Method for correcting dosing amount of SCR system of internal combustion engine

Abstract

The invention relates to a method for correcting a dosing amount (Qm) of an SCR system (25) of an internal combustion engine, in which at least one dosing valve (310) doses a reagent (105) upstream of at least one SCR catalyst, in which the reagent (105) is fed from a tank (100) to the dosing valve (310) at a constant pressure by means of an actuatable pump (120), in which the dosing valve (310) is connected to the SCR system (25). The pressure (104) of the dosing of the reagent (105) of the SCR system (25) is ascertained by means of a pressure sensor (130) in the pump (120), a pressure oscillation (105) at the dosing valve (310) is modeled as a function of the ascertained pressure (105), and a correction of the dosing amount (Qm) is carried out as a function of the modeled pressure oscillation (105) at the dosing valve (310).

Description

Field of the Invention

[0001] The present invention relates to a method for correcting the metering of an SCR system of an internal combustion engine according to the preamble of claim 1.

[0002] Also subject matter of the present invention is a computer program and a computer program product suitable for implementing the method. Background Art

[0003] The reduction of nitrogen oxide emissions of internal combustion engines operating with excess air, especially diesel internal combustion engines, can be carried out by means of the so-called selective catalytic reduction technology (SCR). Here, nitrogen oxides are reduced to nitrogen and water vapor, where gaseous ammonia or ammonia in an aqueous solution or urea in an aqueous solution is used as a reducing agent. Urea is used here as an ammonia carrier. By means of a metering system for a hydrolysis catalytic converter, the reducing agent can be injected into the exhaust system of the internal combustion engine. In the hydrolysis catalytic converter, the reducing agent is converted into ammonia by hydrolysis, and then the ammonia is transported to the SCR catalytic converter itself, also called a DENOX catalytic converter, which reduces the nitrogen oxides present in the exhaust gas. The main components of such a NOx reduction system are a reducing agent storage tank, a pump, a pressure regulator, a pressure sensor, and a metering valve. The pump transports the reducing agent stored in the reducing agent storage tank to the metering valve, and the reducing agent is injected into the exhaust gas stream upstream of the hydrolysis catalytic converter by means of this metering valve. Here, the metering valve is controlled by a signal from a control device, for example, the controller of the internal combustion engine, in order to transport a specific currently required amount of reducing agent. Substances that release ammonia and are present in an aqueous solution, such as urea, are preferably used because these reducing agents can be stored and handled significantly more easily than, for example, gaseous ammonia. In addition, the transportability and metering ability of these solutions can also be carried out using technical means that are significantly simpler than the transport and metering of gaseous substances, for example. Since the reducing agent solution freezes below about -11°C, equipment for heating the reducing agent in the reducing agent container must be provided.

[0004] DE 10 2013 218 897 A1 relates to a method for quantity monitoring of a metering or injection system of an internal combustion engine, especially of a motor vehicle, where the metering or injection system has a pipeline system containing a fluid, and where, in particular, it is provided that a pressure wave (315) of the fluid is generated in the pipeline system, the pressure trend (320) generated by the pressure wave of the fluid is detected, a parameter (325) associated with the propagation speed of the pressure wave of the fluid is determined from the detected pressure trend, the mechanical or hydraulic stiffness of the pipeline system is obtained from the determined parameter associated with the propagation speed of the pressure wave of the fluid, and quantity monitoring is carried out taking into account the obtained stiffness of the pipeline system. Summary of the Invention

[0005] In a first aspect, the invention relates to a method for correcting the metering quantity of an SCR system of an internal combustion engine, wherein at least one metering valve meters a reagent upstream of at least one SCR catalyst, and wherein the reagent is conveyed from a storage tank to the metering valve by means of a controllable pump at a constant pressure, characterized in that the pressure of the reagent metered into the SCR system is acquired by means of a pressure sensor in the pump, wherein a pressure oscillation at the metering valve is modeled depending on the acquired pressure, and wherein the correction of the metering quantity is carried out depending on the modeled pressure oscillation at the metering valve.

[0006] In an advantageous design, the modeling of the pressure oscillation is acquired depending on the speed of sound in the reagent, the density of the reagent, in particular the cross-section of the pressure line between the pump and the metering valve, the volume flow through the metering valve, and the length of the pressure line.

[0007] Advantageously, the invention enables the correction of the metering quantity, which can lead to improved efficiency and reduced emissions in the SCR system.

[0008] In the context of the invention, the metering quantity is determined based on the pressure of the reagent in the pump and the modeled pressure fluctuations at the metering valve. The pressure fluctuations are a function of the speed of sound in the reagent, the density of the reagent, the cross-sectional area of the pressure line, and the length of the pressure line in order to ensure the compliant operation of the SCR pressure line. Taking these factors into account, the invention provides a method for correcting the metering quantity.

[0009] Advantageously, compared to previous methods, the invention provides a more reliable and more consistent metering quantity, which can lead to improved efficiency and a longer service life of the SCR system. By modeling the pressure fluctuations of the metering valve and the corresponding adjustment of the metering quantity, the invention can minimize the influence of fluctuations in the reagent and the SCR system, which results in a more uniform and reliable efficiency.

[0010] Advantageously, the invention can be applied to a wide variety of internal combustion engines, including such internal combustion engines with different types of SCR systems and reagents. By using a universal pressure sensor and modeling the pressure fluctuations of the metering valve, the invention can be easily adapted to different engine configurations and applications, which makes the invention a versatile and broad solution.

[0011] In a special design, the minimum pressure is acquired according to the following formula:

[0012]

[0013] where ρ is the density of the reagent, a is the speed of sound in the reagent, and α is a factor that depends on the cross-section of the pressure line and the volumetric flow of the metering valve in the case of the initial pressure at the start of metering, where

[0014]

[0015] In another design, the maximum pressure is obtained according to the following formula:

[0016]

[0017] where A = 1 / (ρa 2 α 2 ), C = -Δp min , and where the second pressure corresponds to the second pressure at half a period of the pressure oscillation.

[0018] In an advantageous design, the frequency of the pressure oscillation is obtained as a function of the speed of sound, in particular the length of the pressure line between the pump and the metering valve.

[0019] In a particular design, the frequency of the pressure oscillation is obtained according to the following formula:

[0020]

[0021] where f is the frequency of the pressure oscillation, a is the speed of sound, L is the length of the pressure line between the pump and the metering valve in particular, l is the length of the pressure wave of the pressure line structure, and T is the period of the pressure oscillation.

[0022] In a further aspect, the invention relates to a device, in particular a controller and a computer program, which are set up, in particular programmed, to carry out one of the methods described above. In yet another aspect, the invention relates to a machine-readable storage medium on which a computer program is stored. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Embodiments and advantageous designs of the invention are shown in the drawings and are explained in more detail in the following description. Where:

[0024] Figure 1 An SCR system for an internal combustion engine with an intake line is schematically shown;

[0025] Figure 2 An example measurement of the pressure by means of a pressure sensor and the modeled pressure oscillation for the SCR system are shown;

[0026] Figure 3 A first embodiment of the method according to the invention for an SCR system is shown according to a flow chart. Detailed implementation manner

[0027] In Figure 1 is shown an SCR system 25 of an internal combustion engine (not shown) having an intake line, in particular without a return line, wherein only the elements important for the present invention of such a reduction system are shown here. The difference from an SCR system with a separate return line is that there is no own return line, and the return of the metering agent 105 can only be carried out through the intake line 101.

[0028] The storage tank 100 stores a reducing agent solution, for example, an aqueous urea solution 105 also sold under the product name "AdBlue".

[0029] In addition, the concepts of aqueous urea solution 105, metering agent, fluid, Adblue are used as synonyms.

[0030] The aqueous urea solution 105 is conveyed through the line 101 by means of the pump 120 to the metering agent unit 300 (pump mass flow ), and through this metering agent unit, the aqueous urea solution is sprayed into the exhaust passage 400 in front of the catalytic converter K (metering mass flow ).

[0031] For this purpose, a known metering strategy is stored on the controller 200, and this metering strategy obtains the metering mass flow, for example, depending on the exhaust gas mass flow the temperature of the SCR catalytic converter (downstream of the metering valve 310, not shown), the NOx concentrations upstream and downstream of the SCR catalytic converter, and the ammonia filling level for the SCR catalytic converter.

[0032] The pressure in the SCR system 25 is detected by a pressure sensor 130 arranged in the pump 120 or the pump unit. The signal is converted in a pressure-voltage converter (not shown further) and is conveyed to the control device 200, for example, a motor controller. Through this controller 200, the pump 120 can also be controlled and more precisely so that the pressure in the SCR system 25 remains constant. For this purpose, a system pressure p sys is pre-given for the SCR system 25, and this system pressure is especially between 4 bar and 12 bar. The metering agent unit 300 has its own metering valve 310, and this metering valve can be controlled by an electromagnet 312 arranged together with the metering valve 310 in the housing 309 and by the control device 200.

[0033] The understanding on which the present invention is based is that the SCR system is determined by the mechanical or hydraulic conditions of the pipeline system. These conditions can be summarized in the concept of stiffness. Stiffness then depends on a number of different factors, such as the presence of air bubbles in the fluid, the strength of the pipeline determined by the modulus of elasticity, for example, the temperature and pressure of the fluid, and the aging and manufacturing tolerances of the components used. However, the quantitative influence of these factors on stiffness is usually not known or cannot be predicted or can only be obtained at a rather high cost.

[0034] Furthermore, a metering or dosing strategy for the reagent 105 is stored on the controller 200. The dosing strategy depends in a known manner on, for example, the exhaust gas mass flow the temperature of the SCR catalyst, the NOx concentration upstream and downstream of the SCR catalyst, and the ammonia filling level for the SCR catalyst to calculate the dosing quantity.

[0035] Figure 2 An example measurement of the pressure trend of the pressure sensor 130 is shown for the dosing process of the SCR system 25.

[0036] The pressure 104 measured by the pressure sensor 130 is plotted against the time t for the dosing process. Furthermore, the modeled pressure 105 is plotted for the dosing valve 310, which corresponds in particular to the modeled pressure oscillation.

[0037] At the first moment t 1 , the dosing of the reagent 105 is started by means of the dosing valve 310.

[0038] At the zeroing moment t 0 until the sixth moment t 6 , the measured pressure 104 corresponding to the pressure in the pump 120 remains almost constant.

[0039] At the first moment t 1 , the dosing of the reagent 105 is started.

[0040] The modeled pressure 105 shows a distinct pressure oscillation between the first moment t 1 and the sixth moment t 6 . It starts with a negative peak.

[0041] Between the first moment t 1 and the second moment t 2 , the modeled pressure 105 drops until the first flat region.

[0042] Between the second moment t 2 and the third moment t 3 , the modeled pressure 105 remains constant.

[0043] Since the third moment t3 From this point on, the modeled pressure 105 rises again and forms a positive peak, which forms its maximum value at the fourth moment t 4 and forms its maximum value.

[0044] Between the fourth moment and the fifth moment t 4 and t 5 a second pressure plateau is formed.

[0045] From the fifth moment t 5 onwards, the modeled pressure 105 then drops again until the sixth moment t 6 .

[0046] The period T of the pressure oscillation shown corresponds to the time between the first moment t 1 and the sixth moment t 6 , where T = t 6 - t 1 .

[0047] The measured pressure 104 corresponds to the initial pressure p 1 at the first moment t 1 , where p 1 = p(t 1 ).

[0048] The second pressure p 2 here corresponds to the pressure 104 measured at the moment of half the period T, where

[0049] In addition, the third pressure p 3 corresponds to the pressure 104 measured at the sixth moment t 6 .

[0050] In addition, a decay time τ can be defined, during which the pressure drops according to the following formula:

[0051]

[0052] where l is the length of the pressure wave of the pressure pipeline structure, and a is the speed of sound.

[0053] In general form, the frequency f of the modeled pressure oscillation can be calculated according to the following formula:

[0054]

[0055] where f is the frequency, a is the speed of sound, and L is the length of the pressure pipeline 102, especially between the pump 120 and the metering valve 310.

[0056] In a particular design, the length of the pressure pipeline L corresponds to the length l of the pressure wave. Then the frequency is obtained as:

[0057]

[0058] In Figure 3 an exemplary process for the method according to the invention is shown, which is used for the SCR system 25.

[0059] In a first step 500, the enabling conditions for the method are monitored in the controller 200. If the controller 200 for the SCR system 25 detects a pressure-stable system state, the method is enabled. If there is a successful pressure build-up with a system pressure p preferably between 4 bar and 12 bar sys then there is a pressure-stable system state. In particular, if the system pressure p sys reached is detected by the controller 200 for a pre-given time, then there is a stable system state. For this purpose, the controller 200 can monitor the pressure p, and if there is a pre-given system pressure p sys for a pre-given time, the enabling is carried out.

[0060] The method is then continued in step 510.

[0061] In step 510, the metering of the reagent 105 into the SCR system 25 is requested by a metering strategy.

[0062] At a first moment t 1 the metering process starts. From this moment on, the opening time t DM of the metering valve 310 and the measured pressure 104 are continuously monitored by the pressure sensor 130. The closing moment t inj of the metering can end, for example, in the interval between a fourth moment and a fifth moment t 4 , t 5 .

[0063] Furthermore, the metered mass Q m of the reagent 105 is obtained by a function in the controller 200, and the obtaining is as follows:

[0064]

[0065] where p c (t) is the modeled pressure 105 obtained during the metering process, Q stat,V is the volume flow at the initial pressure p 1 , ρ is the density of the reagent 105, A D is the cross-section of the pressure line 102, t 1 is the first moment at the start of the metering, t injis the closing time, at which the metering valve 310 is closed and metering ends.

[0066] Subsequently, the method continues in step 520.

[0067] In step 520, a pressure oscillation caused by the opening of the metering valve 130 or by the metering process in step 510 is obtained depending on the acquired first pressure 104.

[0068] For this purpose, an initial pressure p at a first time t is obtained from the first pressure 104 1 、a second pressure p at the time of half a period T of the pressure oscillation 1 、and a third pressure p at a full period T. 2 3 .

[0069] The period T of the pressure oscillation 105 can be obtained here from the parameters stored in the controller 200, namely the speed of sound a and the length of the pressure line 102, in particular the pressure line between the pump 120 and the metering valve 310:

[0070]

[0071] where f is the frequency of the pressure oscillation 105, a is the speed of sound, L is the length of the pressure line 102 between the pump 120 and the metering valve 310 in particular, and T is the period of the pressure oscillation 105.

[0072] In addition, parameters such as the cross-sectional area A of the pressure line 102 are stored in the controller 200 D 、the volume flow Q through the metering valve 130 in the case of a predefinable pressure p 0 of the installed metering valve 130. stat,V . These parameters are obtained in particular during the application phase for the SCR system 25 and stored in the controller 200. In particular, the initial pressure p 1 is suitable as the predefinable pressure p 0 .

[0073] Subsequently, the minimum pressure Δp and the maximum pressure Δp are obtained from the modeled pressure oscillation 105 min max .

[0074] Here, the minimum pressure Δp is calculated according to the following formula min :

[0075]

[0076] where ρ is the density of the reagent 105, a is the speed of sound in the reagent 105, and α is a factor that depends on the cross-sectional area A of the pressure line 102 D and the initial pressure p at the start of metering 1 for the volume flow Q through the metering valve 130 stat,V where:

[0077]

[0078] The maximum pressure Δp is obtained according to the following formula max :

[0079]

[0080] where A = 1 / (ρa 2 α 2 ), C = -Δp min , and where the second pressure p 2 corresponds to the pressure at half the period T of the pressure oscillation 105

[0081] Subsequently, the method is continued in step 530

[0082] Then in step 530, the corrected mass Q is obtained by integrating the modeled pressure oscillation 105, in particular by integrating the area of the modeled pressure oscillation 105 m,cor . This is done in particular according to the following formula

[0083]

[0084] where p m (t) is the modeled pressure 105 obtained during the metering process, Q stat,V is the volume flow at the initial pressure p 1 , ρ is the density of the reagent 105, A D is the cross-sectional area of the pressure line 102, t 1 is the first moment at the start of metering, t inj is the closing moment at which the metering valve 310 is closed and metering ends

[0085] Subsequently, the method is continued in step 540

[0086] In step 540, the metered mass Q of the metering strategy is corrected using the obtained corrected mass Q m,cor . To this end, the metered mass Q of the metering strategy can preferably be calculated m and the obtained corrected mass Q m ​m,cor the deviation between

[0087] This deviation can then be used as a correction factor in the metering strategy.

[0088] In an alternative embodiment, it is also possible to meter in the corrected mass Q directly via the metering valve 130 m , in particular by multiple calculations to accumulate the corrected mass Q m and then meter it in.

[0089] The method can then be ended or continued in step 510.

Claims

1. Dosing quantity (Q m ) is used for correction, wherein: At least one metering valve (310) meters a reagent (105) upstream of at least one SCR catalytic converter, wherein the reagent (105) is conveyed from a tank (100) to the metering valve (310) at a constant pressure by means of a controllable pump (120), characterized in that a metered pressure (104) of the reagent (105) of the SCR system (25) is detected by means of a pressure sensor (130) in the pump (120), wherein pressure oscillations (105) at the metering valve (310) are modeled as a function of the detected pressure (105), wherein the metered quantity (Q) is controlled as a function of the modeled pressure oscillations (105) at the metering valve (310). m ) correction.

2. The method according to claim 1, characterized in that The speed of sound (a) in the reagent (105), the density (ρ) of the reagent (105), the cross section (A) of the pressure line (102) between the pump (120) and the metering valve (310) are dependent on the speed of sound (a) in the reagent (105), the density (ρ) of the reagent (105), and the cross section (A) of the pressure line (102) between the pump (120) and the metering valve (310). D ), the volume flow (Q) through the metering valve (310) V,stat ) and the length (L) of the pressure line (102) to obtain modeling of the pressure oscillations (105) at the metering valve (310).

3. The method according to any one of the preceding claims, characterized in that The period (T) is obtained depending on the length of the pressure line (102) and the speed of sound (a).

4. The method according to any one of the preceding claims, characterized in that The minimum pressure (Δp min ): Wherein, ρ is the density of the reagent (105), a is the speed of sound in the reagent (105) in the pressure line (102), and α is a factor that depends on the cross-section (A) of the pressure line (102). D ), the volume flow (Q ) of the metering valve (130) at the initial pressure (p1) at the start of the metering stat,V ),in:

5. The method according to any one of the preceding claims, characterized in that The maximum pressure (Δp max ): Where A = 1 / (ρa 2 α 2 ), , and wherein the second pressure (p2) corresponds to the second pressure p2 at half a period (T) of the pressure oscillation.

6. The method according to any one of the preceding claims, characterized in that The frequency (f) of the pressure oscillations (105) is obtained as a function of the speed of sound (a), in particular the length of the pressure line (102) between the pump (120) and the metering valve (310).

7. The method according to claim 6, characterized in that The frequency (f) of the pressure oscillation is obtained according to the following formula: Therein, f is the frequency of the pressure oscillation (105), a is the speed of sound, L is the length of the pressure line (102), in particular between the pump (120) and the metering valve (310), l is the length of the pressure wave of the pressure line structure, and T is the period of the pressure oscillation (105). 8 . Computer program designed to carry out the method according to claim 1 .

9. Electronic storage medium having a computer program according to claim 8. 10 . A device, in particular a control unit ( 200 ), which is designed to carry out the method according to claim 1 .

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