Method for operating an exhaust gas aftertreatment device

Abstract

A method for operating an exhaust gas aftertreatment device (6) for cleaning an exhaust gas flow of an internal combustion engine (4) of a motor vehicle (2), wherein the exhaust gas aftertreatment device (6) has at least one catalytic converter, wherein at least one thermoelectric generator (18) is associated with the catalytic converter, wherein the thermoelectric generator (18) is connected to the catalytic converter in a heat-energy-transferring manner, wherein at least one thermoelectric heating element (20) is associated with the catalytic converter, wherein the thermoelectric heating element (20) is connected to the catalytic converter in a heat-energy-transferring manner, and wherein the thermoelectric heating element (20) is a heating resistor, comprising the steps of: comparing a value (W1) representative of a catalytic converter temperature with a limit value (G2), generating electrical energy with the thermoelectric generator (18) if the value (W1) representative of a catalytic converter temperature is greater than the limit value (G2),Determining a value (W2) representative of an active internal combustion engine (4), Applying electrical energy to the thermoelectric heating element (20) if the value (W2) is representative of an active internal combustion engine (4).

Description

[0001] The invention relates to a method for operating an exhaust gas aftertreatment device for cleaning an exhaust gas flow of an internal combustion engine of a motor vehicle.

[0002] Exhaust gas aftertreatment devices are used to clean combustion gases mechanically, catalytically or chemically after they have left the combustion chamber of an internal combustion engine that powers the motor vehicle in order to comply with legal pollutant limits.

[0003] In order to achieve strict emission conditions, such exhaust aftertreatment devices have several different catalysts, which can be located close to the engine and / or in the vehicle underbody, more remote from the engine.

[0004] Virtually all catalysts have an optimal temperature range in which the efficiency of the respective catalysts is optimal.

[0005] However, each catalyst has a different, better operating temperature window. Overlapping these operating temperature windows, for example, with a catalyst of the same design mounted close to the engine and a catalyst mounted remote from the engine, provides a broader operating temperature window.

[0006] However, it is practically impossible to maintain optimal operating temperature conditions for all catalysts and at the same time achieve high efficiency in removing emissions at different temperatures that occur under different driving conditions, such as cold start, city and highway driving or other engine operating conditions.

[0007] Different operating conditions can lead to different temperatures, which can result in suboptimal operating conditions and higher emissions, unexpectedly higher emissions from the internal combustion engine and / or catalysts that cannot be treated with further downstream catalysts, by-products as secondary emission formation, and can also lead to deactivation of the catalysts through chemical and structural changes.

[0008] Without long-lasting catalysts with a wide operating temperature range, highly efficient catalysts at low and very high temperatures, and effective thermal management, undesirable events such as higher tailpipe emissions or secondary emission products are more likely to occur. Furthermore, the service life of the exhaust aftertreatment device may be shortened.

[0009] From US 6,985,247 B1, an exhaust gas aftertreatment device for cleaning an exhaust gas flow of an internal combustion engine of a motor vehicle with a catalyst and a thermoelectric generator associated with the catalyst is known.

[0010] The object of the invention is therefore to demonstrate ways to avoid unexpectedly higher emissions when shutting down and starting the internal combustion engine. Furthermore, emissions should also be reduced when the temperature of the catalysts drops (cold start) or the engine load increases immediately after starting.

[0011] The object of the invention is achieved by a method for operating an exhaust gas aftertreatment device for cleaning an exhaust gas flow of an internal combustion engine of a motor vehicle, wherein the exhaust gas aftertreatment device has at least one catalyst, wherein at least one thermoelectric generator is associated with the catalyst, wherein the thermoelectric generator is connected to the catalyst in a heat energy-transferring manner, comprising the steps: Comparing a value representative of a catalyst temperature with a limit value, Generate electrical energy with the thermoelectric generator when the value representative of a catalyst temperature is greater than the limit value.

[0012] A thermoelectric generator (TEG) enables the direct conversion of thermal energy into electrical energy. Instead of metals, semiconductor materials are used, which significantly increases efficiency compared to metallic thermocouples. Thermoelectric generators are characterized by their simple design, high reliability, and long service life.

[0013] A thermoelectric generator also includes one or more Peltier elements, which then form a thermal chain for providing electrical energy. A Peltier element is an electrothermal converter that, based on the Peltier effect, generates a temperature difference when a current flows through it, or a current flow when there is a temperature difference (Seebeck effect). Peltier elements can be used both for cooling and—when the current direction is reversed—for heating.

[0014] This allows excess thermal energy, for example, after a journey with the engine off, to be directly converted into electrical energy and temporarily stored, for example, in a vehicle's battery. At the same time, this can prevent the catalytic converter from overheating beyond its operating temperature range during operation. The electrical energy temporarily stored in the battery can then be used again, if necessary, to heat the catalytic converter to raise the temperature to within the operating temperature range.

[0015] By keeping the temperature within the operating temperature window and / or reaching the operating temperature window more quickly, emissions from the internal combustion engine can be reduced.

[0016] According to the invention, at least one thermoelectric heating element is assigned to the catalyst, wherein the thermoelectric heating element is connected to the catalyst in a heat-energy-transferring manner. The following additional steps are then carried out: Determining a value representative of an active internal combustion engine, Applying electrical energy to the thermoelectric heating element when the value is representative of an active internal combustion engine.

[0017] The thermoelectric heating element is an additional heating resistor capable of providing greater heating power than a thermoelectric generator. In other words, the catalytic converter is equipped with an additional electric heater, meaning the catalytic converter is designed as an e-cat. This allows for faster heating when needed.

[0018] According to one embodiment, the catalyst is a NOx storage catalyst. Thus, the catalyst allows for the storage of NOx (nitrogen oxides). For this purpose, it has a structure comprising a suitable support with a noble metal catalyst, such as platinum, and a NOx storage component, such as an alkaline earth metal such as barium.

[0019] According to a further embodiment, the catalyst is an SCR catalyst. Thus, the SCR catalyst is designed for the selective catalytic reduction of nitrogen oxides using urea, which is injected into the exhaust gas stream at a urea injection point.

[0020] The invention further includes a computer program product, a control unit, an exhaust gas aftertreatment device and a motor vehicle with such an exhaust gas aftertreatment device.

[0021] The invention will now be explained with reference to a drawing. It shows: Fig. 1 an internal combustion engine and an exhaust aftertreatment device of a motor vehicle for carrying out an embodiment of the method according to the invention. Fig. 2 a flowchart of the operation of the Fig. 1 shown exhaust aftertreatment device. Fig. 3 another flowchart of the operation of the Fig. 1 shown exhaust aftertreatment device.

[0022] First, the Fig. 1 referred to.

[0023] The Fig. 1 shows an internal combustion engine 4 and an exhaust aftertreatment device 6 of a motor vehicle 2.

[0024] In the present embodiment, the internal combustion engine 4 is a diesel engine, meaning that the diesel engine is operated in lean-burn mode with an excess of oxygen (λ > 1) during normal operation. Alternatively, the internal combustion engine 4 can also be designed as a gasoline engine operating in lean-burn mode to increase engine efficiency.

[0025] In the present exemplary embodiment, the internal combustion engine 4 is turbocharged, so that a turbine of an exhaust gas turbocharger is connected downstream in the exhaust gas flow of the internal combustion engine 4.

[0026] In the present exemplary embodiment, the exhaust aftertreatment device 6, which is arranged downstream of the internal combustion engine 4 in the exhaust gas flow direction, comprises a plurality of catalysts arranged one behind the other in the exhaust gas flow direction. In the present exemplary embodiment, these are a NOx storage catalyst 10, a diesel particulate filter 12, and an SCR catalyst 14.

[0027] The NOx storage catalyst 10 is designed to store NOx (nitrogen oxides). It has a structure with a suitable carrier containing a noble metal catalyst, such as platinum, and a NOx storage component, such as an alkaline earth metal such as barium.

[0028] The diesel particulate filter 12 is designed to reduce the particles present in the exhaust gas stream.

[0029] The SCR catalyst 14 is designed for the selective catalytic reduction of nitrogen oxides using urea, which is injected into the exhaust gas stream at a urea injection point.

[0030] Deviating from the present exemplary embodiment, the number of catalysts can vary; ie, for example, two NOx storage catalysts can also be provided. Likewise, multiple SCR catalysts can be provided. It can also be provided that the SCR catalyst 14 has a coating in order to configure it as a diesel particulate filter (DPF) or diesel particulate filter (SDPF) for reducing the particles and NOx present in the exhaust gas stream.

[0031] The internal combustion engine 4 is assigned a control unit 8, which, for example, causes a change from operation with excess oxygen to substoichiometric operation and vice versa in order to regenerate the NOx storage catalyst 10. For this purpose and for the tasks and functions described below, the control unit has hardware and / or software components.

[0032] Furthermore, in the present exemplary embodiment, a thermoelectric generator 18 is connected downstream of the internal combustion engine in the exhaust gas flow direction, while a thermoelectric generator 8 and a thermoelectric heating element 20 are connected upstream of the NOx storage catalyst 10 and the SCR catalyst 14 in the exhaust gas flow direction.

[0033] It will now also Fig. 2, which shows a first flow chart of the operation of the exhaust gas aftertreatment device 6, in particular the NOx storage catalyst 10.

[0034] The method begins with a step S1100.

[0035] In a further step S1200, a first value W1 representative of a catalyst temperature—in the present embodiment, an inlet temperature of the NOx storage catalyst 10—is read in and compared with a first limit value G1. In the present embodiment, the first limit value G1 has a value of 200°C.

[0036] If the first value W1 is not less than the first limit value G1, the method continues with a further step S1300.

[0037] In step S1300, the first value W1, representative of a catalyst temperature, is compared with a second limit value G2. In the present embodiment, the second limit value G2 has a value of 300°C.

[0038] If the first value W1 is greater than the second limit value G2, the method continues with a further step S1400.

[0039] In step S1400, the thermoelectric generator 18 is activated so that the thermoelectric generator 18 converts heat energy into electrical energy in a generator mode, which is then temporarily stored in the battery 16.

[0040] This continues until the first value W1 is again equal to or less than the second limit value G2.

[0041] If, however, the first value W1 is at least equal to the second limit value G2, the method continues with a further step S1500.

[0042] In step S1500, a second value W2 is determined representative of an active internal combustion engine 4. In the present exemplary embodiment, the second value W2 is a logical variable 1 for an active or running internal combustion engine 4, while a logical variable 0 represents an inactive or stationary internal combustion engine 4.

[0043] If the internal combustion engine 4 is active, the method continues with a further step S1600.

[0044] In step S1600, the thermoelectric heating element 20 is supplied with electrical energy, e.g., from the battery 16, so that the thermoelectric heating element 20 heats the NOx storage catalyst 10. The thermoelectric generator 18, however, is inactive, i.e., it does not supply electrical energy. However, it can also be provided that the thermoelectric generator 18 is operated in a heating mode, thus supporting the heating element 20 in operation to further accelerate the heating process.

[0045] The method then continues with step S1200.

[0046] If, however, the internal combustion engine 4 is inactive, the method continues with a further step S1700.

[0047] In step S1700, the first value W1, representative of a catalyst temperature, is compared with a third limit value G3. In the present embodiment, the third limit value G3 has a value of 50°C.

[0048] If the first value W1 is not greater than the third limit value G3, the method continues with step S1400.

[0049] If, however, the first value W1 is at least equal to the third limit value G3, the method continues with a further step S1800.

[0050] In step S1800, both the thermoelectric generator 18 and the thermoelectric heating element 20 are inactive, ie the thermoelectric generator 18 does not supply electrical energy and the thermoelectric heating element 20 is not supplied with electrical energy.

[0051] The process ends with step S1900.

[0052] Deviating from the present exemplary embodiment, the method sequence may have a different sequence of steps. Multiple steps may also be executed concurrently or simultaneously. Furthermore, individual steps may also be skipped or omitted.

[0053] It will now also Fig. 3, which shows a first flowchart of the operation of the exhaust aftertreatment device 6, in particular the SCR catalyst 14. The SCR catalyst 14 may have a structure to form it as a diesel particulate filter or diesel particulate filter (DPF) for reducing the particles present in the exhaust stream.

[0054] The method begins with a step S2100.

[0055] In a further step S2200, a first value W1 representative of a catalyst temperature—in the present embodiment, an inlet temperature of the SCR catalyst 14—is read in and compared with a first limit value G1. In the present embodiment, the first limit value G1 has a value of 180°C.

[0056] If the first value W1 is not less than the first limit value G1, the method continues with a further step S2300.

[0057] In step S2300, the first value W1, representative of a catalyst temperature, is compared with a second limit value G2. In the present embodiment, the second limit value G2 has a value of 300°C.

[0058] If the first value W1 is greater than the second limit value G2, the method continues with a further step S2400.

[0059] In step S2400, the thermoelectric generator 18 is activated so that the thermoelectric generator 18 converts heat energy into electrical energy in a generator mode, which is then temporarily stored in the battery 16.

[0060] This continues until the first value W1 is again equal to or less than the second limit value G2.

[0061] If, however, the first value W1 is at least equal to the second limit value G2, the method continues with a further step S2500.

[0062] In step S2500, a second value W2 is determined representative of an active internal combustion engine 4. In the present exemplary embodiment, the second value W2 is a logical variable 1 for an active or running internal combustion engine 4, while a logical variable 0 represents an inactive or stationary internal combustion engine 4.

[0063] If the internal combustion engine 4 is active, the method continues with a further step S2600.

[0064] In step S2600, the thermoelectric heating element 20 is supplied with electrical energy, e.g., from the battery 16, so that the thermoelectric heating element 20 heats the SCR catalyst 14. The thermoelectric generator 18, however, is inactive, i.e., it does not supply any electrical energy. However, it can also be provided that the thermoelectric generator 18 is operated in a heating mode, thus supporting the heating element 20 in operation to further accelerate the heating process.

[0065] The process then continues with step S2200.

[0066] If the internal combustion engine 4 is inactive, the method continues with a further step S2700.

[0067] In step S2700, the first value W1, representative of a catalyst temperature, is compared with a third limit value G3. In the present embodiment, the third limit value G3 has a value of 50°C.

[0068] If the first value W1 is not greater than the third limit value G3, the method continues with step S2400.

[0069] If, however, the first value W1 is at least equal to the third limit value G3, the method continues with a further step S2800.

[0070] In step S2800, both the thermoelectric generator 18 and the thermoelectric heating element 20 are inactive, ie the thermoelectric generator 18 does not supply electrical energy and the thermoelectric heating element 20 is not supplied with electrical energy.

[0071] The process ends with step S2900.

[0072] For both based on the Fig. 2 and Fig.3 explanatory embodiment, three different situations are taken into account by a cold start procedure, a start-stop procedure and a procedure at the end of the journey.

[0073] In the cold-start process, the temperature, represented by the first value W1, during the starting process is below a threshold temperature, represented in the present embodiment by the second threshold value G2. An electric heater is then switched on.

[0074] During the start-stop procedure, the electric heater is switched off, but heat dissipation can continue as long as the temperature remains above a threshold temperature, represented by the first threshold value G1. However, if the temperature is below the threshold temperature during the start-up process, the electric heater is switched on.

[0075] During the procedure at the end of the journey, the electric heater is also switched off, but heat dissipation can continue depending on the condition of the battery 16. This means that heat dissipation can continue as long as a significant temperature difference exists, represented in the present embodiment by the third limit value G3. This assumes that the battery 16 still has free capacity to store electrical energy.

[0076] Deviating from the present exemplary embodiment, the method sequence may have a different sequence of steps. Multiple steps may also be executed concurrently or simultaneously. Furthermore, individual steps may also be skipped or omitted.

[0077] In this way, the temperature can be maintained within the operating temperature window and / or the operating temperature window can be reached more quickly, which reduces the emissions of the internal combustion engine 4. List of reference symbols 2 motor vehicles 4 internal combustion engine 6 Exhaust aftertreatment device 8 Control unit 10 NOx storage catalyst 12 diesel particulate filters 14 SCR catalyst 16 Battery 18 thermoelectric generator 20 thermoelectric heating element G1 first limit G2 second limit G3 third limit W1 first value W2 second value S1100 Step S1200 Step S1300 Step S1400 Step S1500 step S1600 step S1700 Step S1800 step S1900 Step S2100 Step S2200 Step S2300 Step S2400 Step S2500 Step S2600 Step S2700 Step S2800 Step S2900 Step

Claims

[1] Method for operating an exhaust gas aftertreatment device (6) for cleaning an exhaust gas flow of an internal combustion engine (4) of a motor vehicle (2), wherein the exhaust gas aftertreatment device (6) has at least one catalyst, wherein at least one thermoelectric generator (18) is associated with the catalyst, wherein the thermoelectric generator (18) is connected to the catalyst in a heat energy-transferring manner, wherein at least one thermoelectric heating element (20) is associated with the catalyst, wherein the thermoelectric heating element (20) is connected to the catalyst in a heat energy-transferring manner, and wherein the thermoelectric heating element (20) is a heating resistor, comprising the steps: Comparing a value (W1) representative of a catalyst temperature with a limit value (G2), Generating electrical energy with the thermoelectric generator (18) when the value (W1) is representative of a catalyst temperature greater than the limit value (G2), Determining a value (W2) representative of an active internal combustion engine (4), Applying electrical energy to the thermoelectric heating element (20) when the value (W2) is representative of an active internal combustion engine (4). [2] Method according to claim 1, wherein the catalyst is a NOx storage catalyst (10). [3] The method of claim 1, wherein the catalyst is an SCR catalyst (14). [4] Computer program product designed to carry out a method according to one of claims 1 to 3. [5] Control unit (8) for operating an exhaust gas aftertreatment device (6) for cleaning an exhaust gas flow of an internal combustion engine (4) of a motor vehicle (2), wherein the exhaust gas aftertreatment device (6) has at least one catalytic converter, wherein at least one thermoelectric generator (18) is associated with the catalytic converter, wherein the thermoelectric generator (18) is connected to the catalytic converter in a heat energy-transferring manner, wherein the control unit (8) is designed to compare a value (W1) representative of a catalytic converter temperature with a limit value (G2) and to generate electrical energy with the thermoelectric generator (18) if the value (W1) representative of a catalytic converter temperature is greater than the limit value (G2), to determine a value (W2) representative of an active internal combustion engine (4), and a thermoelectric heating element (20) associated with the catalytic converter and which is a heating resistor,to be supplied with electrical energy if the value (W2) is representative of an active internal combustion engine (4). [6] Control unit (8) according to claim 5, wherein the catalyst is a NOx storage catalyst (10). [7] Control unit (8) according to claim 5, wherein the catalyst is an SCR catalyst (14). [8] Exhaust gas aftertreatment device (6) for cleaning an exhaust gas flow of an internal combustion engine (4) of a motor vehicle (2), with at least one catalytic converter, wherein at least one thermoelectric generator (18) is assigned to the catalytic converter, wherein the thermoelectric generator (18) is connected to the catalytic converter in a heat energy-transferring manner, wherein at least one thermoelectric heating element (20) is assigned to the catalytic converter, wherein the thermoelectric heating element (20) is connected to the catalytic converter in a heat energy-transferring manner, and wherein the thermoelectric heating element (20) is a heating resistor. [9] Exhaust gas aftertreatment device (6) according to claim 8, wherein the catalyst is a NOx storage catalyst (10). [10] Exhaust aftertreatment device (6) according to claim 8, wherein the catalyst is an SCR catalyst (14). [11] Motor vehicle (2) with an exhaust gas aftertreatment device (6) according to one of claims 8 to 10.

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