of sheet metal and the thickness of the separating walls (3) is less than or equal to 40 µm, prefearably less than or equal to 30 urn. The invention relates to a honeycomb body (1) comprising gas-permeable channels (2). The inner cross-section and number of said channels define a specific geometric surface area (GSA) of the honeycomb body, and they are at least partially separated from one another by separating walls(3). The material and thickness of said walls define a specific heat capacity with regard to the geometric unit area. The honeycomb body comprises an adsorption material provided especially for the adsorption of hydrocarbons. The specific geometric surface area (GSA) of the honeycomb body (1) is greater or equal to 37.5 m K/J [meter Kelvin/joule], preferably greater or equal to 40, especially greater than 60, said geometric surface area being divided by the specific heat capacity (cp)with regard to the area, measured at room temperature without absorption material and eventual other coatings. The honeycomb body (1) can additionally comprise a catalytically active coating which works in an at least oxidative manner. The honeycomb body is preferably constructed of sheet metal layers having a thickness of less than or equal to 40 µm with more than 450 cpsi, especially more than 540 cpsi. This dimensioning of a hydrocarbon trap can be used for the purification of motor vehicle exhaust gases in order to reduce the emission of pollutants during the cold-start phase.

Documents:

IN-PCT-2000-365-KOL-FORM 27.pdf

IN-PCT-2000-365-KOL-FORM-27-1.pdf

in-pct-2000-365-kol-granted-abstract.pdf

in-pct-2000-365-kol-granted-claims.pdf

in-pct-2000-365-kol-granted-correspondence.pdf

in-pct-2000-365-kol-granted-description (complete).pdf

in-pct-2000-365-kol-granted-drawings.pdf

in-pct-2000-365-kol-granted-examination report.pdf

in-pct-2000-365-kol-granted-form 1.pdf

in-pct-2000-365-kol-granted-form 18.pdf

in-pct-2000-365-kol-granted-form 2.pdf

in-pct-2000-365-kol-granted-form 3.pdf

in-pct-2000-365-kol-granted-form 5.pdf

in-pct-2000-365-kol-granted-gpa.pdf

in-pct-2000-365-kol-granted-letter patent.pdf

in-pct-2000-365-kol-granted-priority document.pdf

in-pct-2000-365-kol-granted-reply to examination report.pdf

in-pct-2000-365-kol-granted-specification.pdf

in-pct-2000-365-kol-granted-translated copy of priority document.pdf