The invention relates to a filter cartridge for a reducing agent delivery device, and to a delivery device for reducing agent.

For the purification of the exhaust gases of internal combustion engines, use is made inter alia of exhaust-gas treatment devices into which a re- ducing agent is supplied. In exhaust-gas treatment devices of said type, certain pollutants in the exhaust gas can be reduced in a particularly effective manner by means of the reducing agent. There, use is particularly frequently made of so-called SCR catalytic converters in which nitrogen oxide compounds in the exhaust gas are converted with the aid of ammonia. Ammonia is generally stored in motor vehicles not directly but rather in liquid form, also referred to as a reducing agent precursor solution. A widely used reducing agent precursor solution is urea-water solution, available for example under the trade name AdBlue ^® with a urea content of 32.5 %. The reducing agent precursor solution may be convert- ed into the actual reducing agent in the exhaust-gas treatment device and/or in an exhaust-gas-external generator. The expression "reducing agent" will hereinafter also be used to mean reducing agent precursor solutions and the like. For the delivery of the reducing agent into the exhaust-gas treatment device, a suitable delivery device is generally provided in motor vehicles, which delivery device delivers the reducing agent from a tank. In designing delivery devices of said type, it is a problem that the reducing agent may have impurities, and the delivery device should therefore comprise means for filtering the reducing agent. This is achieved for example by means of exchangeable filter cartridges which are provided in the delivery device. It is also a problem that aqueous reducing agents can freeze. The reducing agent AdBlue ^® freezes for example at -11 ^° C. Such low temperatures may arise in particular during relatively long standstill phases of an internal combustion engine. An increase in volume therefore takes place when freezing occurs. If only a limited space is available for the increase in volume, the increase in volume results in a drastic pressure increase. This is referred to as so-called ice pressure. A delivery device for reducing agent must therefore be designed or operated such that it is not damaged by the freezing of the reducing agent or by the described increase in volume and the ice pressure. This has proven to be a problem in particular in the region of the filter in a delivery device. It is an object of the present invention to solve said highlighted technical problems to the greatest possible extent. It is sought in particular to specify a filter cartridge which is particularly well protected against damage in the event of freezing of a reducing agent tank in a delivery device. Furthermore, it is sought to propose a delivery device which is likewise par- ticularly well adapted to the changed conditions in the interior during and after the freezing of the reducing agent.

Said objects are achieved by means of a filter cartridge according to the features of claim 1 and also by means of a delivery device according to the features of claim 8. Further advantageous refinements of the invention are specified in the dependent claims. The features specified individually in the claims may be combined with one another in any desired technologically meaningful way and may be supplemented by explanatory facts from the description, with further design variants of the invention being highlighted.

The invention relates to a filter cartridge for a delivery device for a reducing agent, having at least one filter wall and at least one supporting wall which, together with the filter wall, forms an interior space, wherein the at least one supporting wall has an outflow opening and a bypass opening, wherein the outflow opening can be coupled to the delivery device and the bypass opening forms a bypass to the filter wall. A filter cartridge has at least one filter wall and at least one supporting wall. A filter wall can be passed through by the medium to be filtered (liquid reducing agent) and, for this purpose, has small openings or pores. Filter walls also preferably have a surface area as large as possible and a wall thickness as small as possible in order to ensure as low as possible a flow resistance through the filter wall for the medium to be filtered. The filtering action of a filter wall is determined by the opening size or the pore size of the filter wall. The filter wall is designed to retain particles in the medium to be filtered which are larger than the opening size or the pore size. The opening size or the pore size is preferably substantially uniform over the entire filter wall in order to obtain a uniform filter action over the entire surface.

By the flow resistance through the filter wall a pressure difference is formed between the interior space of the filter cartridge and an outer space which surrounds the filter cartridge during regular operation of the delivery device. This pressure difference moves the reducing agent through the filter wall during operation and it is determined by the flow resistance of the filter wall and the volume flow rate of reducing agent through the filter wall. This pressure difference is typically small during regular operation in relation to ice pressure (occurring in case of freezing), for example it is smaller than 0.1 bar. During operation, reducing agent is sucked from the outer space into the interior space of a filter cartridge. The pressure in the interior space is therefore usually lower than the pressure at the outer space during operation. In case the delivery device is out of operation or during an interruption of delivery in which no reducing agent is conveyed, there (virtually) does not exist a volume flow rate of reducing agent through the filter wall. Therefore, there does not exist a pressure difference between the interior space and an outer space of the filter cartridge at these times.

The filter wall alone is often not capable of imparting adequate mechanical stability to the filter cartridge. On account of its large surface area and its small wall thickness, the mechanical stability of the filter wall is typically low. The filter cartridge is therefore formed with at least one supporting wall which can permanently predefine the position of the filter wall and which for example (partially or completely) encloses and/or (partially or completely) borders the filter wall. The supporting wall for example predefines a cartridge shape of the filter cartridge in which the at least one wall fits such the supporting wall borders the filter wall. Supporting walls cannot be passed through by the medium to be filtered and have a wall thickness and strength sufficient to maintain the shape of the filter cartridge or to define the shape and position of the filter wall of the filter cartridge. Supporting walls are produced preferably from plastic. A filter cartridge furthermore has, in the region of a supporting wall, (at least) one outflow opening by means of which the filter cartridge can be coupled to a delivery device. Here, the filter cartridge forms an interior space which is delimited in particular only by the supporting walls and filter walls. Here, the interior space forms in particular a reservoir for already filtered reducing agent, which can be extracted via the outflow opening of the one supporting wall, and supplied to the delivery device, as required. Here, it is prefera- ble for the large side surfaces of the side walls/filter walls to substantially predefine the interior space, and for the small edges of the side walls/filter walls to realize the connection to one another. A filter cartridge in a delivery device for reducing agent therefore preferably forms a type of hollow body which delimits an interior space and which is sur- rounded from an outer side. The reducing agent may for example be sucked from the outside through the filter wall into the interior space formed by the filter cartridge. In the event of freezing, the reducing agent remaining in a filter cartridge usually then freezes proceeding from the filter wall in the direction of the centre of the hollow body, or in the di- rection of the centre of the interior space of the filter cartridge. Since the centre of the filter cartridge freezes last a particularly high ice pressure is generally formed in the filter cartridge. The invention discussed here is now based on the concept of providing, in a supporting wall of a filter cartridge, (at least) one bypass opening such that (already filtered) reducing agent can flow back out of the interior space of the filter cartridge again to an outer side of the filter car- tridge, where in particular still unfiltered reducing agent is present. Here, the bypass opening is preferably always open, such that at all times, reducing agent can escape out of the interior space again when a predefined excess pressure prevails in the interior space. A bypass opening past the filter wall serves in particular the purpose of permitting an "emergency discharge" of reducing agent in the event of an undesirably high pressure being generated in the interior space, in particular in the event of freezing. In the event of freezing, a bypass opening of said type makes it possible, for example, for ice pressure generated in the filter cartridge to be dissipated out of the interior space of the filter cartridge. If the freezing of the filtered reducing agent in the interior space begins at the outside and continues in the inward direction, a type of ice jacket is formed which encloses within it an ever decreasing (still liquid) reducing agent volume. The bypass opening is now arranged in particular centrally such that, in the event of freezing, it is in contact with said residual (still liquid) reducing agent volume and ultimately ensures a discharge out of the ice jacket to the outside and thereby prevents a dangerously high pressure rise.

The bypass opening is a highly cost-effective solution for discharging the pressure from the interior space, because no (flexible and/or preloaded) compensation means or the like for discharging the ice pressure are required on the filter cartridge. The bypass opening may be formed in a highly cost-effective manner by means of a simple bore. In particular, it is advantageous for only a single bypass opening to be provided. It should also be noted that a bypass flow of the reducing agent during normal operation is negligibly small, in particular because the filter wall has an adequately low flow resistance. The flow resistance is particularly low if the surface of the filter wall is particularly large and the thickness of the filter wall is particularly small. Furthermore, if appropriate, similar materi- als (for example a sponge, a grid, a sieve etc.) may also be positioned on the bypass opening at the outside, which materials constitute a flow resistance and thereby limit or almost prevent the bypass flow during normal operation.

A coupling device is also particularly advantageously provided in the region of the outflow opening of the filter cartridge, by means of which coupling device the outflow opening can be coupled in a fluid-tight manner to a counterpart, provided correspondingly for the purpose, on an opposite opening on the delivery device. A coupling device may for example be designed as a click-type connection or a screw connection. In a particularly advantageous design variant, the coupling device is designed to be releasable with respect to the delivery device, such that the filter cartridge can be released from the delivery device without thereby being damaged. The filter cartridge is advantageously also exchangeable, such that a plurality of filter cartridges may be used in the delivery device over the service life of a delivery device.

In a further advantageous embodiment of the filter cartridge, the bypass opening has a second diameter which amounts to less than one tenth (1/10) of a first diameter of the outflow opening. The bypass opening is therefore considerably smaller than the outflow opening. The bypass opening preferably has a cross-sectional area which amounts to less than one hundredth (1/100) of the cross-sectional area of the outflow opening. The bypass opening is designed to be so small in relation to the outflow opening that for example the bypass flow is relatively small but adequate for the desired pressure reduction in the event of freezing.

It may also be advantageous for the bypass opening to be covered by a screen element. In other words, this means in particular that precisely one screen element is located on the outside of the filter cartridge so as to span the bypass opening. By means of a screen element, it is firstly possible for the bypass opening to be protected. Secondly, it is possible by means of a screen element for a certain degree of shielding against impurities in the reducing agent to be obtained also in the region of the bypass opening. Here, it is preferable for the passages in the screen element to be several times larger than the (largest) openings/pores in the filter wall.

It is also advantageous for the screen element to be welded or vulcanized to the supporting wall. The technical process of "vulcanization" is known in the art. "Vulcanization" shall in particular mean that the screen element and/or a fastening tool (bonding tape, etc.) are at least partially (materially) integrated in the supporting wall, e.g. by using a rubber material which is treated at elevated pressure and elevated temperature for a given period of time, wherein the rubber material especially solidifies (possibly also shrinks) and a durable connection (for example similar to an adhesive bond) of screen element and supporting wall is formed. It is also possible that the screen element is glued or clamped to the supporting wall. The screen element may for example be produced from plastic. A screen element of said type composed of plastic can be fastened to the supporting wall in a highly cost-effective manner by means of a welding process, in particular if the supporting wall is likewise composed of plas- tic, because generally only very low technical expenditure, and in particular only very low welding temperatures, are required for the welding of plastic.

It is furthermore advantageous if the bypass opening has a second diame- ter which amounts to at least 100 um [micrometres]; preferably even at least 200 um [micrometres] and particularly preferably at least 500 um [micrometres]. Reducing agent in delivery devices normally freezes when the delivery device is at a standstill, when no vibrations act on the delivery device. It may therefore occur that the reducing agent present in the delivery device cools down in liquid form to below the freezing point of the reducing agent, and then abruptly or suddenly freezes in the event of light agitation. For this reason, the pressure generated during freezing, and the increase in volume generated during freezing, arise relatively quickly. It is therefore necessary for the bypass opening to have a diame- ter suitable for rapidly dissipating the ice pressure arising during freezing. A minimum diameter in the specified range for the bypass opening is therefore highly advantageous for reducing the forces generated here. Furthermore, the minimum diameter should be chosen in such a manner that the bypass opening cannot be blocked by frozen reducing agent.

In a further design variant of the filter cartridge, the filter walls forms a (substantially) cylindrical basic shape. Furthermore, a top side and a bottom side are formed in each case by a supporting wall, wherein the out- flow opening is arranged on the top side and the bypass opening is arranged on the bottom side. The top side and the bottom side are often arranged perpendicular to an axis of symmetry of the cylindrical basic shape. By the terms "top side" and "bottom side" no mandatory mounting orientation of the filter cartridge in the delivery device hall be defined, but these terms explain the spatial arrangement of the individual wall sections of the filter cartridge to each other. It is possible for the filter cartridge to be mounted in a delivery device with any orientation of the axis of symmetry (for example horizontally, vertically or obliquely). A filter cartridge designed in this way often freezes from the circumferential surface inwards, such that an inner region of ever decreasing size with liquid reducing agent is formed in a cylindrically shaped ice jacket. In said region, the pressure increases ever further on account of the increase in volume of reducing agent as it freezes. Said pressure cannot be released in the direction of the outflow opening because the latter is con- nected to the delivery device. In the delivery device, too, there is normally only a limited volume into which the increasing pressure could be dissipated. Furthermore, the delivery device often has valves or the like provided within it, which prevent a transmission of the ice pressure and the increase in volume into the delivery device. In addition, the delivery de- vice may already be blocked by frozen reducing agent if the ice pressure rises in the filter cartridge. It is therefore advantageous for the bypass opening to be provided on the opposite bottom side of the filter cartridge. Said bypass opening is often directed towards a relatively large volume filled with (unfiltered) reducing agent, for example is formed at a distance from the base of the filter housing and/or in contact with a compensation element. Such compensation elements may for example be compressible inserts composed of rubber (in the form of a sponge) or similar materials. It is also possible for a type of compressible bellows to be provided there, which may for example be filled with air. The pressure transmitted via the bypass opening can therefore be dissipated into said external space.

The upper supporting wall and the lower supporting wall may be con- nected to one another through the interior space of the filter cartridge by means of at least one connecting structure or with at least one supporting structure. Said supporting structure may be formed for example in the manner of a basket which has openings through which the reducing agent can pass (such that there is no relevant flow hindrance here) and which at the same time supports the filter wall from the inside or from the direction of the interior space.

In a further advantageous variant of the filter cartridge, the supporting wall has a receptacle in which a compressible insert is arranged. Said re- ceptacle and the compressible insert are preferably provided on the outside of the filter cartridge. The receptacle and the compressible insert are preferably provided on the filter cartridge at the point where a bypass opening is also situated. It is also particularly advantageous for the bypass opening, the receptacle and the compressible insert to be provided on the bottom side of a cylindrically shaped filter cartridge. Said bottom side is generally situated opposite the top side, on which an outflow opening and if appropriate a coupling device are situated. Ice pressure building up in the interior of the filter cartridge can thereby be dissipated via the bypass opening to the outside and into the compressible insert. Here, the receptacle and the compressible insert generally do not seal off the bypass opening. A reducing agent flow (bypass flow) through the bypass opening and for example past the compressible insert to an outer side of the filter cartridge therefore remains possible. The insert preferably lies loosely in/on the receptacle. Also claimed within the context of the invention is a delivery device for a reducing agent, which delivery device has a suction point and a discharge point, wherein a delivery path for the reducing agent is formed from the suction point to the discharge point, which delivery path runs at least through a filter cartridge described according to the invention.

The filter cartridge or the filter wall of the filter cartridge therefore divides the delivery path in particular into a first path section from the suc- tion point to the filter wall and a second path section from the filter wall to the discharge point. A pump and (various) valves which are provided for the delivery of the reducing agent in the delivery device are situated preferably in the second path section, such that these are protected against impurities in the reducing agent by the filter cartridge or by the filter wall. From this point of view, the interior space of the filter cartridge is assigned to the second path section, such that practically only filtered reducing agent is present in the second path section. The exterior space around the filter cartridge or around the filter wall is assigned to the first path section. The bypass opening forms a bypass from the se- cond path section to the first path section without the need for flow to pass through the filter wall. The filter wall can therefore be bypassed by means of the bypass opening. Pressure which occurs in the interior space of the filter cartridge or in the second path section can be dissipated via the bypass opening into the exterior space around the filter cartridge, or into the first path section.

In this connection, it is not necessary for the filter cartridge to be detachable from the delivery device. It is also possible for the filter cartridge to be an integral constituent part of the delivery device and/or to be fixedly, in particular non-detachably connected to further components of the delivery device. The filter cartridge may be for example welded, soldered or stamped into the delivery device. Also claimed within the context of the invention is a motor vehicle having an internal combustion engine, having an exhaust-gas treatment device for the purification of the exhaust gases of the internal combustion engine, and having a delivery device according to the invention for deliver- ing reducing agent into the exhaust-gas treatment device. A motor vehicle of said type in particular also has a tank for liquid reducing agent (for example urea-water solution), out of which tank the delivery device can deliver the reducing agent. The invention and the technical field will be explained in more detail below on the basis of the figures. The figures show particularly preferred exemplary embodiments, to which the invention is however not restricted. In particular, note that the figures and in particular the illustrated proportions are merely schematic. In the figures:

Fig. 1: shows a first design variant of a filter cartridge, Fig. 2: shows a second design variant of a filter cartridge, Fig. 3: shows a third design variant of a filter cartridge, Fig. 4: shows a cross section through a filter cartridge, Fig. 5: shows a fourth design variant of a filter cartridge,

Fig. 6: shows a fifth design variant of a filter cartridge,

Fig. 7: shows a delivery device, and Fig. 8: shows a motor vehicle having a delivery device.

Figures 1, 2, 3, 5 and 6 show five different design variants of the filter cartridge 1 according to the invention. The filter cartridge 1 according to Figures 1, 2, 3 and 5 has in each case a cylindrical basic shape 14 formed by the filter wall 3. In the case of the filter cartridge 1 from Figure 6, the basic shape 14 is conical. Here, the filter wall 3 forms a type of circumferential surface of the basic shape 14. The basic shape 14 is closed off on the top side 16 and on the bottom side 17 in each case by a support- ing wall 4. The filter cartridges 1 are preferably in each case approximately rotationally symmetrical with respect to an axis of symmetry 7. The filter wall 3 has in each case an upper edge region 5 and a lower edge region 33. The upper edge region 5 and the lower edge region 33 form in each case an edge of the filter wall 3. There, the filter wall 3 is connected to the supporting walls 4. The supporting walls 4 thus preferably border the filter wall 3. In the individual filter cartridges 1 according to Figures 1, 2, 3, 5 and 6, the filter wall 3 and the supporting walls 4 delimit in each case an interior space 15 of the filter cartridge 1. On the top side 16, an outflow opening 8 is provided in the supporting wall 4, by means of which outflow opening the filter cartridge 1 can be connected to a delivery device (such as for example also a pump). The outflow opening 8 is surrounded in particular by a coupling device 9 by means of which the filter cartridge 1 can be connected in preferably a fluid- tight and detachable manner to a suction opening, which corresponds to the outflow openings 8, on a delivery device.

A freezing direction 6 indicated by arrows in Figures 1, 2, 3, 5 and 6 shows in each case the direction in which the ice can preferably propa- gate when the reducing agent freezes. Accordingly, ice forms firstly at the filter walls 3 situated at the outside. A (cylindrical, conical, round etc.) space with liquid reducing agent is therefore formed which is surrounded by an ice layer (ice jacket). In the design variant according to Figure 6, the liquid reducing agent space remaining in the interior space 15 is also ra- ther conical. The ice layer subsequently expands in the direction of the centre of the interior space 15. The centre of the interior space 15 then preferably freezes more quickly at the top side 16 than at the bottom side 17. It can thus be achieved that the ice pressure builds up in the direction of the bypass opening 10 on the bottom side 17. The bypass opening 10 on the bottom side 17 of the filter cartridge is of different design in each case in the design variants of the filter cartridge 1 illustrated in Figures 1, 2, 3, 5 and 6. Even though in each case (prefera- bly) only a single bypass opening 10 is provided here per filter cartridge 1, it is also possible for a plurality to be provided.

According to Figure 1, the bypass opening 10 on the bottom side 17 is a single bore with a second diameter 12 which is preferably significantly smaller, in particular ten times smaller than a first diameter 11 of the outflow opening 8.

According to Figure 2, the bypass opening 10 is likewise formed with a second diameter 12 which is smaller than a first diameter 11 of the out- flow opening 8. Furthermore, according to Figure 2, a screen element 13 is provided which covers the bypass opening 10.

In the design variant according to Figure 3, the bypass opening 10 has a shoulder 31. As a result of the shoulder 31, in the bypass opening 10, the supporting wall 14 narrows in a tapering fashion (in sections) towards the interior space. By means of such a design of the bypass opening 10, it is possible for the bypass opening 10 to be produced in a particularly cost- effective and precise manner. This may be realized for example by means of a hot mandrel which drills through the supporting wall 4 of the filter cartridge 1 in order to produce the bypass opening 10.

In Figure 5, a bypass opening 10 is likewise formed on the bottom side 17. Provided opposite the bypass opening 10 at the outside on the bottom side 17 is a receptacle 32 in which a compressible insert 27 is held. Ice pressure which builds up in the interior space 15 of the filter cartridge 1 and which is dissipated via the bypass opening 10 can be discharged into the compressible insert 27. In Figure 6, the bypass opening 10 is designed correspondingly to Figure 1. Figure 6 illustrates, as a peculiarity, merely the conical shape of the filter cartridge 1. The different peculiarities and features of the design variants of the filter cartridge 1 according to Figures 1, 2, 3, 5 and 6 may be combined with one another in any desired way.

Figure 4 shows a section through an embodiment of the filter cartridge 1 as per the section line A-A in Figure 3. Figure 4 thus shows the filter wall 3 of the filter cartridge 1. Here, the filter wall 3 has a corrugated structure 29. By means of such a corrugated structure 29, it is possible for a particularly large filter surface area of the filter wall 3 to be realized with a simultaneously relatively small spatial requirement for the filter car- tridge 1. It is also possible to see the bottom side 17 of the filter cartridge 1, viewed in Figure 4 along the axis of symmetry 7. On the bottom side 17, it is possible to see the supporting wall 4 with the bypass opening 10.

Figure 7 illustrates a design variant of the delivery device 2 into which a filter cartridge 1 according to the invention has been inserted. The filter cartridge 1 has been inserted into a cartridge receptacle 28 provided in the delivery device 2. There is a delivery path 20 through the delivery device 2 from the suction point 18 to the discharge point 19. The delivery path 20 is divided by the filter cartridge 1 or by the filter wall 3 of the filter cartridge 1 into a first path section 21 from the suction point 18 to the filter wall 3 and a second path section 22 from the filter wall 3 to the discharge point 19. An ice pressure which builds up in the interior space 15 of the filter cartridge 1 can be dissipated via the bypass opening 10 of the filter cartridge 1 to the outside or into the cartridge receptacle 28. A compressible insert 27 is provided in the cartridge receptacle 28. It is possible for the compressible insert 27 to be a constituent part of the filter cartridge 1, wherein in this regard, reference is made in particular to Figure 5 and the explanations relating thereto. It is however likewise possible for the compressible insert 27 to be placed, as a separate compo- nent, into the delivery device 2 or into the cartridge receptacle 28. The filter cartridge 1 is connected to the delivery device 2 via an outflow opening 8 and a coupling device 9. It is additionally shown in Figure 6 that a heating means 30 of the delivery device 2 extends into the interior space 15 of the filter cartridge 1 through the outflow opening 8. The heating means 30 may at the same time also be a heat-conducting structure which, in a shut-down situation, when the heating means 30 is not operated, dissipates heat from the interior space 15. Since the heating means 30 projects into the filter cartridge 1 from above, it can be ensured that the interior space 15 freezes starting from the top, and the ice pressure is built up lastly in the direction of the bypass opening 10. Figure 6 also shows the freezing direction 6 in which the formation of ice can take place in the delivery device 2 in the region of the filter cartridge 1. Figure 8 shows a motor vehicle 23 having an internal combustion engine 24 and an exhaust-gas treatment device 25 for the purification of the exhaust gases of the internal combustion engine 24. Reducing agent can be delivered into the exhaust-gas treatment device 25 from a tank 26 by means of a delivery device 2. An SCR catalytic converter, for example, may then be provided in the exhaust-gas treatment device, which SCR catalytic converter realizes a conversion of the exhaust gas according to the SCR method.

List of reference symbols

1 Filter cartridge

2 Delivery device

3 Filter wall

4 Supporting wall

5 Upper edge region

6 Freezing direction

7 Axis of symmetry

8 Outflow opening

9 Coupling device

10 Bypass opening

11 First diameter

12 Second diameter

13 Screen element

14 Basic shape

15 Interior space

16 Top side

17 Bottom side

18 Suction point

19 Discharge point

20 Delivery path

21 First path section

22 Second path section

23 Motor vehicle

24 Internal combustion engine

25 Exhaust-gas treatment system

26 Tank

27 Compressible insert Cartridge receptacle Corrugated structure Heating means Shoulder

Receptacle

Lower edge region