Method for operating an exhaust gas aftertreatment device for a combustion engine of a motor vehicle, in particular a motor vehicle - Patent application

Abstract

The present invention relates to a method for operating an exhaust gas aftertreatment device (10) for a combustion engine of a motor vehicle, in which the exhaust gas aftertreatment device (10) includes an oxidation catalyst (14) with a catalytic coating. The exhaust gas aftertreatment device (10) includes a heating element (16) upstream of the oxidation catalyst (14) or as a heating element provided with a catalytic coating, by means of which thermal energy can be actively introduced into the exhaust gas system at a heating point (H). The exhaust gas aftertreatment device (10) includes a metering element (18) capable of introducing a reducing agent into the exhaust gas at an introduction point (E) arranged downstream of the oxidation catalyst (14), and an SCR system (20) arranged downstream of the introduction point (E). In the proposed operating method, the extent to which a target temperature has been reached in the exhaust gas system is checked. If the target temperature is not reached, the present invention proposes a strategy for reaching the target temperature within a defined period of time using the heating element and performing post-injection.

Description

[Technical Field]

[0001] The present invention relates to a method for operating an exhaust gas aftertreatment device for a combustion engine of a motor vehicle, in particular a motor vehicle, according to the preamble of claim 1 . [Background technology]

[0002] A method for operating an exhaust gas aftertreatment device for a combustion engine (also referred to as an internal combustion engine) of a motor vehicle, particularly a motor vehicle, is already known, for example from Patent Document 1. In this method, the exhaust gas aftertreatment device, through which the exhaust gas of the combustion engine can flow, has an oxidation catalyst with a catalytic coating, which is therefore at least partially formed by the catalytic coating. The exhaust gas aftertreatment device further includes a heating element configured to actively introduce thermal energy into the exhaust gas and / or the oxidation catalyst at a heating point, thereby actively heating the exhaust gas and / or the oxidation catalyst at the heating point. The heating element is configured as a heating element located upstream of the oxidation catalyst, i.e., upstream of the catalytic coating. Therefore, the heating point may be located upstream of the oxidation catalyst or upstream of the heating point, or the heating element may be configured as a heating element provided with a catalytic coating and thus connected to or a component of the oxidation catalyst. A metering element is also provided at an introduction point located downstream of the oxidation catalyst and downstream of the heating point, which can introduce, for example, a liquid reducing agent into the exhaust gas, in particular a liquid reducing agent for exhaust gas denitrification. The exhaust gas aftertreatment device further includes an SCR system located downstream of the introduction point, which may include, among other things, an SCR catalyst and a particulate filter.

[0003] Furthermore, Patent Document 2 discloses a method for heating an exhaust gas aftertreatment system of an internal combustion engine. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] European Patent No. 3099905 [Patent Document 2] German Patent Application Publication No. 102019119123 Summary of the Invention [Problem to be solved by the invention]

[0005] The object of the invention is to further develop the method as mentioned at the outset in such a way that the exhaust gas aftertreatment device can be heated particularly advantageously and thus a particularly low-emission operation can be achieved. [Means for solving the problem]

[0006] The above problem is solved by a method with the features of claim 1. Advantageous configurations, including preferred developments of the invention, are set forth in the further claims.

[0007] In order to further develop the method as described in the preamble of claim 1 so that the exhaust gas aftertreatment device can be heated particularly advantageously and thus a very low-emission operation can be achieved, according to the invention, in a first step of the method, for example using an electronic computing device for operating, in particular for controlling or regulating, the exhaust gas aftertreatment device, if it is determined that the first temperature downstream of the heating point, i.e. the first temperature downstream of the heating element, and the second temperature of the SCR system, in particular the SCR catalyst, are below their associated target temperatures and do not exceed the component protection temperature for protecting the components of the exhaust gas aftertreatment device, and if it is determined that the minimum temperature for performing post-injection of the combustion engine has been reached or exceeded, the temperature increase by which the temperature of the SCR system must be increased, i.e. the amount by which it must be increased, so that the second temperature of the SCR system 20 at least reaches the associated target temperature, i.e. reaches or exceeds the target temperature. For example, if in the second step of the method it is determined, in particular using an electronic calculation device, that a temperature increase cannot be achieved within a predetermined time period using only a heating element, i.e., without performing a post-injection, then active heating of the exhaust gases, and thereby of the SCR system, is performed using an active heating element and by performing a post-injection of the combustion engine. However, if in the second step it is determined, in particular using an electronic calculation device, that a temperature increase can be achieved within a predetermined time period using a heating element, in particular without performing a post-injection, then active heating of the exhaust gases, and thereby of the SCR system, is performed using a heating element, but without performing a post-injection.

[0008] The method according to the present invention is therefore an operating strategy for particularly rapid heating and heat retention of an exhaust gas aftertreatment device, in particular configured as a near-engine exhaust gas device, by combining at least one active heating means in the form of a heating element with post-injection. This method, in particular, enables the exhaust gas aftertreatment device to be brought to or maintained at a target temperature favorable for exhaust gas aftertreatment particularly quickly. The invention is based, inter alia, on the following realization and consideration: Exhaust gas aftertreatment devices, also referred to as exhaust gas devices, are used to reduce engine pollutants generated by a combustion engine, for example configured as a diesel engine, and thus contained in the exhaust gas. Since the combustion engine is, for example, configured as a diesel engine, the oxidation catalyst is, for example, configured as a diesel oxidation catalyst (DOC). The catalytic coating of the oxidation catalyst is therefore configured to oxidize components contained in the exhaust gas, such as unburned hydrocarbons (HC) and carbon monoxide (CO). In particular, combustion engines, also referred to as engines, operate superstoichiometrically and therefore lean, i.e., with a superstoichiometric and therefore lean air / fuel mixture, resulting in lean exhaust gases. To purify the exhaust gases, various components and means are integrated into the exhaust system. The first means is an oxidation catalyst, which is particularly the first catalyst in the direction of exhaust gas flow through the exhaust system. The oxidation catalyst is a catalyst with an oxidation function, which can additionally have a nitrogen oxide storage function (NOx function), thus the function of a nitrogen oxide storage catalyst (NSC). For example, active heating means can be arranged upstream of the oxidation catalyst, and possibly also downstream of the oxidation catalyst. Active heating means are realized by heating devices such as the heating elements described above. Therefore, in the following, when the already mentioned or first mentioned active heating means is referred to, this is understood to mean the heating element, unless otherwise specified. The active heating means may be, for example, an electrically heatable element, which is, for example, incorporated in particular at the heating point so as to be able to release heat to the exhaust gases passing through the heating point.The electrically heatable element can be arranged upstream of the oxidation catalyst and thus upstream of the catalytic coating, or the electrically heatable element can be connected to the oxidation catalyst and therefore coated with a catalytic coating, also referred to as catalytically active material. Alternatively, instead of or in combination with one or more electrically heatable elements, other active heating means, such as a burner, can be provided, by means of which heat can be introduced into the exhaust gas, particularly at the heating point. For example, a burner can be used to combust fuel, particularly flameless or with the formation of a flame, thereby introducing heat or thermal energy into the exhaust gas at the heating point.

[0009] Downstream of the oxidation catalyst, and particularly downstream of the heating point, is an inlet point, thus a metering section, in particular a mixing section, where a reducing agent introduced into the exhaust gas is mixed with the exhaust gas. In particular, the reducing agent is a urea solution, which can be supplied with ammonia (NH3) to denitrify the exhaust gas. For example, downstream of the inlet point is an SCR system, for example, configured as a hot-end SCR system, which has at least one SCR catalyst. Each SCR catalyst is formed, for example, by an SCR block. Furthermore, the SCR system includes a particulate filter, for example, a diesel particulate filter (DPF). The particulate filter can be provided with a separate catalytic coating, which is formed as an SCR coating, and this separate catalytic coating forms a separate SCR catalyst. Thus, the particulate filter can be, for example, an SDPF. In particular, in the bottom region of the exhaust gas system, a further metering unit for introducing a reducing agent into the exhaust gas, in particular next to a further SCR catalyst as well as an ammonia slip catalyst (ASC), may be provided, by means of which the nitrogen oxides contained in the exhaust gas are additionally converted, i.e. reduced, and any resulting NH3 slip removed from the exhaust gas.

[0010] The purpose of this design is to ensure that the temperature in the exhaust system is regulated as quickly as possible, particularly by using at least one active heating means, so that the emitted pollutants are efficiently converted during further operation. However, depending on the driving conditions, the exhaust gas mass flow rate is so large that a large portion of the heat introduced into the exhaust system is removed again from the components to be heated. This can lead to slower or insufficient heating or heat retention, since the heat input capacity via the active heating means (aHM) is technically limited. As a result, exhaust gas aftertreatment can be inefficient and undesirable.

[0011] For this reason, the aforementioned operating strategy is proposed, in which the required heat input capacity is achieved by a combination of one or more active heating means and the implementation of at least one post-injection. The aim is to quickly heat the exhaust system to a temperature at which the emitted pollutants are effectively converted at least substantially completely. A first target temperature, also referred to as T_nach_aHM, which is associated with a first temperature prevailing downstream of the heating point, is, for example, 250°C. A second target temperature, also referred to as T_SCR, which is associated with a second temperature of the SCR system, in particular of the SCR catalyst, is, for example, 225°C.

[0012] For this purpose, for example, the temperature increase required for heating the exhaust gas system, also referred to as Soll_T_Hub, is first calculated, particularly as a function of the exhaust gas mass flow rate. Based on the heat input capacity, the exhaust gas mass flow rate, and the heat capacity of the exhaust gas, the amount by which the exhaust gas upstream of the SCR system, particularly upstream of the SCR catalyst, is heated by the active heating means (DeltaT_aHM) compared to the temperature upstream of the active heating means (aHM) or the temperature upstream of the active heating point is calculated. If the heat input capacity required to generate the temperature increase cannot be provided by one or more active heating means quickly enough (the control difference is greater than 0), additional heat is introduced into the exhaust gas system by post-injection. It should be noted here that post-injection is permitted as soon as T_nach_aHM reaches the required minimum temperature, for example, 250°C. Depending on the operating state, the minimum temperature may be reached significantly faster or not at all depending on the operating state of the active heating means.

[0013] At the same time, it is advantageous if the operating strategy includes other features to achieve the best results in terms of component protection and emission reduction. On the one hand, it is desirable to monitor the temperature of the active heating means, for example, configured as a heating disk, or generally of all components of the exhaust gas system, to ensure that it does not rise above the permissible maximum temperature. To prevent this, in particular, the post-injection quantity is first limited or set to zero, and then the power of the active heating means is adjusted. Furthermore, to ensure that the post-injection can be completely converted in the oxidation catalyst and to prevent an increase in pollutant emissions, particularly HC and / or CO emissions, due to a lack of oxygen in the exhaust gas, a post-injection quantity limitation in the form of a λ-dependent quantity control is used.

[0014] In an advantageous configuration of the invention, a second heating element is provided in addition to the heating element, which is designed to actively introduce thermal energy into the exhaust gas and / or the oxidation catalyst at a second heating point located downstream of the heating point, wherein the second heating element is designed as a heating element located downstream of the oxidation catalyst or as a heating element provided with a catalytic coating.

[0015] In an advantageous configuration of the invention, the particulate filter is provided with a second catalytic coating forming a second SCR catalyst.

[0016] In an advantageous embodiment of the invention, the oxidation catalytic converter is also designed to store nitrogen oxides from the exhaust gas.

[0017] Further advantages, features and details of the present invention will become apparent from the following description of preferred embodiments and from the drawings. The features and combinations of features mentioned in the above description and in the following description of the figures and / or shown only in the figures can be used not only in the respective combinations presented, but also in other combinations or alone without departing from the scope of the present invention. [Brief explanation of the drawings]

[0018] [Figure 1] 1 shows a schematic diagram of an exhaust gas aftertreatment device for a combustion engine of a motor vehicle. [Figure 2] 1 shows a block diagram for explaining a method for operating an exhaust gas aftertreatment device. DETAILED DESCRIPTION OF THE INVENTION

[0019] In the drawings, identical or functionally identical elements are designated by identical reference numbers.

[0020] FIG. 1 shows a schematic diagram of an exhaust gas aftertreatment device 10 for a combustion engine of a motor vehicle. The combustion engine is preferably configured as a diesel engine. As indicated by arrow 12 in FIG. 1 , exhaust gases can flow through the exhaust gas aftertreatment device 10. The exhaust gas aftertreatment device 10 includes an oxidation catalyst 14, for example, configured as a diesel oxidation catalyst (DOC), which has a catalytic coating and is therefore at least partially formed by the catalytic coating. The catalytic coating, and thus the oxidation catalyst 14, is configured to oxidize components contained in the exhaust gas, such as unburned hydrocarbons (HC) and carbon monoxide (CO). The exhaust gas aftertreatment device 10 also includes an active heating element 16, also referred to as an active heating means, which is configured to actively introduce thermal energy into the exhaust gas at a heating point H and via the exhaust gas to the oxidation catalyst 14. 1, the heating element is configured as a heating element arranged upstream of the oxidation catalyst 14, and thus upstream of the catalytic coating, whereby the heating element 16 is, in particular, an electrically operable heating element. It is also conceivable that the heating element 16 does not include the catalytic coating of the oxidation catalyst 14. Alternatively, it is also conceivable that the heating element 16 is, as it were, connected to the oxidation catalyst 14, in which case a catalytic coating is provided. Alternatively or additionally to the heating element 16, for example, other active heating means, such as a burner, can be used, with which, for example, fuel can be burned, thereby introducing heat into the exhaust gases, for example at heating point H.

[0021] The exhaust gas aftertreatment device 10 further comprises a metering element 18, by means of which a reducing agent, in particular a liquid, can be introduced into the exhaust gas at an introduction point E. As can be seen from FIG. 1, the introduction point E is arranged downstream of the heating point A, in this case downstream of the heating element 16 and downstream of the oxidation catalyst 14. Furthermore, the introduction point E is arranged upstream of an SCR system 20 of the exhaust gas aftertreatment device 10. The SCR system 20 comprises an SCR catalyst 22 and, in the embodiment shown in FIG. 1, a reducing agent for the SCR catalyst 22. above and a particulate filter 24 arranged on the downstream side. In particular, the particulate filter 24 is a diesel particulate filter. The particulate filter 24 may be provided with a separate catalytic coating, also referred to as an SCR coating. The SCR coating may, for example, form a separate SCR catalyst. In particular, it is conceivable that the SCR catalytic converter 22 is also formed with an SCR coating.

[0022] For example, an electronic computing device, not shown in the drawings, is provided, by means of which the exhaust gas aftertreatment device 10 can be operated, in particular adjusted. In particular, a method for operating the exhaust gas aftertreatment device 10 is carried out by means of the electronic computing device. As will be explained in more detail below, this method allows the exhaust gas aftertreatment device 10 to be heated up particularly quickly, so that the exhaust gas aftertreatment device 10 can perform an especially advantageous aftertreatment of the exhaust gases.

[0023] FIG. 2 shows a block diagram illustrating this method. In block 27, it is determined whether each target temperature of the exhaust gas aftertreatment device 10 has been reached. A first one of the target temperatures corresponds to the temperature in the exhaust gas aftertreatment device 10 downstream W of the heating point H, i.e., downstream of the heating element 16, and is also referred to as T_nach_aHM. For example, the first target temperature is 250° C. A second one of the target temperatures corresponds to the SCR system 20, e.g., 225° C. For example, if the temperature of the SCR system 20, denoted by T_SCR, is 225° C. or higher, i.e., if T_SCR corresponds to the second target temperature or is higher than the second target temperature, and T_nach_aHM is equal to or higher than 250° C., i.e., equal to or higher than the first target temperature, in block 28, no active heating of the exhaust gas aftertreatment device 10 or the exhaust gas is performed. However, if the first and second temperatures, and therefore T_nach_aHM and T_SCR, are below their associated target temperatures, and T_nach_aHM is less than 250°C and T_SCR is less than 225°C, then in block 30 it is checked whether a component protection temperature for protecting the components of the exhaust gas aftertreatment device 10 has been exceeded. If so, then in block 32 no active heating of the exhaust gas or the exhaust gas aftertreatment device 10 is performed. However, if the component protection temperature has not been reached, then in block 34 it is checked whether at least a minimum temperature for performing post-injection has been reached. For example, 250°C is used as the minimum temperature. For example, the minimum temperature is compared with T_nach_aHM. If it is determined in block 34 that the minimum temperature for performing post-injection (NE) has not been reached, i.e., for example, if it is determined in block 34 that T_nach_aHM is less than 250°C, then, for example, in block 36, the exhaust gases and thus the exhaust gas aftertreatment device 10 are actively heated, i.e., warmed, using a heating element 16, which is formed, for example, as an electrically operable heating element and is also referred to as an active heating means, and in this case, post-injection is not performed.

[0024] However, if block 34 determines that the minimum temperature for performing post-injection has been reached, i.e., here, for example, T_nach_aHM is equal to or greater than 250° C., then block 37 calculates the temperature increase by which the second temperature of the SCR system 20, also referred to as actual temperature or T_SCR, must be increased in order for the second temperature of the SCR system 20 to reach the associated target temperature, here 225° C. The temperature increase is also referred to as Soll_T-Hub and is therefore represented by the following formula: Soll_T-Hub=T_SCR_soll-T_SCR_ist

[0025] Here, T_SCR_soll represents the target temperature associated with the second temperature of the SCR system 20, here 225°C.

[0026] In block 38, the control differential is calculated. The control differential is given by: Regeldifferenz=Soll_T_Hub-DeltaT_aHM DeltaT_aHM = Heat input capacity / (exhaust gas mass flow rate CP)

[0027] The heat input capacity is understood to be the heat input capacity of the active heating means.

[0028] In block 40, it is checked whether the control difference can be achieved using active heating means, in particular without performing a post-injection. In other words, in block 40, it is checked whether the control difference is less than 0. If it is less than 0, in block 42, active heating is performed using active heating means, in particular without performing a post-injection. However, if the control difference cannot be achieved using active heating means but without a post-injection, in block 44, active heating is performed using active heating means and by performing a post-injection, in particular a late post-injection.

[0029] In particular, it is conceivable to check in block 40 whether the control difference can be achieved within a predetermined period, namely within X seconds, using only active heating means, i.e. without post-injection. If so, the method continues in block 42; if not, the method continues with the block process in block 44. In particular, X is between 100 and 200 seconds. In other words, for example, the period is in the range from 100 to 200 seconds.

Claims

1. A method for operating an exhaust gas aftertreatment device (10) for a combustion engine of a motor vehicle, comprising: The exhaust gas aftertreatment device (10) through which exhaust gas from the combustion engine can flow comprises: - an oxidation catalyst (14) having a catalytic coating; a heating element (16) designed to actively introduce thermal energy into the exhaust gas and / or the oxidation catalyst (14) at a heating point (H), the heating element (16) being designed as a heating element arranged upstream of the oxidation catalyst (14) or as a heating element provided with the catalytic coating; a metering element (18) capable of introducing a reducing agent into the exhaust gas at an introduction point (E) arranged downstream of the oxidation catalyst (14) and downstream of the heating point (H); an SCR system (20) arranged downstream of said introduction point (E) and comprising an SCR catalyst (22); A method comprising: - calculating a temperature increase by which the second temperature of the SCR system (20) must be increased in order to reach the associated target temperature if it is determined that the first temperature downstream of the heated point (H) and the second temperature of the SCR system (20) are below the respective associated target temperatures and do not exceed a component protection temperature and if a minimum temperature of the combustion engine for performing a post injection has been reached or exceeded; - if it is determined based on a control difference, which is a value obtained by subtracting a temperature rise due to the heat input capacity of the heating element (16) from the temperature rise, that the temperature rise cannot be achieved within a predetermined period using the heating element (16) without performing the post-injection, actively heating the exhaust gas using the heating element (16) and performing the post-injection, and heating the SCR system (20) by actively heating the exhaust gas; - if it is determined based on the control difference that the temperature can be increased within the predetermined period using the heating element (16) without performing the post-injection, actively heating the exhaust gas and actively heating the SCR system (20) using the heating element (16) without performing the post-injection; 10. A method comprising:

2. 2. The method according to claim 1, further comprising providing a second heating element in addition to the heating element (16), the second heating element being configured to actively introduce thermal energy into the exhaust gas and / or the oxidation catalyst (14) at a second heating point arranged downstream of the heating point (H), the second heating element being configured as a heating element arranged downstream of the oxidation catalyst (14) or as a heating element provided with the catalytic coating.

3. The method of claim 1 or 2, wherein the SCR system (20) includes a particulate filter (24) provided with a second catalytic coating forming a second SCR catalyst.

4. 2. The method of claim 1, wherein the oxidation catalyst (14) is also configured to store nitrogen oxides from the exhaust gas.

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