Urea injection control method and device

Abstract

The present invention provides a urea injection control method and device, which are applied to a two-stage SCR after-treatment system. The method comprises: obtaining a first temperature average value of a front-stage SCR, a second temperature average value of a rear-stage SCR, a first nitrogen oxide measured value upstream of the front-stage SCR, a second nitrogen oxide measured value downstream of the front-stage SCR, an exhaust flow rate, and a measured ammonia reserve of the rear-stage SCR; determining a first set urea injection amount of the front-stage SCR according to parameters such as a target mode enabled by an engine, a first temperature average value, a second temperature average value, and the like; determining a second set urea injection amount of the rear-stage SCR according to parameters such as the exhaust flow rate and the second nitrogen oxide measured value, and controlling a urea nozzle of the front-stage SCR to inject urea by using the first set urea injection amount, and controlling a urea nozzle of the rear-stage SCR to inject urea by using the second set urea injection amount, so as to reasonably distribute the urea injection amounts of the two-stage SCRs and improve the conversion efficiency of nitrogen oxides.

Description

Technical Field

[0001] The invention relates to the field of control technology, and in particular to a urea injection control method and device. Background Art

[0002] As emission regulations become more stringent, emission requirements are usually met by adopting a two-stage selective catalytic reduction (SCR) after-treatment system.

[0003] For a two-stage SCR after-treatment system, it is necessary to coordinate the control of the urea injection of the two nozzles to optimize the nitrogen oxide (NOx) conversion efficiency of the two-stage SCR after-treatment system. Therefore, a urea injection control method for a two-stage SCR after-treatment system is urgently needed to improve the NOx conversion efficiency. Summary of the invention

[0004] In view of this, an embodiment of the present invention provides a urea injection control method and device to improve NOx conversion efficiency.

[0005] To achieve the above objectives, the embodiments of the present invention provide the following technical solutions:

[0006] A first aspect of an embodiment of the present invention discloses a urea injection control method, which is applied to a dual-stage SCR post-treatment system. The method includes:

[0007] Obtaining a first temperature average value of a front-stage SCR and a second temperature average value of a rear-stage SCR in the dual-stage SCR aftertreatment system, obtaining a first nitrogen oxide measured value upstream of the front-stage SCR and a second nitrogen oxide measured value downstream of the front-stage SCR, and obtaining an exhaust gas flow rate and a measured ammonia reserve corresponding to the rear-stage SCR;

[0008] Determining a first set urea injection amount of the front-stage SCR according to a target mode enabled by the engine, the first temperature average, the second temperature average, the exhaust flow, the first nitrogen oxide measured value, and the second nitrogen oxide measured value, wherein the target mode is a regeneration mode or a normal mode;

[0009] determining a second set urea injection amount of the rear-stage SCR according to the exhaust flow rate, the second nitrogen oxide measured value, the second temperature average value and the measured ammonia reserve;

[0010] The urea nozzle of the front-stage SCR is controlled to inject urea by using the first set urea injection amount, and the urea nozzle of the rear-stage SCR is controlled to inject urea by using the second set urea injection amount.

[0011] Preferably, determining the first set urea injection amount of the front-stage SCR according to the target mode enabled by the engine, the first temperature average, the second temperature average, the exhaust flow, the first nitrogen oxide measured value, and the second nitrogen oxide measured value includes:

[0012] determining a first target efficiency of the front-stage SCR according to a target mode enabled by the engine, the first temperature average, and the second temperature average;

[0013] Determine a set value of the ammonia nitrogen ratio of the front-stage SCR by using the first temperature average, the first target efficiency, the first nitrogen oxide measured value, and the second nitrogen oxide measured value in combination with a preset specified correction coefficient;

[0014] The product of the set value of the ammonia nitrogen ratio, the exhaust flow rate and the first measured value of nitrogen oxides is calculated to obtain a first set urea injection amount of the front-stage SCR.

[0015] Preferably, determining the first target efficiency of the front-stage SCR according to the target mode enabled by the engine, the first temperature average and the second temperature average includes:

[0016] When the engine is in a normal mode, searching the efficiency setting map of the front-stage SCR according to the first temperature average and the second temperature average to obtain an efficiency base value as a first target efficiency of the front-stage SCR;

[0017] When the engine is in a regeneration mode, obtaining an oxidation catalyst temperature and a particulate filter temperature in the dual-stage SCR post-treatment system;

[0018] searching an efficiency setting map of the front-stage SCR according to the first temperature average and the second temperature average to obtain a basic efficiency value of the front-stage SCR;

[0019] According to the oxidation catalyst temperature and the particle filter temperature, searching for the efficiency correction map of the front-stage SCR to obtain the efficiency correction value of the front-stage SCR;

[0020] A sum of the efficiency base value and the efficiency correction value of the front-stage SCR is calculated to obtain a first target efficiency of the front-stage SCR.

[0021] Preferably, the ammonia nitrogen ratio setting value of the front-stage SCR is determined by using the first temperature average, the first target efficiency, the first nitrogen oxide measured value, and the second nitrogen oxide measured value in combination with a preset specified correction coefficient, including:

[0022] Using the first target efficiency and the first temperature average value to find the ammonia nitrogen ratio setting map of the front-stage SCR to obtain the required ammonia nitrogen ratio of the front-stage SCR;

[0023] Calculating a correction value of the ammonia nitrogen ratio of the front-stage SCR based on the first target efficiency, the first nitrogen oxide measured value, the second nitrogen oxide measured value and a preset specified correction coefficient;

[0024] The sum of the required ammonia nitrogen ratio of the front-stage SCR and the ammonia nitrogen ratio correction value is calculated to obtain the ammonia nitrogen ratio set value of the front-stage SCR.

[0025] Preferably, determining the second set urea injection amount of the post-stage SCR according to the exhaust flow rate, the second nitrogen oxide measured value, the second temperature average value and the measured ammonia reserve includes:

[0026] Determining a required ammonia nitrogen ratio of the post-stage SCR by using the second nitrogen oxide measured value and the second temperature average value;

[0027] Calculating the product of the exhaust flow rate, the second nitrogen oxide measured value and the required ammonia nitrogen ratio of the rear-stage SCR to obtain the required urea injection amount of the rear-stage SCR;

[0028] Using the measured ammonia reserve, searching a urea injection amount correction data table of the rear-stage SCR to obtain a urea injection amount correction value of the rear-stage SCR;

[0029] The difference between the required urea injection amount of the post-stage SCR and the urea injection amount correction value is calculated to obtain a second set urea injection amount of the post-stage SCR.

[0030] Preferably, using the second nitrogen oxide measured value and the second temperature average value to determine the required ammonia nitrogen ratio of the post-stage SCR includes:

[0031] Using the second nitrogen oxide measured value, searching the required conversion efficiency setting data table of the subsequent SCR to obtain the required conversion efficiency of the subsequent SCR;

[0032] The ammonia nitrogen ratio setting map of the rear-stage SCR is searched by using the second temperature average value and the required conversion efficiency of the rear-stage SCR to obtain the required ammonia nitrogen ratio of the rear-stage SCR.

[0033] A second aspect of an embodiment of the present invention discloses a urea injection control device, which is applied to a two-stage SCR post-treatment system. The device includes:

[0034] an acquisition unit, configured to acquire a first temperature average value of a front-stage SCR and a second temperature average value of a rear-stage SCR in the dual-stage SCR aftertreatment system, acquire a first nitrogen oxide measured value upstream of the front-stage SCR and a second nitrogen oxide measured value downstream of the front-stage SCR, and acquire an exhaust gas flow rate and an actually measured ammonia reserve corresponding to the rear-stage SCR;

[0035] a first determining unit, configured to determine a first set urea injection amount of the front-stage SCR according to a target mode enabled by the engine, the first temperature average, the second temperature average, the exhaust flow rate, the first nitrogen oxide measured value, and the second nitrogen oxide measured value, wherein the target mode is a regeneration mode or a normal mode;

[0036] a second determining unit, configured to determine a second set urea injection amount of the post-stage SCR according to the exhaust flow rate, the second nitrogen oxide measured value, the second temperature average value and the measured ammonia reserve;

[0037] The control unit is used for controlling the urea nozzle of the front-stage SCR to inject urea by using the first set urea injection amount, and controlling the urea nozzle of the rear-stage SCR to inject urea by using the second set urea injection amount.

[0038] Preferably, the first determining unit includes:

[0039] A first determination module, configured to determine a first target efficiency of the front-stage SCR according to a target mode enabled by the engine, the first temperature average, and the second temperature average;

[0040] a second determination module, configured to determine a set value of the ammonia nitrogen ratio of the front-stage SCR by using the first temperature average, the first target efficiency, the first nitrogen oxide measured value, the second nitrogen oxide measured value, and a preset specified correction coefficient;

[0041] The calculation module is used to calculate the product of the set value of the ammonia nitrogen ratio, the exhaust flow rate and the first nitrogen oxide measured value to obtain a first set urea injection amount of the front-stage SCR.

[0042] Preferably, the first determining module is specifically used for:

[0043] When the engine is in a normal mode, searching the efficiency setting map of the front-stage SCR according to the first temperature average and the second temperature average to obtain an efficiency base value as a first target efficiency of the front-stage SCR;

[0044] When the engine is in a regeneration mode, obtaining an oxidation catalyst temperature and a particulate filter temperature in the dual-stage SCR post-treatment system;

[0045] searching an efficiency setting map of the front-stage SCR according to the first temperature average and the second temperature average to obtain a basic efficiency value of the front-stage SCR;

[0046] According to the oxidation catalyst temperature and the particle filter temperature, searching for the efficiency correction map of the front-stage SCR to obtain the efficiency correction value of the front-stage SCR;

[0047] A sum of the efficiency base value and the efficiency correction value of the front-stage SCR is calculated to obtain a first target efficiency of the front-stage SCR.

[0048] Preferably, the second determining module is specifically used for:

[0049] Using the first target efficiency and the first temperature average value to find the ammonia nitrogen ratio setting map of the front-stage SCR to obtain the required ammonia nitrogen ratio of the front-stage SCR;

[0050] Calculating a correction value of the ammonia nitrogen ratio of the front-stage SCR based on the first target efficiency, the first nitrogen oxide measured value, the second nitrogen oxide measured value and a preset specified correction coefficient;

[0051] The sum of the required ammonia nitrogen ratio of the front-stage SCR and the ammonia nitrogen ratio correction value is calculated to obtain the ammonia nitrogen ratio set value of the front-stage SCR.

[0052] A urea injection control method and device provided based on the above-mentioned embodiment of the present invention are applied to a two-stage SCR aftertreatment system. The method comprises: obtaining a first temperature average value of a front-stage SCR and a second temperature average value of a rear-stage SCR in the two-stage SCR aftertreatment system, obtaining a first nitrogen oxide measured value upstream of the front-stage SCR and a second nitrogen oxide measured value downstream of the front-stage SCR, and obtaining an exhaust flow rate and a measured ammonia reserve corresponding to the rear-stage SCR; determining a first set urea injection amount of the front-stage SCR according to a target mode enabled by the engine, a first temperature average value, a second temperature average value, an exhaust flow rate, a first nitrogen oxide measured value, and a second nitrogen oxide measured value; determining a second set urea injection amount of the rear-stage SCR according to the exhaust flow rate, the second nitrogen oxide measured value, the second temperature average value, and the measured ammonia reserve; controlling a urea nozzle of the front-stage SCR to perform urea injection by using the first set urea injection amount, and controlling a urea nozzle of the rear-stage SCR to perform urea injection by using the second set urea injection amount. In this scheme, the first temperature average of the front SCR, the second temperature average of the rear SCR, the first nitrogen oxide measured value upstream of the front SCR, the second nitrogen oxide measured value downstream of the front SCR and other parameters in the two-stage SCR post-treatment system are obtained, and the first set urea injection amount of the front SCR and the second set urea injection amount of the rear SCR are determined by the above-mentioned parameters. The first set urea injection amount and the second set urea injection amount are used to control the urea nozzles of the front SCR and the rear SCR to perform urea injection respectively, and the urea injection amount of the two-stage SCR is reasonably allocated to improve the conversion efficiency of nitrogen oxides. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0054] Figure 1 A structural example diagram of a dual-stage SCR post-treatment system provided in an embodiment of the present invention;

[0055] Figure 2 A flow chart of a urea injection control method provided by an embodiment of the present invention;

[0056] Figure 3 A logic example diagram for determining a first set urea injection amount of a front-stage SCR provided in an embodiment of the present invention;

[0057] Figure 4 A logic example diagram for determining a second set urea injection amount of a rear-stage SCR provided in an embodiment of the present invention;

[0058] Figure 5 A structural block diagram of a urea injection control device provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0059] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0060] In this application, the terms "comprises", "comprising" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, an element defined by the sentence "comprising a ..." does not exclude the presence of other identical elements in the process, method, article or device comprising the element.

[0061] To facilitate understanding of the following content, some terms are explained below:

[0062] DOC (diesel oxidation catalyst): oxidation catalyst;

[0063] DPF (Diesel Particulate Filter): particle filter;

[0064] SCR (Selective Catalytic Reduction): Selective Catalytic Reduction;

[0065] ASC (Ammonia Slip Catalyst): Ammonia slip catalyst;

[0066] TC: turbocharger;

[0067] DEF: Urea nozzle;

[0068] NOx: Nitrogen oxides (or nitrogen oxides);

[0069] Ammonia nitrogen ratio: the molar ratio of NH3 in urea to NOx in engine exhaust. The actual injection amount of urea can be calculated by controlling the size of the ammonia nitrogen ratio to make the engine's NOx emission level meet the standard.

[0070] As can be seen from the background technology, as emission regulations become more stringent, emission requirements are usually met by adopting a dual-stage SCR after-treatment system. For the dual-stage SCR after-treatment system, it is necessary to coordinate and control the urea injection of the two nozzles to optimize the nitrogen oxide (NOx) conversion efficiency of the dual-stage SCR after-treatment system.

[0071] The study found that the current control method for the two-stage SCR after-treatment system is relatively simple, usually by giving a smaller ammonia-nitrogen ratio to the front-stage SCR for urea injection, and using the rear-stage SCR to ensure emissions. However, the NOx conversion efficiency of the above method is not high, and it is easy to cause ammonia leakage, and the emission robustness is poor.

[0072] In order to solve the above problems, this scheme proposes a urea injection control method and device, which obtains the first temperature average of the front-stage SCR, the second temperature average of the rear-stage SCR, the first nitrogen oxide measured value upstream of the front-stage SCR, the second nitrogen oxide measured value downstream of the front-stage SCR and other parameters in the two-stage SCR after-treatment system, and determines the first set urea injection amount of the front-stage SCR and the second set urea injection amount of the rear-stage SCR through the above-mentioned parameters. The first set urea injection amount and the second set urea injection amount are used to control the urea nozzles of the front-stage SCR and the rear-stage SCR to perform urea injection respectively, and the urea injection amount of the two-stage SCR is reasonably allocated to improve the conversion efficiency of nitrogen oxides.

[0073] It should be noted that the urea injection control method and device proposed in this scheme are applied to a two-stage SCR post-treatment system, such as Figure 1 As can be seen from the structural example diagram of the two-stage SCR after-treatment system, a set of "SCR+ASC" is added to the front section of "DOC-DPF-SCR-ASC" to form a two-stage SCR after-treatment system. The SCR in the two-stage SCR after-treatment system is divided into a front-stage SCR and a rear-stage SCR.

[0074] See also Figure 2 , shows a flow chart of a urea injection control method provided by an embodiment of the present invention, the urea injection control method is applied to a dual-stage SCR post-treatment system, and the urea injection control method includes:

[0075] Step S201: Obtain a first temperature average value of the front-stage SCR and a second temperature average value of the rear-stage SCR in the two-stage SCR aftertreatment system, obtain a first nitrogen oxide measured value upstream of the front-stage SCR and a second nitrogen oxide measured value downstream of the front-stage SCR, and obtain the exhaust flow rate and the measured ammonia reserve corresponding to the rear-stage SCR.

[0076] Depend on Figure 1It can be seen from the shown content that the two-stage SCR after-treatment system includes a front-stage SCR, a rear-stage SCR, a DOC (oxidation catalyst) and a DPF (particulate filter), etc. In the specific implementation of step S201, the following parameters are obtained: a first temperature average of the front-stage SCR, a second temperature average of the rear-stage SCR, a first nitrogen oxide measured value upstream of the front-stage SCR, a second nitrogen oxide measured value downstream of the front-stage SCR, an exhaust flow rate, and a measured ammonia reserve corresponding to the rear-stage SCR.

[0077] Among them, the first temperature average of the front-stage SCR is called the front-stage SCR temperature average, the second temperature average of the rear-stage SCR is called the rear-stage SCR temperature average, the first nitrogen oxide measured value upstream of the front-stage SCR is called the front-stage SCR upstream NOx measured value, the second nitrogen oxide measured value downstream of the front-stage SCR is called the front-stage SCR downstream NOx measured value, and the measured ammonia reserve corresponding to the rear-stage SCR is called the rear-stage SCR carrier measured ammonia reserve.

[0078] It should be noted that the exhaust gas flow rates passing through the front-stage SCR and the rear-stage SCR are the same, so the exhaust gas flow rate is the exhaust gas flow rate passing through the front-stage SCR and the rear-stage SCR (the unit may be kg / h).

[0079] In addition, the NOx measured value downstream of the front-stage SCR is consistent with the NOx measured value upstream of the rear-stage SCR, so the second nitrogen oxide measured value downstream of the front-stage SCR is also equivalent to the NOx measured value upstream of the rear-stage SCR.

[0080] Based on the first temperature average value, the second temperature average value, the first nitrogen oxide measured value and other parameters obtained above, respectively determining a first set urea injection amount of the front-stage SCR and a second set urea injection amount of the rear-stage SCR;

[0081] The manner of determining the first set urea injection amount is detailed in step S202 , and the manner of determining the second set urea injection amount is detailed in step S203 .

[0082] Step S202: determining a first set urea injection amount of the front-stage SCR according to the target mode enabled by the engine, the first temperature average, the second temperature average, the exhaust flow, the first nitrogen oxide measured value, and the second nitrogen oxide measured value.

[0083] It should be noted that the target mode is the regeneration mode or the normal mode.

[0084] In the specific implementation of step S202, a first target efficiency of the front-stage SCR is determined according to the target mode enabled by the engine, the first temperature average and the second temperature average, wherein the first target efficiency is also referred to as the front-stage SCR target efficiency;

[0085] Determine the ammonia nitrogen ratio setting value of the front-stage SCR by using the first temperature average, the first target efficiency, the first nitrogen oxide measured value, and the second nitrogen oxide measured value in combination with a preset designated correction coefficient, wherein the designated correction coefficient is a NOx difference correction coefficient;

[0086] The product of the ammonia nitrogen ratio setting value of the front-stage SCR, the exhaust flow rate and the first nitrogen oxide measured value is calculated to obtain the first set urea injection amount of the front-stage SCR, that is, the first set urea injection amount=ammonia nitrogen ratio setting value*exhaust flow rate*first nitrogen oxide measured value.

[0087] In some embodiments, the method of determining the first target efficiency is different according to the target mode of engine activation; when the target mode of engine activation is normal mode, the first target efficiency is determined by a first determination method; when the target mode of engine activation is regeneration mode, the first target efficiency is determined by a second determination method; the first determination method and the second determination method are explained respectively below.

[0088] The first determination method: when the engine is in normal mode, the efficiency setting map of the front-stage SCR is searched according to the first temperature average and the second temperature average to obtain an efficiency base value as the first target efficiency of the front-stage SCR.

[0089] That is, if the engine is in normal mode, the first temperature average and the second temperature average are used to find the efficiency setting map of the front-stage SCR to obtain the efficiency base value of the front-stage SCR. At this time, the first target efficiency of the front-stage SCR = the efficiency base value of the front-stage SCR.

[0090] The second determination method: when the engine enables the regeneration mode, the oxidation catalyst temperature and the particulate filter temperature in the two-stage SCR aftertreatment system are obtained; the efficiency setting map of the front-stage SCR is searched according to the first temperature average and the second temperature average to obtain the efficiency base value of the front-stage SCR; according to the oxidation catalyst temperature (DOC temperature) and the particulate filter temperature (DPF temperature), the efficiency correction map of the front-stage SCR is searched to obtain the efficiency correction value of the front-stage SCR; the sum of the efficiency base value and the efficiency correction value of the front-stage SCR is calculated to obtain the first target efficiency of the front-stage SCR.

[0091] That is, if the engine starts the regeneration mode, the efficiency setting map of the front-stage SCR is searched according to the first temperature average and the second temperature average to obtain the efficiency base value of the front-stage SCR; and the efficiency correction map of the front-stage SCR is searched according to the oxidation catalyst temperature and the particulate filter temperature to obtain the efficiency correction value of the front-stage SCR;

[0092] At this time, the first target efficiency of the front-stage SCR=the efficiency base value of the front-stage SCR+the efficiency correction value of the front-stage SCR.

[0093] The above is an explanation of two methods for determining the first target efficiency.

[0094] In some embodiments, for the ammonia nitrogen ratio setting value of the front-stage SCR (referred to as the ammonia nitrogen ratio setting value of the front-stage SCR), the specific method of determining the ammonia nitrogen ratio setting value of the front-stage SCR is:

[0095] Using the first target efficiency and the first temperature average value, searching for the ammonia nitrogen ratio setting map of the front-stage SCR to obtain the required ammonia nitrogen ratio of the front-stage SCR (also referred to as the front-stage SCR required ammonia nitrogen ratio);

[0096] Calculating a pre-stage SCR ammonia nitrogen ratio correction value (also referred to as a pre-stage SCR ammonia nitrogen ratio correction value) based on a first target efficiency, a first nitrogen oxide measured value, a second nitrogen oxide measured value, and a preset specified correction coefficient;

[0097] The sum of the required ammonia nitrogen ratio of the preceding SCR and the correction value of the ammonia nitrogen ratio is calculated to obtain the set value of the ammonia nitrogen ratio of the preceding SCR, that is, the set value of the ammonia nitrogen ratio of the preceding SCR = the required ammonia nitrogen ratio of the preceding SCR + the correction value of the ammonia nitrogen ratio of the preceding SCR.

[0098] In some embodiments, the process of determining the correction value of the ammonia nitrogen ratio of the front-stage SCR is: calculating the product of the first target efficiency and the first nitrogen oxide measured value; and then calculating the difference between the "first nitrogen oxide measured value" and the "product of the first target efficiency and the first nitrogen oxide measured value" to obtain the NOx target value downstream of the front-stage SCR;

[0099] Calculate the difference between the second nitrogen oxide measured value and the NOx target value downstream of the front-stage SCR to obtain a NOx difference value, wherein the NOx difference value=the second nitrogen oxide measured value-the NOx target value downstream of the front-stage SCR;

[0100] Then calculate the product of the NOx difference and the specified correction coefficient to obtain the ammonia nitrogen ratio correction value of the front-stage SCR, that is, the ammonia nitrogen ratio correction value of the front-stage SCR = the NOx difference * the specified correction coefficient.

[0101] Step S203: determining a second set urea injection amount of the post-stage SCR according to the exhaust flow rate, the second nitrogen oxide measured value, the second temperature average value and the measured ammonia reserve.

[0102] In the specific implementation of step S203, the required ammonia nitrogen ratio of the post-stage SCR (also referred to as the required ammonia nitrogen ratio of the post-stage SCR) is determined by using the second nitrogen oxide measured value and the second temperature average value;

[0103] Calculate the product of the exhaust flow rate, the second nitrogen oxide measured value and the required ammonia nitrogen ratio of the rear-stage SCR to obtain the required urea injection amount of the rear-stage SCR, that is, the required urea injection amount of the rear-stage SCR = exhaust flow rate * the second nitrogen oxide measured value * the required ammonia nitrogen ratio of the rear-stage SCR;

[0104] Using the measured ammonia reserve, a urea injection amount correction data table of the post-stage SCR (called post-stage SCR urea injection amount correction CUR based on ammonia reserve) is searched to obtain a urea injection amount correction value of the post-stage SCR, wherein CUR represents a one-dimensional data table;

[0105] The difference between the required urea injection amount of the rear SCR and the urea injection amount correction value is calculated to obtain the second set urea injection amount of the rear SCR, that is, the second set urea injection amount of the rear SCR=the required urea injection amount of the rear SCR-the urea injection amount correction value of the rear SCR.

[0106] In some embodiments, with respect to the required ammonia nitrogen ratio of the rear-stage SCR, the specific process of determining the required ammonia nitrogen ratio of the rear-stage SCR is as follows: using the second nitrogen oxide measured value to search the required conversion efficiency setting data table of the rear-stage SCR (referred to as the rear-stage SCR required conversion efficiency setting CUR) to obtain the required conversion efficiency of the rear-stage SCR;

[0107] It should be noted that the required conversion efficiency setting data table of the post-stage SCR includes the corresponding relationship between the second nitrogen oxide actual measured value and the required conversion efficiency.

[0108] The second temperature average and the required conversion efficiency of the rear-stage SCR are used to find the ammonia nitrogen ratio setting map of the rear-stage SCR (also referred to as the rear-stage SCR ammonia nitrogen ratio setting map) to obtain the required ammonia nitrogen ratio of the rear-stage SCR.

[0109] Step S204: using the first set urea injection amount to control the urea nozzle of the front-stage SCR to perform urea injection, and using the second set urea injection amount to control the urea nozzle of the rear-stage SCR to perform urea injection.

[0110] In the specific implementation of step S204, after the first set urea injection amount and the second set urea injection amount are determined by the above steps S202 and S203, the urea nozzle of the front-stage SCR is controlled to inject urea by the first set urea injection amount, and the urea nozzle of the rear-stage SCR is controlled to inject urea by the second set urea injection amount.

[0111] In the embodiment of the present invention, the first temperature average of the front-stage SCR, the second temperature average of the rear-stage SCR, the first nitrogen oxide measured value upstream of the front-stage SCR, the second nitrogen oxide measured value downstream of the front-stage SCR and other parameters are obtained in the two-stage SCR post-treatment system, and the first set urea injection amount of the front-stage SCR and the second set urea injection amount of the rear-stage SCR are determined by the above-mentioned parameters. The first set urea injection amount and the second set urea injection amount are used to control the urea nozzles of the front-stage SCR and the rear-stage SCR to perform urea injection respectively, and the urea injection amount of the two-stage SCR is reasonably allocated to improve the conversion efficiency of nitrogen oxides, reduce the emission of pollutant gases, and improve emission robustness.

[0112] Through the above Figure 2 As can be seen from the contents of each step, this scheme determines the first set urea injection amount of the front-stage SCR and the second set urea injection amount of the rear-stage SCR respectively. To better understand how to determine the first set urea injection amount and the second set urea injection amount, Figure 3 and Figure 4 Provide detailed explanation.

[0113] See also Figure 3 , shows a logic example diagram for determining the first set urea injection amount of the front-stage SCR, Figure 3 The logic for determining the first set urea injection amount is shown as follows:

[0114] Based on the first temperature average value (the temperature average value of the front-stage SCR) and the second temperature average value (the temperature average value of the rear-stage SCR), the efficiency setting map of the front-stage SCR is searched to obtain the efficiency base value of the front-stage SCR;

[0115] According to the oxidation catalyst temperature (DOC temperature) and the particulate filter temperature (DPF temperature), the efficiency correction map of the front-stage SCR is searched to obtain the efficiency correction value of the front-stage SCR;

[0116] When the engine is in normal mode, Figure 3 The switch of the "switch" logic block in is in the default state, at which time the first target efficiency of the front-stage SCR (the front-stage SCR target efficiency) = the efficiency base value of the front-stage SCR;

[0117] When the engine is in the regeneration mode, the first target efficiency of the front-stage SCR (the front-stage SCR target efficiency) = the efficiency base value of the front-stage SCR + the efficiency correction value of the front-stage SCR.

[0118] It should be noted that Figure 3 The purpose of the "regeneration mode status" logic block in is: when the engine is in the regeneration mode, the "regeneration mode status" logic block outputs 1; when the engine is in the normal mode, the "regeneration mode status" logic block outputs 0;

[0119] When the "Regeneration Mode Status" logic block outputs 0, Figure 3 The switch of the "switch" logic block in the regeneration mode is closed upward; when the "regeneration mode status" logic block outputs 1, Figure 3 The switch of the "Switch" logic block in is closed downward.

[0120] The ammonia nitrogen ratio setting map of the front-stage SCR is found by using the first target efficiency (the front-stage SCR target efficiency) and the first temperature average (the front-stage SCR temperature average) to obtain the required ammonia nitrogen ratio of the front-stage SCR.

[0121] The NOx target value downstream of the front-stage SCR is obtained by using the first target efficiency (the front-stage SCR target efficiency) and the first nitrogen oxide measured value (the NOx measured value upstream of the front-stage SCR);

[0122] The difference between the second nitrogen oxide measured value (the NOx measured value downstream of the front-stage SCR) and the NOx target value downstream of the front-stage SCR is calculated to obtain the NOx difference; the NOx difference is multiplied by a specified correction coefficient (i.e., the NOx difference correction coefficient) to obtain the ammonia nitrogen ratio correction value of the front-stage SCR.

[0123] The ammonia nitrogen ratio setting value of the front-stage SCR = the ammonia nitrogen ratio correction value of the front-stage SCR + the required ammonia nitrogen ratio of the front-stage SCR;

[0124] The product of the set value of the ammonia nitrogen ratio of the front-stage SCR, the exhaust flow rate and the first nitrogen oxide measured value is calculated and converted into units to obtain a first set urea injection amount of the front-stage SCR, and the urea nozzle of the front-stage SCR is controlled to inject urea according to the first set urea injection amount.

[0125] The above is an explanation of the logic for determining the first set urea injection amount of the front-stage SCR. Figure 3 For the specific execution principle in the embodiment of the present invention, please refer to the above Figure 2 The content in step S202 is not repeated here.

[0126] pass Figure 3 It can be seen from the shown content that the target efficiency of the front-stage SCR (equivalent to the conversion efficiency of the front-stage SCR) is determined based on the temperature average of the front-stage SCR and the rear-stage SCR, and the correction of the DOC temperature and the DPF temperature is added when the regeneration mode is enabled, which can effectively control the optimal efficiency distribution; and based on the NOx closed loop downstream of the front-stage SCR, efficient and accurate control of the front-stage SCR can be achieved.

[0127] See also Figure 4 , shows a logic example diagram for determining the second set urea injection amount of the rear SCR, Figure 4 The logic for determining the second set urea injection amount is shown as follows:

[0128] According to the measured value of the second nitrogen oxide downstream of the front-stage SCR (measured value of NOx downstream of the front-stage SCR), the required conversion efficiency setting data table of the rear-stage SCR (rear-stage SCR required conversion efficiency setting CUR) is searched to obtain the required conversion efficiency of the rear-stage SCR;

[0129] By using the required conversion efficiency of the rear-stage SCR and the second temperature average (the rear-stage SCR temperature average), the ammonia nitrogen ratio setting map of the rear-stage SCR (also called the rear-stage SCR ammonia nitrogen ratio setting map) is found to obtain the required ammonia nitrogen ratio of the rear-stage SCR.

[0130] The product of the exhaust flow rate, the second nitrogen oxide measured value (the NOx measured value downstream of the front-stage SCR) and the required ammonia nitrogen ratio of the rear-stage SCR is calculated and converted into units to obtain the required urea injection amount of the rear-stage SCR.

[0131] Based on the measured ammonia reserve (measured ammonia reserve of the rear-stage SCR carrier), the urea injection amount correction data table of the rear-stage SCR (the rear-stage SCR urea injection amount correction CUR based on ammonia reserve) is searched to obtain the urea injection amount correction value of the rear-stage SCR;

[0132] The difference between the required urea injection amount of the rear-stage SCR and the urea injection amount correction value (equivalent to the correction of the required urea injection amount of the rear-stage SCR) is calculated to obtain the second set urea injection amount of the rear-stage SCR, and the urea nozzle of the rear-stage SCR is controlled by the second set urea injection amount to perform urea injection.

[0133] The above is an explanation of the logic for determining the second set urea injection amount of the rear SCR. Figure 4 For the specific execution principle in the embodiment of the present invention, please refer to the above Figure 2 The content in step S203 is not repeated here.

[0134] pass Figure 4 It can be seen from the shown content that the required conversion efficiency of the rear-stage SCR is determined based on the tail NOx level (the actual measured NOx value downstream of the front-stage SCR), and the required ammonia nitrogen ratio of the rear-stage SCR is determined in combination with the average temperature of the rear-stage SCR, thereby obtaining the required urea injection amount of the rear-stage SCR, and the required urea injection amount is corrected based on the actual measured ammonia reserves of the rear-stage SCR carrier to obtain the second set urea injection amount of the rear-stage SCR.

[0135] In general, this scheme can reasonably allocate the urea injection amount of the two-stage SCR based on the temperature average of the two-stage SCR in different modes, improve the conversion efficiency of nitrogen oxides, reduce the emission of pollutant gases, and improve emission robustness.

[0136] Corresponding to the urea injection control method provided by the above embodiment of the present invention, see Figure 5, the embodiment of the present invention further provides a structural block diagram of a urea injection control device, the urea injection control device is applied to a dual-stage SCR post-treatment system, the urea injection control device comprises: an acquisition unit 100, a first determination unit 200, a second determination unit 300 and a control unit 400;

[0137] The acquisition unit 100 is used to obtain a first temperature average value of a front-stage SCR and a second temperature average value of a rear-stage SCR in a two-stage SCR aftertreatment system, and to obtain a first nitrogen oxide measured value upstream of the front-stage SCR and a second nitrogen oxide measured value downstream of the front-stage SCR, and to obtain an exhaust flow rate and a measured ammonia reserve corresponding to the rear-stage SCR.

[0138] The first determination unit 200 is used to determine the first set urea injection amount of the front-stage SCR according to the target mode enabled by the engine, the first temperature average, the second temperature average, the exhaust flow, the first nitrogen oxide measured value, and the second nitrogen oxide measured value, and the target mode is the regeneration mode or the normal mode.

[0139] The second determination unit 300 is used to determine a second set urea injection amount of the subsequent SCR according to the exhaust flow rate, the second nitrogen oxide measured value, the second temperature average value and the measured ammonia reserve.

[0140] The control unit 400 is used to control the urea nozzle of the front-stage SCR to perform urea injection by using the first set urea injection amount, and to control the urea nozzle of the rear-stage SCR to perform urea injection by using the second set urea injection amount.

[0141] In the embodiment of the present invention, the first temperature average of the front-stage SCR, the second temperature average of the rear-stage SCR, the first nitrogen oxide measured value upstream of the front-stage SCR, the second nitrogen oxide measured value downstream of the front-stage SCR and other parameters are obtained in the two-stage SCR post-treatment system, and the first set urea injection amount of the front-stage SCR and the second set urea injection amount of the rear-stage SCR are determined by the above-mentioned parameters. The first set urea injection amount and the second set urea injection amount are used to control the urea nozzles of the front-stage SCR and the rear-stage SCR to perform urea injection respectively, and the urea injection amount of the two-stage SCR is reasonably allocated to improve the conversion efficiency of nitrogen oxides, reduce the emission of pollutant gases, and improve emission robustness.

[0142] Preferably, combined Figure 5 As shown in the figure, the first determination unit 200 includes a first determination module, a second determination module and a calculation module, and the execution principle of each module is as follows:

[0143] The first determination module is configured to determine a first target efficiency of a front-stage SCR according to a target mode enabled by the engine, a first temperature average, and a second temperature average.

[0144] In a specific implementation, the first determination module is specifically used for: when the engine starts the normal mode, searching the efficiency setting map of the front-stage SCR according to the first temperature average and the second temperature average to obtain the efficiency base value as the first target efficiency of the front-stage SCR; when the engine starts the regeneration mode, obtaining the oxidation catalyst temperature and the particulate filter temperature in the two-stage SCR aftertreatment system; searching the efficiency setting map of the front-stage SCR according to the first temperature average and the second temperature average to obtain the efficiency base value of the front-stage SCR; searching the efficiency correction map of the front-stage SCR according to the oxidation catalyst temperature and the particulate filter temperature to obtain the efficiency correction value of the front-stage SCR; calculating the sum of the efficiency base value and the efficiency correction value of the front-stage SCR to obtain the first target efficiency of the front-stage SCR.

[0145] The second determination module is used to determine the ammonia nitrogen ratio set value of the front-stage SCR by using the first temperature average, the first target efficiency, the first nitrogen oxide measured value, the second nitrogen oxide measured value, and a preset specified correction coefficient.

[0146] In the specific implementation, the second determination module is specifically used to: use the first target efficiency and the first temperature average to find the ammonia nitrogen ratio setting map of the front-stage SCR to obtain the required ammonia nitrogen ratio of the front-stage SCR; calculate the ammonia nitrogen ratio correction value of the front-stage SCR based on the first target efficiency, the first nitrogen oxide measured value, the second nitrogen oxide measured value and the preset specified correction coefficient; calculate the sum of the required ammonia nitrogen ratio of the front-stage SCR and the ammonia nitrogen ratio correction value to obtain the ammonia nitrogen ratio setting value of the front-stage SCR.

[0147] The calculation module is used to calculate the product of the set value of the ammonia nitrogen ratio, the exhaust flow rate and the first nitrogen oxide measured value to obtain a first set urea injection amount of the front-stage SCR.

[0148] Preferably, combined Figure 5 As shown in the figure, the second determination unit 300 includes a determination module, a first calculation module, a search module and a second calculation module, and the execution principle of each module is as follows:

[0149] The determination module is used to determine the required ammonia nitrogen ratio of the subsequent SCR by using the second nitrogen oxide measured value and the second temperature average value.

[0150] In the specific implementation, the determination module is specifically used to: use the second nitrogen oxide measured value to find the required conversion efficiency setting data table of the rear-stage SCR to obtain the required conversion efficiency of the rear-stage SCR; use the second temperature average and the required conversion efficiency of the rear-stage SCR to find the ammonia nitrogen ratio setting map of the rear-stage SCR to obtain the required ammonia nitrogen ratio of the rear-stage SCR.

[0151] The first calculation module is used to calculate the product of the exhaust flow rate, the second nitrogen oxide measured value and the required ammonia nitrogen ratio of the rear-stage SCR to obtain the required urea injection amount of the rear-stage SCR.

[0152] The search module is used to search the urea injection amount correction data table of the rear-stage SCR by using the measured ammonia reserve to obtain the urea injection amount correction value of the rear-stage SCR.

[0153] The second calculation module is used to calculate the difference between the required urea injection amount of the subsequent SCR and the urea injection amount correction value to obtain a second set urea injection amount of the subsequent SCR.

[0154] In summary, the embodiment of the present invention provides a urea injection control method and device, which obtains the first temperature average value of the front-stage SCR, the second temperature average value of the rear-stage SCR, the first nitrogen oxide measured value upstream of the front-stage SCR, the second nitrogen oxide measured value downstream of the front-stage SCR and other parameters in the two-stage SCR aftertreatment system, and determines the first set urea injection amount of the front-stage SCR and the second set urea injection amount of the rear-stage SCR by the above-mentioned parameters. The first set urea injection amount and the second set urea injection amount are used to control the urea nozzles of the front-stage SCR and the rear-stage SCR to perform urea injection respectively, and the urea injection amount of the two-stage SCR is reasonably allocated to improve the conversion efficiency of nitrogen oxides.

[0155] Each embodiment in this specification is described in a progressive manner, and the same or similar parts between the embodiments can refer to each other, and each embodiment focuses on the differences from other embodiments. In particular, for the system or system embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and the relevant parts can refer to the partial description of the method embodiment. The system and system embodiments described above are merely schematic, wherein the units described as separate components may or may not be physically separated, and the components displayed as units may or may not be physical units, that is, they may be located in one place, or they may be distributed on multiple network units. Some or all of the modules may be selected according to actual needs to achieve the purpose of the scheme of this embodiment. Ordinary technicians in this field can understand and implement it without creative work.

[0156] Professionals may further appreciate that the units and algorithm steps of each example described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of the two. In order to clearly illustrate the interchangeability of hardware and software, the composition and steps of each example have been generally described in the above description according to function. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professionals and technicians may use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of the present invention.

[0157] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A urea injection control method, characterized in that: The method is applied to a dual-stage SCR post-treatment system, and the method comprises: Obtaining a first temperature average value of a front-stage SCR and a second temperature average value of a rear-stage SCR in the dual-stage SCR aftertreatment system, obtaining a first nitrogen oxide measured value upstream of the front-stage SCR and a second nitrogen oxide measured value downstream of the front-stage SCR, and obtaining an exhaust gas flow rate and a measured ammonia reserve corresponding to the rear-stage SCR; According to the target mode enabled by the engine, the first temperature average and the second temperature average, a first target efficiency of the front-stage SCR is determined; using the first temperature average, the first target efficiency, the first nitrogen oxide measured value, the second nitrogen oxide measured value, combined with a preset specified correction coefficient, an ammonia nitrogen ratio set value of the front-stage SCR is determined; the product of the ammonia nitrogen ratio set value, the exhaust flow rate and the first nitrogen oxide measured value is calculated to obtain a first set urea injection amount of the front-stage SCR; the target mode is a regeneration mode or a normal mode; determining a second set urea injection amount of the rear-stage SCR according to the exhaust flow rate, the second nitrogen oxide measured value, the second temperature average value and the measured ammonia reserve; The urea nozzle of the front-stage SCR is controlled to inject urea by using the first set urea injection amount, and the urea nozzle of the rear-stage SCR is controlled to inject urea by using the second set urea injection amount.

2. The method according to claim 1, characterized in that Determining a first target efficiency of the front-stage SCR according to a target mode enabled by the engine, the first temperature average, and the second temperature average, includes: When the engine is in a normal mode, searching the efficiency setting map of the front-stage SCR according to the first temperature average and the second temperature average to obtain an efficiency base value as a first target efficiency of the front-stage SCR; When the engine is in a regeneration mode, obtaining an oxidation catalyst temperature and a particulate filter temperature in the dual-stage SCR post-treatment system; searching an efficiency setting map of the front-stage SCR according to the first temperature average and the second temperature average to obtain a basic efficiency value of the front-stage SCR; According to the oxidation catalyst temperature and the particle filter temperature, searching for the efficiency correction map of the front-stage SCR to obtain the efficiency correction value of the front-stage SCR; A sum of the efficiency base value and the efficiency correction value of the front-stage SCR is calculated to obtain a first target efficiency of the front-stage SCR.

3. The method according to claim 1, characterized in that Determining a set value of the ammonia nitrogen ratio of the front-stage SCR by using the first temperature average, the first target efficiency, the first nitrogen oxide measured value, and the second nitrogen oxide measured value in combination with a preset specified correction coefficient, includes: Using the first target efficiency and the first temperature average value to find the ammonia nitrogen ratio setting map of the front-stage SCR to obtain the required ammonia nitrogen ratio of the front-stage SCR; Calculating a correction value of the ammonia nitrogen ratio of the front-stage SCR based on the first target efficiency, the first nitrogen oxide measured value, the second nitrogen oxide measured value and a preset specified correction coefficient; The sum of the required ammonia nitrogen ratio of the front-stage SCR and the ammonia nitrogen ratio correction value is calculated to obtain the ammonia nitrogen ratio set value of the front-stage SCR.

4. The method according to claim 1, characterized in that: Determining a second set urea injection amount of the post-stage SCR according to the exhaust flow rate, the second nitrogen oxide measured value, the second temperature average value and the measured ammonia reserve includes: Determining a required ammonia nitrogen ratio of the post-stage SCR by using the second nitrogen oxide measured value and the second temperature average value; Calculating the product of the exhaust flow rate, the second nitrogen oxide measured value and the required ammonia nitrogen ratio of the rear-stage SCR to obtain the required urea injection amount of the rear-stage SCR; Using the measured ammonia reserve, searching a urea injection amount correction data table of the rear-stage SCR to obtain a urea injection amount correction value of the rear-stage SCR; The difference between the required urea injection amount of the post-stage SCR and the urea injection amount correction value is calculated to obtain a second set urea injection amount of the post-stage SCR.

5. The method according to claim 4, characterized in that Determining the required ammonia nitrogen ratio of the post-stage SCR by using the second nitrogen oxide measured value and the second temperature average value includes: Using the second nitrogen oxide measured value, searching the required conversion efficiency setting data table of the subsequent SCR to obtain the required conversion efficiency of the subsequent SCR; The ammonia nitrogen ratio setting map of the rear-stage SCR is searched by using the second temperature average value and the required conversion efficiency of the rear-stage SCR to obtain the required ammonia nitrogen ratio of the rear-stage SCR.

6. A urea injection control device, characterized in that: The device is applied to a dual-stage SCR post-treatment system, and comprises: an acquisition unit, configured to acquire a first temperature average value of a front-stage SCR and a second temperature average value of a rear-stage SCR in the dual-stage SCR aftertreatment system, acquire a first nitrogen oxide measured value upstream of the front-stage SCR and a second nitrogen oxide measured value downstream of the front-stage SCR, and acquire an exhaust gas flow rate and an actually measured ammonia reserve corresponding to the rear-stage SCR; The first determining unit includes: a first determining module, a second determining module and a calculating module; The first determination module is used to determine a first target efficiency of the front-stage SCR according to a target mode enabled by the engine, the first temperature average and the second temperature average; the target mode is a regeneration mode or a normal mode; The second determination module is used to determine the ammonia nitrogen ratio set value of the front-stage SCR by using the first temperature average value, the first target efficiency, the first nitrogen oxide measured value, and the second nitrogen oxide measured value in combination with a preset specified correction coefficient; The calculation module is used to calculate the product of the set value of the ammonia nitrogen ratio, the exhaust flow rate and the first measured value of nitrogen oxides to obtain a first set urea injection amount of the front-stage SCR; a second determining unit, configured to determine a second set urea injection amount of the post-stage SCR according to the exhaust flow rate, the second nitrogen oxide measured value, the second temperature average value and the measured ammonia reserve; The control unit is used for controlling the urea nozzle of the front-stage SCR to inject urea by using the first set urea injection amount, and controlling the urea nozzle of the rear-stage SCR to inject urea by using the second set urea injection amount.

7. The device according to claim 6, characterized in that The first determining module is specifically used for: When the engine is in a normal mode, searching the efficiency setting map of the front-stage SCR according to the first temperature average and the second temperature average to obtain an efficiency base value as a first target efficiency of the front-stage SCR; When the engine is in a regeneration mode, obtaining an oxidation catalyst temperature and a particulate filter temperature in the dual-stage SCR post-treatment system; searching an efficiency setting map of the front-stage SCR according to the first temperature average and the second temperature average to obtain a basic efficiency value of the front-stage SCR; According to the oxidation catalyst temperature and the particle filter temperature, searching for the efficiency correction map of the front-stage SCR to obtain the efficiency correction value of the front-stage SCR; A sum of the efficiency base value and the efficiency correction value of the front-stage SCR is calculated to obtain a first target efficiency of the front-stage SCR.

8. The device according to claim 6, characterized in that The second determining module is specifically used for: Using the first target efficiency and the first temperature average value to find the ammonia nitrogen ratio setting map of the front-stage SCR to obtain the required ammonia nitrogen ratio of the front-stage SCR; Calculating a correction value of the ammonia nitrogen ratio of the front-stage SCR based on the first target efficiency, the first nitrogen oxide measured value, the second nitrogen oxide measured value and a preset specified correction coefficient; The sum of the required ammonia nitrogen ratio of the front-stage SCR and the ammonia nitrogen ratio correction value is calculated to obtain the ammonia nitrogen ratio set value of the front-stage SCR.

Images