Heating device for heating liquids in a reservoir, such as a tank or a container of a vehicle

Systems, methods, and devices are disclosed. In an exemplary embodiment, a heating device for heating liquids in a reservoir, such as a tank or a container of a vehicle is disclosed. The heating device may have a housing which is resistant to the liquid to be heated and has a tubular outer casing closed at one end by a base part and at the other end by a cover part. The heating element may also include an insert inserted into the outer casing of the housing and at least one surface heating element arranged between the outer casing and the insert. Connecting conductors of the heating element may be routed out of the housing sealed, and at least one surface heating element may cover the inner surface of the outer casing, viewed in the circumferential direction of the outer casing, at least over a partial circumference, with which the outer casing may be in thermal contact, and the insert, or at least parts thereof, may be pretensioned and press the at least one surface heating element against the inner surface of the outer casing at least in partial regions.

The present invention relates to a heating device.

Such heating devices are used to heat liquids in a reservoir, in particular of a vehicle, such as a fuel tank or a water container for cooling water or windshield wiper water, in order to counteract freezing of the water or a change in the consistency of the liquid, such as diesel fuel, at low temperatures.

A particular application field is the heating of urea tanks in which urea is stored for mixing with diesel fuel to meet diesel exhaust emission standards. The urea solution used here is also known as AdBlue® (brand of the German Association of the Automotive Industry). In North America, such an additive is referred to as DEF (Diesel Exhaust Fluid).

The process is based on the injection of ammonia into the catalytic converters used in vehicles, which reduces nitrogen oxides. However, since ammonia not only causes a pungent odor but is also dangerous, urea is used which decomposes into ammonia. The AdBlue used is an aqueous solution with a 32.5% urea content and selectively converts the environmentally harmful nitrogen oxide contained in the exhaust gas into water and nitrogen without producing any unwanted by-products. The consumption of this additive is in the range of 2% to 8% of the fuel consumption, so that relatively large containers are required for the urea. This process is known as SCR (Selective Catalytic Reduction).

Since the aqueous urea solution freezes at −11° Celsius (12° Fahrenheit), heatable tanks are required.

A urea solution has very corrosive properties, which is the reason why the usual heating devices, which are installed in the tanks or containers for this purpose, have a housing that is resistant to the liquid to be heated and has a tubular outer casing with a rectangular, round or also oval cross-section. This outer casing is closed at one end by a base part and at the other end by a cover part. An insert with a heating element is inserted into this outer casing. Connecting conductors for the heating element are routed out of the housing, sealed.

DE 10 2016 111 258 A1 describes a heating cartridge with an outer protection tube and an inner sheath tube. A spring element is inserted in an intermediate space between protection tube and sheath tube, which is wave-shaped or meander-shaped when viewed in the cross-section of the heating cartridge. A ceramic PTC element is located at a distance inside the inner sheath tube.

DE 102 58 257 A1 relates to an electrical heating device for heating a liquid in a motor vehicle having a metallic housing immersed in the liquid within which a heating insert is located having one or more heating elements clamped in the metallic housing. The heating elements are plate- or disc-shaped, flat parts that are held on a frame.

DE 10 2005 025 724 A1 (corresponds to U.S. 20090100824 A1) relates to a urea supply system for an exhaust-gas purification catalyst and a heating insert suitable therefor. A connecting line connecting the urea tank to an exhaust gas purification catalytic converter is connected to a defrosting tank in which a fraction of the amount of urea sufficient to start the catalytic converter and storable in the urea tank is defrosted by means of the heating insert. The heating insert consists of a corrosion-resistant tube, a metal housing attached to the tube, and at least one heating element located inside the metal housing. The heating element, which can be plate-shaped, can be held in the metal housing by a mounting frame.

DE 38 15 306 A1 (corresponds to U.S. Pat. No. 4,942,289) describes a heating element that consists of a contact unit having at least one PTC element, contact plates resting on both sides of it and a housing that are pressed together. In a non-pressed state of the heating element, the contact plates are curved and rest with their convex side on the PTC elements. The housing consists of a dimensionally stable light metal and, when non-pressed, has a convex inner wall facing the contact arrangement with a finite radius of curvature greater than the radius of curvature of the contact plates. After pressing the housing and curved contact plates together, the contact plates are under elastic tension. After pressing, the curved contact plates and the inner wall of the housing are aligned flat and under tension.

The problem addressed by the present invention is that of creating a heating device with the features mentioned above, which has a simple structure, allows adaptation to the respective containers and shows high efficiency.

This problem is solved by a heating device for heating liquids in a reservoir with the features of claim1. Advantageous embodiments of this heating device are specified in the dependent Claims.

The heating device according to the invention is characterized in that the at least one surface heating element covers the inner surface of the outer casing, viewed in the circumferential direction of the outer casing, at least over a partial circumference, in thermal contact with the outer casing and preferably resting flush against it. The insert, or at least parts thereof, is pretensioned and thereby presses the at least one surface heating element against the inner surface of the outer casing, at least in partial regions, and preferably flush.

Such an arrangement, although simple in design, achieves good heat transfer from the surface heating element to the tubular outer casing. It is essential here that the surface heating element is pressed on substantially flush by the insert, so that a positive connection and/or a frictional connection between the pressing surface of the insert, the surface heating element and the inner surface of the outer casing is achieved preferably in substantial regions.

This heating device, or even several of these heating devices, can be extended or combined to form larger heating units by bundling several of these heating devices side by side or by positioning and combining several of these heating devices one behind the other.

The surface heating element is preferably held along a slot of the insert which extends in the axial direction relative to the axis of the tubular outer casing. The heating element thus held at one end unwinds from the slot on an outer surface of the insert when viewed in the circumferential direction.

The surface heating element is preferably attached along the slot by at least one clamping part without the need for additional fasteners. Such a clamping part can be designed as a snap lock with intermeshing parts which, once locked, permanently hold the surface heating element to the insert.

The connecting conductors of the surface heating element are preferably routed into an inner area of the insert in the area of the slot in which the surface heating element is held. The clamping part, or the several clamping parts that are used to hold the surface heating element to the insert, can also be used to hold the connecting conductors to it. These clamping parts can also serve as strain relief for the connecting conductors and thus for the connection point between connecting conductor and heating element. For this purpose, at least one clamping part is provided with an opening as a feedthrough for the connecting conductors into the inner region of the insert.

The surface heating element preferably has at least one tab-shaped extension that holds the surface heating element to the insert in the area of the slot. This tab-shaped extension can also be used for a connection to the connecting conductors, so that the connecting conductors are routed into the inner region of the insert via the tab-shaped extension(s).

In addition, the connecting conductors on the tab-shaped extension can be covered with a potting compound.

To achieve the greatest possible heat transfer from the surface heating element to the inner surface of the outer casing, the at least one surface heating element should have a length in the circumferential direction of the outer casing such that the inner surface of the outer casing is completely covered, but no overlapping surfaces of the surface heating element arise. In this way, the entire circumference of the inner surface of the outer casing is covered by the at least one surface heating element.

The insert on which the surface heating element is held has, in a particularly preferred embodiment, a slotted tubular body which is pretensioned in a radial direction to expand its diameter. Such a slotted tubular body can also be referred to as a section of a spiral spring, on the outside of which the at least one surface heating element rests. This pretensioned section of the coil spring presses the at least one surface heating element flush against the inner surface of the outer casing. One end of the coil spring section can be held in the section of the slot on an inner part of the insert, while the other end can move freely in the circumferential direction. This means that the coil spring section, i.e. the outer surface of the insert viewed in radial direction, is clamped at only one end.

In this embodiment, in which the insert has a slotted tubular body as described above, preferably at least one longitudinal edge of the tubular body is rolled or inverted radially inwards along the slot, whereby the surface heating element can then be attached, for example, to the rolled-up longitudinal edge and unwinds around the rolled-up longitudinal edge to the outside of the tubular body. This ensures that the surface heating element is not bent in the area of its attached longitudinal edge and is therefore not damaged.

It is also to be regarded as a preferred measure to roll the two longitudinal edges of the tubular body radially inwards along the slot or to invert them. Such an arrangement can be used if a surface heating element is attached to each of these two edges which, starting from the slot, surround the insert in opposite directions.

Along the slot, the edges that define the slot, or the two rolled or inverted longitudinal edges, can be joined together such that, viewed in cross-section, a V-shaped or U-shaped groove is formed. The surface parts of the insert which form the groove can be dimensioned and tensioned such that the tubular body of the insert, through the V- or U-shaped groove, forms a tongue area which produces a radially outward pretension of the tubular body and thereby presses the surface heating element against the inner surface of the outer casing. The spring tension of the V- or U-shaped section is selected so that the opening width of the V- or U-shaped cross-section of the section increases, and the diameter of the tubular body also increases when the insert is not inserted into the outer casing.

A rail assigned to the insert can be used to attach at least one heating element to the insert or to arrange and connect several inserts one behind the other in the axial direction of the tubular housing. This rail has a profile in cross section with which a corresponding profile of the insert can be connected, preferably a profile located at one edge of the insert along the slot.

It is also provided that in an embodiment which is to be preferred in some applications, the insert, viewed in the cross-sectional direction of the outer casing, is divided into at least two, preferably at least three, partial bodies which are pressed apart from each other in the direction of the at least one surface heating element and thus in the radial direction by spring elements under pretension. For example, coil springs can be used that are inserted in corresponding blind holes in two adjacent surfaces of the partial bodies and thus push the partial bodies apart in the radial direction and thus in the direction of the surface heating element.

The preferred surface heating element is a PTC foil heating element, which can be very thin and can be easily adapted in size to the inner surface of the outer casing to be heated.

As indicated above, several inserts, each having at least one surface heating element, may be held one behind the other in the direction of the longitudinal axis at a common connecting part. For this purpose, the common connecting part can be a connecting rail which has a tongue and groove guide running in the longitudinal direction, to which the respective insert can be connected with a corresponding tongue and groove guide. The rail can then be used to connect several inserts stacked in the longitudinal direction. These stacked inserts are then preferably accommodated in a common outer casing.

For such stacking of several inserts one behind the other, intermeshing parts, such as grooves and projections, can be arranged at the respective adjacent ends to prevent twisting.

To insert an insert, to which the surface heating element is preferably already attached, into the outer casing, an assembly aid is used that has, for example, two rods that engage in the edges of the tubular body, for example in the area of the slot of the insert, in order to press the edges together and thus reduce the diameter of the tubular body; at the same time, the tubular body is pretensioned.

A heating device according to the invention as illustrated inFIG. 1and generally designated by the reference sign1is used to heat liquids in a reservoir of a vehicle, such as a tank or a container.

The heating device1shown comprises a housing2resistant to the liquid to be heated with a tubular outer casing3. This outer casing3is closed at one end by a base part4and at the other end by a cover part5and preferably has a round or oval cross-section to which a longitudinal tube axis6can be assigned.

An insert7is inserted into the outer casing3of housing2. A surface heating element8that is pressed flat against the inside of the outer casing3by the insert7is located between the outer casing3and the insert7. This surface heating element8is supplied with power via connecting conductors9that are routed out of the housing2sealed through the cover part5, said power being provided, for example, by the electrical system of a vehicle.

The at least one surface heating element8covers at least part of the circumference of the inner surface of the outer casing3when viewed in the circumferential direction of the outer casing3and is in thermal contact with the inner surface of the outer casing3. The insert7exerts a compressive force on the surface heating element8that is generated by an outer sheath or tubular body10of the illustrated embodiment.

The jacket10of the insert7has a slot11which runs in the direction of the tube axis6of the outer casing3. This jacket10is pretensioned outwards when inserted into the outer casing3. This means that the insert7, in a state in which it has not yet been inserted into the jacket10, has a diameter greater than the inner diameter or inner dimensions of the outer casing3.

In order to insert this insert7into the outer casing3, the insert7or the jacket10of insert7must therefore be pressed together in the area of slot11. The jacket or the slotted tubular body10can therefore be regarded, relative to its cross-sectional shape, as a section of a coil spring which, however, when viewed in the direction of the tube axis6of the outer jacket3, is dimensioned with a large extension or length.

The insert7of heating device1ofFIG. 1, which is shown inFIG. 2without surface heating element8and inFIGS. 3 and 4with surface heating element8, is provided in the area of slot11at each edge12with an inwardly crimped, rolled or inverted rim or longitudinal edge13. This rim, which is rolled up for example semicircular when viewed from the inside, can be used to employ two rod-shaped auxiliary tools14, as illustrated inFIG. 2, to compress the jacket10of insert7in the area of slot11with these auxiliary tools, thus reducing the outer diameter of insert7.

In the area of slot11, the surface heating element8is held preferably by a strip-shaped connecting part15attached along one edge12of insert7, as illustrated inFIGS. 1, 3 and 4.

As can be seen from the Figures, the corresponding crimped edge13of the jacket10of the insert7serves to route the surface heating element8with a defined radius around the edge12delimiting the slot11onto the outer surface of the insert7.

The surface heating element8, which is shown in more detail inFIG. 5and is preferably a PTC surface heating element, is very thin. Located on one side edge of the rectangular surface heating element8are two tab-shaped extensions, also known as connection tabs16. The two connecting leads9of the surface heating element8are attached in the area of these connection tabs16, whereby the connection points in the area of the connection tabs16are additionally covered with a potting compound17for strain relief, among other things.

The respective tab16of the surface heating element8is each connected to a clamping part18which is part of the strip-shaped connecting part15for fastening the surface heating element8to one edge12along the slot11, preferably using the strip-shaped connecting part15. Such a strip15with two clamping parts18is shown in more detail inFIG. 7A. For this purpose, the respective tab16is inserted into a corresponding opening19of the clamping part18, as illustrated inFIG. 3. In this case, the connecting conductors9are routed out of the area of the strip-shaped connecting part15via one clamping part18and through a further opening20opposite the opening19, as illustrated inFIG. 1.

The clamping part18is composed of a base part21and a cover-shaped hinged part23pivotally connected thereto via a joint22, so that the cover-shaped hinged part23can be opened via the joint22in order to connect the connecting tab16of the surface heating element8to the clamping part18and thus to the strip15, in order then to insert the tab16of the surface heating element8into the clamping part18via the opening19, for example in the form of a recess. Then the free leg of the hinged part23can be connected to the corresponding locking element25of the base part21via locking elements24.

Laterally projecting surface parts26are located in the area of the tabs16on the surface heating element8and serve for additional anchoring of the respective tab16in the respective clamping part18.

The strip-shaped connecting part15is connected to one rim via a tongue and groove guide27running in the longitudinal direction of the insert7, by pushing the connecting part15, which in the embodiment shown has the groove28, in the longitudinal direction onto the tongue29, which is then assigned to edge12or the rolled rim13. Positioning of the groove28on the one hand and the corresponding tongue29on the other hand can also be interchanged so that the strip15has the tongue29and the edge12and respectively, the groove28is associated with the rolled edge13. Preferably the part of the tongue and groove guide27associated with insert7, or respectively with the jacket10of insert7, is designed in one part with the jacket10; however, this part could also be attached to the edge12along slot11using suitable fastening means.

FIGS. 7B and 7Cshow a further embodiment of a clamping part18′ of strip15to which the surface heating element8can be attached. For this clamping part18′, the two tab-shaped connecting parts16, i.e. the connecting tabs as used in the embodiment described above, are positioned at a small distance from each other on the corresponding longitudinal edge of the surface heating element8. The clamping part18′ also has a hinged part23′ that can be pivoted and that is attached via a joint22, having a T-shaped contour when viewed from above onto strip15. While joint22is located at the end of one leg, the other two legs each cover one of the two connection tabs16.

The clamping part18′ can also be arranged, in addition to the clamping parts18that are shown and described in the previous Figures, preferably between the clamping parts18, either as an additional attachment point for the surface heating element8or to secure the connecting conductors9to the insert7. Depending on the type of clamping parts18,18′ used and where they are positioned, the clamping parts18,18′ and the corresponding tabs16and attachment points of the surface heating element8are matched to each other.

It is understandable that the connecting conductors9do not have to be routed into the interior of the insert7via the connection tabs16, as illustrated in the various embodiments, but can also be arranged elsewhere, although the embodiments shown are preferred.

FIGS. 8 and 9show another embodiment of an insert7which, compared to the embodiment of the insert7described above, has a V-shaped groove30in which the jacket10of the insert7, viewed in the circumferential direction, is extended and thus the jacket10is closed. This jacket10is also pretensioned such that its outer circumference, or diameter, is larger than the inner circumference, or diameter, of the outer casing3of the heating device1, in which it is inserted to press the surface heating element8flat against the inside of the outer casing3. The V-shaped surface portion of the jacket10viewed in cross-section supports the pretension force obtained when the jacket10is pressed together to reduce its diameter.

Cutouts32are provided in the bottom area31of the V-shaped groove30, through which the connection tabs16are routed for attaching the surface heating element8. The connecting conductors9can also be routed through these cutouts32. Further cutouts33can also be positioned in the transition area of the jacket10in the V-shaped groove section30to reduce the stiffness of the insert7and to concentrate the deformation occurring during clamping of the jacket10so that the opening angle of the V-shaped groove30is reduced in a defined manner.

FIG. 9shows the insert7ofFIG. 8with a surface heating element8arranged thereon, viewed from the axial direction of the tubular body to which a surface heating element8is attached. According to the embodiment described above, the surface heating element8unwinds over one edge12, which delimits the slot11or the V-shaped groove30, to the outside of the jacket10. The free end34of the surface heating element8can then be routed into the V-shaped groove30via the other edge12that delimits the other side of the V-shaped groove30and attached there if necessary.

The principle difference between the embodiments ofFIGS. 8 and 9and the previously described embodiments can be seen from the schematic cross-sectional illustrations ofFIGS. 10 and 11. Both inserts7are based on the fact that in the de-tensioned state they have an outer diameter that is larger than the inner diameter of the outer casing3of the housing2of the heating device1. When they are inserted into the outer casing3, they are pressed together, indicated by the arrows35, such that the outer diameter of the jacket10decreases, so that after insertion into the outer casing3and release, the pretensioned jacket10expands due to the pretension, thereby pressing the surface heating element8against the inner surface of the outer casing3. In the embodiment of the insert7, which uses the V-shaped groove30, the pretensioning force is increased by the V-shaped surface parts and by the fact that the jacket10is closed in the area of the slot11.

The pretension of the insert7or its jacket10can be set by selecting the material and dimensioning, in particular the material thickness. Preferably, a plastic material with good elastic properties and good temperature stability is used for insert7. Glass fiber filled PA66 is particularly suitable.

FIGS. 12 to 15show various further embodiments of the heating device1in cross section.

The embodiment, as illustrated inFIG. 12, has an insert7, which, viewed in cross-section, consists of two semicircular partial bodies36, the rounded surfaces of which are adapted to the curvature of the inner surface of the outer casing3, so that they press the surface heating element8flat against the inner side of the outer casing3. Between the two partial bodies36there are spring elements37, for example coil springs, which apply a radially outward force to the two partial bodies36so that the respective partial bodies36are pressed apart and exert a pressure on the surface heating element8.FIG. 12also indicates that in such an embodiment two surface heating elements8are used, which are attached in the area of the gap or slot11between the two partial bodies36, in which the spring elements37are also arranged. In addition, the connecting conductors9can be routed between the two partial bodies36in the area of slot11, although this is not shown in detail.

The embodiment of the heating device1, as illustrated inFIG. 13Ain cross-section, as well as the heating device1, as illustrated inFIG. 13B, is based on the principle previously described based onFIG. 12.

InFIG. 13A, insert7is divided into three partial bodies36, viewed in cross-section. As inFIG. 12, at least one spring element37is inserted between the respective adjacent partial bodies36in the respective slots11. These spring elements37thus push the partial bodies36apart towards the inside of the outer casing3.

In the embodiment ofFIG. 13B, insert7is divided into five partial bodies or angular segments36, viewed in cross-section, so that each partial body occupies an angular segment of about 70°, although the angular segments36can also be divided in other ways. Spring elements37are inserted between adjacent angular segments36, for example in corresponding blind holes, which exert a radial outward force on the respective partial body36, as indicated for example by arrow38.

FIG. 14shows an embodiment of the heating device1in cross-section in which, comparable to the embodiment ofFIG. 12, two partial bodies36are used. However, instead of a coil spring37, for example, which can be used in the embodiment ofFIG. 12, a foam body39is inserted as the spring element which, when the insert7is inserted into the outer casing3, is compressed and thus pushes the two partial bodies36apart in order to press the surface heating element8against the inside of the outer casing3. Such foam bodies39can also be used in the embodiments illustrated inFIGS. 13A and 13B.

The embodiment of the heating device1, as illustrated schematically in the cross-section inFIG. 15, is comparable to the one described previously based onFIGS. 1 to 9. However, in this embodiment there are two surface heating elements8which are each attached to slot11of insert7and which, starting from slot11, surround insert7in opposite directions.

In the embodiment ofFIG. 16, several inserts7are accommodated in a common outer casing3, stacked one above the other in the axial direction. If necessary, these Inserts7can be connected via a common rail15, such as the one previously described based onFIGS. 1 to 7. For this purpose, the individual inserts7can be held on the common rail15via a tongue and groove connection.

The inserts7stacked in the longitudinal direction6can have intermeshing parts at the respective adjoining ends to prevent twisting, for example projections or tabs40, which are inserted into correspondingly adapted recesses41of the subsequent insert7. These tabs40and recesses41are also indicated in the embodiments of insert7described above based onFIGS. 2 to 4 and 6.

The heating device according to the invention is characterized by its simple structure and compact design. Only a few components are required, namely the housing2with an outer casing3, base part4and cover part5, the surface heating element8and the insert7. The surface heating element8as a heater is a self-supporting component. A PTC surface heating element is self-regulating when energized and thus heats up, and the tank contents are protected from overheating. The spring element or spring elements used to press the surface heating element8against the inner surface of the outer casing3are mechanical components and practically insensitive to damage. The same applies to a foam element39, with which parts of the insert7are pressed against the surface heating element8with the foam element39making a frictional connection with the parts against which it rests by its expansion behavior.

It is also provided to use an element instead of the foam element, which expands and cures by phase transformation/crosslinking and thus creates a frictional connection between the parts of the insert7.

The heating device1is dimensioned depending on the container in which it is used to heat a liquid. A cylindrical shape of the outer housing with a preferred diameter of the outer casing3from 30 mm to 150 mm is preferred, with a particularly preferred diameter of 40 mm, which is sufficient to provide sufficient space in the interior for the insert7and the necessary spring elements, including the jacket10of the insert7. The length of the heating device1, viewed in the direction of the tube axis6of the outer casing3, is between 30 mm and 300 mm. The outer casing3should be made of a corrosion-resistant material, preferably stainless steel or plastic, with a material thickness of 0.5 mm to 3 mm, preferably in the range of 0.5 mm to 1 mm.

The outer casing3could also have a conical shape, with a correspondingly matched insert7. Such a shape is preferred when the outer casing3is produced by injection molding.

By means of the clamping device described based onFIG. 2(auxiliary tool14), it is possible to insert the insert7, which serves as a spring and pressure device, into the outer casing3without contacting the casing2and thus without any risk of damage. This also makes automated assembly possible. The rolled rims13of the jacket10of the insert7are a simple measure to engage there with the auxiliary tool14. In addition, the rolled rims13ensure that a surface heating element8attached to the interior of insert7can be routed to the outer surface of insert7without bending stress.

For rod-shaped auxiliary tools, as illustrated inFIG. 2, a thickening of the jacket10could also be provided, in the area of which one or more bores or holes are introduced in which a clamping tool, for example with two mandrels, engages.

The surface heating element8can also be glued in the area of slot11or the V-shaped groove30of insert7.

The insert7or its jacket10can be designed such that the slot11or the V-shaped groove30closes when the insert7is inserted into the outer casing3, so that the edges12of the jacket10, which delimit the slot11, abut approximately against each other or the surfaces of the V-shaped groove30lie approximately against each other.

In the case of the V-shaped groove30, the pocket resulting from the groove30is first opened so that the surface heating element8can be inserted and attached. The surface heating element8with its feed lines is threaded through two openings into the bottom of the V-shaped groove30, which can also be U-shaped in cross-section, and thus into the bottom of the pocket in which the corresponding openings are provided. The connection tabs16of the surface heating element8, and thus also the connection area, preferably protrude through the openings at the bottom of the pocket. Tilting is prevented by the surface heating element8being held in a defined position in the winding direction (radial direction) and perpendicular to the winding direction (axial direction).

For insertion of insert7with the surface heating element8attached to it, a uniaxial rolling movement is sufficient to place the surface heating element8on the outer surface of insert7, such that insert7with the surface heating element8can be inserted into the outer casing3of housing2.

When selecting the material, especially for insert7, it must be ensured that there is sufficient spring force over the entire service life of the heating device1and under the expected temperature load of up to 100° C. to press the surface heating element8against the inner surface of the outer casing3. The radial outward spring force exerted by insert7should be 1 N.

High temperature resistant polymers such as PEEK, PA46 Stanyl TW341, PVDF, PI, as well as standard polymers such as PA66 GF, PA12, PC, PET, PP are preferred as materials for insert7. Additional metal inlays can also be used as reinforcement parts to reinforce the insert7.

Spring elements can also be strips of spring steel with a width of 5 mm to 15 mm, preferably about 10 mm, and a thickness of 0.1 mm to 0.5 mm, particularly preferred 0.1 mm, which can be inserted, for example, as parts into the wall of the jacket10of insert7, PA66 GF is particularly suitable for the jacket10of insert7due to its good temperature resistance up to 250° C., if necessary, with additional steel or spring steel inlays.

If spring elements made of a foam material are used, an FKM foam (Viton®) with a temperature resistance of up to 250° C. is preferably used. It is also possible to use a silicone foam with a temperature resistance of up to 280° C.

In a further embodiment, the insert7, divided into several sections as illustrated inFIGS. 12 to 14, with the surface heating element8held therein, can first be inserted into the outer casing3and then sprayed into the spaces in which the foam element or the spring elements are located inFIGS. 12 to 14a liquid phase material which reacts chemically or under heat, expands and presses the surface heating element8against the inner surface of the outer casing3. The foam sets and hardens, thus freezing its shape on the surface heating element8while maintaining the contact pressure of the insert7. Polyurethane spray foam or UF spray foam are preferred for this purpose.

It can be seen that features that are described using only one embodiment can also be used for the other embodiments described without this being expressly mentioned.