Capacitive occupant detection system with Isofix differentiation

Abstract

In addition to the loading mode of a capacitive sensing device (12) of a seat occupancy detection and classification system (10), a second measurement mode is provided that allows for the differentiation of objects (child restraint system or human) with and without a ground connection. Depending on the value of the second measurement, the data are assigned to different groups, which are determined by different thresholds in the loading mode. This means that if the second measurement indicates a ground connection of the object, a higher threshold is applied in the loading mode. In this way, a child restraint system connected to ground via ISOFIX anchorages is classified using the higher threshold, resulting in increased robustness. Typical human seating positions do not have a ground connection and are classified using the lower threshold.

Description

Technical field

[0001] The invention relates to a capacitive detection device, a seat occupancy detection and classification system comprising such a capacitive detection device, a method for operating such a capacitive seat occupancy detection and classification system, and a software module for carrying out the method. Background of the invention

[0002] Seat occupancy detection and / or classification systems are widely used in vehicles, and especially in passenger cars, to provide a seat occupancy signal to various devices, such as a seat belt reminder system (SBR) or an auxiliary restraint system (ARS) activation control system. Seat occupancy detection and / or classification systems include seat occupancy sensors, which are known to exist in a variety of forms and are primarily based on capacitive sensing. An output signal from the seat occupancy detection and / or classification system is typically transmitted to an electronic control unit of the vehicle, for example, to serve as the basis for a decision regarding the deployment of an airbag system towards the vehicle seat.

[0003] A capacitive sensor, sometimes called an "E-field sensor" or "proximity sensor," is a sensor that generates a signal responding to the influence of whatever is detected in an electric field (a person, a part of a person's body, a pet, an object, etc.). A capacitive sensor generally includes at least one antenna electrode to which an oscillating electrical signal is applied when the sensor is switched on, thereby generating an electric field in the area close to the antenna electrode. The sensor includes at least one sensing electrode—which could be one or more of the antenna electrodes themselves—at which the influence of an object or living being on the electric field is detected.

[0004] The various capacitive sensing mechanisms are explained, for example, in the technical paper entitled "Electric Field Sensing for Graphical Interfaces" by J.R. Smith et al., published in IEEE Computer Graphics and Applications, 18 (3): 54-60, 1998. This paper describes the concept of electric field sensing, using it to perform non-contact three-dimensional position measurements, and in particular to detect the position of a human hand to provide a computer with three-dimensional position input. The author distinguishes between different mechanisms within the general concept of capacitive sensing, which he refers to as "loading mode," "shunt mode," and "transmit mode," corresponding to different possible paths of electric current.In "charging mode," an oscillating voltage signal is applied to a transmitting electrode, which generates an oscillating electric field relative to ground. The object being detected modifies the capacitance between the transmitting electrode and ground. In "shunt mode," also known as "coupling mode," an oscillating voltage signal is applied to the transmitting electrode, which generates an electric field relative to a receiving electrode. The displacement current induced at the receiving electrode is measured, allowing the displacement current through the object being detected to be modified. In "transmitting mode," the transmitting electrode is brought into contact with the user's body, who then becomes a transmitter relative to a receiver, either through direct electrical connection or capacitive coupling.

[0005] Capacitive coupling is generally determined by applying an AC voltage signal to a capacitive antenna electrode and measuring the current flowing from the antenna electrode either to ground (in charging mode) or, in coupling mode, to the second electrode (receiving electrode). This current is typically measured using a transimpedance amplifier connected to the sensing electrode, which converts the current flowing into the sensing electrode into a voltage proportional to the current flowing into the antenna electrode.

[0006] Some capacitive sensors are designed as detection-only capacitive sensors with a single detection electrode. Furthermore, capacitive sensors comprising a detection electrode and a shielding electrode, positioned close to each other and mutually insulated, are quite common. This method of "shielding" is well-known in engineering and is frequently used to purposefully mask and thus shape the sensitivity state of a capacitive sensor. For this purpose, the shielding electrode is held at the same AC electrical potential as the detection electrode. Consequently, the space between the detection electrode and the shielding electrode is free of an electric field, and the capacitive shielded detection sensor is insensitive in the direction between the detection and shielding electrodes.

[0007] Many different capacitive occupant detection systems have been proposed, for example, to control the deployment of one or more airbags, such as a driver's airbag, a passenger airbag, and / or a side airbag. US Patent 6,161,070 A, granted to Jinno et al., relates to an occupant detection system including a single antenna electrode mounted on the surface of a passenger seat in a motor vehicle. An oscillator applies an oscillating voltage signal to the antenna electrode, thereby generating a very small electric field around the antenna electrode. Jinno proposes detecting the presence or absence of a passenger in the seat based on the amplitude and phase of the current flowing to the antenna electrode.

[0008] US patent US 6,392,542 B1, granted to Stanley, describes an electric field sensor comprising an electrode that can be placed in a seat and is coupled to a detection circuit that applies an oscillating or pulsed signal to the electrode at a frequency that is "at best weakly responsive" to seat wetness. Stanley proposes measuring the phase and amplitude of the current flowing to the electrode to detect whether the seat is occupied or empty and to compensate for the wetness.

[0009] Others had the idea of ​​using the heating element of a seat heater as an antenna electrode for a capacitive occupancy detection system. International application WO 92 / 17344 A1 discloses an electrically heated vehicle seat with a conductor that can be heated by the flow of an electric current and is arranged in the seat surface, the conductor further constituting an electrode of a two-electrode seat occupancy sensor.

[0010] International patent application WO 95 / 13204 A1 discloses a similar system in which the oscillation frequency of an oscillator connected to the heating element is measured to determine the occupancy status of the vehicle seat. More complex combinations of a seat heater and a capacitive sensor are disclosed, for example, in patents US 7,521,940 B2, US 2009 / 0295199 A1, and US 6,703,845 B2.

[0011] Capacitive antenna electrodes are generally designed to extend essentially across the entire surface of the vehicle seat. This ensures that a passenger can be reliably detected even if they are sitting in an unnatural position, such as in the forwardmost position of the seat.

[0012] The capacitive detection system should be able to distinguish between an empty seat or a seat equipped with a child restraint system (CRS) and a person sitting directly on the seat.

[0013] A reliable method for differentiating between potential seat user classes is essential for meeting stringent safety requirements. Compared to vehicle seat classification systems that use mechanical, load-based resistance measurements, which are also well-established in the field, capacitive measurement offers the advantages of simpler wiring and consistent, reproducible measurement across the entire temperature range specified in standard vehicle requirements.

[0014] A seat occupancy detection and classification system - in particular for detecting and classifying the occupancy of a vehicle seat - based on capacitive sensing measures a physical quantity such as an electric current through a capacitive sensor element or a complex impedance or admittance of the capacitive sensor element, wherein the physical quantity is representative of an electric field between at least one sensing electrode of the capacitive sensor element and a vehicle body.

[0015] The at least one detection electrode can be positioned on or in the vehicle seat. A seat occupant or an object placed on the vehicle seat modifies the electric field of the detection electrode, resulting in a change in the measured physical quantity. Such capacitive seat occupancy detection systems are also known, for example, from patent applications US 2011 0 074 447 A1, US 2006 0 219 460 A1, JP 2009 - 132 224 A, DE 11 2012 000 943 B4 and DE 11 2014 001 890 B4.

[0016] The seat occupancy detection and classification system is a capacitive measurement system used in the passenger seat of a vehicle to classify whether an adult is sitting in the seat, or whether the seat is empty or occupied by a child restraint system (CRS).

[0017] A problem affecting a capacitive sensing device that measures capacitive coupling between an antenna electrode and vehicle ground could occur as follows: - In the case of a standard KRS, i.e., a KRS not connected to mass and attached to the seat by means of the seatbelt, a seat equipped with a KRS is recorded as low capacity, whereas a person sitting directly on the seat is recorded as high capacity; - In the case of a grounded KRS, i.e., an ISOFIX KRS that is electrically connected to the vehicle ground, the system detects a high capacitance, which can lead to an incorrect classification.

[0018] Thus, vehicle seat occupant classification systems based on capacitive sensing are misled in the case of objects placed on a vehicle seat and connected to the vehicle's chassis, such as an ISOFIX child restraint system (KRS). When installed, the KRS is mechanically connected to the chassis via anchor points firmly attached to the vehicle body. ISOFIX child restraint systems are equipped with metal retaining clips configured for quick attachment to these anchor points. These metal retaining clips are part of a metal frame located within the KRS. This metal frame could come within a few millimeters of the antenna electrode.Depending on the proximity of the grounded KRS metal frame to the at least one antenna electrode of the capacitive sensor element, the detected physical quantity could be large enough to cause the vehicle seat occupant classification system to classify an electrically grounded KRS as a "person sitting directly on the seat".

[0019] In such cases, the vehicle seat occupant classification system's ability to correctly classify a seat occupant could be impaired. Similarly, any object connected to the vehicle's ground can lead to an incorrect classification by the vehicle seat occupant classification system due to a relatively small distance between the capacitive sensor element and the object. Object of the invention

[0020] It is therefore an object of the present invention to provide a seat occupancy classification system with high functional robustness, in particular a vehicle seat occupancy classification system that can reliably and correctly classify a seat occupancy without the deficiencies described above and that in particular enables correct classification of a KRS that is attached with the ISOFIX system and that is electrically connected to vehicle ground. Description of the invention

[0021] The problem is solved in one aspect of the present invention by a capacitive sensing device for a seat occupancy detection and classification system. The capacitive sensing device comprises an impedance measurement circuit and a signal processing unit.

[0022] The impedance measurement circuit comprises a signal voltage source configured to provide a periodic electrical measurement signal at an output terminal with respect to a ground potential, and at least one sensing current measuring device configured to measure complex sensing currents with respect to a reference voltage.

[0023] A capacitive sensor comprising at least a first electrically conductive antenna electrode and a second electrically conductive antenna electrode can be electrically connected to the impedance measurement circuit in such a way that - at least the first antenna electrode can be electrically connected to the output terminal in order to receive the electrical measurement signal, and - the second antenna electrode can be electrically connected via at least one controllable, preferably remotely controllable, switching element either to the ground potential or to an alternating current potential of the output terminal.

[0024] The complex detection currents are generated in the capacitive sensor by the provided periodic measurement signal.

[0025] The term “electrically connectable / electrically connected” as used in this application is to be understood as encompassing both galvanic electrical connections and electrical connections resulting from capacitive and / or inductive electromagnetic coupling. The term “configured for” as used in this application is to be understood in particular as specifically programmed, designed, equipped, or arranged.

[0026] It should further be noted that the terms “first” and “second” are used in this application solely for the purpose of differentiation and in no way indicate or anticipate any order or priority.

[0027] The signal processing unit is configured to determine complex impedances from measured currents, at least through the first antenna electrode, with respect to the complex reference potential, and to provide output signals that are representative of the determined complex impedances.

[0028] The invention is based on the concept of eliminating the greatest unknown in establishing a seat occupancy, which is the ground connection state of an object placed on the seat, before complex impedances are determined from measured currents for seat occupancy detection and classification. In this way, the occurrence of measurement conditions with ambiguities regarding seat occupancy classification can be prevented, and a capacitive sensing device with improved robustness for seat occupancy detection—particularly in the presence of grounded objects—can be provided.

[0029] The at least one controllable switching element can form part of the capacitive sensing device or it can form part of another device that is separate from the capacitive sensing device and operatively coupled to it.

[0030] Instead of determining complex impedances from measured currents, the signal processing unit can be configured to determine complex admittances from measured currents without any change to the disclosed subject matter of the invention, because the real and imaginary parts of a complex impedance and its corresponding complex admittance are related to each other by a one-to-one correspondence, as is readily understood by the person skilled in the art.

[0031] The capacitive detection device can be used, in particular, for a vehicle seat occupancy detection and classification system. The term "vehicle," as used in this application, is to be understood as including passenger cars, trucks, and buses.

[0032] The capacitive sensor is preferably operated in the charging mode described in the aforementioned article "Electric field sensing for graphical interfaces" by JR Smith et al., which is hereby incorporated by reference in its entirety with effect for those jurisdictions that permit incorporation by reference. It is also generally intended that the capacitive sensor be operated in transmit mode or in shunt mode in some embodiments or in some operating modes.

[0033] The first electrically conductive antenna electrode and the second electrically conductive antenna electrode are preferably galvanically isolated from each other. The term "galvanically isolated" as used in this application is to be understood in particular as meaning that it does not conduct direct current (DC) between galvanically isolated objects.

[0034] The problem is solved in one aspect of the present invention by a seat occupancy detection and classification system, in particular a vehicle seat occupancy detection and classification system, which comprises a capacitive sensing device as disclosed herein, wherein the capacitive sensor can be electrically connected to the impedance measurement circuit in such a way that a current flowing in or through the second antenna electrode can be measured by the impedance measurement circuit. The signal processing unit is further configured to determine at least one complex impedance from a measured current through the second antenna electrode determined with respect to the complex reference potential.

[0035] The seat occupancy detection and classification system also includes a control and evaluation unit configured to - to receive the output signals provided by the signal processing unit, - depending on a result of the complex impedance from the measured current through the second antenna electrode, at least one threshold value from predefined threshold values ​​for complex impedance, - to compare the complex impedances from the measured current through the first antenna electrode with at least one selected predetermined threshold value and - based on the result of the comparison, to determine a seat occupancy class.

[0036] The current through the second antenna electrode can be measured by the at least one current-sensing device of the impedance measurement circuit. Alternatively, the impedance measurement circuit can include a second current-sensing device for this purpose.

[0037] The present invention proposes, in addition to the normal operating mode, the introduction of a second measurement mode that enables the differentiation of objects (KRS or humans) with and without a ground connection. Depending on the value of the new measurement, the data is assigned to different groups, which are determined by different thresholds in the loading mode. This means that if the new measurement indicates a ground connection of the object, a different threshold is applied in the normal operating mode. Thus, a KRS with a ground connection is classified using the different threshold, leading to increased robustness. Typical human positions do not exhibit a ground connection and are classified by the first threshold.

[0038] The proposed system is a (nearly) independent solution for the ISOFIX KRS, independent of the KRS design.

[0039] Fig. Figures 5A to 5C schematically illustrate the principle on which the operation of the seat occupancy detection and classification system is based. Fig. Figure 5A is a schematic side view of an adult seated in a vehicle seat. The adult seated person is not electrically connected to ground. Due to the electrical interaction between the seated person and the first and second antennas, which are located on a seat cushion of the vehicle seat, an electric current supplied to the first antenna electrode causes an electric current to flow through the second antenna electrode. A measured total capacitance, derived from the determined complex impedance of this configuration, is equal to the capacitance of two capacitors connected in parallel, one capacitor being formed by the first antenna electrode and the seated person, and the other capacitor being formed by the second antenna electrode and the seated person.The seat user therefore generates a relatively large current in the second antenna electrode of the capacitive detection device.

[0040] Fig. Figure 5B is a schematic side view of a child restraint system (CRS) mounted on the vehicle seat but not mechanically and electrically connected to anchorages fixed to the vehicle body. An electric current applied to the first antenna electrode causes an electric current to flow through the second antenna electrode. This current is determined by the electromagnetic coupling governed by the geometric relationship between the two antenna electrodes and is not increased by the CRS due to the weak electromagnetic coupling between each antenna electrode and the CRS.

[0041] Fig. Figure 5C is a schematic side view of a child restraint system (CRS) mounted on the vehicle seat and mechanically and electrically connected to anchors firmly attached to the vehicle body. An electric current applied to the first antenna electrode does not cause an electric current to flow through the second antenna electrode because the current flows through the grounded CRS to ground (the vehicle body).

[0042] Thus, the additional information about the ground connection status of the object on the seat, obtained from the signal of the second antenna electrode, can be advantageously used to select a suitable threshold from predefined thresholds for complex impedance. The signal obtained from the first antenna electrode can then be compared with the suitable threshold for robust and reliable seat occupancy detection and classification.

[0043] The problem is also solved by a seat occupancy detection and classification system, in particular a vehicle seat occupancy detection and classification system, which includes a capacitive detection device as disclosed herein, wherein the capacitive sensor can be electrically connected to the impedance measurement circuit in such a way that the second antenna electrode can be electrically connected via the at least one controllable (remotely controllable) switching element either to the ground potential or to the electrical AC potential of the output terminal.The signal processing unit is further configured to determine at least a first complex impedance from a measured current through the first antenna electrode, wherein the second antenna electrode is electrically connected to the DC potential, and to determine a second complex impedance from a measured current through the first antenna electrode, wherein the second antenna electrode is electrically connected to the AC potential of the output terminal.

[0044] The seat occupancy detection and classification system also includes a control and evaluation unit configured to - to receive the output signals provided by the signal processing unit, - depending on a relationship between the first and second complex impedance, to select at least one threshold from predefined thresholds for complex impedance, - to compare the complex impedances from the measured current through the first antenna electrode with at least one selected predetermined threshold value and - based on the result of the comparison, to determine a seat occupancy class.

[0045] If the object on the seat is connected to ground, virtually no difference can be measured between the first and second complex impedances because the grounded object acts as an electromagnetic shield with respect to the second antenna electrode. This can be advantageously used to distinguish between a grounded and a non-grounded object on the seat, as well as to select a suitable threshold from predefined thresholds for complex impedance. The signal obtained from the first antenna electrode can then be compared with the appropriate threshold for robust and reliable seat occupancy detection and classification.

[0046] It should be noted that instead of actually determining the first complex impedance and the second complex impedance and selecting the threshold value depending on a relationship between the first and second complex impedance, the signal processing unit can be configured to determine at least only a difference between a first complex impedance of the first antenna electrode, where the second antenna electrode is electrically connected to ground potential, and a second complex impedance of the first antenna electrode, where the second antenna electrode is electrically connected to the AC potential of the output terminal.

[0047] In this configuration, the capacitive sensor can be electrically connected to the impedance measurement circuit such that the second antenna electrode can be alternately connected to ground potential and to the AC potential of the output terminal via at least one controllable switching element. The control and evaluation unit is configured to select at least one threshold value depending on the difference between the first and second complex impedances. In other words, this implementation utilizes a "modulation" of the second antenna (between ground and AC potential), and further evaluation is based on the difference in impedances (as a demodulation result).

[0048] In some embodiments of the seat occupancy detection and classification system, the capacitive detection device includes at least one remotely controllable switching element, and the seat occupancy detection and classification system includes a switching remote control unit for remotely controlling the at least one remotely controllable switching element.

[0049] In this way, a reliable distinction can be made between a grounded and a non-grounded object mounted on the seat for the selection of a suitable threshold from predefined thresholds for complex impedance.

[0050] The remote control unit is preferably implemented using a microcontroller. Microcontrollers equipped accordingly, including, for example, a processor unit, a digital data storage unit, a microcontroller system clock, a multiplexer unit, and analog-to-digital converters, are readily available in many variations today.

[0051] In some preferred embodiments of the capacitive seat occupancy detection and classification system, the switching remote control unit is configured to periodically switch the remotely controllable switching element such that it changes the electrical connection of the second antenna electrode for a predetermined period from a state electrically connected to ground potential to a state electrically connected to the AC potential of the output terminal, and after the period has elapsed, back to a state electrically connected to ground potential. If a suitable predetermined period is selected, quasi-continuous operation of the seat occupancy detection and classification system can be achieved with virtually no impairment of operational readiness.

[0052] In a preferred embodiment, a capacitive sensor, which is electrically connected at least to the output terminal of the signal voltage source and to the current measuring device, forms part of the capacitive seat occupancy detection and classification system. This allows a complete seat occupancy detection and classification system to be provided with the advantages mentioned above.

[0053] In another preferred embodiment of the capacitive seat occupancy detection and classification system, the control and evaluation unit is configured to generate a classification output signal indicating the determined seat occupancy class. The classification output signal of the control and evaluation unit can advantageously be transmitted to an electronic control unit of the vehicle, for example, to serve as the basis for a decision regarding the deployment of an airbag system towards the vehicle seat.

[0054] In some configurations of the capacitive seat occupancy detection and classification system, at least one threshold value from predefined threshold values ​​for complex impedance can be represented by a line in a two-dimensional diagram spanned by a real part and an imaginary part of the complex impedance. This allows for flexible and adaptable conditions for distinguishing between seat occupancy classes.

[0055] In yet another aspect of the present invention, the problem is solved by a method for operating one of the disclosed capacitive seat occupancy detection and classification systems, wherein the capacitive sensor can be electrically connected to the impedance measurement circuit in such a way that a current flowing through the second antenna electrode can be measured by the impedance measurement circuit.

[0056] The process includes the following steps: - Providing a periodic electrical measurement signal at the first antenna electrode of the capacitive sensor, - Determining a complex detection current that is generated in the second antenna electrode of the capacitive sensor in response to the periodic electrical measurement signal provided to the first antenna electrode of the capacitive sensor, - Comparing the determined complex acquisition stream with at least one predefined threshold for the complex acquisition stream, - depending on the result of the comparison step, selecting at least one threshold from predefined thresholds for complex impedance, - Determining a complex sensing current that is generated in the first antenna electrode of the capacitive sensor in response to the periodic electrical measurement signal provided to the first antenna electrode of the capacitive sensor, - Determining a complex impedance from the complex detection current measured in the first antenna electrode with respect to the complex reference potential, - Comparing the determined complex impedance with at least one selected predefined threshold for complex impedance and - Determining a seat occupancy class for the determined complex impedance depending on a relationship between the determined complex impedance and at least one selected predefined threshold for complex impedance.

[0057] The relationship between the determined complex impedance and at least one selected predefined threshold for complex impedance can be one of "greater than", "less than", or "equal to". The relationship can also include a constant factor such as "greater than 1.2 times".

[0058] The problem is also solved by a method for operating one of the disclosed capacitive seat occupancy detection and classification systems, wherein the capacitive sensor can be electrically connected to the impedance measurement circuit in such a way that the second antenna electrode can be electrically connected via the at least one remotely controllable switching element either to the ground potential or to the electrical AC potential of the output terminal.

[0059] The process includes the following steps: - Providing a periodic electrical measurement signal at the first antenna electrode of the capacitive sensor, - electrical connection of the second antenna electrode to the ground potential, - Determining an initial complex detection current that is generated in the first antenna electrode of the capacitive sensor in response to the periodic electrical measurement signal provided to the first antenna electrode of the capacitive sensor, - Determining a first complex impedance from the first complex detection current measured in the first antenna electrode with reference to the complex reference potential, - Changing the electrical connection of the second antenna electrode from the ground potential to the alternating current potential of the output terminal, - Determining a second complex detection current that is generated in the first antenna electrode of the capacitive sensor in response to the periodic electrical measurement signal provided to the first antenna electrode of the capacitive sensor, - Determining a second complex impedance from the first complex detection current measured in the first antenna electrode with reference to the complex reference potential, - Determining the difference between the first complex impedance and the second complex impedance, - Comparing the determined difference between the first complex impedance and the second complex impedance with at least one predetermined threshold for the difference of the complex impedance, - depending on the result of the comparison step, selecting at least one threshold from predefined thresholds for complex impedance, - Comparing the determined first complex impedance with at least one selected predefined threshold for complex impedance, - Determining a seat occupancy class for the determined first complex impedance depending on a relationship between the determined first complex impedance and at least one selected predefined threshold for complex impedance.

[0060] The above applies with regard to the relationship between the determined complex impedance and the at least one selected predefined threshold for complex impedance.

[0061] The problem is also solved by a method for operating one of the disclosed capacitive seat occupancy detection and classification systems, wherein the capacitive sensor can be electrically connected to the impedance measurement circuit in such a way that the second antenna electrode can be electrically connected alternately to the ground potential and to the alternating current potential of the output terminal via the at least one remotely controllable switching element.

[0062] The process includes the following steps: - Providing a periodic electrical measurement signal at the first antenna electrode of the capacitive sensor, - alternating connection of the second antenna electrode to the ground potential and to the alternating current potential of the output terminal, - Determining a difference between a first complex impedance of the first antenna electrode, wherein the second antenna electrode is electrically connected to the ground potential, and a second complex impedance of the first antenna electrode, wherein the second antenna electrode is electrically connected to the AC potential of the output terminal, - Comparing the determined difference between the first complex impedance and the second complex impedance with at least one predetermined threshold for the difference of the complex impedance, - depending on the result of the comparison step, selecting at least one threshold from predefined thresholds for complex impedance, - Comparing the determined first complex impedance with at least one selected predefined threshold for complex impedance, - Determining a seat occupancy class for the determined first complex impedance depending on a relationship between the determined first complex impedance and at least one selected predefined threshold for complex impedance.

[0063] In one design, the process steps can be carried out automatically and periodically.

[0064] In yet another aspect of the invention, a software module is provided for controlling the automatic execution of steps of an embodiment of the method disclosed herein.

[0065] The process steps to be performed are converted into program code of the software module, wherein the program code can be implemented in a digital data storage unit of the capacitive vehicle seat occupancy detection and classification system and can be executed by a processor unit of the capacitive vehicle seat occupancy detection and classification system. The digital data storage unit and / or the processor unit can preferably be a digital data storage unit and / or a processor unit of the evaluation unit of the capacitive vehicle seat occupancy detection and classification system. Alternatively or additionally, the processor unit can be another processor unit that is specifically assigned such that it executes at least some of the process steps.

[0066] The software module can enable robust and reliable execution of the process and allow for rapid modification of process steps.

[0067] In yet another aspect of the invention, a seat, in particular a vehicle seat, is provided with a built-in capacitive seat occupancy detection and classification system as disclosed herein. The seat comprises a seat cushion with at least one seat foam element and a seat support configured to receive at least a section of the seat cushion. The seat support and the seat cushion are designed to support the buttocks of a seat user. The seat further comprises a backrest designed to support a portion of the seat user's back. The capacitive sensor is arranged on at least one of the seat cushion and the backrest.

[0068] Thus, a seat, especially a vehicle seat, can be provided with robust and reliable seat occupancy detection and classification.

[0069] Furthermore, the seat can be equipped with at least one pair of anchors configured for mechanical engagement with appropriate fasteners of a KRS.

[0070] In a preferred embodiment of the seat, at least one of the first and second antenna electrodes is formed by an electric seat heating element integrated into the seat. This embodiment combines the advantage of robust and reliable seat occupancy detection and classification with the advantage of reduced equipment requirements. Brief description of the drawings

[0071] 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 drawing. The drawing shows: Fig. 1: schematically a vehicle seat with a first built-in embodiment of a seat occupancy detection and classification system according to the invention; Fig. 2: Schematic details of the operating principle of the seat occupancy detection and classification system according to the invention; Fig. 3: Schematic details of the first built-in embodiment of the seat occupancy detection and classification system according to the invention; Fig. 4: schematically the vehicle seat with a second built-in embodiment of the seat occupancy detection and classification system according to the invention; Fig. 5A to 5C: schematic details of the operating principle of the seat occupancy detection and classification system according to the invention; and Fig. 6: a flowchart of an embodiment of a method according to the invention for operating the seat occupancy detection and classification system according to Fig. 1. Description of preferred designs

[0072] Fig. Figure 1 schematically shows a seat 34 designed as a vehicle seat, which includes a capacitive seat occupancy detection and classification system 10 according to the invention. The vehicle seat is designed as a seat of a passenger car and comprises a seat structure (not shown) by which it can be mounted on a passenger compartment floor of the passenger car, as is well known in the art.

[0073] The seat 34 further comprises a seat support 36, which is supported by the seat structure and is configured to receive a seat cushion 38 to provide comfort to a seat user. The seat cushion 38 of the vehicle seat comprises a seat foam element and a fabric cover, which is Fig. Item 1 has been omitted. The seat support 36 and the seat cushion 38 are designed to support the buttocks of the seat user. A backrest 40 of the seat 34 is designed to support the back of the seat user.

[0074] The vehicle seat occupancy detection and classification system 10 comprises a capacitive sensor 16, a capacitive sensing device 12, and a control and evaluation unit 26. The capacitive sensor 16 is located on the A-surface of the seat cushion 38 beneath the fabric cover. The capacitive sensing device 12 and the control and evaluation unit 26 are installed in the vehicle remotely from the vehicle seat. An output terminal of the control and evaluation unit 26 is connected to an airbag control unit 60. The capacitive sensing device 12 comprises an impedance measurement circuit 14 and a signal processing unit 22.

[0075] The impedance measurement circuit 14 comprises a signal voltage source configured to provide a periodic electrical measurement signal at an output terminal with respect to a ground potential 64, and a sensing current measuring device configured to measure complex sensing currents with respect to a reference voltage. The sensing current measuring device can be configured as a transimpedance amplifier connected to a sensing antenna electrode, converting a current flowing into the sensing antenna electrode into a voltage proportional to the current flowing into the sensing antenna electrode. In principle, any other sensing current measuring device suitable to a person skilled in the art could be used.

[0076] The capacitive sensor 16 comprises a first electrically conductive antenna electrode 18 and a second electrically conductive antenna electrode 20, which are arranged side by side on the A-surface of the seat cushion and are galvanically isolated from each other ( Fig. 3) The first antenna electrode 18 and the second antenna electrode 20 are capacitively coupled, as indicated by a capacitor 30, which is shown to be electrically connected to both antenna electrodes 18 and 20. An object approaching the antenna electrodes 18 and 20 is represented by an unknown capacitor 32, which is connected to ground potential 64, which could, for example, be the ground potential of a vehicle. As the object approaches the antenna electrodes 18 and 20, the respective unknown capacitor 32 changes its capacitance, and a detection current flowing between the antenna electrodes 18 and 20 and ground potential 64 changes.

[0077] The first antenna electrode 18 and the second antenna electrode 20 consist, for example, of thin aluminum foil or, alternatively, of an aluminum-coated plastic material such as polyethylene terephthalate (PET). The capacitive sensor 16 is electrically connected to the impedance measurement circuit 14 such that the first antenna electrode 18 is electrically connected to the output terminal to receive the electrical measurement signal. The second antenna electrode 20 can be electrically connected via a remotely controllable switching element either to the ground potential 64 or to an alternating current potential of the output terminal. In this specific configuration, it is assumed that the second antenna electrode 20 is connected to the impedance measurement circuit 14 in such a way that a current through the second antenna electrode 20 can be measured by the impedance measurement circuit 14.

[0078] In this specific embodiment, both antenna electrodes 18, 20 consist of thin aluminum foil. In an alternative embodiment, only the first antenna electrode 18 consists of thin aluminum foil, and the second antenna electrode 20 is formed by an electric seat heating element installed in the vehicle seat, as is widely known in the art. The operating principle of the capacitive seat occupancy detection and classification system 10 disclosed herein also applies to such an alternative embodiment.

[0079] The complex detection currents to be detected by the current measuring device are generated in the first electrically conductive antenna electrode 18 of the capacitive sensor 16 by the provided periodic measurement signal; i.e., the normal operating mode of the capacitive sensor 16 is the charging mode.

[0080] The signal processing unit 22 is configured to determine complex impedances from measured currents through the first antenna electrode 18, relative to the complex reference potential specified by the electrical measurement signal. The signal processing unit 22 is further configured to provide output signals 24 that are representative of the determined complex impedances.

[0081] The control and evaluation unit 26 is configured to receive the output signals 24 provided by the signal processing unit 22.

[0082] With the second antenna electrode 20 connected to the impedance measurement circuit 14, the signal processing unit 22 is further configured to determine a complex impedance from a measured complex current through the second antenna electrode 20 determined with reference to the complex reference potential.

[0083] Fig. Figure 2 schematically illustrates details of the operating principle of the seat occupancy detection and classification system 10. The diagrams show the real part (expressed as conductance G) and the imaginary part (expressed as capacitance C) of determined complex impedances. A first zone 42 in the left-hand diagram represents complex impedances expected when the seat occupant is a non-grounded human. A second zone 44 represents complex impedances expected when the seat occupant is a grounded KRS 62. A first dashed line 52 in the two-dimensional diagram represents predefined threshold values ​​for the complex current (expressed as complex impedances) for distinguishing between the first zone 42 and the second zone 44.

[0084] Depending on the position of the result of the complex impedance from the measured complex current through the second antenna electrode 20 with respect to the first dashed line 52, the control and evaluation unit 26 is configured to select at least one threshold value from predefined threshold values ​​for complex impedance, as exemplified in the two right-hand diagrams of Fig. 2 is shown.

[0085] The following describes a design of a procedure for operating the capacitive seat occupancy detection and classification system 10 according to Fig. 1 described. In Fig. Figure 6 provides a flowchart of the procedure. It is understood that, in preparing for the use of the capacitive seat occupancy detection and classification system 10, all participating units and devices are in an operational state and as shown in Fig. 1 are configured as shown.

[0086] To carry out the procedure, the control and evaluation unit 26 includes a software module 58. The procedure steps to be performed are converted into program code for the software module 58. The program code is implemented in a digital data storage unit 66 of the control and evaluation unit 26 and can be executed by a processor unit 68 of the control and evaluation unit 26. Alternatively, the software module 58 can be located in and executed by a control unit of the vehicle (for example, the airbag control unit 60), and established data communication means between the control and evaluation unit 26 and the airbag control unit 60 of the vehicle would be used to enable mutual data transfer.

[0087] In a first step 70 of the procedure, a periodic electrical measurement signal is provided to the first antenna electrode 18 of the capacitive sensor 16. Then, in a further step 72, a complex detection current is determined by the detection current measuring device. This complex current is generated in the second antenna electrode 20 of the capacitive sensor 16 in response to the periodic electrical measurement signal provided to the first antenna electrode 18 of the capacitive sensor 16. Following the determination of the complex detection current relative to the complex reference potential, a step 74 is performed by the signal processing unit 22 to determine a corresponding complex impedance. In the next step 76, the determined complex impedance is compared with the predefined threshold values ​​for the complex impedance, which are defined by the first dashed line 52 in the left diagram of [reference missing]. Fig. 2 are represented.

[0088] Depending on the result of step 76 of the comparison, threshold values ​​are selected from predefined threshold values ​​for complex impedance in a further step 78. If the determined complex impedance above the first dashed line 52 in Fig. When the threshold value is 2, the control and evaluation unit 26 selects the threshold values ​​represented by a second dashed line 54, designated as "low load". This is shown in the upper part of the right side of Fig. 2 shown.

[0089] If the determined complex impedance is under the first dotted line 52 in Fig. 2, classification thresholds, represented by a third dashed line 56 designated as "high load", are selected by the control and evaluation unit 26. This is shown in the lower part of the right side of Fig. 2 shown.

[0090] In a further step 80, the signal processing unit 22 determines a complex detection current that is generated in the first antenna electrode 18 of the capacitive sensor 16 in response to the periodic electrical measurement signal provided to the first antenna electrode 18 of the capacitive sensor 16. In the following step 82, a complex impedance is determined from the complex detection current with respect to the complex reference potential.

[0091] In the next step 84, the control and evaluation unit 26 then compares the complex impedance received by the signal processing unit 22 with the selected predefined classification thresholds. For the sake of proof, it is assumed that the second dashed line 54, designated as "low load," was selected by the control and evaluation unit 26. The diagram in the upper part of the right side of Fig. In addition to the first zone 42, and also located above the second dashed line 54, diagram 2 includes a third zone 46, which represents complex impedances expected when the seat occupant is a human connected to mass. Below the second dashed line 54, the diagram includes a fourth zone 48, which represents complex impedances expected when the seat occupant is a non-mass-connected KRS 62.

[0092] In a subsequent step 86, the control and evaluation unit 26 determines a seat occupancy class based on the result of the preceding step 84 of the comparison and depending on a relationship between the determined complex impedance and the selected predefined threshold values ​​for complex impedance. For example, if the complex impedance derived from the measured current through the first antenna electrode 18 lies within the third zone 46, the seat occupancy class "person connected to ground" is selected.

[0093] In a further step 88, the control and evaluation unit 26 generates a classification output signal 28, which indicates the determined seat occupancy class. The classification output signal 28 is transmitted to the airbag control unit 60 to serve as the basis for a decision on whether to deploy an airbag system towards the vehicle seat.

[0094] The control and evaluation unit 26 is configured to automatically and periodically perform the above-described process steps 70-88.

[0095] The diagram in the lower right part of Fig. 2 includes the third zone 46, located above a third dashed line 56, and the fourth zone 48, located below the third dashed line 56. Furthermore, the diagram below the third dashed line 56 includes the second zone 44, which represents complex impedances expected when the seat occupant is a grounded KRS 62.

[0096] Fig.Figure 4 shows a second embodiment of the seat occupancy detection and classification system 10', which is installed in the seat 34. In this embodiment, the first antenna electrode 18 is formed by an electric seat heating element that is installed in the seat cushion 38 of the vehicle seat. The second antenna electrode 20 is formed by an electric seat heating element that is installed in the backrest 40 of the vehicle seat. The method for operating the capacitive seat occupancy detection and classification system 10 disclosed herein also applies to this alternative embodiment of the capacitive seat occupancy detection and classification system 10'.

[0097] Without providing a detailed description, it is further provided that the second antenna electrode 20, with suitable electrical connections to the signal voltage source and to the detection current measuring device, can be used in at least one operating mode of the seat occupancy detection and classification system 10, 10' as an additional detection antenna electrode in the same way as the first antenna electrode 18, in order to improve the performance of the discrimination with regard to seat occupancy.

[0098] Although the invention has been illustrated and described in detail in the drawings and the preceding description, this illustration and description are to be understood as illustrative or exemplary and not as limiting; the invention is not limited to the disclosed embodiments. Reference symbol list 10 Seat occupancy detection and classification system 12 capacitive detection devices 14 Impedance measurement circuit 16 capacitive sensors 18 first antenna electrode 20 second antenna electrode 22 Signal processing unit 24 Output signal 26 Control and evaluation unit 28 Classification output signal 30 Capacitor 32 unknown capacitor 34 seats 36 seat carriers 38 seat cushions 40 Backrest 42 1st Zone 44 2nd Zone 46 3rd Zone 48 4th Zone 52 1st line 54 2nd line 56 3rd line 58 Software module 60 Airbag control unit 62 KRS 64 Mass potential 66 digital data storage unit 68 processor units, steps 70 provide electrical measurement signal 72 Determine the recording current Determine 74 complex impedances 76 complex impedances compared with threshold values Select 78 thresholds 80 Determine the recording current Determine 82 complex impedances 84 complex impedances with selected thresholds Compare 86 88 Determine seat occupancy class Generate classification output signal

Claims

[1] Capacitive detection device (12) for a seat occupancy detection and classification system (10), comprising - a capacitive sensor (16) comprising at least a first electrically conductive antenna electrode (18) and a second electrically conductive antenna electrode (20), - an impedance measurement circuit (14) comprising the following: - a signal voltage source configured to provide a periodic electrical measurement signal at an output terminal with respect to a ground potential (64), and - at least one current sensing measuring device configured to measure complex currents relative to a reference voltage, characterized by that the impedance measurement circuit (14) can be electrically connected to the capacitive sensor (16) in such a way that - at least the first antenna electrode (18) can be electrically connected to the output terminal in order to receive the electrical measurement signal, - the second antenna electrode (20) can be electrically connected via at least one controllable switching element either to the ground potential (64) or to an alternating current potential of the output terminal, wherein the complex sensing currents in the capacitive sensor (16) are generated by the provided periodic measurement signal, and the capacitive sensing device (12) has a signal processing unit (22) configured to - to determine at least a first complex impedance from a measured current through the first antenna electrode (18) when the second antenna electrode (20) is electrically connected to the ground potential (64), and - to determine a second complex impedance from a measured current through the first antenna electrode (18) when the second antenna electrode (20) is electrically connected to the alternating current potential of the output terminal, and - to provide output signals (24) that are representative of the determined complex impedances; and that the capacitive sensing device (12) has a control and evaluation unit (26) configured to - to receive the output signals (24) provided by the signal processing unit (22), depending on a relationship between the first and second complex impedance, to select at least one threshold from predefined thresholds for complex impedance, - to compare the complex impedances from the measured current through the first antenna electrode (18) with at least one selected predetermined threshold value and - based on the result of the comparison, to determine a seat occupancy class. [2] Seat occupancy detection and classification system (10), in particular vehicle seat occupancy detection and classification system (10), comprising - a capacitive detection device (12) according to claim 1, wherein the capacitive sensor (16) can be electrically connected to the impedance measuring circuit (14) in such a way that a current through the second antenna electrode (20) can be measured by the impedance measuring circuit (14), and wherein the signal processing unit (22) is further configured to to determine at least a complex impedance from a measured current through the second antenna electrode (20) determined with reference to the complex reference potential, and - a control and evaluation unit (26) configured to to receive the output signals (24) provided by the signal processing unit (22), depending on a result of the complex impedance from the measured current through the second antenna electrode (20), at least one threshold value is selected from predefined threshold values ​​for complex impedance, to compare the complex impedances from the measured current through the first antenna electrode (18) with at least one selected predetermined threshold value and based on the result of the comparison, to determine a seat occupancy class. [3] Seat occupancy detection and classification system (10), in particular vehicle seat occupancy detection and classification system (10), comprising a capacitive detection device (12) according to claim 1. [4] Seat occupancy detection and classification system (10), in particular vehicle seat occupancy detection and classification system (10), comprising - a capacitive detection device (12) according to claim 1, wherein the capacitive sensor (16) can be electrically connected to the impedance measuring circuit (14) in such a way that the second antenna electrode (20) can be electrically connected alternately to the ground potential (64) and to the electrical AC potential of the output terminal via the at least one controllable switching element, and wherein the signal processing unit (22) is further configured to determine at least one difference between the first complex impedance and the second complex impedance, and - a control and evaluation unit (26) configured to select at least one threshold value from predefined threshold values ​​for complex impedance, depending on the difference between the first and second complex impedances, to compare the complex impedances from the measured current through the first antenna electrode (18) with at least one selected predetermined threshold value and based on the result of the comparison, to determine a seat occupancy class. [5] Seat occupancy detection and classification system (10) according to claim 3 or 4, wherein the capacitive detection device (12) comprises at least one remotely controllable switching element and the seat occupancy detection and classification system (10) comprises a switching remote control unit for remotely controlling the at least one remotely controllable switching element. [6] Capacitive seat occupancy detection and classification system (10) according to claim 5, wherein the switching remote control unit is configured to periodically switch the remotely controllable switching element such that it changes an electrical connection of the second antenna electrode (20) for a predetermined period from a state electrically connected to the electrical ground potential (64) to a state electrically connected to the electrical AC potential of the output terminal and, after the period has elapsed, back to a state electrically connected to the electrical ground potential (64). [7] Capacitive seat occupancy detection and classification system (10) according to any one of claims 2 to 6, further comprising a capacitive sensor (16), wherein the capacitive sensor (16) is electrically connected at least to the output terminal of the signal voltage source and to the detection current measuring device. [8] Capacitive seat occupancy detection and classification system (10) according to any one of claims 2 to 7, wherein the control and evaluation unit (26) is configured to generate a classification output signal (28) indicating the determined seat occupancy class. [9] Capacitive seat occupancy detection and classification system (10) according to any one of claims 2 to 6, wherein the at least one threshold value from the predetermined threshold values ​​for complex impedance can be represented by a line in a two-dimensional diagram spanned by a real part and an imaginary part of the complex impedance. [10] Method for operating the capacitive seat occupancy detection and classification system (10) according to claim 2, comprising the following steps: - Providing (70) a periodic electrical measurement signal at the first antenna electrode (18) of the capacitive sensor (16), - Determining (72) a complex detection current generated in the second antenna electrode (20) of the capacitive sensor (16) in response to the periodic electrical measurement signal provided to the first antenna electrode (18) of the capacitive sensor (16), - Comparing (76) the determined complex acquisition stream with at least one predetermined threshold for the complex acquisition stream, - depending on the result of the step of comparing (76), selecting (78) at least one threshold from predefined thresholds for complex impedance, - Determining (80) a complex detection current generated in the first antenna electrode (18) of the capacitive sensor (16) in response to the periodic electrical measurement signal provided to the first antenna electrode (18) of the capacitive sensor (16), - Determining (82) a complex impedance from the complex detection current measured in the first antenna electrode (18) with respect to the complex reference potential, - Comparing (84) the determined complex impedance with at least one selected predefined threshold for complex impedance, and - Determining (86) a seat occupancy class for the determined complex impedance depending on a relationship between the determined complex impedance and at least one selected predefined threshold for complex impedance. [11] Method for operating the capacitive seat occupancy detection and classification system (10) according to claims 3 to 9, comprising the following steps: - Providing (70) a periodic electrical measurement signal at the first antenna electrode (18) of the capacitive sensor (16), - electrical connection of the second antenna electrode (20) to the ground potential (64), - Determining a first complex detection current that is generated in the first antenna electrode (18) of the capacitive sensor (16) in response to the periodic electrical measurement signal provided to the first antenna electrode (18) of the capacitive sensor (16), - Determining a first complex impedance from the first complex detection current measured in the first antenna electrode (18) with reference to the complex reference potential, - Changing the electrical connection of the second antenna electrode (20) from the ground potential (64) to the alternating current potential of the output terminal, - Determining a second complex detection current that is generated in the first antenna electrode (18) of the capacitive sensor (16) in response to the periodic electrical measurement signal provided to the first antenna electrode (18) of the capacitive sensor (16), - Determining a second complex impedance from the first complex detection current measured in the first antenna electrode (18) with respect to the complex reference potential, - Determining the difference between the first complex impedance and the second complex impedance, - Comparing the determined difference between the first complex impedance and the second complex impedance with at least one predetermined threshold for the difference of the complex impedance, - depending on the result of the comparison step, selecting at least one threshold from predefined thresholds for complex impedance, - Comparing the determined first complex impedance with at least one selected predefined threshold for complex impedance, - Determining a seat occupancy class for the determined first complex impedance depending on at least one relationship between the determined first complex impedance and the at least one selected predefined threshold for complex impedance. [12] Method for operating the capacitive seat occupancy detection and classification system (10) according to claims 4 to 9, comprising the following steps: - Providing (70) a periodic electrical measurement signal at the first antenna electrode (18) of the capacitive sensor (16), - alternating connection of the second antenna electrode (20) to the ground potential (64) and to the alternating current potential of the output terminal, - Determining a difference between a first complex impedance of the first antenna electrode (18), wherein the second antenna electrode (20) is electrically connected to the ground potential (64), and a second complex impedance of the first antenna electrode (18), wherein the second antenna electrode (20) is electrically connected to the AC potential of the output terminal, - Comparing the determined difference between the first complex impedance and the second complex impedance with at least one predetermined threshold for the difference of the complex impedance, - depending on the result of the comparison step, selecting at least one threshold from predefined thresholds for complex impedance, - Comparing the determined first complex impedance with at least one selected predefined threshold for complex impedance, - Determining a seat occupancy class for the determined first complex impedance depending on at least one relationship between the determined first complex impedance and the at least one selected predefined threshold for complex impedance. [13] Seat (34), in particular vehicle seat, comprising - a seat cushion (38) with at least one seat foam element, - a seat support (36) configured to receive at least a section of the seat cushion (38), wherein the seat support (36) and the seat cushion (38) are intended to support the buttocks of a seat user, - a backrest (40) designed to support the back of the seat user, and - a seat occupancy detection and classification system (10) according to any one of claims 2 to 9, wherein the capacitive sensor (16) is arranged on at least one of the seat cushion (38) and the backrest (40). [14] Seat (34) according to claim 13, wherein at least one of the first antenna electrode (18) and the second antenna electrode (20) is formed by an electric seat heating element which is installed in the seat (34). [15] Software module (58) for carrying out the method according to any one of claims 10 to 12, wherein the method steps to be carried out are converted into a program code of the software module (58), wherein the program code can be implemented in a digital data storage unit of the capacitive seat occupancy detection and classification system (10) or a separate control unit and can be executed by a processor unit of the capacitive seat occupancy detection and classification system (10) or a separate control unit. [16] Use of the capacitive seat occupancy detection and classification system (10) according to any one of claims 2 to 9 in a vehicle seat comprising: - a seat structure for mounting the vehicle seat on a passenger compartment floor of the vehicle, - a seat cushion (38) with at least one seat foam element, - a seat support (36) which is supported by the seat structure and is configured to receive the seat cushion (38), wherein the seat support (36) and the seat cushion (38) are intended to support the buttocks of a seat user, - a backrest (40) designed to support the back of the seat user, wherein the capacitive sensor element (16) is arranged on at least one of the seat cushion (38) and the backrest (40).

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