Capacitive seat occupancy detection and classification system

Abstract

Capacitive seat occupancy detection and classification system (16), in particular vehicle seat occupancy detection and classification system (16), comprising an impedance measurement circuit (18) and a control and evaluation unit (30), characterized in that the impedance measurement circuit (18) comprises the following: - a signal voltage source (20) designed to apply periodic electrical measurement signals to an output terminal (22), wherein a capacitive sensor (36) can be electrically connected to the output terminal (22) to receive the electrical measurement signals, and wherein the signal voltage source (20) is designed to generate periodic measurement signals of N different fundamental frequencies, where N is a natural number of at least 3, - a sensing current measuring circuit (24) designed to determine complex sensing currents generated in the capacitive sensor (36) by the provided periodic measurement signals of at least N different fundamental frequencies, - a signal processing unit (26) designed to to determine a complex impedance from each of the specified sensing currents with reference to a complex reference potential, and to provide output signals (28) that are representative of the complex impedances that have been determined at at least N different fundamental frequencies, and that the control and evaluation unit (30) is designed to to receive the output signals (28) provided by the signal processing unit (26), to compare each of the complex impedances that have been determined at at least N different fundamental frequencies with predetermined threshold values, based on the result of the comparison, to determine a seat occupancy class for each of the complex impedances that have been determined at at least N different fundamental frequencies and to determine a final seating class derived by a majority decision from the seating classes determined for each of the complex impedances determined at one of the at least N different fundamental frequencies, where N is equal to [(2 xn) + 1], where n is a natural number greater than 1, representing the number of potential resonances or electromagnetic (EM) narrowband interferences.

Description

Technical field

[0001] The invention relates to a capacitive seat occupancy detection and classification system, in particular a vehicle seat occupancy detection and classification system, a method for operating such a capacitive seat occupancy detection and classification system and a vehicle seat comprising such a capacitive seat occupancy detection and classification system. Background of the invention

[0002] The use of vehicle seat occupancy detection and / or classification systems is widespread today in vehicles, particularly passenger cars, to provide a seat occupancy signal to various devices, for example, for the purpose of a seat belt reminder system (SBR) or activation control for an auxiliary restraint system (ARS). Many seat occupancy detection and / or classification systems incorporate seat occupancy sensors based on capacitive sensing.

[0003] The term "capacitive sensor" refers to a sensor that generates a signal responding to the influence of the detected object (a person, a part of a person's body, a pet, an object, etc.) on an electric field. A capacitive sensor generally comprises at least one antenna electrode to which an oscillating electrical signal is applied, and which then emits an electric field into a region of space near the antenna electrode while the sensor is operating. The sensor has at least one sensing electrode, which may be identical to or different from the emitting antenna electrode, and at which the influence of an object or living being on the electric field is detected.

[0004] Vehicle seat occupancy detection and / or classification systems are known to be used as a means of assessing the potential activation of a built-in passenger restraint system in the vehicle, such as an airbag. An output signal from the seat occupancy detection and / or classification system is normally transmitted to an electronic control unit of the vehicle to serve, for example, as a basis for a decision to deploy an airbag system for the vehicle seat.

[0005] International Patent Application WO 2011 / 079092 A1 describes an occupant detection system and a method for detecting an occupant seated in a vehicle. An electrode is positioned in the seat near the expected location of an occupant to detect the presence of an occupant in its vicinity. The electrode may be integrated with a seat heater. A control circuit controls the seat heater. A signal generator is coupled to the electrode and is designed to output multiple signals at multiple frequencies to the electrode. The occupant detection circuit detects voltages that respond to the multiple signals at multiple frequencies and, based on the detected voltages, determines whether the seat is occupied. An LC circuit coupled to the electrode and the control circuit suppress the capacitance generated by the control circuit.

[0006] Document EP 2 572 943 A1 discloses a combined heating and capacitive occupant detection system. The system includes a heating element that also serves as an antenna electrode for a capacitive detection circuit. The system further includes a common-mode choke connected to the heating element's terminals to couple the heating element to a DC power supply. The capacitive detection is designed to inject two AC currents of two different frequencies into the heating element and, based on calculations taking into account the common-mode choke's behavior, determine seat occupancy.

[0007] Other systems or methods for the detection and / or classification of vehicle occupants are known, for example, from the publications DE 10 2007 063 034 A1, DE 10 2011 005 551 A1 and DE 11 2010 004 513 T5. Object of the invention

[0008] It has been observed that a capacitive measuring circuit of a vehicle seat occupancy detection and / or classification system designed for operation with a carrier frequency of > 1 MHz (for example, 4 to 6 MHz) is easily disturbed by resonances present in the measuring system due to parasitic inductances and capacitances.

[0009] The invention is therefore based on the objective of providing a capacitive measuring circuit for a vehicle seat occupancy detection and / or classification system with improved robustness with regard to the ability to correctly classify a seat occupancy. General description of the invention

[0010] According to one aspect of the present invention, the problem is solved by a capacitive seat occupancy detection and classification system, in particular a vehicle seat occupancy detection and classification system, comprising an impedance measurement circuit and a control and evaluation unit.

[0011] The impedance measurement circuit comprises a signal voltage source designed to provide periodic electrical measurement signals at an output terminal. A capacitive sensor is electrically connected to the output terminal to receive these signals. The signal voltage source is designed to generate periodic measurement signals of N different fundamental frequencies, where N is a natural number of at least 3 (i.e., 3, 4, 5, etc.).

[0012] Furthermore, the impedance measurement circuit includes a sensing current measurement circuit designed to determine complex sensing currents generated in the capacitive sensor by the provided periodic measurement signals of at least N different fundamental frequencies. These complex sensing currents indicate the position of an object relative to the capacitive sensor.

[0013] Furthermore, the impedance measurement circuit includes a signal processing unit designed to determine a complex impedance from each of the determined sensing currents with reference to a complex reference potential and to provide output signals representative of the complex impedances determined at at least N different fundamental frequencies.

[0014] The capacitive seat occupancy detection and classification system then comprises a control and evaluation unit designed to receive the output signals provided by the signal processing unit, to compare each of the complex impedances determined at at least N different fundamental frequencies with predetermined thresholds, and, based on the result of the comparison, to determine a seat occupancy class for each of the complex impedances determined at at least N different fundamental frequencies.

[0015] The control and evaluation unit is further designed to determine a final seat occupancy class derived from a majority decision among the seat occupancy classes determined for each of the complex impedances determined at one of the at least N different fundamental frequencies.

[0016] According to an important aspect of the invention, N is equal to [(2 x n) + 1], where n is a natural number greater than 1 representing the number of potential resonances or electromagnetic (EM) narrowband interferences. That is, N can be equal to 5, 7, 9, etc., which advantageously increases the possibility that only a small fraction of the various fundamental frequencies are disturbed by a number n of resonances or electromagnetic (EM) narrowband interferences that exist due to parasitic inductances and capacitances.

[0017] The term "vehicle" as used in this application shall be understood in particular to include passenger cars, trucks and buses.

[0018] The term “electrically connectable or connectable”, as used in this application, is to be understood as encompassing galvanic electrical connections or connections as well as connections or connections that are made by capacitive and / or inductive electromagnetic coupling.

[0019] The term “designed for” as used in this application is understood in particular to mean specially programmed, designed, set up or arranged.

[0020] The term “fundamental frequency”, as used in this application, is understood in particular to mean a lowest sinusoidal frequency in a Fourier analysis of a periodic electrical measurement signal.

[0021] The phrase “different fundamental frequencies”, as used in this application, is understood in particular to mean that the two periodic measurement signals with different fundamental frequencies do not overlap in the frequency domain.

[0022] It should also be noted that the terms “first”, “second”, etc. are used in this application for the purpose of differentiation only and are in no way intended to indicate or anticipate any order or priority.

[0023] By incurring the expense of generating additional periodic electrical measurement signals and providing them to a capacitive sensor, improved robustness can be achieved in the ability to correctly classify seat occupancy. This is based on the understanding that, for a given number of different fundamental frequencies, there is a high probability that only a fraction of these frequencies will be affected by resonances caused by parasitic inductances and capacitances present in an installed capacitive seat occupancy detection and classification system.

[0024] The seat occupant classes can be determined from a group of predetermined seat occupant classes, which may include, among others, "empty", "child", "child in a child restraint system" and "adult".

[0025] In some embodiments, the N different fundamental frequencies, where N is a natural number of at least 3, are spaced at equal intervals in the frequency domain.

[0026] In some embodiments, the N different fundamental frequencies, where N is a natural number of at least 3, are randomly placed in the frequency domain.

[0027] Preferably, the 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, some embodiments also consider operating the 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 with effect for the purposes of the case law that permits incorporation by reference.

[0028] Preferably, the control and evaluation unit is designed to generate an output signal indicating the specific final seat occupancy class. This allows the information regarding the specific final seat occupancy class to be easily transmitted to an electronic control unit of the vehicle, for example, to serve as a basis for a decision to use an additional restraint system (ARS), such as an airbag system, for the vehicle seat, for example via a CAN communication link, as is generally known in the field.

[0029] In a preferred embodiment of the capacitive seat occupancy detection and classification system, N is equal to [(2 x n) + 1 + k], where n is a natural number greater than 1 representing the number of potential resonances, and k is the number of potential narrowband interferences of the impedance measurement circuitry in an installed state of the seat occupancy detection and classification system. This allows for improved robustness with respect to the ability to correctly classify a seat occupancy, even when n resonances and k electromagnetic (EM) narrowband interferences are present.

[0030] Preferably, the different fundamental frequencies are selected from a frequency range between 1 MHz and 10 MHz for improved seat occupancy detection and classification capability.

[0031] In some embodiments, the signal voltage source is designed to simultaneously generate the periodic measurement signals of at least N different fundamental frequencies. In this way, one measurement frequency remains virtually unaffected, compared to the case of using a periodic measurement signal of a single fundamental frequency.

[0032] However, if the focus of an application is not on achieving a high measurement frequency of the capacitive seat occupancy detection and classification system, the signal voltage source can be designed to sequentially generate the periodic measurement signals of at least N different fundamental frequencies.

[0033] In some embodiments of the capacitive seat occupancy detection and classification system, the majority decision to determine a final seat occupancy class among the seat occupancy classes determined for each of the complex impedances determined at the at least N different fundamental frequencies can be expressed as M>n+12+p with p <n+12, where M is the number of complex impedances for which a specific seat occupancy class has been determined, and p is a natural number including zero.

[0034] When p = 0, the majority decision is based on a simple majority, since M is greater than N2=12⋅(2n+1)=n+12 must be.

[0035] A case where p ≠ 0 can be advantageously chosen to achieve a higher level of reliability in determining the final seat occupancy class. For example, in the case of n = 4, which results in a number N of different fundamental frequencies equal to 9, p could be chosen as 0, 1, 2, 3, and 4 (the case of p = 0 was discussed above).

[0036] In this way, the majority decision can be based on the requirement that M must be equal to or greater than 6 (at p = 1), that M must be equal to or greater than 7 (at p = 2), that M must be equal to or greater than 8 (at p = 3), and that M must be equal to 9 (at p = 4). This allows the majority decision for determining the final seat allocation class to be adjusted to take into account the criticality of specific seat allocation classes.

[0037] According to a further aspect of the invention, a vehicle seat is provided. The vehicle seat 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, and a seat base that is supported by the seat structure and designed to receive the seat cushion. The seat base and the seat cushion are intended to support the buttocks of a seat occupant.

[0038] Furthermore, the vehicle seat includes a backrest designed to support the back of the seat occupant. The vehicle seat then includes an embodiment of the vehicle seat occupant detection and classification system disclosed above, wherein the capacitive sensor is arranged on the seat cushion or on the backrest of the vehicle seat.

[0039] This allows a vehicle seat equipped with a robust seat occupant detection and classification system to be provided with improved robustness in terms of its ability to correctly classify seat occupancy.

[0040] According to yet another aspect of the invention, a method for operating the capacitive seat occupancy detection and classification system disclosed herein is provided.

[0041] The process includes the following steps: - Providing a periodic electrical measurement signal of a first fundamental frequency from at least N different fundamental frequencies for the capacitive sensor, where N is equal to [(2 xn) + 1], where n is a natural number greater than 1, which is the number of potential resonances or electromagnetic (EM) narrowband interferences, - Determining a complex sensing current that is generated in the capacitive sensor in response to the provided periodic electrical measurement signal, - Determine, based on a complex reference potential, a complex impedance from the determined sensing current, - Comparing the specific complex impedance with predetermined threshold values, - Determining a seat occupancy class for a given complex impedance, - Repeat the preceding steps for the remaining periodic measurement signals of at least N different fundamental frequencies, and - Determining a final seating class by making a majority decision among the seating classes that have been determined for each of the complex impedances that have been determined at at least N different fundamental frequencies. Brief description of the drawings

[0042] 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 which displays a capacitive seat occupancy detection and classification system according to the invention; Fig. 2 shows an electrical equivalent circuit of a capacitive sensor mounted in a vehicle seat and connected to an impedance measurement circuit of the capacitive seat occupancy detection and classification system according to Fig. 1 is connected; Fig. 3 a flowchart of a procedure for operating the capacitive seat occupancy detection and classification system according to Fig. 2 is; and Fig. 4 illustrates a calculated capacity that is theoretically compatible with the capacitive seat occupancy detection and classification system according to Fig. 1 can be measured by inserting periodic measurement signals in a frequency range between 2 MHz and 7 MHz and in the presence of a resulting resonance at a frequency of 5 MHz. Description of preferred embodiments

[0043] Fig. Figure 1 schematically shows a vehicle seat 10, which incorporates a capacitive seat occupancy detection and classification system 16 according to the invention. The vehicle seat 10 is designed as a seat for a passenger car 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.

[0044] 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 a seat occupant. The seat cushion 12 of the vehicle seat 10 comprises a seat foam element and a fabric cover, which is Fig. 1 is omitted. The seat base and seat cushion 12 are intended to support the buttocks of the seat occupant. A backrest 14 of the vehicle seat 10 is intended to support the back of the seat occupant.

[0045] The vehicle seat occupant detection and classification system 16 comprises a capacitive sensor 36, an impedance measurement circuit 18, and a control and evaluation unit 30. The capacitive sensor 36 is located on the A-surface of the seat cushion 12 beneath the fabric cover. The impedance measurement circuit 18 and the control and evaluation unit 30 are installed in the vehicle away from the vehicle seat 10.

[0046] Fig. Figure 2 shows an electrical equivalent circuit of the capacitive sensor 36, which is mounted in the vehicle seat 10 and connected to the impedance measurement circuit 18 of the capacitive seat occupancy detection and classification system 16.

[0047] The capacitive sensor 36 has a sensing electrode terminated by a sensing node 42 and a sensing frame impedance 38, which is primarily capacitive in nature, connected between the sensing node 42 and a seat frame that forms part of the seat structure and in Fig. 2 is represented by a seat frame node 46. In the example shown, the impedance between the frame node 46 and a vehicle body node 48, which in principle can be a combination of capacitance, resistance, and inductance, is chosen only as a capacitance 40. The capacitance is selected such that it easily shows where the resonance originates. Furthermore, according to Fig. Figure 2 shows that an inductor describes a wiring inductance 50 between the seat frame and a measuring mass 54. Fig. Figure 2 includes another inductor to represent a wiring inductance 52 between the vehicle body node 48 and the measuring ground 54. It should be noted that each of the impedances between the seat frame and a measuring ground 54, or between the vehicle body node 48 and the measuring ground 54, can in principle be a combination of capacitance, resistance, and inductance. In the example shown, these impedances are represented as simple inductors for illustrative purposes.

[0048] The capacitive sensor 36 is electrically connected to the impedance measurement circuit 18. The capacitive sensor 36 is designed to operate in charging mode. A sensing current flowing through the sensing node 42 indicates the position of an object relative to the capacitive sensor 36. An object approaching the sensing electrode is represented in the equivalent electrical circuit diagram by Fig. 1 represented by an unknown impedance 44 (shown as a capacitor) connected to an earth potential formed by the vehicle body node 48.

[0049] The impedance measurement circuit 18 comprises a signal voltage source 20, a sensing current measurement circuit 24, and a signal processing unit 26. The signal voltage source 20 is designed to provide periodic electrical measurement signals at an output terminal 22 at various fundamental frequencies within a frequency range of 1 MHz to 10 MHz. The capacitive sensor 36 is electrically connected to the output terminal 22 via the sensing current measurement circuit 24 to receive the periodic electrical measurement signals. The sensing current measurement circuit 24 is designed to determine complex sensing currents generated in the capacitive sensor 36 by the provided periodic measurement signals. The signal processing unit 26 is designed to determine a complex impedance of each of the determined sensing currents using a complex reference potential provided to the output terminal 22 of the signal voltage source 20.The signal processing unit 26 is further designed to provide output signals 28 that are representative of the specified complex impedances.

[0050] Due to the in Fig. In the additional electrical paths shown between the seat frame node 46, the vehicle body node 48 and the measuring mass 54, resonant vibrations can be generated at a frequency close to a fundamental frequency of the electrical measurement signal, thereby introducing an intolerably large measurement error.

[0051] A result of an exemplary calculation based on the equivalent circuit from Fig. 2 and the following values ​​is in Fig. Figure 4 shows the following for periodic measurement signals used in a frequency range between 2 MHz and 7 MHz: - Capacitance representing the unknown impedance 44: 50 pF - Capacitance representing the sensing rack impedance 38: 50 pF - Capacitance representing the impedance 40 between the seat frame and the vehicle body: 2 nF - Wiring inductance 50 / resistance representing the impedance between the seat frame node 46 and the measuring ground 54: 300 nH, 10 mΩ - Wiring inductance 52 / resistance indicating the impedance between the vehicle body node 48 and the measuring ground 54: 200 nH, 10 mΩ

[0052] In Fig. Figure 4 illustrates the specific complex impedance as a calculated capacitance. It is derived from Fig. 4. It is evident that an intolerably large measurement occurs if the fundamental frequency of the electrical measurement signal is selected close to 5 MHz.

[0053] The capacitive seat occupancy detection and classification system 16 according to the invention solves this problem by inserting periodic measurement signals of N different fundamental frequencies, where N is a natural number of at least 3, as will be described later.

[0054] For this purpose, the signal voltage source 20 is designed to generate periodic measurement signals of N different fundamental frequencies, where N is a natural number of at least 3. In this specific embodiment, the signal voltage source 20 is designed to generate the measurement signals of different fundamental frequencies sequentially. The signal processing unit 26 is designed to provide output signals 28 that are representative of the complex impedances determined at the N different fundamental frequencies.

[0055] The control and evaluation unit 30 is designed to receive the output signals 28, which are representative of the complex impedances, as input signals, and it is designed to compare each of the complex impedances, which have been determined at the N different fundamental frequencies, with two distinct, predetermined threshold values.

[0056] The control and evaluation unit 30 is designed to determine a seat occupancy class for each of the complex impedances determined at the N different fundamental frequencies, based on the comparison results. The seat occupant classification includes the occupancy classes "empty", "child", and "adult".

[0057] The number N can be selected in advance without knowledge of a number n of resonances or a number k of narrowband EM interferences that exist in the relevant frequency range in the installed state of the capacitive seat occupancy detection and classification system 16.

[0058] If prior information about a number n of resonances in the relevant frequency range is available, for example from measurements, the number N can be selected according to N = (2 x n) + 1. In the theoretical example from Fig. 4 is n equals 1, and a number N of 3 would be suitably chosen.

[0059] Preliminary information about a number n of resonances and a number k of narrowband electromagnetic interferences in the relevant frequency range can be obtained, for example, from a measurement taken with the capacitive seat occupancy detection and classification system 16 installed. Narrowband electromagnetic interferences can be detected by first performing an interference detection measurement by switching off the signal voltage source 20 and measuring a potentially interfering current at the sensing current measurement circuit 24. The fundamental frequencies for the periodic measurement signals near which an interfering current has been detected are omitted during a subsequent resonance suppression measurement and detection. In this case, the number N can be selected according to N = (2 x n) + 1 + k.

[0060] In this particular embodiment, no prior information about resonances or narrowband electromagnetic interference is available. The number N of fundamental frequencies of periodic measurement signals was selected as 9. The fundamental frequencies are equally spaced within the frequency domain in the frequency range between 1 MHz and 10 MHz.

[0061] The control and evaluation unit 30 is further designed to determine a final seat occupancy class derived from a majority decision among the seat occupancy classes determined for each of the complex impedances determined at one of the 9 different fundamental frequencies, as described in a procedure for operation below.

[0062] Furthermore, the control and evaluation unit 30 is designed to generate an output signal 32 that indicates the specific final seat occupancy class. The output signal 32 generated by the control and evaluation unit 30 can be fed to an airbag control unit 56 of the vehicle via a CAN communication link 34 for the purpose of airbag activation control. For example, if the specific final seat occupancy class is "adult", an airbag of the vehicle seat 10 is deployed.

[0063] Below is described an embodiment of a method for operating the capacitive seat occupancy detection and classification system 16 according to Fig. 1 described. A flowchart of the procedure is shown in Fig. 3. When preparing for the use of the capacitive seat occupancy detection and classification system 16, it is understood that all affected units and devices are in an operational state and as described in the Fig. 1 and Fig. 2 are illustrated.

[0064] In a first step 58 of the procedure, a periodic electrical measurement signal of a first fundamental frequency of the 9 different fundamental frequencies is provided to the capacitive sensor 36 by the signal voltage source 20.

[0065] In a next step 60, a complex sensing current, which is generated in the capacitive sensor 36 in response to the provided periodic electrical measurement signal, is determined by the sensing current measurement circuit 24.

[0066] In a further step 62, the signal processing unit 26 determines a complex impedance based on the specified sensing current with reference to the complex reference potential provided by the output terminal 22 of the signal voltage source 20. In the next step 64, an output signal 28, representative of the specified complex impedance, is provided to and received by the control and evaluation unit 30.

[0067] Then, in a further step 66, the control and evaluation unit 30 compares the determined complex impedance with predetermined threshold values ​​located in a digital data storage unit (not shown) of the control and evaluation unit 30.

[0068] Based on the result of the comparison in step 66, the control and evaluation unit 30 determines a seat occupancy class for the specified complex impedance from a group of predetermined seat occupancy classes in a next step 68.

[0069] The preceding steps 58-68 are repeated for the remaining periodic measurement signals of the 9 different fundamental frequencies.

[0070] In the following step 70, the control and evaluation unit 30 determines a final seat occupancy class by making a majority decision among the seat occupancy classes that have been determined for each of the complex impedances that have been determined at the 9 different fundamental frequencies.

[0071] The majority decision can be considered a condition of M>n+12+p . with p <n+12 expressed as M is the number of complex impedances for which a specific seat occupancy class has been determined by the control and evaluation unit 30, and p is a natural number including zero. In this specific embodiment, n is equal to 4 and p is selected as 2. Consequently, the majority decision condition means that the control and evaluation unit 30 must have determined the same seat occupancy class for (M=) 7 complex impedances, which were determined at the 9 different fundamental frequencies, in order to determine this seat occupancy class as the final seat occupancy class.

[0072] Then, in a further step 72, the control and evaluation unit 30 generates an output signal 32 that indicates the determined final seat occupancy class if the condition for the majority decision was met. The output signal 32 is transmitted to the airbag control unit 56 to serve as the basis for a decision on whether to deploy an airbag system for the vehicle seat 10. List of reference symbols 10 vehicle seats 12 seat cushions 14 Backrest 16 Seat occupancy detection and classification system 18 Impedance measurement circuit 20 Signal voltage source 22 Output port 24 Sense current measuring device 26 Signal processing unit 28 Output signal 30 Control and evaluation unit 32 Output signal 34 Communication link 36 capacitive sensors 38 Sensing frame impedance 40 seat frame vehicle body capacity 42 tapping nodes 44 unknown impedance 46 seat frame nodes 48 vehicle body nodes 50 Wiring inductance (seat frame ground) 52 Wiring inductance (chassis ground) 54 Measuring masses 56 Airbag control unit Steps: 58 Providing a periodic electrical measurement signal (f1) 60 Determining a complex sensing flow 62 Determining the complex impedance 64 Providing an output signal 66 Comparing complex impedance with threshold values 68 Determining the seat occupancy class 70 Determining the final seat occupancy class 72 Generating an output signal

Claims

[1] Capacitive seat occupancy detection and classification system (16), in particular vehicle seat occupancy detection and classification system (16), comprising an impedance measurement circuit (18) and a control and evaluation unit (30), characterized by , that the impedance measurement circuit (18) comprises the following: - a signal voltage source (20) designed to apply periodic electrical measurement signals to an output terminal (22), wherein a capacitive sensor (36) can be electrically connected to the output terminal (22) to receive the electrical measurement signals, and wherein the signal voltage source (20) is designed to generate periodic measurement signals of N different fundamental frequencies, where N is a natural number of at least 3, - a sensing current measuring circuit (24) designed to determine complex sensing currents generated in the capacitive sensor (36) by the provided periodic measurement signals of at least N different fundamental frequencies, - a signal processing unit (26) designed to to determine a complex impedance from each of the specified sensing currents with reference to a complex reference potential, and to provide output signals (28) that are representative of the complex impedances that have been determined at at least N different fundamental frequencies, and that the control and evaluation unit (30) is designed to to receive the output signals (28) provided by the signal processing unit (26), to compare each of the complex impedances that have been determined at at least N different fundamental frequencies with predetermined threshold values, based on the result of the comparison, to determine a seat occupancy class for each of the complex impedances that have been determined at at least N different fundamental frequencies and to determine a final seating class derived by a majority decision from the seating classes determined for each of the complex impedances determined at one of the at least N different fundamental frequencies, where N is equal to [(2 xn) + 1], where n is a natural number greater than 1, representing the number of potential resonances or electromagnetic (EM) narrowband interferences. [2] Capacitive seat occupancy detection and classification system (16) according to claim 1, wherein the control and evaluation unit (30) is designed to generate an output signal (32) indicating the determined final seat occupancy class. [3] Capacitive seat occupancy detection and classification system (16) according to one of the preceding claims, wherein N is equal to [(2 xn) + 1 + k], where n is a natural number greater than 1, n represents the number of potential resonances and k is a number of potential narrowband interferences of the impedance measurement circuit (18) in the installed state. [4] Capacitive seat occupancy detection and classification system (16) according to one of the preceding claims, wherein the different fundamental frequencies are selected from a frequency range between 1 MHz and 10 MHz. [5] Capacitive seat occupancy detection and classification system (16) according to one of the preceding claims, wherein the signal voltage source (20) is designed to simultaneously generate the periodic measurement signals of at least N different fundamental frequencies. [6] Capacitive seat occupancy detection and classification system (16) according to any of the preceding claims, wherein the majority decision for determining a final seat occupancy class from the seat occupancy classes determined for each of the complex impedances determined at the at least N different fundamental frequencies is considered M>n+12+p with p <n+12can be expressed where M is the number of complex impedances for which a specific seat occupancy class has been determined, and p is a natural number including zero. [7] Capacitive seat occupancy detection and classification system (10) according to one of the preceding claims, further comprising a capacitive sensor (36), wherein the capacitive sensor (36) is electrically connected to the output terminal (22) of the signal voltage source (20) and to the sensing current measuring circuit (24). [8] Vehicle seat (10), comprising - a seat 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 (14) designed to support the back of the seat occupant, and - a vehicle seat occupancy detection and classification system (16) according to claim 7, wherein the capacitive sensor (36) is arranged on the seat cushion (12) or on the backrest (14). [9] Method for operating the capacitive seat occupancy detection and classification system (16) according to any one of claims 1 to 7, comprising the following steps: - Providing (58) a periodic electrical measurement signal of a first fundamental frequency from at least N different fundamental frequencies for the capacitive sensor (36), where N is equal to [(2 xn) + 1], where n is a natural number greater than 1 representing the number of potential resonances or electromagnetic (EM) narrowband interferences, - Determining (60) a complex sensing current that is generated in the capacitive sensor (36) in response to the provided periodic electrical measurement signal, - Determine (62) using a complex reference potential, a complex impedance from the determined sensing current, - Comparing (66) the determined complex impedance with predetermined threshold values, - Determining (68) a seat occupancy class for the given complex impedance, - Repeat the preceding steps (58-68) for the remaining periodic measurement signals of at least N different fundamental frequencies, and - Determining (70) a final seating class by making a majority decision among the seating classes that have been determined for each of the complex impedances that have been determined at at least N different fundamental frequencies. [10] Use of the capacitive seat occupancy detection and classification system (16) according to claim 7 in a vehicle seat (10) comprising the following: - a seat 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 (14) designed to support the back of the seat occupant, wherein the capacitive sensor element (36) is arranged on the seat cushion (12) or on the backrest (14).

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