Control device and method for controlling an exhaust gas aftertreatment system

Abstract

The present invention provides a control device (100) and a method (300) for controlling an exhaust aftertreatment system (10) including a diesel particulate filter (20). The method (300) includes the step of: in response to determining that the temperature of exhaust gas entering the diesel particulate filter (20) is equal to or lower than 325°C, controlling the NOx concentration of the exhaust gas entering the diesel particulate filter (20) to at least 200 ppm and equal to or less than 600 ppm. An exhaust aftertreatment system (10) and a vehicle (1) including the control device (100) are also described.

Description

Technical Field

[0001] This disclosure generally relates to a method for controlling an exhaust aftertreatment system including a diesel particulate filter. It also generally relates to a control device configured to control the exhaust aftertreatment system including the diesel particulate filter. Furthermore, this disclosure generally relates to a computer program and a computer-readable medium. Additionally, this disclosure generally relates to a vehicle. Background Technology

[0002] Exhaust aftertreatment systems, such as those for vehicles, can include various catalysts and filters configured to treat exhaust gases to obtain a desired tailpipe composition. Tailpipes release emissions into the surrounding environment and therefore must meet emission requirements under current legislation or other standards. Such legislation or standards typically specify maximum levels for many tailpipe pollutants, including carbon monoxide (CO), hydrocarbons (HC), nitrogen oxides (NOx), and particulate matter (PM). NOx primarily comprises NO2 and NO.

[0003] Vehicle exhaust aftertreatment systems may include, for example, diesel oxidation catalysts (DOC), diesel particulate filters (DPF), and selective catalytic reduction (SCR) catalysts and / or ammonia slip catalysts (ASC). Additionally, exhaust gas recirculation (EGR) may also be used to reduce NOx emissions.

[0004] Diesel particulate filters (DPFs) accumulate particulate matter during operation and therefore must be regenerated periodically to remove any combustible particulate matter, primarily composed of soot. There are two different techniques for DPF regeneration: active regeneration and passive regeneration. Active regeneration can be performed by temporarily increasing the exhaust gas temperature (typically at least around 600°C), causing the soot to be oxidized by oxygen and thus removed from the DPF. In contrast, passive regeneration is a method in which NO2 is used to oxidize the soot substantially continuously at the DPF's normal operating temperature. NO2 constitutes a portion of the NOx in the exhaust gas. While NO2 is an effective oxidant for soot, the NO in NOx can in turn inhibit the DPF, resulting in a lower oxidation rate of soot. For this reason, DPFs are often coated with a catalyst configured to oxidize NO to NO2. This type of DPF is often referred to as a catalytic diesel particulate filter (cDPF).

[0005] WO 2014 / 016616 A1 discloses an example of a method for controlling an exhaust gas aftertreatment system, wherein the exhaust gas aftertreatment system includes a first SCR unit, a second SCR unit disposed downstream of the first SCR unit, and a DPF located between the first and second SCR units. The operating temperature range of the first SCR unit differs from that of the second SCR unit. According to the method, when the temperature of the first SCR is within its operating range, a metered supply of reductant is provided to the first SCR, and when the temperature of the second SCR is within its operating range, a metered supply of reductant is provided to the second SCR. When the DPF should be passively regenerated, the metered supply to the first SCR unit is reduced or stopped to allow NOx in the exhaust gas stream to pass through the first SCR unit and regenerate the DPF. The remaining NOx leaving the DPF can then be removed by the second SCR unit, provided that the second SCR is within its operating range. If the DPF should be actively regenerated, the metered supply to the SCR can continue with the SCR temperature being within acceptable limits. Summary of the Invention

[0006] The purpose of this invention is to more effectively utilize the passive regeneration of diesel particulate filters in exhaust aftertreatment systems.

[0007] This objective is achieved through the subject matter of the appended independent claims.

[0008] According to this disclosure, a method is provided for controlling an exhaust gas aftertreatment system including a diesel particulate filter. The method is performed by a control device. The method includes the step of: in response to determining that the temperature of the exhaust gas entering the diesel particulate filter is equal to or lower than 325°C, controlling the NOx concentration of the exhaust gas entering the diesel particulate filter to be equal to or lower than 600 ppm.

[0009] Sufficient passive regeneration of the DPF particularly avoids the accumulation of excessive back pressure in the exhaust aftertreatment system, which can increase fuel consumption in combustion engines connected to the exhaust aftertreatment system. Furthermore, efficient passive regeneration of the DPF significantly reduces the need for active regeneration, which is beneficial because active regeneration is typically accompanied by fuel loss and can often temporarily increase tailpipe emissions. This method passively regenerates the diesel particulate filter without sacrificing the ability to achieve the desired tailpipe composition of the exhaust gas. More specifically, according to this method, when the exhaust gas temperature is equal to or below 325°C, the NOx concentration upstream of the DPF is reduced to a lower concentration than is typically considered necessary for passive regeneration of the DPF. This also promotes the ability to achieve the desired tailpipe composition. This is because the risk of high tailpipe emissions due to the conventional use of high NOx concentrations in the DPF is minimized during DPF regeneration.

[0010] The step of controlling the NOx concentration in the exhaust gas entering the diesel particulate filter may also include controlling the NOx concentration to at least 200 ppm. This further improves the passive regeneration of the DPF.

[0011] The exhaust aftertreatment system may include a first selective catalytic reduction catalyst disposed upstream of the diesel particulate filter. In this case, controlling the NOx concentration in the exhaust gas entering the diesel particulate filter may include controlling the amount of reducing agent used for the first selective catalytic catalyst. Therefore, the NOx concentration can be controlled efficiently and accurately. This further ensures a robust exhaust aftertreatment system that can operate over a relatively wide temperature range.

[0012] The exhaust aftertreatment system may include a second selective catalytic reduction catalyst positioned downstream of the diesel particulate filter (DPF). This allows for efficient reduction of NOx concentration downstream of the DPF.

[0013] If the exhaust aftertreatment system includes a second selective catalytic reduction catalyst disposed downstream of the diesel particulate filter, the method may further include controlling the amount of reducing agent used for the second selective catalytic reduction catalyst based on the desired maximum tailpipe NOx concentration. Therefore, ultra-low tailpipe NOx emissions can be achieved.

[0014] The method may further include the step of: controlling the NOx concentration of the exhaust gas entering the diesel particulate filter to above 600 ppm in response to determining that the temperature of the exhaust gas entering the diesel particulate filter has increased to a temperature equal to or above 350°C. Therefore, if desired, the exhaust aftertreatment system can operate over a wide temperature range while still achieving very good passive regeneration of the DPF. More specifically, passive regeneration can be further enhanced after the exhaust aftertreatment system has already been operating at relatively low exhaust gas temperatures.

[0015] This disclosure also relates to a computer program including instructions that, when executed by a control device, cause the control device to perform the method described above.

[0016] This disclosure also relates to a computer-readable medium including instructions that, when executed by a control device, cause the control device to perform the method described above.

[0017] Furthermore, according to this disclosure, a control device is provided configured to control an exhaust gas aftertreatment system including a diesel particulate filter. The control device is configured to control the NOx concentration of the exhaust gas entering the diesel particulate filter to be equal to or less than 600 ppm in response to determining that the temperature of the exhaust gas entering the diesel particulate filter is equal to or less than 325°C.

[0018] The control device has the same advantages as those described above regarding the corresponding method for controlling an exhaust aftertreatment system including a diesel particulate filter.

[0019] The control device can be configured to control the NOx concentration in the exhaust gas entering the diesel particulate filter to at least 200 ppm.

[0020] The exhaust aftertreatment system may also include a first selective catalytic reduction catalyst disposed upstream of the diesel particulate filter. In this case, the control device can be configured to control the NOx concentration of the exhaust gas entering the diesel particulate filter by controlling the amount of reducing agent used for the first selective catalytic reduction catalyst.

[0021] The exhaust aftertreatment system may include a second selective catalytic reduction catalyst disposed downstream of the diesel particulate filter. In this case, the control device may also be configured to control the amount of reductant used for the second selective catalytic reduction catalyst based on the desired maximum threshold tailpipe NOx concentration.

[0022] The control device can also be configured to control the NOx concentration of the exhaust gas entering the diesel particulate filter to be higher than 600 ppm in response to determining that the temperature of the exhaust gas entering the diesel particulate filter has increased to a temperature equal to or higher than 350°C.

[0023] Furthermore, an exhaust gas aftertreatment system is provided. The exhaust gas aftertreatment system includes a diesel particulate filter and the control device described above.

[0024] This disclosure also relates to a vehicle that includes the control device described above. Attached Figure Description

[0025] Figure 1 A schematic side view of the vehicle is shown.

[0026] Figure 2 An exemplary embodiment of an exhaust gas aftertreatment system is schematically illustrated.

[0027] Figure 3 The flowchart illustrating a method for controlling an exhaust gas aftertreatment system according to an exemplary embodiment of the present disclosure is shown schematically.

[0028] Figure 4 The diagram schematically illustrates a device that can be incorporated into, included in, or configured as part of a control unit for controlling an exhaust gas aftertreatment system.

[0029] Figure 5a The diagram shows the CO2 produced on the cDPF at various temperatures from 255°C to 506°C, varying with NO concentration.

[0030] Figure 5bexpress Figure 5a A more detailed graph of the results shows the CO2 produced as a function of NO concentration at temperatures ranging from 255°C to 354°C. Detailed Implementation

[0031] The invention will now be described in more detail with reference to exemplary embodiments and the accompanying drawings. However, the invention is not limited to the exemplary embodiments discussed and / or shown in the drawings, but may vary within the scope of the appended claims. Furthermore, the drawings should not be considered to be drawn to scale, as some features may have been exaggerated to more clearly illustrate the invention or its features.

[0032] When the terms “upstream” and “downstream” are used in this disclosure, they should be considered as the direction of flow of exhaust gas relative to the exhaust gas passing through the exhaust gas aftertreatment system.

[0033] Furthermore, in this disclosure, the term "tailpipe" should be understood to refer to exhaust gas discharged from the exhaust gas aftertreatment system. Therefore, the tailpipe is the exhaust gas discharged from the exhaust gas aftertreatment system into the surrounding environment.

[0034] According to this disclosure, a method for controlling an exhaust aftertreatment system including a diesel particulate filter (DPF) is provided. The method is performed by a control device thus configured. More specifically, this disclosure relates to a method for controlling an exhaust aftertreatment system for the purpose of passively regenerating the diesel particulate filter (DPF). Carbon soot accumulates in the DPF from the exhaust gases treated in the exhaust aftertreatment system. This soot must be removed periodically to prevent the accumulation of excessive back pressure, which, for example, could lead to additional fuel costs if the exhaust aftertreatment system is used to treat exhaust gases from a combustion engine.

[0035] A DPF can be passively regenerated by oxidizing soot with NO2, which is present in the exhaust gas entering the DPF. NO2 is a very effective oxidizer for this purpose, and it is generally accepted in the art that the ability to passively generate a DPF increases with the amount of NOx in the exhaust gas entering the DPF. However, the inventors have found that this is inaccurate for all operating conditions of exhaust gas aftertreatment systems including DPFs. More specifically, the inventors have found that at lower temperatures, the ability to passively regenerate a DPF may actually decrease with increasing NOx concentration.

[0036] Therefore, the method for controlling an exhaust gas aftertreatment system including a DPF includes the step of: controlling the NOx concentration of the exhaust gas entering the DPF to be equal to or less than 600 ppm in response to determining that the temperature of the exhaust gas entering the diesel particulate filter is equal to or less than 325°C. In other words, the method of this disclosure includes the step of: reducing the NOx concentration upstream of the DPF in response to determining that the temperature of the exhaust gas entering the diesel particulate filter is equal to or less than 325°C, such that the NOx concentration of the exhaust gas entering the DPF is equal to or less than 600 ppm. According to one embodiment of the method, the step of controlling the NOx concentration of the exhaust gas entering the DPF to be equal to or less than 600 ppm is performed in response to determining that the temperature of the exhaust gas entering the diesel particulate filter is equal to or less than 300°C.

[0037] Responding to the determination that the exhaust gas temperature is equal to or below 325°C (or 300°C), controlling the NOx concentration of the exhaust gas entering the DPF to equal to or below 600 ppm means that the NOx concentration upstream of the DPF is reduced to a lower level than conventionally used. This relatively large reduction in the NOx concentration upstream of the DPF contrasts with the conventional strategy of passively regenerating the DPF using relatively high NOx concentrations, based on the generally accepted knowledge in the art that the ability of passively regenerating the DPF increases with increasing NOx levels.

[0038] Although the NOx concentration decreases to 600 ppm or less in response to the determination that the temperature of the exhaust gas entering the DPF is 325°C (or 300°C) or lower, passive regeneration of the DPF requires the presence of some NO2, therefore the NOx concentration of the exhaust gas entering the DPF should not be too low. For this reason, it is appropriate to perform a step of controlling the NOx concentration of the exhaust gas entering the DPF to maintain the NOx concentration at or above 200 ppm. Preferably, the NOx concentration of the exhaust gas entering the DPF is controlled to be at or above 300 ppm.

[0039] As described above, the exhaust gas aftertreatment system includes a DPF. The DPF is preferably a catalytic DPF (cDPF). In other words, the DPF can be suitably coated with a catalyst. This reduces the risk of passive regeneration of the DPF by NO inhibition of NOx. The catalytic coating is preferably composed of platinum (Pt) or platinum (Pt). Platinum has the ability to oxidize NO to NO2 with high conversion using O2 over a wide temperature range. According to an alternative, the catalytic coating may contain platinum (Pt) and palladium (Pd). If desired, other catalytic elements or compounds, such as Ru, Rh, Ir, and / or Cu, can also be used in the catalytic coating.

[0040] The method may include the step of monitoring the temperature of the exhaust gas entering the DPF. Therefore, this step can be performed according to any previously known technique. For example, the temperature can be monitored using one or more temperature sensors arranged immediately upstream of the DPF. Alternatively, the temperature of the exhaust gas entering the DPF can be monitored using a temperature model of the exhaust aftertreatment system, which takes into account temperatures measured elsewhere in the exhaust aftertreatment system and / or the operating conditions of the combustion engine connected to the exhaust aftertreatment system. The method may also include the step of determining whether the temperature of the exhaust gas entering the DPF is equal to or below 325°C (or 300°C).

[0041] If the exhaust gas temperature entering the DPF is above 325°C, the exhaust gas treatment system can therefore be controlled according to conventional strategies, if necessary, to achieve the desired tailpipe composition while also allowing passive regeneration of the DPF. In some cases, this may include actively controlling the NOx concentration upstream of the DPF. In other cases, this strategy may include not actively reducing the NOx concentration upstream of the DPF. In the latter case, the NOx concentration may simply be reduced downstream of the DPF to achieve the desired tailpipe composition. At exhaust gas temperatures of approximately 350°C or higher, the ability to oxidize soot in the DPF generally increases with the amount of NOx in the exhaust gas. Therefore, higher NOx concentrations may be appropriate when the exhaust gas temperature entering the DPF is 325°C or lower. However, it should be noted that passive regeneration of the DPF can also occur at relatively low NOx concentrations, although at a considerably low rate. Therefore, when the exhaust gas temperature is above 325°C, the NOx concentration of the exhaust gas entering the DPF should be at least 300 ppm, preferably at least 600 ppm.

[0042] Therefore, the method according to this disclosure may include the following steps: in response to determining that the temperature of the exhaust gas entering the diesel particulate filter has increased from a temperature of 325°C or less to a temperature of 350°C or greater, controlling the NOx concentration of the exhaust gas entering the diesel particulate filter to a higher concentration than that in the previous step when the exhaust gas temperature was 325°C or less. Specifically, the method may include the step of: in response to determining that the temperature of the exhaust gas entering the diesel particulate filter has increased to a temperature equal to or greater than 350°C, controlling the NOx concentration of the exhaust gas entering the diesel particulate filter to a level greater than 600 ppm.

[0043] Therefore, the step of controlling the NOx concentration in the exhaust gas entering the DPF to 600 ppm or less in response to determining that the temperature of the exhaust gas entering the DPF is equal to or lower than 325°C can be performed by any previously known method and depending on the configuration of the exhaust gas aftertreatment system (e.g., catalyst arrangement). For example, in response to determining that the temperature of the exhaust gas entering the DPF is equal to or lower than 325°C, the control of the NOx concentration in the exhaust gas upstream of the DPF can be performed by exhaust gas recirculation (EGR), a NOx absorber, and / or a selective catalytic reduction (SCR) catalyst.

[0044] According to one example, the exhaust aftertreatment system includes an SCR catalyst upstream of the DPF. By controlling the amount of reductant used in the SCR located upstream of the DPF, the exhaust gas entering the DPF can achieve a desired NOx concentration. Therefore, this method may include the step of controlling the NOx concentration of the exhaust gas entering the diesel particulate filter by controlling the amount of reductant used in the first SCR located upstream of the DPF.

[0045] According to one alternative, the exhaust gas aftertreatment system may include two SCRs arranged in parallel upstream of the DPF. The exhaust gas flow can be split into two partial flows as needed via the two parallel SCRs, or the entire exhaust gas flow can be guided via one or the other of the parallel SCRs. The two partial flows can then be recombined before passing through the DPF. It should be noted that parallel SCRs are not considered limited to the physical arrangement of SCRs parallel to each other in the exhaust gas aftertreatment system, but only to mean that they are arranged such that the exhaust gas flow can be distributed between them simultaneously, rather than the two SCRs being sequentially arranged in the direction of exhaust gas flow through the system. If the exhaust gas aftertreatment includes two parallel SCRs, these SCRs may, for example, have different operating temperature ranges. Therefore, depending on the temperature of the exhaust gas upstream of the SCR, the exhaust gas can be guided via the SCR with the appropriate operating temperature range.

[0046] The method may further include the step of controlling the exhaust gas aftertreatment system to obtain a desired tailpipe composition. More specifically, the method may include the step of controlling the degree of conversion of gaseous components in the exhaust gas and / or components of the exhaust gas aftertreatment system downstream of the DPF to obtain a desired tailpipe composition. For example, the exhaust gas aftertreatment system may include an SCR disposed downstream of the DPF. The SCR disposed downstream of the DPF may be operated to achieve a desired NOx concentration in the tailpipe. The reduction of NOx in the SCR can be controlled by controlling the amount of reducing agent used. Therefore, the method may further include the step of controlling the amount of reducing agent used for the SCR disposed downstream of the DPF based on a desired maximum threshold tailpipe NOx concentration. For example, this maximum threshold tailpipe NOx concentration may be selected to at least meet current legislation regarding tailpipe emissions.

[0047] According to one alternative, the exhaust aftertreatment system comprises both a selective catalytic converter (SCR) positioned upstream of the drain filter (DPF) and an SCR positioned downstream of the DPF. In such a system, a conflict often exists between simultaneously achieving low NOx tailpipe emissions and providing passive regeneration conditions for the DPF. If the upstream SCR is used too aggressively, the DPF regeneration capacity may be insufficient. Conversely, if the upstream SCR is used too moderately, the target tailpipe NOx emissions may not be achieved. Meeting both requirements can present a difficult optimization problem. Therefore, suboptimal treatment may require a larger downstream SCR catalyst volume, meaning a higher cost for the exhaust aftertreatment system and potentially fuel efficiency losses in combustion engines connected to the system due to higher back pressure. However, with this approach, at certain temperatures, the upstream SCR can be used to a degree greater than is generally considered achievable for passive regeneration of the DPF. This eliminates the conflict between achieving the target tailpipe NOx emissions and passive DPF regeneration. This, in turn, results in a more robust aftertreatment system for achieving challenging duty cycles at low to medium temperature boundaries.

[0048] If desired, the exhaust gas aftertreatment system may also include, for example, an ammonia slip catalyst (ASC) disposed downstream of the DPF and SCR. The ASC is typically configured to convert any excess reducing agent leaving the SCR into N2 and water. If desired, the exhaust gas aftertreatment system may also include additional catalysts and / or filters as known in the art.

[0049] The execution of the methods for controlling exhaust gas aftertreatment systems, as described herein, can be managed by programming instructions. These instructions are typically in the form of computer programs that, when executed in or by a control device, cause the control device to perform desired control actions. Such instructions can usually be stored on a computer-readable medium.

[0050] This disclosure also relates to a control device configured to control an exhaust gas aftertreatment system according to the methods described above. The control device can be configured to perform any of the steps of the methods for controlling an exhaust gas aftertreatment system as described herein.

[0051] More specifically, the control device is configured to control an exhaust aftertreatment system including a diesel particulate filter (DPF). The control device is configured to control the NOx concentration of the exhaust gas entering the DPF to be equal to or less than 600 ppm in response to determining that the temperature of the exhaust gas entering the DPF is equal to or less than 325°C.

[0052] The control device can also be configured to monitor the temperature of the exhaust gas entering the DPF and determine whether the temperature of the exhaust gas entering the DPF is equal to or lower than 325°C. Alternatively, the control device can be configured to receive information from another device configured to determine whether the temperature of the exhaust gas entering the DPF is equal to or lower than 325°C.

[0053] The control device can be configured to control the NOx concentration of the exhaust gas entering the diesel particulate filter to be equal to or higher than 200 ppm, preferably equal to or higher than 300 ppm. The control device can be configured to perform this control in response to determining that the temperature of the exhaust gas entering the DPF is equal to or lower than 325°C. Alternatively or additionally, the control device can be configured to control the NOx concentration of the exhaust gas entering the diesel particulate filter to be equal to or higher than 200 ppm at any time when it is desired to passively regenerate the diesel particulate filter. In practice, this can mean that the control device can be configured to control the NOx concentration to at least 200 ppm when the exhaust aftertreatment system is in operation.

[0054] If the exhaust gas aftertreatment system includes a selective catalytic reduction (SCR) catalyst disposed upstream of the DPF, the control device can be configured to control the NOx concentration of the exhaust gas entering the DPF by controlling the amount of reductant used for the SCR. The control device can also be configured to control the amount of reductant used for the SCR based on the temperature and NOx concentration of the exhaust gas upstream of the SCR.

[0055] The control device can also be configured to control the exhaust gas aftertreatment system to obtain a desired tailpipe composition. More specifically, the control device can be configured to control the degree of conversion of gaseous components in the exhaust gas and / or the operation of components of the exhaust gas aftertreatment system downstream of the DPF to obtain a desired tailpipe composition. For example, the control device can be configured to control the amount of reducing agent used for the SCR disposed downstream of the DPF based on a desired maximum threshold tailpipe NOx concentration.

[0056] The control unit may be part of an exhaust aftertreatment system including a DPF, or it may be located remotely to this exhaust aftertreatment system but configured to communicate with it. The control unit may be located in a vehicle, such as a heavy-duty vehicle. However, if desired, portions of the control unit may be located remotely to the vehicle, for example, at a remote control center or the like. The vehicle may also include a combustion engine, such as a diesel engine, and an exhaust aftertreatment system configured to treat the exhaust gases produced by the combustion engine.

[0057] Figure 1A schematic side view of an example of vehicle 1 is shown. Vehicle 1 includes a powertrain 2, which includes an internal combustion engine 3 and a gearbox 4. A clutch (not shown) may be arranged between the internal combustion engine 3 and the gearbox 4. The gearbox 4 is connected to the drive wheels 7 of vehicle 1 via an output shaft 6 of the gearbox 4. Vehicle 1 also includes an exhaust aftertreatment system 10. Vehicle 1 may optionally be a hybrid vehicle, in which case the vehicle includes an electric motor (not shown) in addition to the combustion engine 3. Vehicle 1 may be a heavy-duty vehicle, such as a bus or truck.

[0058] Figure 2 An exemplary embodiment of an exhaust aftertreatment system 10 is schematically illustrated, which can be controlled according to the methods described herein. The exhaust aftertreatment system 10 can be configured to treat exhaust gases emitted by a vehicle (e.g., Figure 1 The exhaust gas produced by the combustion engine 3 of the vehicle 1) shown is thus connected to the combustion engine 3. The exhaust gas flow through the exhaust aftertreatment system 10 is indicated by arrow 12. The exhaust aftertreatment system 10 includes a diesel particulate filter 20 (DPF). The DPF 20 may suitably be a catalytic diesel particulate filter cDPF. The DPF is configured for its passive generation.

[0059] The exhaust gas aftertreatment system 10 may further include a first selective catalytic reduction catalyst 16 (SCR) disposed upstream of the DPF 20. The SCR is configured to convert NOx into N2 and water, thereby reducing the NOx concentration in the exhaust gas. For this purpose, a reducing agent is injected into the exhaust gas upstream of the SCR. The reducing agent can typically be ammonia or a urea solution. For the purpose of injecting the reducing agent upstream of the first SCR 16, the exhaust gas aftertreatment system 10 may include a first dosing device 14 configured to introduce the reducing agent into the exhaust gas stream. The amount of NOx reduced in the SCR can be controlled by controlling the amount of reducing agent used. The amount of reducing agent used may also be determined based on the temperature of the exhaust gas entering the SCR and the concentration of NOx in the exhaust gas entering the SCR. Controlling the amount of SCR used to achieve a desired reduction in NOx concentration is well known to those skilled in the art and will not be described further in this disclosure.

[0060] The exhaust gas aftertreatment system 10 may also include a second selective catalytic reduction catalyst 24 disposed downstream of the DPF 20. Furthermore, the exhaust gas aftertreatment system 10 may include a second metering device 22 configured to introduce a reducing agent into the exhaust gas stream upstream of the second SCR 22.

[0061] The exhaust gas aftertreatment system 10 may also include various sensors known in the art, such as temperature sensors and / or NOx sensors. Such sensors can be used to determine various parameters desired for the desired control of the exhaust gas aftertreatment system to obtain a desired tailpipe composition. If desired, such sensors can also be used to control specific components of the exhaust gas aftertreatment system. For example, the exhaust gas treatment system may include a temperature sensor 18 configured to determine the temperature of the exhaust gas entering the DPF 20, such as… Figure 2 As shown. The temperature sensor 18 can be arranged immediately upstream of the DPF 20. By using the temperature sensor 18, it is possible to determine, for example, whether the temperature of the exhaust gas entering the DPF 20 is equal to or lower than 325°C.

[0062] The exhaust aftertreatment system can be controlled by the control device 100 configured accordingly. The control device 100 can therefore be part of the exhaust aftertreatment system, but can also be any other control device that includes an exhaust aftertreatment system or arrangement (e.g., a vehicle). The control device 100 may include one or more control units. In cases where the control device includes multiple control units, each control unit may be configured to control a certain function, or a certain function may be divided among more than one control unit. By way of example only, the control device may include a first control unit configured to monitor the temperature of the exhaust gas entering the DPF and a second control unit configured to control the NOx concentration of the exhaust gas entering the DPF.

[0063] It should be noted that, although Figure 2 An exhaust gas aftertreatment system 10 comprising two SCRs 16 and 24 is shown, with a DPF 20 arranged between the SCRs; however, this disclosure is not limited to such exhaust gas aftertreatment systems. In fact, this method can be performed in any exhaust gas aftertreatment system that includes a DPF (which can be passively regenerated), as long as NO in the exhaust gas upstream of the DPF is present. X The possibility of NOx concentration. This control of NOx concentration can be achieved, for example, through exhaust gas recirculation (EGR), NOx absorbers, and / or selective catalytic reduction (SCR) as described above. However, as... Figure 2 As shown, an exhaust aftertreatment system that includes two SCRs and a DPF arranged between the SCRs has certain advantages. For example, it enables improved NOx conversion after the combustion engine has started, because the upstream SCR can be heated more quickly and therefore starts operating earlier than, for example, an SCR arranged downstream of the DPF.

[0064] Figure 3 A flowchart illustrating, schematically, a method 300 for controlling an exhaust gas aftertreatment system according to an exemplary embodiment of the present disclosure is shown. The exhaust gas aftertreatment system controlled by method 300 includes a DPF and may, for example, have the features described above. Figure 2The exemplary embodiment shown describes the configuration. The method may include step S101 of monitoring the temperature of the exhaust gas entering the DPF. For example, this can be achieved by using a temperature sensor, such as... Figure 2 The temperature sensor 18 shown directly measures the temperature immediately upstream of the DPF to perform step S101. Alternatively, the temperature of the exhaust gas entering the DPF can be derived by modeling the exhaust aftertreatment system, taking into account temperatures measured elsewhere in the exhaust aftertreatment system and / or the operating conditions of the combustion engine connected to the exhaust aftertreatment system. The method may also include step S102, which determines whether the temperature of the exhaust gas entering the DPF is equal to or below 325°C.

[0065] Method 300 includes step S103, which, in response to determining that the temperature of the exhaust gas entering the DPF is equal to or lower than 325°C, controls the NOx concentration of the exhaust gas entering the DPF to be equal to or lower than 600 ppm. Step S103 may include controlling the NOx concentration of the exhaust gas entering the DPF within the range of 200-600 ppm, preferably 300-600 ppm. If the exhaust gas aftertreatment system includes an SCR disposed upstream of the DPF, step S103 can be performed by controlling the amount of reducing agent used for the SCR to obtain the desired NOx concentration.

[0066] The method may also include step S104, which controls any component or operating parameters of the exhaust gas aftertreatment system downstream of the DPF in order to obtain the desired tailpipe composition.

[0067] If it is determined that the temperature of the exhaust gas entering the DPF is not 325°C or lower, method 300 can return to step S101 after step 102. Alternatively, the method can proceed to step S105, controlling the NOx concentration of the exhaust gas entering the DPF to at least 300 ppm, preferably higher than 600 ppm. After step S105, method 300 can return to step S101.

[0068] Method 300 can be performed continuously or intermittently (e.g., at predetermined intervals), and thus after step S103 and possibly step S104, it returns to the beginning as indicated by arrow 107.

[0069] Figure 4 An exemplary embodiment of the device 500 is illustrated schematically. The control device 100 described above may, for example, include, be composed of, or be included in the device 500.

[0070] Device 500 includes non-volatile memory 520, a data processing unit 510, and read / write memory 550. Non-volatile memory 520 has a first memory element 530 in which computer programs, such as an operating system, are stored to control the functions of device 500. Device 500 also includes a bus controller, a serial communication port, I / O devices, an A / D converter, a time and date input and transmission unit, an event counter, and an interrupt controller (not depicted). Non-volatile memory 520 also has a second memory element 540.

[0071] A computer program P is provided, comprising instructions for controlling an exhaust aftertreatment system including a diesel particulate filter. The computer program includes instructions for controlling the NOx concentration of the exhaust gas entering the diesel particulate filter to be equal to or less than 600 ppm in response to determining that the temperature of the exhaust gas entering the diesel particulate filter is equal to or less than 325°C.

[0072] Program P can be stored in memory 560 and / or read / write memory 550 in executable or compressed form.

[0073] The data processing unit 510 can perform one or more functions, that is, the data processing unit 510 can implement a part of the program P stored in the memory 560 or a part of the program P stored in the read / write memory 550.

[0074] Data processing device 510 can communicate with data port 599 via data bus 515. Non-volatile memory 520 is intended to communicate with data processing unit 510 via data bus 512. Separate memory 560 is intended to communicate with data processing unit 510 via data bus 511. Read / write memory 550 is adapted to communicate with data processing unit 510 via data bus 514. Communication between components can be achieved through communication links. Communication links can be physical connections (such as optoelectronic communication lines) or non-physical connections (such as wireless connections, such as radio links or microwave links).

[0075] When data is received on data port 599, it can be temporarily stored in the second memory element 540. Once the received input data has been temporarily stored, the data processing unit 510 is ready to execute the code as described above.

[0076] Part of the methods described herein can be implemented by the device 500 through a data processing unit 510 that runs a program stored in memory 560 or read / write memory 550. When the device 500 runs the program, the methods described herein are executed.

[0077] To demonstrate the effectiveness of the methods described herein, experimental tests were conducted to investigate the soot oxidation rate in cDPF (a catalytic coating essentially composed of Pt). The soot oxidation rate was monitored using the generated CO2. For all tests, the gas mixture used contained 6% O2 and 5% H2O, and was used for 25,000 h⁻¹. -1 The space velocity. Changing the NO concentration and the gas temperature. Since NO is inherently oxidized to NO2 in cDPF, the NO concentration can be considered as corresponding to the NOx concentration in the exhaust gas during operation of an exhaust gas aftertreatment system including a cDPF.

[0078] Figure 5a The CO2 produced varies with NO concentration at various temperatures ranging from 255°C to 506°C. Figure 5b The CO2 produced varies with NO concentration at various temperatures from 255°C to 354°C. Figure 5b Therefore, it means Figure 5a More detailed graphs of some of the test results are shown below.

[0079] like Figure 5a As shown, at higher test temperatures, the carbon soot oxidation rate increases with increasing NO concentration. However, as... Figure 5b As observed, when the NO concentration is above 600 ppm, the soot oxidation rate actually decreases with increasing NO concentration at temperatures below approximately 300°C. This indicates that the maximum NOx concentration should not be exceeded when the exhaust gas temperature is below 300°C. At approximately 300°C, there is no increase in regeneration performance when NO is increased above 600 ppm. At approximately 350°C, there is a slight increase in regeneration performance when the NO concentration exceeds 600 ppm.

[0080] Interestingly, it's noteworthy that most of the regeneration performance was achieved at a NO concentration of 300 ppm across all test temperatures up to approximately 350°C. This indicates that when exhaust gas temperatures are around 300°C or lower, NOx reduction upstream of the DPF can be very high while still achieving good passive regeneration of the DPF. Therefore, in an exhaust aftertreatment system, for example, comprising a first SCR disposed upstream and a second SCR disposed downstream of said SCR, the catalyst volume of the second SCR can be smaller to provide the desired NOx conversion, resulting in the desired tailpipe composition. A smaller second SCR not only improves vehicle fuel economy due to lower back pressure but also reduces the cost of the SCR.

Claims

1. A method (300) for controlling an exhaust gas aftertreatment system (10) executed by a control device (100), the exhaust gas aftertreatment system (10) comprising a diesel particulate filter (20) and a first selective catalytic reduction catalyst (16) disposed upstream of the diesel particulate filter (20). The method (300) includes the following steps (S103): In response to determining that the temperature of the exhaust gas entering the diesel particulate filter (20) is equal to or lower than 325°C, the NOx concentration of the exhaust gas entering the diesel particulate filter (20) is controlled to be at least 200 ppm and equal to or lower than 600 ppm by controlling the amount of reducing agent used for the first selective catalytic reduction catalyst (16).

2. The method (300) according to claim 1, wherein the exhaust aftertreatment system (10) further comprises a second selective catalytic reduction catalyst (24) disposed downstream of the diesel particulate filter (20).

3. The method (300) according to claim 2 further includes controlling the amount of reducing agent used for the second selective catalytic reduction catalyst (24) based on the desired maximum threshold tailpipe NOx concentration.

4. The method (300) according to any one of claims 1-3 further comprises the following step: In response to determining that the temperature of the exhaust gas entering the diesel particulate filter (20) has increased to a temperature equal to or higher than 350°C, the NOx concentration of the exhaust gas entering the diesel particulate filter (20) is controlled to be higher than 600 ppm.

5. A computer program product comprising instructions that, when executed by a control device (100), cause the control device (100) to perform the method according to any one of the preceding claims.

6. A computer-readable medium comprising instructions that, when executed by a control device (100), cause the control device (100) to perform the method according to any one of claims 1 to 4.

7. A control device (100) configured to control an exhaust gas aftertreatment system (10), the exhaust gas aftertreatment system (10) including a diesel particulate filter (20) and a first selective catalytic reduction catalyst (16) disposed upstream of the diesel particulate filter (20). The control device (100) is configured to, in response to determining that the temperature of the exhaust gas entering the diesel particulate filter (20) is equal to or lower than 325°C, control the NOx concentration of the exhaust gas entering the diesel particulate filter (20) to be at least 200 ppm and equal to or less than 600 ppm by controlling the amount of reducing agent used for the first selective catalytic reduction catalyst (16).

8. The control device (100) according to claim 7, wherein the exhaust aftertreatment system (10) further comprises a second selective catalytic reduction catalyst (24) disposed downstream of the diesel particulate filter (20), and The control device (100) is also configured to control the amount of reducing agent used for the second selective catalytic reduction catalyst (24) based on the desired maximum threshold tailpipe NOx concentration.

9. The control device (100) according to claim 7 or 8, wherein the control device (100) is further configured to control the NOx concentration of the exhaust gas entering the diesel particulate filter (20) to be higher than 600 ppm in response to determining that the temperature of the exhaust gas entering the diesel particulate filter (20) has increased to a temperature equal to or higher than 350°C.

10. An exhaust gas aftertreatment system (10) comprising a diesel particulate filter (20) and a control device (100) according to any one of claims 7 to 9.

11. A vehicle (1) comprising a control device (100) according to any one of claims 7 to 9.

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