DE102004046918A1 - Device for catalytic conversion of unwanted constituents of exhaust gases from engine into less harmful constituents has section of catalyser assembly which when heater is not available is first set in operation in cold start phase - Google Patents

Abstract

The device for the catalytic conversion of unwanted constituents of exhaust gases from an internal combustion engine into less harmful constituents has a heater unit (6) installed inside a section (7) of a catalyser assembly (3) which when the heater is not available is first set in operation in a cold start phase, and/or is at a distance from the axial ends of the catalyser assembly by a measurement which is about 20 per cent of the axial longitudinal extent of the catalyser assembly.

Description

The The invention relates to a device for converting unwanted Components of exhaust gases from an internal combustion engine into less harmful components according to the generic term of claim 1.

Around to reduce an emission load of internal combustion engines and thus a better environmental compatibility To achieve it, it has long been known in the exhaust system so-called Use catalysts for exhaust gas purification. Such catalysts point frequently a housing and a monolith, often ceramic, stored therein, its surface with a porous, catalytic layer is provided. When flowing through the Catalyst, the combustion gases from the catalytic Coating of the catalyst converted. The transformation process however, requires a certain minimum temperature, which is about 400 ° C. Especially in a cold start phase of the internal combustion engine, in which the exhaust gas only has a temperature of about 100 ° C, found by the Catalyst almost no reduction of pollutants instead. Much more heated the exhaust gas in the cold start phase, first the catalyst until this his Operating temperature has reached. To improve pollutant reduction, especially in the cold start phase of the internal combustion engine, are therefore different solutions, such as additional heaters for heating the catalyst, known.

From the DE 2 230 663 a device is known for converting unwanted components of exhaust gases from an automotive engine into less harmful components. The device has a housing with an inlet and an outlet as well as a catalyst device arranged in the housing. In order to keep a cold start phase of the motor vehicle engine as short as possible, an electric heater is provided for conductive heat transfer to at least a portion of the catalyst so that it reaches its operating temperature faster. For this purpose, the heating device has an electrical heating element arranged centrally in the catalytic converter and extending substantially over the entire length of the catalyst, which is arranged in a tubular component.

From the DE 41 10 395 A1 is known an electrically heatable catalyst for internal combustion engines. The catalyst has a housing and a support arranged therein with a plurality of mutually parallel, honeycomb-like channels, which are coated with a catalytically effective against the exhaust gas layer. At least a portion of the surface of the carrier has at least one electrically conductive resistance heating layer, which is arranged on the flow input side of the catalyst.

From the DE 196 02 266 A1 an electrically heatable exhaust gas catalyst of an internal combustion engine is known, which has a designed as a metal carrier catalyst heating zone downstream of which a further catalyst body is provided. The heating zone extends only over a partial region of the exhaust gas flow cross section. In order to guide a disproportionate share of the exhaust gas flow through the heating zone, a nozzle-like constriction of the flow cross-section is provided upstream of the same.

From the DE 195 34 903 A1 are known an apparatus and a method for exhaust treatment with secondary air injection in internal combustion engines. For this purpose, the device for pollutant reduction connected to the fuel supply system of the internal combustion engine fuel line, which is provided with a shut-off device operated by an electronic control and exhaust temperature depending fuel in a secondary air-carrying line feeds. During the cold start of the internal combustion engine, the transformation temperature of the catalyst is achieved faster by igniting the fuel-air mixture produced in an atomizer.

Finally, out of the EP 0 775 807 B1 a device for cleaning exhaust gases of an internal combustion engine with an electrically heated catalyst device known. This comprises a catalyst support consisting of a columnar honeycomb body in which a sheet of a metal foil and a sheet of a deformed metal foil are superimposed. Furthermore, the catalyst device has an outer metal cylinder that receives the catalyst carrier and an electrical current passage to generate heat by supplying electricity. On an end surface of the electrically heated catalyst carrier a plurality of electrically insulated ceramic rods are arranged, whose end portions are held on the outer peripheral portions of the electrically heated catalyst carrier.

The present invention employs dealing with the problem, for a device initially mentioned Kind an improved embodiment specify with which in particular a faster start of a Catalyst arrangement and thus an improved reduction of pollutant emissions can be achieved in the cold start phase.

According to the invention this Problem with the objects the independent one claims solved. Advantageous embodiments are the subject of the dependent Claims.

The The invention is based on the general idea of a device for the catalytic conversion of undesirable constituents of exhaust gases from an internal combustion engine into less harmful components an in an exhaust line bypass-arranged and the exhaust gases in the longitudinal direction flow-through Catalyst arrangement by means of an electric heater to heat, with the heater within a range the catalyst assembly, the non-existent heater would start in a cold start phase first, arranged and / or by the axial ends of the catalyst assembly is spaced by a degree, which at least about 20% of the axial length of the catalyst assembly lies. The catalyst arrangement consists essentially either from a single catalyst body or of a plurality of catalyst bodies arranged side by side and / or in succession. The Electric heater heats at least a part of / the Catalyst body (s) while a start phase.

By the inventive arrangement the electric heater can be a particularly effective heating the catalyst arrangement or the catalyst body can be achieved, without that there is a significant loss of heating energy. Because the Heating device is compared to an input side or end the catalyst assembly arranged heater much more effective and more economical, since the heating energy directly on catalytic effective zones of the catalyst arrangement is transmitted and radiation losses, as with an input or end arranged heating device occur can be avoided.

Furthermore have temperature measurements on catalyst assemblies without a heater shown in the cold start phase that the catalyst arrangement initially not in an upstream side Range, but further back, that is spaced from the upstream side of the Catalyst arrangement starts. The area within which the catalyst assembly first starts, lets by simultaneous temperature measurements on different areas determine the catalyst arrangement. Because the onset of the catalyst arrangement is always with an exothermic reaction and thus with a significant Jump / increase in the temperature of the starting region of the catalyst arrangement connected.

According to the invention, it is provided exactly to heat the areas of the catalyst assembly, which in a catalyst assembly without an electric heater would jump first. In the invention, the heater is therefore not flow input side the catalyst arrangement, but in one of them spaced apart and arranged downstream area, causing the quick start an optimal range of the catalyst arrangement supported or accelerates and thus the short-term initiated exothermic reaction in the cracked region of the catalyst arrangement to the other Heating used and the cold start phase are significantly shortened can. The solution according to the invention is achieved thus that for the Starting, the so-called "light-off" of the catalyst arrangement, necessary heat input as required and the power consumption of the electrical Heating device to achieve the catalyst activation on a necessary minimum reduced becomes. As a result, in the invention, the heater needs only during a short time interval to be turned on, what more The result is that the cost of necessary additional components for the entry of the thermal energy in the catalyst arrangement can also be minimized.

By the solution according to the invention can be thus a reduction in the onset of the catalyst arrangement required Achieve heating energy with a simultaneously shortened cold start phase, resulting in an overall improved energy balance and an improved energy balance Set environmental behavior.

The solution according to the invention is based continue on the general idea that to heat up the Catalyst arrangement or the / of the catalyst body (s) serving heating itself having a catalytic coating. This offers the great advantage that a catalytic effect can be achieved even faster because the electric heater very fast to the catalytic Conversion of exhaust gases required temperature of about 400 ° C reached and thereby significantly shorten the cold start phase. At the same time it heats up electric heater the surrounding catalyst body and shortened thereby a period of time required to activate it.

According to an advantageous embodiment of the solution according to the invention, the catalyst arrangement has at least two catalyst bodies arranged one behind the other in the flow direction and designed as disks. The catalyst bodies can each be formed as monoliths or be composed of several individual catalyst (circle) segments, so that an individual structure of the catalyst arrangement is conceivable. Preferably, the discs are arranged spaced apart in the flow direction, where by itself can distribute the exiting from an upstream catalyst disc exhaust gases in an intermediate space between the two catalyst disks evenly and homogenized and can enter with uniform distribution over the cross section of the catalyst disk in the next catalyst disk. This improves the efficiency of the catalyst arrangement, since a virtually uniform flow through the entire catalyst arrangement takes place and overloading of individual areas can be avoided.

Is appropriate the heating device is arranged between two panes. This simplifies to one the arrangement of the heater and allows the other a parallel Heating of adjacent catalyst disks and exhaust gases.

According to one advantageous development of the solution according to the invention comprises the catalyst arrangement at least one receptacle in the form of a hole or a cutout for Recording of the heater on. This facilitates in particular at monolithically formed catalyst bodies, the arrangement of the electrical Heating device or makes the inventive arrangement of the heater only possible on monolithic catalyst arrangements. Without the recording according to the invention should the electric heater in a conventional manner along the end the catalyst assembly are arranged, whereby the cold start phase extended and the environmental behavior deteriorates.

at a preferred embodiment is aligned the recording for the electric heater with a passage opening in a housing surrounding the catalyst assembly. This allows one particularly simple installation or replacement of the electric heater and increases the ease of maintenance of the device according to the invention. At the same time In this way maintenance and / or repair costs are reduced.

Further important features and advantages of the invention will become apparent from the Dependent claims, from the drawings and from the associated description of the figures the drawings.

It it is understood that the above and the following yet to be explained features not only in the specified combination, but also in other combinations or alone, without to leave the scope of the present invention.

preferred embodiments The invention are illustrated in the drawings and in the following description explains where like reference numerals refer to the same or functionally same or similar Refer to components.

there show, in each case schematically,

1 a longitudinal section through an inventive device for the catalytic conversion of exhaust gases,

2 a cross section through the device according to the invention according to the section line AA in 1 .

3 a representation like in 1 but with a different catalyst arrangement,

4 a diagram illustrating the effect of the inventive arrangement of the electric heater in comparison to a device without a heater.

Corresponding 1 has a device according to the invention 1 for the catalytic conversion of undesirable constituents of exhaust gases from an internal combustion engine (not shown) into less harmful constituents, at least one in an exhaust gas line 2 Bypass-free arranged catalyst arrangement 3 on which of the exhaust gases in the longitudinal direction 4 can be flowed through. The catalyst arrangement 3 exists according to 1 from a single, preferably monolithic, catalyst body 5 , or according to 3 from several side by side and / or behind one another arranged catalyst bodies 5 . 5 ' . 5 '' . 5 ''' ,

Furthermore, at least one electric heating device 6 provided, which at least a part of the catalyst body 5 heated in a start phase. As the catalyst arrangement 3 Only then becomes active and only then causes a reduction of the pollutant emission, if an activation energy necessary for the conversion is available, it is desirable to have a catalyst working temperature at which the catalyst arrangement 3 starts to reach as early as possible. The start of the device 1 or the catalyst arrangement 3 is referred to as a so-called "light-off." In particular, during the cold start of the internal combustion engine, however, it takes a certain time until the required catalyst working temperature and thus the start of the catalyst arrangement 3 be achieved. To the cold start phase and thus the phase in which the device 1 only a conditional reduction of pollutant emission causes to keep as short as possible, the electric heater 6 can be used, and the catalyst arrangement 3 heat until it starts and through the then resulting exothermic reaction in the catalytic conversion of the exhaust gases itself generates enough energy.

To the onset of the catalyst arrangement 3 With as little energy and as fast as possible to reach the heater should 6 Moreover, be arranged in an area in which the catalyst arrangement 3 without heating device 6 heated the fastest. Measurements of the temperature balance, in particular in the cold start phase of a conventional catalyst, have shown that the onset of the catalyst arrangement 3 not in a front end portion of the same, but in the flow direction 4 further back. Therefore, according to the invention, the heating device 6 within a range 7 the catalyst arrangement 3 , the heater is not present 6 in a cold start phase would start first, and / or from the axial ends of the catalyst assembly 3 spaced at a distance which is at least about 20% of the axial length of the catalyst assembly 3 lies.

This offers the advantage that compared to a front end on the catalyst assembly 3 arranged heating device 6 less heat energy is radiated useless outwards and only, for example, a housing 8th or a subfloor of a motor vehicle, not shown, heated. Since the catalyst arrangement 3 without heating device 6 in the area 7 Moreover, the fastest heating is for the catalyst assembly to start 3 in this area 7 at least heating energy necessary, so that the onset of the catalyst assembly 3 can be achieved with significantly lower power than heating in another area. In particular, the heat input necessary for the "light-off" is introduced into the catalyst arrangement 3 localized, which is the power consumption to achieve activation of the catalyst arrangement 3 reduced to the necessary minimum. In addition, this also allows the heater 6 and other associated components, such as a power source not shown, are made smaller and less expensive.

According to 1 there is the catalyst arrangement 3 as mentioned above from only a single catalyst body 5 , at least one recording 9 in the form of a bore or a cutout for receiving the heating device 6 having. The recording 9 Aligns with a passage opening 10 in which the catalyst arrangement 3 surrounding housing 8th , This allows a particularly simple installation or replacement of the heater 6 , which in particular repair and / or maintenance costs can be reduced. The sectional view of the arrangement of the heater 6 in the recordings 9 according to the section line AA in 1 is in 2 showing here the heaters 6 exemplarily radiating from a center 12 are arranged starting.

In general, it is also conceivable that the catalyst arrangement 3 from several side by side and / or behind one another arranged catalyst bodies 5 . 5 ' exists (cf. 2 and 3 ). So has the catalyst arrangement 3 according to 3 five in the flow direction 4 one behind the other and formed as disks catalyst body 5 on. It is also conceivable, however, a smaller or a higher number of consecutively located and trained as slices Katalysatorkör pern 5 , The discs are in the flow direction 4 spaced apart, so that between two catalyst bodies, for example between the catalyst body 5 and catalyst body 5 ' a gap 11 is present, the homogenization of the exhaust gases between the individual catalyst bodies 5 and 5 ' serves and the possibility to arrange the heater 6 offers.

Through the gaps 11 is a homogenization or homogenization of the by the catalyst body 5 reached flowed exhaust gases, which then distributed over the cross section evenly distributed through the subsequent catalyst body 5 ' stream. As a result, in particular, an efficiency of the catalyst arrangement 3 improved, as an overload of individual areas of the catalyst body 5 respectively. 5 ' can be avoided.

It is conceivable, as mentioned above, that the heating device 6 between two discs, that is in the space 11 is arranged. This causes on the one hand a heating of the passing exhaust gases and on the other hand a heating of the gap 11 adjacent catalyst bodies 5 '' and 5 '' ,

Generally, a downstream side 13 a front catalyst body 5 '' or an upstream side 14 a downstream catalyst body 5 ''' also be coated with an electrical conductive paste, which serves as a heating device 6 acts.

Preferably, the heating device 6 a ceramic or a metallic carrier or an optionally doped SiC carrier with a respectively printed thereon heat conductor structure, which is constructed for example in thick film technology. In addition, it is conceivable that the SiC support has a porous structure. The SiC carrier can also serve as a heating element itself, wherein it is advantageous to provide a doping with which the electrical conductivity of the SiC carrier is adapted for resistance heating.

In a particularly advantageous embodiment of the solution according to the invention, the heating device 6 itself a catalytic coating, whereby the cold start phase of the catalyst assembly 3 can be shortened further. The catalytic coating of the heater 6 achieves the required catalyst working temperature very quickly, which allows the catalytic conversion to be initiated at a very early stage. It is conceivable that the catalytic coating of the heater 6 is identical to a coating at least one catalyst body 5 ,

According to 4 is a comparison of a cold start phase with a start of the catalyst arrangement 3 with and without heater 6 shown. On the abscissa while the time is removed, whereas on a left ordinate a flow input side of the catalyst assembly 3 prevailing temperature and on a right ordinate a hydrocarbon concentration of the exhaust gases after exiting the catalyst assembly 3 is applied.

• – Kurve B den zeitabhängigen Verlauf der Temperatur auf der Strömungseingangsseite einer Katalysatoranordnung 3 mit erfindungsgemäß angeordneter Heizeinrichtung 6,
• – Kurve C den zeitabhängigen Verlauf der Kohlenwasserstoffkonzentration ausgangsseitig dieser Katalysatoranordnung 3 mit Heizvorrichtung 6,
• – Kurve D den zeitabhängigen Verlauf der Temperatur auf der Strömungseingangsseite einer Katalysatoranordnung 3 ohne Heizeinrichtung 6 und
• – Kurve E den zeitabhängigen Verlauf der Kohlenwasserstoffkonzentration ausgangsseitig der letzteren Katalysatoranordnung 3 ohne Heizeinrichtung 6.

The following shows:

• Curve B shows the time-dependent course of the temperature on the flow input side of a catalyst arrangement 3 with inventively arranged heating device 6 .
• Curve C shows the time-dependent course of the hydrocarbon concentration on the outlet side of this catalyst arrangement 3 with heating device 6 .
• Curve D shows the time-dependent course of the temperature on the flow input side of a catalyst arrangement 3 without heating device 6 and
• Curve E shows the time-dependent course of the hydrocarbon concentration on the output side of the latter catalyst arrangement 3 without heating device 6 ,

For a catalyst without a heater 6 the catalyst arrangement jumps 3 only at a time t ₂ , from which the flow-input side temperature greatly increases according to curve D and at the same time the hydrocarbon concentration on the output side of the catalyst arrangement 3 greatly reduced according to curve E.

In a device according to the invention 1 with a heater 6 will the heater 6 switched on at time t ₁ for a short time interval according to curve H, whereupon the hydrocarbon concentration is reduced significantly according to curve C immediately. The catalyst arrangement 3 thus jumps to the heater 6 initiate exothermic reactions that take over the further heating of the catalyst assembly, immediately, the input-side temperature according to curve B is substantially identical to curve D or that input side temperature, which in a device without a heater 6 was measured.

The diagram according to 4 shows that in inventive arrangement of the heater 6 that is, when the heater is arranged 6 in a region of the catalyst arrangement 3 , which would start first without a heater in a cold start phase, starting the catalyst arrangement 3 by brief operation of the heater 6 advanced from the time t ₂ to the time t ₁ and thereby the cold start phase can be significantly shortened, which leads to an earlier reduction of pollutant emissions and thus an improved environmental performance. Compared to a device without heating device 6 There is no significant increase in the temperature at the flow inlet side of the catalyst arrangement 3 , what according to 4 at the almost identical course of the curves B and D is visible.

Out 4 will be further appreciated that compared to a device without heater 6 the demand-based supply of heating energy at time t ₁ leads to an instantaneous drop in the hydrocarbon concentration according to curve C.

In summary, the essential features of the solution according to the invention can be characterized as follows:
The invention provides, in a device 1 for the catalytic conversion of exhaust gases, a heater 6 within a range 7 the catalyst arrangement 3 , the heater is not present 6 in a cold start phase would first start to dispose and / or spaced a distance from the axial ends of the catalyst assembly 3 which is at least 20% of the axial length of the catalyst assembly 3 lies. In this way, on the one hand, it is achieved that the heating device 6 just in place heating energy in the catalyst arrangement 3 enters, at the most likely with a cracking of the catalyst assembly 3 is to be expected and thereby the onset of the catalyst arrangement 3 required to be entered heating energy is reduced to a minimum. On the other hand, compared to an arrangement of the heater 6 , For example, flow input side of the catalyst assembly 3 , avoided that the heater 6 much unused energy radiates and only a portion of the heating energy is used to the catalyst assembly 3 to heat.

Ideally, the heater rejects 6 even a catalytic coating on, causing the heater 6 itself acts as a catalyst and thus an earlier reduction of pollutant emissions can be achieved.

Claims (13)

Contraption ( 1 ) for the catalytic conversion of undesired constituents of exhaust gases from an internal combustion engine into less harmful constituents, - with at least one in an exhaust gas line ( 2 ) arranged bypass-free and of the exhaust gases in the longitudinal direction ( 4 ) throughflowable catalyst arrangement ( 3 ) consisting essentially of a catalyst body ( 5 ) or of a plurality of catalyst bodies arranged side by side and / or in succession ( 5 . 5 ' ), with at least one electric heating device ( 6 ), which at least a part of the / the catalyst body ( 5 ) is heated in a starting phase, characterized in that the heating device ( 6 ) within a range ( 7 ) of the catalyst arrangement ( 3 ), which in the absence of a heating device ( 6 ) would first jump in a cold start phase, and / or from the axial ends of the catalyst assembly ( 3 ) is spaced at a distance which is at least about 20% of the axial longitudinal extent of the catalyst arrangement ( 3 ) lies. Contraption ( 1 ) for the catalytic conversion of undesired constituents of exhaust gases from an internal combustion engine into less harmful constituents, - with at least one in an exhaust gas line ( 2 ) arranged bypass-free and of the exhaust gases in the longitudinal direction ( 4 ) throughflowable catalyst arrangement ( 3 ) consisting essentially of a catalyst body ( 5 ) or of a plurality of catalyst bodies arranged side by side and / or in succession ( 5 . 5 ' ), with at least one electric heating device ( 6 ), which at least a part of the / the catalyst body ( 5 . 5 ' ) in a starting phase, - in particular according to claim 1, characterized in that the heating device ( 6 ) has a catalytic coating. Apparatus according to claim 1 or 2, characterized in that the catalyst arrangement ( 3 ) at least two in the flow direction ( 4 ) one behind the other and formed as discs catalyst body ( 5 . 5 ' ) having. Apparatus according to claim 3, characterized in that the discs in the flow direction ( 4 ) are spaced from each other. Apparatus according to claim 3 or 4, characterized in that the heating device ( 6 ) is arranged between two discs. Device according to one of claims 1 to 5, characterized that a SiC carrier serves as a heating element. Device according to one of claims 1 to 6, characterized in that the heating device ( 6 ) has a ceramic or a metallic carrier or a SiC carrier with a respectively printed thereon Heizleitererstruktur. Device according to claim 7, characterized in that the heat conductor structure is constructed using thick-film technology. Device according to one of claims 6 to 8, characterized that the SiC carrier a porous one Structure has. Device according to one of claims 1 to 9, characterized in that a downstream side ( 13 ) of a front catalyst body ( 5 ' ) or an upstream side ( 14 ) of a downstream catalyst body ( 5 '' ) is coated with an electrically conductive paste which acts as a heating device ( 6 ) serves. Device according to claim 10, characterized in that the catalytic coating of the heating device ( 6 ) is identical to a coating of the catalyst body (s) ( 5 ). Device according to one of claims 1 to 11, characterized in that the catalyst arrangement ( 3 ) at least one recording ( 9 ) in the form of a bore or a cutout for receiving ( 9 ) of the heater ( 6 ) having. Device according to claim 12, characterized in that the receptacle ( 9 ) with a passage opening ( 10 ) in a catalyst arrangement ( 3 ) surrounding housing ( 8th ) flees.