DE102022201948B4 - System for monitoring and increasing the safety of a battery system, in particular a battery system of a motor vehicle that serves as a drive energy storage device - Google Patents

Abstract

System for monitoring and increasing the safety of a battery system (20) which has a plurality of battery cells (10), each battery cell (10) having a cell housing (26) and each cell housing (26) having a pole-free housing side on which no cell pole is arranged, a venting device (11) being provided on a pole-free housing side, which extends at least over part of the pole-free housing side, at least one cell housing (26) being assigned a detection element (14) which is functionally connected to a signal processing device (22) and/or a battery management system (23), the detection element (14) being arranged outside the cell housing (26) in its local vicinity in such a way that fluid escaping through the venting device (11) can be detected in the region of the outlet with the aid of the detection element (14), the detection element (14) being part of a flat carrier unit (13) which is attached to the outside of the Cell housing (26) is arranged adjacent and/or wherein the cell housing (26) is at least partially arranged on a support structure (12) and the carrier unit (13) is arranged between the venting device (11) and the support structure (12), characterized in that the detection element (14) is arranged directly below the venting device (11) and the carrier unit (13) is designed as a single- or multi-layer mat (28), wherein one or more detection circuits with one or more detection elements (14) are integrated into the carrier unit (13).

Description

The invention relates to a system for monitoring and increasing the safety of a battery system, in particular a battery system of a motor vehicle that serves as a drive energy storage device. In this respect, reference is also made to motor vehicles with such battery systems.

Drive energy storage devices are understood to mean, in particular, energy storage devices that supply drive energy for the direct drive of a motor vehicle. In this context, reference is made in particular to battery systems with lithium-ion battery cells and/or with battery cells that are connected together to form a total voltage of at least 48 V, preferably at least 100 V or more preferably at least 200 V. In particular, the invention relates to battery systems with battery cells that are connected together to form a total voltage between 48 V and 1,200 V, in particular 100 V to 800 V or 200 V to 800 V. The invention relates in particular to battery cells with a prismatic housing.

A major challenge in connection with such battery cells and battery modules and battery systems containing such battery cells is to ensure a high level of functional reliability. In particular, overheating of individual battery cells, which is also referred to as "thermal runaway" or "thermal propagation", must be avoided. In order to detect the onset of such overheating at an early stage, there are already various proposals that aim in particular at monitoring the pressure and/or temperature of individual battery cells.

Out of US 2006 / 0 093 896 A1 A battery cell with a cell housing is known, on the outside of which a strain gauge known as a "safety device" is to be arranged. The strain gauge is to be used to monitor the swelling state of the battery cell and to determine the pressure inside the cell housing depending on a change in the length of the strain gauge. It is recommended that the strain gauge be arranged on one of the large surfaces of the cell housing, while a vent opening in the cell housing is arranged on a small surface opposite the cell poles.

Out of JP 5 341 156 B2 A cell housing with several battery cells is known, each of which has a vent opening on its underside. Below the battery cells there is a pressure chamber in which a pressure sensor is arranged as a detection element. The pressure sensor is intended to monitor the pressure chamber in order to activate a fire extinguishing device if an increase in pressure is detected.

Out of EN 10 2010 038 860 A1 A warning system for monitoring critical conditions in battery systems is known, in particular in lithium-ion battery systems. According to this warning system, one or more sensors of the same type or sensors of different types should interact with a control unit and with means for issuing warning signals. A specific structure of a battery system with individual battery cells and a specific arrangement of corresponding sensors is not disclosed. It is merely pointed out that temperature sensors, pressure sensors, gas sensors, voltage sensors and motion sensors are suitable sensor types.

Out of EN 10 2017 214 289 A1 A battery module and a vehicle with a battery module are known, the battery module having two battery cells, each with a safety valve for venting the battery cell. The safety valve of the battery cell is arranged on one side of the battery cell facing a cavity, each battery cell having a separate cavity on the safety valve of the battery cell, the cavity being delimited by the battery cell, a sealing element and a membrane, and a part of the membrane being designed to be opened by excess pressure in the cavity. With this battery module, only problems that have already led to an increase in pressure in the battery cell can be detected.

Independent of the overheating problem described above, there are other problems that are not detected with the battery systems known from the state of the art.

The invention is based on the object of providing a system for monitoring and increasing the safety of a battery system, with which potential dangerous conditions of a battery cell can be detected that are independent of the pressure of the battery cell, in particular dangerous conditions caused by the leakage of electrolyte and/or other fluids from a battery cell. Such dangerous conditions can occur, for example, due to a leak, in particular if such a leak occurs due to manufacturing (material and/or production defects), wear (aging), load (mechanical stress on the cell housing) or age (material fatigue).

The object is achieved according to the invention with the features of claim 1. Further practical embodiments and advantages of the Invention are described in conjunction with the dependent claims.

A system according to the invention for monitoring and increasing the safety of a battery system has several battery cells, with a cell housing being provided for each battery cell, i.e. each battery cell has a separate cell housing. Each cell housing has at least one pole-free housing side on which no cell pole is arranged. On such a pole-free housing side, a venting device is provided in the system according to the invention, which extends at least over part of the pole-free housing side, with at least one cell housing being assigned a detection element which is functionally connected to a signal processing device and/or a battery management system. The detection element is arranged outside the cell housing in its local vicinity in such a way that fluid escaping through the venting device can be detected in the area of the outlet with the aid of the detection element. The core idea of the invention is therefore to be able to detect potential dangerous states of a battery cell that are independent of the pressure of the respective battery cell or battery cells by providing and arranging one or more detection elements. For example, a leak in a battery cell can be detected even if this is not initially associated with an increase in pressure and/or temperature within the battery cell.

It is preferred if a detection element is assigned to a plurality of cell housings, for example every fourth cell housing, every third cell housing, every second cell housing or even every cell housing. In particular, if a detection element is assigned to each cell housing, in the event of a detection with the aid of the detection element, with a suitably designed evaluation architecture, namely an individual assignment of each detection element to a corresponding signal processing device and/or a battery management system, it can be determined exactly at which battery cell the respective detection took place.

An electrically conductive element can be provided as a simple detection element, in particular in the form of a wire, e.g. metal wire, a conductive strip or another electrically conductive structure, which can also be a combination of wire and strip. During a "thermal runaway", hot gases escape through the venting device, which then come into contact with the detection element and increase its temperature. This initially leads to a change in resistance and can also lead to melting through later on. If melting through occurs, the electrical connection is interrupted and the battery management system, the signal processing device or an evaluation unit can detect the "thermal runaway". If the detection element and the battery management system, the signal processing device or an evaluation unit are suitably designed, electrical resistance changes can also be detected and a reliably heralding "thermal runaway" can be detected.

Alternatively or in addition, a detection element can also have a separate indicator element, for example an indicator element which, regardless of the temperature, also reacts to contact with liquid and/or to contact with a gas flow and an associated flow force of a gas with a change in resistance or an interruption of the electrical connection.

In particular, when a large number of detection elements are arranged in a battery system with a large number of cell housings, it is preferred in terms of manufacturing and assembly technology if the detection element is part of a flat carrier unit which is arranged on the outside adjacent to the cell housing. Such a carrier unit is understood to be any structure that is larger than the detection element and serves to arrange one or more detection elements in a specific relative position to the carrier unit and to fix them thereon. In particular, several detection elements can be pre-assembled on a corresponding carrier unit in a desired relative arrangement to one another and to the carrier unit. To assemble the detection elements of a battery system, it is then only necessary during final assembly in the production process to bring one or more carrier units with the detection elements pre-assembled thereon into a desired relative position adjacent to the outside of the cell housing. The size of a carrier unit is preferably adapted to the size of a battery module, in particular by having the same width and/or the same length. The height of a carrier unit is preferably significantly less than the larger of the two dimensions length and width, in particular a maximum of 10 percent, preferably a maximum of 5 percent and more preferably a maximum of 1 percent.

By arranged adjacently is meant in particular that there is as direct a path as possible from the venting device to the detection element. This is particularly the case if the carrier unit is arranged directly on the outside adjacent to the cell housing. Alternatively, the carrier unit can also be arranged indirectly adjacent, in that one or more intermediate elements are arranged between the cell housing and the carrier unit. In this case, however, it is preferred if the one intermediate element or the several intermediate elements each have at least one through-opening, via which a direct, i.e. resistance-free path leads from the venting device of the cell housing to the detection element. Such a path is to be understood in particular as a fluid path, so that fluid, for example electrolyte, escaping from the venting device of a battery cell or from an area immediately around the venting device drips or flows onto the detection element due to gravity, without first having to pass through an intermediate element.

A system according to the invention is kept simple in terms of manufacturing technology and construction if the cell housings are at least partially arranged on a support structure and the support unit is arranged between the ventilation device and the support structure. This applies in particular if the support unit and the support structure are both designed as flat structures, so that a layered structure results. This can be assembled particularly well if at least one dimension, length or width, of the support unit and support structure has the same size. In particular, the length and width of the support unit and support structure are the same size, so that they can be arranged directly flush on top of one another in order to achieve the desired relative position between the support unit and support structure. For the same reason, at least one dimension (length or width) of the cell housings or a plurality of interconnected cell housings, e.g. a module made up of a plurality of cell housings, is also preferably the same size as the corresponding dimension of the support unit and/or the support structure.

The system according to the invention has a very low component weight and only requires a small amount of installation space because the support unit is designed as a single- or multi-layer mat. If the mat is a flexible, elastically bendable and/or elastically deformable element in the direction of thickness, this has the further advantage that assembly and manufacturing tolerances between the support structure and the respective cell housings can be compensated.

In the system according to the invention, one or more detection circuits with one or more detection elements are integrated into the carrier unit. In this way, several detection elements can be functionally connected to one another, for example in order to make a sensible design for the respective application with regard to the complexity of the resolution (should each position of a detection element be individually detectable or is it sufficient if a problem in a battery cell can be assigned to a specific battery module), the weight and the cost of the system.

In terms of material technology, it is preferred for a system according to the invention if the mat is made from a compounded material with one or more polymer components and one or more filler materials. Materials that have high thermal conductivity and are electrically insulating are particularly preferred. In this context, reference is made to thermoplastic materials, elastomers and thermosetting materials. Examples of filler materials include aluminum powder, Al ₂ O ₂ powder and graphite powder, in particular nano-graphite powder.

In a further practical embodiment of a system according to the invention, the support structure has at least one cavity for receiving and/or discharging fluids that have escaped from the battery cells. The fluids can be both gaseous and liquid fluids. For example, a channel can be provided through which gases can spread unhindered to a gas sensor. In this way, a gas leakage due to a malfunction or leak can be detected regardless of the location of the leakage and regardless of the detection element in the area of the venting device.

If, in a system according to the invention which has a support structure, a bursting section is formed on the support structure in the region of at least one detection element, the safety can be further increased by the bursting section. In particular, a bursting element can be formed on the support structure as a bursting section by providing a reduced material thickness in a discrete region of the support structure. In this case, a problem which can be detected by means of the detection element (for example an electrolyte leak which did not arise due to increased internal pressure in a battery cell) but does not immediately lead to the destruction of the bursting section can be detected and remedied before subsequent damage occurs, for example due to electrolyte spreading in a battery system. It is then possible to repair the damage detected by the detection element, in particular before the bursting section fails.

A further manufacturing advantage of a system according to the invention can arise if the at least one detection element is enclosed by at least two layers of the carrier unit and/or a recess is formed in the carrier unit in the region of the at least one detection element. In this case, the two or more layers can be pressed together or otherwise connected to one another, with detection elements being arranged as freely accessible elements in the respective recess. In this context, particular reference is made to detection elements that are arranged in corresponding recesses hanging from a wire, a line or another connecting element, in which the wire, the line or the other connecting element is stretched through the recess. The wire, the line or the other connecting element is preferably fixed by the interconnected layers of the carrier unit.

A mat designed as a carrier unit of a system according to the invention is preferably produced by casting, extrusion or lamination. Not only is production simple and cost-effective, but carrier units with a particularly low thickness and correspondingly low component weight can also be produced.

• 1 eine erste Ausführungsform eines erfindungsgemäßen Systems in einer schematischen Seitenansicht,
• 2a eine weitere Ausführungsform mit einem an der Tragstruktur im Bereich des mindestens einen Detektionselements ausgebildeten Berstabschnitt,
• 2b eine weitere Ausführungsform mit einem Hohlraum zum Aufnehmen und Abführen von aus den Batteriezellen ausgetretenen Fluiden,
• 2c eine Darstellung einer Ausführungsform mit zwei Batteriezellen mit schematischer Darstellung einer elektrischen Detektionsschaltung,
• 3 eine erste Möglichkeit einer elektrischen Detektionsschaltung mit den Detektionselementen eines erfindungsgemäßen Systems
• 4 eine weitere Möglichkeit einer elektrischen Detektionsschaltung mit den Detektionselementen eines erfindungsgemäßen Systems,
• 5 eine weitere Möglichkeit einer elektrischen Detektionsschaltung mit den Detektionselementen eines erfindungsgemäßen Systems,
• 6a eine Schnittdarstellung gemäß der Linie A-A in 5 durch eine erste Variante einer als Matte ausgebildeten Trägereinheit,
• 6b eine Schnittdarstellung gemäß der Linie A-A in 5 durch eine zweite Variante einer als Matte ausgebildeten Trägereinheit und
• 7 eine weitere Möglichkeit einer Anordnung der Detektionselemente eines erfindungsgemäßen Systems, die elektrisch so verschaltet sind wie in der Ausführungsform gemäß 5.

Further practical embodiments of the invention are described below in conjunction with the drawings.

• 1 a first embodiment of a system according to the invention in a schematic side view,
• 2a a further embodiment with a bursting section formed on the support structure in the region of the at least one detection element,
• 2 B a further embodiment with a cavity for receiving and draining fluids leaking from the battery cells,
• 2c a representation of an embodiment with two battery cells with a schematic representation of an electrical detection circuit,
• 3 a first possibility of an electrical detection circuit with the detection elements of a system according to the invention
• 4 another possibility of an electrical detection circuit with the detection elements of a system according to the invention,
• 5 another possibility of an electrical detection circuit with the detection elements of a system according to the invention,
• 6a a sectional view along the line AA in 5 by a first variant of a carrier unit designed as a mat,
• 6b a sectional view along the line AA in 5 by a second variant of a carrier unit designed as a mat and
• 7 another possibility of arranging the detection elements of a system according to the invention, which are electrically connected as in the embodiment according to 5 .

1 shows a first embodiment of a system according to the invention for monitoring and increasing the safety of a battery system. Only one battery cell 10 of this system is shown as an example in a side view, although the entire system is formed from several such battery cells 10 and a corresponding arrangement of the other elements described below. The direction of gravity is indicated by the downward arrow g. The battery cell 10 has a cell housing 26, which is designed prismatically here. Two poles 25 are arranged on the outside on the right and left outside of the cell housing 26.

The bottom and top of the cell housing 26 are pole-free housing sides. A venting device 11 is provided on the pole-free lower housing side, which extends over part of the lower housing side. The venting device 11 allows gases to flow out of the interior of the cell housing 26 in the event of a pressure increase within the cell housing 26. Liquids should not pass through the venting device 11 during normal operation of the battery cell 10 and should remain within the cell housing 26. In the event of material fatigue, manufacturing defects, a defective venting device 11 or another leak in the area around the venting device 11, an undesirable leakage of liquid, in particular electrolyte, can still occur.

In the embodiment shown, the cell housing 26 is arranged on a support structure 12. A support unit 13 is arranged between the support structure 12 and the lower housing side of the cell housing 26. Part of the support unit 13 is a detection element 14, which in this embodiment has a separate indicator element 14a. In the embodiment shown, the detection element 14 is connected via an electrical line 27 to a signaling device 22 and via the signaling device 22 to a battery management system 23. The signaling device 22 and the battery management system 23 together form an evaluation unit 24, by means of which Changes to the detection element 14 can be detected.

As in 1 As can be seen, the support structure 12 has an opening directly below the detection element 14 that leads to an underrun protection space 16. The underrun protection space 16 is delimited on the underside by a base plate 18 (of the underrun protection). Gases or other gaseous fluids that enter the underrun protection space 16 can be detected quickly by means of a gas sensor 17. The gas sensor 17 is also connected to the signaling device 22 and via the signaling device 22 to the battery management system 23. Gas and other gaseous fluids can in particular also enter the underrun protection space through the carrier unit 13. For this purpose, the carrier is designed to be at least partially gas-permeable.

In the embodiment shown, the detection element 14 is arranged directly below the venting device 11 in such a way that liquids that escape from the cell housing 26 through the venting device 11 or directly next to the venting device 11 due to a leaky venting device 11 or due to other technical problems inevitably come into contact with the detection element 14. The detection element 14 is designed in such a way that the escape of liquids can be detected with the detection element 14 using the evaluation unit 24. This can be done in particular by the electrical resistance of the detection element 14 changing upon contact with a liquid and such a change being detectable in a corresponding detection circuit.

In the embodiment shown, the detection element 14 is part of a mat 28 and is embedded in this mat 28. The mat 28 is preferably designed such that the mat 28 creates a secure connection between the cell housing 26 of the battery cell 10 and the support structure 12, in particular through an adhesive effect and/or through a surface structure with a lotus effect. The mat 28 is further preferably made from a material that has a high thermal conductivity in order to be able to dissipate heat well from the battery cell 10. Furthermore, electrically conductive elements are preferably embedded in the mat 28 in order to connect the at least one detection element 14 to the evaluation unit 24 and optionally to further detection elements 14.

The 2a , 2 B and 2c as well as the 3 to 7 show further embodiments and views of systems according to the invention in different views, whereby the same reference numerals are always used for identical or at least functionally equivalent elements. Unless otherwise described, these embodiments are designed in the same way as those in 1 This also applies to elements that have been partially omitted to simplify the illustrations, such as the electrical line 27 in the 2a and 2 B .

The embodiments according to 2a and 2 B differ essentially in the area around the venting device 11, which is marked with the dashed circle.

In the embodiment according to 2a a bursting section 19 is provided on the support structure 12 directly below the detection element 14. In the embodiment shown, this is designed as a section with reduced material thickness. As a result, fluids that pass through the venting device 11 initially only reach the detection element 14. Only when the pressure and/or the temperature causes the bursting section 19 to be destroyed, for example due to a "thermal runaway", can fluid, as described above in connection with 1 described, further towards the underrun protection area 16. This results in a two-stage warning system in which conclusions can be drawn about the type of event depending on the design of the system and the parameters of a specific dangerous situation.

In the embodiment according to 2 B Not only is a bursting section 19 provided on the support structure, but a channel 29 is also formed. Fluids, in particular gases or liquids escaping from the venting device 11, for example electrolyte, can be collected via the channel 29 and transported out of the battery system or to another suitable location. In the event of a "thermal runaway", the bursting section 19 opens, in particular by melting or bursting.

2c serves to illustrate a battery system 20 with two battery cells 10, which are arranged directly adjacent to each other, with the view being directed towards a pole side of the cell housing 26. The design of the cell housing 26 essentially corresponds to the embodiment of 1 . In the presentation of 2c It can be seen that each vent opening 11 is assigned a detection element 14 with a separate indicator element 14a. An electrically conductive section of the carrier unit 13, which in turn is designed as a mat 28, serves as the detection element 14. On the outside of the mat 28, the An electrical line 27 is connected to the detection element 14, which forms a detection circuit via an evaluation unit 24.

In the 3 and 4 Two different possibilities of detection circuits are shown for the same battery system 20, which is formed from four battery modules 21. In the embodiment shown, each battery module 21 has five battery cells 10 by way of example, with a detection element 14 and a separate indicator element being provided on each battery cell 10.

At the 3 In the embodiment shown, the detection elements 14 and the separate indicator elements 14a of all battery cells 10 are connected to one another via a single electrical line 27. These thus form a detection circuit with an evaluation unit 24.

At the 4 In the embodiment shown, a separate detection circuit is provided for each battery module 21, wherein all detection circuits are monitored by the same evaluation unit 24.

The embodiment of 3 is particularly easy to implement, while the embodiment of 4 enables to determine in which battery module 21 a malfunction or an unusual event has occurred. The embodiment of 4 delivers more precise results, enables partial shutdown of a battery module 21 that is not functioning properly, and makes it easier to locate and eliminate a fault. The partial shutdown can be carried out in particular by means of a circuit breaker, a pyro-fuse or by means of another suitable switching mechanism as soon as a critical condition has been detected in a battery module 21.

For the sake of completeness, it is pointed out that the complexity of the detection circuits can be increased even further, in particular by providing a detection circuit for each battery cell 10 or for every two battery cells 10 or every three battery cells 10, if necessary in each case with the possibility of partially switching off only the battery cells 10 that are jointly connected by means of a detection circuit if a fault or a danger has been detected or is imminent.

5 shows a carrier unit 13 in the form of a mat 28, which is intended for a battery system 20 with four battery modules 21, in particular for a battery system as in 3 illustrated battery system 20. The detection elements 14 and the separate indicator elements 14a are embedded in the mat 28. The detection elements 14 are continued on the outside of the mat 28 as electrical lines 27.

In the 6a and 6b are two different embodiments of the 5 shown mat 28.

The embodiment according to 6a shows wires or other lines as detection elements 14, which here have a circular cross-section and - viewed in the thickness direction x - are arranged approximately centrally in the mat 28. The thickness x of the mat 28 can be determined as required and is preferably always larger than the diameter of the detection element 14 so that it can be arranged in a protected manner within the mat 28. The mat 28 is formed from a single layer in this embodiment.

At the 6b In the embodiment shown, the mat 28 is formed from three partial layers 13a, 13b, 13c. These are preferably firmly connected to one another, in particular by lamination. The detection elements 14 and in 6b Separate indicator elements (not shown) are preferably firmly connected to one of the partial layers 13a, 13b, 13c. It is particularly preferred to first glue or weave or knit the detection elements 14 and any indicator elements to the middle partial layer 13b and then apply the other two partial layers 13a, 13c to the outside in order to arrange the detection elements 14 in a protective manner in the mat 28.

7 shows a further embodiment of a mat 28 serving as a carrier unit 13, in which the detection elements 14 and separate indicator elements 14a of two battery modules 21 are part of a detection circuit via an electrical line 27. In this embodiment, which can also be combined with other detection circuits, a clearance 30 in the sense of a through-opening is provided in the mat 28 around the separate indicator elements 14a. As a result, the indicator elements 14a and, in the illustration, also some of the immediately adjacent detection elements 14 are arranged freely floating within the clearance 30. In the embodiment shown, the clearance 30 is shown with a rectangular basic shape. However, it can alternatively also have any other shape, in particular a circular, oval, square, trapezoidal, polygonal or other basic shape.

The features of the invention disclosed in the present description, in the drawings and in the claims can be used individually or also in any combinations are essential for the realization of the invention in its various embodiments. The invention can be varied within the scope of the claims and taking into account the knowledge of the competent person skilled in the art.

List of reference symbols

10

Battery cell

11

Ventilation device

12

Supporting structure

13

Carrier unit

13a

Sub-layer

13b

Sub-layer

13c

Sub-layer

14

Detection element

14a

separate indicator element

15

Battery management system

16

Underrun protection space

17

Gas sensor

18

Base plate of the underrun protection

19

Burst section

20

Battery system

21

Battery module

22

Signal processing device

23

Battery management system

24

Evaluation unit

25

pole

26

Cell housing

27

electrical line

28

mat

29

channel

30

Clearance

Claims (6)

System for monitoring and increasing the safety of a battery system (20) which has a plurality of battery cells (10), each battery cell (10) having a cell housing (26) and each cell housing (26) having a pole-free housing side on which no cell pole is arranged, a venting device (11) being provided on a pole-free housing side, which extends at least over part of the pole-free housing side, at least one cell housing (26) being assigned a detection element (14) which is functionally connected to a signal processing device (22) and/or a battery management system (23), the detection element (14) being arranged outside the cell housing (26) in its local vicinity in such a way that fluid escaping through the venting device (11) can be detected in the region of the outlet with the aid of the detection element (14), the detection element (14) being part of a flat carrier unit (13) which is attached to the outside of the Cell housing (26) is arranged adjacent and/or wherein the cell housing (26) is at least partially arranged on a support structure (12) and the carrier unit (13) is arranged between the venting device (11) and the support structure (12), characterized in that the detection element (14) is arranged directly below the venting device (11) and the carrier unit (13) is designed as a single- or multi-layer mat (28), wherein one or more detection circuits with one or more detection elements (14) are integrated into the carrier unit (13). System according to the preceding claim, characterized in that the mat (28) is made of a compounded material with one or more polymer components and one or more filler materials. System according to one of the two preceding claims, characterized in that the support structure (12) has at least one cavity for receiving and/or discharging fluids leaking from the battery cells (10). System according to one of the three preceding claims, characterized in that a bursting section (19) is formed on the support structure (12) in the region of at least one detection element (14). System according to one of the preceding claims, characterized in that the at least one detection element (14) is enclosed by at least two layers of the carrier unit (13) and/or a recess is formed in the carrier unit (13) in the region of the at least one detection element (14). System according to one of the five preceding claims, characterized in that the mat (28) is produced by casting, extruding or laminating.

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