Capacitive occupant classification sensor with load-dependent antenna range

Abstract

A capacitive sensor element (130) of a vehicle seat occupant detection and classification device (18) comprises a first electrically conductive antenna element (132) and at least one second electrically conductive antenna element (134), which are arranged adjacent to the first electrically conductive antenna element (132) without galvanic connection to each other. At least one electrically conductive bridging element (146) is fixedly attached to at least one elastic spacer element (148) which has elastic mechanical properties in a specified direction (54).If a mechanical load (F) is applied to the capacitive sensor element (130) in the specified direction (54) which is equal to or greater than a predetermined value for the mechanical load (F), the at least one electrically conductive bridging element (146) provides at least one galvanic contact between the first electrically conductive antenna element (132) and the second electrically conductive antenna element (134).

Description

Technical field

[0001] The present invention generally relates to a capacitive sensor element of a vehicle seat occupant detection and classification device, a vehicle seat occupant detection and classification device comprising such a capacitive sensor element, and a vehicle seat comprising such a vehicle seat occupant detection and classification device. Background of the invention

[0002] The use of vehicle seat occupancy detection systems is now widespread in vehicles, particularly passenger cars, to provide a seat occupancy signal to various devices, for example, for use in a seat belt reminder (SBR) system or as activation control for an auxiliary restraint system (ARS). Seat occupancy detection systems comprise seat occupancy sensors, which are known to exist in a number of variations, such as those based on capacitive sensing, deformation sensing, or pressure / force sensing. To meet requirements for easy integration and field suitability, weight-sensitive seat occupancy sensors are typically located on the B-surface of a vehicle seat, i.e., between the foam core of a seat cushion and the seat shell or cushion support springs.

[0003] Furthermore, vehicle seat occupancy detection systems are known to be used as a means of assessing a potential activation of an installed passenger restraint system in the vehicle, such as an airbag.

[0004] Capacitive detection systems for vehicles, using capacitive sensors operating in charging mode, are also used to detect vehicle seat occupancy. The capacitive sensors can be configured as capacitive measuring sensors without a protective electrode, featuring a single sensing electrode. Alternatively, they can be configured as capacitive protective sensing sensors with a sensing electrode and a protective electrode, positioned proximally and isolated from each other.

[0005] It is also known in the field to combine capacitive sensors and weight-sensitive sensors in vehicle seat occupancy detection systems.

[0006] For example, US patent 7,180,306 B2 describes an occupant detection system comprising a weight sensor and an electric field sensor, each operationally coupled to a seat. The electric field sensor generates an electric field from at least one electrode in the base of the seat, triggers a response to the occupant's influence, and is capable of distinguishing the response to the state of a seated infant or child from other seated states. If a weight measurement from the weight sensor falls below a threshold, or if the electric field sensor detects a child's seated state, a signal processor deactivates an associated restraint actuator.The electric field sensor can include multiple electrodes over a first and a second region at varying proximity to a seated infant or child, or at least one electrode in conjunction with a shield or void over at least one of the regions.

[0007] Another occupant detection device with combined sensors for detecting an occupant sitting in the front passenger seat of a vehicle is described in patent application US 2002 / 0038947A1. The occupant detection device includes several electric field sensors located in the lower and rear sections of the seat, as well as a mechanical load sensor and an accelerometer. The electric field sensors are connected to a control unit comprising a high-frequency oscillator, a resistor, a voltage buffer, and a detector. Antenna electrodes are selected by the selectors and connected between the resistor and the voltage buffer. An analog-to-digital converter performs an analog-to-digital conversion on the output signals of the selected electric field sensors.Digital output signals from the electric field sensors, the mechanical load sensor and the accelerometer are connected to a central unit which determines seat occupancy according to predetermined criteria based on the sensor output signals.

[0008] In another prior art solution, disclosed in document EP 2 062 789 A1, an occupant detection system for a vehicle seat combines a capacity-based occupancy sensor and a weight-based occupancy sensor. The capacity-based sensor includes an antenna array and provides an occupancy signal when an adult occupies the seat. The weight-based occupancy sensor is a switching sensor integrated within the antenna array of the capacity-based sensor. The switching sensor provides an occupancy signal even when an adult occupies the vehicle seat. The occupant detection system further includes a controller that sends an error message if the weight-based sensor, and not the capacity-based sensor, detects occupancy.

[0009] Further methods or devices for capacitive object detection in vehicles are known by way of example from the publications DE 198 12 626 A1 and DE 10 2009 055 424 A1, while a combined resistance and capacitance measurement system is disclosed in DE 10 2011 006 344 A1.

[0010] A disadvantage of using vehicle seat occupancy detection and classification devices based solely on capacitive sensor elements is the inability to correctly classify seat occupancy when vehicle-grounded objects, such as an electrical device connected to the vehicle chassis via a charging cable or a child restraint seat (CRS, such as ISOFIX) grounded by hooks mechanically connected to the vehicle body, are placed on the seat. The vehicle seat occupancy detection and classification device relies on measurements of a physical quantity, such as an electric current through the capacitive sensor element, or a complex impedance or apparent conductance of the capacitive sensor element, where the physical quantity represents an electric field between the capacitive sensor and the vehicle body.The vehicle body is electrically connected to a vehicle ground. The capacitive sensor element can be positioned on or inside the vehicle seat. A seat occupant or an object placed on the vehicle seat modifies the electrical field, resulting in a change in the physical quantity. In this way, an object connected to ground, due to a relatively small distance between the capacitive sensor element and the grounded object, can lead to a misclassification by the vehicle seat occupant detection and classification device.

[0011] Vehicle seat occupant detection and classification devices based on mechanical load sensors can function well in the presence of an ISOFIX CRS or a grounded electrical device. These devices do not add significant weight to the seat. Compared to load-based resistance measurement, capacitive measurement offers the advantages of simpler wiring and stable, reproducible measurement over the entire temperature range specified in typical vehicle requirements.

[0012] The need to use mechanical load sensors to close the information gap described above increases the hardware effort, complexity and cost of such vehicle seat occupancy and classification devices. Object of the invention

[0013] It is therefore desirable to provide a vehicle seat occupant detection system that is able to reliably and correctly classify seat occupancy without the disadvantages described above. General description of the invention

[0014] According to one aspect of the present invention, the problem is solved by a capacitive sensor element of a vehicle seat occupant detection and classification device, wherein the capacitive sensor element comprises the following: - a first electrically conductive antenna element that can be electrically connected to a capacitance measurement circuit to determine the capacitance of the capacitive sensor element, - at least one second electrically conductive antenna element, arranged adjacent to the first electrically conductive antenna element without any galvanic connection to each other, - at least one electrically conductive bridging element arranged such that it partially overlaps the first electrically conductive antenna element and the second electrically conductive antenna element in a specified direction, and - at least one elastic spacer element that exhibits elastic mechanical properties at least in the specified direction.

[0015] The at least one electrically conductive bridging element is fixedly attached to the at least one elastic spacer element. The first electrically conductive antenna element and the second electrically conductive antenna element remain galvanically isolated from each other when a mechanical load, less than a predetermined value, is applied to the capacitive sensor element in the specified direction.

[0016] Furthermore, the at least one electrically conductive bridging element provides at least one galvanic contact between the first electrically conductive antenna element and the second electrically conductive antenna element when a mechanical load equal to or greater than the predetermined value for the mechanical load is applied to the capacitive sensor element in the specified direction.

[0017] The term “overlap in one direction”, as used in this application, is understood to mean an overlap of two objects as seen in that direction.

[0018] The seat occupant classification may have at least two classes selected from a group consisting of "empty", "child" and "adult".

[0019] The term "electrically connectable" or "connectable," as used in this application, is to be understood as encompassing galvanic electrical connections as well as connections established by capacitive and / or inductive electromagnetic coupling. The term "galvanic contact," as used in this application, is understood in particular to mean an electrical contact capable of conducting direct current (DC). Similarly, the term "galvanically isolated," as used in this application, is understood in this sense, specifically to mean that it does not conduct direct current (DC) between galvanically isolated objects.

[0020] The term “elastic”, as used in this application, is understood in particular to mean the property of exhibiting reversible deformation when an external force is applied, and it is intended to include reversible deformation according to linear and non-linear stress-strain behavior, such as rubber or latex.

[0021] The term “firmly attached”, as used in this application, is understood in particular to mean that an object moves in the same way as a moving object that is firmly attached to it, and vice versa.

[0022] It is hereby noted that the terms "first", "second", etc. are used for distinguishing purposes only and are in no way intended to indicate or anticipate any order or priority.

[0023] The predetermined value for the mechanical load can be chosen such that an adult seat occupant causes at least one electrically conductive bridging element to establish a galvanic contact between the first electrically conductive antenna element and the second electrically conductive antenna element. This increases the overall sensitive antenna element area, resulting in a larger reading from the capacitance measuring circuit.

[0024] An electrical device placed on the seat cushion and connected to the vehicle chassis does not cause at least one electrically conductive bridging element to establish a galvanic contact between the first and second electrically conductive antenna elements. Similarly, by appropriately arranging the bridging elements, an ISOFIX CRS will not trigger the bridging elements due to the CRS's low weight distribution. Consequently, the entire sensitive antenna element area is that of the first electrically conductive antenna element, resulting in a lower reading from the capacitance measuring circuit.

[0025] Due to the force-dependent sensitive antenna element area, the capacitive sensor element therefore makes it possible to distinguish between an adult seat occupant and, for example, an electrical device connected to the vehicle ground or an ISOFIX CRS placed on the seat cushion.

[0026] The invention is based on the understanding that grounded electrical devices and an ISOFIX CRS could result in high capacitance values ​​but always have a low weight distribution, i.e., low surface pressure exerted on the capacitive sensor element. Seatbelt-mounted CRSs are not normally connected to ground and therefore have low capacitance values. However, these seatbelt-mounted CRSs could result in high surface pressures. This means that a seatbelt-mounted CRS could cause at least one electrically conductive bridging element to establish a galvanic contact between the first and second electrically conductive antenna elements. Due to the low capacitance values, however, this is not problematic. High capacitance values ​​combined with high surface pressure values ​​only occur with adult seat occupants.These criteria are used to enable the desired differentiation of seat occupancy. Capacitive measurement is concentrated on areas with high surface pressure, and there is no need to measure mechanical load and capacity independently.

[0027] A wide variety of capacitance measurement circuits for determining the capacitance of the capacitive sensor element are known in the field, and these will therefore not be described in detail here. Any capacitance measurement circuit that appears suitable to a person skilled in the art can be used.

[0028] The term “determining a capacity”, as used in this application, is to be understood as encompassing an absolute measurement of a capacity value as well as a measurement of a capacity value relative to an arbitrarily determined capacity of zero.

[0029] Preferably, the at least one capacitive sensor is operated in charging mode. The term "charging mode," as used in this application, is to be understood in particular as a mode for measuring a displacement current caused by the presence of a grounded object near a single sensing electrode (see J. Smith et al., Electric field sensing for graphical interfaces, IEEE Comput. Graph. Appl., 18(3):54-60, 1998). In general, it is also considered in some embodiments to operate the at least one capacitive sensor in transmit mode or in parallel mode. These two modes are also described in the aforementioned article, which is incorporated herein by reference.

[0030] In a preferred embodiment of the capacitive sensor element, at least one of the first electrically conductive antenna element and the second electrically conductive antenna element have a planar shape and are arranged and mounted on a planar surface of an electrically insulating support element. In this way, a simple shape of the capacitive sensor element can be achieved.

[0031] If at least one of the first electrically conductive antenna element and the second electrically conductive antenna element is designed as an electrically conductive strip that is firmly attached to a surface of an electrically insulating substrate, a reliable and cost-effective embodiment of the capacitive sensor element with low manufacturing tolerance margins can be provided.

[0032] In some embodiments, the electrically insulating substrate can be formed by a printed circuit board substrate, and the first and second electrically conductive antenna elements are formed from conductive layers, e.g., metal layers, which are laminated onto the printed circuit board substrate, for example, using an etching process. In other embodiments, the electrically insulating substrate can be formed by a polymer layer or film, and the first and second electrically conductive antenna elements are formed from a conductive material, e.g., a conductive graphite material, a metal, or a conductive polymer, which is deposited or printed onto the substrate.

[0033] In a further preferred embodiment of the capacitive sensor element, a region enclosed by the second electrically conductive antenna element comprises a region enclosed by the first electrically conductive antenna element. The term "region enclosed by an object," as used in this application, is understood in particular to mean a region of the smallest regular quadrilateral that completely covers the object in the specified direction. In this way, a compact shape of the capacitive sensor element can be achieved.

[0034] In yet another preferred embodiment, the capacitive sensor element further comprises a third electrically conductive antenna element, which is arranged adjacent to the first electrically conductive antenna element and the second electrically conductive antenna element without galvanic connection.

[0035] The first electrically conductive antenna element forms a single loop. An area enclosed by the second electrically conductive antenna element encompasses an area enclosed by the first electrically conductive antenna element. An area enclosed by the first electrically conductive antenna element encompasses an area enclosed by the third electrically conductive antenna element.

[0036] The first electrically conductive antenna element and the third electrically conductive antenna element remain galvanically isolated from each other when a mechanical load, which is below a predetermined value for the mechanical load, is applied to the capacitive sensor element in the specified direction.

[0037] The at least one electrically conductive bridging element provides at least one galvanic connection / contact between the first electrically conductive antenna element and the third electrically conductive antenna element when a mechanical load equal to or greater than the predetermined value is applied to the capacitive sensor element in the specified direction. In this way, a very compact shape of the capacitive sensor element can be achieved, with a significant difference between the total sensitive antenna area under an applied mechanical load below the predetermined value and the total sensitive antenna area under an applied mechanical load equal to or greater than the predetermined value.

[0038] In some embodiments, the single loop formed by the first antenna element can have an elliptical, in particular circular, shape, or it can have a rectangular, in particular square, shape.

[0039] In another preferred embodiment, the capacitive sensor element comprises - several second electrically conductive antenna elements arranged in a plane and adjacent to the first electrically conductive antenna element without galvanic connection to each other and without galvanic connection to the first electrically conductive antenna element, - several electrically conductive bridging elements, each arranged such that they partially overlap the first electrically conductive antenna element and at least one of the second electrically conductive antenna elements in the specified direction, and - several elastic spacer elements that exhibit elastic mechanical properties at least in the specified direction.

[0040] Each of the several electrically conductive bridging elements is firmly attached to one of the several elastic spacer elements.

[0041] The first electrically conductive antenna element and one specific of the several second electrically conductive antenna elements, which are partially overlapped by one specific of the several electrically conductive bridging elements, remain galvanically isolated from each other when a mechanical load, which is smaller than a specific predetermined value for the mechanical load, is applied in the specified direction to the specific one of the several elastic spacer elements to which the specific one of the several electrically conductive bridging elements is rigidly attached.

[0042] The specific one of the several electrically conductive bridging elements provides at least one galvanic contact between the first electrically conductive antenna element and the specific one of the several second electrically conductive antenna elements, which it partially overlaps, when a mechanical load equal to or greater than the specific predetermined value for the mechanical load is applied in the specified direction to the specific one of the several elastic spacer elements to which the specific one of the several electrically conductive bridging elements is firmly attached.

[0043] In this way, the capacitive measurement is concentrated on areas of high surface pressure. It is unnecessary to measure the applied mechanical load and capacitance independently, thus avoiding misclassification of objects such as the ISOFIX CRS and electronic devices connected to ground. It should be noted that, depending on the configuration and arrangement of the multiple secondary electrically conductive antenna elements and the corresponding bridging elements, a CRS could activate some of the secondary antenna elements, but will never activate all of the bridging elements.

[0044] The advantage of this system is as follows: CRS (Combined Safety Seats) either have a high weight distribution or a high capacitance. Strapped-in CRS are not normally connected to ground, so they have a low capacitance. However, they are heavy and activate some or all of the bridging elements. ISOFIX CRS can have a high capacitance due to grounding, but they are secured by the ISOFIX connectors, so they have a low weight distribution and only activate a few bridging elements. Thus, the sensitivity of the capacitive sensor element is automatically adjusted by the activation of the bridging elements, enabling differentiation between adult seat occupants and ISOFIX CRS seats.

[0045] In some preferred embodiments, the capacitive sensor element further comprises an electrically conductive protective electrode, which is arranged proximally to and galvanically insulated from the first electrically conductive antenna element, the second electrically conductive antenna element or the multiple second electrically conductive antenna elements, and, if applicable, the third electrically conductive antenna element. The electrically conductive protective electrode substantially overlaps, in the specified direction, the area enclosed by one of the first electrically conductive antenna elements, the second electrically conductive antenna element, or the multiple second electrically conductive antenna elements, and, if applicable, the third electrically conductive antenna element.

[0046] In this way, a capacitive sensor element can be provided that can be used as a capacitive protective sensing sensor element. The technique of "protection" is well-known in the field and is frequently used to deliberately mask and thus shape the sensitivity state of a capacitive sensor element. For this purpose, the capacitance measurement circuit is designed to keep the protective electrode at the same electrical potential as the first electrically conductive antenna element.

[0047] According to a further aspect of the invention, a vehicle seat occupant detection and classification device is provided, comprising at least one embodiment of the disclosed capacitive sensor element, a capacitance measuring circuit for determining a capacitance of the capacitive sensor element, and an evaluation unit designed to receive an output signal from the capacitance measuring circuit and to provide a seat occupant classification based on a level of the received output signal and at least one predetermined threshold of the output signal.

[0048] In this way, the advantages provided by the disclosed capacitive sensor element also apply to the vehicle seat occupant detection and classification device.

[0049] According to a further aspect of the invention, a vehicle seat is provided which comprises a seat structure for erecting the vehicle seat on a passenger compartment floor of the vehicle, a seat cushion with at least one seat foam element, a seat base supported by the seat structure and designed to receive the seat cushion, wherein the seat base and the seat cushion are provided to support the buttocks of a seat occupant, a backrest provided to support the back of the seat occupant, and an embodiment of the disclosed vehicle seat occupant detection and classification system.

[0050] In this way, the advantages provided by the disclosed capacitive sensor element also apply to the vehicle seat. Brief description of the drawings

[0051] Further details and advantages of the present invention will become apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings, wherein: Fig. Figure 1 schematically shows a vehicle seat and a vehicle seat occupant detection and classification device in a combined perspective and partial exploded view, comprising a capacitive sensor element according to the invention; Fig. 2. Schematic details of the capacitive sensor element according to Fig. 1 shows in an exploded view; Fig. 3a a schematic top view of the capacitive sensor element according to the Fig. 1 and Fig. 2 is in a mechanically unstressed state, Fig. 3b is a schematic cross-sectional view of a section of the capacitive sensor element in the mechanically unloaded state, Fig. 4a a schematic top view of the capacitive sensor element according to the Fig. 1 and Fig. 2 is in a state of applying a mechanical force greater than a predetermined value, Fig. 4b is a schematic cross-sectional view of the section of the capacitive sensor element in the state of applying a mechanical force greater than the predetermined value. Fig. 5 a schematic top view of an alternative embodiment of a capacitive sensor element according to the invention, Fig. 6 Sensing parts of the alternative embodiment of the capacitive sensor element according to Fig. 5 illustrated in three different mechanical load situations, Fig. 7 the activation of the sensing parts of the capacitive sensor element according to Fig. 5 illustrates for a seat occupied by an ISOFIX CRS, and Fig. 8 the activation of the sensing parts of the capacitive sensor element according to Fig. Figure 5 illustrates a seat occupied by a strapped-in CRS. Description of preferred embodiments

[0052] The following discloses embodiments of capacitive sensor elements according to the invention. The individual embodiments are described with reference to a particular figure and are identified by a preceding number of the particular embodiment. Features whose function is the same or fundamentally the same in all embodiments are identified by reference numerals consisting of the preceding number of the embodiment to which they refer, followed by the number of the feature. If a feature of an embodiment is not described in the corresponding description of the figure, or if a reference numeral mentioned in a description of the figure is not shown in the figure itself, reference is made instead to the description of a preceding embodiment.

[0053] Fig. Figure 1 schematically illustrates (not to scale) a vehicle seat 10 with an installed vehicle seat occupant detection and classification device 18, comprising a capacitive sensor element 130 according to the invention, in a combined perspective and partial exploded view.

[0054] The vehicle seat 10 is formed by a passenger car seat and comprises a seat structure (not shown) by which it is erected on a passenger compartment floor of the passenger car, as is generally known in the field. The vehicle seat 10 further comprises a seat base supported by the seat structure and designed to receive a seat cushion 12 to provide comfort to the seat occupant. The seat cushion 12 of the vehicle seat 10 comprises a seat foam element and a fabric cover, which is Fig. Item 1 has been omitted. The seat base and seat cushion 12 are intended to support the buttocks of the seat occupant. A backrest 16 of the vehicle seat 10 is intended to support the back of the seat occupant.

[0055] The seat cushion 12 comprises an upper surface (A-surface 14) and a base surface (B-surface). The seat base has an upper surface to receive the seat cushion 12, such that the B-surface of the seat cushion 12 is in mechanical contact with the upper surface of the seat base. A rear edge of the seat cushion 12 is proximal to the backrest 16, and a front edge of the seat cushion 12, intended to support the lower thigh area of ​​an adult seat occupant, is distal to the backrest 16.

[0056] The vehicle seat occupant detection and classification device 18 comprises the capacitive sensor element 130, a capacitance measuring circuit 20 for determining the capacitance of the capacitive sensor element 130, and an evaluation unit 26. The capacitive sensor element 130 is located on the A-surface 14 of the seat cushion 12 under the fabric cover. The capacitance measuring circuit 20 and the evaluation unit 26 are installed in the vehicle away from the vehicle seat 10.

[0057] The capacitance measuring circuit 20 comprises a signal generation unit 22 for generating a periodic, time-dependent signal to be applied to the capacitive sensor element 130, and a sensing circuit 24 for sensing a physical quantity that indicates a capacitance of the capacitive sensor element 130.

[0058] The evaluation unit 26 is designed to receive an output signal from the capacitance measuring circuit 20, which indicates the capacitance of the capacitive sensor element 130 as an input signal, and is designed to provide a seat occupant classification based on the level of the received input signal and two distinct predetermined threshold values ​​for the input signal. The seat occupant classification includes the occupancy classes "empty," "child," and "adult." The evaluation unit 26 is further designed to generate an output signal 28 that indicates a seat occupancy classification. The output signal 28 generated by the evaluation unit 26 is fed to an airbag control unit 58 of the vehicle via a CAN communication link 56 for the purpose of airbag activation control. For example, if the transmitted output signal 28 represents the occupancy class "adult," an airbag of the vehicle seat 10 is deployed.

[0059] Now, with reference to the Fig. 2, Fig. 3a and Fig. 3b the capacitive sensor element 130 comprises a first electrically conductive antenna element 132, a second electrically conductive antenna element 134 and a third electrically conductive antenna element 136. The first electrically conductive antenna element 132, the second electrically conductive antenna element 134 and the third electrically conductive antenna element 136 have a planar design and are arranged on and attached to a planar surface of an electrically insulating support element 138.

[0060] The first electrically conductive antenna element 132 is formed by a narrow metal strip (compared to a lateral extension of the electrically conductive antenna element) shaped as a single rectangular loop and comprising two terminals 144 at the ends of the loop, through which it is electrically connected to the capacitance measuring circuit 20. The second electrically conductive antenna element 134 is shaped as a U-shaped metal strip and is arranged adjacent to the first electrically conductive antenna element 132 such that the open side of the U faces the two terminals 144 of the first electrically conductive antenna element 132.The third electrically conductive antenna element 136 is formed as a rectangular piece of sheet metal, which is arranged adjacent to both the first electrically conductive antenna element 132 and the second electrically conductive antenna element 134, such that the single loop of the first electrically conductive antenna element 132 almost completely surrounds the third electrically conductive antenna element 136, and the rectangular piece of sheet metal forming the third electrically conductive antenna element 136 is arranged inside the U-shape of the second electrically conductive antenna element 134.

[0061] Thus, an area enclosed by the second electrically conductive antenna element 134 includes an area enclosed by the first electrically conductive antenna element 132, which in turn includes an area enclosed by the third electrically conductive antenna element 136, resulting in a compact installation area for the capacitive sensor element 130.

[0062] How to best get from the Fig. 3a and Fig. As can be seen in Figure 3b, the first electrically conductive antenna element 132, the second electrically conductive antenna element 134 and the third electrically conductive antenna element 136 do not have a galvanic connection with each other.

[0063] The first electrically conductive antenna element 132, the second electrically conductive antenna element 134, and the third electrically conductive antenna element 136 are readily formed by applying an electrically conductive material to an upper surface 140 of the electrically insulating support element 138, which is designed as an electrically insulating substrate consisting of a polyethylene terephthalate (PET) layer. The bottom surface of the electrically insulating support element 138 is equipped with an electrically conductive layer applied to the PET layer and designed to serve as a protective electrode 142. The electrically conductive material of the antenna elements and / or the protective electrode, e.g., a metal, a graphite material, or an electrically conductive polymer, can be applied to the substrate by, for example, printing, deposition, lamination, or any other suitable application technique.

[0064] The protective electrode 142 is arranged proximally and is insulated from the first electrically conductive antenna element 132, the second electrically conductive antenna element 134, and the third electrically conductive antenna element 136. The electrically conductive protective electrode 142 overlaps, in a specified direction 54, which is directed towards the upper surface 140 of the electrically insulating support element 138 and perpendicular to it, substantially the area enclosed by the first electrically conductive antenna element 132, the second electrically conductive antenna element 134, and the third electrically conductive antenna element 136.

[0065] Furthermore, the capacitive sensor element 130 comprises four electrically conductive bridging elements 146, each arranged such that they partially overlap the first electrically conductive antenna element 132, the second electrically conductive antenna element 134 and the third electrically conductive antenna element 136 in the specified direction 154.

[0066] For this purpose, each of the electrically conductive bridging elements 146 is designed as a circular metal ring, which is arranged, with respect to one direction opposite to the specified direction 54, over one of the four corners of the individual electrically conductive loop of the first electrically conductive antenna element 132. Each of the electrically conductive bridging elements 146 is fixedly attached to one of four identically designed elastic spacer elements 148 of the capacitive sensor element 130. Each of the four elastic spacer elements 148, which are made of an electrically non-conductive PET, is designed to have a transverse element 150 having an upper surface and a lower surface, both of which are arranged substantially parallel to the upper surface 140 of the electrically insulating support element 138. The lower surface is arranged so that it faces the electrically insulating support element 138.Each elastic spacer 148 has an electrically conductive bridging element 146 fixedly attached to the lower surface of the transverse element 150. Furthermore, each elastic spacer 148 comprises a projection 152, which is formed integrally at each end of the transverse element 150 and projects perpendicularly from the transverse element 150 to the electrically insulating support element 138. One projection 152 of each elastic spacer 148 is attached to the second electrically conductive antenna element 134 by means of an adhesive, and the other projection 152 of each elastic spacer 148 is attached to the third electrically conductive antenna element 136.

[0067] As in Fig. Figure 3b shows a mechanically unloaded state in which no external force is applied in the specified direction 54, and each of the electrically conductive bridging elements 146 is arranged in a spaced-apart relationship to the first electrically conductive antenna element 132, the second electrically conductive antenna element 134 and the third electrically conductive antenna element 136.

[0068] The elastic spacer elements 148 have elastic mechanical properties in the specified direction 54 and are capable of being reversibly deflected when an external force is applied in the specified direction 54. If a mechanical load F is applied to the capacitive sensor element 130 in the specified direction 54, at least one of the electrically conductive bridging elements 146 approaches the first electrically conductive antenna element 132, the second electrically conductive antenna element 134, and the third electrically conductive antenna element 136.

[0069] As long as the mechanical load F applied to the capacitive sensor element 130 in the specified direction 54 is below a predetermined value for the mechanical load F, which is essentially selected to be below a mechanical load F applied to the vehicle seat 10 by an electrical device placed on the seat or by an ISOFIX child restraint seat, the first electrically conductive antenna element 132, the second electrically conductive antenna element 134, and the third electrically conductive antenna element 136 remain galvanically isolated from each other. Under this condition of mechanical load F, the first electrically conductive antenna element 132, which is connected to the capacitance measuring circuit 20, is the only sensing part of the capacitive sensor element 130.An electronic device, or, if the bridging elements 146 are arranged appropriately, an empty ISOFIX CRS, which is grounded, for example, to a vehicle body and positioned on the seat cushion 12 of the vehicle seat 10, causes a mechanical load F on the bridging elements 146, which fall under this condition. Thus, the output signal from the capacitance measuring circuit 20, which indicates a capacitance of the capacitive sensor element 130, remains below the lower of the two predetermined threshold values, and the evaluation unit 26 generates an output signal 28 indicating the seat occupancy classification "empty".

[0070] As soon as the mechanical load F applied to the capacitive sensor element 130 in the specified direction 54 is equal to or greater than the predetermined value for the mechanical load F, which is the case when a child is positioned in a child seat or an adult on the seat cushion 12, at least one galvanic contact is provided between the first electrically conductive antenna element 132, the second electrically conductive antenna element 134, and the third electrically conductive antenna element 136 by means of the electrically conductive bridging elements 146. This situation is described in the Fig. 4a and Fig. Figure 4b illustrates this. In this way, the second electrically conductive antenna element 134 and the third electrically conductive antenna element 136 are galvanically connected to the capacitance measuring circuit 20, as is the first electrically conductive antenna element 132.

[0071] Under this mechanical load condition F, the first electrically conductive antenna element 132, the second electrically conductive antenna element 134, and the third electrically conductive antenna element 136 become sensing elements of the capacitive sensor element 130. Thus, when the vehicle seat 10 is occupied by the child in the child seat, the output signal from the capacitance measuring circuit 20, which indicates a capacitance of the capacitive sensor element 130, lies above the lower of the two predetermined thresholds and below the higher of the two predetermined thresholds, and the evaluation unit 26 generates an output signal 28 that indicates the seat occupancy classification "child".Furthermore, when the vehicle seat 10 is occupied by the adult, the output signal from the capacitance measuring circuit 20, which indicates a capacitance of the capacitive sensor element 130, is above the upper of the two predetermined threshold values, and the evaluation unit 26 generates an output signal 28 that indicates the seat occupancy classification “adult”.

[0072] In this particular embodiment, as it appears in Fig. As shown in Figure 4a, the transverse element 150 is designed to be deflected in the specified direction 54 when the mechanical load F is applied. However, other embodiments also consider configuring the projections 152 of the elastic spacer element 148 to be deflected under the influence of the mechanical load F, or configuring both the transverse element 150 and the projections 152 to be deflected in the specified direction 54 when the mechanical load F is applied.

[0073] An alternative embodiment of a capacitive sensor element according to the invention is shown schematically in a top view in Fig. 5 illustrates.

[0074] The capacitive sensor element 230 comprises a first electrically conductive antenna element 232 and several, for example, sixteen, second electrically conductive antenna elements 234. The first electrically conductive antenna element 232 and the second electrically conductive antenna element 234 of the several second electrically conductive antenna elements 234 are planar and are arranged on and attached to a planar surface of an electrically insulating support element 238. It should be noted that the number of sixteen second electrically conductive antenna elements 234 is given only as a specific example, and that in other embodiments the number of second electrically conductive antenna elements 234 may be three, one hundred, or any other suitable number.

[0075] The first electrically conductive antenna element 232 is formed by a narrow metal strip (compared to a lateral extension of the electrically conductive antenna element), which is meandering in shape and includes two terminal blocks 244 at the ends of the meander, through which it is electrically connected to the capacitance measuring circuit 20 in the same way as in Fig. Figure 1 shows the first embodiment of the capacitive sensor element 130, which can be connected to the first electrically conductive antenna element 232. One of the terminals 244 is connected to the meandering section of the first electrically conductive antenna element 232 via a passage in the electrically insulating support element 238. Along a central section, the first electrically conductive antenna element 232 comprises four pairs of spur lines 60 extending perpendicularly and coplanarly. The second electrically conductive antenna elements 234 of the sixteen second electrically conductive antenna elements 234 are identical, formed as rectangular pieces of sheet metal, arranged in a plane, and adjacent to the first electrically conductive antenna element 232. The sixteen second electrically conductive antenna elements 234 are arranged adjacently in a 4x4 configuration, resulting in a compact installation area for the capacitive sensor element 230.

[0076] In a mechanically unstressed state, the first electrically conductive antenna element 232 and the several sixteen second electrically conductive antenna elements 234 have no galvanic connection with each other.

[0077] The first electrically conductive antenna element 232 and the several second electrically conductive antenna elements 234 are easily formed by applying an electrically conductive material to an upper surface 240 of the electrically insulating support element 238, which is designed as an electrically insulating substrate consisting of a polyethylene terephthalate (PET) layer. The bottom surface of the electrically insulating support element 238 is equipped with an electrically conductive layer applied to the PET layer and designed to serve as a protective electrode 242. The electrically conductive material of the antenna element and / or the protective electrode, e.g., a metal, a graphite material, or an electrically conductive polymer, can be applied to the substrate by, for example, printing, deposition, lamination, or any other suitable application technique.

[0078] The protective electrode 242 is arranged proximally and is insulated from the first electrically conductive antenna element 232 and the several second electrically conductive antenna elements 234. The electrically conductive protective electrode 242 overlaps, in the specified direction 54, which is directed towards the upper surface 240 of the electrically insulating support element 238 and perpendicular to it, substantially the area enclosed by one of the first electrically conductive antenna elements 232 and the several second electrically conductive antenna elements 234.

[0079] Furthermore, the capacitive sensor element 230 comprises several electrically conductive bridging elements 246, each of which is arranged such that it partially overlaps the first electrically conductive antenna element 232 and a second electrically conductive antenna element 234 of the several second electrically conductive antenna elements 234 in the specified direction 54.

[0080] Each of the electrically conductive bridging elements 246 is designed similarly to the electrically conductive bridging elements 146 of the first embodiment of the capacitive sensor element 130. Each of the electrically conductive bridging elements 246 is fixedly attached to one of several elastic spacer elements 248 of the capacitive sensor element 230. Each of the elastic spacer elements 248 is identical to the elastic spacer elements 148 of the first embodiment of the capacitive sensor element 130 and has elastic mechanical properties in the specified direction 54.

[0081] The electrically conductive bridging elements 246 are fixedly attached to the elastic spacer elements 248, as described for the first embodiment of the capacitive sensor element 130.

[0082] The first electrically conductive antenna element 232 and one specific of the several second electrically conductive antenna elements 234, which are partially overlapped by one specific of the several electrically conductive bridging elements 246, remain galvanically isolated from each other when a mechanical load F, which is less than a specific predetermined value for the mechanical load F, is applied in the specified direction 54 to the specific one of the several elastic spacer elements 248 to which the specific one of the several electrically conductive bridging elements 246 is rigidly attached. Under this mechanical load F condition, the first electrically conductive antenna element 232 is the only sensing part of the capacitive sensor element 230.

[0083] If a mechanical load F is applied to the capacitive sensor element 230 in the specified direction 54, at least one of the several electrically conductive bridging elements 246 approaches the first electrically conductive antenna element 232 and one of the several second electrically conductive antenna elements 234.

[0084] The portion of the mechanical load F applied to one of the several elastic spacers 248 results in an individual surface pressure. For example, the mechanical load F may have a non-homogeneous spatial distribution perpendicular to the specified direction 54.

[0085] If a mechanical load F equal to or greater than the specified predetermined value for the mechanical load F in the specified direction 54 is applied to the specific one of the several elastic spacer elements 248 to which the specific one of the several electrically conductive bridging elements 246 is fixedly attached, the specific one of the several electrically conductive bridging elements 246 provides at least one galvanic contact between the first electrically conductive antenna element 232 and the specific one of the several second electrically conductive antenna elements 234, which it partially overlaps. Under this condition of mechanical load F, the first electrically conductive antenna element 232 and the specific one of the several second electrically conductive antenna elements 234 become sensing parts of the capacitive sensor element 230.The more galvanic contacts are provided between the first electrically conductive antenna element 232 and the several second electrically conductive antenna elements 234, the larger the output signal of the capacitance measuring circuit 20 becomes.

[0086] Fig. Figure 6 schematically shows the sensing elements of the capacitive sensor element 230 in three different mechanical load situations: - the surface pressure is lower than any specific predetermined value for the elastic spacer elements 248, the first electrically conductive antenna element 232 is the only sensing part (left); - the surface pressure is greater than any specific predetermined value for the elastic spacer elements 248, the first electrically conductive antenna element 232 and the several second electrically conductive antenna elements 234 are sensing parts (center); and - the surface pressure is greater than specific predetermined values ​​of three of the elastic spacer elements 248, the first electrically conductive antenna element 232 and the highlighted three second electrically conductive antenna elements 234 are sensing parts of the capacitive sensor element 230 (right).

[0087] The specific predetermined values ​​for the surface pressure to provide at least one galvanic contact between the first electrically conductive antenna element 232 and one specific of the several second electrically conductive antenna elements 234, which it partially overlaps, may be the same or may differ from each other, depending on a desired sensor response, which may be specific for an expected spatial distribution of the applied mechanical load F.

[0088] The Fig. 7 and Fig. Figure 8 schematically illustrates the difference in the activation of the sensing elements of the capacitive sensor element between a seat occupied by an ISOFIX CRS and a seat occupied by a belted CRS. Belted CRS are not normally connected to ground, so they have low capacitance. However, they have a high weight and activate some or all of the bridging elements. This is schematically shown in Figure 8. Fig. 8 illustrates.

[0089] In contrast, ISOFIX CRS anchors can have a high capacity due to their grounding, but they are secured by the ISOFIX hooks, resulting in poor weight distribution and bridging only through some of the bridging elements. This is shown schematically in Fig. Figure 7 illustrates where the mechanical installation surface of the ISOFIX CRS is shown as a dotted surface. List of reference symbols 10 vehicle seats 12 seat cushions 14 A-area 16 Backrest 18 Vehicle seat occupant detection and classification device 20 Capacitance measuring circuit 22 Signal generation unit 24 sensor circuit 26 evaluation units 28 Output signal 30 capacitive sensor element 32 first electrically conductive antenna element 34 second electrically conductive antenna element 36 third electrically conductive antenna element 38 electrically insulating support element 40 upper surface 42 Protective electrode 44 Terminal block 46 electrically conductive bridging element 48 elastic spacer element 50 transverse elements 52 Approach 54 specified direction 56 CAN communication connection 58 Airbag control unit 60 branch lines F mechanical load

Claims

[1] Capacitive sensor element (130) of a vehicle seat occupant detection and classification device (18), wherein the capacitive sensor element (130) comprises a first electrically conductive antenna element (132) which can be electrically connected to a capacitance measuring circuit (20) for determining a capacitance of the capacitive sensor element (130). characterized by - at least a second electrically conductive antenna element (134) which is arranged adjacent to the first electrically conductive antenna element (132) without any galvanic connection to each other, - at least one electrically conductive bridging element (146) arranged such that it partially overlaps the first electrically conductive antenna element (132) and the second electrically conductive antenna element (134) in a specified direction (54), - at least one elastic spacer element (148) which has elastic mechanical properties at least in the specified direction (54), wherein the at least one electrically conductive bridging element (146) is fixedly attached to the at least one elastic spacer element (148), wherein the first electrically conductive antenna element (132) and the second electrically conductive antenna element (134) remain galvanically isolated from each other when a mechanical load (F) which is smaller than a predetermined value for the mechanical load (F) is applied to the capacitive sensor element (130) in the specified direction (54), and wherein the at least one electrically conductive bridging element (146) provides at least one galvanic contact between the first electrically conductive antenna element (132) and the second electrically conductive antenna element (134) when a mechanical load (F) equal to or greater than the predetermined value for the mechanical load (F) is applied to the capacitive sensor element (130) in the specified direction (54). [2] Capacitive sensor element (130) according to claim 1, wherein at least one of the first electrically conductive antenna element (132) and the second electrically conductive antenna element (134) has a planar design and is arranged on and attached to a planar surface (140) of an electrically insulating support element (138). [3] Capacitive sensor element (130) according to claim 1 or 2, wherein at least one of the first electrically conductive antenna element (132) and the second electrically conductive antenna element (134) is designed as an electrically conductive strip which is firmly attached to a surface of an electrically insulating substrate. [4] Capacitive sensor element (130) according to one of the preceding claims, wherein a region enclosed by the second electrically conductive antenna element (134) comprises a region enclosed by the first electrically conductive antenna element (132). [5] Capacitive sensor element (130) according to one of the preceding claims, further comprising a third electrically conductive antenna element (136) arranged adjacent to the first electrically conductive antenna element (132) and the second electrically conductive antenna element without galvanic connection, wherein the first electrically conductive antenna element (132) forms a single loop, an area enclosed by the second electrically conductive antenna element (134), encompasses an area enclosed by the first electrically conductive antenna element (132), an area enclosed by the first electrically conductive antenna element (132), includes an area enclosed by the third electrically conductive antenna element (136), and wherein the first electrically conductive antenna element (132) and the third electrically conductive antenna element (136) remain galvanically isolated from each other when a mechanical load (F) smaller than the predetermined value for the mechanical load (F) is applied to the capacitive sensor element (130) in the specified direction (54), and wherein the at least one electrically conductive bridging element (146) provides at least one galvanic contact between the first electrically conductive antenna element (132) and the third electrically conductive antenna element (136) when a mechanical load (F) equal to or greater than the predetermined value for the mechanical load (F) is applied to the capacitive sensor element (130) in the specified direction (54). [6] Capacitive sensor element (230) according to one of claims 1 to 3, comprising - several second electrically conductive antenna elements (234) arranged in a plane and adjacent to the first electrically conductive antenna element (232) without galvanic connection to each other and without galvanic connection to the first electrically conductive antenna element (232), - several electrically conductive bridging elements (246), each arranged such that they partially overlap the first electrically conductive antenna element (232) and at least one of the several second electrically conductive antenna elements (234) in the specified direction (54), - several elastic spacer elements (248) which exhibit elastic mechanical properties at least in the specified direction (54), wherein each of the several electrically conductive bridging elements (246) is fixedly attached to one of the several elastic spacer elements (248), wherein the first electrically conductive antenna element (232) and a specific one of the several second electrically conductive antenna elements (234), which are partially overlapped by a specific one of the several electrically conductive bridging elements (246), remain galvanically isolated from each other when a mechanical load (F) that is smaller than a specific predetermined value for the mechanical load (F) is applied in the specified direction (54) to the specific one of the several elastic spacer elements (248) to which the specific one of the several electrically conductive bridging elements (246) is fixedly attached, and wherein the specific one of the several electrically conductive bridging elements (246) provides at least one galvanic contact between the first electrically conductive antenna element (232) and the specific one of the several second electrically conductive antenna elements (234) which it partially overlaps, when a mechanical load (F) equal to or greater than the specific predetermined value for the mechanical load (F) in the specified direction (54) is applied to the specific one of the several elastic spacer elements (248) to which the specific one of the several electrically conductive bridging elements (246) is fixedly attached. [7] Capacitive sensor element (130; 230) according to one of the preceding claims, further comprising an electrically conductive protective electrode (142; 242) arranged proximally to the first electrically conductive antenna element (132; 232), the second electrically conductive antenna element or the multiple second electrically conductive antenna elements (134; 234) and, if applicable, the third electrically conductive antenna element (136) and galvanically isolated from them, wherein the electrically conductive protective electrode (142; 242) substantially overlaps in the specified direction (54) the area enclosed by one of the first electrically conductive antenna element (132; 232), the second electrically conductive antenna element or the multiple second electrically conductive antenna elements (134; 234) and, if applicable, the third electrically conductive antenna element (136). is. [8] Vehicle seat occupant detection and classification device (18), comprising - at least one capacitive sensor element (130; 230) according to one of claims 1 to 7, - a capacitance measurement circuit (20) for determining a capacitance of the capacitive sensor element (130; 230), and - an evaluation unit (26) configured to receive an output signal from the capacitance measurement circuit (20) and to provide a seat occupant classification based on a level of the received output signal and at least one predetermined threshold of the output signal. [9] Vehicle seat (10), comprising a seating structure for erecting the vehicle seat (10) on a floor of a passenger compartment of the vehicle, a seat cushion (12) with at least one seat foam element, a seat base supported by the seat structure and designed to receive the seat cushion (12), wherein the seat base and the seat cushion (12) are intended to support the buttocks of a seat occupant, a backrest (16) designed to support the back of the seat occupant, and a vehicle seat occupant detection and classification system (18) according to claim 8. [10] Use of the vehicle seat occupant detection and classification device (18) according to claim 8 in a vehicle seat (10) comprising a seat base designed to receive a seat cushion (12) with at least one seat foam element, wherein the seat base and the seat cushion (12) are provided to support the buttocks of a seat occupant, and comprising a backrest (16) provided to support the back of the seat occupant, wherein the at least one capacitive sensor element (30) is arranged on either the seat cushion (12) or the backrest (16). [11] Use of the capacitive sensor element (130; 230) according to one of claims 1 to 7 in a vehicle seat occupant detection and classification device (18) according to claim 8.

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