CAPACITIVE AREA SENSOR

Abstract

A capacitive surface sensor for a vehicle seat or a steering wheel has at least one electrically insulating carrier layer and one electrically conductive layer allocated to each side of the carrier layer. The carrier layer is a three-dimensionally malleable layer and at least one of the electrically conductive layers forms a direct bond with the carrier layer.

Claims

1. A capacitive area sensor for a vehicle seat or a steering wheel having at least one electrically insulating carrier layer and one electrically conductive layer assigned to each side of the carrier layer, wherein the carrier layer is a three-dimensionally malleable layer and at least one of the electrically conductive layers forms a direct bond with the carrier layer.

2. Capacitive area sensor as in claim 1, wherein each respective electrically conductive layer forms a direct bond with each respective carrier layer on both sides of the carrier layer.

3. Capacitive area sensor as in claim 1, wherein each respective electrically conductive layer is formed by a lacquer.

4. Capacitive area sensor as in claim 1, wherein each respective electrically conductive layer is formed by a paste.

5. Capacitive area sensor as in claim 1, wherein each respective electrically conductive layer is a vapor-deposited layer.

6. Capacitive area sensor as in claim 1, wherein each respective electrically conductive layer is a layer applied by spraying.

7. Capacitive area sensor as in claim 1, wherein each respective electrically conductive layer is a layer applied by screen printing.

8. Capacitive area sensor as in claim 1, wherein each respective electrically conductive layer is a layer containing a precious metal or a precious metal alloy.

9. Capacitive area sensor as in claim 8, wherein each respective electrically conductive layer is a layer containing essentially silver.

10. Capacitive area sensor as in claim 1, wherein the carrier layer is formed from ethylene propylene diene (monomer) rubber (EPDM).

11. Capacitive area sensor as in claim 1, wherein the carrier layer is formed of polyolefin.

12. Capacitive area sensor as in claim 1, wherein the carrier layer is formed of a plastic foam.

13. Capacitive area sensor as in claim 1, wherein each respective electrically conductive layer has a thickness in the range of 1 nm to 100 μm.

14. Capacitive area sensor as in claim 1, wherein each respective electrically conductive layer has a smaller outer limit than the carrier layer.

15. Capacitive area sensor as in claim 1, wherein one of the electrically conductive layers is smaller in its outer dimensions than the other electrically conductive layer.

16. Capacitive area sensor as in claim 12, wherein the carrier layer is formed of a polyurethane foam.

17. Capacitive area sensor as in claim 13, wherein each respective electrically conductive layer has a thickness in the range from 1 nm to 50 μm.

18. Capacitive area sensor as in claim 1, wherein each respective electrically conductive layer has a resistance value in a range from 0.06 Ohm/square to 600 Ohm/square.

19. Capacitive area sensor as in claim 19, wherein each respective electrically conductive layer has a resistance value in a range from 6 Ohm/square to 60 Ohm/square.

20. Capacitive area sensor as in claim 19, wherein each respective electrically conductive layer has a resistance value in a range from 0.1 Ohm/square to 10 Ohm/square.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] FIG. 1 is a cross-section of a capacitive area sensor according to a first embodiment.

[0029] FIG. 2 is a cross-section of a capacitive area sensor according to a second embodiment.

[0030] FIG. 3 is a schematic cross-section of the layer structure of a steering wheel.

[0031] FIG. 4 shows the layer structure of a heating layer, as can be used in FIG. 3.

[0032] FIG. 5 shows a further layer structure of a heating layer, as can be used in FIG. 3.

[0033] FIG. 6 shows a third layer structure of a heating layer, as can be used in FIG. 3.

[0034] FIGS. 7a to 7e show various details of different structures for electrically conductive layers.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0035] The preferred embodiments of the present invention will now be described with reference to FIGS. 1-7 of the drawings. Identical elements in the various figures are designated with the same reference numerals.

[0036] A capacitive area sensor according to the invention that is provided for use in a vehicle seat or in a steering wheel and is generally designated by reference numeral 1, comprises at least one electrically insulating carrier layer 2 and one respective electrically conductive layer 3, 4 assigned to each side of the carrier layer 2, as shown in FIG. 1.

[0037] The carrier layer 2 is made from a thin three-dimensionally malleable material, preferably from an ethylene propylene diene (monomer) rubber (EPDM), a polyolefin, an elastomer or foam, with polyurethane foam being preferred. If the carrier layer 2 consists of a foam material, it should be closed-porous foam, or at least foam with a small pore size.

[0038] The carrier layer 2 has a thickness in the range from 0.01 mm to 3 mm, with a thickness of 0.05 mm to 2 mm or from 0.07 mm to 1.5 mm being preferred in order to achieve a layer structure which is as thin as possible.

[0039] At least on one side of the carrier layer 2, the electrically conductive layer 3 assigned to this side is applied such that it has a direct, i.e., adhesive-free bond with the carrier layer 2. In order to obtain such a direct, adhesive-free bond, namely by avoiding an adhesive layer, the conductive layer 3 is applied as a lacquer or as a paste. It is also provided that the conductive layer 3 is vapor-deposited onto the respective side of the carrier layer 2 by means of PVD or CVD methods.

[0040] As FIG. 1 shows, the conductive layer 4, which is associated with the other surface side of the carrier layer 2, can only be placed on the carrier layer 2 (this is indicated in FIG. 1 by a gap between the carrier layer 2 and the conductive layer 4, which is otherwise not present).

[0041] FIG. 2 shows a capacitive area sensor 1 which corresponds in its layer structure to that shown in FIG. 1. However, in FIG. 2, the second sensor layer 4 is also a layer that is applied in a direct bond with the carrier layer 2, i.e., adhesive-free, in a manner as described above with reference to the conductive layer 3. The electrically conductive layer 3 and the electrically conductive layer 4 can have the same or different layer thicknesses, depending on the area of application of the capacitive area sensor 1.

[0042] For the respective conductive layer 3 or 4, a thickness of 1 nm to 100 μm, preferably a thickness of 1 nm to 50 μm, even more preferably a thickness of 1 nm to 20 μm, is intended. This results in a layer structure for the capacitive area sensor 1 with the carrier layer 2 and the two conductive layers 3 and 4 having a very small thickness, which may be approximately 1 mm, in particular depending on the thickness of the carrier layer 2.

[0043] Due to the materials used for the carrier layer 2 as described above, the carrier layer 2 has certain elasticity so that it is three-dimensionally malleable in order to adapt it to the circumstances, for example when the capacitive area sensor is placed around a steering wheel rim. It is also of particular advantage that the electrically conductive layers 3 and/or 4 are in direct, adhesive-free contact with the carrier layer 2, namely in a manner, in particular by the method of applying the conductive layers 3, 4 onto the carrier layer 2, that allows them to adapt to the stretching behavior of the carrier layer 2.

[0044] The conductive layer 3 and/or 4 can be produced by a lacquer, which is applied to the carrier layer 2 by means of a spray head, with the advantage that the layer thickness of the conductive layer 3 or 4 can be adjusted very precisely and the layer can also penetrate into uneven surfaces of the carrier layer 2, for example pores. After drying, the layer that is moist after the spraying process is intimately bonded to the carrier layer 2, in particular when the lacquer contains constituents that etch the surface of the carrier layer 2.

[0045] To obtain even thicker conductive layers 3 or 4 on the carrier layer 2, the respective conductive layer can be applied to the carrier layer 2 as a lacquer or paste by a brush-like applicator.

[0046] In particular, if the conductive layer is to be masked on the carrier layer 2, it can be applied by screen printing; however, an application by spraying or a paste application or an application by means of PVD or CVD methods using masks is also possible.

[0047] FIG. 3 shows a cross-section through the layer structure of a steering wheel in which the capacitive area sensor, as shown in FIGS. 1 and 2, is integrated.

[0048] Such a steering wheel has a steering wheel core 5, which is embedded in a foam jacket 6. A heating layer 7 is applied to the foam jacket 6 and glued to the foam jacket 6 via an adhesive layer 11, for example a double-sided adhesive tape. Located on the outer side of the heating layer 7 is the area sensor 1, which is also connected to the heating layer 7 via an adhesive layer 9, together with the carrier layer 2 and the two conductive layers 3 and 4 covering the carrier layer 2. The outer conductive layer 3 is covered by a steering wheel cover 10, which is glued to the area sensor 1 via a further adhesive layer 8. Optionally, a laminating layer 12, which serves to improve the haptics of the steering wheel, can be interposed between the area sensor 1 and the cover.

[0049] The capacitive area sensor 1 has very flexible properties due to the materials used for the carrier layer 2 and the conductive layers 3, 4, and can be produced with a very thin layer thickness.

[0050] It is to be pointed out that the Figures, in particular the layer thicknesses shown therein, are not to scale.

[0051] FIGS. 4 to 6 show various heating layers 7, as can be used in the layer structure of a steering wheel, which is illustrated in FIG. 3, or also in a vehicle seat.

[0052] In the structure shown in FIG. 4, a heating wire 13 is embedded between a lower foam layer 14 and an upper foam layer 15. The purpose of the upper foam layer 15 is to insulate the heating wire 13 from the electrically conductive layer 4 of the capacitive area sensor 1. A film of ethylene propylene diene rubber (EPDM), which is characterized by its elastic and well-insulating properties, is also preferably used for this layer.

[0053] In an alternative design as shown in FIG. 5, the heating layer 7 can also comprise only one heating wire 13, which is applied to a nonwoven 16 and is covered on its side facing the area sensor 1.

[0054] As shown in FIG. 6, the foam layer 14, as shown in the heating layer 7 of FIG. 4, can be replaced by a non-woven layer 17 on the side facing the steering wheel core 5.

[0055] A nonwoven fabric of polyester having a preferred thickness in the range from 0.5 mm to 1.5 mm is used, for example, as a non-woven layer 16 or 17, as shown in FIGS. 5 and 6.

[0056] FIGS. 7a to 7e show various details of different structures for the electrically conductive layers 3 and 4, which can be applied to the carrier layer 2 by using corresponding masks. However, it is also provided that one of the electrically conductive layers 3 and 4 is connected as a metal foil with a respective structure as shown in FIGS. 7a to 7e to the carrier layer 2.

[0057] The metal foils, which in particular serve as a shielding layer on the lower side of the carrier layer 2, can have the form of meanders, star-shaped rays, and the like, in particular in the form of Greek meanders or Greek double meanders such that contiguous and thus interconnected electrical structures remain. Such patterns show a very good stretching behavior and thus a resilience, which can follow the stretching behavior of the carrier layer 2, such that they are particularly adapted to the conditions when used on a steering wheel or a seat.

[0058] The metal foils, which in particular serve as a shielding layer on the lower side of the carrier layer 2, can also have the form of a chessboard such that contiguous and thus interconnected electrically conductive structures remain.

[0059] There has thus been shown and described a novel capacitive area sensor which fulfills all the objects and advantages sought therefor. Many changes, modifications, variations and other uses and applications of the subject invention will, however, become apparent to those skilled in the art after considering this specification and the accompanying drawings which disclose the preferred embodiments thereof. All such changes, modifications, variations and other uses and applications which do not depart from the spirit and scope of the invention are deemed to be covered by the invention, which is to be limited only by the claims which follow.

REFERENCE NUMERAL LIST

[0060] 1 Area sensor [0061] 2 Carrier layer [0062] 3 Electrically conductive layer [0063] 4 Electrically conductive layer [0064] 5 Steering wheel core [0065] 6 Foam jacket [0066] 7 Heating layer [0067] 8 Adhesive layer [0068] 9 Adhesive layer [0069] 10 Steering wheel cover [0070] 11 Adhesive layer [0071] 12 Laminating layer [0072] 13 Heating wire [0073] 14 Lower foam layer [0074] 15 Upper foam layer [0075] 16 Non-woven [0076] 17 Non-woven layer