Method for correcting a dosage quantity of an SCR system of an internal combustion engine

Abstract

Method for correcting a dosing quantity (Q m ) of an SCR system (25) of an internal combustion engine, in which at least one metering valve (310) meters a reagent (105) upstream of at least one SCR catalyst, in which reagent (105) is conveyed from a tank (100) by means of a controllable pump (120) at constant pressure to the metering valve (310), wherein by means of a pressure sensor (130) in the pump (120), a pressure (104) of a metered addition of reagent (105) of the SCR system (25) is determined, wherein a pressure oscillation (105) at the metering valve (310) is modeled as a function of the determined pressure (105), wherein a correction of the metered quantity (Q m ) is carried out.

Description

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

[0002] The present invention also relates to a computer program and a computer program product which are suitable for carrying out the method. State of the art

[0003] The reduction of nitrogen oxide emissions from an internal combustion engine operating with excess air, particularly a diesel engine, can be achieved using Selective Catalytic Reduction (SCR) technology. This involves reducing nitrogen oxides to nitrogen and water vapor, with either gaseous ammonia, ammonia in aqueous solution, or urea in aqueous solution being used as the reducing agent. The urea serves as the ammonia carrier. Using a dosing system for a hydrolysis catalyst, the reducing agent is injected into the exhaust tract of the internal combustion engine. In the hydrolysis catalyst, it is converted to ammonia by hydrolysis, which is then converted into ammonia in the actual SCR catalyst, also known as a DENOX catalyst, which reduces the nitrogen oxides present in the exhaust gas.The essential components of such a NOx reduction system are a reducing agent tank, a pump, a pressure regulator, a pressure sensor, and a metering valve. The pump conveys the reducing agent stored in the reducing agent tank to the metering valve, by means of which the reducing agent is injected into the exhaust stream upstream of the hydrolysis catalyst. The metering valve is controlled by signals from a control device, for example the control unit of the internal combustion engine, to supply a specific, currently required amount of reducing agent. Ammonia-releasing substances present in aqueous solution, such as urea, are preferably used, since these reducing agents are significantly easier to store and handle than, for example, gaseous ammonia.Furthermore, the pumping and dosing of these solutions is technically much simpler than, for example, the pumping and dosing of gaseous substances. Since the reducing agent solutions freeze below approximately -11°C, devices for heating the reducing agent must be provided in the reducing agent tank.

[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, in particular of a motor vehicle, wherein the metering or injection system has a line system containing fluid, and wherein it is provided in particular that a fluidic pressure wave is generated in the line system (315), that the pressure curve generated by the fluidic pressure wave is detected (320), that a variable correlating with the propagation speed of the fluidic pressure wave is determined from the detected pressure curve (325), that the mechanical or hydraulic stiffness of the line system is determined from the determined variable correlating with the propagation speed of the fluidic pressure wave (330), and that the quantity monitoring takes place taking into account the determined stiffness of the line system. Disclosure of the invention

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

[0006] In an advantageous embodiment, the modeling of the pressure oscillation is determined as a function of a speed of sound in the reagent, a density of the reagent, a cross-section of a pressure line, in particular between the pump and the dosing valve, a volume flow through the dosing valve and the length of the pressure line.

[0007] Advantageously, the invention enables a correction of the dosing quantity, which can lead to improved efficiency and emission reduction in the SCR system.

[0008] In the present invention, the dosing quantity is determined based on the reagent pressure in the pump and the modeled pressure oscillation at the dosing valve. The pressure oscillation is a function of the speed of sound in the reagents, the density of the reagents, the cross-sectional area of ​​the pressure line, and the length of the pressure line to ensure proper operation of the SCR pressure line. Taking these factors into account, the invention provides a method for correcting the dosing quantity.

[0009] Advantageously, the invention provides a more reliable and consistent dosing rate compared to previous methods, which can lead to improved performance and a longer service life of the SCR system. By modeling the pressure oscillation of the dosing valve and adjusting the dosing rate accordingly, the invention can minimize the effects of fluctuations in the reagents and the SCR system, resulting in more consistent and reliable performance.

[0010] Advantageously, the invention can be applied to a wide range of internal combustion engines, including those with different types of SCR systems and reagents. By using a generic pressure sensor and modeling the pressure oscillation of the dosing valve, the invention can be easily adapted to different engine configurations and applications, making it a versatile and widely used solution.

[0011] In a special embodiment, a minimum pressure is determined according to the following formula: Δpmin=ρa2a2−1+1+4p1ρa2a22, with p the density of the reagent, a the speed of sound in the reagent, α a factor depending on the cross-section of the pressure line, a volumetric flow of the dosing valve at an initial pressure to start dosing with: α=Qstat,VP1ρ.

[0012] In a further embodiment, a maximum pressure is determined according to the following formula: Δpmax=−B+B2−4AC2A with A = 1 / (ρa 2 α 2 ), B=(2p2−Δpmin) / (αaρ)−1,C=−Δpmin and a second pressure corresponding to a second pressure at half a period of the pressure oscillation.

[0013] In an advantageous embodiment, a frequency of the pressure oscillation is determined as a function of the speed of sound, corresponding to a length of the pressure line, in particular between the pump and the dosing valve.

[0014] In a special embodiment, the frequency of the pressure oscillation is determined according to the following formula: f=a4(L+l2);T=1f with f the frequency of the pressure oscillation, a the speed of sound, L the length of the pressure line, in particular between the pump and the dosing valve, I the length of the pressure wave of the pressure line structure and T the period of the pressure oscillation.

[0015] In further aspects, the invention relates to a device, in particular a control unit and a computer program, which are configured, in particular programmed, to execute one of the methods. In yet another aspect, the invention relates to a machine-readable storage medium on which the computer program is stored. Short description of the drawings

[0016] Embodiments and advantageous embodiments of the invention are illustrated in the drawing and explained in more detail in the following description. Fig. 1 shows schematically an SCR system with an intake line for an internal combustion engine, Fig. 2 shows an example measurement of the pressure via the pressure sensor and the modeled pressure oscillation for an SCR system, Fig. 3 shows a first embodiment of the method according to the invention for an SCR system using a flow chart. Embodiments of the invention

[0017] In the Fig. Figure 1 shows an SCR system 25 with an intake line, in particular without a return line, of an internal combustion engine (not shown). Only the elements of such a reduction system relevant to the invention are shown here. The difference from SCR systems with separate return lines is that there is no separate return line; a return flow of dosing agent 105 is only possible via the intake line 101.

[0018] A tank 100 stores a reducing agent solution, for example, a urea-water solution 105, which is also marketed under the product name "AdBlue." The terms urea-water solution 105, dosing agent, fluid, and AdBlue are used synonymously.

[0019] The urea water solution 105 is conveyed via a line 101 by means of a pump 120 to a dosing agent unit 300 (pump mass flow ̇̇ṁ p ), through which it is injected into the exhaust gas duct 400 in front of a catalyst K (metering mass flow ṁ D ).

[0020] For this purpose, a known dosing strategy is stored on the control unit 200, which, depending on, for example, an exhaust gas mass flow ṁ exh , a temperature of an SCR catalyst (downstream of the metering valve 310, not shown), NOx concentrations upstream and downstream of the SCR catalyst and an ammonia fill level for the SCR catalyst, the metering mass flow ṁ D determined.

[0021] The pressure in the SCR system 25 is detected by a pressure sensor 130, which is arranged in the pump 120 or pump unit. The signal is converted in a pressure-voltage converter (not shown) and fed to a control device 200, for example, an engine control unit. This control unit 200 can also control the pump 120 in such a way that the pressure in the SCR system 25 is kept constant. For this purpose, a system pressure p sys This pressure is predetermined, in particular between 4 and 12 bar. The dosing agent unit 300 has the actual dosing valve 310, which is controlled by an electromagnet 312, which is arranged together with the dosing valve 310 in a housing 309 and can be controlled by the control device 200.

[0022] The invention is based on the realization that SCR systems are subject to mechanical and hydraulic conditions of the piping system. These can be summarized in the term "stiffness." Stiffness depends on a number of different factors, such as the presence of air inclusions in the fluid, the strength of the lines determined, for example, by the modulus of elasticity, the temperature and pressure of the fluid, as well as the aging and manufacturing tolerances of the components used. However, the quantitative influence of these factors on stiffness is usually unknown or predictable, or can only be determined with relatively great effort.

[0023] Furthermore, a dosing strategy for the reagent 105 is stored on the control unit 200. The dosing strategy calculates in a known manner depending on, for example, an exhaust gas mass flow ṁ exh, a temperature of the SCR catalyst, a NOx concentration upstream and downstream of the SCR catalyst and an ammonia fill level for the SCR catalyst.

[0024] The Fig. 2 shows an example measurement of the pressure curve of the pressure sensor 130 for a dosing process for an SCR system 25.

[0025] The pressure 104 measured by the pressure sensor 130 is plotted against time t for a dosing process. Furthermore, the modeled pressure 105, in particular, this corresponds to the modeled pressure oscillation, for the dosing valve 310 is plotted.

[0026] At a first point in time t 1 a dosing of reagent 105 starts by means of the dosing valve 310.

[0027] Between the zeroth time t 0 up to a sixth time t 6 the measured pressure 104, which corresponds to the pressure in the pump 120, remains almost constant.

[0028] At the first time t 1 a dosing of reagent 105 is started. The modeled pressure 105 shows between the first time t 1 and the sixth time t 6 a pronounced pressure oscillation, starting with a negative wave crest.

[0029] Between a first time t 1 and a second time t 2 the modeled pressure 105 drops to a first plateau.

[0030] Between the second time t 2 and the third time t 3 the modeled pressure 105 remains constant.

[0031] From the third time t 3 the modeled pressure 105 rises again and a positive wave crest forms, which reaches its maximum at a fourth time t 4 .

[0032] Between the fourth and fifth time t 4 ; t 5a second pressure plateau forms.

[0033] From a fifth point in time t 5 the modeled pressure 105 then drops again until a sixth time t 6 .

[0034] The period T of the pressure oscillation shown corresponds to the time between the first time t 1 and the sixth time t 6 , with T = t 6 - t 1 .

[0035] A measured pressure 104 corresponds to an initial pressure p 1 , at the first time t 1 with p 1 = p(t 1 ).

[0036] A second print p 2 corresponds to the measured pressure 104 at the time of half the period T with p2=p(T2).

[0037] A third print p 3 continues to correspond to the measured pressure 104 at the sixth time t 6 .

[0038] Furthermore, a decay time τ can be defined in which the pressure decreases according to the following formula: τ=1a, with I the length of the pressure wave of the pressure line structure and a the speed of sound.

[0039] In a general form, the frequency f for the modeled pressure oscillation can be calculated according to the following formula: f=a4(L+l2);T=1f where f is the frequency, 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.

[0040] In a special embodiment, the length of the pressure line L corresponds to the length of the pressure wave I. The frequency is then: f=a6L;T=1f.

[0041] In the Fig. 3 shows the exemplary sequence for the method according to the invention for an SCR system 25.

[0042] In a first step 500, an enable condition for the method is monitored in the control unit 200. The method is enabled when the control unit 200 detects a pressure-stable system state for the SCR system 25. A pressure-stable system state exists when a successful pressure build-up with a stable system pressure p sys , preferably between 4 and 12 bar. In particular, the stable system state can be present when the reached system pressure p sys is detected for a preset time by the control unit 200. For this purpose, the control unit 200 can monitor the pressure p and the release takes place when the specified system pressure p sys for a specified period of time. The method then continues in a step 510.

[0043] In a step 510, a dosing of reagent 105 into the SCR system 25 is requested by a dosing strategy.

[0044] The dosing starts at a first time t 1 From this point on, the opening time t DM of the metering valve 310, the measured pressure 104 by the pressure sensor 130. The closing time t inj The dosage can be adjusted, for example, in the interval between the fourth and fifth time point t 4 , t 5 end.

[0045] Furthermore, the metered mass Q m of reagent 105 is determined by a function in the control unit 200 as follows: Qm=βρAD∫t1t1+tinj2pc(t)ρdt β=Qstat,VAD2p1ρ,pc(t) the determined modeled pressure 105 during the dosing process, Q stat,V the volumetric flow at the initial pressure p 1 , ρ the density of the reagent 105, A D the cross-section of the pressure line 102, t 1 the first time at which dosing starts, t injthe closing time at which the dosing valve 310 is closed and dosing ends.

[0046] The method then continues in a step 520.

[0047] In a step 520, the pressure oscillation caused by the opening of the metering valve 130 or by the metering process in step 510 is determined as a function of the determined first pressure 104.

[0048] For this purpose, the initial pressure p 1 at the first time t 1 , a second print p 2 at a time of half the period T and a third pressure p 3 to the full period T of the pressure oscillation from the first pressure 104.

[0049] The period T of the pressure oscillation 105 can be determined from 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, stored in the control unit 200: f=a6L;T=1f with f the frequency of the pressure oscillation 105, a the speed of sound, L the length of the pressure line 102, in particular between the pump 120 and the metering valve 310 and T the period of the pressure oscillation 105.

[0050] Furthermore, the control unit contains 200 parameters such as the cross-section A D the pressure line 102, a volumetric flow Q stat,V through the metering valve 130 at a preset pressure p 0 of the installed metering valve 130. These parameters are determined in particular in an application phase for the SCR system 25 and stored in the control unit 200. As a predeterminable pressure p 0 The initial pressure p is particularly suitable 1 .

[0051] Subsequently, a minimum pressure Δp min and a maximum pressure Δp max determined from the modeled pressure oscillation 105.

[0052] The minimum pressure Δp is calculated minaccording to the following formula: Δpmin=ρa2a2−1+1+4p1ρa2a22, with ρ the density of the reagent 105, a the speed of sound in the reagent 105, α a factor depending on the cross section A D the pressure line 102, a volumetric flow Q stat,V through the metering valve 130 at an initial pressure p 1 to start dosing with: α=Qstat,Vp1ρ.

[0053] The maximum pressure Δp max is determined according to the following formula: Δpmax=−B+B2−4AC2A with A=1 / (ρa2α2),B=(2p2−Δpmin) / (αaρ)−1,C=−Δpmin and the second pressure p 2 , which corresponds to a pressure at half a period T of the pressure oscillation 105.

[0054] The method then continues in a step 530.

[0055] In a step 530, a corrected mass Q m,corby integrating the modeled pressure oscillation 105, in particular the surface areas of the modeled pressure oscillation 105. This is done in particular by the following formula: Qm,cor=βρAD∫t1t1+tinj2pm(t)ρdt with β=Qstat,VAD2p1ρ,pm(t) the determined modeled pressure 105 during the dosing process, Q stat,V the volumetric flow at the initial pressure p 1 , ρ the density of the reagent 105, A D the cross-section of the pressure line 102, t 1 the first time at which dosing starts, t inj the closing time at which the dosing valve 310 is closed and dosing ends. The method then continues in a step 540.

[0056] In a step 540, the metered mass Q m the dosing strategy with the determined corrected mass Q m,corFor this purpose, a deviation between the metered mass Q m the dosing strategy and the determined corrected mass Q m,cor be calculated.

[0057] This deviation can then be incorporated into the dosing strategy as a correction factor.

[0058] In an alternative embodiment, the corrected mass Q m be metered in via the metering valve 130, in particular the corrected mass Q m accumulated over several calculations and then dosed.

[0059] The method can then be terminated or continued in a step 510. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2013 218 897 A1

[0004]

Claims

[1] Method for correcting a dosing quantity (Q m ) of an SCR system (25) of an internal combustion engine, in which at least one metering valve (310) meters a reagent (105) upstream of at least one SCR catalyst, in which reagent (105) is conveyed from a tank (100) by means of a controllable pump (120) at constant pressure to the metering valve (310), characterized by that by means of a pressure sensor (130) in the pump (120), a pressure (104) of a dosing of reagent (105) of the SCR system (25) is determined, wherein a pressure oscillation (105) at the dosing valve (310) is modeled as a function of the determined pressure (105), wherein a correction of the dosing quantity (Q m ) is carried out. [2] Method according to claim 1, characterized bythat the modelling of the pressure oscillation (105) at the dosing valve (310) as a function of a sound velocity (α) in the reagent (105), a density (ρ) of the reagent (105), a cross-section (A D ) a pressure line (102), in particular between the pump (120) and the metering valve (310), a volume flow (Q V,stat ) through the metering valve (310) and the length (L) of the pressure line (102). [3] Method according to one of the preceding claims, characterized by that a period (T) is determined as a function of the length of the pressure line (102) and the speed of sound (a). [4] Method according to one of the preceding claims, characterized by that a minimum pressure (Δp min ) is determined using the following formula: Δpmin=ρa2α21+4p1ρa2α2−1+2, with ρ the density of the reagent (105), a the speed of sound in the reagent (105) in the pressure line 102, α a factor depending on the cross-section (A D ) of the pressure line (102), a volumetric flow (Q stat,V ) of the dosing valve (130) at an initial pressure (p1) to start dosing with: α=Qstat,Vp1ρ. [5] Method according to one of the preceding claims, characterized by that a maximum pressure (Δp max ) is determined using the following formula: Δpmax=−B+B2−4AC2A with A=1 / (ρa2α2),B=(2p2−Δpmin) / (αaρ)−1,C=−Δpmin and a second pressure (p2) which corresponds to a second pressure p2 at half a period (T) of the pressure oscillation. [6] Method according to one of the preceding claims, characterized bythat a frequency (f) of the pressure oscillation (105) is determined as a function of the speed of sound (a), corresponding to a length of the pressure line (102), in particular between the pump (120) and the metering valve (310). [7] Method according to claim 6, characterized by that the frequency (f) of the pressure oscillation is determined according to the following formula: f=a4(L+l2);T=1f with f the frequency of the pressure oscillation (105), a the speed of sound, L the length of the pressure line (102), in particular between the pump (120) and the metering valve (310), I the length of the pressure wave of the pressure line structure and T the period of the pressure oscillation (105). [8] Computer program which is designed to carry out a method according to one of claims 1 to 7. [9] An electronic storage medium comprising a computer program according to claim 8. [10] Device, in particular control device (200), which is designed to carry out a method according to one of claims 1 to 7.

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