Abstract:
A capacitive sensor module with a sensor electrode which is used to detect the entry of an object into a space ahead of the sensor electrode, wherein the sensor electrode is formed from a wire. Parallel to the sensor electrode, auxiliary electrodes extend within a plastic carrier that possesses recesses to receive the sensor electrode and the auxiliary electrodes and partially surrounds them along their circumference. The sensor electrodes can be pressed into the plastic carrier by overcoming an elastic forming force and are held within their recesses by the elastic reshaping process.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The invention involves a sensor module for use in or on motor vehicles. 
         [0002]    The invention particularly involves a sensor module with a sensor electrode which will be used in order to prevent the entry of an object into a space ahead of the sensor electrode. At least one auxiliary electrode extends parallel to the sensor electrode. 
         [0003]    Such sensor arrays are used in vehicles within various fields. 
         [0004]    A capacitive sensor array with a sensor electrode with whose aid the approach of an object is to be detected, and with a control and evaluation circuit that is linked to the sensor electrode and detects a capacity change of the sensor electrode as compared to mass by periodically linking the sensor electrode with an operating voltage at a predetermined frequency and evaluating at least one parameter of a current or voltage progression that is dependent on the periodic charging and discharging of the sensor electrode in order to detect the capacity change is, for example, known in the U.S. Pat. No. 5,730,165 as well as the corresponding patent document DE 196 81 725 B4. The parameter of a current or voltage progression that is dependent on the periodic charging and discharging of the sensor electrode herein consists of a voltage that can be measured over a condenser and depends on a charge that is accumulated in the condenser, wherein this charge is accumulated by periodically charging the sensor electrode by linking it to the operating voltage and subsequently discharging it again by connecting it to the condenser. Another such capacitive sensor is known from the patent document EP 1 339 025 B1. 
         [0005]    A capacitive sensor array with a sensor electrode, with a mass background electrode that is mounted with a gap behind the sensor electrode, and with a shielding electrode that is arrayed between the sensor electrode and the mass background electrode and is linked to the sensor electrode via a control and evaluation circuit in such a manner that its potential follows the potential of the sensor electrode is, for example, known from the publications EP 0 518 836 A1, U.S. Pat. No. 6,825,752 52, DE 101 31 243 C1 and DE 10 2006 044 778 A1. The provision of an shielding electrode between the sensor electrode and the background electrode that is on mass potential as known from these printed documents has the advantage that the sensitivity of the capacitive sensor that is formed in this manner towards changes in the space ahead of the sensor electrode, e.g. by the introduction of objects, is heightened. This is particularly due to the fact that the field which spreads out from the sensor electrode ranges more strongly into the space ahead of the sensor electrode (detection range) because a large part of the field is no longer short circuited to the background electrode that is connected to mass potential, as would be the case if there were no shielding electrode. Due to the circumstance that the shielding electrode is connected to the sensor electrode in such a manner that it follows its potential, a strong electrical field is formed between the shielding electrode and the background electrode; specifically, however, practically no field is formed between the sensor electrode and the shielding electrode whose potential follows. 
         [0006]    The known arrangement of a sensor electrode, shielding electrode and background electrode is commonly surrounded with an electrical insulator, such as a plastic layer, so that an insulating layer, such as a plastic layer, is present on the sensor electrode and therefore between the sensor electrode and the space to be monitored ahead of the sensor electrode, namely the detection zone. 
         [0007]    The production and maintenance of such sensor arrays is difficult and costly. Particularly the orientation of the electrodes towards each other and the permanent fixation of the orientation throughout their entire length, even during operation, are critical factors. 
       SUMMARY OF THE INVENTION 
       [0008]    The invention is therefore based upon the task of enabling a more cost effective and more robust structure in a sensor array of the initially described variety. 
         [0009]    The invention solves this task with a sensor array possessing the attributes of claim  1 . 
         [0010]    The capacitive sensor array in accordance with the invention possesses a sensor electrode which can be used to detect the entry of an object into a space ahead of the sensor electrode. The sensor electrode is formed from a segment of a first cable or wire. At least one auxiliary electrode extends parallel to the sensor electrode, wherein the first auxiliary electrode is formed from a segment of the second cable or wire. 
         [0011]    A plastic carrier has recesses to receive and guide the sensor electrode, wherein at least one longitudinally shaped recess is formed to receive one sensor electrode. Within the recesses, the sensor electrodes are at least partly surrounded by the plastic carrier along their circumference and thereby held within the recess. The plastic carrier and the limits of the recesses are formed and matched to the sensor electrodes in terms of their shaping and material selection so that the sensor electrodes can be pressed into the recesses by application of an elastic or plastic forming force and are held within their recesses by the elastic reshaping processes. 
         [0012]    Depending on whether the sensor electrodes are mantled cables or wires, part or the entire forming process may take place within the cables, or both the plastic carrier material and the cable, or only the plastic carrier material, may be formed. 
         [0013]    The invention therefore provides a sensor module which allows the formation of a sensitive capacitive proximity sensor in a simple manner and from separate components. The sensor electrodes are pressed into the carrier material as cables or wires and kept at a defined distance from each other within it. Stable intervening spaces and orientation are ensured throughout the entire mounting distance with the carrier material in accordance with the invention. Due to the carrier forming process, it is possible to guide the sensor electrodes reproducibly and precisely within a desired arrangement and orientation towards each other. 
         [0014]    The embodiment with separate components for the sensor electrodes on the one hand and the carrier material on the other hand allows very effective production. The carrier can be commonly produced by extrusion from a suitable plastic material, while the cables or wires are available mass wares. The individual components are easily combined with each other and also easily separated from each other again, which simplifies repair in case of defects. 
         [0015]    Depending on requirements, the recesses can be formed so as to be safeguarded against confusion, e.g. with differing sizes for different wire or cable diameters. In this manner, the sensor electrode and auxiliary electrodes may be formed from differing cable types. Due to the specified mount recess, the possibility of switching cables during assembly is largely excluded. 
         [0016]    In accordance with the invention, the carrier may be formed as a straight lined body with parallel straight lined wiring segments. However it is also possible to form the carrier with a bend or arch, for example if the sensor module is to be used in correspondingly formed parts of a motor vehicle. 
         [0017]    In accordance with a preferred embodiment, not only a sensor electrode and a first auxiliary electrode are built into the carrier, but an additional auxiliary electrode is also intended to be mounted. In this manner, an initially explained array with a sensor electrode, shielding electrode (first auxiliary electrode) and background electrode (second auxiliary electrode can be built. Herein the electrodes are commonly held in corresponding recesses in a straight lined arrangement. 
         [0018]    The three electrodes which lie beside each other or behind each other preferably have varying gaps, wherein the sensor electrode is farther away from the two auxiliary electrodes than the two auxiliary electrodes from each other. In other words, there is a larger distance between the sensor electrode and the shielding electrode than between the shielding electrode and the background electrode. 
         [0019]    In a further embodiment, at least one of the electrodes is formed from a mantled cable. It is fundamentally possible to form one or more of the electrodes from wires in order to influence the spread and detection of electrical fields to the lowest possible degree. However mantled cables are preferably used, due to the simplicity of handling, robustness and their insensitivity to environmental influences. 
         [0020]    In a preferred embodiment, the carrier possesses a holding segment and a fastening segment, wherein the holding segment is intended to hold the various electrodes and has the corresponding recesses. The fastening segment is used to position and fasten the sensor module in its intended location, for example on the inside of a bumper in a motor vehicle. The fastening segment may have fastening elements for this purpose. Alternatively the fastening segment may be glued in at its intended location. 
         [0021]    A preferred mode of fastening the sensor module is by using a clip provided at the intended location which is able to grasp around the fastening segment on the sensor module, so that the sensor module is held within the clip in a stable but detachable manner. For this purpose, the clip may be formed e.g. from spring steel or an elastic plastic material. 
         [0022]    In a further embodiment, the carrier is integrally formed with a corresponding component of a motor vehicle, such as a bumper. A segment of the corresponding motor vehicle component then has the recesses into which the sensor electrodes are embedded. In this manner, it is possible to provide appropriate recesses within all components of a series, but to provide the corresponding electrodes and circuits only in those places where this function is actually desired in the respective vehicle. 
         [0023]    Advantageous and/or preferred embodiments are described in the Sub-Claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]    The invention is now explained in further detail using the included figures. 
           [0025]      FIG. 1  shows the carrier of a sensor module in accordance with the invention in a first embodiment; 
           [0026]      FIG. 2  shows a frontal view of a sensor module in accordance with the invention; 
           [0027]      FIG. 3  shows the sensor module from  FIG. 2  in a perspective view; 
           [0028]      FIG. 4  shows a schematic view of the connection of the sensor module to a control and evaluation circuit. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0029]      FIG. 1  shows a carrier  1  which possesses a fastening segment  2  and a mount segment  3 . The mount segment  3  contains recesses  4 A,  4 B,  4 C which serve to receive the electrodes. The carrier  1  is formed as an extrusion body out of plastic. The recesses  4 A,  4 B,  4 C each possess circular empty spaces within their cross-sections, which are opened along a circular segment. Cables or wires can be pressed in through these openings to be held within the recesses. 
         [0030]      FIG. 2  shows the carrier with inserted electrodes  5 A,  5 B and  5 C as well as a fastening clip  6 . 
         [0031]    The electrode  5 A is placed in the recess  4 A, the electrode  5 B in the recess  4 B, and the electrode  5 C in the recess  4 C. 
         [0032]    The clip grasps around the fastening segment  2 , fixing it firmly in place. The clip  6  has suitable elasticity and angled receiving edges in order to allow easy insertion of the fastening segment  2  into the clip  6 . 
         [0033]    This view shows that the wires or cables  5 A,  5 B,  5 C are held in their respective inserted positions, since they are grasped along their circumference to more than half of their circumference. Even though the cables are equidistantly arranged in this example, distribution with differing gaps can be implemented without problems. Differing wire thicknesses can also be used without difficulty. 
         [0034]      FIG. 3  shows the arrangement from  FIG. 2  in a perspective view, wherein the cables or wires  5 A,  5 B,  5 C are partly brought out of the carrier. The control and evaluation electronics are connected in this segment. 
         [0035]      FIG. 4  shows a principle diagram of the corresponding switching of the sensor module in accordance with the invention. The electrode  5 A as the second auxiliary electrode or background electrode is connected to the control circuit  10  and lies on mass potential. The electrode  5 B is the active shielding electrode or first auxiliary electrode and is likewise connected to the control circuit  10 . The sensor electrode  5 C is arranged adjacent to the fastening segment  2  and also connected to the control circuit  10 . 
         [0036]    In such a structure, the electrode would, during installation into a vehicle, be oriented, for example, so that the clip  6  is arranged on the inside of a bumper, so that the electrode  5 A faces the vehicle. The sensor electrode  5 C then faces the bumper side and can, for example, detect the approach of a user&#39;s legs or feet. In this manner, for example, it is possible to detect the approach of feet in the area below a bumper to trigger automatic opening of a rear hatch in the vehicle. 
         [0037]    A corresponding arrangement of the exemplary embodiment within a bumper is shown in  FIGS. 5A and 5B . Two sensor modules are arranged within the inside of a bumper that faces the road-side covering. 
         [0038]    The control and evaluation circuit  10  detects a capacity change in the capacity of the sensor electrode  5 C as compared to a reference potential by periodically charging and discharging the sensor electrode with a predetermined frequency and evaluating at least one parameter of a current or voltage progression that is dependent on the periodic charging and discharging of the sensor electrode in order to detect the capacity change. The periodic charging and discharging is, for example, implemented by periodically connecting the sensor electrode  5 C at the predetermined frequency to a specified potential, such as the operating voltage potential. The voltage progression may, for example, consist of the voltage progression at the connection of the sensor electrode. The parameter may, for example, consist of a voltage that is measured over a condenser that accumulates a charge, or a specific number of periods of charging and discharging until a switching threshold is exceeded by a voltage measured at the sensor electrode. The shielding electrode  5 B is connected to the sensor electrode via the control and evaluation circuit in such a manner that its potential largely follows the potential of the sensor electrode. The connection takes place so that the shielding electrode  5 B has no influence on the capacity change in the sensor electrode that is measured in comparison to the reference potential. The term of “following” herein aims to describe that the potential of the shielding electrode  5 B must not necessarily be equal to the potential of the sensor electrode  5 C, and that there may be a time delay between the progression of the potential of the sensor electrode and the potential of the shielding electrode. The word “largely” furthermore intends to express that the shielding electrode does not have to follow the potential of the sensor electrode throughout the full periods of charging and discharging the sensor electrode; it is sufficient for it to follow this potential at least in partial segments of the periods, for example that it follows the potential of the sensor electrode while the sensor electrode charges, and drops to mass potential while the sensor electrode discharges, while the potential of the sensor electrode still remains at a potential that differs from mass. 
         [0039]    The background electrode is, for example, set to a constant potential such as mass or operating voltage. Alternatively, the background electrode may be periodically placed on mass and another potential, such as the operating voltage, at the specified frequency, wherein this should preferably occur in a complementary relation to the sensor electrode, as it is, for example, described in the parallel pending patent application by the Applicant with the title “Capacitive sensor array with a sensor electrode, a shielding electrode and a background electrode”. The detection area of the sensor array, originating from the sensor electrode  4 C, extends into an angle area which faces away from the shielding electrode  5 B. 
         [0040]    The entire array or individual electrodes may be surrounded by insulator materials. A plastic layer that surrounds the sensor electrode may be provided particularly between the sensor electrode and the detection area. It is particularly advantageous if this layer is surrounded by a first thickness and an outer plastic layer of a second thickness that is arranged at a specified distance, wherein the insulator materials are arranged so that the relative dielectricity constant initially assumes a relatively high value of the surrounding plastic layer as the distance from the sensor electrode increases, then drops to a value that approaches the value of 1 (for example, the value of air) and then rises again to a relatively high value of the outer plastic layer. 
         [0041]    It was shown that when a space was specifically created between the plastic layer that forms the outer surface which may be contaminated by environmental influences and the plastic layer that surrounds the sensor electrode with a dielectricity constant that approximates the value of 1, it was possible to reduce or avoid the interfering influences of moisture contamination. Corresponding additional layers can be applied e.g. using common coating procedures in the completion of assembly. 
         [0042]    Numerous variations are possible within the scope of the invention. In particular, the plastic carrier can be designed as desired, e.g. with further fastening segments, with mechanical stabilization braces or thickened areas, or from a variety of materials. It is significant that the carrier has recesses into which the wires or cables can be placed to form sensor or auxiliary electrodes, and in which they are held. 
         [0043]    In principle, it is also possible to form carriers whose number of recesses exceeds the number of electrodes which will be used in an application. For instance, it would then be possible to form universal carriers in which sensor cables are placed at differing intervals as needed, or sensor cables with differing cross-sections are placed. The same carrier can then be used to form different sensor arrays.