DE102021200702A1 - Filter assembly for a metering system, metering system - Google Patents

Abstract

The invention relates to a filter assembly (1) for a metering system for metering an aqueous urea solution into an exhaust line of an internal combustion engine, comprising a filter unit (2) with a hollow-cylindrical screen section (3) and at least one of the filter unit (2) in front and/or downstream thermally conductive element (4) which delimits a flow path (7) for the aqueous urea solution.
The invention also relates to a dosing system with such a filter assembly (1).

Description

The invention relates to a filter assembly for a dosing system that serves to dose an aqueous urea solution into an exhaust system of an internal combustion engine. In addition, the invention relates to a dosing system with such a filter assembly.

State of the art

The exhaust gases from internal combustion engines in vehicles must comply with certain pollutant limits due to legal requirements. To comply with these limit values, exhaust aftertreatment systems are used, by means of which the concentration of particles and/or nitrogen oxides in the exhaust gas can be reduced. The operation of such an exhaust aftertreatment system generally requires the introduction of an oxidizing and/or reducing agent, for example an aqueous urea solution, into an exhaust system of the internal combustion engine. The aqueous urea solution causes the formation of ammonia in the exhaust line, which reacts with the nitrogen oxides contained in the exhaust gas in a downstream catalytic converter to form harmless nitrogen and water (“selective catalytic reduction”). The nitrogen oxide concentration in the exhaust gas falls accordingly.

To introduce the aqueous urea solution into an exhaust line of an internal combustion engine, a metering system is generally used, which includes a tank, a delivery module and a metering module. With the help of the delivery module, the aqueous urea solution can be removed from the tank and fed to the dosing module. With the help of the dosing module, the aqueous urea solution can be dosed as a spray into the exhaust system of the combustion engine. In order to protect the dosing module from the entry of harmful particles, a filter is generally provided, which is connected upstream of the dosing module.

A dosing system of the type mentioned above is exemplified by the published application DE 10 2017 201 124 A1 out. A filter is integrated in the delivery module to protect against harmful particles. The known dosing system thus has increased functional reliability.

Since the aqueous urea solution freezes at temperatures below -11°C, the dosing system is usually completely emptied when the combustion engine is switched off to protect against ice pressure damage. Depending on the design of the system, however, complete emptying can be problematic, so that a residual amount remains in the system. If this residual amount freezes, this can lead to ice pressure damage and thus to leaks in the system. Furthermore, the cold start capability of the system deteriorates since the frozen residue must first be thawed.

The object of the present invention is to remedy this. To solve the problem, the filter assembly with the features of claim 1 is proposed. Advantageous developments of the invention can be found in the dependent claims. In addition, a dosing system with such a filter assembly is specified.

Disclosure of Invention

The filter assembly proposed for a metering system for metering an aqueous urea solution into an exhaust system of an internal combustion engine comprises a filter unit with a hollow-cylindrical screen section and at least one heat-conducting element upstream and/or downstream of the filter unit, which delimits a flow path for the aqueous urea solution.

When installing the filter assembly in the dosing system, the filter assembly can be arranged such that the thermally conductive element of the filter assembly has an area of overlap with a heat source. For example, an exhaust line that carries hot exhaust gas to be cleaned can serve as a heat source. The heat is then conducted via the heat-conducting element to the filter unit of the filter assembly, so that it cannot freeze at low outside temperatures or - if ice has already formed - can be thawed more quickly.

With the help of the proposed filter assembly, an external heat source can be used to thaw the filter unit even if it is not located directly on the filter unit. This is because the heat from the external heat source is fed to the filter unit via the heat-conducting element.

The thermally conductive element is preferably connected upstream of the filter unit, so that it is ensured that it can be supplied with an aqueous urea solution. Alternatively or additionally, the thermally conductive element can be connected downstream of the filter unit. In this way, the outflow of aqueous urea solution from the filter unit can be ensured. Advantageously, the direction of flow of the aqueous urea solution through the filter assembly can be reversed.

The filter assembly proposed for a dosing system can not only be used to filter an aqueous urea solution, but also to filter other liquids. Inso far expand the possible uses of a filter assembly according to the invention.

The thermally conductive element of the proposed filter assembly is preferably made entirely or partially of metal or a thermally conductive plastic. Because these materials have a high thermal conductivity and are therefore particularly well suited for forming a heat-conducting element. For this purpose, thermally conductive plastics are filled with a thermally conductive filler, for example metal particles, carbon black or graphite. In this way, a material with a high thermal conductivity can also be achieved on the basis of a plastic.

In order to optimize the heat transfer from the thermally conductive element to the filter unit, it is proposed that the filter unit and the thermally conductive element be connected, preferably pressed. For example, the filter unit and the heat-conducting element can be placed one inside the other in sections, so that they have a common overlapping area in the axial direction. For pressing, the overlapping area can be formed with an oversize pressing.

According to a preferred embodiment of the invention, the filter unit and the heat-conducting element are accommodated in a common housing. The common housing enables pre-assembly of the assembly and increases the robustness of the arrangement.

In a development of the invention, it is proposed that the filter unit and the heat-conducting element be surrounded at least in sections by an insulating material. The insulating material prevents heat from being released to the environment. This means that heat losses are reduced. As a result, more heat can be supplied to the filter unit. The insulating material can be, for example, a jacket or tube made of an insulating material, such as foam rubber.

In order to ensure the transfer of heat from the external heat source to the heat-conducting element, the heat-conducting element is preferably not surrounded by an insulating material in the region of overlap with the external heat source. In the case of a jacket or tube made of insulating material, this is cut out in the overlapping area.

The heat-conducting element of the proposed filter assembly can be designed in the form of a hollow cylinder, at least in sections, and have at least one radial bore. The at least one radial bore enables a flow path arranged radially on the inside to be connected to a flow path arranged radially on the outside. The aqueous urea solution can therefore flow through the heat-conducting element at least in sections, then be guided outwards via the at least one radial bore, so that the heat-conducting element is also flowed around by the aqueous urea solution. The flow through the filter unit is preferably from radially outside to radially inside, so that the filtrate can be discharged centrally.

The thermally conductive element can be designed in one or more parts. The multi-part design has the advantage that, for example, an end section for connection to the filter unit can be designed as a separate part. This simplifies production and also allows the use of a different material. In a multi-part design of the heat-conducting element, the multiple parts are preferably coupled in the axial direction. The coupling can also be implemented via a press connection, for example.

The filter unit of the proposed filter assembly is preferably surrounded by at least one sealing ring or one sealing lip in an outer peripheral area. The sealing ring or the sealing lip directs the aqueous urea solution in the direction of the screen section so that it is completely filtered. At the same time, the flow path of the aqueous urea solution is sealed off from the outside. The outer peripheral area of the filter unit that has the sealing ring or the sealing lip is therefore preferably arranged downstream of the screen section in the direction of flow of the aqueous urea solution.

In addition, a metering system for metering an aqueous urea solution into an exhaust system of an internal combustion engine is proposed. The dosing system includes a filter assembly according to the invention, the filter assembly being downstream of a delivery module for the aqueous urea solution or being integrated into the delivery module. In particular, the cold start behavior of the dosing system can be improved with the aid of the filter assembly according to the invention.

• 1 einen schematischen Längsschnitt durch eine erste erfindungsgemäße Filter-Baugruppe,
• 2 einen schematischen Längsschnitt durch eine zweite erfindungsgemäße Filter-Baugruppe,
• 3 einen schematischen Längsschnitt durch eine dritte erfindungsgemäße Filter-Baugruppe und
• 4 einen schematischen Längsschnitt durch eine vierte erfindungsgemäße Filter-Baugruppe.

Preferred embodiments of the invention are explained in more detail below with reference to the accompanying drawings. These show:

• 1 a schematic longitudinal section through a first filter assembly according to the invention,
• 2 a schematic longitudinal section through a second filter assembly according to the invention,
• 3 a schematic longitudinal section through a third filter assembly according to the invention and
• 4 a schematic longitudinal section through a fourth filter assembly according to the invention.

Detailed description of the drawings

The one in the 1 The filter assembly 1 shown comprises a filter unit 2 and a thermally conductive element 4 which is firmly connected to the filter unit 2 and which in the present case is designed in two parts. A first part 4.1 is designed as a hollow cylinder and has an inner peripheral surface 5 which delimits a flow path 7 for a liquid to be filtered, for example an aqueous urea solution. A second part 4.2, which is attached axially to the first part 4.1 and is connected to it, has at least one radial bore 9, via which the flow path 7 is deflected from radially inside to radially outside. The element 4 is thus also flowed around by the liquid in the area of an outer peripheral surface 6 . The filter unit 2 and the heat-conducting element 4 are accommodated in a common housing 8 in order to delimit the flow path 7 . The flow path 7 is delimited in the axial direction by a sealing lip 11 which covers the filter unit 2 in an outer peripheral region 10 which is arranged downstream of a screen section 3 of the filter unit 2 . The liquid is fed to the screen section 3 in this way. The filtrate is discharged centrally from filter unit 2.

The thermally conductive element 4 in the 1 The filter assembly 1 shown has an overlap area with an external heat source 12 . Because of this, the heat-conducting element 4 heats up and conducts the heat 13 in the direction of the filter unit 2 . In doing so, it heats the liquid which flows both through and around the heat-conducting element 4 . This reduces the risk of the liquid freezing at low outside temperatures. If it is already frozen, it can be thawed faster with the help of heat 13.

A simplified version of a filter assembly 1 according to the invention is shown in FIG 2 shown. Here the heat-conducting element 4 is made in one piece. In addition, the liquid to be filtered only flows around the heat-conducting element 4 on the outer circumference, so that the radial bore 9 is omitted. Otherwise, the embodiment is the same as that of 1 . In the simplified embodiment, the surface area of the heat-conducting element 4 that comes into contact with the liquid is smaller. As a result, less heat is transferred from the element 4 to the liquid.

Of the 3 a filter assembly 1 can be seen which has a one-piece heat-conducting element 4 which delimits a flow path 7 for the liquid to be filtered both via an inner peripheral surface 5 and via an outer peripheral surface 6 . The surface available for heat transfer accordingly corresponds to the embodiment of FIG 1 .

The one in the 4 Filter assembly 1 shown represents a further development, which basically with all in the 1 until 3 illustrated embodiments can be combined. In the 4 a thermally conductive element 4 is connected upstream and downstream of the filter unit 2 . The upstream thermally conductive element 4 is analogous to the thermally conductive element 4 in FIG 3 illustrated embodiment designed. The downstream thermally conductive element 4 is analogous to the first part 4.1 of the thermally conductive element 4 in FIG 1 illustrated embodiment designed. The downstream thermally conductive element 4 also has an area of overlap with an external heat source 12, so that heat from the external heat source 12 is transferred to the thermally conductive element 4, which in turn transfers the heat 13 to the liquid.

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• DE 102017201124 A1 [0004]

Claims (9)

Filter assembly (1) for a metering system for metering an aqueous urea solution into an exhaust system of an internal combustion engine, comprising a filter unit (2) with a hollow-cylindrical screen section (3) and at least one thermally conductive element ( 4) defining a flow path (7) for the aqueous urea solution. Filter assembly (1) after claim 1 , characterized in that the thermally conductive element (4) is made entirely or partially of metal or a thermally conductive plastic. Filter assembly (1) after claim 1 or 2 , characterized in that the filter unit (2) and the heat-conducting element (4) are connected, preferably pressed. Filter assembly (1) according to one of the preceding claims, characterized in that the filter unit (2) and the heat-conducting element (4) are accommodated in a common housing (8). Filter assembly (1) according to one of the preceding claims, characterized in that the filter unit (2) and the heat-conducting element (4) are surrounded at least in sections by an insulating material. Filter assembly (1) according to one of the preceding claims, characterized in that the heat-conducting element (4) is designed in the form of a hollow cylinder, at least in sections, and has at least one radial bore (9). Filter assembly (1) according to one of the preceding claims, characterized in that the heat-conducting element (4) is made in several parts and the several parts (4.1, 4.2) are coupled in the axial direction. Filter assembly (1) according to one of the preceding claims, characterized in that the filter unit (2) is surrounded in an outer peripheral area (10) by at least one sealing ring or a sealing lip (11), the outer peripheral area (10) preferably being in the direction of flow of the aqueous urea solution is arranged downstream of the screen section (3). Metering system for metering an aqueous urea solution into an exhaust system of an internal combustion engine, comprising a filter assembly (1) according to one of the preceding claims, wherein the filter assembly (1) is downstream of a delivery module for the aqueous urea solution or is integrated into the delivery module.

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