WO2021084048A1

WO2021084048A1 - Load profile-sensitive sensor for seat occupancy detection and/or classification

Info

Publication number: WO2021084048A1
Application number: PCT/EP2020/080470
Authority: WO
Inventors: Frank Althaus; Laurent Lamesch
Original assignee: Iee International Electronics & Engineering S.A.
Priority date: 2019-10-31
Filing date: 2020-10-29
Publication date: 2021-05-06
Also published as: LU101461B1

Abstract

A load profile-sensitive sensor (10) for seat occupancy detection and/or classification comprises a plurality of force-sensing resistors (30-42) that are arrangeable at predetermined locations of a seat (54), a plurality of electric resistors (12-18) electrically connected in series, and electric lines (24, 26) with terminal ends that are connected to ends of the plurality of electric resistors (12-18). Each force-sensing resistor (30-42) is electrically connected in parallel to at least one electric resistor (12- 18) either individually or in a series connection with at least another force-sensing resistor (30-42). An electric resistance of the force-sensing resistors (30-42) is larger in a non-conducting state by at least a predetermined factor and is smaller in a conducting state by at least a predetermined factor than an electric resistance of the at least one electric resistor (12-18) to which it is connected in parallel. An electric resistance of each electric line that interconnects two of the electric resistors (12-18), of each electric line that connects one of the force-sensing resistors (30-42) in parallel to the at least one electric resistor (12-18), and the electric lines (24, 26) connected to ends of the plurality of electric resistors (12-18) is smaller by at least a predetermined factor than an electrical resistance of any electric resistor (12-18) of the plurality of electric resistors (12-18).

Description

Load Profile-Sensitive Sensor for Seat Occupancy Detection and/or

Classification

Technical field

[0001] The invention generally relates to seat occupancy detection and/or classification, in particular for automotive applications. More specifically, the invention relates to a load profile-sensitive sensor for seat occupancy detection and/or classification, and a seat occupancy detection and/or classification device comprising such load profile-sensitive sensor.

Background of the Invention

[0002] Seat occupancy detection and/or classification devices are nowadays widely used in vehicles, in particular in passenger cars, for providing a seat occupancy signal for various appliances, for instance for the purpose of a seat belt reminder (SBR) system or an activation control for an auxiliary restraint system (ARS). Seat occupancy detection systems include seat occupancy sensors that are known to exist in a number of variants, e.g. based on capacitive sensing, on deformation sensing or on sensing of pressure/force. In order to meet requirements regarding easy integration and feared robustness, weight-sensitive seat occupancy sensors have typically been arranged on the B-surface of a vehicle seat, i.e. between a foam body of a seat cushion and a seat pan or cushion-supporting springs of the vehicle seat.

[0003] Further, seat occupancy detection/classification devices particularly for vehicle seats are known to be employed as a means of assessing a potential activation of an installed vehicle passenger restraint system, such as an airbag. An output signal of the seat occupant detection and/or classification system is usually transferred to an electronic control unit of the vehicle to serve, for instance, as a basis for a decision to deploy an air bag system to the vehicle seat. For this purpose, the vehicle seat occupancy detection/classification device should be able to distinguish an empty seat or a seat equipped with a child restraint system (CRS), from a person directly sitting on the seat. Vehicle seat occupancy detection/classification devices that are based on mechanical load sensors can operate well in a presence of a CRS such as the wide-spread ISOFIX system (compatible to the “ISOFIX” standard ISO 13216) or others. Flowever, seat occupancy detection/classification devices which use non-profile measuring sensors have an issue in meeting reliability requirements for discriminating a CRS.

[0004] A type of mechanical load sensor that is widely employed in automotive applications is the force-sensing resistor (FSR). In a typical FSR, a paste-like sensing film is sandwiched between two electrically conducting electrodes, which are covered by polymer films. An electric resistance between the electrodes drops sharply when a predetermined force is applied to the sensing film. FSRs are known to exhibit only moderate precision and relatively large signal drift. Alternatively an arrangement where two electrically conducting electrodes are used without the sensing film layer is also possible.

[0005] For vehicle seat occupancy detection/classification devices it is known to use a plurality of FSRs in a two-dimensional matrix configuration. Such devices, however, require a dedicated electronic control unit for signal evaluation, resulting in quite large hardware effort and costs, which is also true for vehicle seat occupancy detection/classification devices based on a matrix of capacitive sensors.

Object of the invention

[0006] It is therefore an object of the invention to provide an improved load- sensitive sensor to be employed in a seat occupancy detection/classification device that is able to reliably distinguish an empty seat or a seat equipped with a child restraint system (CRS) from a person directly sitting on the seat. The sensor preferably has a simple and hardware-saving design and omits the need of a dedicated electronic control unit for signal evaluation.

General Description of the Invention

[0007] In one aspect of the present invention, the object is achieved by a load profile-sensitive sensor for seat occupancy detection and/or classification that comprises a plurality of force-sensing resistors that are arrangeable at predetermined locations of a seat, a plurality of electric resistors, which are electrically connected in series and electric lines with terminal ends that are connected to ends of the series connection of the plurality of electric resistors. [0008] The term “electric resistor”, as used in the present application, shall particularly be understood as a passive electronic component whose electric resistance is intended to be constant in principle with the exception that it can be subject to aging and to variation with temperature.

[0009] Each force-sensing resistor is electrically connected in parallel to at least one electric resistor either individually or in a series connection with at least another force-sensing resistor. An electric resistance of the force-sensing resistors is larger in a non-conducting state by at least a predetermined factor and is smaller in a conducting state by at least a predetermined factor than an electric resistance of the at least one electric resistor to which it is connected in parallel. An electric resistance of each electric line that interconnects two of the electric resistors, of each electric line that connects one of the force-sensing resistors in parallel to the at least one electric resistor, and the electric lines connected to ends of the plurality of electric resistors is smaller by at least a predetermined factor than an electrical resistance of any electric resistor of the plurality of electric resistors.

[0010] With the proposed configuration of electric resistors and force-sensing resistors, a force-sensing resistor that is arranged at a predetermined location of a seat will virtually short-circuit the at least one electric resistor to which it is connected in parallel if a force is acting on the force-sensing resistor by which it is transferred from the non-conducting state to the conducting state. It will be noted that a force-sensing resistor does not need to be arranged in proximity to the respective at least one electric resistor to which it is connected in parallel. To the contrary, the force-sensing resistor may be arranged independently of the at least one electric resistor to which it is connected in parallel at an appropriate location of the seat. It is thus possible to arrange the different force-sensing resistors in appropriate locations distributed over the seat while the respective electrical resistors may be arranged at a distance of the fore sensing resistors outside of the main seating area of the seating surface e.g. in a border zone of the seat.

[0011 ] The plurality of electric resistors and the plurality of force-sensing resistors are arranged to form an electric circuit whose electric resistance can be measured between the electric lines having terminal ends. The electric resistance of the electric circuit changes depending on the state of each force-sensing resistor of the plurality of force-sensing resistors. Therefore, in a suitable configuration, a simple measurement of the electric resistance of the electric circuit can provide a profile of the mechanical load that is applied to the seat in which the load profile- sensitive sensor is installed. From this, a seat occupancy can be detected and/or a seat occupancy class can be determined.

[0012] In particular, the invention is applicable with advantage in the automotive sector; i.e. in vehicle seats. The term “automotive”, as used in the present application, shall particularly be understood as being suitable for use in vehicles including passenger cars, trucks, semi-trailer trucks and buses. Other fields of applications are other passenger transportation sectors, for example aviation or maritime.

[0013] In preferred embodiments, the profile-sensitive sensor further comprises at least one reference resistor that is identically designed to at least one electric resistor of the plurality of electric resistors. The at least one reference resistor is electrically connected to one of the electric lines having terminal ends on the one hand and is electrically connected to an extra electric line with a terminal end of the other hand. All electric lines that are connected to the reference resistor have an electric resistance that is smaller by at least a predetermined factor than an electrical resistance of the reference resistor.

[0014] Due to the identical design of the at least one reference resistor and its close positioning to the plurality of electric resistors, the resistance temperature characteristic and an aging behavior of the at least one reference resistor will be very similar to those of the plurality of electric resistors. The load profile-sensitive sensor is the preferably configured to measure the resistance of the at least one reference resistor and to use the measured resistance of the at least one reference resistor to eliminate temperature drift and aging effects of the plurality of electric resistors.

[0015] Preferably, the plurality of electric resistors comprises between three and 50 or even 100 electric resistors. Within this range, a compromise between a hardware effort regarding the electric resistors and a related number of force sensing resistors and a resolution of a load profile to be sensed can be found for a large number of potential applications. [0016] In preferred embodiments of the load profile-sensitive sensor, the electric resistance of each electric resistor of the plurality of electric resistors is equal to an average electric resistance value within predetermined tolerance margins. In this way, it can be enabled to distinguish an area of a load profile generated by an adult seat occupant and an area of a load profile generated by a child seat by simply determining a number of activated force-sensing resistors; i.e. force sensing resistors that have been transferred into a conducting state.

[0017] Preferably, the predetermined tolerance margin may be less than ±10%, and, more preferably, less than ±5% of the average electric resistance value.

[0018] Preferably, at least one force-sensing resistor of the plurality of force sensing resistors is electrically connected in parallel to two electric resistors of the plurality of electric resistors. If the at least one force-sensing resistor is transferred into a conducting state, the two electric resistors of the plurality of electric resistors are short-circuited, and a resistance of the electric circuit formed by the plurality of electric resistors and the plurality of force-sensing resistors drops by a larger amount. In this way, the at least one force-sensing resistor can be assigned a higher importance and/or priority than that of other force-sensing resistors. This can for instance be advantageous if the child seat generates a load profile with an area size similar to that of an adult occupant but has a different shape. In this case, the at least one force-sensing resistor with an assigned higher importance can be placed in a region of the load profile area where the load profile generated by the adult occupant can transfer the at least one force-sensing resistor into the conducting state but not the one generated by the child seat.

[0019] In preferred embodiments of the load profile-sensitive sensor, the plurality of electric resistors comprises a subset of electric resistors that is characterized by having an equal electrical resistance within predetermined tolerance margins and further includes at least one electric resistor having an electric resistance outside the predetermined tolerance margins. This can be another way of assigning the at least one force-sensing resistor a higher importance and/or priority than that of other force-sensing resistors.

[0020] Preferably, the at least one electric resistor having an electric resistance outside the predetermined tolerance margins has an electric resistance that is substantially larger than the electrical resistance shared by the subset of electric resistors. In a possible embodiment, the electric resistance of the at least one electric resistor may be larger by a factor between 1.5 and 5.0.

[0021] In preferred embodiments of the load profile-sensitive sensor, at least two force-sensing resistors of the plurality of force-sensing resistors are electrically connected in parallel to at least one electric resistor of the plurality of electric resistors, either individually or as a series connection.

[0022] If the at least two force-sensing resistors are electrically connected in parallel to at least one electric resistor in a series connection, a logical AND- function concerning force-sensing resistors being transferred into a conducting state can beneficially be implemented.

[0023] If the at least two force-sensing resistors are electrically connected in parallel to at least one electric resistor individually, a logical OR-function or a redundancy function concerning force-sensing resistors being transferred into a conducting state can beneficially be implemented.

[0024] In preferred embodiments of the load profile-sensitive sensor, the electric resistors of the plurality of electric resistors, the electric lines that are connected to the electric resistors and, if applicable, the reference resistor and the electric lines that are connected to the reference resistor comprise a cured electrically conductive ink. At least the electric resistors of the plurality of electric resistors and the electric lines connected to the electric resistors are attached to a common dielectric foil carrier. It will be noted that the force-sensing resistors do not need to be arranged in proximity to the respective electric resistors to which they are connected in parallel. Each force-sensing resistor may be arranged independently of the at least one electric resistor to which it is connected in parallel at an appropriate location of the seat. It is thus possible to arrange the different force sensing resistors in appropriate locations distributed over the seat while the respective electrical resistors may be arranged at a distance from the force sensing resistors outside of the seating surface in a border zone of the seat. The electric resistors may e.g. be arranged on the common dielectric foil carrier in a zone, which will be arranged, after mounting the load profile-sensitive sensor in a vehicle seat, outside of a normal seating area of the seat. This has the advantage that the electrical resistors are not subjected to the mechanical stress of a passenger sitting in the normal seating area of the seat thereby reducing the effect of the mechanical stress on the aging of the resistors.

[0025] In this way, an application of high-precision, cost-effective manufacturing methods such as screen printing and ink jet printing is facilitated, resulting in low manufacturing tolerances. Electrically conductive inks are commercially available in many variations.

[0026] By that, the load profile-sensitive sensor can be designed as a foil sensor with the known benefits of low thickness, cost-effective production and low tolerance margins.

[0027] In another aspect of the present invention, the object is achieved by a seat occupancy detection and/or classification device. The seat occupancy detection and/or classification device comprises at least one embodiment of the load profile- sensitive sensor disclosed herein, and further includes an electronic control unit.

[0028] The electronic control unit is configured for determining an electric string resistance between the electrical lines having terminal ends that are connected to ends of the plurality of electric resistors, and is further configured for generating, on the basis of the determined electric string resistance, an output signal that represents a seat occupancy state or a seat occupancy class.

[0029] The phrase “being configured to”, as used in this application, shall in particular be understood as being specifically programmed, laid out, furnished or arranged.

[0030] The benefits described herein in context with the load profile-sensitive sensor fully apply to the proposed seat occupancy detection and/or classification device.

[0031] The task of determining the electric string resistance assigned to the electronic control unit is simple enough to be taken over by another electronic control unit that is not specifically dedicated to the function of seat occupancy detection and/or classification. Thus, further benefits with regard to a saving of parts and costs can be achieved by implementing the above-mentioned tasks to another electronic control unit that is already provided for another function, for instance an air bag electronic control unit of a vehicle. [0032] Preferably, the classification signal can be selected from, without being limited to, a group of classes including “empty”, “child”, “adult and “child restraint system (CRS)”.

[0033] In preferred embodiments of the seat occupancy detection and/or classification device, the electronic control unit is further configured for determining an electric reference resistance between the electrical line having a terminal end that is connected to an end of the plurality of electric resistors as well as to the reference resistor and the extra electric line having a terminal end that is connected to the reference resistor. The electronic control unit is also configured to use the measured resistance of the at least one reference resistor to eliminate temperature drift and aging effects of the plurality of electric resistors and for generating the output signal that represents a seat occupancy state or a seat occupancy class on the basis of the determined electric string resistance as well as on the basis of the determined electric reference resistance.

[0034] These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

[0035] It shall be pointed out that the features and measures detailed individually in the preceding description can be combined with one another in any technically meaningful manner and show further embodiments of the invention. The description characterizes and specifies the invention in particular in connection with the figures.

Brief Description of the Drawings

[0036] Further details and advantages of the present invention will be apparent from the following detailed description of not limiting embodiments with reference to the attached drawing, wherein:

Fig. 1 schematically shows a vehicle seat equipped with a seat occupancy detection and/or classification device comprising a load profile-sensitive sensor in accordance with the invention, in an installed state; and

Fig. 2 shows a layout of a possible embodiment of the load profile-sensitive sensor pursuant to Fig. 1. Description of Preferred Embodiments

[0037] Fig. 1 schematically shows a seat 54 equipped with a seat occupancy detection and/or classification device 44 comprising a possible embodiment of a load profile-sensitive sensor 10 in accordance with the invention, in an installed state in a side view. The seat 54 is designed as a vehicle seat of a passenger car and includes a seat structure (not shown) by which it is erected on a passenger cabin floor of the passenger car, as is well known in the art.

[0038] The seat 54 further includes a seat base 56 supported by the seat structure and configured for receiving a seat cushion 58 for providing comfort to a seat occupant. The seat cushion 58 of the vehicle seat comprises a seat foam member and a fabric cover, which has been omitted in Fig. 1. The seat base 56 and the seat cushion 58 are provided for supporting a bottom of the seat occupant. A backrest 60 of the seat 54 is provided for supporting a back of the seat occupant.

[0039] The load profile-sensitive sensor 10 is located on the A-surface of the seat cushion 58, underneath the fabric cover.

[0040] The seat occupancy detection and/or classification device 44 uses an electronic control unit 46 of the vehicle that is powered by the vehicle on-board voltage system 62. The main purpose of the electronic control unit 46 is to control an activation of an installed vehicle passenger restraint system, which is formed by a plurality of air bags. The air bag electronic control unit 46 (in the following also simply referred to as electronic control unit for brevity) has three resistive input ports 48, 50, 52 to which the load profile-sensitive sensor 10 is operatively connected (Fig. 2).

[0041] Fig. 2 shows a layout of a possible embodiment of the load profile- sensitive sensor 10 pursuant to Fig. 1. The load profile-sensitive sensor 10 comprises a plurality of electric resistors 12-18, which are electrically connected in series. In the present embodiment the plurality of electric resistors 12-18 comprises four electric resistors 12-18, but in alternative embodiments the plurality of electric resistors can include between three and 50 electric resistors, as is indicated in Fig. 2 by a dotted line. [0042] The electric resistors 12-18 comprise a cured electrically resistive ink and may be made by dispensing electrically resistive ink onto a dielectric foil carrier 22 using a screen printing or inkjet printing process, followed by a curing process.

[0043] In the present embodiment, an electric resistance of each electric resistor 12-18 of the plurality of electric resistors 12-18 is equal to an average electric resistance value within predetermined tolerance margins, which may be selected to be ±5%.

[0044] In alternative embodiments of the load profile-sensitive sensor, the plurality of electric resistors may comprise a subset of electric resistors that is characterized by having an equal electrical resistance within predetermined tolerance margins, and the load profile-sensitive sensor may further include at least one electric resistor having an electric resistance outside the predetermined tolerance margins.

[0045] Two electric lines 24, 26 with terminal ends are connected to ends of the chain of plurality of electric resistors 12-18. The electric lines 24, 26 with terminal ends comprise cured electrically conductive ink, comprising for instance silver or copper, and may also be made by dispensing electrically conductive ink onto the same dielectric foil carrier 22 as the electric resistors 12-18, using a screen printing or inkjet printing process, followed by a curing process.

[0046] The terms “cured electrically resistive ink” and “cured electrically conductive ink”, as used in the present application, shall particularly be understood such that both cured inks are electrically conductive and that a specific electrical conductivity of the cured electrically conductive ink is larger than a specific electrical conductivity of the cured electrically resistive ink.

[0047] The load profile-sensitive sensor 10 further comprises a plurality of force sensing resistors 30-42. In the present embodiment the plurality of force-sensing resistors 30-42 comprises seven force-sensing resistors 30-42, but in alternative embodiments the plurality of force-sensing resistors can include a lower or a larger number of force-sensing resistors. The plurality of force-sensing resistors 30-42 is arranged at predetermined locations of the A-surface of the seat cushion 58.

[0048] Each force-sensing resistor 30-42 is electrically connected in parallel to at least one electric resistor 12-18, either individually or in a series connection with at least another force-sensing resistor 30-42. Electric lines that connect the force sensing resistors 30-42 to the electric resistors 12-18 comprise cured electrically conductive ink and may be made using one of the earlier mentioned processes.

[0049] An electric resistance of each electric line that interconnects two of the electric resistors 12-18, of each electric line that connects one of the force-sensing resistors 30-42 in parallel to the at least one electric resistor 12-18, and the electric lines 24, 26 connected to ends of the chain of the plurality of electric resistors 12- 18 is smaller by at least a predetermined factor, which may be selected to be 50, than an electrical resistance of any electric resistor of the plurality of electric resistors 12-18.

[0050] In a non-conducting state, when no mechanical load is applied to the force-sensing resistors 30-42, an electric resistance of the force-sensing resistors 30-42 is larger by at least a predetermined factor, which may be selected to be 100, than an electric resistance of the at least one electric resistor 12-18 to which it is connected in parallel.

[0051] In a conducting state, when a mechanical load is applied to the force sensing resistors 30-42 that exceeds a predetermined mechanical load threshold, an electric resistance of the force-sensing resistors 30-42 is smaller by at least a predetermined factor, which may be selected to be 30, than an electric resistance of the at least one electric resistor 12-18 to which it is connected in parallel.

[0052] Because of this switch-like functional behavior, the force-sensing resistors 30-42 are shown as switch symbols in Fig. 2.

[0053] Some force-sensing resistors 30, 32 are individually electrically connected in parallel to a distinct one 12, 14 of the plurality of electric resistors 12-18. In a conducting state, these force-sensing resistors 30, 32 virtually short-circuit the electric resistor 12, 14 to which they are connected in parallel.

[0054] A string resistance, which can be measured between the electric lines 24, 26 having terminal ends, depends on the number of force-sensing resistors 30-42 being in the conducting state. The string resistance has a maximum value if none of the force-sensing resistors 30-42 is in the conducting state, and has a minimum value if all of the force-sensing resistors 30-42 are in the conducting state. [0055] One force-sensing resistor 34 is individually electrically connected in parallel to two electric resistors 12, 14 of the plurality of electric resistors 12-18. In a conducting state, this force-sensing resistor 34 virtually short-circuits the electric resistors 12, 14 to which it is connected in parallel, resulting in a larger drop of the string resistance. Consequently, a higher importance is assigned to this force sensing resistor 34. The force-sensing resistor 34 may, for instance, be arranged in a center region of the seat cushion 58, in which no mechanical load is to be expected from a CRS, but in which a major part of a mechanical load is to be expected from an adult seat occupant.

[0056] Two force-sensing resistors 36, 38 are electrically connected in a series connection in parallel to the same electric resistor 16 of the plurality of electric resistors 12-18. Only in case that both of the two force-sensing resistors 36, 38 are transferred into a conducting state by a sufficiently large applied mechanical load, the electric resistor 16 will virtually be short-circuited. This configuration of the two force-sensing resistors 36, 38 introduces a logical AND-function, by which the two locations on the seat cushion 58 at which the two force-sensing resistors 36, 38 are positioned become logically linked to each other. For instance, the two force sensing resistors 36, 38 may be arranged at both side regions of the seat cushion 58, in which mechanical load from arms of an ISOFIX CRS is to be expected. By logically linking the two positions with an AND-function, the reliability of detecting/classifying a child in a CRS can substantially be improved.

[0057] Two force-sensing resistors 40, 42 are electrically connected individually in parallel to the same electric resistor 18 of the plurality of electric resistors 12-18. In case that at least one of the two force-sensing resistors 40, 42 is transferred into a conducting state by a sufficiently large applied mechanical load, the electric resistor 18 will virtually be short-circuited. This configuration of the two force sensing resistors 40, 42 introduces a logical OR-function, or a redundancy function, by which the two locations on the seat cushion 58 at which the two force sensing resistors 40, 42 are positioned become logically linked to each other.

[0058] Furthermore, the load profile-sensitive sensor 10 comprises a reference resistor 20 that is identically designed to the electric resistors 12-18 of the plurality of electric resistors 12-18. The reference resistor 20 is electrically connected to one of the electric lines 26 having terminal ends on the one hand and is electrically connected to an extra electric line 28 with a terminal end of the other hand. The extra electric line 28 having a terminal end is electrically connected to one 52 of the resistive input ports 48-52 of the electronic control unit 46.

[0059] The reference resistor 20 comprises a cured electrically resistive ink and may also be made by dispensing electrically conductive ink onto the same dielectric foil carrier 22 as the electric resistors 12-18, using a screen printing or inkjet printing process, followed by a curing process.

[0060] All electric lines 26, 28 that are connected to the reference resistor 20 have an electric resistance that is smaller by at least a predetermined factor, which may be selected to be 50, than an electrical resistance of the reference resistor 20. The electric lines 26, 28 that connect the reference resistor 20 comprise cured electrically conductive ink and may be made using one of the processes mentioned in context with the electric lines that connect the plurality of electric resistors 12-18.

[0061] The electronic control unit 46 is configured for determining an electric string resistance between the two electric lines 24, 26 having terminal ends that are connected to two 48, 50 of its three resistive input ports 48, 50, 52. The electronic control unit 46 is further configured for determining an electric reference resistance, which is defined as the electric resistance between the one electrical line 26 having a terminal end that is connected to an end of the plurality of electric resistors 12-18 as well as to the reference resistor 20, and the extra electric line 28 having a terminal end that is connected to the reference resistor 20.

[0062] It is noted herewith that the order of determining the electric string resistance and of determining the electric reference resistance is irrelevant.

[0063] Further, the electric control unit 46 is configured for generating an output signal that represents a seat occupancy state or a seat occupancy class on the basis of the determined electric string resistance as well as on the basis of the determined electric reference resistance.

[0064] To this end, the electronic control unit 46 calculates e.g. the ratio between the determined electric string resistance and the determined electric reference resistance, to obtain a corrected string resistance, which accounts for any aging or temperature drift effects that affect the electric resistors 12-18 as well as the reference resistor 20.

[0065] Then, the electronic control unit 46 compares the corrected string resistance with predetermined threshold values for the string resistance, which delimit the various seat occupancy classes, and selects the seat occupancy class that is associated with the interval in which the corrected string resistance is found to lie. The generated output signal is further used within the electronic control unit 46 as a means of assessing a potential activation of the air bag system of the vehicle seat 54.

[0066] While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments.

[0067] Other variations to be disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality, which is meant to express a quantity of at least two. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting scope.

List of Reference Symbols

10 load profile-sensitive sensor

12 electric resistor

14 electric resistor

16 electric resistor

18 electric resistor

20 reference resistor

22 dielectric foil carrier

24 electric line

26 electric line

28 electric line

30 force-sensing resistors

32 force-sensing resistors

34 force-sensing resistors

36 force-sensing resistors

38 force-sensing resistors

40 force-sensing resistors

42 force-sensing resistors

44 seat occupancy detection and/or classification device

46 (air bag) electronic control unit

48 resistive input port

50 resistive input port

52 resistive input port

54 seat

56 seat base

58 seat cushion

60 backrest

62 on-board voltage system

Claims

1. Load profile-sensitive sensor (10) for seat occupancy detection and/or classification, comprising

- a plurality of force-sensing resistors (30-42) that are arrangeable at predetermined locations of a seat (54),

- a plurality of electric resistors (12-18), which are electrically connected in series,

- electric lines (24, 26) with terminal ends that are connected to ends of the plurality of electric resistors (12-18), wherein each force-sensing resistor (30-42) is electrically connected in parallel to at least one electric resistor (12-18) either individually or in a series connection with at least another force-sensing resistor (30-42), wherein an electric resistance of the force-sensing resistors (30-42) is larger in a non-conducting state by at least a predetermined factor and is smaller in a conducting state by at least a predetermined factor than an electric resistance of the at least one electric resistor (12-18) to which it is connected in parallel, and wherein an electric resistance of each electric line that interconnects two of the electric resistors (12-18), of each electric line that connects one of the force sensing resistors (30-42) in parallel to the at least one electric resistor (12-18), and the electric lines (24, 26) connected to ends of the plurality of electric resistors (12-18) is smaller by at least a predetermined factor than an electrical resistance of any electric resistor (12-18) of the plurality of electric resistors (12-18).

2. The load profile-sensitive sensor (10) as claimed in claim 1 , further comprising at least one reference resistor (20) that is identically designed to at least one electric resistor (12-18) of the plurality of electric resistors (12-18), and that is electrically connected to one of the electric lines (26) having terminal ends on the one hand and is electrically connected to an extra electric line (28) with a terminal end of the other hand, wherein all electric lines (26, 28) that are connected to the reference resistor (20) have an electric resistance that is smaller by at least a predetermined factor than an electrical resistance of the reference resistor (20), and wherein said load profile-sensitive sensor is configured to measure the resistance of the at least one reference resistor and to use the measured resistance of the at least one reference resistor to eliminate temperature drift and aging effects of the plurality of electric resistors.

3. The load profile-sensitive sensor (10) as claimed in claim 1 or 2, wherein the plurality of electric resistors (12-18) comprises between three and 100 electric resistors (12-18).

4. The load profile-sensitive sensor (10) as claimed in any one of the preceding claims, wherein the electric resistance of each electric resistor (12-18) of the plurality of electric resistors (12-18) is equal to an average electric resistance value within predetermined tolerance margins.

5. The load profile-sensitive sensor (10) as claimed in any one of the preceding claims, wherein at least one force-sensing resistor (34) of the plurality of force sensing resistors (30-42) is electrically connected in parallel to two electric resistors (12, 14) of the plurality of electric resistors (12-18).

6. The load profile-sensitive sensor (10) as claimed in any one of the preceding claims, wherein the plurality of electric resistors (12-18) comprises a subset of electric resistors that is characterized by having an equal electrical resistance within predetermined tolerance margins and further includes at least one electric resistor having an electric resistance outside the predetermined tolerance margins.

7. The load profile-sensitive sensor (10) as claimed in any one of the preceding claims, wherein at least two force-sensing resistors (40, 42) of the plurality of force-sensing resistors (30-42) are electrically connected in parallel to at least one electric resistor (18) of the plurality of electric resistors (12-18), either individually or as a series connection.

8. The load profile-sensitive sensor (10) as claimed in any one of the preceding claims, wherein the electric resistors (12-18) of the plurality of electric resistors (12-18), the electric lines that are connected to the electric resistors (12-18) and, if applicable, the reference resistor (20) and the electric lines that are connected to the reference resistor (20) comprise a cured electrically conductive ink, and wherein at least the electric resistors (12-18) of the plurality of electric resistors (12-18) and the electric lines connected to the electric resistors (12-18) are attached to a common dielectric foil carrier (22).

9. A seat occupancy detection and/or classification device (44), comprising

- at least one load profile-sensitive sensor (10) as claimed in any one of the preceding claims,

- an electronic control unit (46) that is configured for determining an electric string resistance between the electrical lines (24, 26) having terminal ends that are connected to ends of the plurality of electric resistors (12-18), and is further configured for generating, on the basis of the determined electric string resistance, an output signal that represents a seat occupancy state or a seat occupancy class.

10. The seat occupancy detection and/or classification device (44) as claimed in claim 9, wherein the electronic control unit (46) is further configured for determining an electric reference resistance between the electrical line (26) having a terminal end that is connected to an end of the plurality of electric resistors (12-18) as well as to the reference resistor (20) and the extra electric line (28) having a terminal end that is connected to the reference resistor (20), and wherein the electronic control unit (46) is configured to use the measured resistance of the at least one reference resistor (20) to eliminate temperature drift and aging effects of the plurality of electric resistors and to generate the output signal that represents a seat occupancy state or a seat occupancy class on the basis of the determined electric string resistance as well as on the basis of the determined electric reference resistance.