Sensor system for a motor vehicle

Abstract

A sensor system for a motor vehicle is provided. The sensor system comprises a flat shielding element which is electrically conductive and to which an electric potential can be applied, and at least one capacitive sensor element which includes an electrically conducting structure which is arranged on one side of the shielding element. As electrically conducting structure the sensor element includes at least one sensor conductor which forms a sewing thread and is sewn onto the one side of the shielding element.

Claims

1. A sensor system for a motor vehicle, which comprises: a flat shielding element comprising a fabric of metal threads which is electrically conductive and to which a first electric potential is applied, and at least one capacitive sensor element, which includes an electrically conducting structure which is arranged on a first side of the shielding element, wherein as electrically conducting structure, the at least one capacitive sensor element includes at least one sensor conductor which forms a sewing thread and is sewn onto the first side of the shielding element, wherein a second potential is applied to the at least one sensor conductor, such that the fabric of metal threads of the shielding element masks any parasitic capacitance between the at least one sensor conductor and any electrically conductive material disposed adjacent a second side of the shielding element, wherein the second side of the shielding element is opposite and spaced apart from the first side of the shielding element, a holding thread, wherein the sensor conductor and the holding thread together form a seam, wherein the sensor conductor and/or the holding thread at least partially extend through the shielding element.

2. The sensor system according to claim 1, wherein the sensor conductor forms the bottom thread or face thread of the seam which is formed in the shielding element.

3. The sensor system according to claim 1 wherein the shielding element includes a plurality of interconnected layers of different materials, wherein at least one of the layers is the fabric of metal threads.

4. The sensor system according to claim 3, wherein in addition to the fabric of metal threads, the shielding element includes at least one non-conducting layer selected from the group consisting of an adhesive material, a foam material and a fleece.

5. The sensor system according to claim 4, wherein the fabric of metal threads is arranged between at least two non-conducting layers or adjacent to at least two non-conducting layers of the shielding element in a sandwich construction.

6. The sensor system according to claim 1, wherein the fabric of metal threads comprises a wire fabric with warp threads and weft threads, which are offset with respect to heating conductors and/or sensor conductors by an angle unequal to 90°.

7. The sensor system according to claim 1, wherein for measuring a quantity to be measured a modulated measurement signal is applied to the sensor element and a change in the phase and/or amplitude of the measurement signal is evaluated.

8. The sensor system according to claim 1, wherein the first potential and the second potential are the same, the sensor system further comprising a circuit arrangement which drives the first potential and the second potential.

9. The sensor system according to claim 8, wherein the second potential is a modulated measurement signal, and for measuring a quantity to be measured, the modulated measurement signal is applied to the sensor element and a change in the phase and/or amplitude of the measurement signal is evaluated, and wherein the first potential applied to the shielding element has the same phase as the measurement signal applied to the sensor element.

10. The sensor system according to claim 9, wherein the measurement signal for the sensor element also is applied to the shielding element.

11. The sensor system according to claim 1, wherein the sensor system is provided and formed to be integrated into a vehicle steering wheel or into a vehicle seat.

12. The sensor system according to claim 1, wherein the sensor system includes at least one heating element which is arranged on the second side of the shielding element.

13. The sensor system according to claim 12, wherein the heating element includes at least one heating conductor which is sewn onto the second side of the shielding element.

14. The sensor system according to claim 13, wherein the heating conductor itself forms a sewing thread which is interlaced with the shielding element and/or at least one further sewing thread.

15. The sensor system according to claim 13, wherein the heating conductor is sewn onto the second side of the shielding element by means of the holding thread which fixes the heating conductor on the other side of the shielding element.

16. The sensor system according to claim 15, wherein the holding thread is made of a non-conducting material.

17. The sensor system according to claim 1, wherein the sensor conductor is interlaced with at least one further sewing thread.

18. The sensor system according to claim 15, wherein the sensor conductor is interlaced with at least one further sewing thread and the sensor conductor and the holding thread form at least one seam and in doing so form bottom thread and face thread of the seam.

19. The sensor system according to claim 1, wherein the first and second potentials are the same.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will be explained in detail below by means of several exemplary embodiments with reference to the Figures of the drawing,

(2) FIG. 1 in a partly sectional perspective view schematically shows the structure of a steering wheel rim of a vehicle steering wheel, wherein a shielding element, a heating element and a capacitive sensor element are integrated into the steering wheel rim,

(3) FIG. 2 schematically shows the steering wheel rim of FIG. 1 in cross-section;

(4) FIG. 3 shows a schematic representation of an exemplary embodiment of a sensor system with a shielding element, a heating element and a capacitive sensor element, wherein the sensor element is formed as sewing thread,

(5) FIGS. 4A-4G show exemplary embodiments of sensor arrangements with a shielding element, a heating element and a capacitive sensor element, wherein different layers are present, which form the shielding element and/or adjacent layers;

(6) FIG. 5 shows the operating principle of a capacitively operating sensor using the example of a sensor integrated into a steering wheel rim

(7) FIG. 6 shows a circuit arrangement for providing a measurement signal and a voltage signal for a sensor system.

DETAILED DESCRIPTION

(8) FIG. 1 shows a partly sectional, perspective view of the structure of a steering wheel rim 10 of a vehicle steering wheel. In its interior, the steering wheel rim 10 includes a metallic skeleton 1 which is surrounded by a dielectric 2. The dielectric 2 for example consists of a foamed material, such as a polyurethane foam or a synthetic rubber. It can also be provided that the dielectric 2 consists of several layers of different material. The dielectric 2 subsequently will also be referred to as foam layer.

(9) The foam layer 2 is surrounded by a heating layer 3 which includes one or more heating elements. In particular, the heating layer 3 comprises an electrically conductive material which heats up due to its ohmic resistance, as soon as a voltage is applied. Such electrically conductive material for example is formed by a heating wire which is formed in the heating layer 3. In the following, no distinction is made between the heating layer 3 and the heating elements formed in the same, since the heating elements form the heating layer.

(10) Towards the outside, the heating layer 3 is adjoined by a shielding element 4. The shielding element 4 includes at least one layer which is electrically conductive and to which an electric potential can be applied, for example via a contact pad. It can be provided that in addition to such electrically conductive layer the shielding element 4 includes further layers. Exemplary embodiments thereof will be explained with reference to FIGS. 4A to 4G.

(11) The shielding element 4 is surrounded by a sensor layer 5 which includes at least one capacitive sensor element. The capacitive sensor element comprises at least one single- or multipart electrically conductive element, which in the considered exemplary embodiment is formed by a sensor wire. Instead of a sensor wire, other conductive elements having capacitive properties, such as e.g. flat conductors or electrically conductive foils, also can be employed. In the following, no distinction is made between the sensor layer 5 and the capacitive sensor elements formed in the same, since the capacitive sensor elements form the sensor layer.

(12) The sensor layer 5 is adjoined by a cover 6 of the steering wheel rim 10, which for example is made of leather and represents the outer envelope of the steering wheel rim 10.

(13) The heating element 3, the shielding element 4 and the sensor element 5 are arranged in the steering wheel rim in a coaxial arrangement and form successive layers of the steering wheel rim 10.

(14) To the capacitive sensor element 5 an evaluation unit (not shown) is associated, which measures the change in a measurement quantity, for example a measuring current, in dependence on the capacitive coupling of the capacitive sensor element to a reference potential. Such evaluation unit is described for example in DE 10 2009 055 424 A1, to which reference is made in so far.

(15) By means of such evaluation unit it can be detected whether a vehicle occupant or another object is present in the surroundings of the capacitive sensor element 5. The corresponding measurement principle is shown schematically in FIG. 5 and will be explained below with reference to the same.

(16) There is schematically shown a steering wheel L and a vehicle chassis C of a motor vehicle. The steering wheel L forms an electrode El1 which is provided by an electrically conducting structure of a capacitive sensor element integrated into the steering wheel rim L. The vehicle chassis C forms an imaginary second electrode El2 which provides a reference potential, usually the ground potential. Between the electrodes El1, El2 an electric field E exists. Its strength and hence the capacitance between the electrodes El1, El2 is influenced by a dielectric which is located in the electric field between the electrodes El1, El2. Such dielectric also is the human body. The closer the human body comes to electrode El1, the larger are the changes in capacitance.

(17) When a person P present in the driver seat S touches the steering wheel rim, so that the hands of the driver get in the direct vicinity of the electrode El1, this leads to a strong change in the capacitance of the capacitive sensor element. Thus, placing a hand on or lifting the same from the vehicle steering wheel can be detected via a capacitive measurement (so-called hands-off recognition).

(18) The described operating principle clearly shows that a capacitive sensor arrangement for detecting the presence of a person correspondingly also can be integrated for example into the vehicle seat S, for example in the form of a sensor mat which is located between a seat cover and a seat cushion. Another application is the arrangement of a capacitive sensor arrangement at a safety belt system.

(19) In a capacitive measurement it is important that the considered electrode of the capacitive sensor element, for example the electrode El1 of FIG. 5, as little as possible is subjected to parasitic capacitances which impede or prevent a meaningful measurement. In the structure described in FIG. 1, however, such parasitic capacitances in principle are formed by capacitances which are present between the sensor element 5 and the heating element 3 and between the sensor element 5 and the metallic skeleton 1. This will be explained below with reference to FIG. 2.

(20) FIG. 2 shows a schematic representation of a sectional view through a steering wheel rim according to FIG. 1, wherein the skeleton 1 simply is shown circular in cross-section and the layers 3, 4, 5 simply are shown to be circular. The layer 6 of FIG. 1 is not shown in FIG. 2. Without the electrically conductive shielding element 4, a parasitic capacitance would be present on the one hand between the skeleton 1 and the sensor element 5 and on the other hand between the heating element 3 and the sensor element 5. In a manner known per se, these capacitances depend on the difference of the respective radii r1, r2, r4 and the dielectric constant of the foam layer 2. It should also be considered that the parasitic capacitances can change and thereby distort a measurement result. Such change for example is effected in that the heating wire of the heating element 3 expands when heated, whereby the distances between the individual layers are changed. A change in the parasitic capacitance also can be effected by mechanical manipulation, for example by deformation of the foam layer 2 when the steering wheel rim is actuated by the driver.

(21) By using the electrically conductive shielding element 4, these parasitic capacitances are masked out. The capacitive sensor element 5 hence detects only those changes in capacitance which are connected with a desired measurement.

(22) Thus, an electrically conductive shielding element 4 is provided, which is located between the heating element 3 and the capacitive sensor element 5 and which shields the capacitive sensor element 5 against the heating element 3. In the exemplary embodiment of FIGS. 1 and 2 shielding also is effected against the skeleton 1. What is also conceivable, however, are exemplary embodiments in which the capacitive sensor element 5 is arranged on the inside of the shielding element 4 and the heating element 3 is arranged on the outside of the shielding element 4, for which case merely a parasitic capacitance between the heating element 3 and the sensor element 5 is masked out by the shielding element 4.

(23) In further exemplary embodiments, a heating layer 3 or heating elements are omitted. For this case, only the elements or layers 1, 2, 4, 5, 6 are provided in the exemplary embodiment of FIG. 1. The shielding element 4 represents a shield against the skeleton 1.

(24) For providing the function of a capacitive shield, an electric potential is applied to the shielding element 4. In principle, this can be any reference potential. In one exemplary embodiment it is provided that the shielding element 4 is driven to the same potential as the electrically conducting structure of the sensor element 5.

(25) FIG. 6 shows a corresponding circuit arrangement. The circuit arrangement comprises a measurement signal generator 91 which for example provides a sinusoidal measurement signal. After low-pass filtering by a low-pass filter 92, the same is supplied to two amplifiers 93, 94, which each comprise an operational amplifier OP1, OP2 and a resistor R1, R2. Via a further operational amplifier OP3, a reference voltage U.sub.ref is provided. Via a multiplexer 95, a potential for the shielding element 4 is provided at a contact 96 and a measurement signal for the sensor element 5 is provided at a contact 97. The evaluation of the measurement signal is effected in that changes of the measurement signal, which are based on a change in capacitance, are supplied to a further evaluation 99 via a low-pass filter 98.

(26) One function of the illustrated circuit consists in detecting the impedance of a sensor element 5 connected to the contact 97 and in reporting the detected impedance to a microprocessor system. The impedance is measured for example in that a sinusoidal voltage is applied to the sensor element 5 and the current response triggered thereby is measured. Changes in the impedance are measured as amplitude and phase changes of the detected current.

(27) Another function of the illustrated circuit consists in the provision of a voltage at the contact 96 which is electrically connected with the shielding element 4. Since the voltage signal is generated by the same circuit assembly, in particular the same measurement signal generator 91, as the measurement signal provided at the contact 97, the signals or voltages provided at the two contacts 96, 97 have the same phase. In principle, however, it is also possible that a separate circuit is provided for providing a certain potential at the contact 96, to which the shielding element 4 is driven for providing an “active shield” against parasitic capacitances. Since the applied potential and the measurement signal have the same phase, a particularly effective shielding of the sensor element 5 against parasitic capacitances is effected.

(28) Shielding element 4 and sensor element 5 thus have the same electric potential. A capacitance between the sensor element 5 and the shielding element 4 thereby is suppressed completely. In this way, there is merely detected a change in capacitance which is accompanied by a desired measurement, for example the detection of the presence of a person or the detection of the hand of a person resting on the steering wheel rim.

(29) The connection between shielding element 4, heating element 3 and capacitive sensor element 5 will be explained below with reference to several exemplary embodiments. In these exemplary embodiments, a heating conductor of the heating element 3 and/or a sensor conductor of the capacitive sensor element 5 is formed as sewing thread which is sewn up with a further thread. The shielding element 4 forms a carrier material for the individual threads.

(30) Thus, according to the schematic sectional representation of FIG. 3 a sensor system is provided, which comprises a flat shielding element 4, a heating conductor 30 of a heating element, and a sensor conductor 50 of a capacitive sensor element. Furthermore, there is provided a holding thread 70 of a non-conducting material.

(31) The shielding element 4 provides a flat carrier material for the heating conductor 30, the sensor conductor 50 and the holding thread 70. It includes at least one layer which is electrically conductive and to which an electric potential can be applied. For example, the shielding element 4 comprises a metal fabric which is formed by warp wires and weft wires.

(32) The heating conductor 30 for example is formed by a wire which can be sheathed with a paint insulation 31. By the holding thread 70, it is fixed on the one side of the shielding element 4. The course of the holding thread 70 vertically to the course of the heating conductor 30 is to be understood schematically and by way of example only. In principle, the holding thread 70 can adopt any course which allows a fixation of the heating conductor 30 on the one side of the flat shielding element 4.

(33) On the other side of the shielding element 4 the sensor conductor 50 is arranged, which represents an electrically conducting structure of a capacitive sensor element. The sensor conductor 50 for example is formed by a wire which can be sheathed with a paint insulation. It is formed as sewing thread, i.e. it has a thickness and flexibility such that it is usable in a sewing process.

(34) In the exemplary embodiment of FIG. 3, for example, it is provided that the sensor conductor 50 and the holding thread 70 together form a seam 8, wherein the sensor conductor 50 forms the bottom thread and the holding thread 70 forms the face thread of the seam 8. The sensor conductor 50 and the holding thread 70 correspondingly form two sewing threads N1, N2.

(35) Thus, there is provided a structure in which the heating element and the capacitive sensor element are formed on different sides of a flat shielding element 4, which serves as carrier material, wherein the heating element and/or the capacitive sensor element include structures in the form of a sewing thread which can be sewn up on the carrier material with a further thread.

(36) The configuration of FIG. 3 is to be understood by way of example only and can undergo various modifications. In a first modification it can be provided that the sensor wire 50 is fixed on the one side of the shielding element 4 by means of a holding thread, while the heating conductor on the other side of the shielding element is provided without such holding thread. By reversing the conditions of FIG. 3, the heating thread and the holding thread form a seam in such configuration, wherein heating conductor and holding thread form face thread and bottom thread of a seam.

(37) A further modification can provide that the holding thread 70, which in FIG. 3 is formed as non-conducting thread, likewise is formed by an electrically conducting wire or other conductor which can be sheathed with an insulating layer. Such further conducting wire can represent a part of a further capacitive sensor or a further heating element.

(38) A further modification provides that both the heating conductor 30 and the sensor conductor 50 are sewn onto the respective side of the shielding element 4 by a respectively associated holding thread. The holding threads then for example are sewn up with each other (forming face thread and bottom thread) or are each sewn up separately with the carrier material 4.

(39) With a further modification no holding thread is realized at all, and the heating conductor 30 and the sensor conductor 50 themselves form face thread and bottom thread. However, this involves the disadvantage that due to the contact between face thread and bottom thread or between heating conductor and sensor conductor a mutual capacitive interference can occur, which actually should be prevented by the shielding element 4. In such a case, however, it might be provided that the distance between the connecting points of heating conductor 30 and sensor conductor 50 is chosen large, in order to minimize a mutual interference.

(40) FIGS. 4A to 4G show exemplary embodiments for the structure of a sensor element corresponding to FIG. 3. The sensor element is constructed as multi-layer system. In FIGS. 4A, 4B, 4C and 4D it is provided that the shielding element 4 has a multi-layer structure. In FIGS. 4C, 4F, 4G it is provided that further layers are present, which adjoin the shielding element 4.

(41) FIG. 4A shows an exemplary layer structure in which the shielding element 4 consists of five layers, an electrically conductive layer 41 with a wire fabric, an adhesive layer 42, 43 arranged above and below the same, a foam layer 44, and a fleece 45. On the two sides of the shielding element 4, as described with respect to FIG. 3, a heating conductor 30 of a heating element and a sensor conductor 50 of a sensor element are arranged. In particular by integrating a fleece into the shielding element 4 as layer 45, a secure sewing up of the respective wires 30, 50, 70 on the shielding element 4 is facilitated.

(42) The exemplary embodiment of FIG. 4B in principle corresponds to the exemplary embodiment of FIG. 4A. In the exemplary embodiment of FIG. 4B, however, it is provided that the electrically conducting wire fabric 41 is oriented in a way other than in the exemplary embodiment of FIG. 4A. This is indicated by a different dashing of the layer 41 in FIGS. 4A, 4B. In FIG. 4A, for example, it is provided to arrange the warp wires and weft wires of the wire fabric at right angles or parallel to the sensor wires 50 and heating wires 30, respectively. In FIG. 4B it is provided to offset the warp wires and weft wires of the wire fabric by an angle unequal to 90°, for example of 45° with respect to the heating wires 30 and sensor wires 50. In this way, an increased stretchability of the entire element is achieved.

(43) In FIG. 4C, the shielding element is formed by the electrically conductive layer 41, an adhesive layer 43 and a fleece 45. On the upper side, an adhesive layer 42′ and a foam layer 44′ are formed in addition.

(44) In FIG. 4D, the shielding element consists of an upper electrically conducting layer 41, an adhesive layer 43 located thereunder, and a fleece layer 45.

(45) In FIG. 4E, the shielding element 4 consists of only one layer which is electrically conductive and for example formed by a wire fabric.

(46) In FIG. 4F, an adhesive layer 42′ and a foam layer 44′ are placed over the structure of FIG. 4E. In FIG. 4G, an adhesive layer 42′ and a fleece 55′ are placed over the structure of FIG. 4E.

(47) The design variants according to FIGS. 4A to 4G can be realized with a heating conductor 30 or a sensor conductor 50 as face thread or bottom thread and possibly by using one or more additional holding threads, as described with reference to FIG. 3 and the respective modifications.

(48) A further modification consists in that the realization of a heating layer and the use of a heating conductor 30 is omitted. Otherwise, the described sensor structure remains the same.

(49) The invention is not limited in its configuration to the exemplary embodiments described above, which merely are to be understood by way of example. For example, the used materials and forms of the described electrically conducting structures merely are to be understood by way of example.