Controls

Abstract

The invention relates to a control device (148), in particular a control device for an electric heating device (100) with a PTC element as an auxiliary heater in a motor vehicle, the control device having a control housing (146) in which a printed circuit board (122, 300) equipped with at least one power switch (308) is arranged, the printed circuit board being placed on a cooling surface (510) in a heat-conducting manner under the action of a prestressing force via an elastic prestressing element. The invention aims to provide a control device which allows good heat transfer between the power switch and the cooling surface and requires only a few components and can therefore be manufactured more easily and at a lower cost, and for this purpose it is proposed that the prestressing element is formed by an elongated piece of a soft elastic plastic component (550) extruded with at least one through hole.

Description

Technical Field

[0001] The invention relates to a control device, in particular for an electric heating device with a PTC element as an auxiliary heater in a motor vehicle. Background Art

[0002] In the prior art, control devices are fully described, for example, in EP 1 872 986 A1 or EP 2 337 425 A1, in particular for control devices of electric heating devices with ceramic PTC elements for heating motor vehicles. The control device in such an electric heating device usually has a control housing, which surrounds the control component and is provided with a plug connector for connecting control signals and / or currents to be controlled. The above examples and the electric heating device of EP 3 334 242 A1 implement such a concept in which the control device is integrally arranged with the power supply part. The control device has at least one power switch, which emits power loss during operation. This is usually provided to the medium to be heated. Therefore, the power switch is not only provided with a cooling element, which dissipates the power loss and thus offsets the overheating of the power switch. On the contrary, the cooling element is thermally connected to the fluid to be heated. For this purpose, the cooling element can be arranged in a heating chamber, which is separated from the receiving chamber of the control housing by a partition wall, and the part of the cooling element adjacent to the power switch is accommodated in the heating chamber. Typically, a partition wall is provided between the heating chamber and the receiving chamber of the control housing, which delimits both the heating chamber and the receiving chamber of the control housing. The control housing may also accommodate a contact area of ​​a PTC heating assembly, which typically extends into the heating chamber and includes at least one PTC element. Therefore, in the prior art, the interior of the control housing is also referred to as a connection chamber, because in the connection chamber, the contact area is electrically connected.

[0003] The above-mentioned features are also applicable to realizing the control device according to the present invention in an electric heating device having a ceramic PTC element as an auxiliary heater.

[0004] Control units in automotive engineering are subject to the conditions prevailing there. The control components inside the control units are subject to considerable vibrations. It goes without saying that the control housing must be as tight as possible so that neither dust nor moisture can penetrate it. However, the installed components must not only be vibration-resistant. The aim is to achieve a design that provides the required functionality with as few components as possible. The components should be easy to manufacture, scalable and insensitive to handling during production. Despite the above conditions, the components must remain functional over the entire service life of the motor vehicle.

[0005] The invention relates in particular to the problem of placing a power switch on a cooling element in a heat-conducting manner under the effect of a pretensioning force. To this end, there is already no shortage of proposals in the prior art.

[0006] For example, EP 1 395 098 A1 discloses a control device for an electric heating device with a PTC element, wherein a cooling element directly bears against a power switch mounted on a printed circuit board in a heat-conducting manner and protrudes from the printed circuit board on the opposite side of the power switch. The cooling element and the power switch are surrounded by a C-shaped spring claw, which holds the two components together under the action of a pre-tensioning force.

[0007] In the construction principle known from US Pat. No. 5,812,375, the power switch is placed with an electrically insulating film, which is inserted between the power switch and the heat sink, which engages in a receiving opening of a printed circuit board, and the power switch is electrically connected to the strip conductors of the printed circuit board. On the side opposite the heat sink, an elastomer component with a U-shaped cross section rests on the power switch and is supported on the housing cover of the control housing. For this purpose, the housing cover has a projection surrounded by a pretensioning device, which is U-shaped in cross section.

[0008] DE 100 34 572 A1 discloses a control device for an auxiliary heater of a motor vehicle, in which an at least partially elastic pressure projection protrudes from a housing cover and is arranged opposite a cooling shroud which is coupled to a heating chamber in a heat-conducting manner. A power switch is arranged between the pressure projection and the cooling shroud, against which the power switch rests with the interposition of a possibly elastic, heat-conducting but electrically insulating membrane.

[0009] In order to support the printed circuit board in a vibration-free manner on the housing base of the control housing, DE 196 00 619 A1 proposes a pretensioning device in the form of an elastomer strip acting on the power switch, which presses the intermediate layer of the power switch and the printed circuit board against the outer edge of the control housing.

[0010] The solutions known from the prior art still have disadvantages. The solution previously known from DE 196 00 619 A1 is not always suitable in practice because it requires a raised edge region against which the printed circuit board rests. In electric heating devices having a structural unit comprising a control component and a power supply component, the edge region of the control device is not always located below the edge region of the control housing.

[0011] Furthermore, a certain height must sometimes be bridged between the power switch and the housing cover, so that the elastomer strip known from DE 196 00 619 A1 is not suitable for placing the power switch on the cooling element under prestressing.

[0012] In view of this, EP 2 466 989 A1 from the present applicant proposes a support structure which is arranged between the housing cover and the printed circuit board and supports an elastic clamping device made of compressed plastic, which protrudes through the printed circuit board and rests on the power switch so that the power switch is placed on the cooling surface of the heat sink which is thermally connected to the heating chamber under the action of the pre-tensioning force. Summary of the invention

[0013] The present invention aims to provide a control device which allows a good heat transfer between the power switch and the cooling surface and which uses fewer components than the solution previously known from EP 2 466 989 A1 and can therefore be manufactured more easily and at a lower cost.

[0014] In order to solve the above problems, the present invention provides a control device.

[0015] In this solution, the pretensioning element consists of an elongated piece of a soft elastic plastic component extruded with at least one through-hole.

[0016] The plastic part is extruded by the tester. This allows the pretensioning element to be produced at low cost. The plastic material used to make the pretensioning element can be silicone or another plastic material, in particular a plastic material that is heat-resistant and can be significantly compressed or deformed. With regard to heat resistance, preferred plastics are thermosetting plastics or elastomers.

[0017] The pretensioning element has at least one through hole. Due to manufacturing tolerances, the through hole extends in the extrusion direction and therefore in the longitudinal direction of the plastic component. At least one through hole increases the ability of the pretensioning element to permanently store elastic pretensioning forces by changing the shape of the plastic component. Therefore, the application of the power switch against the cooling surface under the action of the pretensioning force is not only due to the pretensioning force generated by the compressibility of the plastic component. Instead, the desired pretensioning force is set by the specific shaping of the plastic pretensioning element in the form of the molded part. The pretensioning element can have a plurality of through holes that are adjacent to each other and / or arranged one above the other in a direction substantially transverse to the transmission direction of the pretensioning force. The through hole can have any desired cross-sectional shape. The cross section of the through hole can be rectangular, circular, elliptical, polygonal or irregular.

[0018] Preferably, the pretensioning element is placed on the inside on a cover of the control housing, wherein the cover has a projection which positively holds the pretensioning element. In this way, despite having a relatively unspecific construction, the pretensioning element is positively held and positioned at least along its length by the cover above the printed circuit board inside the control housing.

[0019] The pretensioning element can also form a form-fitting surface which compulsorily surrounds the power switch and / or the printed circuit board, in particular the matching surface of the printed circuit board. In a first alternative, the soft elastic plastic part forms a form-fitting surface formed by extrusion, which interacts with the contour of the power switch so as to position and fix the power switch in the transmission direction of the pretensioning force below the pretensioning element. In a second alternative, it is assumed that the power switch is preferably located on the side of the printed circuit board facing the actual heating chamber of the electric heating device, while the pretensioning element is supported on the cover of the control housing and is therefore arranged on the side of the printed circuit board opposite to the heating chamber. Therefore, the pretensioning force is not directly transmitted to the power switch. Instead, the pretensioning force is transmitted to the printed circuit board and from the printed circuit board to the power switch, so that the power switch is placed in a thermally conductive manner on a cooling surface under the action of the pretensioning force, which is associated with a heat sink connected to the heating chamber in a thermally conductive manner. A further improvement reduces the mechanical load on the power switch so that the pretensioning force does not cause any relative movement between the terminals of the power switch and the printed circuit board. Instead, the printed circuit board together with the power switch is held in the direction of the cooling surface under the effect of the pre-tensioning force.

[0020] The power switch according to the invention can be formed, for example, by a MOSFET or an IGBT. The application of the cooling surface can be carried out by inserting an electrically insulating film, for example a polyimide film, so as to electrically separate the cooling surface from the power switch but still allow good heat conduction from the power switch to the cooling surface.

[0021] The prestressing element, which is designed as a molded plastic component, can press a plurality of power switches arranged adjacent to one another in a row on a printed circuit board against one or more cooling surfaces under the effect of a prestressing force. Such a uniform molded component neatly bridges the gaps between adjacent power switches on the printed circuit board without causing a prestressing effect there. Preferably, such an elongated piece of the plastic component protrudes beyond the power switches on their respective outer sides, so that the power switches are forcibly held and restrained in the length direction of the elongated piece by the deformation associated with the prestressing.

[0022] In an alternative configuration, the pretensioning element has a plurality of pretensioning bodies, each of which is associated with a power switch. Each respective pretensioning body has at least one, preferably more, of the above-mentioned through holes, which are aligned in the arrangement already discussed above and with respect to the transmission direction of the pretensioning force. The pretensioning bodies are formed integrally into a single pretensioning element. To this end, adjacent pretensioning bodies are connected to each other by connecting webs extending transversely to the respective through holes. The connecting webs can be deformed to adjust the lateral distance between the pretensioning bodies. After mounting on the printed circuit board, this deformation compensates for any positional deviations of the power switch. In view of the good adaptability of the lateral distance between the individual pretensioning bodies, the connecting webs are preferably in the form of an integral hinge.

[0023] The solution according to the invention offers the advantage that the pretensioning element can be manufactured as an extruded plastic part with specific dimensions. The number of through holes, their alignment and arrangement relative to one another sometimes allow a rather high degree of deformation or compression, so that the molded part formed from plastic can be used in various control devices. Thus, the pretensioning element can be used in a manufacturing process as a continuous product and can be provided as a suitable elongated piece as a pretensioning element in a control device.

[0024] The solution according to the invention can thus be realized at low cost. A continuously supplied material can be used on an elongated piece to form the prestressing element of different control devices, which sometimes have different dimensions with regard to the distance between the power switch and the control housing cover and / or with regard to the shape and number of the power switches on which the prestressing element is supported.

[0025] In particular, the individual pretensioning bodies can be designed to positively surround a standard power switch, wherein the connecting webs allow this design to be used even in the case of differently designed control devices, provided that the power switches are preferably arranged adjacent to one another in a row or column.

[0026] According to its parallel aspect, the present invention proposes an electric heating device. The electric heating device has a connection chamber and a heating chamber in a manner known from EP 2 466 989A1, wherein the connection chamber is surrounded by a control housing, and the heating chamber is surrounded by a heater housing. A partition wall is provided between the connection chamber and the heating chamber. The partition wall usually forms a closure of the heating chamber and a closure of the control housing. In view of this, the partition wall will also be referred to as the base of the control housing hereinafter. At least one PTC heating assembly protrudes into the heater housing from the partition wall as a heating fin. The PTC heating assembly can be accommodated in the partition wall or positioned and fixed relative to the partition wall by plug-in contact. The PTC heating assembly has at least one PTC element and a strip conductor electrically connected to the at least one PTC element for energizing the at least one PTC element with different polarities. The strip conductor is electrically connected in the control housing. For this reason, the strip conductor extends into the connection chamber and can be plug-in contacted with a printed circuit board that also supports a power switch or another printed circuit board provided for grouping a heating circuit including several PTC heating assemblies. The heat sink is exposed in the heating chamber, and the heating chamber is connected to a cooling surface arranged in the connection chamber in a heat-conducting manner. The power switch abuts against the cooling surface, so that the power consumed by the power switch can also be used to heat the fluid to be heated in the heating device. The fluid can be a liquid fluid or a gaseous fluid, in particular air.

[0027] The prestressing is achieved by means of a prestressing element, which has already been discussed above, and which consists of an elongated piece of a plastic component having at least one through hole extending in the extrusion direction of the extruded elongated piece. The prestressing element is usually supported on a housing cover on the inner surface of the control housing surrounding the connection chamber, i.e. on the side opposite the partition wall. The housing cover, which is usually arranged there, can have the above-mentioned protrusions for forcibly holding and fixing the prestressing element. The deformation of the sheet material, which usually forms the housing cover, also serves to reinforce the housing cover. Thus, the cooling element, which is usually arranged in the extension of this cooling surface in the transmission direction of the prestressing force, as well as the heat sink can be arranged at any desired position in the heating chamber. By deforming the cover of the control housing, its rigidity can be adjusted even when a relatively thin sheet material is selected, so that the prestressing element can be placed at any desired position in the control housing. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Further details and advantages of the present invention will be apparent from the following description in conjunction with the accompanying drawings, in which:

[0029] Figure 1 An exploded perspective view of an embodiment of an electric heating device is shown.

[0030] Figure 2 The top view of the upper housing part with the printed circuit board is shown.

[0031] Figure 3 Shows Figure 2 A cross-sectional view along line III-III is shown.

[0032] Figure 4 A top perspective view of a printed circuit board is shown.

[0033] Figure 5 Shown according to Figure 2 A view of an alternative configuration for a pretensioning element. DETAILED DESCRIPTION

[0034] Figure 1 An exemplary embodiment of an electric heating device 100 is shown having a multi-part housing which comprises a lower housing part 102 formed from plastic and an upper housing part 104 formed integrally from metal by die casting.

[0035] The lower housing member 102 is channel-shaped and surrounds a heating chamber 106 to which an inlet nozzle and an outlet nozzle 110 protruding from a base 108 are provided. These inlet ports and outlet ports 110 are integrally formed with the lower housing member 102 by injection molding.

[0036] The inlet and outlet ports 110 protrude above the base 108 , extending at right angles from a planar surface formed by the base 108 .

[0037] A plurality of PTC heating assemblies 112 are shown in the figure between the upper housing part 104 and the lower housing part 102, with PTC elements arranged in the PTC heating assemblies 112, which are electrically contacted via strip conductors. The strip conductors are electrically connected via contact lugs 114. The PTC heating assemblies 112 are held in plug-in contact in a receiving portion 116, which is provided for this purpose in a partition wall 117 of the upper housing part 104. The details of this configuration are described in EP 3 334 242 A1, which again refers to the applicant.

[0038] Further elements of the heating device 100 are shown between the lower housing part 102 and the upper part 104. Reference numeral 118 denotes a high-voltage plug-in element which is screwed to the lower housing part 104 and has contact elements which protrude into a connection chamber 120 of the upper housing part 104. These contact elements are electrically connected to a printed circuit board, which is referenced by reference numeral 122 and which can be accommodated in the groove-shaped upper housing part 104. Reference numeral 124 denotes a seal which seals the lower housing part 102 relative to the upper housing part 104 and thus the heating chamber 106.

[0039] The holding element 126 provided with the elastic protrusion has a heating component receiving portion 128 that individually accommodates each of the individual PTC heating components 112, and the heating component receiving portion 128 is engaged with the outer peripheral surface of each of the individual PTC heating components 112. In the assembled state, the holding element 126 is also engaged with the lower housing part 104 forcibly and / or frictionally.

[0040] The contact device 130 is arranged above the upper housing part 104 and below the printed circuit board 122, which electrically connects all the contact lugs 114 and groups the individual PTC heating components 112 into heating circuits. An electrical connection is made between the contact device 130 and the circuit board 122 via the contact lugs 132 protruding from the contact device 130. The control signal plug element connected to the printed circuit board 122 and protruding from the printed circuit board 122 is shown with reference numeral 134. The control signal plug element 134 is screwed onto the printed circuit board 122.

[0041] Shown above the printed circuit board 122 are a further circumferential seal 136 and a control housing cover 138 , by means of which the connection chamber 120 of the upper housing part 104 is covered and sealed.

[0042] After assembly, the connecting rod 140 engages at the rear with a locking projection 142 provided on the lower housing part 102 and the upper housing part 104 in order to positively and captively connect the two parts 102, 104 to one another. Details of this are described in EP 2796 804 A1.

[0043] The control housing cover 138 forms a control housing 146 together with the upper housing part 104 and the seal 136. In this case, the control housing cover 138 and the upper housing part 104, due to their metallic material, form a shield around a control device 148 accommodated in the control housing 146, which is primarily formed by a printed circuit board 122. A terminal 150 protrudes from the control housing 146 in the direction of the plug-in elements 118, 134. The terminal 150 serves to connect the metal control housing 146 to the grounded phase and is screwed onto the control housing 146.

[0044] exist Figure 1 In FIG. 1 , reference numeral 152 denotes a projection of the control housing cover 138 .

[0045] Figure 3 A printed circuit board 300 is shown, which is generally designated by reference numeral 300 and is equipped on one side with components generally designated by reference numeral 306 and also includes a power switch 308. Figure 2 As shown on the left, according to Figure 1 The power current contact elements 442 of the high-voltage plug element 118 are directly contacted in the printed circuit board 300, for which purpose the printed circuit board 300 has a contact lug receiving portion 304. An insulating web characterized by reference numeral 446 is accommodated in a T-shaped receiving portion of the printed circuit board 300 in order to increase the clearance and creepage distance between the individual power current contact elements 442.

[0046] When the printed circuit board 300 is inserted, the power switch 308 lies flat against a cooling surface 510 formed by the upper housing part 104, in particular by the partition wall 117. The printed circuit board 300 is modified in the region of the power switch 308 to be particularly thermally conductive. Figure 3 It has been shown that a cooling shield 512 which is associated with the respective cooling surface 510 and forms a heat sink is provided in each case to the Figure 3 The cooling shroud 512 is also slightly offset inwardly and toward the heating chamber 106. The cooling shroud 512 is formed as an elongated rib and is exposed in the heating chamber 106.

[0047] Figure 4 A first embodiment of a plastic component is shown, which is characterized by reference numeral 550 and forms a prestressing element in the sense of the invention. The plastic component 550 is spaced apart from the semi-finished product and cut to length. The plastic component 550 protrudes above three power switches 308 arranged on the printed circuit board 300. The plastic component 550 is manufactured by extrusion. The plastic component 550 is penetrated by a plurality of through holes 552 extending longitudinally through the plastic component 550, so that a continuous channel is formed in the extrusion direction and thus in the plastic component 550. In an embodiment, four through holes 552 are arranged in a lower row and four through holes 552 are arranged in a row above the lower row one above the other. Thus, two through holes 552 are arranged one above the other in the transmission direction of the prestressing force that strikes the printed circuit board 300 at right angles.

[0048] like Figure 4 As shown, the lower side of the plastic component 550 facing the power switch 308 is outwardly inclined and provided with an inward protrusion, so that the plastic component 550 abuts against the inclined surface of the power switch 308 and forcibly surrounds the power switch 308 on its inner surface facing the center of the printed circuit board 300. Therefore, the plastic component 550 is fixed relative to the corresponding power switch 308 transversely to its longitudinal extension.

[0049] exist Figure 4In the embodiment, the plastic component 550 ends in the longitudinal direction, wherein the first power switch 30 or the last power switch 308 of the power switches 308 is arranged in series on the printed circuit board 300. When the control housing is closed, the plastic component 550 is forcibly held in the protrusion 152 of the control housing cover 138 in the circumferential direction.

[0050] exist Figure 5 In the embodiment shown, the extrusion direction of the plastic component 550 extends transversely to the longitudinal extension of the printed circuit board 300. Here, the through-hole 552 also extends in the extrusion direction. The plastic component has three pretensioning bodies 556 connected to one another via connecting webs 554. The connecting webs 554 extend in a plane parallel to the circuit board 300. This plane is projected in the direction of the printed circuit board by limiting webs 558 provided in pairs for each pretensioning body 556, wherein the limiting webs 558 provided in pairs each accommodate the upper region of the power switch 308 between them and forcibly surround the upper region of the power switch 308. Obviously, the connecting webs 554 are connected to one another in the center by an integral hinge 560.

[0051] exist Figure 5 In the illustrated configuration, the lateral distance between adjacent power switches 308 is selected such that the pretensioning bodies 556 are each arranged above the power switches 308 in the direction of transmission of the pretensioning force, wherein the limiting webs 558 extend substantially along a straight line between the pretensioning bodies 556. If the power switches 308 are arranged closer together, the result is a bending of the connecting webs 454, wherein the webs can bend at the height of the integral hinge 560. Thus, the lateral distance can be reduced by the plastic component 550 without significant resistance. If the lateral distance of the power switches 308 is increased, the uniform plastic component 550 can be stretched in the region of the integral hinge 560 or, if necessary, also plastically stretched. Alternatively, the individual pretensioning bodies can be separated from one another in the center, so that the plastic component 550, which is initially manufactured uniformly by extrusion, is separated into individual pretensioning bodies 556.

[0052] Reference numerals list

[0053] 100 Heating device

[0054] 102 heater housing

[0055] 104 upper housing parts

[0056] 106 Heating Chamber

[0057] 108 base

[0058] 110 inlet and outlet ports

[0059] 112 PTC heating element

[0060] 114 contact lug

[0061] 116 Receiving Department

[0062] 117 partition wall

[0063] 118 High voltage plug-in components

[0064] 120 Connection Room

[0065] 122, 300 printed circuit board

[0066] 124, 136 seals

[0067] 126 Holding element

[0068] 128 Heating component receiving part

[0069] 130 contact device

[0070] 132 contact lug

[0071] 134 Control signal plug-in components

[0072] 138 Control housing cover

[0073] 140 connecting rod

[0074] 142 locking protrusion

[0075] 146 control housing

[0076] 148 Control Device

[0077] 150 Binding Post

[0078] 152 bulge

[0079] 304 Contact lug receiving portion

[0080] 306 parts

[0081] 308 power switch

[0082] 400 Temperature Sensor

[0083] 440 power plug

[0084] 442 Power current contact element

[0085] 446 Insulation Web

[0086] 454 connection web

[0087] 480 control power plug

[0088] 500 Pre-tensioning element

[0089] 510 cooling surface

[0090] 512 Cooling shroud / radiator

[0091] 516 Inner surface of cooling shroud

[0092] 550 plastic parts

[0093] 552 through hole

[0094] 554 Connecting web

[0095] 556 pre-tensioner

[0096] 560 integrated hinge

Claims

1. A control device, comprising a control housing, in which a printed circuit board equipped with at least one power switch is arranged, wherein the at least one power switch is placed on a cooling surface in a heat-conducting manner under the action of a prestressing force via an elastic prestressing element, characterized in that The pretensioning element is an elongated piece of a soft elastic plastic component extruded with at least one through hole, the soft elastic plastic component is longitudinally extended through the at least one through hole of the soft elastic plastic component, and the at least one through hole provides the pretensioning element with the ability to permanently store elastic pretensioning force by changing the shape of the soft elastic plastic component.

2. The control device according to claim 1, characterized in that: The pretensioning element bears against a control housing cover of the control housing on the inside, and the control housing cover has a projection which positively holds the pretensioning element.

3. The control device according to claim 2, characterized in that: The control housing cover is formed from a metal sheet, and the projection has a reinforcing effect on the metal sheet.

4. The control device according to claim 1, characterized in that: A plurality of through holes are arranged adjacent to each other in a direction substantially transverse to a transmission direction of the pretensioning force.

5. The control device according to claim 1, characterized in that: A plurality of through holes are arranged one above another along the transmission direction of the pre-tensioning force.

6. The control device according to claim 1, characterized in that: The pretensioning element forms a form-fitting surface which positively surrounds the power switch and / or a mating surface associated with the printed circuit board.

7. The control device according to claim 1, characterized in that: The pretensioning element is arranged between a plurality of power switches and a control housing cover, and the plurality of power switches are held between the control housing cover and an associated cooling surface under the effect of a pretensioning force.

8. The control device according to claim 1, characterized in that: The pretensioning element has a plurality of pretensioning bodies, each of which is associated with one of a plurality of power switches and which are connected to one another via a connecting web extending transversely to the at least one through hole.

9. An electric heating device, comprising a control housing surrounding a connecting chamber and a heater housing surrounding a heating chamber, the connecting chamber and the heating chamber being separated from each other by a partition wall, at least one PTC heating component protruding from the partition wall into the heater housing as a heating fin, wherein: The PTC heating assembly has a contact lug and at least one PTC element, wherein the contact lug is conductively connected to the at least one PTC element and is electrically connected in a control housing for energizing the PTC element with different polarities, wherein a heat sink is exposed in the heating chamber, and the heat sink is connected to a cooling surface arranged in a connecting chamber in a heat-conducting manner, wherein a printed circuit board equipped with at least one power switch is arranged in the connecting chamber, and the at least one power switch is placed on the cooling surface in a heat-conducting manner under the action of a pre-tensioning force via an elastic pre-tensioning element, characterized in that the pre-tensioning element is an elongated piece of a soft elastic plastic component extruded with at least one through-hole, the soft elastic plastic component is longitudinally extended through the at least one through-hole of the soft elastic plastic component, and the at least one through-hole provides the pre-tensioning element with the ability to permanently store elastic pre-tensioning force by changing the shape of the soft elastic plastic component.

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