Method for achieving higher metrology quality accuracy in a pressure-regulated metrology system with at least two metering valves

Abstract

This invention relates to a method for operating a pressurized metering system, the metering system including a delivery module, at least two tolerant metering valves, and a pressure sensor. During pressure regulation, an adaptation factor is determined for each metering valve from at least two system mass balances of the metering system, based on at least two adaptation cycles with different drive ratios for the metering valves. The drive control of the at least two metering valves is then adapted using the adaptation factor.

Description

Technical Field

[0001] This invention relates to a method for operating a metering system in which pressure regulation is combined with adaptive control of at least two metering valves to improve the metering accuracy of the entire system. Furthermore, the invention relates to a computer program that, when run on a computer, implements each step of the method, and to a machine-readable storage medium storing the computer program. Finally, the invention relates to an electronic controller configured to implement the method. Background Technology

[0002] Pressure-regulated metering systems are typically based on the principle that a pump provides the desired system pressure and regulates it to the narrowest possible range around a defined threshold, and a metering device, typically a metering valve, measures the desired mass from this pressure by setting a matching valve opening time. In such systems, the accuracy of the metering mass depends primarily on the tolerances of the metering valve.

[0003] In so-called non-reflux "volume measurement systems," the high accuracy typically found in (reciprocating piston) pumps is utilized, along with the characteristic that, in a static state, the mass delivered by the pump, known with extremely high precision, also leaves the system again as a metered mass. Here, due to the principle of volume measurement combined with the small mass tolerance of the reciprocating piston pump, a very high average mass accuracy is achieved. However, regarding pressure, there is usually no closed-loop regulation loop; more precisely, the system pressure is generated based on the pre-control and tolerances of the pump and metering valve, and there is no readjustment of the system pressure. This typically leads to a large tolerance in the generated system pressure. Therefore, the prior art offers high pressure stability at the cost of higher metering quality tolerance in pressure-regulated systems, or better metering quality tolerance at the cost of higher pressure fluctuations in purely pre-controlled "volume measurement systems."

[0004] Methods and apparatuses for operating internal combustion engines, particularly in motor vehicles, are also known, in which an SCR (Selective Catalytic Reduction) catalytic converter is arranged in the exhaust system of the motor vehicle. The SCR catalytic converter reduces nitrogen oxides (NOx) contained in the exhaust gas of the internal combustion engine to nitrogen in the presence of a reducing agent. This can significantly reduce the proportion of nitrogen oxides in the exhaust gas. Ammonia (NH3) is required for the reaction. An ammonia-releasing agent is used as the reactant, which is mixed with the exhaust gas. Typically, an aqueous urea solution is used for this purpose, which is injected into the exhaust system upstream of the SCR catalytic converter.

[0005] To deliver and meter the reducing agent solution from the reducing agent tank, a hydraulic metering system is typically provided. This system includes a delivery pump, pressure lines, at least one metering module with at least one metering valve, and necessary sensing devices and electronic control devices. Metering systems with two or more metering modules and metering valves are also known. The delivery pump delivers the reducing agent solution from the reducing agent tank to the metering module through the pressure lines. For on-demand metering, the required or desired metered mass of the reducing agent solution is metered into the exhaust system via the metering valve.

[0006] When the metering valve is actuated, that is, when current is applied for actuation, the metering valve opens. The metering valve remains open for a fixed actuation duration, thus the reducing agent is injected into the exhaust system. When the metering valve is no longer actuated, that is, when no current is applied, the metering valve closes again. The actuation duration and the pressure in the pressure line, and therefore in the metering valve, are important factors determining the metering quality of the metered feed, in addition to the geometry of the nozzle disc. Here, variations in the tolerances during nozzle disc manufacturing or in the nozzle disc geometry due to deposits during operation can significantly affect the static flow rate of the metering valve.

[0007] DE 10 2016 220 795 A1 describes a method for operating a pressurized metering system with a metering valve. During pressure regulation, adaptation is performed to the tolerant metering valve. Adaptation is preferably performed using an adaptation factor. Through the combined action of pressure regulation and adaptation of the drive, high accuracy in metering input is achieved.

[0008] DE 10 2010 031 655 A1 describes a method for operating a pressure-regulated metering system for an SCR catalyst. The pressure regulator adjusts the pressure in the SCR system by adjusting the drive of the delivery pump based on the current requirement for the opening duration of the metering valve. The purpose of this adjustment is to match the pre-existing actual pressure with the desired pressure. A key advantage of the method described here is the use of adaptive pre-control for regulation. In adaptive pre-control, the adjustment signal of the delivery pump motor under different drive controls of the metering valve is learned. Once the adaptive pre-control has learned two or more points, it is used to determine the next required adjustment signal for the delivery pump motor. While other actuators in the metering system can be used as adjustment signals besides the delivery pump motor, the delivery pump motor provides an extremely accurate signal. As a result, pressure overshoot and undershoot, and the associated long settling times, that occur with large metering variations are avoided, thus optimizing the quality of regulation. Summary of the Invention

[0009] This invention relates to a method for operating a pressurized metering system, the metering system comprising: a delivery module having typically small delivery tolerances; at least two metering valves typically having larger tolerances; pressure lines connecting the delivery module to the metering valves; and pressure sensors disposed between the delivery module and the metering valves. It is important to note that this metering system has no loops and is therefore a closed system when there is no metering input, and there is no leakage of metered mass. The metering system is, for example, a metering system used for SCR catalysts, in which a reducing agent solution is injected into the SCR catalyst.

[0010] There are adaptation cycles corresponding to the number of metering valves. As a specific example, there are two adaptation cycles for two metering valves. In each adaptation cycle, the metering valves are driven with different drive ratios, so the proportion of the mass fed through each metering valve is different for each adaptation cycle. Different drive ratios are typically achieved in conventional metering strategies. Specialized test measurements are usually not required. The appropriate adaptation cycle is selected based on the metering quality requirements, thus standardizing the metering feed for each adaptation cycle to the same metering quality. Therefore, the duration of the adaptation cycle is correspondingly longer under lower metering quality requirements than under higher metering quality requirements.

[0011] When pressure regulation is performed in a metering system, the adaptation factor for each metering valve is determined by the system mass balance of all systems associated with the adaptation cycle. This results in a system of equations in which the number of equations obtained from the system mass balance for different adaptation cycles corresponds to the number of unknowns, i.e., the adaptation factor for each metering valve. For this purpose, reference is also made to DE 10 2016 220 795 A1, which is incorporated herein by reference. This yields the tolerant static flow rate through each valve, which can then be compensated for by adaptation.

[0012] An adaptation factor is used to adapt the drive control of a tolerance-controlled metering valve. By calculating the adaptation factor, the deviation between the actual metering mass supplied by the metering valve and the standard metering mass can be quantified, and this deviation can be corrected by adapting the drive control of the metering valve using the adaptation factor. When the adaptation factor is 1, the actual metering mass supplied by the metering valve corresponds to the standard metering mass. The imagined, perfect metering mass of reducing agent supplied by a tolerance-free metering valve is called the standard metering mass.

[0013] In a volumetric metrology system, high accuracy of the metered mass can be achieved because the entire mass being transported, typically with small tolerances, is completely metered due to the absence of a loop. Here, the high accuracy of the transport module is utilized to obtain high accuracy and therefore low tolerance of the transported mass. A reciprocating piston pump or diaphragm pump in the transport module should be used as an example, which transports a predetermined amount of volume in each stroke by the pump's element space, i.e., a reciprocating piston.

[0014] The result is that the advantages of a pressure-regulated system, namely, the small tolerance of the pressure at the metering input, are combined with the advantages of a volumetric measurement system, namely, the complete small tolerance of the metering mass delivered and then also metered, in order to obtain a generally high accuracy of the metering mass during the metering process through at least two metering valves.

[0015] The system mass balance preferably includes the mass delivered by the conveying module and the mass fed in by standard metering valves. Because the metering system has no loops and is therefore closed, a system mass balance should be achieved where the sum of the stated parameters is zero. This is based on the premise that the metering system has no leaks.

[0016] For qualitative evaluation, the adaptation factor is determined only when the drive-control ratios differ sufficiently from each other across different adaptation cycles. This is particularly important when the method is implemented under conventional metering strategies. A ratio threshold can be set for this purpose. That is, two different adaptation cycles can be considered suitable for determining the two adaptation factors according to the proposed method when the ratio of the mass normally metered through one of the two metering valves to the mass normally metered through all the metering valves over a given cycle (i.e., the proportion of the mass normally metered through the metering valves to the total normally metered mass), and the ratio of the mass normally metered through one of the two metering valves to the mass normally metered through all the metering valves over other adaptation cycles differ from the ratio threshold by more than the ratio threshold. Otherwise, the measurement is not adopted. Larger differences in ratios across different adaptation cycles are advantageous for evaluation. The result is robust use of the method in operation.

[0017] Optionally, it can be specified that the adaptation factor is repeatedly calculated for different adaptation cycles. Then, multiple adaptation factors are calculated for each metering valve. These multiple adaptation factors are then weighted and averaged. Finally, the averaged adaptation factor is used for the adaptation of the metering valve. This improves the robustness of the method.

[0018] For the special case where the feed is metered through only one metering valve during the adaptation period, it is preferable to first determine the adaptation factor for that metering valve (through which the feed is metered) solely from the system mass balance during the adaptation period. This is also effective when the feed is decisively metered through one metering valve within an adaptation period, while simultaneously metering a very small, essentially negligible mass through another / multiple other metering valves. As an example, the feed is metered through only this first metering valve during the first adaptation period, so it is preferable to determine the adaptation factor for this first metering valve solely for the first adaptation period. When the feed is also metered through at least another metering valve, the determined adaptation factor is taken into account when determining the adaptation factor for said other metering valve from the system mass balance. In the previous example, when the feed is metered through only the second metering valve or through both metering valves during the second adaptation period, the first adaptation factor is taken into account when determining the second adaptation factor for the second metering valve from the system mass balance. This simplifies the calculation of the adaptation factor.

[0019] When these metering valves are rarely in operation, their tolerances are initially typically within the tolerance range of the delivery pump. In this case, the deviation between the actual metered mass supplied by the metering valve and the standard metered mass is usually small and often does not require adaptation. During operation, the metering valves may become clogged, thus increasing the deviation from the standard state. To reduce unnecessary adaptation and perform adaptation only in the metering valves (where a large deviation is highly probable), it can be stipulated that adaptation of the drive of at least two metering valves is only performed using the adaptation factor when the adaptation factor differs from 1 (the standard metered mass corresponding to the actual metered mass) by an adaptation factor threshold.

[0020] Nevertheless, even in adaptation scenarios where no metering valve is installed, data on the static flow rate through the metering valve is still obtained. This data can be used to monitor the metering valve, thereby enabling targeted replacement of the metering valve (“Pinpointing”).

[0021] The computer program is configured to perform each step of the method, particularly when executed on a computer or controller. The computer program enables the method to be implemented in a conventional electronic controller without requiring structural changes. For this purpose, the computer program is stored on a machine-readable storage medium.

[0022] An electronic controller according to the present invention is obtained by running a computer program on a conventional electronic controller, the settings of which are adapted to the duration of opening. Attached Figure Description

[0023] Embodiments of the present invention are shown in the accompanying drawings and will be explained in detail in the following description.

[0024] Figure 1 A metering system is shown that can operate using an embodiment of the method according to the invention; Figure 2 A flowchart of one embodiment of the method according to the present invention is shown; Figure 3 The diagram illustrates how the derived adaptation factor can be used continuously during adaptation. Detailed Implementation

[0025] The present invention will now be illustrated using a metering system in the form of an SCR (Selective Catalytic Reduction) system as an example.

[0026] Figure 1 An SCR system is shown as a metering system 10 for delivering a reductant via a pressure line 11 to an SCR catalyst (not shown). This metering system includes a delivery module 12, which includes a delivery pump 13 configured to deliver the reductant from a reductant tank 14. In this embodiment, the delivery pump 13 is configured as a reciprocating piston pump or a diaphragm pump. The delivery module 12 is connected to two metering modules 15 and 16 via the pressure line 11. Each metering module 15, 16 has metering valves DV1 and DV2, respectively, and is located at different points in an exhaust system (not shown). The reductant is delivered by the delivery module 12 via the pressure line 11 to the metering modules 15, 16 at desired metered masses, where it is then metered into the exhaust system via metering valves DV1, DV2. Furthermore, the pressure line 11 has a pressure sensor 17 in a common section that measures the actual pressure in the pressure line 11. The pressure sensor 17 and the delivery module 12 are connected to an electronic controller 18 and form a common regulation loop. The electronic controller 18 controls the delivery pump 13 by pressure regulation based on the actual pressure and the desired pressure measured by the pressure sensor 17. The electronic controller 18 is also connected to and can control metering valves DV1 and DV2. The driving and control of metering valves DV1 and DV2 are adapted within the electronic controller. It should be noted that in this metering system 10, there is no loop to the reducing agent tank 14; therefore, the delivery module 12, pressure line 11, and metering modules 15 and 16 form a closed system. The pressure p established by the delivery pump 13 remains constant until the metering feed. The delivered reducing agent dosage is also not recirculated and is metered entirely into the exhaust system through metering valves DV1 and DV2 during metering feed.

[0027] Figure 2A flowchart of one embodiment of the method according to the invention is shown. Initially, the actual pressure 20 is measured by pressure sensor 17 and pressure regulation 21 is performed on metering system 10. During the implementation of metering requests 30, 40 (see below) via metering valves DV1, DV2, pressure regulation 21 is continuously performed in the closed pressure regulation loop.

[0028] In this application, the parameter is indicated by the index above the parentheses, signifying which adaptation cycle the parameter pertains to. In the first adaptation cycle 1, a metering quality request 30 is issued to metering valves DV1 and DV2. This metering requirement 30 includes the desired metering quality to be metered into the exhaust system through each of the two metering valves DV1 and DV2. The metering quality request 30 thus indirectly predetermines the drive ratio for the two metering valves DV1 and DV2. The metering quality request 30 is part of a conventional metering strategy, independent of the method according to the invention. Metering feed 31 is performed through the two metering valves DV1 and DV2 according to the metering requirement 30.

[0029] At the end of the first adaptation cycle 1, the metering quality of the 32 complete deliveries was determined. In the case of a reciprocating piston pump, the mass of reducing agent delivered in each stroke is determined by the piston volume. To determine the complete metered mass delivered... The mass of reducing agent delivered in each stroke is multiplied by the number of strokes performed during adaptation cycle 1. Furthermore, the desired metered mass is calculated by electronic controller 18 for the first adaptation cycle 1, resulting in a standard metered feed to the first metering valve DV1. And calculate the second mass of the standard ground metering input for the second metering valve DV2. The standard metering valve's assumption of perfectly metering the input reducing agent mass is called the standard metered input reducing agent mass. By definition, a standard metering valve has no tolerance regarding the mass of reducing agent to be metered by that standard metering valve. Therefore, the standard metered input mass... , Aside from the temperature effect, which can be easily compensated for, it depends only on the actual pressure and therefore has very small tolerances based on pressure regulation 21. For the first adaptation cycle 1, the following system mass balance can be listed according to Equation 1: (Formula 1), It is the first adaptation factor for the first metering valve DV1 and This is the second adaptation factor for the second metering valve DV2. The adaptation factor will be further explained below.

[0030] In the second adaptation cycle 2, another metering quality request 40 is issued to metering valves DV1 and DV2. The metering pre-set 40 specifies a different drive ratio for the two metering valves DV1 and DV2 than the drive ratio in the first adaptation cycle 1. The metering pre-set 40 is also part of a conventional metering strategy, implemented independently of the method according to the invention. According to the metering pre-set 40, another metering feed 41 is performed through the two metering valves DV1 and DV2.

[0031] Similarly, at the end of the second adaptation cycle 2, the metering quality of 42 complete deliveries was determined. Furthermore, the desired metering quality is determined by the electronic controller 18 for the second adaptation cycle 2, and the first mass 43 is calculated for the standard metering input to the first metering valve DV1. And calculate the second mass of the standard ground metering input for the second metering valve DV2. Standardized measurement of the input mass , Aside from the temperature effect, which can be easily compensated for, it depends only on the actual pressure and therefore has very small tolerances based on pressure regulation 21. For the second adaptation cycle 2, the following system mass balance can be derived according to Equation 2: (Formula 2), It is also the first adaptation factor for the first metering valve DV1 and It is the second adaptation factor for the second metering valve DV2.

[0032] Next, an inspection was conducted to qualitatively assess whether the drive ratios of the two metering valves, DV1 and DV2, were sufficiently different during the two adaptation cycles 1 and 2. For this purpose, for the first adaptation cycle 1, a standard mass metered through the first metering valve DV1 was calculated according to Formula 3. The mass fed in by standard measurement through the first metering valve DV1 The mass fed in is measured in a standard manner through the second metering valve DV2. The first proportion of the sum : (Formula 3).

[0033] For the second adaptation cycle, a second ratio was formed similarly according to Formula 4. : (Formula 4).

[0034] Check 50, first proportion Second ratio Is the difference greater than the predetermined proportional threshold? This means that the first proportion Second ratio Is the difference greater than the proportional threshold? If not, then the measurements for the two adaptation periods 1 and 2 are extremely similar and the measurements described in 51 are not adopted.

[0035] If the first ratio Second ratio The difference is greater than the proportional threshold. Then, according to formulas 1 and 2, the first adaptation factor for the first metering valve DV1 is calculated by system equilibrium. and the second adaptation factor for the second metering valve DV2 First adaptation factor This describes the difference between the actual metered input mass and the standard metered input mass of the reducing agent for the first metering valve DV1. The deviation between them, and the second adaptation factor This describes the difference between the actual metered input and the standard metered input of the reducing agent for the second metering valve DV2. The deviation between them.

[0036] According to Formula 5, the second fitness factor of 60 is calculated from Formulas 1 and 2 as follows. : (Formula 5).

[0037] Then, according to Formula 6, the second fitness factor of 70 is calculated from Formulas 1, 2, and 5 as follows. : (Formula 6).

[0038] In another embodiment, not shown here, multiple adaptation factors may be incorporated for each metering valve DV1, DV2 in a separate adaptation cycle, and then the multiple adaptation factors may be weighted and averaged to obtain an adaptation factor for the adaptation 80 of the drive control of metering valves DV1, DV2, as described below. , .

[0039] In another embodiment, not shown here, for the case where the feed is essentially metered only through the first metering valve DV1 during the first adaptation cycle 1 (and similarly possibly, essentially metered only through the second metering valve DV2), the first adaptation factor for the first metering valve DV1 is first determined by system mass balance during the first adaptation cycle 1. In this case, in the system mass balance of Equation 2, the term... It is zero because no mass is measured. The feed is metered through the second metering valve DV2. When the feed is metered through both metering valves DV1 and DV2, the second adaptation factor during the second adaptation cycle 2 is then calculated from the system mass balance according to Formula 2. The first fitness factor was taken into account at that time. .

[0040] During pressure regulation 30, adaptation 80 is performed on the drive control of metering valves DV1 and DV2 based on the volume measurement principle of the basic metering system. For each metering valve DV1 and DV2, an adaptation factor is applied. , The standard valve flow characteristic line stored in the electronic controller 18 is used below to correct the error. In order to obtain the adapted valve flow characteristic curve according to Formula 7. : (Formula 7).

[0041] After adaptation, the valve flow characteristic line The method takes into account both the actual metered mass of the reducing agent and the standard metered mass of the reducing agent. The deviation between them. Based on this adapted valve flow characteristic line. Adjust the required valve actuation duration. As a result, adjust according to the adaptation factor. , And thus the quality of the reducing agent delivered intact. and the mass of the reducing agent fed in a standardized manner Adjust the valve drive duration. This results in a significant reduction in the static mass tolerance of metering valves DV1 and DV2 after adjusting the valve drive duration.

[0042] Figure 3 Three variants are shown exemplarily for the first metering valve DV1, namely, the derived fitness factor. How can this be used in adaptation 80? To this end, we consider the value 1 with respect to the calculated adaptation factor. The adaptation factors used in adaptation 80 are shown. The three variation curves are 100, 101, and 102. A value of 1.0 is used for the fitness factor employed. This means that no adaptation is performed (80). In the first variant shown in the first variation curve 100, the calculated adaptation factor... This same principle applies to the driven metering valve DV1, thus the calculated adaptation factor... Corresponding to the fitness factors used ( = ).

[0043] In the second variant shown in the second variation curve 101, the calculated adaptation factor The adaptation factor derived from adaptation 80 The valve is only continuously and linearly switched on when its value deviates from the ideal value by more than 0.08. This can be advantageous when minor deviations in the flow quality of one of the standard metering valves should not be corrected, and larger deviations should be corrected at least more frequently.

[0044] In the third variant shown in the third variation curve 102, below the lower adaptation factor threshold... The fitness factor used when (in this example it is 0.82 and therefore differs from the value 1 by 0.18) Following the derived fitness factor Upper fitness factor threshold In this example, it is 1.18, and therefore also differs from the value 1 by 0.18. Above the second fitness factor threshold... At that time, the adaptation factor used Then, following the calculated fitness factor As in the second variant (second variation curve 101), a fitness factor around the ideal value of 1.0 is also generated here for the calculated value. The range in which no adaptation is performed (80), and therefore the adaptation factor used. It becomes 1. Without using the adaptation factor. Scope and full use of adaptation factors There is a linear transition between the ranges. When minor deviations in the flow quality of one of the standard metering valves should not be corrected, and when larger deviations are present, the calculated adaptation factor should be taken into full account. In such cases, this variant may be advantageous.

Claims

1. A method for operating a pressure metering system (10) without a loop, said metering system comprising a delivery module (12), at least two metering valves (DV1, DV2) and a pressure sensor (17), characterized in that, During pressure regulation (21), from at least two adaptation cycles (1, 2) with different drive ratios for the metering valves (DV1, DV2), for each metering valve (DV1, DV2), an adaptation factor (60, 70) is obtained from at least two system mass balances of the metering system (10). , The adaptation factor ( , ) is used to quantify the deviation between the metering quality actually supplied by the metering valve and the standard metering quality, and with the aid of the adaptation factor ( , Adaptation (80) to the drive control of at least two metering valves (DV1, DV2) is performed to correct the deviation.

2. The method according to claim 1, characterized in that, Each system mass balance includes at least one mass transported through the transport module (12). The mass of the input is measured by the metering valves (DV1, DV2) in accordance with the standard. ).

3. The method according to claim 1 or 2, characterized in that, Only when the mass fed in for adaptation cycle (1) is metered by one of the two metering valves (DV1, DV2) in accordance with standard procedures. The mass of the input is measured by standard through all metering valves (DV1, DV2). + The proportion of ) The ratio of (2) to other adaptation cycles () The difference exceeds the proportional threshold ( Only when this is done can the fitness factors (60, 70) be calculated. , ).

4. The method according to claim 1 or 2, characterized in that, Repeatedly calculate (60, 70) the adaptation factors for different adaptation cycles. , ), in order to obtain multiple adaptation factors for each metering valve (DV1, DV2) , ), where multiple adaptation factors are applied for each metering valve (DV1, DV2). , The weighted average is calculated and the weighted average adaptation factor is used for the adaptation of the metering valves (DV1, DV2) (80).

5. The method according to claim 1 or 2, characterized in that, When the feed is mainly metered through only one metering valve (DV1) during the adaptation period (1), the first adaptation factor is determined from the system mass balance only for the metering valve (DV1) metered during the adaptation period (1). ), and determine at least one second adaptation factor for at least one of the other metering valves (DV2) from one or more corresponding system mass balances. When the feed is also metered through at least one of the other metering valves (DV2), the first adaptation factor is taken into account. ).

6. The method according to claim 1 or 2, characterized in that, Only when the fitness factors differ from each other by a fitness factor threshold of 1 ( , Only when the adaptation factor is used () , Adaptation (80) to drive the at least two metering valves (DV1, DV2).

7. A computer program product comprising a computer program configured to perform each step of the method according to any one of claims 1 to 6.

8. A machine-readable storage medium having a computer program configured to perform each step of the method according to any one of claims 1 to 6 stored thereon.

9. An electronic controller (18) configured to operate the metering system (10) by means of any one of claims 1 to 6.

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