DE102014105288A1 - Filter heating for urea solution and method for producing a filter heating for urea solution - Google Patents

Abstract

Described is a filter heating for urea solution, with a heat conductor cut out of sheet metal (4), which consists of a series of juxtaposed strips (4a), which are connected to an adjacent strip (4a) at one end, and a wall (3 ) of plastic, which surrounds a space provided for receiving a filter (1), wherein the heating conductor (4) is liquid-tightly enclosed in the wall (3). According to the invention it is provided that the wall (3) has a corrugated shape and the heating conductor (4) to the wall (3) is bent suitably. In addition, a method for producing a filter heater (1) for urea solution is described.

Description

The invention is based on a filter heater for reducing agent with the features of the preamble of claim 1, as for example from the DE 10 2008 014 415 A1 is known. Reducing agent is needed in exhaust gas purifying catalysts. Usually, urea solution is used as the reducing agent.

Urea solution is chemically very corrosive. The heating conductor of a filter heating for urea solution is therefore usually protected by a plastic housing from contact with the corrosive urea solution. Because of the relatively poor conductivity of plastics, the thicker such a plastic housing, the worse the thermal coupling of the heating elements to urea solution. In general, therefore, the aim is to make the plastic housing of a filter heating for urea solution as thin as possible so that heat generated by the heating elements can be delivered to urea solution as quickly and efficiently as possible. However, the production of a liquid-tight plastic housing with small wall thicknesses becomes increasingly problematic. Since even very small amounts of urea solution can destroy the heating element, even tiny leakage points must be reliably avoided.

This requirement to create a thin-walled but nevertheless reliable liquid-tight housing is made more difficult by the fact that the plastic housing has to withstand the mechanical loads caused by frozen urea solution. The volume of urea solution expands by about 11% upon freezing. Depending on the level, therefore, a significant ice pressure may occur that must not damage the plastic housing.

Object of the present invention is to show a way how a filter heating for urea solution can be created, which allows a better thermal coupling to urea solution and thus a faster thawing of urea ice.

This object is achieved by a filter heater having the features specified in claim 1 and by a method according to claim 10. Advantageous developments of the invention are the subject of dependent claims.

A filter heating according to the invention for urea solution has a wall of plastic surrounding a space provided for receiving a filter. The wall is preferably an annular wall. It is also possible that the wall surrounds the space for receiving a filter only U- or C-shaped.

The wall has a corrugated shape, preferably a zigzag corrugated shape, and contains a sheet metal, preferably corrosion-resistant steel sheet, cut out heating conductor which is bent to fit the wall. The corrugated shape has several advantages. On the one hand, the wall can well balance the volume changes associated with the freezing and thawing of urea solutions by deforming and expanding as needed. On the other hand, the corrugated shape of the wall causes a particularly large area over which heat generated by the heating conductor can be delivered to surrounding urea solution. In frost, therefore, a larger amount of urea solution can be thawed very quickly in a volume adjacent to the wall. In addition, because of the bending of the heat conductor, a larger heat conductor length can be arranged in the wall for a given extent of the filter heating and thus reduce the heat conductor temperature for the same heat output.

In the wall, a heating element is arranged, which is cut out of sheet metal. The heating conductor consists of a series of juxtaposed strips connected at their ends. Such a heating conductor can be made by cutting into a sheet metal strip a series of slots which alternately emanate from its longitudinal edges. Between the slots are then the strips of the heating conductor, which are connected at their ends with adjacent strips via a web. The webs are formed by the material of the sheet metal strip, which remains between the end of a slot and the corresponding longitudinal edge of the strip.

After the heating conductor is cut out of the sheet metal strip, it is folded to fit the corrugated shape of the ring wall, for example by bending the webs between adjacent strips of the heating conductor. Webs at one end of the strips are bent in the opposite direction as webs at the other end of the strip. Adjacent strips of the heat conductor are then rotated relative to one another about a geometric axis extending along their longitudinal direction. But there are also other arrangements of heating strips conceivable. Thus, for example, not the strips, but the webs are rotated to each other, the heating element can be arranged bifilar or consist of several individual sections.

An advantageous development of the invention provides that the wall has on both sides of a strip of the heating element each only a thickness of at most 1.5 mm, preferably at most 1.3 mm, more preferably not more than 1.1 mm. Such thin walls can be practically not liquid-tight manufacture by molding a heat conductor cut out of sheet metal. Do you want one Due to its low mechanical stability, the heat conductor in the injection mold must be positioned with a larger number of support punches. During the injection process, the support punches can be withdrawn only when the position of the heating element is already sufficiently stabilized by injected plastic. In order that subsequently injected plastic can reliably close the gaps created by the support punches in a liquid-tight manner, wall thicknesses of more than 1.5 mm are required. With thinner wall thicknesses after retracting the support stamp plastic can no longer reliably reach the left of the support stamps gaps, so that the plastic housing of the heat conductor is no longer liquid-tight or mechanically weakened and thus unreliable weld lines arise.

With a method according to the invention according to claim 10 even filter heaters can be realized with a plastic housing whose wall thickness is less than 1 mm. For this purpose, the housing is first produced separately without the heat conductor cut out of sheet metal. In accordance with the invention, a plastic housing with a double-walled wall, preferably a double-walled annular wall, is produced by injection molding and the heating conductor is arranged later in the plastic housing. For example, an injection mold may have a core around which the double-walled wall is injected. Such a core is more rigid than a sheet metal strip and may have a greater strength than a heat conductor cut out of sheet metal, so that it does not have to be supported by punches. In addition, the mechanical stability of the heating element is additionally weakened by its meandering shape, which is not the case with the core of the injection mold. If a plastic housing is produced in this way, the heating conductor can then be inserted into the double-walled annular wall of the plastic housing.

Another possibility is to produce the inner and the outer wall of the plastic housing separately by injection molding and then to arrange the heating element in the plastic housing by joining the two walls with the interposition of the heating element and welded together.

If the plastic housing is manufactured separately, it must be sealed liquid-tight after the heating element has been placed in the plastic housing. In the method according to the invention, the plastic housing is sealed liquid-tight by welding. If the plastic housing was produced by injection molding with a double-walled wall and the heating element was inserted into the wall, can on the open end of the wall a wall curved strip, for example, a U- or C-shaped bent strip or in the case of an annular wall a ring, put on and this welded to the wall.

As the material for the wall of a filter heating according to the invention preferably polyethylene is used. In conventional filter housings, polyphenylene sulfide or polyphthalamide is used because of the lower thermal expansion and better thermal conductivity. Polyethylene has a very high thermal expansion, which is about eight times the thermal expansion of steel. A high thermal expansion of the plastic housing of a filter heater leads to conventionally produced filter heaters to the fact that when cooling after Umvoritzen the heat conductor high mechanical stresses occur, which can lead to a detachment of the housing of the heating element or even stress cracks. However, if the housing of a filter heater is initially made without the heating conductor and the heating conductor is later inserted into the housing, the high thermal expansion coefficient of polyethylene is not a serious problem. In a thin-walled housing and the relatively poor heat conduction of polyethylene is largely insignificant. Polyethylene has the advantage of a very good diffusion density against urea solution as well as good weldability.

A further advantageous development of the invention provides that a filter insert surrounded by the wall and / or the wall have projections which form a thermal bridge from the wall to the filter insert. These projections are preferably elongated and can extend in the axial direction of the wall. For example, when the wall is corrugated, the projections may be parallel to the corrugated wall corrugations, such as ribs or ridges. In particular, wave crests of the corrugated wall can abut as projections on the filter insert.

The filter cartridge may have protrusions that bear against the wall or the wall may rest against the filter cartridge with projections, for example wave crests. The wave crests can be increased on the side facing the filter element by ribs or webs (that is, they are elongated in the direction perpendicular to the wall). Preferably engage projections of the filter insert and the wall into each other, for example in the manner of a tongue and groove joint.

Further details and advantages of the invention will become an embodiment below Explained with reference to the accompanying drawings. Show it:

1 an embodiment of a filter heating for urea solution with a filter cartridge;

2 in the 1 shown filter heater without housing and filter cartridge;

3 a sectional view of the filter heater without heat conductor;

4 a sectional view of the filter heater with heating conductor;

5 a detailed view of the section B of 4 ; and

6 a detailed view too 1 ,

In 1 are a filter heater 1 for urea solution and a filter cartridge 2 shown. The filter heater 1 has a plastic housing with an annular wall 3 , which has a zigzag corrugated shape and the filter element 2 surrounds. In the ring wall 3 is liquid-tight a heat conductor 4 enclosed, to the ring wall 3 suitably bent zigzag. 2 shows the in 1 illustrated filter heater 1 without the plastic housing and the filter. 3 shows a sectional view of the filter heater 1 without filter element and without heating conductor. 4 shows a sectional view of the filter heater 1 without filter element and with heating conductor 4 , 5 shows the detail B of the 4 ,

The filter insert 2 has a radially inner filter sheet and a radially outer filter sheet attached to an upper plastic ring 2a and a lower plastic ring, not shown, are attached. The filter insert 2 has an end face, for example, on the upper ring 2a , one or more connections 2 B to remove filtered urea solution. Urea solution can enter the filter cartridge through both the radially outer and radial inner filter sheets. Urea solution can thus on the one hand from the gap between the annular wall 3 and radially inwardly flow through the outer filter sheet and radially outwardly through the radially inner filter sheet. Advantageously, the filter has a very large filter surface.

The filter can be placed standing in a tank. Dirt particles settle to the bottom of a tank and can form a swamp there. In a vertical arrangement, such a sump practically can not lead to premature failure of the filter, since the filter can usually protrude with an upper portion of a possibly existing sump.

The filter insert 2 can be at one axial end on the ring wall 3 rest. The filter insert 2 but also completely in the of the ring wall 3 surrounded interior. The filter insert 2 can on the ring wall 3 be attached, for example by the filter cartridge 2 clipped into the ring wall. Another possibility is that the filter cartridge has a brim on the ring wall 3 rests and is welded to this.

The heating conductor 4 is cut out of sheet metal, for example of steel. The sheet thickness can be, for example, 0.2 to 0.4 mm. The heating conductor 4 consists of a series of juxtaposed strips 4a that with adjacent stripes 4a each connected at one end. The Stripes 4a are preferably arranged in parallel and at one end with an adjacent strip 4a over a footbridge 4b connected. The heating conductor 4 can be made by slits are cut in a sheet metal strip perpendicular to the longitudinal direction, which alternately emanate from the two longitudinal edges. The heating conductor 4 is bent zigzag by the webs 4b bent alternately, for example by all the webs 4b at the top of the strip 4a radially inward and all the ridges 4b at the lower end of the strips 4a bent radially outward. Neighboring stripes 4a of the heating conductor 4 are then rotated relative to each other, namely a geometric axis that runs along the longitudinal direction of the strips.

The Heizeiter 4 is in the embodiment at one end with a polymeric PTC element 5 (PPTC) connected in series. The PPTC 5 protects the filter heater 1 from overheating. When the temperature of the PPTC 5 exceeds a threshold temperature increases its electrical resistance so that heating power is reduced to almost zero. The PPTC 5 is at one end of a strip of the heating element 4 connected. This strip is shorter than its adjacent strip and also has a different width. By the width of this strip to which the PPTC 5 is connected, the thermal coupling of the PPTC 5 to the heating conductor 4 be set. The PPTC 5 is to a connector pin 6 connected, which protrudes from the plastic housing. A second connector pin 7 is on a strip at the other end of the heat conductor 4 appropriate.

However, it is also conceivable other types of temperature limitations or - fuses, z. B. bimetallic switch.

The plastic housing of the filter heater can be made of polyethylene, for example. The ring wall 3 is a double-walled ring wall with an inner ring wall 3a and an outer ring wall 3b , The inner ring wall 3a and the outer one ring wall 3b are corrugated in a zigzag parallel to each other, so each consists of a sequence of transverse to the circumferential direction of the annular wall 3 running mountains and valleys. A mountain on the outside forms a valley on the inside and vice versa. The radial distance of the mountains from the valleys is thus a multiple of the wall thickness.

The heating conductor 4 is between the inner ring wall 3a and the outer ring wall 3b enclosed liquid-tight. The inner ring wall 3a and the outer ring wall 3b preferably each have a thickness of not more than 1.5 mm, for example, the inner ring wall 3a and the outer ring wall 3b have a thickness of 0.5 mm to 1.0 mm.

The plastic housing of the filter heater shown is produced by injection molding. For this purpose, an injection mold can be used, which has a core or a plurality of cores, around which or the zigzag corrugated double-walled annular wall 3 is sprayed around. It is possible to use a single core, which is bent in a zigzag shape, so that a zigzag corrugated slit between the inner ring wall 3a and the outer ring wall 3b is produced. It is also possible to use several cores, which are arranged side by side in the injection mold and in each case only a part of the intermediate space for the heating element 4 create. For example, each of the cores may have a V-shaped cross-section and be spaced from the adjacent core. In this way, during the injection molding between adjacent cores intermediate walls 3c which creates the inner ring wall 3a with the outer ring wall 3b connect.

When the plastic housing is removed from the injection mold, then the zigzag curved heating conductor 4 in the plastic housing between the inner ring wall 3a and the outer ring wall 3b inserted. partitions 3c can only use one side of a strip in this production method 4a of the heating conductor 4 be arranged, as on the other side of the jetty 4b which the strip 4a with its adjacent strip connects, otherwise not in the space between the inner ring wall 3a and the outer ring wall 3b could be inserted. On the other side of the strip 4a but can be a curtain wall 3c be provided, which the gap between adjacent strips 4a up to the connecting bridge 4b can fill.

In the illustrated embodiment are partitions 3c in each case only in the outward elevations of the zigzag wavy shape of the annular wall 3 arranged. It is equally possible to use partitions 3c in each case only in the inwardly directed elevations of the zigzag wavy annular wall 3 to arrange or only a part of the maximum possible partitions 3c to provide in the plastic housing.

After inserting the heating conductor 4 between the inner ring wall 3a and the outer ring wall 3b the plastic housing becomes the gap between the inner ring wall 3a and the outer ring wall 3b liquid-tight closed by a weld. It is possible that the inner ring wall 3a and the outer ring wall 3b be welded directly to each other. Another possibility is on the ring wall 3 a ring 8th to set up and this with the inner ring wall 3a and the outer ring wall 3b to weld. The ring 8th can thus form a lid which closes the plastic housing. The ring 8th is preferably made of the same material as the ring wall 3 , so for example made of polyethylene. The ring 8th is preferably part of the filter cartridge 2 , The filter insert 2 in this case has a brim on the ring wall 3 is present and welded to this.

The ring wall 3 is hot pressed after the heating conductor 4 in the ring wall 3 was inserted. The hot pressing can be done before or after the welding and improves the thermal coupling of the heating element 4 to the ring wall 3 , When hot pressing the inner ring wall 3a and the outer ring wall 3b by radial pressure against the heating conductor 4 and pressed against each other. The temperature should not be too high; the deformation of the plastic must still be done in the plastic range.

The ring wall 3 can be a plug housing 9 for connecting the heating conductor 4 to form a power source. The connector housing 9 may have guide elements, for example, webs or grooves for a mating connector. The ring wall 3 can form a chamber in which the two ends of the heating conductor 4 and the PPTC 5 are arranged. The chamber can be an extension of the connector housing 9 be the same cross-section, as is the case in the embodiment shown. Chamber and connector housing 9 have a partition through which the connections are made tight.

To the thermal coupling of the filter cartridge 2 to the filter heater 1 To improve the filter cartridge 2 and / or the plastic housing of the filter heater 1 projections 2c . 3d exhibit the thermal bridges from the ring wall 3 to the filter cartridge 2 form. The projections 2c . 3d are elongated and extend in the axial direction of the annular wall 3 , Preferably, the projections engage 2c of the filter insert 2 and the projections 3d the ring wall 3 each other. Advantageously, the contact surface between the ring wall 3 and the filter cartridge 2 increases and thus improves the thermal contact.

For example, each radially inwardly facing wave crest 3d the zigzag wavy ring wall 3 on the filter element 2 abutment, in particular on a projection 2c of the filter insert 2 issue. Preferably, the wave crest forms 3d the ring wall 3 or the filter cartridge 2 or the lead 2c of the filter insert 2 a groove into which the projection 2c the filter insert or the projection 3d engages the wall

LIST OF REFERENCE NUMBERS

1

filter heater

2

filter

2a

Plastic ring

2 B

connections

2c

head Start

3

ring wall

3a

inner ring wall

3b

outer ring wall

3c

partition

3d

head Start

4

heating conductor

4a

strip

4b

web

5

PPTC

6

first connector pin

7

second connector pin

8th

ring

9

plug housing

QUOTES INCLUDE IN THE DESCRIPTION

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

Cited patent literature

• DE 102008014415 A1 [0001]

Claims (14)

Filter heater for reducing agent, with a heating conductor cut out of sheet metal ( 4 ) consisting of a series of juxtaposed strips ( 4a ), which is adjacent to a strip ( 4a ) are each connected at one end, and a wall ( 3 ) made of plastic, the one for receiving a filter cartridge ( 1 ), wherein the heating conductor ( 4 ) liquid-tight in the wall ( 3 ), characterized in that the wall ( 3 ) has a corrugated shape and the heating conductor ( 4 ) to the wall ( 3 ) is bent suitably. Filter heater according to claim 1, characterized in that the wall ( 3 ) has a zigzag corrugated shape and the heating conductor ( 4 ) to the wall ( 3 ) is bent suitably zigzag. Filter heater according to one of the preceding claims, characterized in that the wall ( 3 ) is made of polyethylene. Filter heater according to one of the preceding claims, characterized in that the wall ( 3 ) on both sides of a strip ( 4a ) of the heating conductor ( 4 ) each has a thickness of at most 1.5 mm, preferably at most 1.3 mm, particularly preferably at most 1.1 mm. Filter heater according to one of the preceding claims, characterized in that the wall ( 3 ) a double-walled wall with an inner wall ( 3a ) and an outer wall ( 3b ), wherein the heating conductor ( 4 ) between the inner wall ( 3a ) and the outer wall ( 3b ), where the wall ( 3 ) Partitions ( 3c ) having the inner wall ( 3a ) with the outer wall ( 3b ) and between adjacent strips ( 4a ) of the heating conductor ( 4 ) and along alongside each strip ( 4a ) of the heating conductor ( 4 ) at most on one side an intermediate wall ( 3c ) is arranged. Filter heater according to one of the preceding claims, characterized in that the wall ( 3 ) is sealed liquid-tight by a weld. Filter heater according to one of the preceding claims, characterized in that the wall ( 3 ) a plug housing ( 9 ) for connecting the heating conductor ( 4 ) forms a power source. Filter heater according to one of the preceding claims, characterized in that the heating conductor ( 4 ) with a PPTC ( 5 ) is connected in series by the PPTC ( 5 ) to a strip ( 4a ) at one end of the heating conductor ( 4 ), this strip ( 4a ) shorter than its adjacent strip ( 4a ) and has a different width. Filter heater according to claim 7, characterized in that the wall ( 3 ) forms a chamber in which the two ends of the heating conductor ( 4 ) and the PPTC ( 5 ) are arranged. Method for producing a filter heater ( 1 ) for reducing agent, wherein a plastic housing is produced by injection molding, which is a wall ( 3 ) has a corrugated shape, from sheet metal a heating conductor ( 4 ), which consists of a series of interconnected strips ( 4a ), the heating conductor ( 4 ), the heating conductor ( 4 ) in the wall ( 3 ) and the wall ( 3 ) is sealed liquid-tight by welding. A method according to claim 10, characterized in that by injection molding the plastic housing with a double-walled wall ( 3 ) and the heating conductor ( 4 ) in the wall ( 3 ) is inserted. Method according to claim 11, characterized in that the double-walled wall ( 3 ) is sealed liquid-tight by welding, by after insertion of the heating conductor ( 4 ) a strip bent to match the wall or a ring ( 8th ) on the wall ( 3 ) and with the wall ( 3 ) is welded. Method according to one of claims 10 to 12, characterized in that the wall ( 3 ) is hot pressed after the heating conductor ( 4 ) in the wall ( 3 ) was arranged. Method according to one of claims 10 to 13, characterized in that the heating conductor ( 4 ) of a series of juxtaposed strips ( 4a ), which is adjacent to a strip ( 4a ) are connected at one end, and the heating conductor ( 4 ) is bent by adjacent strips ( 4a ) of the heating conductor ( 4 ) are rotated relative to each other.

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