DEVICE FOR THE SUCTION FILTRATION OF FLUIDS

Abstract

The invention relates to a device for the suction filtration of fluids, such as urea solutions for exhaust gas after-treatment systems, comprising a tank (2) storing the fluid, and a filter element (34) arranged therein provided with a filter medium (32), which separates the tank contents from a clean-side inner filter cavity (20) and extends from the bottom area (10) of the tank (2) to a filling level height (28), which corresponds to a part of the filling volume of the tank (2). On the filter cavity (20), a suction connection (22) is provided, via which the cleaned fluid can he discharged by way of a suction pressure corresponding to a system operating pressure. The invention is characterized in that the filter element (34) is provided with a filler medium (32), which is air-impermeable if suction pressures are within the range of a low system operating pressure.

Description

The invention relates to a device for the suction filtration of fluids, such as urea solutions for exhaust gas after-treatment systems, comprising a tank storing the fluid, and a filter element arranged therein, provided with a filter medium, which separates the tank contents from a clean-side inner filter cavity and extends from the bottom area of the tank to a filling level height, which corresponds to a part of the filling volume of the tank, wherein on the filter cavity, a suction connection is provided, via which the cleaned fluid can be discharged by way of a suction pressure corresponding to a system operating pressure. The invention further relates to a filter element provided for use with such a device.

Devices for the suction filtration of fluids, such as liquid operating means, fuels or the like, are used in widely different fields. Due to the increasing requirements related to the emission behavior of internal combustion engines, there has been an increased use more recently of exhaust gas after-treatment systems with which for a selective catalytic reduction of nitrogen oxides, an aqueous urea solution, which is stored in a tank, is injected into an exhaust gas stream, in order, in conjunction with an SCR catalytic converter, to extract ammonia as the actual reducing agent. The urea solution can be obtained under the trade name “Adblue” at gas stations as an additional operating fluid for motor vehicles, for filling the respective storage tank. High demands are placed on the purity of the urea solution for the operational safety of the associated injector system. Impurities can lead to blockages of channels and/or dosing pumps and/or valves in the injector system. Because the urea solution provided for filling can contain different impurities, and because, in particular, the danger also exists that during the filling process a quantity of contaminant may be introduced into the tank, it is necessary to filter the urea solution which is drawn from the tank.

For this purpose, a device of the aforementioned kind is known from the document WO 2011/124637 A1, in which the filter element serving as a suction filter is integrated into the tank storing the urea solution. The operating behavior of this device is not optimal for use in motor vehicles. Thus, the safe operation of the system depends on the filling level height in the tank not falling below the upper edge of the filter medium of the filter element. As soon as this is the case, there is the danger that air is suctioned out of the tank via the unused, i.e. exposed, part of the filter medium, and passes into the system. For a useful operation of motor vehicles, however, it must be required that the filling level height is able to be lowered down to the bottom area of the tank, in order in this way to remove a large fill quantity from the tank.

In view of these problems, the object of the invention is to provide a device for suction filtration which, with a filter element integrated in the respective tank, is distinguished by a highly favorable operating behavior.

This object is achieved according to the invention by a device which has the features of claim 1 in its entirety.

According to the characterizing portion of claim 1, an essential feature of the invention is that the filter element has a filter medium, which is air-impermeable if suction pressure lies within the range of a low system operating pressure. This avoids the danger that, as soon as the filling level in the tank has fallen below the level of the upper edge of the filter medium, such that a part of the filter medium above the fluid level is exposed, air is suctioned out of the tank via the filter medium into the clean-side inner filter cavity. Without the entry of air, practically the entire volume of the tank surrounding the filter element can be used.

In particularly advantageous exemplary embodiments of the invention, the suction connection on the filter cavity is disposed at the upper end thereof remote from the tank bottom. This arrangement not only eliminates the problem that during ongoing operation, air could be suctioned in when the fill level falls below the upper edge of the filter element, but furthermore also guarantees a particularly safe start-up of the system after periods of downtime. Because the filter medium is not air permeable, air initially located within the filter cavity of the filter element does not escape as the tank is filled. During startup of the pump, the quantity of air contained in the filter element is discharged via the head-side suction connection. Because no urea solution is also discharged with this process, the quantity of air can be eliminated using normal ventilation processes, for example self-actuated pump venting, after which the system is ready to operate free of air. This ventilation process can occur automatically after filling processes.

An air-impermeable filter medium for the pressure gradient in question can be formed from a melt-blown fiber material, wherein plastic fibers made, in particular, of PA 66, can be provided.

In particularly advantageous exemplary embodiments, a filter medium is provided having a wall thickness in the range of 5 mm and a filter fineness in the range of 10 μm. In the case of filter media constructed in such a manner, the filter medium, as a result of the capillary effect, is completely suctioned full with the relevant fluid, even if parts of the filter medium lie above the fill level, such that the filter medium is air-impermeable for low suction pressures over the entire height thereof.

The subject matter of the invention according to claim 6, is also a filter element, which is provided for use with a device for suction filtration with one of the claims 1 to 5.

The invention is explained in greater detail below based on an exemplary embodiment shown in the figure. They show in:

FIG. 1 a highly simplified functional sketch of the device according to the prior art for suction filtration of a urea solution, wherein the filling level height in the associated tank lies above the upper edge of the filter element;

FIG. 2 a representation of the device of the prior art according to FIG. 1, wherein the filling level height is located below the upper edge of the filter element;

FIG. 3 a sketch representation, similar to FIGS. 1 and 2, of an exemplary embodiment of the device according to the invention for suction filtration, wherein an operating state before start-up is shown;

FIG. 4 a corresponding sketch representation of the exemplary embodiment of the invention, wherein a state after start-up is shown, and

FIGS. 5 and 6 corresponding sketch representations, showing states of the exemplary embodiment of the invention with fill level heights in the tank lowered to different degrees.

The invention is described below based on an example that is provided for the suction filtration of an aqueous urea solution, as is known under the name “Adblue”, and which can be used for exhaust gas after-treatment systems of internal combustion engines. The invention is based on the relevant prior art documented in WO 2011/124637 A1, as is represented in FIGS. 1 and 2, principally in the manner of simplified function sketches. The figures show a simplified representation of a tank, identified by 2, which holds a supply of the urea solution. A filter element 4 serving as a suction filter is disposed within the circular cylindrical interior of the tank 2 in such a manner that it forms an inner cylinder, which is disposed on the bottom 10 of the tank 2, concentric to the side walls 6 and 8 of the tank 2. The filter medium 12 of the filter element 4 extends from a base plate 14 lying on the tank bottom 10, to a cover plate 18 located at the upper edge 16 of the filter element 4, and, with base plate 14 and cover plate 18, delimits an inner filter cavity 20 forming the clean-side during the filtration process. Located on the base plate 14 is a suction connection 22, from which a cleaned urea solution can be discharged via an opening 24 in the tank bottom 10, as indicated with flow arrows 26.

FIG. 2, in contrast to FIG. 1, illustrates an operating state of the device of the prior art, in which the filling level height 28 in the tank 2 has fallen below the upper edge 16 of the filter element 4. As soon as this occurs during the operation of the device, and thereby exposes a part of the filter medium 12 in the airspace of the tank 2, air is able to enter, as is indicated with flow arrow 30, into the filter cavity 20 if a low pressure is present therein in comparison to the airspace of the tank 2. So long is this is not the case, urea solution can flow according to the geodetic pressure, via the wet part of the filter medium 12 into the filter cavity 20, and exit via the suction connection 22. However, in the event that during operation the volume flow flowing out via the filter medium 12 falls to less than the possibly required suction volume of the associated pump, low-pressure develops in the filter cavity 20, such that air is suctioned out of the airspace of the tank 2 into the filter cavity 20, the filter cavity is suctioned empty of the clean-side urea solution, and the suctioned air is conveyed within the system. Consequently, safe operation is guaranteed only if the filling level height 28 remains above the element upper edge 16, which means that not the entire fill quantity of the tank is usable.

FIGS. 3 through 6 show the functionality of the device according to the invention, which differs from the prior art shown in FIGS. 1 and 2. In the invention, the filter element 34, which is disposed on the bottom 10 of the tank 2, as in the prior art shown in FIGS. 1 and 2, and is provided for suction filtration, has a filter medium 32, which is air-impermeable for low suction pressures. Further unlike the prior art, the suction connection 22 in the exemplary embodiment shown in FIGS. 3 through 6 is not located at the lower base plate 14 of the filter element 34, but rather at the upper cover plate 18. FIG. 3 illustrates a state of the device prior to start-up of the system and when filling the tank 2 to a filling level height 28 above the filter element 34. A quantity of air initially located in the filter cavity 20 before a start-up of the downstream pump device remains enclosed in the filter cavity 20 due to the air-impermeability of the filter medium 34, such that during the filling process, an overpressure develops due to geodetic pressure of the urea solution in the filter cavity 20 surrounding the filter element 34, such that merely a low bottom layer 36 of inflowing urea solutions is formed, above which a quantity of air is located, see FIG. 3. If, starting from the state shown in FIG. 3, the system is put into operation, this quantity of air is then discharged out of the filter cavity 20 by the associated pump, see arrow 38.

To carry out a ventilation operation in the head-side arrangement of the suction connection 22 by means of the pump device, for example by means of a self-ventilating pump, the entire air content is discharged from the filter cavity 20, until the cleaned fluid initially forming only the bottom layer 36 in the cavity, has risen to the level of the suction connection 22. The filter element 34 is now free of air, and the device is ready for operation. This state is shown in FIG. 4.

FIGS. 5 and 6 show further phases of operation with a filling level height 28 lowered to different degrees. The filter cavity 20 remains filled completely with the cleaned urea solution, i.e. free of air, due to the air-impermeability of the filter medium 34. Therefore, the entire fill quantity of the tank 2 can be used without the danger of air entering into the system, see FIG. 6 showing the state of the practically completely emptied tank 2.

While the invention is described above based on a device provided for the suction filtration of an aqueous urea solution (Adblue), it is understood that the invention can be applied equally advantageously for other fluids, for which a suction filtration absent the danger of air entry is required. As already mentioned, the ventilation process can be carried out automatically subsequent to a filling. A melt-blown fiber material can be advantageously used as a filter medium 32 particularly suited for the invention. Such a filter medium 32, having a wall thickness of approximately 5 mm and a filter fineness in the range of 10 μm, is distinguished by a high capillary effect, such that even with only partial wetting with a fluid, such as an aqueous urea solution, it is completely sucked full over the entire length thereof, and is thus air-impermeable for the relevant low suction pressures. Whereas the suction filtration occurs by means of a respective suction pump (not shown) connected to the suction connection 22, it is understood that downstream pump devices may be provided as pressure boosters in order to generate desired operating pressures, for example, injection pressures for Adblue applications.

Claims

1. A device for the suction filtration of fluids, such as urea solutions for exhaust gas after-treatment systems, comprising a tank (2) storing the fluid, and a filter element (4) disposed therein, provided with a filter medium (12), which separates the tank contents from a clean-side inner filter cavity (20) and which extends from the bottom area (10) of the tank (2) to a filling level height (28), which corresponds to a part of the filling volume of the tank (2), wherein a suction connection (22) is provided on the filter cavity (20) via which the cleaned fluid can be discharged by way of a suction pressure corresponding to a system operating pressure, characterized in that the filter element (34) has a filter medium (32), which is air-impermeable if suction pressures lie within the range of a low system operating pressure.

2. The device according to claim 1, characterized in that the suction connection (22) is disposed on the filter cavity (20) at the upper end thereof remote from the tank bottom (10).

3. The device according to claim 1, characterized in that the filter medium (32) has a melt-blown fiber material.

4. The device according to claim 1, characterized in that the filter medium (32) has plastic fibers made, in particular, of PA 66.

5. The device according to claim 1, characterized in that the filter medium (32) has a wall thickness in the range of 2 mm to 10 mm, preferably 5 mm, and fineness in the range of 5 μm to 30 μm, preferably 10 μm.

6. A filter element for use with a device for suction filtration according to claim 1, characterized in that it has a filter medium (32), which is air-impermeable for low suction pressures.

7. The filter element according to claim 6, characterized in that at a clean-side inner filter cavity (20), there is a suction connection (22) that is arranged at the end of the filter cavity (20) which lies removed from the bottom (10) of a tank (2) accommodating the filter element (34).