DE102017220533A1 - A method of operating a reagent dosing system, apparatus and conduit network for carrying out the method - Google Patents

Abstract

The invention relates to a method for operating a reagent dosing system (10), which is set up to convey a reagent (14) along a conveying direction (15) through a line network (N) to a dosing element (D1) which contains the reagent (14). dosed into an exhaust gas duct (16) of an internal combustion engine (18) upstream of an SCR catalytic converter (20), characterized in that the ductwork (N) has a main duct (H), a first duct branch (L1) and a further duct branch (L2) for transferring reagent (14), wherein after completion of the metering operation by the first line branch (L1) downstream metering element (D1) and a further line branch (L2) downstream further metering element (D2), the reagent (14) in such a way from the first Line branch (L1) and / or the at least one further line branch (L2) is taken that in total so much reagent (14) is removed that in the case of a rearrangement of the Reagenzmi Is prevented by a line branch (L1) in the other line branch (L2) due to a hydrostatic compensation, a loading of the first metering element (D1) or the further metering element (D2) with reagent (14). The invention further relates to a line network, a control unit, by means of which the reagent dosing system is operated, and a control program product with a computer program stored on a machine-readable carrier for carrying out the method.

Description

The invention relates to a method for operating a reagent dosing system, which doses a reagent in the exhaust passage of an internal combustion engine upstream of an SCR catalyst, and a device and a line configuration for carrying out the method.

The invention further relates to a pipeline network, a control unit, with the aid of which the reagent dosing system is operated, and a control program product with a computer program stored on a machine-readable carrier for carrying out the method.

State of the art

For the aftertreatment of the exhaust gas of an internal combustion engine, a selective catalytic reduction (SCR) with the aim of reducing nitrogen oxides (NOx) in the exhaust gas can be used. In this case, a defined amount of a selectively acting reagent is metered into the exhaust passage of the internal combustion engine. The reagent may be ammonia, which is obtained for example from a precursor in the form of a urea-water solution in the exhaust gas channel by hydrolysis.

Such a reagent dosing system is for example from the published patent application DE 196 07 073 A1 known. The urea-water solution is conveyed through a line from a tank to a metering valve and metered into an exhaust passage of an internal combustion engine upstream of an SCR catalyst, wherein the metering rate is determined by means of the metering valve.

In current reagent dosing systems, as they are known under the name DENOXTRONIC Applicant, a pump sucks the urea-water solution from a reagent tank and compacts them to the required system for atomization pressure of, for example, 3 to 9 bar. Taking into account, for example, current engine data and catalyst data, the metering rate of the reagent is adjusted to the maximum possible NOx reduction.

The commonly used, defined in DIN standards urea-water solution has the property of freezing at about -11 ° C. The volume expansion of the urea-water solution accompanying freezing can lead to damage to the lines and other components such as, for example, the pump or the metering valve. Therefore, it can be provided, after the stopping of the internal combustion engine or after switching off the reagent metering system, the urea-water solution from the reagent metering system, in particular from the metering valve to suck back into the tank. This ensures that the reagent dosing can freeze at temperatures of -11 ° C or below, without any damage to be feared by the volume expansion of the freezing urea-water solution.

In the published patent application DE 10 2010 031 651 A1 a reagent dosing system is described with a metering valve. After switching off the reagent dosing system, the reagent is sucked out of the line system, in particular from the metering valve, for example by pumping by means of a pump against the conveying direction in the metering operation. Also, systems with two SCR catalysts arranged in series, each with a metering valve upstream of the respective catalyst, are known from US Pat DE 102012221905 ,

It would therefore be desirable to provide a method and apparatus that allow for easy emptying of a reagent metering system based on multiple injection sites after the reagent dosing system is shut down.

Disclosure of the invention

The invention relates to a method for operating a reagent dosing system, which is set up to convey a reagent along a conveying direction through a line network to a dosing element, which doses the reagent into an exhaust passage of an internal combustion engine downstream of an SCR catalyst, characterized in that A main line, a first line branch and a further line branch for transferring reagent, wherein after completion of the dosing by the downstream of the first line branch metering and downstream of the other leg further dosing the reagent removed such from the first leg or the at least further leg is that in total so much reagent is removed, that in the case of a rearrangement of the reagent from one line branch in the other line branch in a row hydrostatic balancing de s reagent, re-acting on the first metering element or the further metering element is prevented. It is understood that the reagent can be removed either from the first leg or the second leg or alternatively from the first leg and the second leg in the context of the method. Furthermore, the invention relates to a pipeline network for a Reagent dosing system, having a main line which is connected to a first line branch and / or at least one further line branch for transfer of reagent, wherein the first line branch and the at least one further line branch are connected via a branch element, wherein the line network is set up such that in total so much reagent can be removed that in the case of a rearrangement of the reagent from one line branch into the respective other line branch as a result of hydrostatic compensation, a renewed loading of the first metering element or the further metering element with reagent omitted.

The inventive method is particularly applicable in the context of the device according to the invention, since it is for the case when reagent is removed from at least one of the line branches, they are hydraulically connected to each other, which can lead to that in the case of a position difference or height difference between the one and the other line branch can come to volume compensation movements of the reagent within the first and the further line branch, whereby even in the case of suction of reagent from at least one of the line branches of the other line branch can be re-supplied with reagent. This is problematic, in particular, when the reagent in the respective line branch again penetrates so far that the metering elements connected at the ends to the respective line branch are refilled. In particular, these metering elements are particularly sensitive at low temperatures with respect to a volume expansion of the liquid reagent (ice pressure), whereby such refilling of the metering, in particular at temperatures at which the reagent performs a phase transition from the liquid phase into the solid phase, always to prevent is.

Such a displacement of reagent occurs, in particular, when one of the line branches lies at least partially at a higher hydrostatic level relative to the respective other line branch, which means that there is a height difference between partial areas of the respective line branches. As a result, due to the hydrostatic pressure of the liquid column when opening the dosing, as is usually done during a suction, it comes to a fluid shift from the higher branch to the lower branch, whereby a refilling of the lower branch can be done. Exactly this can be prevented in the context of a suction process in the context of the method according to the invention as well as in the context of the device according to the invention.

In a further preferred embodiment, the first line branch and the further line branch are connected by a branch element, the reagent being taken from the first line branch and / or the further line branch. The use of a branch element is advantageous, since in this way a liquid reservoir can be created between the first line branch and the further line branch, which acts as a buffer element. By removing from at least one of the line branches, it can be ensured that the position of the removal point or removal points can be adapted to the course of the respective branches or to the respective height level differences of the partial branches, so that in each case sufficient reagent from the dosing and from parts the line branches can be removed, so that damage to the metering element or the respective line branches can be reliably prevented by ice pressure. It should be understood that corresponding reagent can be removed from both the first and the further line branch. The removal point of the respective line branch thus also depends on the respective positioning of the line branches relative to each other.

In a further advantageous embodiment of the invention, removal from the first line branch and / or the further line branch takes place such that ventilation of the branch element is prevented. This can be done constructively in the context of the pipeline network, that the positioning of the sampling points is provided accordingly, that they are positioned with a corresponding safety distance to the branch element, as well as in the context of the method, since in the process only so much reagent from the respective Is removed line branches that ventilation of the branch element can be safely prevented.

In a further preferred embodiment of the invention, the first line branch has a first volume and the further line branch has a further volume, wherein a maximum of one third of the first volume or of the further volume, preferably one quarter of the first volume or of the further volume, preferably of the line branch with the lower volume, is taken. It is understood that the respective line branches can be formed with the same or different volume. In the case of different volumes for the respective line branches, the above-mentioned values are respectively taken from the line branch with the respective lower volume.

By means of the abovementioned measures it can be reliably prevented that one of the metering elements is refilled by a fluid transfer within the respective line branches, and that a ventilation of the branch element positioned between the first and the further line branches takes place.

In a further preferred embodiment of the method, a further volume of at least 10%, at most 20%, preferably 13%, of the volume of the first line branch or the volume of the further line branch is taken from one or both of the line branches. By means of the aforementioned measure, it can be ensured that a further amount of liquid is removed from the respective line branches, whereby an improved protection against frost damage, which can be caused by freezing of the reagent at low temperatures, is prevented.

In a further preferred embodiment of the method, the main line has a further volume, with an additional 5% of the volume of the main line being removed from the first line branch and / or the further line branch. By this measure, a frost damage due to the ice pressure of the reagent at low temperatures can be further prevented.

In a further preferred embodiment of the pipeline network according to the invention, the pipeline network has a hydrostatic level compensation element. By positioning at least one hydrostatic level compensating element, in particular a siphon, in at least one of the line branches, preferably in the line branch, which has a lower hydrostatic level than the other line branch. In this way it can be ensured that the pressurization and the associated displacement of the liquid column in the case of an opening of at least one of the metering elements can be compensated accordingly by the hydrostatic compensation element. By means of this measure, a corresponding re-admission of an already sucked-back section of at least one line branch during a suction process can be reliably prevented.

In a further preferred embodiment, the first line branch and / or the further line branch has a removal point, which is arranged in the first line branch and / or in the further line branch, that in the case of a rearrangement of the reagent from one line branch into the other line branch in sequence a hydrostatic compensating movement of the liquid volume, a renewed pressurization of the first metering element or of the further metering element with reagent is omitted. By choosing the respective positioning of the sampling point in the first and / or in the second leg can be ensured that on the one hand a safe removal of the reagent to protect the line branches and the metering done by ice pressure, as well as a refilling of the at least one metering in the course of a suction can. In addition, it can be ensured by a sufficient distance of the sampling points to the branching element, which connects the first and the other line branch with each other, that ventilation of the branching element is prevented by the sucked back by the metering air during a suction process.

The implementation of the method in the form of a computer program, which is preferably stored on a data carrier, in particular on a memory in the form of software and is available in a control device for carrying out the method or by the provision of an integrated circuit, in particular an ASIC advantageous, since this causes particularly low costs, especially if an executive controller is still used for other tasks and applications, and therefore already exists anyway. Suitable data carriers for providing the computer program are, in particular, magnetic, optical and electrical memories, as are frequently known from the prior art.

Further advantages and embodiments of the invention will become apparent from the further description and the accompanying drawings.

list of figures

• 1 shows a schematic overview of a reagent dosing system according to a first embodiment and its connection to an exhaust passage of an internal combustion engine;
• 2 shows the reagent dosing system 1 as a technical environment, in which a method according to the invention runs, in an enlarged view 1 ,
• 3 shows a flowchart of the method;
• 4 shows a further embodiment of a pipeline network, which serve for description as a technical environment for further embodiments of the method according to the invention; and
• 5 shows a still further embodiment of a pipeline network, which serve for description as a technical environment for further embodiments of the method according to the invention.

Detailed description

1 shows a reagent dosing system 10 one in a tank 12 stocked reagent 14 via a pipeline network N to an exhaust duct 16 an internal combustion engine 18 promotes, being the conduit network N a first line branch L1 and at least one more leg of the line L2 having, via a branch element with a main line H are connected, and at the end of each a metering element D1 and D2 is located, by the metering elements D1 and D2 the reagent 14 each upstream of a first SCR catalyst 20 and to a second SCR catalyst 22 is metered. During the dosing process, the reagent 14 along the main line or along the first line branch or the second line branch L1 . L2 in the direction of a conveying direction 15 promoted. For the reagent 14 it is preferably a urea-water solution, which is a precursor of the in the SCR catalysts 20 . 22 required reagent represents ammonia. The following is only the term reagent 14 used.

The reagent 14 is from a feed pump 24 brought to an operating pressure, for example, 3 to 9 bar. This operating pressure preferably corresponds to the operating pressure of the reagent dosing system 10 , The dosing rate of the reagent 14 in the respective SCR catalyst 20 . 22 is through the the SCR catalysts 20 . 22 upstream dosing D1 or. D2 adjusted, wherein the metering elements D1 . D2 from a controller 26 be controlled. It is understood that the corresponding metering rate cumulatively or alternatively by an additional admission of the feed pump 24 through the control unit 26 can be done.

For controlling the dosing elements D1 . D2 or the feed pump 24 is a control line 27 intended to exchange data. The control unit 26 is via the control line 27 continue with another pump 28 connected, which is adapted to the reagent 14 After completion of the dosing process, suck it back out of the mains N. A possible Rücksaugvorgang can in principle be initiated, in particular, when the outside temperatures below a temperature threshold, which is usually slightly above the freezing temperature of the detergent-water solution of about -11 ° C. Through the suck-back process by means of the pump 28 is therefore the reagent 14 from the other line branch L2 and / or from the first leg of the line L1 (shown in dashed lines) and the dosing elements connected thereto D1 and D2 aspirated, wherein the reagent 14 from the dosing elements D1 and D2 completely and out of the line branches L1 and or L2 is at least partially sucked back to damage the pipe network N or the particularly sensitive dosing D1 and D2 by a temperature-induced volume expansion of the reagent (ice pressure) to prevent.

In the context of the method according to the invention, however, the reagent is only to the extent of the first line branch L1 and / or the further line branch L2 taken that on the one hand ventilation of the branching element A is prevented and on the other hand in total so much reagent 14 is taken that in the case of a rearrangement of the reagent 14 from the higher lying first line branch L1 in the lower lying line branch L2 as a consequence, a hydrostatic compensation of the reagent 14 , a renewed admission of the further metering element D2 is prevented. The reagent 14 is through a first sampling point E1 from the first leg L1 and another withdrawal point E2 from the other line branch L2 taken. By aspirating typically the metering D1 and or D2 open it so that it passes through the sucked reagent 14 to a suction of air in the line branches L1 or. L2 comes. This is the reagent 14 However, only sucked back so far that the branch element is not ventilated. This can be done in the context of the process by the extracted amount of the reagent 14 and / or by a corresponding positioning of the sampling points E1 . E2 in the respective line branches L1 . L2 respectively. The above-mentioned measures can equally also with respect to the avoidance of a volume rearrangement of the reagent 14 in the line branches L1 . L2 be adjusted accordingly.

For this purpose, an embodiment of the pipeline network is particularly suitable N in which the first line branch L1 a volume V1 and the further line branch L2 a volume V2 which are identical. The main branch here has a volume V3 on. An example is the pipeline network N now designed so that the volume V1 a volume of 4700 mm ³ , the volume V2 a volume of 4700 mm ³ and the main line has a volume of 6300 mm ³ . However, these values can only be seen as examples and can basically be scaled arbitrarily. Also an asymmetric distribution of the volumes between the first leg L1 and the further line branch L2 is possible in principle. Furthermore, in the first embodiment of the pipeline network N to see that the dosing element D1 opposite the metering element D2 is at a different hydrostatic height level. Whereby a first section A1 of the first line branch L1 at the same hydrostatic level is like a section A2 of the second line branch L2 , whereas another section A3 of the first line branch L1 has a rising in height course, and that metering D1 opposite the metering element D2 a height difference of h1 having. The partial volumes of the first section A1 and the further section A3 of the first line branch L1 are preferably 3000 mm ³ for the volume V ₁₁ in the first part A1 and the further volume V ₁₂ for the further section A3 is 1700 mm ³ .

The procedure is in 3 explained in the context of a flowchart. This will be done in a first step SU1 (see. 3 ) a volume of VR1 from the first leg L1 and a volume VR2 from the second leg L2 sucked back that in a range of 10 to 20% of the total volume V1 of the first line branch L1 or. V2 of the second line branch L2 is. The volume is preferably about 13% of the total volume of the respective line branch L1 . L2 , based on 4700 mm ³ as the total volume for the first leg L1 and the second leg L2 in about 600 mm ³ .

In a further process step SU2 will be another 10% of the total volume V1 or. V2 from the first leg L1 and the second leg L2 in the tank 12 sucked back. In a further step SU3 will be another 5% of the volume V3 the main line, which in the present case is 6300 mm ³ , from the first line branch L1 and from the second leg L2 sucked back. In a further step SU4 becomes the reagent 14 from the first leg L1 and the further line branch L2 sucked back up to an upper limit O (cf. 2 ), wherein the volume sucked back in about one third of the total volume of the respective leg L1 . L2 equivalent. With the present exemplary numerical values, one-third of the respective volume of the line branches is thus ever L1 . L2 from 4700 mm ³ thus in about 1570 mm ³ from the respective sub-branches L1 and L2 sucked back. By the above measures can gradually to the risk of Eisdruckbeschädigung the first metering D1 or of the further metering element D2 or the associated line branches L1 and L2 responds, and also a volume rearrangement between the sub-branches L1 and L2 safely prevented.

In the 4 and 5 is another embodiment of a reagent dosing system 10 with a pipeline network N shown in addition in the second leg L2 a hydrostatic leveling element 30 in the form of a siphon 32 having. Otherwise, the correspond in the 4 and 5 Embodiments shown the embodiments of the 1 to 3 , therefore also regarding the rest of the description to the description of the 1 to 3 Reference is made.

By using the hydrostatic compensating element 30 in the form of a siphon 32 may be a volume shift of the reagent 14 due to the different hydrostatic height level h2 of the first metering element D1 opposite the second metering element D2 or the associated sections of the line branches A3 in the first leg and A2 be balanced accordingly in the second leg. This is especially true when the subsections A1 and A2 be located at the same hydrostatic height level, as well as in 5 represented by an inclination of the entire system of about 15 °, a corresponding hydrostatic volume displacement also with respect to the sections A1 and A2 of the first line branch L1 and it second line branch L2 result. In this way, on the one hand, in particular the typical hydrostatic height differences can be compensated, which result from a corresponding cable routing within a vehicle, as well as in 5 Figure 4 illustrates a variation of the hydrostatic pressure resulting from typical driving situations, for example on the mountain, of a vehicle into which the reagent dosing system 10 is integrated. In the 3 in the context of the method described Rücksaugschritte are also in the context of the embodiment according to 4 and 5 applicable accordingly.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The 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

• DE 19607073 A1 [0004]
• DE 102010031651 A1 [0007]
• DE 102012221905 [0007]

Claims (13)

Method for operating a reagent dosing system (10), which is set up to convey a reagent (14) along a conveying direction (15) through a pipeline network (N) to a dosing element (D1), which deposits the reagent (14) into an exhaust gas channel (15). 16) of an internal combustion engine (18) upstream of an SCR catalyst (20) metered, characterized in that the line network (N) a main line (H), a first line branch (L1) and another line branch (L2) for the transfer of reagent (14), wherein after completion of the metering operation by the first line branch (L1) downstream metering element (D1) and a further line branch (L2) downstream further metering element (D2), the reagent (14) in such a way from the first line branch (L1) and / or the at least further line branch (L2) is taken that in total so much reagent (14) is removed that in the case of a rearrangement of the reagent of a Leitungszw eig (L1) in the respective other line branch (L2) due to a hydrostatic compensation, an admission of the first metering element (D1) or the further metering element (D2) with reagent (14) is prevented. Method according to Claim 1 , characterized in that the first line branch (L1) and the further line branch (L2) are connected by a branch element (A), wherein the reagent (14) from the first line branch (L1) and / or the further line branch (L2) becomes. Method according to Claim 2 , characterized in that a removal from the first line branch (L1) and / or the further line branch (L2) takes place in such a way that ventilation of the branching element (A) is prevented. Method according to Claim 1 to 3 , characterized in that the first line branch (L1) has a first volume (V1) and the further line branch (L2) has a further volume (V2), wherein a maximum of one third of the first volume (V1) or of the further volume (V2), Preferably, a quarter of the first volume (V1) or the further volume (V2), preferably the line branch (L1, L2) is taken with the smaller volume. Method according to one of the preceding claims, wherein a further volume of at least 10%, at most 20%, preferably 13% of the volume (V1) or the volume (V2) from one or both of the line branches (L1, L2) is removed. Method according to one of the preceding claims, wherein the main line (H) has a volume (V3), wherein in addition a further 5% of the volume (V3) from the first line branch (L1) and / or the further line branch (L2) is removed. Line network (N) for a reagent dosing system (10), having a main line (H), which is connected to a first line branch (L1) and / or at least one further line branch (L2) for the transfer of reagent (14), wherein the first line branch (L1) and the at least one further line branch (L2) are connected via a branch element (A), wherein the line network (N) is set up so that in total so much reagent (14) can be removed that in the case of a rearrangement of the reagent (14) from one line branch (L1) into the respective other line branch (L2) as a result of hydrostatic compensation, a renewed loading of the first metering element (D1) or of the further metering element (D2) with reagent (14) is omitted. Line network (N) to Claim 8 wherein the first line branch (L1) and / or the further line branch (L2) comprises a hydrostatic level compensation element (30). Line network (N) to Claim 7 or 8th in which the first line branch (L1) and / or the further line branch (L2) has a removal point (E1, E2) which is arranged in the first line branch (L2) and / or in the further line branch (L2), that in the case of Rearrangement of the reagent (14) of a line branch (L1) in the other line branch (L2) due to a hydrostatic compensation, a renewed loading of the first metering (D1) or the other metering element (D2) with reagent (14) is omitted. Line network (N) to Claim 8 to 10 , wherein the first line branch (L1) and / or the further line branch (L2) has a removal point (E1, E2), which is arranged in such a way in the first line branch (L1) and / or in the further line branch (L2), that a ventilation of Branch element (A) is omitted. Control device (S), which is adapted by a corresponding integrated circuit and / or by a stored on a memory computer program to perform a method according to any one of the preceding claims. A computer program that causes the controller (26) to perform a method according to any one of the preceding claims when executed on the controller (S). Machine-readable storage medium with a computer program stored thereon Claim 13 ,

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