Device and method for exhaust aftertreatment of an internal combustion engine

Abstract

Exhaust aftertreatment system for an internal combustion engine (10), comprising an exhaust system (40) with an exhaust channel (42) in which a first catalyst (50, 98) is arranged, downstream of the first catalyst (50, 98) a first exhaust aftertreatment component (52, 54) for the selective catalytic reduction of nitrogen oxides is arranged, and further downstream a second exhaust aftertreatment component (56, 58) for the selective catalytic reduction of nitrogen oxides is arranged, wherein downstream of the first exhaust aftertreatment component (52, 54) for the selective catalytic reduction of nitrogen oxides and upstream of the second exhaust aftertreatment component (56, 58) for the selective catalytic reduction of nitrogen oxides a low-temperature NOx storage catalyst (96) is arranged, characterized in that the exhaust system (40) has a first bypass channel (70) for the low-temperature NOx storage catalyst. (96) exhibitswherein a first exhaust flap (74) and a second exhaust flap (76) are arranged in the first bypass channel (70) downstream of a branch (66) of the bypass channel (70) from the exhaust channel (42) and upstream of the low-temperature NOx storage catalyst (96).

Description

[0001] The invention relates to an exhaust aftertreatment system for the exhaust aftertreatment of an internal combustion engine, in particular a diesel engine, and to a method for operating such an exhaust aftertreatment system.

[0002] Current and increasingly stringent emissions legislation places high demands on raw engine emissions and exhaust aftertreatment in combustion engines. The requirements for further reductions in fuel consumption and the tightening of emissions standards regarding permissible nitrogen oxide emissions pose a challenge for engine developers. In gasoline engines, exhaust gas purification is achieved in the familiar manner via a three-way catalytic converter, as well as additional catalysts upstream and downstream of the three-way converter. Diesel engines currently employ exhaust aftertreatment systems that include an oxidation catalyst, a catalyst for the selective catalytic reduction of nitrogen oxides (SCR catalyst), a particulate filter for the separation of soot particles, and, if necessary, further catalysts. Ammonia is preferably used as the reducing agent.Because handling pure ammonia is complex, vehicles typically use a synthetic, aqueous urea solution, which is mixed with the hot exhaust gas stream in a mixing unit upstream of the SCR catalyst. This mixing heats the aqueous urea solution, causing it to release ammonia into the exhaust system. A commercially available aqueous urea solution generally consists of 32.5% urea and 67.5% water.

[0003] Every catalytic exhaust gas purification system requires exceeding a minimum temperature, the so-called light-off temperature, to become effective. During a cold start of a vehicle, the combustion engine and the exhaust aftertreatment components are at approximately ambient temperature. Even with a high energy input into the exhaust system, the thermal inertia of the exhaust system must first be overcome and radiation and convection losses compensated for in order to achieve at least partial effectiveness of the exhaust aftertreatment components. During this time, the raw emissions from the combustion engine are emitted largely untreated. Depending on the energy input into the exhaust system, this period can be shortened, but it can never be reduced to zero.

[0004] In diesel engines, it is known to install a NOx storage catalyst upstream of an SCR exhaust aftertreatment system. This catalyst achieves good conversion performance even in the 120-200°C range, whereas the SCR catalyst itself only enables the conversion of nitrogen oxide emissions from approximately 180°C. The exhaust aftertreatment components can be individually or collectively supported by electric heating elements or thermal exhaust gas burners during their warm-up phase, particularly up to the respective light-off temperature.

[0005] From DE 10 2016 001 197 B3, an exhaust aftertreatment system for an internal combustion engine is known, in which the exhaust channel downstream of an exhaust outlet of the internal combustion engine and upstream of a turbine of an exhaust gas turbocharger branches into a first exhaust channel and a second exhaust channel, wherein the exhaust flow through the two exhaust channels can be controlled by means of exhaust flaps, and wherein a NOx storage catalyst is arranged in one of the exhaust channels. The NOx storage catalyst can be brought up to its operating temperature particularly quickly after a cold start in order to reduce NOx emissions during the cold start phase.

[0006] From DE 10 2017 214 572 A1, an internal combustion engine with an exhaust aftertreatment system is known, in which an oxidation catalyst, a low-temperature nitrogen oxide storage catalyst and a particulate filter with an SCR coating are arranged in the direction of flow of an exhaust gas through an exhaust system of the internal combustion engine.

[0007] Furthermore, US 2011 061 371 A1 discloses an internal combustion engine with an exhaust aftertreatment system comprising an exhaust system in which a NOx storage catalyst and an HC storage catalyst are arranged, wherein a fuel tank vent is connected to the exhaust duct, and wherein the unburned hydrocarbons from the tank vent are used to regenerate the NOx storage catalyst.

[0008] Furthermore, DE 10 2016 209 610 A1 discloses an exhaust aftertreatment system for a diesel engine, wherein an oxidation catalyst, a particulate filter, and a catalyst for the selective catalytic reduction of nitrogen oxides are arranged in the exhaust system of the diesel engine in the direction of flow. It is provided that the amount of reducing agent is adjusted accordingly, based on the metered amount of reducing agent and the NOx concentration in the exhaust channel downstream of the SCR catalyst, in order to keep ammonia slip as low as possible.

[0009] Furthermore, it is known from the prior art to arrange one or more exhaust aftertreatment components upstream of a turbine in an exhaust gas turbocharger in order to utilize the higher exhaust gas temperature upstream of the turbine for faster heating to the light-off temperature of this exhaust aftertreatment component. Insulation for reducing heat losses at the walls of the exhaust system is also known. All these devices require a certain time to activate. After a cold start of the combustion engine, the pollutant load in the exhaust gas can be high due to suboptimal combustion, and the exhaust aftertreatment is usually not operating within its optimal range, at least with regard to the temperature of the exhaust gas or the exhaust aftertreatment components.Thus, after a cold start of the combustion engine, at least some of the pollutants emitted by the combustion engine are released into the environment unconverted. During this period, a particularly polluting driving style can already lead to exceeding the permissible emission limits of an RDE (Real Driving Emissions) test, meaning that even with a subsequent 100% conversion rate, the entire driving cycle would have to be considered "failed." NOx emissions are particularly critical here, as they increase disproportionately with increasing driving dynamics.

[0010] The invention is based on the objective of further developing the exhaust system of the internal combustion engine in such a way that improved exhaust aftertreatment is possible and, in particular, nitrogen oxide tailpipe emissions can be reduced after a cold start of the internal combustion engine.

[0011] According to the invention, this problem is solved by an exhaust aftertreatment system for an internal combustion engine, comprising an exhaust system with an exhaust channel in which a first catalyst, a first exhaust aftertreatment component for the selective catalytic reduction of nitrogen oxides, and a second exhaust aftertreatment component for the selective catalytic reduction of nitrogen oxides are arranged. A low-temperature NOx storage catalyst is arranged downstream of the first exhaust aftertreatment component and upstream of the second exhaust aftertreatment component. In this context, a low-temperature NOx storage catalyst is understood to be a storage catalyst that exhibits a high NOx storage capacity in a temperature range of 40°C to 100°C, but emits the stored nitrogen oxides again unconverted at higher temperatures.Such a low-temperature NOx storage catalyst can therefore achieve a significant, albeit temporary, reduction in NOx emissions very soon after a cold start of the combustion engine. By combining it with a particulate filter with an SCR coating or an SCR catalyst, which is heated to its light-off temperature during the cold start phase and reaches this temperature before the nitrogen oxides are desorbed from the downstream low-temperature NOx storage catalyst, nitrogen oxide emissions during the cold start phase of the combustion engine can be significantly reduced.By positioning the low-temperature NOx storage catalyst downstream of the first exhaust aftertreatment component for the selective catalytic reduction of nitrogen oxides and upstream of the second exhaust aftertreatment component, the subsequent exhaust aftertreatment components can be heated to their operating temperature by the exhaust gas and, if necessary, additionally supported by heating elements, before the nitrogen oxides thermally desorb from the low-temperature NOx storage catalyst. This allows NOx tailpipe emissions to be minimized, particularly during the cold start phase of the combustion engine.

[0012] The features mentioned in the dependent claims enable advantageous further developments and non-trivial improvements to the exhaust aftertreatment system specified in the independent claim.

[0013] In a preferred embodiment of the invention, the exhaust system has a first bypass channel for the low-temperature NOx storage catalyst. In this way, the low-temperature NOx storage catalyst can be decoupled from the exhaust gas stream to prevent thermal desorption of the nitrogen oxides retained in the low-temperature NOx storage catalyst before the downstream second exhaust aftertreatment component has sufficient NOx conversion activity for the selective catalytic reduction of nitrogen oxides.

[0014] It is preferred that the first bypass channel branches off from the exhaust channel downstream of the first exhaust aftertreatment component for the selective catalytic reduction of nitrogen oxides, particularly downstream of a particulate filter with an SCR coating, and rejoins the exhaust channel of the combustion engine upstream of the second exhaust aftertreatment component for the selective catalytic reduction of nitrogen oxides, particularly upstream of an SCR catalyst in an underbody position of a motor vehicle. This allows the SCR catalysts to be used for nitrogen oxide reduction as soon as they reach their operating temperature. During this heating phase, it prevents stored NOx emissions from the low-temperature NOx storage catalyst from desorbing and thus being emitted before they can be converted by the SCR catalysts.

[0015] In a preferred embodiment of the exhaust aftertreatment system, a first exhaust flap is arranged in the exhaust channel downstream of a branch of the bypass channel from the exhaust channel and upstream of the low-temperature NOx storage catalyst, and a second exhaust flap is arranged in the bypass channel. This allows the exhaust gas flow from the combustion engine to be easily directed either through the exhaust channel and thus through the low-temperature NOx storage catalyst or through the bypass.

[0016] In a preferred embodiment of the invention, a heating element, preferably an electrically heated catalyst, is arranged downstream of the low-temperature NOx storage catalyst and upstream of the second exhaust aftertreatment component for the selective catalytic reduction of nitrogen oxides, in particular upstream of one or more SCR catalyst(s) arranged in the underbody of a motor vehicle. This downstream electrically heated catalyst comprises an electric heating element, preferably an electric heating disc. The heating element allows the exhaust aftertreatment components for the selective catalytic reduction of nitrogen oxides to be heated to their light-off temperature essentially independently of the exhaust gas flow from the combustion engine.In this context, "essentially independent of the exhaust gas flow" means that while the exhaust gas is used as a carrier flow for convective heat transfer from the heating element to the corresponding exhaust aftertreatment component, the energy used for heating originates primarily from the heating element and not, or only to a small extent, from the exhaust gas of the combustion engine. A carrier flow may be necessary to prevent localized overheating in an electric heating element, thus preventing it from shutting down or suffering thermal damage. In the case of a heating element in the form of an exhaust gas burner, the burner's exhaust gas itself constitutes the carrier flow.

[0017] It is particularly advantageous if the heating element is electrically heated, especially as an electric heating disc. An electric heating element eliminates the need for an additional exhaust burner, thus avoiding the associated costs. Furthermore, no additional fuel lines are required for the exhaust burner. An electric heating element can be connected using relatively simple electrical wiring. An electric heating element, in the form of a heating disc upstream of the particulate filter or an electrically heated filter substrate, can also support particulate filter regeneration, thereby reducing or shortening the need for engine heating to initiate the regeneration process.

[0018] Alternatively or additionally, it is advantageous for the heating element to be designed in the form of an exhaust gas burner. Since the exhaust gas burner itself generates a heat transfer current with its exhaust gas, a particularly simple and effective convective heat transfer to the relevant exhaust aftertreatment components, especially the SCR catalysts located under the vehicle's floor, is possible.

[0019] In a preferred embodiment of the invention, a second bypass channel is provided, which branches off from the exhaust gas channel downstream of the low-temperature NOx storage catalyst and re-enters the exhaust gas channel downstream of the second exhaust aftertreatment component for the selective catalytic reduction of nitrogen oxides. This second bypass allows at least a portion of the exhaust gas flow to bypass the further exhaust aftertreatment components for the selective catalytic reduction of nitrogen oxides. This is particularly advantageous when the exhaust gas is cold, as it eliminates the need for additional cooling of these exhaust aftertreatment components, making them easier to heat up using an electric heating element.Thus, at least one of the SCR catalysts located under the floor can be heated relatively quickly to its operating temperature for the selective catalytic reduction of nitrogen oxides, which can further improve the efficiency of the exhaust aftertreatment system, especially during the cold start phase of the combustion engine.

[0020] It is preferred that the second bypass is fluidically connected to the first bypass. This allows the exhaust gas from the first bypass to be routed into the second bypass, thereby creating additional possibilities for controlling the exhaust gas flow with regard to its distribution and routing. This enables the fastest possible heating of the exhaust aftertreatment components and thus maximizes the efficiency of the exhaust aftertreatment system.

[0021] In an advantageous embodiment of the exhaust aftertreatment system, a third exhaust flap is arranged in the exhaust channel downstream of the second branch and upstream of the electrically heated catalyst, and a fourth exhaust flap is arranged in the second bypass channel. These additional exhaust flaps allow for appropriate control and distribution of the exhaust flow to at least one of the bypass channels and the main exhaust channel. This provides additional degrees of freedom, which further improves the heating of the exhaust aftertreatment components.

[0022] In a further advantageous embodiment of the exhaust aftertreatment system, the first catalyst is designed as a NOx storage catalyst. A NOx storage catalyst can retain nitrogen oxides from approximately 90–100°C and therefore requires lower temperatures than an SCR catalyst. Thus, a NOx storage catalyst can be heated to its operating temperature in a comparatively short time. Furthermore, by arranging the NOx storage catalyst upstream of the exhaust aftertreatment component for the selective catalytic reduction of nitrogen oxides, and thus upstream of the low-temperature NOx storage catalyst, it heats up even faster than the low-temperature NOx storage catalyst.This ensures that the NOx storage catalyst has reached its operating temperature and can effectively retain nitrogen oxides before the low-temperature NOx storage catalyst reaches its upper limit temperature and the stored nitrogen oxides desorb.

[0023] Alternatively, it is advantageous for the first catalyst to include an oxidation catalyst. A first catalyst containing at least one oxidation catalyst enables the exothermic conversion of unburned fuel components. This exothermic conversion supports the heating of the SCR coating on the particulate filter or the SCR catalyst, allowing the SCR catalyst to reach its light-off temperature before the low-temperature NOx storage catalyst reaches its upper temperature limit and the stored nitrogen oxides desorb. This ensures that at least one of the NOx-reducing exhaust aftertreatment components has reached its operating temperature at all times, effectively reducing nitrogen oxide emissions.To increase the conversion efficiency for HC and CO and to accelerate the heating of the downstream first exhaust aftertreatment component for the selective catalytic reduction of nitrogen oxides, at least one oxidation catalyst can be fitted with a heating element upstream or downstream. This heating element is preferably designed as an electrically heated element, in particular as an electric heating disc.

[0024] In a preferred embodiment of the invention, the first exhaust aftertreatment component for the selective catalytic reduction of nitrogen oxides is an SCR catalyst or a particulate filter with an SCR coating. A particulate filter with an SCR coating combines the functionality of a particulate filter with that of an SCR catalyst. This may eliminate the need for an additional close-coupled SCR catalyst, reducing the cost of the exhaust aftertreatment system and simplifying assembly. Furthermore, an additional SCR catalyst with an exhaust gas flow length of less than 50 mm can be installed upstream or downstream of the particulate filter with the SCR coating to increase the overall NOx conversion capacity of the first exhaust aftertreatment component for the selective catalytic reduction of nitrogen oxides.

[0025] To increase the operating range in which at least one of the SCR catalysts operates within the required temperature range by using different positions in the exhaust system, the first exhaust aftertreatment component for the selective catalytic reduction of nitrogen oxides is preferably designed as a particulate filter with an SCR coating, preferably as a particulate filter with an SCR coating located close to the engine. Furthermore, the second exhaust aftertreatment component for the selective catalytic reduction of nitrogen oxides is designed as the SCR catalyst, which is preferably located in an underbody position of the vehicle farther from the engine. In this context, a position close to the engine is understood to mean a position in the exhaust system with an exhaust gas flow length of less than 80 cm from at least one exhaust valve of the internal combustion engine.A position far from the engine is defined by an exhaust gas flow length of at least 30 cm between the exit of the first exhaust aftertreatment component for the selective catalytic reduction of nitrogen oxides and the entry into the second exhaust aftertreatment component for the selective catalytic reduction of nitrogen oxides.

[0026] According to the invention, a method for the exhaust aftertreatment of an internal combustion engine with an exhaust aftertreatment system according to the invention is proposed, which comprises the following steps: - Cold start of the internal combustion engine, wherein an exhaust gas flow from the internal combustion engine is passed through the first exhaust aftertreatment component and the low-temperature NOx storage catalyst, wherein - the nitrogen oxide emissions from the combustion engine, which are not converted or stored in the upstream exhaust aftertreatment components, are stored in the low-temperature NOx storage catalyst, and wherein - a rear electrically heated catalyst is located downstream of the low-temperature NOx storage catalyst.

[0027] A method according to the invention can minimize nitrogen oxide emissions from the combustion engine during the cold start phase. In this process, at least one of the further exhaust aftertreatment components is heated to its operating temperature for the selective catalytic reduction of nitrogen oxides before thermal desorption of the nitrogen oxides retained in the low-temperature NOx storage catalyst takes place.

[0028] In a preferred embodiment of the method, a heating element of the rear electrically heated catalyst remains activated after a cold start of the combustion engine until at least one other exhaust aftertreatment component for the selective catalytic reduction of nitrogen oxides has reached its light-off temperature. This reduces the heating time of the SCR catalysts located under the vehicle floor to their operating temperature. Once the SCR catalysts have reached a predetermined temperature level, the heating power of the electrically heated catalyst can be reduced or deactivated to increase its service life and save energy.

[0029] An improved version of the process involves directing a first partial exhaust gas flow through the rear electrically heated catalyst and the second exhaust aftertreatment component for the selective catalytic reduction of nitrogen oxides immediately after a cold start of the combustion engine. A second partial flow is routed through the second bypass channel. This allows for faster heating of the SCR catalysts located under the vehicle floor, as not the entire, still-cold exhaust gas flow passes through them. This limits the exhaust gas mass flow that needs to be heated by the rear electric heating element, resulting in faster heating of the SCR catalysts located under the vehicle floor.

[0030] In a further improvement of the process, it is provided that the second bypass channel is closed, preferably completely closed, once a threshold temperature for the exhaust gas and / or the further exhaust aftertreatment component for the selective catalytic reduction of nitrogen oxides is reached. If the SCR catalysts have reached a threshold temperature, preferably a temperature of approximately 300°C, complete conversion of the nitrogen oxide emissions by the exhaust aftertreatment component for the selective catalytic reduction of nitrogen oxides can be achieved. In this case, it is advantageous to close the second bypass channel to reduce the slip of unconverted nitrogen oxides and, if applicable, other pollutants such as ammonia.

[0031] In an advantageous embodiment of the method, the first bypass for the low-temperature NOx storage catalyst is closed when the low-temperature NOx storage catalyst is at least 80%, preferably at least 95%, discharged. If the low-temperature NOx storage catalyst is essentially empty, no further nitrogen oxides are stored at higher exhaust gas temperatures, as these would immediately desorb. To prevent leakage of nitrogen oxide emissions, it is advantageous to also close the second bypass channel in this operating state.Thus, in this operating state, the exhaust aftertreatment system functions like a known exhaust aftertreatment system with dual dosing, wherein at least upstream of the particulate filter with SCR coating and preferably additionally upstream of the underfloor SCR catalysts, a dosing module is provided, with which a reducing agent for the selective catalytic reduction of nitrogen oxides can be introduced into the exhaust channel.

[0032] Unless otherwise stated in individual cases, the various embodiments of the invention mentioned in this application can be advantageously combined with one another.

[0033] The invention is explained below in exemplary embodiments with reference to the accompanying drawings. Identical components or components with the same function are identified by the same reference numerals. The drawings show: Figs.1 an internal combustion engine with an air supply system and an exhaust system with an exhaust aftertreatment system according to the invention; Figs. 2 a schematic representation of an exhaust aftertreatment system according to the invention for an internal combustion engine; Figs. 3 the exhaust aftertreatment system according to the invention in a first operating position immediately after a cold start of the internal combustion engine; Figs. 4 the exhaust aftertreatment system according to the invention in a second operating position in which the low-temperature NOx storage catalyst is discharged; and Figs. 5 the exhaust aftertreatment system according to the invention in a third operating position in which the exhaust aftertreatment system is heated through and a conversion of the nitrogen oxide emissions takes place by the SCR catalysts.

[0034] Figs. Figure 1 shows a schematic representation of an internal combustion engine. 10with an air supply system 20 and an exhaust system 40 The internal combustion engine 10 In this embodiment, it is a direct-injection diesel engine and has several combustion chambers. 12 on. At the combustion chambers 12 Each is a fuel injector. 14 for injecting fuel into the respective combustion chamber 12 arranged. The internal combustion engine 10 is with its admission 16 with an air supply system 20 and with its outlet 18 with an exhaust system 40 connected. The internal combustion engine 10 It also includes a high-pressure exhaust gas recirculation system with a high-pressure exhaust gas recirculation valve, through which exhaust gas from the internal combustion engine is recirculated. 10 from the outlet 18 to the entrance 16 can be traced back. At the combustion chambers 12Inlet valves and outlet valves are arranged, with which a fluidic connection to the air supply system is established. 20 to the combustion chambers 12 or from the combustion chambers 12 to the exhaust system 40 can be opened or closed.

[0035] The air supply system 20 includes an intake duct 28 , in which, in the direction of flow of fresh air through the intake duct 28 an air filter 22 , downstream of the air filter 22 an air mass meter 24 , in particular a hot-film air mass meter, downstream of the air mass meter 24 a compressor 26 an exhaust gas turbocharger 36 , downstream of the compressor 26 a throttle valve 30 and further downstream an intercooler 32 are arranged. The air mass meter can be used in this process. 24 also in a filter housing of the air filter 22be arranged so that the air filter 22 and the air mass meter 24 forms an assembly. Downstream of the air filter. 22 and upstream of the compressor 26 is a junction 34 provided for, to which an exhaust gas recirculation line 86 a low-pressure exhaust gas recirculation 80 into the intake manifold 28 leads to.

[0036] The exhaust system 40 includes an exhaust duct 42 , in which in the direction of flow of an exhaust gas from the internal combustion engine 10 through the first exhaust duct 42 a turbine 44 the exhaust gas turbocharger 36 is arranged, which the compressor 26 in the air supply system 20 driven by a shaft. The exhaust gas turbocharger 36 is preferably used as an exhaust gas turbocharger 36 designed with variable turbine geometry. This involves a turbine wheel of the turbine. 44Adjustable guide vanes are installed upstream, which direct the flow of exhaust gas onto the turbine blades. 44 can be varied. Downstream of the turbine 44 are several exhaust aftertreatment components 46 , 50 , 52 , 54 , 56 , 58 , 60 , 64 , 96 , 98 This is planned to take place immediately downstream of the turbine. 44 The first component of the exhaust aftertreatment system is a NOx storage catalyst. 98 arranged. The NOx storage catalyst 98 can a heating element 46 It can be in the form of a front electric heating element, either upstream or downstream of the NOx storage catalyst. 98 is a particulate filter 52 with a coating 54 Arranged for the selective catalytic reduction of nitrogen oxides. Downstream of the particulate filter. 52is a low-temperature NOx storage catalyst 96 in the exhaust duct 42 arranged downstream of the low-temperature NOx storage catalyst 96 are preferably located in the underbody of a motor vehicle, at least one additional SCR catalyst 56 , preferably two additional SCR catalysts 56 , 58 planned. The SCR catalyst 56 is a rear electrically heated catalytic converter 64 installed upstream to prevent heating of the SCR catalyst 56 , 58 essentially independent of the exhaust flow of the combustion engine 10 to enable this. Downstream of the last SCR catalyst 58 is an ammonia barrier catalyst 60 planned. Downstream of the NOx storage catalyst 98 and upstream of the particulate filter 52 with the SCR coating 54 is a first dosing module 38 for dosing a reducing agent92 into the exhaust duct 42 Provided. Downstream of the particulate filter 52 branches off an exhaust gas recirculation line 86 at a branch from the exhaust duct 42 downstream of the low-temperature NOx storage catalyst. 96 and upstream of the SCR catalyst 56 , 58 Another dosing module is located in the subfloor. 62 arranged to use reducing agents 92 to be metered into the exhaust manifold. Furthermore, a bypass channel is required. 70 provided for, with which the exhaust gas of the combustion engine 10 on the low-temperature NOx storage catalyst 96 can be routed around it. Furthermore, a second bypass channel is available. 72 provided for, with which the exhaust gas at the SCR catalysts 56 , 58 and the ammonia barrier catalyst 60 can be routed along the underbody. Furthermore, the exhaust system includes 40 a plurality of exhaust flaps74 , 76 , 78 , 88 , with which the exhaust gas of the combustion engine 10 into one of the bypass channels 70 , 72 or into the exhaust gas recirculation channel 86 the low-pressure exhaust gas recirculation 80 can be directed.

[0037] Alternatively or additionally to the NOx storage catalyst 98 It can also include at least one oxidation catalyst. 50 can be used. Furthermore, instead of the particulate filter, they can be used. 52 with the SCR coating 54 an SCR catalyst 56 and an uncoated particle filter 52 or a particulate filter 52 with a catalytically effective coating or a particle filter 52 provided with SCR coating.

[0038] Exhaust gas recirculation 80 includes, in addition to the exhaust gas recirculation line 86 an exhaust gas recirculation cooler 82and an exhaust gas recirculation valve 84 , via which the exhaust gas recirculation is carried out through the exhaust gas recirculation line 86 It is controllable. At the exhaust gas recirculation line. 86 exhaust gas recirculation 80 is a temperature sensor 48 provided for, via which an exhaust gas temperature in the exhaust gas recirculation 80 can be determined to control exhaust gas recirculation 80 to activate as soon as the exhaust gas temperature in the exhaust gas recirculation 80 has exceeded a defined threshold. This prevents water vapor or reducing agent contained in the exhaust gas for the selective catalytic reduction of nitrogen oxides, in particular liquid urea solution, from condensing out and being recirculated in the exhaust gas. 80 or in the air supply system 20 leading to damage or deposits. Downstream of the branch and upstream of the exhaust gas recirculation cooler. 82Can a filter be provided to prevent particles from entering the exhaust gas recirculation system? 80 to minimize. The exhaust gas recirculation channel 86 flows into a junction 34 into the intake manifold 28 of the air supply system.

[0039] In the exhaust system 40 is a temperature sensor 48 provided for, with which an exhaust gas temperature in the exhaust system 40 can be monitored to ensure effective and efficient exhaust aftertreatment of the combustion engine's exhaust gas. 10 to enable this. Furthermore, differential pressure sensors 99 designed to create a pressure difference across the particle filter 52 to determine. In this way, the loading status of the particulate filter can be determined. 52 The system determines when a defined loading level is exceeded and initiates a regeneration of the particulate filter. 52 be initiated.

[0040] The internal combustion engine 10is equipped with an engine control unit 90 connected via signal lines (not shown) to the pressure and temperature sensors 48 , 99 as well as with the fuel injectors 14 of the internal combustion engine 10 and the dosing elements 38 , 62 is connected.

[0041] In Figs. Figure 2 is a schematic representation of the exhaust system. 40 an internal combustion engine 10 shown with an exhaust aftertreatment system according to the invention. In the exhaust duct 42 The exhaust system includes a front electrically heated catalytic converter in position I near the engine, in the direction of exhaust gas flow through the exhaust system. 46 , downstream of the first electrically heated catalyst 46 a NOx storage catalyst 98 or an oxidation catalyst 50 and further downstream a particulate filter 52 with a coating 54arranged for the selective, catalytic reduction of nitrogen oxides. In this context, a position close to the engine is defined as one with an exhaust gas flow length of less than 80 cm from an exhaust outlet of the combustion engine. 10 to understand. In this context, an inlet-side end face of the oxidation catalyst exhibits 50 or the NOx storage catalyst 98 an exhaust gas flow length of less than 60 cm, preferably less than 45 cm, particularly preferably less than 30 cm from the exhaust valves of the internal combustion engine 10 on. The oxidation catalyst 50 or the NOx storage catalyst 98 has a catalyst volume of preferably 1.0 to 3.5 dm³ 3 preferably from 1.3 to 2.5 dm 3 , especially preferably from 1.5 to 2.2 dm 3 Alternatively to an oxidation catalyst 50 or a NOx storage catalyst 98A three-way catalytic converter or an open particulate filter with a precious metal coating may also be used. This first catalytic converter 50 , 98 is an exhaust aftertreatment component for the selective catalytic reduction of nitrogen oxides, in particular a particulate filter 52 with an SCR coating 54 , downstream. The average exhaust gas flow length between the outlet face of the first catalyst. 50 , 98 and the inlet face of the particle filter 52 The exhaust gas flow length is less than 40 cm, preferably less than 30 cm, and in particular less than 20 cm. The particulate filter 52 with the SCR coating, it has a volume of preferably 2.5 to 5.5 dm³ 3 , especially preferably from 2.8 to 4.2 dm 3 , especially from 3.0 to 4.0 dm 3 on. Between the first catalyst 50 , 98and the first exhaust aftertreatment component 52 A first dosing module is needed for the selective, catalytic reduction of nitrogen oxides. 38 arranged, with which a reducing agent 92 , in particular aqueous urea solution, into the exhaust duct 42 of the internal combustion engine 10 It can be dosed in. The spray preparation of the reducing agent. 92 can be supported in a known manner by an exhaust gas mixer (not shown).

[0042] The first exhaust aftertreatment component 52 A low-temperature NOx storage catalyst is used for the selective catalytic reduction of nitrogen oxides. 96 downstream, which exhibits high NOx storage efficiency, particularly in a temperature range up to 150°C. The dimensioning of the low-temperature NOx storage catalyst 96It should be selected such that it has a NOx storage capacity of 0.9 g to 3.0 g NOx with a storage efficiency of more than 90% at an exhaust gas temperature of 70° to 100°C and a space velocity of less than 200,000 dm 3 / h. Taking into account the installation space typically available in passenger cars, a volume requirement for the low-temperature NOx storage catalyst is calculated. 96 from 1.0 to 5.0 dm 3 preferably from 1.5 to 3.0 dm 3 , especially from 1.9 to 2.5 dm 3 To ensure rapid desorption of the NOx in the low-temperature storage catalyst 96 To exclude retained nitrogen oxides, the low-temperature NOx storage catalyst is used. 96 spaced away from the first exhaust aftertreatment component 52 for the selective catalytic reduction of nitrogen oxides and preferably in an underfloor position IIarranged in a motor vehicle. The mean exhaust gas flow length from the outlet face of the first SCR exhaust aftertreatment component. 52 up to the inlet face of the low-temperature NOx storage catalyst 96 preferably at least 40 cm, preferably at least 55 cm, particularly preferably at least 70 cm.

[0043] The low-temperature NOx storage catalyst 96 Also located under the floor of a motor vehicle is a rear electrically heated catalytic converter. 64 or an exhaust gas burner connected downstream.

[0044] Downstream of the rear electrically heated catalyst 64 or of the burner are preferably a first SCR catalyst 56 and another SCR catalyst 58 arranged. Through the two SCR catalysts 56 , 58 Firstly, the axial heat conduction between the two SCR catalysts should be reduced. 56 , 58can be reduced. Secondly, the two SCR catalysts can 56 , 58 exhibit different coatings, carrier materials and channel geometries.

[0045] Downstream of the last SCR catalyst 58 is an ammonia barrier catalyst 60 , which can effectively reduce any ammonia slip that may be present through the exhaust aftertreatment system by oxidizing the ammonia.

[0046] Between the low-temperature NOx storage catalyst 96 and the SCR catalyst 56 A second dosing module is preferably used. 62 for the introduction of reducing agents 92 , in particular aqueous urea solution, into the exhaust duct 42 This is also planned for this dosing module. 62 Can the mixing of the reducing agent 92The exhaust gas is processed by an exhaust gas mixer. This exhaust gas mixer can be located upstream or downstream of the rear electrically heated catalytic converter. 64 be arranged. The volume of the second exhaust aftertreatment component 56 , 58 For the selective catalytic reduction of nitrogen oxides, the value is preferably in the range of 2.0 to 8.0 dm³. 3 , particularly preferably in the range of 2.5 to 5.0 dm 3 , especially in the range of 3.0 to 4.5 dm 3 Provided there is more than one SCR catalyst 56 The first SCR catalyst should be used. 56 a volume of 0.8 to 2.0 dm³ 3 , preferably from 1.0 to 1.5 dm 3 exhibit.

[0047] To ensure rapid heating of the second exhaust aftertreatment component 56 , 58 To enable the selective, catalytic reduction of nitrogen oxides, a second bypass channel is used. 72to the second exhaust aftertreatment component 56 , 58 as well as the upstream rear electrically heated catalytic converter 64 laid. The second bypass channel 72 preferably flows downstream of the ammonia barrier catalyst. 60 back into the exhaust duct 42 , but alternatively it can also be located downstream of the first SCR catalyst 56 or downstream of the second SCR catalyst 58 back into the exhaust duct 42 flow into each other.

[0048] For maximum efficiency in the thermal desorption of the low-temperature NOx storage catalyst 96 and to ensure sufficient subsequent conversion of the nitrogen oxides released in the process, it is advisable to use the low-temperature NOx storage catalyst. 96 a first bypass channel 70 to lay the first bypass channel. 70 at a first fork 66from the exhaust duct 42 off. The second bypass channel branches off at a second junction. 68 from the exhaust duct 42 from and joins at a junction 94 back into these. The first bypass channel can then be accessed. 70 and the second bypass channel 72 as in Figs. 2 shown to be fluidically connected to each other, so that the low-temperature NOx storage catalyst 96 exhaust gas also bypasses the SCR catalysts 56 , 58 can be routed in a subfloor position.

[0049] In the exhaust duct 42 is downstream of the first branch 66 and upstream of the low-temperature NOx storage catalyst 96 a first exhaust flap 74 arranged. Furthermore, in the first bypass channel 70 a second exhaust flap 76 arranged. In the exhaust duct 42 is downstream of the second branch 68and upstream of the electrically heated catalyst 64 a third exhaust flap 78 planned. In the second bypass channel 72 is a fourth exhaust flap 88 planned.

[0050] The operating strategy of the exhaust aftertreatment system is divided into three phases. The first phase, which occurs immediately after the cold start of the combustion engine, is... 10 This occurs, in Figs. Figure 3 shows this. After the combustion engine starts, 10 the first catalyst 50 , 98 , the particulate filter 52 with the SCR coating and the low-temperature NOx storage catalyst 96 from the exhaust gas of the combustion engine 10 through which the exhaust gas from the combustion engine flows. 10 downstream of the low-temperature NOx storage catalyst 96 virtually free of nitrogen oxides. The rear electrically heated catalytic converter 64In the underbody position, the optional front electrically heated catalytic converter is activated. 46 in a position close to the engine I can be additionally activated. The bypass channel 72 around the SCR catalysts 56 , 58 in underfloor position II It is switched in such a way that only a partial flow of the exhaust gas from the combustion engine is used. 10 through the SCR catalysts 56 , 58 in underfloor position II flows, while another partial flow passes through the second bypass channel 72 is routed. The exhaust gas flow is expediently routed through the SCR catalysts. 56 , 58 The flow rate is set to 10–150 kg / h, particularly 20–100 kg / h, and most preferably 30–80 kg / h. This is intended to ensure faster heating of the SCR catalysts. 56 , 58 in underfloor position II This can be achieved because not the entire, still cold, exhaust gas mass flow needs to be heated.

[0051] In Figs. Figure 4 shows a second phase of the exhaust aftertreatment process for an internal combustion engine. After ensuring sufficient conversion capacity by the SCR catalysts. 56 , 58 in the subfloor II as a result of sufficient heating and conversion performance of the exhaust aftertreatment component located near the engine 52 , 54 The bypass channel is used for the selective, catalytic reduction of nitrogen oxides. 70 around the low-temperature NOx storage catalyst 96 switched in such a way that the low-temperature NOx storage catalyst 96 and the SCR catalysts 56 , 58 in underfloor position IIOnly a partial exhaust gas flow is used. This partial exhaust gas flow is preferably adjusted to 10–150 kg / h, particularly to 20–100 kg / h, and most preferably to 30–80 kg / h, provided that the temperature in the SCR catalysts is still within the light-off temperature range of 160°C to 230°C. Above this temperature range of the SCR catalysts 56 , 58 The exhaust gas partial flow can be increased. This occurs above a certain temperature of the SCR catalysts. 56 , 58 The SCR catalysts are exposed to temperatures of 250°C, preferably 300°C. 56 , 58 with the full exhaust gas flow advantageous, so that above this temperature the bypass channels 70 , 72 be sealed. The rear electrically heated catalytic converter 64 in underfloor position II This only occurs at very low exhaust gas or substrate temperatures of the SCR catalysts. 56 , 58for example, < 200°C to keep the SCR catalysts warm 56 , 58 activated.

[0052] In a third operating phase, which is also referred to as normal operation, the entire exhaust system 40 sufficiently warmed up so that the bypass channels 70 , 72 at least largely sealed off. In this operating state, the exhaust aftertreatment system corresponds to a twin-dosing system with a particulate filter located close to the engine. 52 with SCR coating 54 and at least one SCR catalyst 56 , 58 in underfloor position, each containing a dosing module 38 , 62 is assigned. Such normal operation is in Figs. 5 shown. Reference symbol list 10 Internal combustion engine 12 Combustion chamber 14 Fuel injector 16 Admission 18 Outlet 20 Air supply system 22 air filters 24 air mass meters 26 compressors 28 Intake manifold 30 Throttle valve 32 Intercoolers 34 Junction 36 exhaust gas turbochargers 38 Dosing module 40 Exhaust system 42 Exhaust duct 44 Turbine 46 front electrically heated catalytic converter 48 Temperature sensor 50 Oxidation catalyst 52 particle filters 54 SCR coating 56 SCR catalyst 58 SCR catalyst 60 Ammonia barrier catalyst 62 second dosing module 64 rear electrically heated catalytic converter 66 first branch 68 second branch 70 first bypass channel 72 second bypass channel 74 first exhaust flap 76 second exhaust flap 78 third exhaust flap 80 Low-pressure exhaust gas recirculation 82 Exhaust gas recirculation coolers 84 Exhaust gas recirculation valve 86 Exhaust gas recirculation line 88 fourth exhaust flap 90 Control unit 92 Reducing agents 94 Junction 96 Low-temperature NOx storage catalyst 98 NOx storage catalyst 99 Differential pressure sensor QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 102016001197 B3

[0005] DE 102017214572 A1

[0006] US 2011061371 A1

[0007] DE 102016209610 A1

[0008]

Claims

[1] Exhaust aftertreatment system for an internal combustion engine (10), comprising an exhaust system (40) with an exhaust channel (42) in which a first catalyst (50, 98) is arranged, downstream of the first catalyst (50, 98) a first exhaust aftertreatment component (52, 54) for the selective catalytic reduction of nitrogen oxides is arranged and further downstream a second exhaust aftertreatment component (56, 58) for the selective catalytic reduction of nitrogen oxides is arranged, characterized by , that a low-temperature NOx storage catalyst (96) is arranged downstream of the first exhaust aftertreatment component (52, 54) for the selective catalytic reduction of nitrogen oxides and upstream of the second exhaust aftertreatment component (56, 58) for the selective catalytic reduction of nitrogen oxides. [2] Exhaust aftertreatment system according to claim 1, characterized by, that the exhaust system (40) has a first bypass channel (70) for the low-temperature NOx storage catalyst (96). [3] Exhaust aftertreatment system according to claim 2, characterized by , that the first bypass channel (70) branches off downstream of the first exhaust aftertreatment component (52, 54) for the selective catalytic reduction of nitrogen oxides from the exhaust channel (42) and flows back into the exhaust channel (42) of the combustion engine (10) upstream of the second exhaust aftertreatment component (56, 58). [4] Exhaust aftertreatment system according to one of claims 2 or 3, characterized by , that in the exhaust channel (42) downstream of a branch (66) of the bypass channel (70) from the exhaust channel (42) and upstream of the low temperature NOx storage catalyst (96) a first exhaust flap (74) and in the first bypass channel (70) a second exhaust flap (76) are arranged. [5] Exhaust aftertreatment system according to any one of claims 1 to 4, characterized by, that downstream of the low-temperature NOx storage catalyst (96) and upstream of the second exhaust aftertreatment component (56, 58) a rear electrically heated catalyst (64) is arranged for the selective catalytic reduction of nitrogen oxides. [6] Exhaust aftertreatment system according to any one of claims 1 to 5, characterized by , that a second bypass channel (72) is provided, which branches off from the exhaust channel (42) downstream of the low-temperature NOx storage catalyst (96) and re-enters the exhaust channel (42) downstream of the second exhaust aftertreatment component (56, 58) for the selective catalytic reduction of nitrogen oxides. [7] Exhaust aftertreatment system according to claim 6, characterized by , that the second bypass channel (72) is fluidically connected to the first bypass channel (70). [8] Exhaust aftertreatment system according to claims 5 to 7, characterized by, that in the exhaust channel (42) downstream of the second branch (68) and upstream of the electrically heated catalyst (64) a third exhaust flap (78) and in the second bypass (72) a fourth exhaust flap (88) are arranged. [9] Exhaust aftertreatment system according to any one of claims 1 to 6, characterized by , that the first catalyst (50, 98) is designed as a NOx storage catalyst (98) or at least includes an oxidation catalyst (50). [10] Exhaust aftertreatment system according to any one of claims 1 to 7, characterized by , that the exhaust aftertreatment components (52, 54, 56, 58) for the selective catalytic reduction of nitrogen oxides are an SCR catalyst (56, 58) or a particulate filter (52) with an SCR coating (54). [11] Method for exhaust aftertreatment of an internal combustion engine (10) with an exhaust aftertreatment system according to any one of claims 1 to 10, comprising the following steps: - Cold start of the internal combustion engine (10), wherein an exhaust gas flow from the internal combustion engine (10) is passed through the first exhaust aftertreatment component (52, 54) and the low-temperature NOx storage catalyst (96), wherein - the nitrogen oxide emissions from the combustion engine (10) that are not converted or stored in the upstream exhaust aftertreatment components (50, 98, 52, 54) are stored in the low-temperature NOx storage catalyst (96), and wherein - a rear electrically heated catalyst (64) is electrically heated downstream of the low temperature NOx storage catalyst (96). [12] Method according to claim 11, characterized by, that a heating element of the rear electrically heated catalyst (64) remains activated after the cold start of the combustion engine (10) until at least one further exhaust aftertreatment component (56, 58) for the selective catalytic reduction of nitrogen oxides has reached a predetermined temperature level. [13] Method according to claim 11 or 12, characterized by , that immediately after a cold start of the combustion engine (10) a first partial flow of the exhaust gas stream is directed via the rear electrically heated catalyst (64) and the further exhaust aftertreatment component (56, 58) for the selective catalytic reduction of nitrogen oxides and a second partial flow is directed via the second bypass channel (72). [14] Method according to any one of claims 11 to 13, characterized by, that the second bypass channel (72) is closed from the point at which a threshold temperature is reached for the exhaust gas or the further exhaust gas aftertreatment component (56, 58) for the selective, catalytic reduction of nitrogen oxides. [15] Method according to any one of claims 11 to 14, characterized by , that the first bypass (70) for the low temperature NOx storage catalyst (96) is closed when the low temperature NOx storage catalyst (96) is discharged to at least 80%.

Images