Device for providing a liquid additive

Abstract

Method for operating a device (1) for providing a liquid additive, comprising at least one suction point (17) for extracting liquid additive from a tank (2), a valveless delivery line (6) extending from the suction point (17) to a delivery unit (3), and a valveless positive displacement pump (4), wherein the positive displacement pump (4) is configured to pump the liquid additive from the tank (2) via the suction point (17) along the delivery line (6) to the delivery unit (3), wherein the positive displacement pump (4) has at least one seal (19) of the delivery line (6) which can be moved along the delivery line (6) for pumping the liquid additive, comprising at least the following steps: a. Determining an operational stop of the device (1); b. Determining the position (45) of the seal (19) within the positive displacement pump (4); and c. Changing the position (45) of the seal (19) if the position (45) of the seal does not correspond to a designated parking position (44), wherein the positive displacement pump (4) has a rotary drive (8) and a movable pump element (9), wherein the movable pump element (9) is moved for conveying in accordance with a rotary motion (32), characterized in that barbs (40) are provided on the movable pump element (9) which can interlock when the movable pump element (9) is moved with a rotary motion (32) against the conveying direction (5) and the barbs (40) are locked in the park position (44) after step c).

Description

[0001] The invention relates to a method for operating a device for supplying a liquid additive. Such devices are used particularly in the automotive sector to supply a liquid additive (fuel, water, ammonia, etc.) to an exhaust gas treatment system. Exhaust gas treatment systems are used especially for cleaning exhaust gases from diesel combustion engines, in which the conversion of nitrogen oxide compounds in the exhaust gas to harmless substances (nitrogen, carbon dioxide, and water) takes place with the aid of a reducing agent – ​​the process of selective catalytic reduction (SCR), which is known to those skilled in the art. This reducing agent can, for example, be supplied to the exhaust gas treatment system as a liquid additive. A urea-water solution is frequently used as the liquid additive in this context.A 32.5 percent urea-water solution is available under the trade name AdBlue® as an additive for exhaust gas treatment.

[0002] Devices for supplying a liquid additive for motor vehicles should be designed to be as cost-effective as possible and with as few different components as possible.

[0003] US Patent 2009 / 0301064A1 discloses an improved system and method for supplying urea to an exhaust gas treatment system. A urea pump assembly for an exhaust gas treatment system is provided. The pump assembly comprises a housing that includes a housing chamber, a first fluid inlet, and a first fluid outlet, the first fluid inlet being in fluid communication with the first fluid outlet via a first line. The housing further includes a second fluid inlet and a second fluid outlet, the second fluid inlet being in fluid communication with the second fluid outlet via a second flexible line. The second flexible line is located within a portion of the housing chamber and is in thermal communication with the first line.The pump assembly further includes a pump located in the housing chamber, the pump engaging with the second line and configured to move fluid between the second fluid inlet and the second fluid outlet.

[0004] US Patent 2005 / 0047925 A1 discloses a peristaltic pumping device and a pumping method. The pumping device comprises at least one rotor roller rotatable with respect to an occlusion of substantially constant radius. A recess is formed in the enclosure, extending beyond the substantially constant radius of the enclosure.

[0005] A problem with typical liquid additives is that they can freeze at low temperatures. AdBlue®, for example, freezes at -11 °C. Such low temperatures can occur in motor vehicles, especially during extended periods of inactivity in winter. Freezing causes the aqueous additive to expand in volume. This expansion can damage the system that delivers the liquid additive. This is particularly problematic for components that pump the liquid additive (such as pumps).

[0006] It is possible to design the liquid additive dispensing device in such a way that it is not damaged by the liquid additive freezing. This concept is typically relatively expensive. Another option is to empty the liquid additive dispensing device after the internal combustion engine has stopped running, so that no liquid additive can freeze in the device during a standstill. However, this concept requires additional actions after the engine has stopped, which may involve noise and increased stress on energy storage systems.

[0007] Based on this, the object of the present invention is to solve or at least alleviate the described technical problems. In particular, a method for operating a device for supplying liquid additive (especially urea-water solution) is to be provided, which enables particularly good protection of the device against freezing of the liquid additive.

[0008] These problems are solved by a method according to the features of claim 1. Further advantageous embodiments of the method are specified in the dependent claims. The features listed individually in the claims can be combined with one another in any technologically meaningful way and can be supplemented by explanatory details from the description, thereby showing further embodiments of the invention.

[0009] The invention relates to a method for operating a device for providing a liquid additive, which has at least the following components: - a suction point for extracting liquid additive from a tank, - a valve-free delivery line that runs from the suction point to a supply unit, and - a valveless positive displacement pump, wherein the positive displacement pump is designed to pump the liquid additive from the tank via the suction point along the delivery line to the supply unit, and wherein the positive displacement pump has at least one seal of the delivery line which can be moved along the delivery line to pump the liquid additive.

[0010] The procedure now includes at least the following steps: a) Determining when the device has stopped operating; b) Determining the position of the seal within the positive displacement pump; and c) Changing the position of the seal if the position of the seal does not correspond to a designated parking position, whereby the

[0011] The positive displacement pump has a rotary drive and a movable pumping element, wherein the movable pumping element is moved for conveying in a rotary motion, wherein barbs are provided on the movable pumping element which can interlock when the movable pumping element is moved with a rotational direction opposite to the conveying direction and the barbs are locked in the park position according to step c).

[0012] A suction point is, in particular, an opening where a delivery line for conveying the liquid additive into the tank opens. Liquid additive is drawn from the tank into the delivery line through the suction point when the device's pump delivers liquid additive. The suction point is preferably located in a lower area of ​​the tank (especially at the bottom) so that the tank can be emptied as completely as possible via the suction point.

[0013] In other words, a valve-free delivery line means that the liquid additive does not pass through any valves on its way from the suction point through the delivery line to a dispensing unit. In particular, it does not pass through any valves in the pump located in the dispensing unit. The only exception is a (metering) valve that may be provided in the dispensing unit. Therefore, a valve may be provided in the dispensing unit, and yet a valve-free delivery line, as described here, is still implemented. The delivery line is preferably formed by a hose and / or a channel, which is, for example, located in a block or base plate of the dispensing unit. Such a channel in a block can, for example, be designed as bores.

[0014] The delivery unit is preferably an injector through which the liquid additive (in particular a urea-water solution) can be supplied to an exhaust gas treatment device. The delivery unit can include a nozzle that ensures fine atomization of the liquid additive in the exhaust gas treatment device. Alternatively or additionally, the delivery unit can also include a metering device (in particular a metering valve) with which the liquid additive can be portioned or dosed as required. Dosing with a metering valve is typically achieved by the opening time of the metering valve. The duration for which the metering valve is open is typically proportional to the amount of liquid additive dosed. This relationship enables precise dosing.

[0015] A positive displacement pump used here is a pump in which the liquid additive is conveyed through at least one self-contained volume. This self-contained volume prevents backflow of the liquid additive. Positive displacement pumps are to be distinguished from centrifugal pumps, in which a liquid is conveyed, for example, via propellers and / or agitators. With positive displacement pumps, backflow of the liquid additive is generally not possible when the pump is switched off, whereas with centrifugal pumps, backflow is possible when the propeller or agitator is no longer moving.

[0016] With centrifugal pumps, the flow rate regularly depends on the pressure differential the pump generates, because a reverse flow occurs parallel to the discharge flow, which depends on the pressure differential generated by the pump. This reverse flow and the discharge flow are superimposed to determine the flow rate. This relationship typically does not exist with positive displacement pumps. At least within the range of intended pressure differentials, the flow rate is not influenced by the generated pressure differential. Particularly at low flow velocities, positive displacement pumps can achieve a constant pressure increase, whereas with centrifugal pumps, the potential for pressure increase depends heavily on the volume of fluid being pumped.

[0017] Valveless positive displacement pumps are positive displacement pumps in which the liquid additive does not flow through any (separate) valves when entering and exiting the pump volumes. These valveless positive displacement pumps preferably have at least one seal on the delivery line. This seal forms at least one closed pump volume within the positive displacement pump and can be moved along the delivery line in a specific direction to pump the liquid additive. This movement also shifts the pump volumes filled with the liquid additive, thus pumping the liquid additive.

[0018] Preferably, the positive displacement pump is a positive displacement pump with a reversible flow direction. The reversibility of the positive displacement pump's flow direction means, in particular, that the pump can be operated with two different / opposite flow directions. Preferably, a drive is provided whose drive direction can be switched. Reversing the drive's operating direction also reverses the positive displacement pump's flow direction. By reversing the positive displacement pump's flow direction, it becomes possible to empty the device's delivery line in the opposite direction to the usual flow direction. Liquid additive located in the delivery line is pumped back into the tank via the suction point.

[0019] Such a positive displacement pump in a device for supplying a liquid additive makes it possible to empty the delivery line without the need for many different additional components. For emptying, the delivery direction of the positive displacement pump can be reversed to empty the pump from the dispensing unit towards the tank.

[0020] The shutdown of the device in step a) occurs, for example, in conjunction with the deactivation of a motor vehicle in which the described device is integrated. After a shutdown, the device would also be deactivated, and there is a risk that it will be exposed to low ambient temperatures, causing the liquid additive it contains to freeze and resulting in damage. To prevent this, the subsequent steps of the deactivation procedure are performed (afterward).

[0021] In step b), the position of the seal within the positive displacement pump is determined. The at least one seal is preferably moved by the positive displacement pump during operation. The seal's position at the end of the pumping cycle can be determined computationally and / or with a sensor that detects the seal's position. Such a sensor can also be arranged on the pump's drive and monitor the drive's position. The drive of the positive displacement pump is preferably (rigidly) connected to the seal in such a way that the drive's position provides information about the seal's position.

[0022] The designated parking position of the seal is a position within the positive displacement pump where at least one seal is to be located during a standstill phase of the device. Specifically, a (single) parking position is defined for the positive displacement pump, so that the seal is moved to this parking position when the pump stops, regardless of its current position. The parking position is stored and can be recalled, particularly in a control unit. When at least one seal is in this parking position, the risk of damage to the device from freezing liquid additive is particularly low, or even minimized.

[0023] This active monitoring and adjustment of the seal position on the positive displacement pump at every operating stop or at an operating stop when critical ambient temperatures are present, allows for gentle operation and thus also permanently accurate pumping / dosing.

[0024] If the drive is a rotary drive, the monitored position of the drive can be, for example, the angle of rotation. A rotary drive can be particularly cost-effective, for instance, using an electric motor whose direction of rotation can be reversed by changing the electrical polarity. The moving pump element performs either a rotation or an eccentric rotational oscillation, in which it maintains its basic orientation but is displaced according to a rotational movement. This so-called eccentric rotational oscillation of a moving pump element can be generated by a rotating eccentric driven by a rotary drive. A rotary drive and a correspondingly moving pump element enable a particularly energy-efficient drive mode for the positive displacement pump.

[0025] This concept is also transferable to other pumps for the described devices. In particular, it is possible to provide components on the movable pump element that ensure a particularly good seal of at least one pump volume when the movable pump element is moved slightly (for example, by a few degrees) against the direction of delivery. These components are designed in the form of barbs, and in particular, harpoon-shaped barbs. The barbs create a fluid-tight seal against a surface of the pump volume by being pressed against a surface of the pump volume when the movable pump element is moved slightly against the direction of delivery. The barbs are preferably designed so that they release from the surface of the pump volume when the movable pump element continues to move against the direction of delivery.When released, the barbs can, for example, fold or flip over. This allows free movement of the movable pump element against the flow direction, enabling the pump to be emptied. To reseal the pump fluid-tight using the barbs, the movable pump element should first be moved back in the flow direction so that the barbs return to their initial position. The pump volumes can then be resealed with a (slight) movement against the flow direction. The described seal provided by the barbs is preferably enhanced compared to the normal seal of the pump volumes, such that the barbed seal prevents any liquid additive from passing through even at pressures above the operating pressure.For example, this enhanced seal may also be sufficient to prevent ice pressure on components of the liquid additive delivery device, which occurs when the liquid additive freezes inside the device. A hook structure may be provided on the housing of the positive displacement pump to facilitate the engagement of the barbs. By engaging the barbs in the parked position, it can be ensured that liquid additive cannot breach the seal in the parked position, even if the pressure increases significantly due to the volume expansion of the freezing liquid additive.

[0026] The method is also advantageous if the positive displacement pump has at least one flexible sealing element to form the at least one seal, wherein the flexible sealing element is suitable for increasing at least one pump volume of the positive displacement pump when a pressure above an operating pressure of the device occurs within the at least one pump volume.

[0027] The flexible sealing element can be, for example, a diaphragm, a hose, an impeller, and / or a squeeze disc. During operation of the positive displacement pump, the flexible sealing element is deformed to displace the at least one seal. The flexible sealing element preferably also forms at least a section of a wall within the pump volume. Several types of positive displacement pumps that incorporate a flexible sealing element to form at least one seal are described below.

[0028] A flexible sealing element can have a very large surface area facing the pump volume (at least one of the volumes) and, in particular, forms large portions of the pump volume wall (e.g., more than 50% or even more than 70%). Furthermore, the sealing element is flexible to provide a movable seal. Therefore, a pump with a flexible sealing element offers the possibility of providing a very large compensation volume to accommodate the volume expansion of the liquid additive during freezing.

[0029] Furthermore, the method is advantageous if, in the intended parking position, an inlet of the positive displacement pump is closed by at least one seal.

[0030] The positive displacement pump preferably has an inlet through which liquid additive is drawn into the pump and an outlet through which the pump discharges the liquid additive. The positive displacement pump preferably forms a section of a delivery line through the device. The section of the delivery line between the inlet and the outlet (or a portion thereof) constitutes the at least one pump volume of the positive displacement pump. If an inlet of the positive displacement pump is closed, it is ensured that no liquid additive can flow from a section of the delivery line upstream of the inlet into the at least one pump volume of the positive displacement pump. Preferably, no seal is then (simultaneously) arranged at the outlet, so that the outlet of the positive displacement pump remains unobstructed.Then, in the event of volume expansion of the liquid additive during freezing, a volume equalization can take place between the at least one pump volume of the positive displacement pump and a section of the delivery line in the direction of flow behind the outlet.

[0031] Furthermore, the method is advantageous if, in the intended parking position, an outlet of the positive displacement pump is closed by at least one seal.

[0032] If an outlet of the positive displacement pump is closed, it is ensured that no liquid additive can flow from a section of the delivery line downstream of the outlet into the pump's at least one volume. Preferably, no seal is (simultaneously) provided at the inlet, so that the pump's inlet remains open. Then, in the event of volume expansion of the liquid additive during freezing, a volume equalization can occur between the pump's at least one volume and a section of the delivery line upstream of the inlet.

[0033] Furthermore, the procedure is advantageous if an inlet and an outlet of the positive displacement pump are open in the intended parking position.

[0034] Then, in the event of a volume expansion of the liquid additive during freezing, a volume equalization is possible both between the at least one pump volume of the positive displacement pump with a section of the delivery line in the flow direction before the inlet and with a section of the delivery line in the flow direction behind the outlet.

[0035] Furthermore, the method is advantageous if the positive displacement pump has a rigid total pump volume that does not change even when the pressure in the positive displacement pump is above an operating pressure of the device, and if, in the intended park position, both the inlet and the outlet are closed by the at least one seal.

[0036] Positive displacement pumps with a fixed overall volume are, in particular, pumps that have an outer rigid casing containing the at least one pump volume. This rigid casing typically does not include any components that could compress significantly when frozen and thus release additional volume. Such positive displacement pumps with a fixed overall volume could be destroyed if, during freezing, significant displacements of liquid additive and / or frozen additive were to occur within the pump. For this reason, it is advantageous for such pumps if both the inlet and outlet are closed when the device is shut down. This protects the positive displacement pump from displacements within the at least one pump volume during freezing.

[0037] A positive displacement pump that is particularly advantageous for the described method has an internal stator and a movable pump element arranged externally around the stator.

[0038] According to a first concept, the movable pump element is surrounded by a stationary housing. The movable pump element moves within the stationary housing. According to a second concept, the movable pump element is arranged around an internal stator. The movable pump element moves around the stator. In the first concept, the pumping volumes, through which the liquid additive is conveyed by the positive displacement pump, are located between the housing and the movable pump element, while in the second concept, they are located between the movable pump element and the stator. The flexible sealing element can then be formed by either the external stator or the internal movable pump element.

[0039] Furthermore, it is advantageous if the positive displacement pump is a peristaltic pump. In a peristaltic pump, constrictions or closures are moved along a delivery line in the direction of delivery. These constrictions or closures can create multiple closed pumping volumes along the delivery line.

[0040] These constrictions or blockages push the liquid additive (especially a urea-water solution) along the delivery line through the peristaltic pump. Typically, the constrictions or blockages form at the upstream end of the delivery path in the peristaltic pump and move continuously towards the downstream end of the delivery line. At the downstream end, the constrictions or blockages then clear. A peristaltic pump enables particularly gentle and precise delivery of the liquid additive, resulting in very low stress and friction within the liquid. This prevents crystallization of components of the liquid additive within the pump.

[0041] Furthermore, a device is considered advantageous if the positive displacement pump is a type of peristaltic pump. In a peristaltic pump, a hose is compressed at various points, creating constrictions or blockages in the delivery path formed by the hose. The compressed sections of the hose are displaced, thus conveying the liquid additive along the delivery path. Such a peristaltic pump is a particularly simple and therefore cost-effective variant of a peristaltic pump, making it especially advantageous for a device supplying liquid additives. In a peristaltic pump, the flexible sealing element is typically formed by the hose.

[0042] The device is further advantageous if the positive displacement pump is an impeller pump. In an impeller pump, the movable pumping element is an impeller that can rotate within a housing. The housing has an inlet and an outlet through which liquid additive can flow into the housing (inlet) and out of the housing (outlet). The impeller has impeller arms that seal against the outer surface of the housing, thus forming separate pumping volumes within the housing. A rotational movement of the impeller shifts the pumping volumes formed by the impeller arms, allowing the liquid additive to flow from the inlet to the outlet. In a region between the outlet and the inlet, the impeller arms are compressed or pressed together by a recess in the housing. This significantly reduces the pumping volumes between the impeller arms.Therefore, a significantly smaller amount of liquid additive is conveyed from the outlet to the inlet than from the inlet to the outlet.

[0043] The impeller is designed so that its direction of rotation can be reversed. This reverses the pump's flow direction. The inlet then acts as the outlet, and vice versa. A special design of the impeller arms is necessary to allow for this reversal. The impeller arms must not become misaligned within the housing during the reversal of rotation and thus prevent it from rotating.

[0044] The impeller can also be designed so that its arms wedge themselves against the housing, or at least partially brace themselves within it, when the impeller is moved even slightly (for example, by a few degrees) against the previously used flow direction. This allows for a particularly good seal of the pump volumes, preventing backflow of liquid additive through the positive displacement pump. Such a seal can be advantageous, for example, to ensure that the positive displacement pump is tightly sealed when the device is deactivated, preventing ice pressure from opening it. An impeller pump is typically a pump with a fixed total pump volume. It typically has a housing in which the impeller is located, and this housing could potentially be damaged by the expansion of liquid additive within the pump.Therefore, with an impeller pump, it is particularly advantageous if both the inlet and the outlet are sealed when the pump is switched off.

[0045] The positive displacement pump can be located in a housing on the tank for the liquid additive, and the delivery line between the positive displacement pump and the supply unit can have a length of at least 1 meter.

[0046] Preferably, the positive displacement pump is arranged in a housing that can be placed on the underside of a tank, in the tank base. The tank base can, for example, have a chamber separated from the tank's interior, in which the positive displacement pump is located. This chamber can also be designed as a housing that can be inserted into an opening in the tank's base. The housing is preferably free of liquid additive when the tank's interior is filled with liquid additive. The suction point for extracting the liquid additive from the tank is preferably located directly on an outer surface of this housing and thus opens into the tank's interior.

[0047] The invention is particularly applicable to a motor vehicle comprising an internal combustion engine, an exhaust gas treatment device for cleaning the exhaust gases of the internal combustion engine, and a device with which a liquid additive can be supplied to the exhaust gas treatment device and which can be operated using the described method. In particular, this is a conveying system for urea-water solution to an SCR catalyst, as explained above.

[0048] The invention and its technical context are explained in more detail below with reference to the figures. The figures show particularly preferred embodiments, to which, however, the invention is not limited. It should be noted in particular that the figures, and especially the depicted dimensions, are only schematic. They show: Fig. 1: a first embodiment of the described device, Fig. 2: a second embodiment of the described device, Fig. 3: a third embodiment of the described device, Fig. 4: a diagram describing the pumping method using a typical positive displacement pump, Fig. 5: a first design variant of a pump for the described process, Fig. 6: a second design variant of a pump for the described process, Fig. 7: a third design variant of a pump for the described process, Fig. 8: a motor vehicle comprising a device for the described method, Fig. 9: a fourth embodiment of a pump for the described process, and Fig. 10: a fifth design variant of a pump for the described process.

[0049] The same reference symbols were always assigned to identical components in the figures. The following section will first describe the... Fig. 1 to Fig. Figure 3, which represent different embodiments of a device 1, are jointly explained insofar as these representations have commonalities. These devices 1 are suitable / configured for carrying out the described method and enable the metered addition of liquid additive to an exhaust gas treatment device.

[0050] The device 1 according to Fig. 1 to Fig. Each component 3 has a delivery line 6 extending from a suction point 17 in a tank 2 to a supply unit 3. The liquid additive (in particular, a urea-water solution) can be stored in the tank 2. The suction point 17 is located on an interior 36 of the tank 2, and liquid additive can enter the delivery line 6 from the tank 2 at the suction point 17. A positive displacement pump 4 is provided in the delivery line 6, which can convey the liquid additive along the delivery line 6 in the direction 5. The positive displacement pump 4 has a rotary drive 8, which can be controlled by a control unit 7. Furthermore, a pressure sensor 10 is arranged downstream of the positive displacement pump 4 in the delivery line 6 in the direction 5, which can be used to monitor the pressure built up by the positive displacement pump 4 in the delivery line 6.Tank 2 is equipped with a level and quality sensor 16, which can be used to monitor the fill level and, if necessary, the quality of the liquid additive in tank 2. The level and quality sensor 16 is, for example, an ultrasonic sensor that emits ultrasonic waves which are reflected by a liquid surface into tank 2 and return to the level and quality sensor 16, allowing the fill level in tank 2 to be determined by measuring the time of flight. Measuring the time of flight of the ultrasonic waves to a reference surface (not shown) in the liquid additive can also be used for quality measurement.

[0051] According to Fig. In the first section, the supply unit 3 is equipped with a passive valve 28, which opens automatically and supplies liquid additive as soon as the pressure in the delivery line 6 in the delivery direction 5 downstream of the positive displacement pump 4 exceeds a certain limit. Such a supply unit has a particularly simple design. The supply unit 3 can additionally include a filter 27, which protects the passive valve from contamination.

[0052] According to Fig. 2 A more complex supply unit 3 is provided, which can be actively controlled by the control unit 7 depending on the pressure measured by the pressure sensor 10. For this purpose, the supply unit 3 has an actively controllable injector valve 29. With such a supply unit 3, it is possible to actively determine the pressure at which the dosing takes place. This makes it possible to change the pressure in order to adjust a spray effect and / or a spray profile of the supply unit 3.

[0053] Fig. Figure 3 shows a variant design with a provisioning unit 3, which is the Fig. 2 corresponds. Additionally, the device 1 is arranged in a housing 11, which is located at the bottom of the tank 2. The level and quality sensor 16 is also provided in the housing 11, and the suction point 17 is also located on the housing 11. This enables a particularly simple and cost-effective design of the device 1. The delivery line 6 between the supply unit 3 and the positive displacement pump 4 preferably has a length 30, which is greater than 1 m and preferably less than 5 m.

[0054] Fig. Figure 4 schematically shows the structure of a peristaltic pump, which is a typical positive displacement pump 4 for the described process. The delivery direction 5, which extends along the delivery line 6, is visible. The delivery line 6 is divided into different pump volumes 18 by seals 19. The seals 19 move along the delivery direction 5 through the delivery line 6. This forces the liquid additive along the delivery direction 5. The seals 19 are formed by constrictions and / or closures in the delivery line 6 itself, which form along the delivery direction 5 at an upstream end 37 of the delivery line 6 in the positive displacement pump 4 and open again at a downstream end 38 of the delivery line 6 in the positive displacement pump 4.

[0055] Fig. Figure 5 shows a positive displacement pump 4 in which a movable pump element 9, designed as an eccentric 21, is movable according to a rotational movement. This movable pump element 9 has protrusions 31. The delivery line 6 is formed within the positive displacement pump 4 by a hose 20. Due to the protrusions 31, the hose 20 is deformed by the hose 20 when the movable pump element 9 rotates, so that seals 19 are formed and separate pump volumes 18 are created in the delivery line 6. When the movable pump element 9 rotates, the seals 19 and the pump volumes 18 move, so that the liquid additive is moved through the delivery line 6 along the delivery direction 5. The flexible sealing element 46 for forming the seals 19 is shown in the positive displacement pump 4 according to Figure 5. Fig. 5 of the hose 20. The current position 45 of the two seals 19 and the desired parking position 44 are shown. When the seals 19 are in the parking position 44, both the inlet 25 and the outlet 26 are open and accessible, so that in case of freezing, volume equalization can take place with the positive displacement pump 4. The inlet 25 and the outlet 26 are connected to the positive displacement pump 4 according to Fig. 5 the areas where the eccentric 21 begins to affect the hose 20.

[0056] Fig. Figure 6 shows a positive displacement pump 4, which has a movable pump element 9 designed as an impeller 22. This impeller 22 is movable in an impeller chamber 23 according to a rotational movement 32. The impeller 22 has impeller arms 39 which bear against a wall of the impeller chamber 23 and form seals 19 with the wall of the impeller chamber 23. Thus, separate pump volumes 18 are formed between the impeller arms 39. Liquid additive can flow into the impeller chamber 23 through an inlet 25 and flow out of the impeller chamber 23 through an outlet 26. The impeller chamber 23 is largely cylindrical, with the impeller 22 arranged axially symmetrically in the impeller chamber 23.The impeller chamber 23, however, has a recess 24 through which the pump volumes 18 are compressed between the impeller arms 39 of the impeller 22, so that, with a given rotational movement 32 of the impeller, the liquid additive can only flow from the inlet 25 to the outlet 26 and not from the outlet 26 to the inlet 25. Such a pump has a fixed total pump volume 47, which does not allow any volume change in the event of freezing. Therefore, the parking positions 44 for the seals 19 are arranged here at the inlet 25 and the outlet 26 in order to close the inlet 25 and the outlet 26 when the pump stops. For this purpose, the position 45 of the seals 19 is adjusted to the parking position 44.

[0057] Fig. Figure 7 shows a positive displacement pump 4 for the described device. The positive displacement pump 4 has a movable pump element 9, which is moved by an eccentric 21 in a range of motion 33 according to a rotational movement 32. The rotational movement 32 is according to Fig. Figure 7 below left shows a coordinate system. Due to the rotational movement 32, the movable pump element 9 performs an eccentric pendulum motion. The movable pump element 9 itself does not rotate. However, each section 34 of the movable pump element 9 is moved according to the rotational movement 32. This is indicated by the vector arrows 35, which extend from the rotational movement 32 in the coordinate system to the section 34 and do not change for each section 34 of the movable pump element 9 during the eccentric pendulum motion. The movable pump element 9 forms at least one seal 19 in the housing 11, which limits at least one pump volume 18. The seal 19 moves within the housing 11 due to the rotational movement 32. This movement results in the pumping of liquid additive.The liquid additive is conveyed by the positive displacement pump 4 along the conveying direction 5 from an inlet 25 of the positive displacement pump 4 to an outlet 26 of the positive displacement pump 4. For such a pump, the explanations given above regarding the position of the seals and the desired parking position are applicable accordingly, whereby, depending on where volume equalization is to be possible in the event of shutdown, the seals 19 can be moved into the suitable (predetermined) parking positions.

[0058] Fig. Figure 8 shows a motor vehicle 12 comprising an internal combustion engine 13 and an exhaust gas treatment device 14 for cleaning the exhaust gases of the internal combustion engine 13. An SCR catalyst 15 is arranged in the exhaust gas treatment device 14, with which selective catalytic reduction can be carried out to clean the exhaust gases of the internal combustion engine 13. A liquid additive for the selective catalytic reduction process can be supplied to the exhaust gas treatment device 14 by means of a supply unit 3. The supply unit 3 is supplied with liquid additive from tank 2 by a device 1. For this purpose, the supply unit 3 is connected to the device 1 or the tank 2 by a delivery line 6.

[0059] Fig. Figure 9 shows a positive displacement pump 4 in which the movable pump element 9 is arranged externally around a stationary stator 41. The pump volumes 18, through which the liquid additive is conveyed by the positive displacement pump 4 in the conveying direction 5, are arranged between the movable pump element 9 and the stationary stator 41. The movable pump element 9 forms a flexible sealing element 46. The stator 41 has an inlet 25 and an outlet 26 through which the liquid additive can flow into and out of the pump volumes 18. The pump volumes 18 are sealed from each other by seals 19. The movable pump element 18 is elliptically shaped, and the stator 41 is round. Preferably, the shorter axis of the elliptical shape of the movable pump element 18 corresponds to the diameter of the movable pump element 18. This preferably results in at least two seals 19.The stator 41 and the movable pump element 9 are in contact at the seals 19. The movable pump element 9 can be moved according to a rotational movement 32. The rotational movement 32 is possible in two directions. One direction of the rotational movement 32 corresponds to a delivery direction 5 of the liquid additive through the positive displacement pump 4. Due to the rotational movement 32, the seals 19 move and the pump volumes 18 are displaced from the inlet 25 to the outlet 26. The stator has a lug 42 between the outlet 26 and the inlet 25. The function of this lug 42 corresponds to the function of the indentation 24 in the [unclear text]. Fig. Figure 6 illustrates a variant of a positive displacement pump. The outlet 26 is sealed fluid-tight against the inlet 25 by the nose 42. Preferably, the movable pump element 9 is elastic for this purpose. The movable pump element 9 therefore deforms at the nose 42 so that, despite the nose 42, it can rotate completely around the stator 41 in accordance with the rotational movement 32. An exemplary position 45 of the seal 19 in a parked position 44 is shown here, which allows for volume equalization with the pump volumes 18 through both the inlet 25 and the outlet 26.

[0060] In Fig.Figure 10 shows an embodiment of a positive displacement pump 4 according to the invention. Here, too, a movable pump element 9 can be moved according to a rotational movement 32. The rotational movement 32 is possible in two directions. One direction of the rotational movement 32 corresponds to a conveying direction 5 of the liquid additive by the positive displacement pump 4. The movable pump element 9 is arranged in a housing 11 and forms a flexible sealing element 46. The housing 11 has an inlet 25 and an outlet 26. The movable pump element 9 has several projections 31 that bear against the housing 11 and thus form seals 19. Between the seals 19, the housing 11, and the movable pump element 9 are closed pump volumes 18, through which the liquid additive is conveyed during a rotational movement 32 of the movable pump element 9.Between the inlet 25 and the outlet 26, the housing has a recess 24 that prevents liquid additive from flowing back from the outlet 26 to the inlet 25 against the direction of flow 5. When a protrusion 31 of the movable pump element 9 passes through the recess 24 during rotation 32, this protrusion 31 is compressed. Barbs 40 are provided on the protrusions 31, which can engage with the housing 11 when the movable pump element 9 is moved against the direction of flow 5. The engagement of these barbs 40 increases the tightness of the seals 19. A hook structure 43 can be provided on the housing 11, which facilitates the engagement of the barbs 40 with the protrusions 31.

[0061] Although specific configurations of various devices have been illustrated in the figures above, it is obvious that technical details of one embodiment may be shown separately or may occur in combination with technical details of other embodiments / the preceding explanations. Therefore, it is pointed out here that a combination of the illustrated technical features is only to be considered "mandatory" if this has been explicitly stated above or if the functionality of the device or the method would otherwise no longer be guaranteed.

[0062] The described device for providing liquid additive is particularly cost-effective and can also be emptied, so that no damage to the device occurs due to freezing of the liquid additive. Reference symbol list 1 Device 2 Tank 3 Deployment unit 4 positive displacement pump 5 Direction of conveyance 6 Conveyor line 7 Control unit 8 Rotary drive 9 movable pump element 10 Pressure sensor 11 cases 12 Motor vehicle 13 Internal combustion engine 14 Exhaust gas treatment device 15 SCR catalyst 16 Level and quality sensor 17 Intake point 18 pump volume 19 Sealing 20 hoses 21 eccentrics 22 impellers 23 Impeller chamber 24 indentations 25 Admission 26 Outlet 27 filters 28 Passive valve 29 Injector valve 30 cable length 31 Survey 32 Rotational movement 33 Range of motion Section 34 35 vector arrow 36 Interior 37 upstream end 38 downstream end 39 impeller arms 40 barbs 41 Stator 42 Nose 43 hook structure 44 Parking position 45 Position 46 flexible sealing element 47 Total pump volume

Claims

[1] Method for operating a device (1) for providing a liquid additive, comprising at least one suction point (17) for taking liquid additive from a tank (2), a valveless delivery line (6) extending from the suction point (17) to a delivery unit (3), and a valveless positive displacement pump (4), wherein the positive displacement pump (4) is configured to pump the liquid additive from the tank (2) via the suction point (17) along the delivery line (6) to the delivery unit (3), wherein the positive displacement pump (4) has at least one seal (19) of the delivery line (6) which can be moved along the delivery line (6) for pumping the liquid additive, comprising at least the following steps: a. Determining an operational stop of the device (1); b. Determining the position (45) of the seal (19) within the positive displacement pump (4); and c. Changing the position (45) of the seal (19) if the position (45) of the seal does not correspond to a designated parking position (44), wherein the positive displacement pump (4) has a rotary drive (8) and a movable pumping element (9), wherein the movable pumping element (9) is moved for pumping according to a rotary motion (32), characterized by , that barbs (40) are provided on the movable pump element (9) which can interlock when the movable pump element (9) is moved with a rotational movement (32) against the direction of conveying (5) and the barbs (40) are locked in the park position (44) after step c). [2] Method according to one of the preceding claims, wherein the positive displacement pump (4) has at least one flexible sealing element (46) to form the at least one seal (19), wherein the flexible sealing element (46) is suitable to increase at least one pump volume (18) of the positive displacement pump (4) when a pressure above an operating pressure of the device (1) occurs within the at least one pump volume (18). [3] Method according to one of the preceding claims, wherein in the intended parking position (44) an inlet (25) of the positive displacement pump (4) is closed by the at least one seal (19). [4] Method according to one of the preceding claims, wherein in the intended parking position (44) an outlet (26) of the positive displacement pump (4) is closed by the at least one seal (19). [5] Method according to one of the preceding claims, wherein the positive displacement pump (4) has a rigid total pump volume (47) which does not change even when the pressure in the positive displacement pump (4) is above an operating pressure of the device and wherein in the intended park position (44) both the inlet (25) and the outlet (26) are closed by at least one seal (19). [6] Motor vehicle (12) comprising an internal combustion engine (13), an exhaust gas treatment device (14) for cleaning the exhaust gases of the internal combustion engine (13) and a device (1) by which a liquid additive can be supplied to the exhaust gas treatment device (14) and which can be operated by a method according to one of the preceding claims.

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