Method and system for exhaust treatment device

Abstract

This invention relates to methods and systems for exhaust gas treatment equipment. Methods and systems for exhaust gas treatment equipment are provided. In one example, the system includes a dilute NO₂ disposed upstream of a selective catalytic reduction unit. x The trap, in which the air supply unit is positioned in the selective catalytic reduction unit and dilute NO x Air is injected between the traps, wherein the air supply device is activated in response to the exhaust being rich and the exhaust temperature exceeding the limit temperature.

Description

[0001] Cross-references to related applications

[0002] This application claims priority to German patent application No. 102018201868.5, filed on February 7, 2018. The entire contents of the above-mentioned application are incorporated herein by reference in their entirety for all purposes. Technical Field

[0003] This manual generally relates to adjusting the operating parameters used in selective catalytic reduction (SCR) units. Background Technology

[0004] As emission standards become more stringent, reducing NO x Increasingly attracting attention. Types of emission treatment can include nitrogen oxide storage catalysts (also known as NSR catalysts, e.g., NO...) x Storage and reduction catalysts) or dilute NO x The trap (LNT) can represent two exemplary aftertreatment devices for the catalytic conversion of nitrogen oxides. Alternative technologies may include selective catalytic reduction (SCR) devices, which utilize a reducing agent solution applied thereto to reduce nitrogen oxides.

[0005] LNT catalysts can store nitrogen oxides (NOx) at temperatures below a threshold, where the NOx stored thereon can be reduced in the presence of an air-rich / fuel mixture. Hydrocarbons and carbon monoxide can be used as reducing agents. In contrast, SCR units can increase reduction efficiency at temperatures above a threshold, thus enabling SCR and LNT to operate in series to treat NOx emissions over a wider range of exhaust temperatures.

[0006] Therefore, to meet stricter emission guidelines, it is desirable to pair LNT catalysts and SCR units in exhaust treatment systems to increase the temperature range in which nitrogen oxides can be reduced. However, this can lead to problems. In one example, the rich mixture used to reduce nitrogen oxides captured by the LNT catalyst can leak through the LNT, allowing the rich exhaust mixture to reach the SCR unit, which can reduce the life of the SCR unit.

[0007] Choung illustrates an example method for addressing a rich exhaust flow to an SCR unit in US2017 / 0167337. In this method, an air supply device is arranged upstream of the SCR catalyst. If the combustion mixture is rich (e.g., λ less than 1), air is supplied to the exhaust flow via the air supply device to increase the air-fuel ratio to greater than 1.

[0008] However, the inventors have recognized the potential problems of such systems. As an example, the air supply can lower the exhaust temperature, which can reduce the efficiency of the SCR unit and decrease the reduction of nitrogen oxides. Additionally, air can oxidize the reducing agent disposed on or injected into the SCR unit, thereby increasing the consumption of the reducing agent. Summary of the Invention

[0009] In one example, the aforementioned problem can be addressed by using dilute NO2, arranged upstream of the selective catalytic reduction catalyst in the exhaust channel. x The problem is solved by a trap system. The air supply unit is located in the dilute NO... x Between the trap and the selective catalytic reduction catalyst. The system also includes a controller storing computer-readable instructions that, when executed, cause the controller to regulate the airflow from the air supply unit when the exhaust is rich and the exhaust temperature is above a threshold. In this way, air from the air supply unit flows only when the exhaust temperature is above the threshold.

[0010] As an example, by allowing rich exhaust gas to flow to the SCR when the rich exhaust temperature is below a threshold, the SCR can continue to process nitrogen oxides during the current engine operating parameters or later engine operating parameters. Furthermore, reductant stored on or supplied to the SCR can be conserved, thereby reducing reductant consumption.

[0011] It should be understood that the above overview is provided to introduce some concepts further described in the detailed embodiments in a simplified form. These overviews are not intended to identify key or essential features of the claimed subject matter, and the scope of the claimed subject matter is uniquely defined by the appended claims. Furthermore, the claimed subject matter is not limited to embodiments that address any of the shortcomings mentioned above or in any part of this disclosure. Attached Figure Description

[0012] Figure 1 A schematic diagram of an exemplary exhaust system and an internal combustion engine is shown.

[0013] Figure 2 The progress of combustion air ratio is shown.

[0014] Figure 3 A method for processing exhaust flow is shown.

[0015] Figure 4 Additional embodiments of a method for processing exhaust flow are shown.

[0016] Figure 5 Additional embodiments of a method for processing exhaust flow are shown.

[0017] Figure 6 Show Figure 5 Further developments in the method shown.

[0018] Figure 7 The results show the temperature dependence of the converted nitrogen oxide content on different SCR catalysts.

[0019] Figure 8 A schematic diagram of an engine included in a hybrid vehicle is shown.

[0020] Figure 9 A method for selectively introducing air into the junction between the LNT and SCR catalyst is shown.

[0021] Figure 10 The engine operation sequence is shown, illustrating the adjustment of various engine operating parameters during LNT regeneration. Detailed Implementation

[0022] The following description relates to systems and methods for exhaust aftertreatment equipment. For example... Figure 1 As shown, the exhaust aftertreatment device may include dilute NO₂ upstream of the selective catalytic reduction (SCR) catalyst relative to the exhaust flow direction. x A trap (LNT). An air supply device arranged in a portion of the exhaust passage between the LNT and the SCR catalyst can be activated in response to exhaust being rich and the exhaust temperature being above the limit temperature. In one example, the air supply device is activated only in response to exhaust being rich and its temperature being above the limit temperature. A method for activating the air supply device in response to feedback from various sensors and / or condition estimation at the SCR catalyst is shown in [illustration]. Figure 3-6 middle. Figure 7 The NOx conversion efficiency of the SCR catalyst is shown at various temperatures. Figure 8 A schematic diagram of a hybrid vehicle is shown. Figure 9 An alternative method for operating an air supply device is shown. Figure 10 The engine operating sequence is shown, with various curves illustrating the adjustments made in response to other conditions.

[0023] This disclosure is based on the inventors' understanding that contact between the rich exhaust gas mixture and the SCR catalyst has an adverse effect on the performance of the SCR catalyst, especially at high temperatures, such as those commonly observed during desulfurization (DeSOx). This impairment of SCR catalyst performance can be permanent and is due to the deactivation of the catalyst material, which can be a result of the sintering process and / or reduction of copper in the SCR catalyst.

[0024] Furthermore, such damage to SCR catalyst performance is difficult to predict, and therefore can only be insufficiently accounted for when predicting the optimal amount of reductant (e.g., urea solution) to be supplied from the outside. If the performance of the SCR catalyst deteriorates due to contact with a mixture of hot, rich exhaust gas, but the same amount of urea solution is still supplied, this results in undesirable ammonia release and / or lower NOx conversion. In other words, when the SCR catalyst deteriorates due to exposure to hot, rich exhaust gas, it can be configured to store less reductant (e.g., ammonia). Therefore, the amount of urea injected into the exhaust gas can be based on the estimated catalytic activity of the SCR catalyst, which may not include SCR catalyst deterioration. Consequently, ammonia leakage from the SCR catalyst and NOx can occur. x Reduction can lower [the level of the virus].

[0025] Therefore, this disclosure relates to protecting the SCR catalyst from the effects of a rich exhaust mixture at high temperatures by supplying air to the exhaust stream upstream of the SCR catalyst via an air supply device under rich conditions and when the exhaust stream temperature exceeds a limiting temperature. Due to the oxygen contained in the air, the rich (e.g., reducing) components in the exhaust stream can be oxidized. This increases the combustion air ratio λ. Thus, the rich exhaust mixture does not reach the SCR catalyst and irreversible degradation of the SCR catalyst is prevented.

[0026] Therefore, LNT and SCR catalysts can be used together for the catalytic treatment of exhaust streams. This enables efficient catalytic treatment of exhaust streams over a wide temperature range, effectively removing nitrogen oxides from the exhaust stream while protecting the SCR catalyst from degradation and related decline in its catalytic activity.

[0027] An exhaust system according to this disclosure for receiving exhaust flow generated by an internal combustion engine includes an LNT catalyst, an air supply device disposed downstream of the LNT catalyst, an SCR or filter catalyst disposed downstream of the air supply device, a temperature sensor for determining the temperature of the exhaust flow, and a λ sensor. The λ sensor may be disposed upstream of or downstream of the LNT catalyst and upstream of the SCR catalyst, for example, upstream of or downstream of the air supply device.

[0028] If the λ sensor is not already positioned downstream of the air supply unit and upstream of the SCR catalyst, another λ sensor may optionally be positioned in this location so that the combustion air ratio of the exhaust stream supplied to the SCR catalyst can be directly determined and checked.

[0029] An alternative exhaust system for receiving exhaust flow generated by an internal combustion engine includes an LNT catalyst, an air supply unit disposed downstream of the LNT catalyst, an SCR catalyst disposed downstream of the air supply unit, a temperature sensor for determining the temperature of the exhaust flow upstream of the SCR catalyst, and a control and / or adjustment unit designed and configured to output control signals to the air supply unit based on sensor signals from the temperature sensor and according to the operating mode of the internal combustion engine.

[0030] An internal combustion engine (sometimes also called a combustion engine) is a combustion engine used to convert the chemical energy contained in fuel into mechanical work. Internal combustion engines can be constructed, for example, as self-igniting or spark-ignition engines. Gasoline or diesel fuel can be used, for example. The indicated flow direction refers to the direction of the exhaust flow from the internal combustion engine in the exhaust direction.

[0031] Possible operating modes for an internal combustion engine are rich operating mode (where a rich air / fuel mixture is supplied to the internal combustion engine), lean operating mode (where a lean air / fuel mixture is supplied to the internal combustion engine), and stoichiometric operating mode (where a stoichiometric air / fuel mixture is supplied to the internal combustion engine).

[0032] The exhaust system is formed by an exhaust pipe through which exhaust flows and a catalyst and sensors are arranged, such that the exhaust flow can also flow through the catalyst, and the properties of the exhaust flow (e.g., its composition, temperature, etc.) can be determined by the sensors.

[0033] The exhaust system includes an air supply unit. This is used to supply air to the exhaust stream upstream of the SCR catalyst. The combustion air ratio λ can be controlled or adjusted by controlling or adjusting the amount of air supplied. Furthermore, the exhaust stream temperature can be reduced through the air supply.

[0034] For example, the air supply device can be controlled based on sensor signals (such as the λ sensor described below) and temperature sensors, such that the supply of air can increase the combustion air ratio λ of the exhaust stream reaching the SCR catalyst.

[0035] If the temperature upstream of the SCR catalyst is higher than the optimal temperature (e.g., 300°C), then a temperature reduction can be particularly advantageous. This can promote higher conversion rates of nitrogen oxides and improve the durability of the SCR catalyst. The effect of a temperature reduction can be considered when controlling or adjusting the supply air volume.

[0036] A temperature sensor used to determine the exhaust gas temperature is positioned upstream of the SCR catalyst. For example, the temperature sensor can determine the exhaust gas temperature directly after it leaves the internal combustion engine. For this purpose, the temperature sensor can be positioned upstream of the LNT catalyst.

[0037] To determine the temperature of the exhaust gas reaching the SCR catalyst as accurately as possible, a temperature sensor can be positioned downstream of the air supply unit between the air supply unit and the SCR catalyst. This advantageously allows for consideration of temperature variations in the exhaust gas due to the air supply. Furthermore, the temperature sensor is preferably positioned close to the SCR catalyst upstream. This ensures thorough mixing of the exhaust gas with the supplied air before temperature determination.

[0038] A limiting temperature (e.g., an optimal temperature) can be specified, such that it varies depending on the location of the temperature sensor in the exhaust system. For example, a higher limiting temperature can be specified for a temperature sensor located upstream of the LNT catalyst than for a temperature sensor located downstream of the LNT catalyst, because in this case, cooling of the exhaust flow before reaching the SCR catalyst should be taken into account. In other words, the limiting temperature is related to the optimal temperature of the SCR catalyst used to treat nitrogen oxides, where the limiting temperature increases as the temperature sensor moves upstream and further away from the SCR catalyst, due to the cooling of the exhaust as it flows toward the SCR catalyst.

[0039] A temperature sensor determines whether the exhaust flow temperature exceeds a limiting temperature. For example, this limiting temperature could be in the range of 500°C. This limiting temperature is provided so that the air supply device is activated or kept active only when the limiting temperature is exceeded, because SCR catalyst degradation only occurs when in contact with the rich exhaust mixture at that point. In other words, even if rich exhaust is flowing, if the exhaust temperature does not exceed the limiting temperature, SCR catalyst degradation may not occur, and the air supply device can be deactivated, preventing air from flowing into the exhaust pipe.

[0040] According to this disclosure, in an alternative arrangement, the λ sensor is positioned upstream or downstream of the LNT catalyst and upstream of the air supply unit, and therefore also upstream of the SCR catalyst.

[0041] A λ sensor is a sensor that supplies a measurement signal through which the combustion air ratio λ (e.g., the ratio of the actual mass of air available for combustion to the minimum stoichiometric mass of air required for complete combustion) is determined. A λ sensor can be constructed, for example, as a λ probe that compares the residual oxygen content in the exhaust gas with the oxygen content of the ambient air at that time, thereby determining the combustion air ratio. A λ sensor can also be constructed as a NOx sensor, because in addition to determining the NOx content, such a NOx sensor can also output the combustion air ratio.

[0042] Therefore, the combustion air ratio upstream or downstream of the LNT catalyst can be determined via a λ sensor.

[0043] If a λ sensor is positioned downstream of the LNT catalyst, it can be determined whether the exhaust gas after passing through the LNT catalyst is a rich mixture (λ<1), a stoichiometric mixture (λ=1), or a lean mixture (λ>1). If a rich mixture is supplied to the LNT catalyst for regeneration, the time at which LNT catalyst regeneration can be achieved can be determined via the λ sensor, as a rich mixture can also be detected downstream at this time. This time is also known as λ breakout.

[0044] If the λ sensor detects that the combustion air ratio λ < 1 and the exhaust temperature exceeds the limit temperature, air can be supplied to the exhaust stream via the air supply device, and the combustion air ratio can be increased, for example, to a value of λ ≥ 1. For example, the air supply device can remain active as long as the λ sensor detects that the combustion air ratio λ < 1 and the exhaust temperature exceeds the limit temperature.

[0045] On the other hand, if the combustion air ratio λ>1 is detected by a λ sensor located downstream of the LNT catalyst or the exhaust temperature does not exceed the limit temperature, then the SCR catalyst is not at risk of deterioration and the exhaust can be after-treated by the SCR catalyst to remove nitrogen oxides, without airflow from the air supply unit.

[0046] Alternatively, a λ sensor can be positioned upstream of the LNT catalyst to determine the combustion air ratio λ. If a combustion air ratio λ < 1 is detected, a rich exhaust mixture (e.g., for LNT catalyst regeneration) is supplied to the exhaust system. From the time the combustion air ratio λ < 1 is detected, air can be supplied to the exhaust stream via an air supply device (e.g., activated if the exhaust stream temperature exceeds a limiting temperature). This reduces contact between the SCR catalyst and the rich exhaust stream at high temperatures.

[0047] If the combustion air ratio is λ<1, it can be expected that the combustion air ratio downstream of the LNT catalyst will also be λ<1 after a certain time span.

[0048] This time span, and therefore time t1, can be determined, for example, using online model calculations, at which time a combustion air ratio λ < 1 is expected downstream of the LNT catalyst. Such model calculations can consider, for example, the amount of nitrogen oxides and / or oxygen stored in the LNT catalyst, the rate of decrease of stored nitrogen oxides and / or stored oxygen with temperature and combustion air ratio λ, and the amount of reducing compounds supplied to the LNT catalyst, which can be determined by the combustion air ratio λ and temperature. Temperature variations within the LNT catalyst can also optionally be considered. Similar calculations can be performed on the vehicle using data stored in a multi-input lookup table.

[0049] When time t1 is reached, if the exhaust gas temperature exceeds the limit temperature, the air supply device can be activated to supply air. If the air supply device has not been activated when the combustion air ratio λ < 1, but at time t1, the air supply advantageously occurs only when actually needed. For example, undesirable cooling of the exhaust gas due to air supply can be prevented. That is, the SCR device can be pretreated with oxygen before it is estimated that the environment around the SCR device will be rich. In this way, a delay can be performed, where the delay is based on the estimated amount of time required for the exhaust gas environment around the SCR device to be rich. Once the delay has elapsed, air can flow from the air supply device to the exhaust line.

[0050] Optionally, a time t0 can be specified before time t1, wherein when time t0 is reached, the air supply device has been activated so that air has been supplied to the exhaust flow since time t0.

[0051] If the air supply device is activated at time t0, greater protection of the SCR catalyst from the rich exhaust mixture can be achieved because the air supply device is only activated when the actual air-fuel ratio λ < 1 is detected or time t1 is reached, but it has already been activated at time t0. This prevents the rich exhaust mixture from penetrating into the SCR catalyst during the response time of the air supply device (e.g., between detecting the air-fuel ratio λ < 1 or reaching time t1 and activating the air supply device).

[0052] Alternatively, if there is a request to operate the internal combustion engine in a rich operating mode, or if one of the arrival times is t1 or t0, the air supply system may already be activated. In this alternative, the use of the λ sensor can be omitted. It is not necessary to assess the combustion air ratio to activate and / or deactivate the air supply system.

[0053] In other words, when a request to operate the internal combustion engine in rich mode is received, if the combustion air ratio λ < 1 is detected by a λ sensor arranged downstream of the LNT catalyst, the air supply device is activated at time t1 or time t0 when the combustion air ratio λ < 1 is detected by a λ sensor arranged upstream of the LNT catalyst, wherein the combustion air ratio λ determined by the λ sensor arranged upstream of the LNT catalyst specifies the times t1 and t0.

[0054] On the other hand, as described below, when the combustion air ratio λ>1 is detected by the λ sensor arranged downstream of the LNT catalyst, when there is a request to operate the internal combustion engine in lean mode, when the combustion air ratio λ≥1 is detected by the λ sensor arranged upstream of the LNT catalyst, or at time t2, the air supply device is deactivated.

[0055] If the λ sensor upstream of the LNT catalyst detects a combustion air ratio λ > 1, there is no risk to the SCR catalyst, and the exhaust stream can be aftertreated by the SCR catalyst regardless of the exhaust stream temperature to remove nitrogen oxides.

[0056] With the two arrangement options for the λ sensor and an alternative variant of the exhaust system without a λ sensor, because air is supplied to the initially rich exhaust mixture, the contact between the SCR catalyst and the rich exhaust mixture at high temperatures (e.g., when exceeding the limiting temperature) can be reduced, resulting in an increased combustion air ratio. In one example, the amount of air supplied to the exhaust stream is high enough that the combustion air ratio of the exhaust stream reaching the SCR catalyst is λ > 1.

[0057] Therefore, the decrease in SCR catalyst activity due to contact with the rich exhaust mixture at high temperatures can be prevented. The efficiency of the SCR catalyst can be maintained for a relatively long period during the removal of nitrogen oxides from the exhaust stream. Furthermore, the SCR catalyst can be monitored more precisely (e.g., to determine the required amount of urea solution to be supplied and to mitigate the release of unwanted excess ammonia) because the decrease in catalyst activity caused by contact with the rich exhaust mixture at high temperatures (which would otherwise need to be considered) is mitigated. In other words, the predicted required amount of urea solution corresponds better to the actual required amount.

[0058] According to different variant embodiments, the exhaust system may include an additional λ sensor. This additional λ sensor may be arranged upstream of the LNT catalyst or downstream of the LNT catalyst and upstream of the SCR catalyst, for example, upstream of the air supply unit. If the first λ sensor is arranged upstream of the LNT catalyst, the additional λ sensor is preferably arranged downstream of the LNT catalyst and upstream of the SCR catalyst. If the first λ sensor is arranged downstream of the LNT catalyst and upstream of the SCR catalyst, the additional λ sensor is preferably arranged upstream of the LNT catalyst. In other words, the λ sensor may be arranged both upstream of the LNT catalyst and downstream of the LNT catalyst and upstream of the SCR catalyst.

[0059] Another λ sensor is also used to determine the combustion air ratio and can be constructed in the same way as the λ sensor described above, such as a λ probe or a nitrogen oxide sensor.

[0060] The air supply device can be activated based on a sensor signal from a λ sensor located upstream of the LNT catalyst. For example, when a combustion air ratio λ < 1 is detected, the air supply device can be prepared for activation (e.g., via a valve of the pre-pressurized air supply device).

[0061] Once the air supply unit is deactivated in all cases, the air-fuel ratio λ ≥ 1 downstream of the LNT catalyst is detected by a λ sensor located downstream of the LNT catalyst, or the exhaust temperature no longer exceeds the limit temperature.

[0062] Alternatively, the combustion air ratio λ can be determined again. Furthermore, it can be checked whether there are requests to operate the internal combustion engine in stoichiometric or lean operating modes. If λ ≥ 1 or such requests exist, the air supply can be deactivated.

[0063] Optionally, the time t2 at which the combustion air ratio will be λ≥1 can be estimated. If time t2 is reached, the air supply unit can be deactivated. Otherwise, the air supply unit remains active.

[0064] According to another variant embodiment, the exhaust system may also include a control and / or adjustment unit designed and configured to output control signals to the air supply device (e.g., to activate or deactivate the air supply to the exhaust flow) based on sensor signals from a temperature sensor and sensor signals from one or more λ sensors and / or the operating mode of the internal combustion engine.

[0065] Based on instructions or programming code corresponding to one or more programs, the control and / or adjustment unit receives signals from temperature sensors and one or more λ sensors and / or engine controllers (which specify the operating mode of the internal combustion engine as input data), processes these input data, and sends control signals to the air supply unit as an actuator in response to the processed input data.

[0066] Based on the exhaust gas temperature determined by a temperature sensor, the air-fuel ratio determined by a λ sensor, and / or the operating mode of the internal combustion engine, the control and / or adjustment unit can output control signals as described above. For example, if a λ sensor located downstream of the LNT catalyst detects an air-fuel ratio λ < 1 and an exhaust gas temperature exceeding a limit temperature, a control signal for activating the air supply device can be sent. If a λ sensor located upstream of the LNT catalyst detects an air-fuel ratio λ < 1 and / or an exhaust gas temperature exceeding a limit temperature, a control signal for preparing the air supply device for activation can also be sent. If time t0 is reached and the exhaust gas temperature exceeds the limit temperature, a control signal can be sent to activate the air supply device. If an air-fuel ratio λ ≥ 1 is detected, or time t2 is reached, or the exhaust gas temperature does not exceed (or no longer exceeds) the limit temperature, a control signal can be sent to deactivate the air supply device. Further configurations for outputting control signals for activating or deactivating the air supply device are disclosed in the options for activating or deactivating the air supply device explained above.

[0067] The air supply unit can be automatically controlled by a control and / or adjustment unit, enabling rapid changes between activation and deactivation of the air supply unit, and rapid response to changes in the combustion air ratio and / or exhaust temperature and / or the operating mode of the internal combustion engine.

[0068] According to another variant embodiment, the particulate filter may be arranged downstream of the LNT catalyst and upstream of the SCR catalyst (e.g., upstream of the air supply unit). The particulate filter may be configured as, for example, an uncoated diesel particulate filter (DPF), a particulate filter with a catalyst coating (CDPF), or a particulate filter with integrated SCR functionality (SDPF).

[0069] According to another variant embodiment, the exhaust system may include a supply device for supplying ammonia forming agent to the exhaust stream, which is arranged downstream of the LNT catalyst (e.g., downstream of the air supply device) and upstream of the SCR catalyst. The amount of ammonia forming agent supplied via the supply device may be controlled or adjusted, for example, based on the amount of air supplied via the air supply device and thus the amount of oxygen.

[0070] The control and / or adjustment unit may also optionally be configured and constructed to output control signals to the supply device to supply ammonia forming agent to the exhaust stream based on sensor signals from the λ sensor and the temperature sensor. The amount of ammonia forming agent supplied may be adapted to, for example, the amount of air supplied to the exhaust stream.

[0071] The motor vehicle according to this disclosure has an exhaust system as described above. A motor vehicle refers to a vehicle powered by an internal combustion engine (e.g., a land vehicle, an air vehicle, or a water vehicle). In this respect, the foregoing statements used to explain the exhaust system according to this disclosure also apply to describing the motor vehicle according to this disclosure. The advantages of the motor vehicle according to this disclosure correspond to the advantages of the exhaust system according to this disclosure and its variant embodiments.

[0072] The method for processing exhaust streams generated by an internal combustion engine according to this disclosure includes the following features, which can be performed in the stated order, but may also be performed in a different order as needed, wherein the method includes determining the temperature of the exhaust stream upstream of the SCR catalyst, passing the exhaust stream through an LNT catalyst and an SCR catalyst disposed downstream of the LNT catalyst, determining the combustion air ratio λ in the exhaust stream downstream of the LNT catalyst and upstream of the SCR catalyst, and activating an air supply device disposed downstream of the LNT catalyst and upstream of the SCR catalyst if the combustion air ratio is λ<1 and the temperature of the exhaust stream exceeds a limit temperature.

[0073] Another method for processing exhaust streams generated by an internal combustion engine according to this disclosure includes the following features, which can be performed in the stated order, but may also be performed in a different order as needed: the method includes determining the temperature of the exhaust stream upstream of the SCR catalyst, passing the exhaust stream through an LNT catalyst and an SCR catalyst disposed downstream of the LNT catalyst, determining the combustion air ratio λ of the exhaust stream upstream of the LNT catalyst, and activating an air supply device disposed downstream of the LNT catalyst and upstream of the SCR catalyst if the combustion air ratio is λ < 1 and the temperature of the exhaust stream exceeds a limit temperature.

[0074] Another method for processing exhaust flow generated by an internal combustion engine according to this disclosure includes the following features, which can be performed in the stated order, but may also be performed in a different order as needed: the method includes determining the temperature of the exhaust flow upstream of the SCR catalyst, passing the exhaust flow through the LNT catalyst and the SCR catalyst disposed downstream of the LNT catalyst, and activating an air supply device disposed downstream of the LNT catalyst and upstream of the SCR catalyst if the temperature of the exhaust flow exceeds a limit temperature and there is a request to operate the internal combustion engine in a rich operating mode.

[0075] The method according to this disclosure can be performed, for example, via one of the exhaust systems according to this disclosure as explained above. In this respect, the foregoing statements explaining the exhaust systems according to this disclosure also serve to describe the method according to this disclosure. The advantages of the method according to this disclosure correspond to the advantages of the exhaust systems according to this disclosure and their corresponding variants.

[0076] According to the method of this disclosure, changes in the combustion air ratio λ at the SCR can be predicted or estimated indirectly by means of other parameters (e.g., by means of the combustion air ratio λ upstream of the LNT or the operating mode of the internal combustion engine). In other words, there are multiple options for determining the combustion air ratio λ, i.e., by detection by sensors or by estimation by models. For example, the combustion air ratio determined based on the measurement signal from a λ sensor (e.g., a λ sensor arranged upstream or downstream of the LNT catalyst) and other combustion air ratios obtained by models can be used to control the air supply device, i.e., to determine whether to supply air to the exhaust stream.

[0077] In any case, if the temperature of the exhaust stream exceeds the limit temperature (e.g., the limit temperature of 500°C), then only air can be supplied to the exhaust stream.

[0078] Therefore, if the limiting temperature is not exceeded or no longer exceeded, the air supply will not be activated or the air supply device will be deactivated. This ensures that air is supplied only to the exhaust stream when the limiting temperature is exceeded. This prevents the SCR catalyst from deteriorating due to contact with the rich exhaust mixture at high temperatures.

[0079] According to different variant embodiments, when the exhaust temperature exceeds the limit temperature and either the combustion air ratio is λ < 1 or there is a request to operate the internal combustion engine in a rich operating mode, time t1 is estimated, and the model can also be used for time t1. If time t1 has not been reached, the air supply device remains disabled. On the other hand, if time t1 has been reached, the air supply device is activated.

[0080] Optionally, a time t0 prior to time t1 can be specified. The decision regarding whether the air supply unit is activated can then be based on the arrival of time t0 rather than time t1. If time t0 has not been reached, the air supply unit is deactivated or remains deactivated. Once time t0 is reached, the air supply unit is activated.

[0081] In other words, if a rich exhaust mixture is detected upstream of the LNT catalyst when the temperature exceeds the limit, or if there is a request to operate the internal combustion engine in a rich operating mode and a specified time t1 or t0 is subsequently reached, the air supply is activated. This prevents the rich exhaust mixture from permeating into the SCR catalyst at high temperatures, and the duration of the air supply is kept as short as possible to minimize any adverse effects of the air supply (e.g., undesirable cooling of the exhaust flow).

[0082] According to another variant embodiment, the method may further include deactivating the air supply device under certain conditions. Deactivation may occur if the temperature of the exhaust stream does not exceed the limit temperature, the combustion air ratio λ of the exhaust stream downstream of the LNT catalyst and upstream of the SCR catalyst is λ≥1, the combustion air ratio λ of the exhaust stream upstream of the LNT catalyst is λ≥1, or there is a request to operate the internal combustion engine in stoichiometric or lean operating mode.

[0083] Therefore, depending on the selected alternative, the combustion air ratio λ downstream of the LNT or the combustion air ratio λ upstream of the LNT can be determined, or a specific request for internal combustion engine operation can be made for the first, second, or consecutive time and the corresponding conditions can be checked.

[0084] Each of the methods according to this disclosure can be combined with one of the stated conditions. Decisions regarding the activation and deactivation of the air supply device can be performed based on the same parameters, making control or adjustment simple and requiring as few sensors as possible.

[0085] Therefore, if activation of the air supply unit is triggered due to exceeding the limit temperature and a request for a rich operating mode, deactivation is preferably triggered due to no longer exceeding the limit temperature or a request to operate the internal combustion engine in a stoichiometric or lean operating mode. In this combined variant, the λ sensor may be undesirable.

[0086] Further preferred combinations are determined by the downstream combustion air ratio λ or the upstream combustion air ratio λ and temperature of the LNT to decide whether to activate or deactivate it.

[0087] If the decision to deactivate the air supply is based on a combustion air ratio λ ≥ 1 upstream of the LNT or a request to operate the internal combustion engine in stoichiometric or lean operating mode, then the time t2 at which the combustion air ratio downstream of the LNT catalyst will reach λ ≥ 1 can be arbitrarily estimated. If time t2 is reached, the air supply is deactivated. If time t2 is not reached, the air supply remains active. Time t2 can also be estimated via a model.

[0088] In other words, deactivation does not occur simultaneously with the existing conditions, but rather occurs at time t2 with a time delay. Therefore, it reliably prevents contact between the SCR catalyst and the rich exhaust mixture at high temperatures.

[0089] If the combustion air ratio upstream of the LNT catalyst is λ≥1, then the estimated combustion air ratio downstream of the LNT catalyst will be λ≥1 at time t2. After time t2 is reached, it should be assumed that there is no longer a rich exhaust mixture downstream of the LNT catalyst. If time t2 is reached, the air supply device can be shut down.

[0090] Therefore, the contact between the SCR catalyst and the rich exhaust mixture at high temperatures can be reduced. Advantageously, it eliminates the need to determine the combustion air ratio λ of the exhaust stream downstream of the LNT catalyst and any sensors required for this purpose.

[0091] According to different variant embodiments, the method may further include preparing to activate the air supply device if there is a request to operate the internal combustion engine in a rich operating mode when the combustion air ratio is λ<1 upstream of the LNT or the temperature of the exhaust stream exceeds the limit temperature.

[0092] The air supply to the exhaust flow can be prepared by adjusting the air supply device (e.g., a valve on a pre-pressurized air supply device). This reduces the response time of the air supply device.

[0093] According to a further variant embodiment, the method may also include supplying an ammonia forming agent to an exhaust stream downstream of the LNT catalyst and upstream of the SCR catalyst.

[0094] The supply of the ammonia-forming mixture can be based on the exhaust gas temperature, the combustion air ratio λ upstream and / or downstream of the LNT, and / or the operating mode of the internal combustion engine. These influencing factors affect the amount of air to be supplied to the exhaust gas flow, allowing the amount of ammonia-forming agent to be supplied to be determined based on the supplied air volume. Therefore, the amount of ammonia required for exhaust gas treatment by the SCR catalyst can be supplied as precisely as possible, mitigating unwanted ammonia release.

[0095] Figure 1 Example configurations with the relative positioning of various components are shown. If elements are shown to be in direct contact or directly connected, such elements may be referred to as being in direct contact or directly connected, respectively, in at least one example. Similarly, in at least one example, elements shown to be adjacent to or next to each other may be adjacent to or next to each other, respectively. As an example, components in coplanar contact may be referred to as being in coplanar contact. As another example, in at least one example, elements positioned separately from each other with only space between them and no other components may be referred to as such. As yet another example, elements shown as being above or below each other, on opposite sides, or to the left or right of each other may be considered relative to each other. Furthermore, as shown, in at least one example, the topmost element or element point may be referred to as the “top” of the component, and the bottommost element or element point may be referred to as the “bottom” of the component. As used herein, top / bottom, up / down, above / below may be relative to the vertical axis of the drawing and used to describe the positioning of the elements in the drawing relative to each other. Thus, in one example, an element shown above other elements is positioned vertically above the other elements. As yet another example, the shapes of the elements depicted in the figure may be described as having those shapes (e.g., such as circles, straight lines, planar shapes, curved shapes, circular shapes, chamfered shapes, angled shapes, etc.). Furthermore, in at least one example, elements shown intersecting each other may be described as intersecting elements or intersecting each other. Additionally, in one example, an element shown inside another element or an element shown outside another element may be considered to be so. It should be understood that one or more components described as “fundamentally similar and / or identical” differ from each other based on manufacturing tolerances (e.g., within a 1-5% deviation).

[0096] Turn now Figure 1 The diagram schematically illustrates an exhaust system 1 connected to an internal combustion engine 2. The internal combustion engine 2 may be configured as a self-ignition engine and may operate, for example, using diesel fuel. The internal combustion engine generates an exhaust stream 3 received by the exhaust system 1. Described in the flow direction of the exhaust stream 3, the exhaust system 1 of the exemplary embodiment includes a λ sensor 9, an LNT catalyst 4, a λ sensor 8, an air supply device 5, a temperature sensor 7 for determining the temperature T of the exhaust stream 3, and an SCR catalyst 6. The exhaust stream 3 may be conducted through an exhaust duct, along which each component of the exhaust system 1 may be arranged.

[0097] Lamb sensors 8 and 9 are configured as lambda probes. Alternatively, only one lambda sensor 8 or 9 may exist.

[0098] Temperature sensor 7, λ sensor 8 and 9, and air supply device 5 are signal-connected to control and / or adjustment unit 10, which can output control signals to air supply device 5 based on the signals from λ sensor 8, 9 and temperature sensor 7.

[0099] SCR catalyst 6 may also optionally include a particulate filter function and be configured as an SDPF catalyst (e.g., a particulate filter combined with an SCR catalyst). Figure 1 As shown, a supply device 11 for supplying an ammonia-forming agent (e.g., urea solution) to the exhaust stream 3 may be arranged between the air supply device 5 and the temperature sensor 7, such that the SCR catalyst 6 can receive the amount of ammonia required for the conversion of nitrogen oxides. The supply device 11 may also be optionally controlled via a control and / or adjustment unit 10.

[0100] The combustion air ratio λ of the exhaust stream 3 leaving the internal combustion engine 2 can be specified by the corresponding engine controller. For example, the combustion air ratio λ can be greater than or equal to 1 across multiple engine operating modes. The exhaust stream 3 is then after-treated in the exhaust system 1 via the LNT catalyst 4 and SCR catalyst 6, without any additional air supplied to the exhaust stream 3 via the air supply device 5. Additional exhaust aftertreatment devices (e.g., particulate filters) may optionally be present. Alternatively, some exhaust gas can be mixed with fresh air and returned to the internal combustion engine 2 as supply air. This is called exhaust gas recirculation (EGR).

[0101] To regenerate the LNT catalyst, the internal combustion engine 2 can sometimes be operated with an air-rich / fuel mixture. Therefore, the exhaust stream 3 exiting the internal combustion engine 2 also has a combustion air ratio λ less than 1. The end of regeneration can be established by referring to a combustion air ratio λ1 < 1 downstream of the LNT catalyst 4. λ1 can correspond to feedback from the λ sensor 8. Operation of the internal combustion engine 2 with an air-rich / fuel mixture can occur until the end of regeneration, but can also be carried out over a longer time span (e.g., beyond λ breakthrough).

[0102] By means of exhaust system 1, exhaust mixtures with a combustion air ratio λ1 < 1 generated when the internal combustion engine 2 operates with an air-fuel mixture are prevented from reaching the SCR catalyst 6 at high temperatures T (i.e., temperatures exceeding the limit temperature TG). For this purpose, exhaust system 1 can be referred to as follows. Figure 2 , Figure 3 , Figure 4 Operate as described above.

[0103] Now go to Figure 2 It shows the dependence of the combustion air ratio λ over time at different locations in exhaust system 1. Curve A shows the progression of the combustion air ratio λ2, where λ2 differs from λ1 in that λ2 is sensed upstream of LNT 4 via λ sensor 9, while λ1 is sensed via... Figure 1The λ sensor 8 downstream of the LNT is sensed. First, λ2 > 1 is applied (e.g., a lean exhaust mixture is detected). At approximately 10 seconds, a lean-to-rich transition occurs, for example, the internal combustion engine 2 no longer operates with a lean air / fuel mixture but instead operates with a rich air / fuel mixture, for example, to regenerate the LNT catalyst 4. Therefore, a rich exhaust mixture is also detected upstream of the LNT catalyst 4 (e.g., λ2 < 1). At approximately 30 seconds, a rich-to-lean transition occurs (e.g., the internal combustion engine 2 now operates with a lean air / fuel mixture again). Therefore, λ2 > 1 is detected with a small time delay.

[0104] Curve C shows the desired progression of the combustion air ratio λ upstream of the SCR catalyst 6. This combustion air ratio is minimized to 1, ensuring that rich exhaust gas does not reach the SCR catalyst 6.

[0105] However, without further measures (such as air supply), the progress of the combustion air ratio λ upstream of the SCR catalyst 6 (in this case corresponding to the combustion air ratio λ1) corresponds to the progress of curve B and the rich exhaust mixture arrives at the SCR catalyst 6 in about 15 to 35 seconds.

[0106] To prevent this, air is supplied to exhaust stream 3 downstream of LNT catalyst 4 and upstream of SCR catalyst 6, the amount of which increases the combustion air ratio λ upstream of SCR catalyst 6 until it at least corresponds to curve C (e.g., at least a stoichiometric combustion air ratio exists). The amount of air or oxygen required for this is... Figure 2 The shaded area corresponds to the difference between curves C and B. Although the shaded area shows the adjustment from a rich to a stoichiometric exhaust mixture, it should be understood that the airflow rate from the air supply unit can be adjusted to increase the air-fuel ratio of the exhaust mixture to a lean ratio.

[0107] Now go to Figure 3 The diagram illustrates a flowchart of a method 300 for processing exhaust flow 3 generated by an internal combustion engine 2. Instructions for performing method 300 and the remainder of the methods included herein can be generated by a controller based on instructions stored in the controller's memory and in conjunction with information from sensors in the engine system (such as those referenced above). Figure 1 and Figure 8 The controller uses signals received by the sensor described below to perform actions. According to the method described below, the controller can employ the engine actuator of the engine system to regulate engine operation.

[0108] After the internal combustion engine 2 is started at 302, it initially operates in lean mode at 304. Furthermore, the temperature T of the exhaust stream 3 is determined and compared at 306 with a limiting temperature TG, for example, 500°C. Preferably, the temperature T of the exhaust stream 3 is compared with the limiting temperature TG immediately upstream of the SCR catalyst 6. The combustion air ratio λ2 of the exhaust stream 3 upstream of the LNT catalyst 4 is determined via a separate λ sensor 9.

[0109] If the combustion air ratio λ2 is not less than 1 and T≤TG is applied, the lean operating mode continues without further action. That is, the air supply device will not allow air to flow into the exhaust passage. On the other hand, if it is determined that the combustion air ratio λ2<1 or T>TG is applied, the air supply device 5 is ready to be activated at 308.

[0110] Furthermore, the combustion air ratio λ1 downstream of the LNT catalyst 4 and upstream of the SCR catalyst 6 is determined by the λ sensor 8. As long as the combustion air ratio λ1 is not less than 1 at 310 or T≤TG is applied, the air supply device 5 remains in a ready-to-use but off state, where its airflow rate is essentially zero at 312. The exhaust stream 3 flows through the SCR catalyst 6 without further intervention.

[0111] If the combustion air ratio λ1 < 1 and T > TG is applied, the air supply device 5 is activated at 314, supplying air to the exhaust stream 3. The air supply device 5 remains activated as long as the combustion air ratio λ1 < 1 and T > TG is applied. If the combustion air ratio λ1 ≥ 1 or T ≤ TG is applied, the air supply device 5 is deactivated again.

[0112] The sequence of alternative methods 400 for processing the exhaust flow 3 generated by the internal combustion engine 2 is as follows: Figure 4 This is illustrated schematically. (Based on...) Figure 3 Compared to the previous method, the combustion air ratio λ2 is not determined and the additional λ sensor 9 can be omitted. If a request for a rich operating mode for the internal combustion engine 2 is present at 406 (e.g., the engine controller of the internal combustion engine 2 outputs a corresponding control signal), or T>TG is applied, activation preparation of the air supply device 5 occurs. Thus, steps 402, 404, 408, 410, 412, and 414 of method 400 can be combined with... Figure 3 The steps 302, 304, 308, 310, 312 and 314 of method 300 are basically the same.

[0113] Another alternative method 500 for processing the exhaust flow 3 generated by the internal combustion engine 2 is in the following order: Figure 5 This is illustrated schematically. (Based on...) Figure 3Unlike method 300, method 500 does not provide preparation for activating the air supply device 5, although this may be optionally added. Steps 502 and 504 of method 500 are compatible with... Figure 3 The steps of method 300, 302, and 304 are basically the same.

[0114] For a combustion air ratio λ2 < 1 and T > TG at 506, the time t1 at which the combustion air ratio λ1 downstream of LNT catalyst 4 will become less than 1 is estimated by the model at 508. Furthermore, a time t0 is specified, which is prior to time t1.

[0115] If time t0 has not been reached at point 510, the air supply device 5 is deactivated or remains deactivated at point 512. The time t0 is checked again. If time t0 has been reached, the air supply device 5 is activated at point 514, supplying air to the exhaust stream 3.

[0116] according to Figure 5 Further possible advancements in Method 500 Figure 6 As shown in the diagram. This begins with activating the air supply device at 602. Therefore, air is supplied to exhaust stream 3. In the next step, the combustion air ratio λ2 at 606 and the temperature T of exhaust stream 3 at 604 are determined. If λ2 < 1 and T > TG, i.e., a rich exhaust mixture exists upstream of the LNT catalyst 4 at high temperature, the air supply device 5 remains activated and air is supplied to exhaust stream 3.

[0117] If the temperature T does not exceed the limiting temperature TG, the air supply device 5 is deactivated at 608. On the other hand, if λ2 < 1 is not applied (e.g., there is a stoichiometric or lean exhaust mixture upstream of the LNT catalyst 4), the time t2 for the combustion air ratio downstream of the LNT catalyst to be λ1 ≥ 1 is estimated at 610.

[0118] If time t2 has not been reached at 612, the air supply device 5 remains active at 602. On the other hand, if time t2 has been reached, the air supply device 5 is deactivated at 608.

[0119] Alternatively, continue according to Figure 5 Method 500, for example via Figure 1 The λ sensor 8 determines the combustion air ratio λ1 downstream of LNT catalyst 4 and upstream of SCR catalyst 6. Figure 6 (Not shown in the diagram). If the combustion air ratio λ1≥1 or T≤TG is determined to be in use, then the air supply device 5 is shut down again.

[0120] Figure 7 The diagram shows the proportion of nitrogen oxides converted under different conditions based on the temperature of the SCR catalyst, which can be used for... Figure 1In SCR catalyst 6, it can be seen that the proportion of nitrogen oxides converted by the unused SCR catalyst 6 (i.e., the catalyst pretreated at 600 °C) is approximately the same as the proportion of nitrogen oxides converted by the SCR catalyst 6 exposed to dilute conditions at 650 °C.

[0121] On the contrary, from Figure 7 It can be seen that the proportion of nitrogen oxides converted in SCR catalyst 6 (i.e., SCR catalyst 6 used according to the prior art) which is alternately exposed to dilute and rich conditions at 650 °C is significantly reduced.

[0122] Because of the air supply, SCR catalyst 6 is not exposed to undesirable rich conditions at high temperatures. Therefore, the proportion of converted nitrogen oxides corresponds to... Figure 7 The curve shown is for "SCR under lean conditions at 650°C". Compared with the curve for "SCR under lean-rich conditions at 650°C", a considerable improvement can be seen, namely, a greater proportion of nitrogen oxides are converted and emissions are reduced.

[0123] This disclosure further simplifies the monitoring of SCR catalyst 6. Typically, the ammonia storage capacity of SCR catalyst 6 is monitored to supply the optimal amount of urea solution to the SCR catalyst 6 and prevent unwanted ammonia release. In this case, the ammonia storage capacity is predicted using a model that considers the amounts of nitrogen oxides and ammonia supplied. Furthermore, normal aging of SCR catalyst 6 under lean conditions due to high temperature and the presence of water is considered. On the other hand, the decrease in SCR catalyst 6 due to the supply of a rich exhaust mixture is not considered.

[0124] This causes a deviation between the actual and predicted ammonia storage capacity in the event of a decrease due to the rich exhaust mixture. Since this disclosure substantially prevents such a decrease, this results in better consistency between the predicted and actual ammonia storage capacity. Consequently, the amount of urea solution supplied also corresponds more accurately to the required amount of urea solution, and unwanted ammonia release is prevented.

[0125] Figure 8 A schematic diagram of a hybrid vehicle system 806 is shown, which can obtain propulsion power from an engine system 808 and / or an onboard energy storage device. Operable energy conversion devices, such as generators, can absorb energy from vehicle motion and / or engine operation, and then convert the absorbed energy into an energy form suitable for storage by the energy storage device.

[0126] Engine system 808 may include engine 810 having multiple cylinders 830. In one example, engine 810 may be similar to Figure 1Engine 2 is used. Engine 810 includes an engine intake port 823 and an engine exhaust port 825. Engine intake port 823 includes an intake throttle valve 862 fluidly connected to engine intake manifold 844 via intake passage 842. Air may enter intake passage 842 via air filter 852. Engine exhaust port 825 includes an exhaust manifold 848 leading to exhaust passage 835, which directs exhaust gas to the atmosphere. Engine exhaust port 825 may include one or more emission control devices 870 mounted in a tightly coupled position. One or more emission control devices may include a three-way catalytic converter, a lean NO... x This includes components such as a filter trap, a diesel particulate filter, and an oxidation catalyst. It should be understood that other components, such as various valves and sensors, may be included in the engine, as further detailed herein. In some embodiments, where the engine system 808 is a turbocharged engine system, the engine system may also include a supercharging device, such as a turbocharger (not shown).

[0127] In one example, emission control device 870 is a first emission control device arranged upstream of second emission control device 872 relative to the exhaust flow direction. Air supply device 874 may be arranged at the junction between the first emission control device 870 and the second emission control device 872. Air supply device 874 may be activated in response to an exhaust mixture being rich and the exhaust temperature being above a limiting temperature. In some examples, air supply device 874 may be a compressor. Alternatively or additionally, air supply device 874 may be an auxiliary device configured to allow air to flow into engine exhaust port 825.

[0128] Vehicle system 806 may also include control system 814. Control system 814 is shown receiving information from a plurality of sensors 816 (various examples of which are described herein) and sending control signals to a plurality of actuators 881 (various examples of which are described herein). As an example, sensors 816 may include an exhaust gas sensor 126, a temperature sensor 128, and a pressure sensor 129 located upstream of the emission control device. Other sensors, such as additional pressure, temperature, air-fuel ratio, and composition sensors, may be coupled to various locations within vehicle system 806. As another example, actuators may include a throttle valve 862.

[0129] The controller 812 can be configured as a conventional microcomputer, including: a microprocessor unit, input / output ports, read-only memory, random access memory, keep-alive memory, a controller area network (CAN) bus, etc. The controller 812 can be configured as a powertrain control module (PCM). The controller can switch between sleep and wake-up modes to achieve additional energy efficiency. The controller can receive input data from various sensors, process the input data, and trigger actuators in response to the processed input data based on instructions or codes programmed into the controller corresponding to one or more routines.

[0130] In some examples, the hybrid vehicle 806 includes multiple torque sources available for one or more wheels 859. In other examples, the vehicle 806 is a conventional vehicle with only an engine, or an electric vehicle with only one or more electric motors. In the example shown, the vehicle 806 includes an engine 810 and an electric motor 851. The electric motor 851 may be a motor or a motor / generator (M / G). When one or more clutches 856 are engaged, the crankshaft of the engine 810 and the electric motor 851 can be connected to the wheels 859 via a transmission 854. In the depicted example, a first clutch 856 is disposed between the crankshaft and the electric motor 851, and a second clutch 856 is disposed between the electric motor 851 and the transmission 854. A controller 812 may send signals to the actuators of each clutch 856 to engage or disengage the clutch, thereby connecting or disconnecting the crankshaft from the electric motor 851 and its connected components, and / or connecting or disconnecting the electric motor 851 from the transmission 854 and its connected components. The transmission 854 may be a gearbox, a planetary gear system, or other type of transmission. The powertrain can be configured in various ways, including as a parallel, series, or series-parallel hybrid vehicle.

[0131] Motor 851 receives power from traction battery 861 to provide torque to wheel 859. Motor 851 can also operate as a generator, for example, during braking operations, to provide power to charge battery 861.

[0132] Now go to Figure 9 It shows a method 900 for adjusting the fuel content of exhaust gas upstream of an SCR unit.

[0133] Method 900 begins at 902 and may include determining, estimating, and / or measuring one or more current engine operating parameters. Current engine operating parameters may include, but are not limited to, one or more of manifold vacuum, throttle position, engine speed, vehicle speed, exhaust temperature, and air-fuel ratio.

[0134] Method 900 proceeds to 904, which may include determining whether the air-fuel ratio immediately upstream of the SCR is greater than or equal to 1. The air-fuel ratio immediately upstream of the SCR may be substantially equal to λ1 as described above. Alternatively or concurrently, the air-fuel ratio immediately upstream of the SCR may be equal to the air-fuel ratio downstream of the LNT. In some examples, the air-fuel ratio may increase after flowing through the LNT because the LNT may consume some amount of hydrocarbons in the exhaust gas during its regeneration. If the air-fuel ratio is greater than or equal to 1, method 900 proceeds to 906 to maintain the current operating parameters and not activate the air supply device.

[0135] If the air-fuel ratio is less than 1, method 900 proceeds to 908, which may include determining whether the exhaust temperature is below a limiting temperature. As mentioned above, the limiting temperature may be based on the temperature at which rich exhaust gas can degrade the SCR catalyst. In one example, the limiting temperature is equal to 500°C. If the exhaust temperature is below the limiting temperature, method 900 proceeds to 906 as described above. In this way, even if the exhaust gas flowing into the SCR unit is rich, the air supply device will not be activated because the cooling provided by the air supply device would further reduce the efficiency of the SCR used to treat nitrogen oxides. Additionally, rich exhaust gas below the limiting temperature will not degrade the performance of the SCR, which would result in no air requirement.

[0136] If the exhaust temperature is greater than or equal to the limit temperature, method 900 proceeds to 910 to activate the air supply device.

[0137] At 912, method 900 may include allowing air to flow into a portion of an exhaust passage upstream of the SCR catalyst and downstream of the LNT. In one example, the flow rate of the air supply device may be adjusted based on the air-fuel ratio. For example, the flow rate of the air supply device may be increased as the air-fuel ratio becomes richer. Alternatively or additionally, the flow rate may be set to increase the air-fuel ratio to at least a stoichiometric air-fuel ratio. In this way, by increasing the air-fuel ratio to a stoichiometric air-fuel ratio, the degradation of the SCR catalyst via hot rich exhaust gas can be mitigated. Method 900 may continue to monitor the air-fuel ratio and exhaust temperature. If an air-fuel ratio equal to or greater than 1 exists, or if the exhaust temperature is below a limiting temperature, the air supply device may be deactivated and air may no longer flow between the LNT and SCR.

[0138] In some examples of method 900, method 900 may also include a delay, wherein the delay is based on the indication that the exhaust gas is rich or the exhaust gas temperature is greater than the limit temperature at a portion of the exhaust passage upstream of the SCR catalyst, rather than at the SCR catalyst itself. Thus, the delay may be based on the amount of time required for the environment surrounding the SCR catalyst to become rich and for the temperature to exceed the limit temperature. Once both conditions are met, the delay is completed and the air supply device is activated.

[0139] Now go to Figure 10The graph 1000 illustrates the adjustment of the exhaust treatment equipment in response to one or more sensed conditions. Curve 1010 shows the LNT regeneration request, curve 1020 shows feedback from a λ sensor upstream of the LNT and dashed line 1022 shows the stoichiometric air-fuel ratio, curve 1030 shows feedback from a λ sensor downstream of the LNT and upstream of the SCR catalyst and dashed line 1032 shows the stoichiometric air-fuel ratio, dashed line 1034 shows the increased air-fuel ratio due to airflow from the air supply unit, curve 1040 shows the exhaust temperature and dashed line 1042 shows the temperature limit, and curve 1050 shows the air supply flow rate from the air supply unit. In one example, the increased air-fuel ratio is sensed by λ sensors downstream of the LNT and upstream of the SCR catalyst. Thus, when dashed line 1034 is shown, curve 1030 can represent the air-fuel ratio when no air is supplied from the air supply unit. Time increases from left to right in the graph.

[0140] Before t1, the LNT requests regeneration (curve 1010). Regeneration can occur in response to the LNT load exceeding a threshold load, based on the NOx or sulfides stored thereon. Alternatively, the threshold load can be based on elapsed time, where the nitrogen- or sulfur-containing compounds captured by the LNT are tracked over time. An air-fuel ratio measured by λ sensors upstream and downstream of the LNT is above 1, indicating that the engine is operating lean. Thus, despite the request, LNT regeneration has not yet occurred. At t1, the engine operating conditions are adjusted to rich operation so that LNT regeneration can be performed.

[0141] Between t1 and t2, LNT regeneration occurs when the λ value upstream of the LNT (e.g., λ2) drops below 1 to a rich air-fuel ratio. Hydrocarbons in the exhaust gas help desorb nitrogen oxides and convert them into nitrogen and water. However, the λ value downstream of the LNT and upstream of the SCR (e.g., λ1) can remain above 1 between t1 and t2. Thus, even if the exhaust temperature is above the limiting temperature, the flow rate from the air supply device remains essentially zero. At t2, the λ value downstream of the LNT and upstream of the SCR catalyst is equal to the stoichiometric λ value (e.g., 1). In this way, the portion of the time between t1 and t2 can represent the delay applied to activate the air supply device.

[0142] Between t2 and t3, LNT regeneration continues. The λ value upstream of the LNT continues to decrease to a richer air-fuel ratio. The λ value downstream of the LNT and upstream of the SCR catalyst decreases to below 1. Thus, the air supply flow rate increases to a positive-zero rate to mitigate the SCR catalyst's exposure to exhaust gas at temperatures above its limit. In one example, the air supply flow rate is set based on the difference between the downstream λ value of the LNT and the stoichiometric air-fuel ratio. Thus, the corrected air-fuel ratio (e.g., the actual air-fuel ratio reaching the SCR catalyst) equals 1. Thus, between t2 and t3, curve 1030 represents the exhaust gas air-fuel ratio in the absence of an air supply. In this way, SCR catalyst degradation is mitigated. At t3, as the airflow from the air supply cools the exhaust gas, the exhaust temperature can begin to decrease.

[0143] Between t3 and t4, as the λ value downstream of the LNT and upstream of the SCR catalyst further decreases below the stoichiometric air-fuel ratio, the air supply flow rate continues to increase. The exhaust temperature continues to decrease towards the limiting temperature. At t4, the exhaust temperature equals the limiting temperature.

[0144] Between t4 and t5, the exhaust temperature drops below the limit temperature. This reduces the likelihood of SCR catalyst degradation. In response, the air supply flow rate also decreases to zero. In this way, rich exhaust gas can flow to the SCR catalyst during LNT regeneration. At t5 and thereafter, LNT regeneration continues, where the λ values ​​of the exhaust gas upstream and downstream of the LNT are below stoichiometry. Because the exhaust temperature is below the limit temperature, the air supply flow rate remains zero when the air supply unit is shut down.

[0145] In this manner, in response to exhaust gas being rich and its temperature exceeding the limit temperature, the exhaust gas composition can be adjusted upstream of the SCR catalyst and downstream of the LNT. The exhaust gas composition can be adjusted via an air supply device, wherein the flow rate from the air supply device can be adjusted to increase the exhaust gas composition to at least the stoichiometric composition. When the exhaust gas is rich and its temperature is above the limit temperature, the technical effect of increasing the oxygen content of the exhaust gas flowing to the SCR unit is to mitigate the degradation of the SCR unit.

[0146] In another representation, the exhaust system for receiving the exhaust flow generated by the internal combustion engine includes an LNT catalyst, an air supply device disposed downstream of the LNT catalyst, an SCR catalyst disposed downstream of the air supply device, a temperature sensor for determining the temperature of the exhaust flow upstream of the SCR catalyst, and at least one λ sensor disposed upstream or downstream of the LNT catalyst and upstream of the SCR catalyst.

[0147] The first example of the exhaust system also includes an additional λ sensor, which is arranged upstream or downstream of the LNT catalyst and upstream of the SCR catalyst, wherein at least one λ sensor is a first λ sensor and the additional λ sensor is a second λ sensor.

[0148] A second example of an exhaust system (optionally including the first example) further includes a control and / or adjustment unit configured and constructed to output control signals to the air supply unit based on sensor signals from a temperature sensor and sensor signals from the first and second λ sensors and / or the operating mode of the internal combustion engine.

[0149] A third example of an exhaust system (optionally including the first and / or second examples) further includes an LNT catalyst, an air supply device disposed downstream of the LNT catalyst, an SCR catalyst disposed downstream of the air supply device, a temperature sensor for determining the temperature of the exhaust flow upstream of the SCR catalyst, and a control and / or adjustment unit designed and configured to output a control signal to the air supply device based on the sensor signal from the temperature sensor and the operating mode of the internal combustion engine.

[0150] A fourth example of an exhaust system (optionally including one or more of the first to third examples) also includes a particulate filter disposed downstream of the LNT catalyst and upstream of the SCR catalyst.

[0151] A fifth example of an exhaust system (optionally including one or more of the first to fourth examples) also includes a supply device arranged upstream of the SCR catalyst and downstream of the LNT catalyst for supplying ammonia forming agent to the exhaust stream.

[0152] A sixth example of an exhaust system (optionally including one or more of the first to fifth examples) further includes a control and / or adjustment unit that is further designed and configured to output control signals to a supply device to supply ammonia forming agent to the exhaust flow based on sensor signals from a temperature sensor and sensor signals from the first and second λ sensors and / or the operating mode of the internal combustion engine.

[0153] In another representation, a method for processing exhaust streams generated by an internal combustion engine includes determining the temperature T of the exhaust stream upstream of the SCR catalyst, passing the exhaust stream through an LNT catalyst and an SCR catalyst disposed downstream of the LNT catalyst, determining the combustion air ratio λ1 of the exhaust streams downstream of the LNT catalyst and upstream of the SCR catalyst, and determining if the combustion air ratio is λ1 < 1 and the exhaust stream temperature T exceeds a limiting temperature T. G This activates the air supply unit located downstream of the LNT catalyst and upstream of the SCR catalyst.

[0154] In another representation, additionally or alternatively, a method for processing exhaust streams generated by an internal combustion engine includes determining the temperature T of the exhaust stream upstream of the SCR catalyst, passing the exhaust stream through an LNT catalyst and an SCR catalyst disposed downstream of the LNT catalyst, determining the combustion air ratio λ2 of the exhaust stream upstream of the LNT catalyst, and determining if the combustion air ratio is λ2 < 1 and the exhaust stream temperature T exceeds a limiting temperature T. G This activates the air supply unit located downstream of the LNT catalyst and upstream of the SCR catalyst.

[0155] In another representation, additionally or alternatively, a method for treating exhaust streams generated by an internal combustion engine includes determining the temperature T of the exhaust stream upstream of the SCR catalyst, passing the exhaust stream through an LNT catalyst and an SCR catalyst disposed downstream of the LNT catalyst, and if the temperature T of the exhaust stream exceeds a limiting temperature To. G If there is a request to operate the internal combustion engine in a rich operating mode, the air supply device located downstream of the LNT catalyst and upstream of the SCR catalyst is activated.

[0156] A first example of one of the above methods also includes, where if the temperature T of the exhaust stream exceeds the limiting temperature T... G If the combustion air ratio is λ2<1 or there is a request to operate the internal combustion engine in a rich operating mode, then the estimated time t1 for the combustion air ratio λ1 downstream of the LNT catalyst to be λ1<1 is determined. If time t1 is not reached, the air supply device remains off, and if time t1 is reached, the air supply device is activated.

[0157] A second example of one of the above methods (optionally including the first example) further includes specifying a time t0 before time t1, wherein if time t0 is not reached, the air supply device remains deactivated, and wherein if time t0 is reached, the air supply device is activated.

[0158] A third example of one or more of the above methods (optionally including the first and / or second examples) further includes: wherein if the temperature T of the exhaust stream does not exceed the limiting temperature T G If the air-fuel ratio λ1 of the exhaust stream downstream of the LNT catalyst and upstream of the SCR catalyst is λ1≥1, or the air-fuel ratio λ2 of the exhaust stream upstream of the LNT catalyst is λ2≥1, or there is a request to operate the internal combustion engine in stoichiometric or lean operating mode, then the air supply device shall be deactivated.

[0159] A fourth example of one or more of the above methods (optionally including one or more of the first to third examples) further includes: wherein if the combustion air ratio is λ2≥1, or there is a request to operate the internal combustion engine in stoichiometric or lean operating mode, the time t2 at which the combustion air ratio downstream of the LNT catalyst will be estimated to be λ1≥1 is estimated, wherein if time t2 is reached, the air supply device is deactivated, and wherein if time t2 is not reached, the air supply device remains activated.

[0160] A fifth embodiment of one or more of the above methods (optionally including one or more of the first to fourth examples) further includes: wherein if the combustion air ratio of the exhaust stream upstream of the LNT catalyst is λ2 < 1, there is a request to operate the internal combustion engine in a rich operating mode or the temperature T of the exhaust stream exceeds the limit temperature T. G Then prepare to activate the air supply unit.

[0161] A sixth example of one or more of the above methods (optionally including one or more of the first to fifth examples) further includes: wherein an ammonia forming agent is supplied to an exhaust stream downstream of the LNT catalyst and upstream of the SCR catalyst.

[0162] One embodiment of the system includes: dilute NO upstream of a selective catalytic reduction catalyst arranged in the exhaust passage. x The trap is arranged in a rarefaction NO x An air supply device between the trap and the selective catalytic reduction catalyst, and a controller having computer-readable instructions stored thereon, which, when executed, enable the controller to: regulate the airflow from the air supply device when the exhaust is rich and the exhaust temperature is above a threshold. A first example of the system also includes: wherein the air supply device is configured to allow air to enter the selective catalytic reduction catalyst and dilute NO. x An exhaust passage upstream of the trap, wherein the airflow increases with the increase of the difference between the λ value and the stoichiometric λ in the exhaust. A second example of the system (optionally including the first example) further includes: wherein the λ value is determined by a selective catalytic reduction catalyst disposed upstream of and in dilute NO. x An exhaust gas sensor downstream of the trap provides the value. A third example of the system (optionally including the first and / or second examples) further includes: wherein the λ value is provided by an exhaust gas sensor arranged upstream of the dilute NOx trap. A fourth example of the system (optionally including one or more of the first to third examples) further includes: wherein instructions further enable the controller to respond to exhaust gas upstream of the dilute NOx trap for both rich and dilute NOx. x Between the trap and the selective catalytic reduction catalyst, the airflow from the air supply is stoichiometric or dilute and delayed, where the delay is based on dilute NO. xAn estimate of when the exhaust gas between the trap and the selective catalytic reduction catalyst will be rich. A fifth example of the system (optionally including one or more of the first to fourth examples) further includes: wherein the instruction also enables the controller to reduce the airflow from the air supply unit in response to the exhaust gas being rich and the exhaust temperature being below a threshold. A sixth example of the system (optionally including one or more of the first to fifth examples) further includes: wherein the instruction also enables the controller to respond to lean NO... x The exhaust temperature upstream of the trap is greater than the threshold and dilute NO x The exhaust temperature between the trap and the selective catalytic reduction catalyst is below a threshold to delay the airflow from the air supply unit, where the delay is based on dilute NO. x An estimate of when the exhaust temperature between the trap and the selective catalytic reduction catalyst will exceed a threshold. A seventh example of the system (optionally including one or more of the first through sixth examples) also includes: wherein the exhaust gas responds to lean NO... x The trap regeneration request is rich.

[0163] Implementations of the method include: responding to dilute NO x The lamp trap (LNT) is regenerated and air flows into the exhaust passage when the exhaust temperature in a portion of the exhaust passage between the LNT and the selective catalytic reduction (SCR) catalyst exceeds a limiting temperature. A first example of the method further includes a limiting temperature greater than 400°C. A second example of the method (optionally including the first example) further includes: air flowing into a portion of the exhaust passage in response to a λ value of the exhaust gas in that portion being lower than the stoichiometric λ. A third example of the method (optionally including the first and / or second examples) further includes: the LNT being upstream of the SCR catalyst, and the λ value being based on feedback from an exhaust gas sensor disposed upstream of the LNT or in a portion of the exhaust passage. A fourth example of the method (optionally including one or more of the first to third examples) further includes: air flow further includes activating an air supply device positioned to allow air to flow directly into a portion of the exhaust passage. A fifth example of the method (optionally including one or more of the first to fourth examples) further includes: air flow further includes adjusting the air flow rate in response to the difference between the exhaust gas air-fuel ratio and the stoichiometric air-fuel ratio in a portion of the exhaust passage. A sixth example of the method (optionally including one or more of the first to fifth examples) further includes: wherein the air flow rate increases as the difference increases.

[0164] Examples of exhaust systems for engine systems include: dilute NO₂ disposed upstream of a selective catalytic reduction (SCR) catalyst in the exhaust passage relative to the exhaust flow direction. xThe exhaust system includes a light trap (LNT), an airflow device positioned between the LNT and the SCR catalyst to directly inject air into the exhaust passage, a first sensor positioned between the LNT and the SCR catalyst, and a second sensor positioned upstream of the LNT (each of the first and second sensors is configured to sense the exhaust composition), a temperature sensor positioned between the LNT and the SCR catalyst and configured to sense the temperature of the exhaust, and a controller having computer-readable instructions stored in its non-transitory memory, which, when executed, enable the controller to activate the airflow device in response to a λ value received from the first sensor indicating that the air-fuel ratio of the exhaust is less than the stoichiometric air-fuel ratio and a temperature sensor indicating that the exhaust temperature is greater than or equal to a limiting temperature. A first example of the exhaust system further includes instructions that enable the controller to delay the activation of the airflow device in response to a λ value received from the second sensor indicating that the air-fuel ratio of the exhaust is less than the stoichiometric air-fuel ratio and a λ value received from the first sensor indicating that the air-fuel ratio of the exhaust is greater than or equal to the stoichiometric air-fuel ratio. A second example of an exhaust device (optionally including the first example) further includes: wherein the delay is based on the time elapsed until a λ value from the first sensor indicates that the air-fuel ratio is less than the stoichiometric air-fuel ratio. A third example of an exhaust device (optionally including the first and / or second examples) further includes: wherein the controller is further instructed to delay the activation of the airflow device in response to an exhaust temperature below a limiting temperature when the λ values ​​provided by the first and second sensors indicate that the air-fuel ratio is less than the stoichiometric air-fuel ratio, wherein the delay is based on the time elapsed until the exhaust temperature exceeds the limiting temperature. A fourth example of an exhaust device (optionally including one or more of the first to third examples) further includes instructions to further enable the controller to adjust the airflow rate from the airflow device based on the difference between the exhaust air-fuel ratio and the stoichiometric air-fuel ratio, wherein the airflow rate increases as the difference increases.

[0165] It should be noted that the example control and estimation routines included herein can be used with various engine and / or vehicle system configurations. The control methods and routines disclosed herein can be stored as executable instructions in non-transitory memory and can be executed by a control system including controllers and various sensors, actuators, and other engine hardware. The specific routines described herein can represent one or more of any number of processing strategies, such as event-driven, interrupt-driven, multitasking, multithreading, etc. Thus, the various actions, operations, and / or functions shown can be executed in the order shown, in parallel, or omitted in some cases. Similarly, the order of processing is not necessarily necessary to achieve the features and advantages of the example embodiments described herein, but is provided for ease of illustration and description. One or more of the shown actions, operations, and / or functions can be repeatedly executed according to the specific strategy used. Furthermore, the described actions, operations, and / or functions can be graphically represented as code to be programmed into a non-transitory memory of a computer-readable storage medium in an engine control system, wherein the described actions are performed by executing instructions in a system including various engine hardware components and electronic controllers.

[0166] It should be understood that the configurations and routines disclosed herein are exemplary in nature, and these specific embodiments should not be considered limiting, as many variations are possible. For example, the above-described techniques can be applied to V-6, I-4, I-6, V-12, opposed 4 and other engine types. The subject matter of this disclosure includes all novel and non-obvious combinations and sub-combinations of the various systems and configurations disclosed herein, as well as other features, functions and / or characteristics.

[0167] As used herein, unless otherwise stated, the term “approximately” is interpreted as meaning a range of ±5%.

[0168] The following claims specifically point to certain combinations and sub-combinations considered novel and non-obvious. These claims may refer to a "one" element or a "first" element or its equivalent. Such claims should be understood to include the incorporation of one or more such elements, neither requiring nor excluding two or more such elements. Other combinations and sub-combinations of the disclosed features, functions, elements, and / or characteristics may be claimed by amending these claims or by presenting new claims in this or related applications. Such claims, whether broader, narrower, identical, or different in scope than the original claims, are also considered to be included within the subject matter of this disclosure.

Claims

1. A system comprising: Rare NO x The trap is positioned upstream of the selective catalytic reduction catalyst in the exhaust passage; An air supply device is arranged in the dilute NO x Between the trap and the selective catalytic reduction catalyst; and A controller having computer-readable instructions stored thereon, which, when executed, cause the controller to: When the exhaust is rich and the exhaust temperature is greater than the threshold, the airflow from the air supply device is adjusted. as well as In response to the exhaust temperature upstream of the rare NOx trap being greater than the threshold and in the rare NOx trap x The exhaust temperature between the trap and the selective catalytic reduction catalyst is less than the threshold, delaying the airflow from the air supply unit, wherein the delay is based on the dilute NO. x An estimate of when the exhaust temperature between the trap and the selective catalytic reduction catalyst will exceed the threshold; The instructions further enable the controller to: respond to the exhaust gas in the dilute NO x The upstream of the trap is rich in NO and the exhaust gas is in the dilute NO x The airflow from the air supply unit is stoichiometric or dilute between the trap and the selective catalytic reduction catalyst, wherein the delay is based on the dilute NO. x An estimate of when the exhaust gas between the trap and the selective catalytic reduction catalyst will be rich; and The instructions also enable the controller to reduce the airflow from the air supply device in response to the exhaust being rich and the exhaust temperature being less than the threshold.

2. The system of claim 1, wherein the air supply device is configured to allow air to enter the selective catalytic reduction catalyst and the dilute NO. x In the exhaust passage upstream of the trap, and wherein the airflow increases as the difference between the exhaust λ value and the stoichiometric λ increases.

3. The system of claim 2, wherein the λ value is sensed by an exhaust gas sensor disposed upstream of the selective catalytic reduction catalyst and downstream of the dilute NOx trap.

4. The system according to claim 2, wherein the λ value is determined by the arrangement of the dilute NO x The exhaust sensor upstream of the trap detects the airflow.

5. The system of claim 1, wherein the exhaust gas responds to dilute NO x The trap regeneration request is rich.

6. A method comprising: In response to rare NO x The trap, i.e., the LNT, is regenerated and the exhaust temperature in a portion of the exhaust passage between the LNT and the selective catalytic reduction catalyst, i.e., the SCR catalyst, exceeds the limit temperature, causing air to flow into that portion of the exhaust passage; In response to an exhaust temperature upstream of the LNT being greater than a threshold and an exhaust temperature between the LNT and the SCR being less than the threshold, the flow of the air is delayed, wherein the delay is based on an estimate of when the exhaust temperature between the LNT and the SCR will exceed the threshold; In response to the exhaust gas in the dilute NO x The upstream of the trap is rich in NO and the exhaust gas is in the dilute NO x The flow of air is delayed between the trap and the selective catalytic reduction catalyst in a stoichiometric or dilute manner, wherein the delay is based on the dilute NO. x An estimate of when the exhaust gas between the trap and the selective catalytic reduction catalyst will be rich; and In response to the exhaust being rich and the exhaust temperature being less than the threshold, the airflow is reduced.

7. The method according to claim 6, wherein the limiting temperature is greater than 400°C.

8. The method of claim 6, further comprising: In response to the exhaust gas in the portion of the exhaust passage having a value λ lower than the stoichiometric λ, air is allowed to flow into the portion of the exhaust passage.

9. The method of claim 8, wherein the LNT is upstream of the SCR catalyst, and wherein the λ value is based on feedback from an exhaust sensor disposed upstream of the LNT or in the portion of the exhaust passage.

10. The method of claim 6, wherein causing airflow further comprises activating an air supply device, the air supply device being positioned to allow air to flow directly into said portion of the exhaust passage.

11. The method of claim 6, wherein causing airflow further comprises adjusting the airflow rate in response to the difference between the exhaust air-fuel ratio and the stoichiometric air-fuel ratio in the portion of the exhaust passage.

12. The method of claim 11, wherein the air flow rate increases as the difference increases.

13. An exhaust device for an engine system, comprising: Rare NO x The trap, or LNT, is positioned upstream of the selective catalytic reduction catalyst (SCR catalyst) in the exhaust passage, relative to the direction of the exhaust flow. An airflow device arranged between the LNT and the SCR catalyst is positioned to directly inject air into the exhaust passage; A first sensor is arranged between the LNT and the SCR catalyst, and a second sensor is arranged upstream of the LNT, each of the first and second sensors being configured to sense exhaust composition; A temperature sensor is disposed between the LNT and the SCR catalyst and is configured to sense the exhaust temperature. and A controller having computer-readable instructions stored in its non-transitory memory, which, when executed, cause the controller to: In response to a λ value received from the first sensor indicating that the exhaust air-fuel ratio is less than the stoichiometric air-fuel ratio and the temperature sensor indicating that the exhaust temperature is greater than or equal to the limit temperature, the airflow device is activated. In response to an exhaust temperature upstream of the LNT being greater than a threshold and an exhaust temperature between the LNT and the SCR being less than the threshold, activation of the airflow device is delayed, wherein the delay is based on an estimate of when the exhaust temperature between the LNT and the SCR will exceed the threshold; In response to the exhaust gas in the dilute NO x The upstream of the trap is rich in NO and the exhaust gas is in the dilute NO x Between the trap and the selective catalytic reduction catalyst, there is a stoichiometric or dilute flow rate, delaying the gas flow from the gas flow device, wherein the delay is based on the dilute NO. x An estimate of when the exhaust gas between the trap and the selective catalytic reduction catalyst will be rich; and In response to the exhaust being rich and the exhaust temperature being less than the threshold, the airflow from the airflow device is reduced.

14. The exhaust device of claim 13, wherein the instruction further enables the controller to: delay activation of the airflow device in response to a λ value received from the second sensor indicating that the air-fuel ratio of the exhaust is less than the stoichiometric air-fuel ratio and a λ value received from the first sensor indicating that the air-fuel ratio of the exhaust is greater than or equal to the stoichiometric air-fuel ratio when the exhaust temperature is greater than or equal to the limit temperature.

15. The exhaust device of claim 14, wherein the delay is based on the time elapsed until the λ value from the first sensor indicates that the air-fuel ratio is less than the stoichiometric air-fuel ratio.

16. The exhaust device of claim 13, wherein the instruction further enables the controller to: delay activation of the airflow device in response to the exhaust temperature being less than the limit temperature when the λ value provided by the first sensor and the second sensor indicates that the air-fuel ratio is less than the stoichiometric air-fuel ratio, wherein the delay is based on the time elapsed until the exhaust temperature exceeds the limit temperature.

17. The exhaust device of claim 13, wherein the instruction further enables the controller to: adjust the airflow rate from the airflow device based on the difference between the air-fuel ratio of the exhaust and the stoichiometric air-fuel ratio, wherein the airflow rate increases as the difference increases.

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