Exhaust gas system

p0001The present invention relates to an exhaust system for the purification of an exhaust gas of an internal combustion engine, in particular for the purification of exhaust gases of a diesel engine of an automobile.

p0002Due to legal regulations, which place higher and higher demands on the exhaust systems in automotive engineering, these exhaust systems have been steadily developed in the past. A large number of components are used, each of which fulfills different functions within the exhaust system. For example, starting catalysts are known which have a particularly small volume and thus reach their starting temperature, which is necessary for the catalytic conversion, rapidly after a cold start of the internal combustion engine. Furthermore, electrically heatable catalysts, for example, are also known which also enable an improved cold start behavior of the exhaust system. So-called adsorbers have the task, in the exhaust system of an internal combustion engine, Contaminants contained in the exhaust gas for a certain period of time, which are preferably stored until a downstream catalytic converter has reached its operating temperature. Particulate traps or particulate filters are particularly used in exhaust systems of diesel engines, which collect soot particles contained in the exhaust gas, the collected particulate accumulations being continuously or discontinuously reacted, for example by supplying high thermal energy.

p0003From the <patcit id="pcit0001" dnum="WO0034632A"><text>WO-A-00/34632</text></patcit> An exhaust gas treatment system is known in which two catalyst support bodies and a soot filter are formed. A first catalyst support body is used for the oxidation of hydrocarbons, while a second catalyst support body is a reaction of NO to NO₂ Catalysed.

p0004Object of the present invention is to provide an exhaust system for purifying an exhaust gas of an internal combustion engine, in particular for purifying exhaust gases of a diesel engine of an automobile which ensures a particularly effective implementation contained in exhaust gas pollutants, in which a continuous regeneration of a arranged in the exhaust system particulate trap is ensured .

p0005This object is achieved by an exhaust system with the features of claim 1. Further advantageous refinements of the exhaust system are described in the dependent claims.

p0006The exhaust gas system according to the invention for purifying an exhaust gas of an internal combustion engine, in particular a diesel engine of an automobile, can be flowed through by the exhaust gas in a flow direction, the exhaust system having the following components in the flow direction:<ol><li>1. a catalytic converter for the conversion of carbon monoxides and hydrocarbons contained in the exhaust gas,</li><li>2. An oxidation catalyst for the conversion of nitric oxide contained in the exhaust gas, and</li><li>3. a particle trap for collecting particles contained in the exhaust gas.</li></ol>

p0007The particle trap has freely continuous channels in which swirling points and stabilizing points and / or deflecting devices are arranged.

p0008The proposed arrangement of said components in the exhaust system has particularly positive effects with regard to the regeneration of the particle trap. These positive effects unexpectedly result from this cascading of the above-mentioned components, as will be explained in more detail below.

p0009The catalytic converter arranged upstream serves in particular the reaction of carbon monoxides and hydrocarbons. The carbon monoxide content in the exhaust gas of diesel engines is generally relatively low and increases only more as the soot boundary approaches. This has its origin, in particular, in the mostly lean (with air surplus) operating strategy of the diesel engine with regard to the combustion of the fuel. In this case, increased hydrocarbon fractions are caused, for example, in excessively emaciated areas of the fuel / air mixture, which can not be implemented in time at low temperatures in the combustion chamber (partial load). An increase in the hydrocarbon fractions in the exhaust gas is also given at times very rich (with air deficiency) combustion. The catalytic converter,

p0010Owing to the fact that the catalytic converter has already converted the substantial portion of carbon monoxides and unsaturated hydrocarbons, the oxidation catalyst serves, in particular, downstream of the reaction of nitrogen oxides still present in the exhaust gas. Nitrogen oxides are intensified particularly in the case of an almost stoichiometric combustion up to an average air excess (approximately to λ = 3). The nitrogen dioxide content in the exhaust gas is usually between 5 and 15%. The oxidation catalyst now has a catalytically active coating which effects a conversion of the nitric oxides into nitrogen dioxides. The nitrogen dioxide content in the exhaust gas is thus significantly increased, preferably to a proportion in the exhaust gas of more than 50%, in particular higher than 80% or even 95%. Such conversion rates are achieved in this case because the upstream catalytic converter has already converted other pollutants substantially into harmless constituents. The high proportion of nitrogen dioxide produced by the oxidation catalyst has a particularly positive effect with regard to the regeneration of the downstream particle traps.

p0011Particles and in particular soot occur in the exhaust gas during the combustion of the fuel under extreme air deficiency and are typical of the combustion in the diesel engine because of the locally very inhomogeneous air-fuel mixture. The particles usually deposit frequently on the coatings of the components and / or on the outer wall, such as, for example, in the discharge zone, of the exhaust system. In the case of load changes, they are then ejected in the form of a particle cloud. These particles are retained with the particle trap arranged downstream in accordance with the invention due to diffusion and adsorption processes and are continuously chemically converted. And chemically reacted continuously. This ensures continuous regeneration of the particle trap and prevents clogging of the flow paths inside the particle trap. This regeneration process is promoted in a surprisingly effective manner by the nitrogen dioxide previously produced by the oxidation catalyst. As a result, on the one hand effective conversion of the soot particles is ensured and, on the other hand, a pressure increase in the exhaust system due to plugged flow paths is avoided. The arrangement of all components in the vicinity of the motor, ie in particular not on the underbody of an automobile, is preferred. Thus, sufficiently high temperatures are ensured over the operating time of the internal combustion engine (also directly after a cold start), so that the currently applicable exhaust emission values ​​with regard to the individual,

p0012Furthermore, the particle trap is arranged directly downstream of the oxidation catalyst in the direction of flow, preferably with a spacing less than 50 mm, in particular even less than 20 mm. In such an embodiment of the exhaust system, it is particularly advantageous to accommodate the oxidation catalytic converter and the particle trap in a common housing. This permits a particularly space-saving arrangement of oxidation catalytic converter and particle traps, this being important in particular with regard to a motorized arrangement of the exhaust system.

p0013According to a further embodiment of the exhaust system, the exhaust gas system has a turbocharger, the catalytic converter being arranged upstream of the turbocharger and the oxidation catalytic converter being arranged downstream of the turbocharger. Charging is a method for increasing the performance of an internal combustion engine, which is used in particular in connection with diesel engines. During charging, the air required for the engine combustion process is compressed by a working machine so that a larger air mass flows into the cylinder or combustion chamber per working cycle of the internal combustion engine. For this purpose, the compressor is, for example, driven by a turbocharger which utilizes the exhaust gas energy. The coupling to the motor is not mechanical, but proceeds purely thermally, Whereby the principle of accumulating charge is mainly used in automobile construction. The arrangement of the catalytic converter upstream of such a turbocharger ensures a very rapid reaching of the operating temperature of the catalytic converter since in this way heat removal of the exhaust gas due to the contact with components of the turbocharger is avoided. In addition, the catalytic arrangement of the catalytic converter is ensured. In this case, it is particularly advantageous for the catalytic converter to be connected directly to the internal combustion engine and, in particular, to be arranged in an exhaust manifold. It is also possible to install a plurality of small converters in a separate exhaust gas line of an exhaust manifold, Which are preferably attached directly to / with the connection point of the exhaust manifold and internal combustion engine. Because of the proximity to the combustion chambers or the cylinders of the internal combustion engine, the thermal light-off behavior of the catalytic converter is clearly supported.

p0014According to yet another embodiment of the exhaust system, the oxidation catalytic converter has at least two zones wherein the zone furthest away from the internal combustion engine is designed with a higher specific heat capacity than the remaining ones of the at least two zones. The oxidation catalyst usually has a honeycomb structure, wherein partition walls form passages through which an exhaust gas can pass. The increase in the specific heat capacity (in particular of the surface-specific heat capacity) can be ensured, for example, by a thicker design of the partition walls. If, for example, the partition walls have a thickness of less than 0.03 mm in the upstream zone of the oxidation catalyst, the partition walls in a central zone have a thickness of approximately 0.03 to 0.06 mm, Wherein a downstream zone is formed, for example, with a thickness of the partition walls which is at least 0.08 mm. The number of zones as well as the thickness of the partition walls is to be aligned in particular with regard to the composition of the exhaust gas and its thermal energy. The specific heat capacity increasing in the direction of flow has the consequence that the oxidation catalytic converter reaches its operating temperature very early in upstream zones, whereby the catalytic reaction initiated there generates so much exothermic energy that the downstream zones are also rapidly heated up. The zone with the high heat capacity also represents a type of heat accumulator even after the combustion engine has been switched off,

p0015According to a further embodiment, the particle trap has a total volume (walls plus cavities) which is less than 75% of a displacement volume of the internal combustion engine, in particular less than 50% and preferably even less than 25%. In circumstances such as, for example, in the case of a motor arrangement and / or a very short-term, discontinuous regeneration of the particle traps, the total volume can also be further reduced, if necessary to a size less than 5% or 1% of the displacement volume of the internal combustion engine. The displacement volume is the sum of the volumes of the cylinders or combustion chambers of the internal combustion engine, in which the combustion of the fuel takes place.

p0016The particle trap thus has a very small overall volume, on the one hand a space-saving arrangement and, on the other hand, an effective chemical conversion of the particles is ensured. The particulate trap can in particular be so small as the oxidation catalyst arranged upstream produces as much nitrogen dioxide as to ensure a continuous regeneration of the particle trap and a large storage volume is not required for soot particles to be recycled.

p0017In this case, it is particularly advantageous that the particle trap has freely continuous channels in which swirling points and calming points and / or deflecting devices are arranged. As a result, the probability of reacting particles with nitric oxide is increased in a simple manner in which the residence time of particles (in particular soot) is extended in the particle trap. In the case of freely flowing flow paths, this takes place by means of a sufficient number of swirling and stabilizing points and / or by deflections which favor the deposition of the particles on the walls. While a particle flying with the exhaust stream has only a small chance of reacting with other exhaust gas components, these chances are drastically increased, When the particle is held in a swirling or settling position or deposited on a partition wall. All the nitrogen oxides that are still present are then suitable for a reaction and thus rapidly separate the particles. The particle trap can therefore not become clogged, but is constantly regenerated.

p0018According to a further embodiment, the catalytic converter has a converter volume which is at most half as large as a catalyst volume of the oxidation catalytic converter. The converter volume and the catalyst volume are respectively the outer volumes (walls plus channels) of the at least one converter or of the oxidation catalyst. Such a small design of the catalytic converter supports the light-off behavior as well as a space-saving arrangement.

p0019According to yet another embodiment of the exhaust system, at least one, preferably each component of the exhaust system has a honeycomb structure with ducts through which exhaust gas can flow, which is formed with at least partially structured sheet metal foils. The particle structure of the converter and / or of the oxidation catalyst has at least one channel density of 600 cpsi ("cells per square inch"), in particular greater than 1000 cpsi. The particle trap may need somewhat larger channel cross sections so that these have a channel density greater than 200 cpsi, in particular 400 cpsi or 600 cpsi, whereby always sufficient surface for the attachment of the particles is made available. If the oxidation catalytic converter is designed with a honeycomb structure comprising sheet metal foils,

p0020The exhaust system according to the invention will now be explained in detail with reference to the particularly preferred embodiments shown in the drawings. Show it:<dl id="dl0001"><dt>FIG</dt><dd>An embodiment of the exhaust system,</dd><dt>FIG</dt><dd>A plan view of a component of the exhaust system with a honeycomb structure,</dd><dt>FIG</dt><dd>2 shows an embodiment of the particle trap of the exhaust system in a schematic detail view, and FIG</dd><dt>FIG</dt><dd>5 shows a further embodiment of the exhaust system in a motoma arrangement.</dd></dl>

p0021<figref idrefs="f0001">FIG</figref> Shows schematically and perspectively an exhaust system 1 for the purification of an exhaust gas of a diesel engine. The exhaust gas system 1 flows in the flow direction 3 successively from the internal combustion engine 2 or the diesel engine through the exhaust system 1 with a preferred flow direction 3. The exhaust system 1 comprises in succession a catalytic converter 4, in particular for converting carbon monoxides and hydrocarbons contained in the exhaust gas, an oxidation catalytic converter 5 , In particular for the conversion of nitrogen monoxides contained in the exhaust gas, and a particle trap 6 for collecting particulates contained in the exhaust gas, in particular carbon black. Since the illustrated exhaust system 1 partially has a plurality of exhaust gas strands upstream of a turbocharger 7, the illustrated embodiment is equipped with two catalytic converters 4, Which are arranged very close to the internal combustion engine 2. In this case, it is also possible to arrange the catalytic converters 4 in the exhaust gas strands one or more exhaust manifolds 8 which is connected directly to the internal combustion engine 2. The illustrated oxidation catalytic converter 5 has a plurality of zones 9, the zones 9 in the flow direction 3 of the exhaust gas having an increasing specific heat capacity. With a distance 10 less than 50 mm, the particle trap 6 is arranged immediately downstream of the oxidation catalytic converter 5 in the flow direction 3. The particle trap 6 has a total volume 11, which is preferably less than 75% of a displacement volume 12 of the internal combustion engine 2. The displacement volume 12 corresponds to the sum of the individual volumes of the cylinders 21 of the internal combustion engine 2.

p0022The illustrated exhaust system 1 is preferably arranged in the direct vicinity of the internal combustion engine 2. In particular, one of the components 4, 5, 6 is to be arranged in the underbody of an automobile.

p0023<figref idrefs="f0002">FIG</figref> Shows a top view of a catalytic converter 4 or an oxidation catalytic converter 5 with a honeycomb structure 19. The honeycomb structure 19 has ducts 13 which can be passed through with an exhaust gas and which is formed with at least partially structured sheet metal films 20. For this purpose, smooth sheet metal foils 23 and structured sheet metal foils 20 were first stacked and subsequently twisted together, the honeycomb structure 19 being arranged in a jacket tube 22 for increasing the stability of the component. The honeycomb structure 19 is preferably designed with a catalytic coating, which is characterized, in particular, by a very rugged surface and consequently also by a high effectiveness with respect to the conversion of pollutants.

p0024<figref idrefs="f0002">FIG</figref> Shows schematically and perspectively a detailed view of a particle trap 6. The particle trap 6 is constructed from a structured sheet metal foil 20 and a smooth sheet metal foil 23 with openings 24 and forms free-flowing channels 13. Vane-like deflecting devices 16 with openings 25 lead to the effects as described above are. The deflection devices 16 have settling points 15 and swirling points 14, the deflection devices 16 swirling the exhaust gas so that the particles are longer in the particle trap 6 and thus can react more easily with other components of the exhaust gas. Depending on the exact configuration of the deflection devices 16, particles are also projected against the sheet metal foils 20 and 23 where they remain adherent.

p0025<figref idrefs="f0003">Fig. 4</figref> Shows schematically a further embodiment of the exhaust system 1 in motomaher 2 arrangement. The exhaust system 1 is for cleaning an exhaust gas of an internal combustion engine 2, in particular a diesel engine of an automobile, and flows through the exhaust gas in a flow direction 3. In the flow direction 3, the exhaust system 1 has at least one catalytic converter 4, in particular for converting carbon monoxide and hydrocarbons contained in the exhaust gas, an oxidation catalytic converter 5, in particular for the conversion of nitric oxide contained in the exhaust gas, and a particle trap 6 for collecting particulates contained in the exhaust gas . In the illustrated embodiment, the catalytic converters 4 are arranged particularly close to the combustion chambers of the engine, Specifically, a small catalytic converter 4 is arranged in each outlet of the combustion chambers in the exhaust manifold 28. Thus, the catalytic converters 4 are even arranged upstream of the turbocharger 7, which is designed in particular as an exhaust gas turbocharger, which serves to compress the fresh air (fresh air supply 27) supplied to the engine.

p0026In the illustrated exhaust system 1, the oxidation catalytic converter 5 and the particle trap 6 are arranged in a common housing 26. The particle trap 6 has a total volume 11 which is smaller than 75% of a displacement volume 12 of the internal combustion engine 2, in particular less than 50% and preferably even less than 25%. In order to ensure the highest possible temperatures for regenerating the particle trap 6 during the operation of the internal combustion engine 2 and the exhaust system 1, the particle trap 6 is arranged at a distance from the engine which is preferably less than 80 cm. The distance is preferably the path length of the exhaust gas until the particle trap 6 is reached.

p0027The exhaust system according to the invention ensures a very effective conversion of pollutants (in particular carbon monoxide, unsaturated hydrocarbons, nitrogen oxides, carbon black) contained in the exhaust gas of a diesel engine, with a particularly positive effect with regard to the regeneration of the particle trap. More specifically, the increased nitrogen dioxide production of the oxidation catalyst, because of the upstream catalytic converter, results in the particle trap providing a sufficient amount of nitrogen dioxide to ensure continuous regeneration. As a result, clogged ducts are prevented and the currently applicable exhaust gas limits are clearly below.

Reference list

p0028<dl id="dl0002"><dt>1</dt><dd>Exhaust system</dd><dt>2</dt><dd>Combustion engine</dd><dt>3</dt><dd>Flow direction</dd><dt>4</dt><dd>converter</dd><dt>5</dt><dd>Oxidation catalyst</dd><dt>6</dt><dd>Particle trap</dd><dt>7</dt><dd>turbocharger</dd><dt>8th</dt><dd>Exhaust manifold</dd><dt>9</dt><dd>Zone</dd><dt>10</dt><dd>distance</dd><dt>11</dt><dd>Total volume</dd><dt>12</dt><dd>Displacement volume</dd><dt>13</dt><dd>channel</dd><dt>14</dt><dd>Swirling point</dd><dt>15</dt><dd>Rehabilitation center</dd><dt>16</dt><dd>Deflection device</dd><dt>17</dt><dd>Converter volume</dd><dt>18</dt><dd>Catalyst volume</dd><dt>19</dt><dd>Honeycomb structure</dd><dt>20</dt><dd>Structured sheet metal foil</dd><dt>21</dt><dd>cylinder</dd><dt>22</dt><dd>Casing pipe</dd><dt>23</dt><dd>Smooth sheet metal foil</dd><dt>24</dt><dd>Breakthrough</dd><dt>25</dt><dd>opening</dd><dt>26</dt><dd>casing</dd><dt>27</dt><dd>Fresh air supply</dd><dt>28</dt><dd>Exhaust manifold</dd></dl>distance