LU93318B1

LU93318B1 - Sensor Unit for Seat Occupant Detection and/or Seat Belt Buckle Status Detection

Info

Publication number: LU93318B1
Application number: LU93318A
Authority: LU
Inventors: Dietmar Jungen; Holger Lorenz; Harald Schon
Original assignee: Iee Sa
Priority date: 2016-11-22
Filing date: 2016-11-22
Publication date: 2018-06-07

Abstract

A vehicle sensor circuit (110; 210) for a vehicle seat occupancy detection system and/or a vehicle seat belt buckle monitoring system comprises a plurality of electrical sensor switches (112; 212) electrically connected in series, a plurality of electrical resistors (114; 214), wherein an electrical resistor (114; 214) of the plurality of electrical resistors (114; 214) is connected in parallel to each electrical sensor switch (112; 212) of the plurality of electrical sensor switches (112; 212). A first output line (116; 216) is arranged at one end of the series-connected plurality of electrical sensor switches (112; 212) and a second output line (118; 218) is arranged at an opposite end of the series-connected plurality of electrical sensor switches (112; 212). A total electrical resistance (Rtotai) that is measurable between the first output line (116; 216) and the second output line (216; 218) is unambiguously representative of the switching states of the electrical sensor switches (112; 212) of the plurality of electrical sensor switches (112; 212). (Fig. 2) 93318

Description

Sensor Unit for Seat Occupant Detection and/or Seat Belt Buckle Status Detection

Technical field [0001] The invention relates to a vehicle sensor circuit for at least one out of a vehicle seat occupancy detection system and a vehicle seat belt buckle monitoring system and a vehicle sensor unit comprising such vehicle sensor circuit.

Background of the Invention [0002] Today's automotive safety standards require automotive vehicles to be equipped with seat belt reminder (SBR) systems for reminding a vehicle passenger to fasten the seat belt associated to the occupied vehicle seat. While until now those seat belt reminder systems were mainly associated with front seats of the vehicle, future standards will require also rear seat to be equipped with such seat belt reminder systems.

[0003] Seat belt reminder systems typically comprise a seat occupancy detection sensor associated with a vehicle seat for detecting a presence of an occupant on the respective seat and for generating a signal indicative of such presence, and a seat belt fastening detector for determining a seat belt usage condition and for generating a signal indicative thereof. Quite common, an electronic control unit then uses the signals of the seat occupancy sensor and the seat belt fastening detector in order to determine whether the actual seat occupancy would require a non-fastened seat belt to be fastened and, if this is the case, to issue a corresponding warning signal.

[0004] The seat occupancy sensors may comprise pressure-sensing devices integrated in the respective passenger seat for detecting a pressure induced by the presence of a passenger into the seat. The pressure-sensing devices, as e.g. disclosed in DE 42 37 072 C1, comprise a plurality of individual force sensors, which are connected in a suitable manner to a control unit designed for measuring a pressure-depending electrical property of said individual pressure sensors.

[0005] The seat belt fastening detectors typically comprise mechanical or magnetic buckle switches for detecting whether a latch of the seat belt is inserted into the seat belt buckle. One such buckle switch is e.g. disclosed in US

Patent 5,871,063 A. As an alternative to the buckle switches, seat belt fastening detectors have been proposed which generate a buckled/unbuckled signal based on the tension in the seat belt.

[0006] Usually for their models, car manufacturers employ an existing electrical and electronical architecture, including electronic control units, which needs to be usable for a number of years without major changes, for economic reasons. In this context, input signal lines of the employed electronic control units are a valuable asset.

[0007] For example, a vehicle seat belt reminder system for a three-seat rear bench of a vehicle requires in total six input signal lines in an electronic control unit (e.g. an airbag control unit) to acquire all six pieces of information: three times a seat belt buckle status, and three times a seat occupant detection status.

Object of the invention [0008] It is therefore in particular an object of the invention to alleviate the requirement regarding a number of input lines of an electronic control unit for a vehicle seat belt reminder system that complies with future safety regulations and standards, including individual detection at multiple rear seating positions, in order to save costs and parts for the electronic control unit and corresponding cabling.

General Description of the Invention [0009] In one aspect of the present invention, the object is achieved by a vehicle sensor circuit for at least one out of a vehicle seat occupancy detection system and a vehicle seat belt buckle monitoring system. The vehicle sensor circuit comprises a plurality of electrical sensor switches, a plurality of electrical resistors, a first output line and a second output line.

[0010] The electrical sensor switches of the plurality of electrical sensor switches are electrically connected in series. Each electrical sensor switch of the plurality of electrical sensor switches is configured to change a switching state in a reversible manner from a first switching state to a second switching state if a physical quantity corresponding to at least a pre-determined threshold value for the physical quantity is applied to the sensor switch.

[0011] The term “vehicle”, as used in this application, shall particularly be understood to encompass passenger cars, trucks and buses.

[0012] The phrase “being configured to”, as used in this application, shall in particular be understood as being specifically programmed, laid out, furnished or arranged.

[0013] The phrase “in a reversible manner”, as used in this application, shall in particular encompass the existence of a hysteresis.

[0014] It is further noted herewith that the terms “first”, “second”, etc. are used in this application for distinction purposes only, and are not meant to indicate or anticipate a sequence or a priority in any way.

[0015] For instance, the first switching state of an electrical sensor switch may be the closed state, and the second switching state of the electrical sensor switch may be the open state. In another embodiment, the first switching state of the electrical sensor switch may be the open state, and the second switching state of the electrical sensor switch may be the closed state.

[0016] The plurality of electrical resistors has resistance values that are mutually distinct. They are selected such that the resistance of each electrical resistor is distinct from any arithmetic sum of any potential combination of the other electrical resistors of the plurality of electrical resistors. An electrical resistor of the plurality of electrical resistors is connected in parallel to each electrical sensor switch of the plurality of electrical sensor switches.

[0017] The phrase “mutually distinct”, as used in this application, shall be understood such that the resistances of any two electrical resistors of the plurality of electrical resistors differ from each other by at least 20%, more preferable by at least 30% and, most preferred, by at least 50% of the smaller one of the resistances of the electrical resistors under consideration.

[0018] The phrase “distinct from any arithmetic sum”, as used in this application, shall be understood such that the resistance of any electrical resistor of the plurality of electrical resistors differs from any arithmetic sum of any potential combination of the other electrical resistors of the plurality of electrical resistors by at least 2%, more preferable by at least 5% and, most preferred, by at least 10% of the resistance of the electrical resistor under consideration.

[0019] The first output line is electrically connected to an open connection of the electrical sensor switch of the plurality of electrical sensor switches that is arranged at one end of the series-connected plurality of electrical sensor switches.

[0020] The second output line is electrically connected to an open connection of the electrical sensor switch of the plurality of electrical sensor switches that is arranged at an opposite end of the series-connected plurality of electrical sensor switches.

[0021] A total electrical resistance that is measurable between the first output line and the second output line is unambiguously representative of the switching states of the electrical sensor switches of the plurality of electrical sensor switches. In others words, momentary switching states of the electrical sensor switches of the plurality of electrical sensor switches can be determined by simply measuring the total electrical resistance between the first output line and the second output line.

[0022] One advantage of the disclosed vehicle sensor circuit lies in that a complete seat belt buckle monitoring and/or a seat occupant detection for a seat arrangement with multiple seating positions can be accomplished using only one output line and a common ground line. In fact, based on the total electrical resistance, which is unambiguously representative of the switching states of the electrical sensor switches of the plurality of electrical sensor switches, it is possible to determine in which of the seating positions a specific switching status is present.

[0023] Another advantage lies in the simplicity of the circuit.

[0024] The vehicle sensor circuit in accordance with the invention can further beneficially facilitate meeting future Euro NCAP (European New Car Assessment Programme) requirements regarding additional functionalities of seat belt reminder systems regarding rear seat occupancy detection and rear seat belt buckle status detection.

[0025] In a preferred embodiment of the vehicle sensor circuit, the plurality of electrical resistors comprises a total of n electrical resistors, wherein n is a natural number larger than or equal to two, and wherein the resistances R, of the electrical resistors of the plurality of electrical resistors are chosen according to

Rj=2'_1-R0 for i = 1,2.....n-1,n wherein Ro denotes a selectable constant resistance value.

[0026] In this way, optimally separated levels, namely equidistant levels of the total electrical resistance can be accomplished for the 2n different switching state configurations, by which an easy and robust evaluation of the measurable total electrical resistance can be facilitated.

[0027] In some preferred embodiments of the vehicle sensor circuit, the selectable constant resistance value Ro lies in a range between and including 100 Ω and 100 kQ. In this way, a reasonable balance between a power demand of the vehicle sensor circuit in operation and a signal-to-noise ratio for determining the total electrical resistance can be achieved.

[0028] Preferably, the plurality of electrical sensor switches includes at least one force-sensitive sensor switch that is configured to detect a vehicle seat occupancy status. For this type of sensor switch, the applied physical quantity is a mechanical load that may be externally applied by a vehicle seat occupant.

[0029] In suitable embodiments, a vehicle sensor circuit for a vehicle seat occupancy detection system as well as for a combined seat belt buckle monitoring and seat occupant detection unit can be provided that requires only one input line to an electronic control unit (ECU) in addition to a common ground line.

[0030] In some preferred embodiments of the vehicle sensor circuit, the plurality of electrical sensor switches includes three force-sensitive sensor switches for detecting a vehicle seat occupancy status. Each one of the three force-sensitive sensor switches is configured to be disposed at one of three juxtaposed seating positions. The three force-sensitive sensor switches are arranged on a common carrier.

[0031] In this way, a vehicle sensor circuit for a vehicle seat occupancy detection system for a vehicle rear seat bench with three seating positions can be provided that requires only one input line to an ECU in addition to a common ground line and that can be installed at the rear seat bench in an easy and fast manner.

[0032] Preferably, at least one of the force-sensitive sensor switches is formed as a foil-type switching member. By that, a flat and compact design of a vehicle seat occupancy detection system for a vehicle rear seat bench or a combined seat belt buckle monitoring and seat occupant detection system can be accomplished.

[0033] In some preferred embodiments of the vehicle sensor circuit, the plurality of electrical sensor switches includes at least one buckle switch member that is configured to detect a vehicle seat belt fastening status.

[0034] For this type of sensor switch, the applied physical quantity may, for instance, be a mechanical force applied to a resilient member of a seat belt buckle by inserting a seat belt latch, or it may be a magnetic field applied to a magnetosensitive switch such as a reed switch, by inserting a seat belt latch.

[0035] In suitable embodiments, a vehicle sensor circuit for a seat belt buckle monitoring system as well as for a combined seat belt buckle monitoring and seat occupant detection system can be provided that requires only one input line to an electronic control unit (ECU) in addition to a common ground line.

[0036] In some preferred embodiments of the vehicle sensor circuit, the plurality of electrical sensor switches includes three buckle switch members for detecting a vehicle seat belt fastening status. Each one of the three buckle switch members is configured to be disposed at a seat buckle that is assigned to one of three juxtaposed seating positions.

[0037] In this way, a vehicle sensor circuit for seat belt buckle monitoring for a vehicle seat belt reminder system applicable for a vehicle rear seat bench with three seating positions that requires only one input line to an ECU in addition to a common ground line can be provided.

[0038] In another aspect of the invention, a vehicle sensor unit is provided that comprises at least one embodiment of the disclosed vehicle sensor circuit and an electronic control unit that comprises electrical resistance measurement means for determining the total electrical resistance of the vehicle sensor circuit.

[0039] The electronic control unit is configured to determine a total electrical resistance of the vehicle sensor circuit, to compare the determined total electrical resistance with a plurality of predetermined thresholds for the total electrical resistance, and to identify switching states of the plurality of electrical sensor switches, depending on a result of the comparison.

[0040] In this way, a seat belt buckle monitoring system as well as a combined seat belt buckle monitoring and seat occupant detection system can be provided that requires only one input line to an electronic control unit (ECU) in addition to a common ground line.

[0041] Preferably, the electronic control unit comprises a processor unit and a digital data memory unit. The processor unit is configured to consecutively execute steps, in a periodic manner, of determining the total electrical resistance of the vehicle sensor circuit, of comparing the determined total electrical resistance with a plurality of predetermined thresholds for the total electrical resistance, and of identifying switching states of the plurality of electrical sensor switches, depending on a result of the comparison. The plurality of predetermined thresholds for the total electrical resistance resides in the digital data memory unit. A reliable and easy-to-use solution of the vehicle sensor unit with easy-implementable options for modification can be provided in this way.

[0042] In some embodiments, the vehicle sensor unit is configured to output an information representing the identified switching states of the plurality of electrical sensor switches to a higher-level vehicle control unit. This enables a direct processing of the information representing the identified switching states and a fast realization of predetermined measures, if applicable.

Brief Description of the Drawings [0043] 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 shows a circuit diagram of a vehicle sensor circuit in accordance with the invention,

Fig. 2 schematically illustrates a vehicle sensor unit including the vehicle sensor circuit pursuant to Fig. 1, and

Fig. 3 schematically illustrates another vehicle sensor unit including an alternative vehicle sensor circuit in accordance with the invention.

Description of Preferred Embodiments [0044] In the following, embodiments of a vehicle sensor circuit in accordance with the invention are disclosed. The individual embodiments are identified by a prefix cipher of the particular embodiment. Features whose function is the same or basically the same in all embodiments are identified by reference numbers made up of the prefix cipher of the embodiment to which it relates, followed by the numeral of the feature.

[0045] Fig. 1 shows a circuit diagram of vehicle sensor circuit 110 for a vehicle seat occupancy detection system in accordance with the invention.

[0046] The vehicle sensor circuit 110 comprises a plurality of n =3 electrical sensor switches 112-(, 1122, 1123 electrically connected in series. The plurality of electrical sensor switches 112i, 1122, 1123 includes three identically designed force-sensitive sensor switches that are configured to detect a vehicle seat occupancy status. Each one of the three force-sensitive sensor switches is configured to be disposed at a center of a B-surface of one of three juxtaposed seating positions 132, 134, 136 (Fig. 2) of a rear seat bench cushion of a vehicle designed as a passenger car (not shown). Each force-sensitive sensor switch is designed as a foil-type switching member known in the art. The three force-sensitive sensor switches are arranged on a common carrier 130.

[0047] The force-sensitive sensor switches are configured to change a switching state in a reversible manner from a first switching state to a second switching state if a physical quantity given by a mechanical load corresponding to a predetermined threshold value is applied to the force-sensitive sensor switch, usually generated by the weight of a seat occupant. The first switching state of the force-sensitive sensor switches is the open switching state. The second switching state of the force-sensitive sensor switches is the closed switching state.

[0048] The vehicle sensor circuit 110 further includes a plurality of n = 3 electrical resistors 114i, 1142, 1143 having resistance values that are selected to be mutually distinct, namely resistance values of 300 Ω, 600 Ω and 1200 Ω, respectively. R, (i = 1, 2, 3) shall denote the value of the respective electrical resistances of the electrical resistors 114i, 1142, 1143 of the plurality of electrical resistors 114-j, 1142, 1143.

[0049] One electrical resistor 114i, 1142, 1143 of the plurality of electrical resistors 114i, 1142, 1143 is connected in parallel to each electrical sensor switch 112i, 1122, 1123 of the plurality of electrical sensor switches 112i, 1122, 1123. The resistance values R, of the plurality of electrical resistors 114i, 1142, 1143 are selected such that the resistance R, of each electrical resistor 114, is distinct from any arithmetic sum of any potential combination of the other electrical resistors 114k (k= 1, 2, 3; k# i) of the plurality of electrical resistors 114i, 1142, 1143, which is 1800 Ω for the electrical resistor 114^ 1500 Ω for the electrical resistor 1142 and 900 Ω for the electrical resistor 1143.

[0050] The vehicle sensor circuit 110 is equipped with a first output line 116 and a second output line 118. The first output line 116 is electrically connected to an open connection of the electrical sensor switch 1123 of the plurality of electrical sensor switches 112i, 1122, 1123 that is arranged at one end of the series-connected plurality of electrical sensor switches 112^ 1122, 1123. The second output line 118 is electrically connected to an open connection of the electrical sensor switch 112i of the plurality of electrical sensor switches 112i, 1122, 1123 that is arranged at an opposite end of the series-connected plurality of electrical sensor switches 112i, 1122, 1123.

[0051] Between the first output line 116 and the second output line 118 a total electrical resistance Rtotai is measurable that is unambiguously representative of the switching states of the electrical sensor switches 112i, 1122, 1123 of the plurality of electrical sensor switches 112i, 1122, 1123.

[0052] The following Table 1 provides total electric resistances Rtotai that are measurable between the first output line 116 and the second output line 118 for the 23 = 8 possible switching state configurations (cases). For the sake of simplicity, the electrical resistance of a force-sensitive sensor switch in the closed switching state is assumed to be 0 Ω.

Table 1 [0053] As presented in Table 1, the vehicle sensor circuit 110 is able to generate eight values for a total electrical resistance Rtotai that are unambiguously representative of the eight different configurations for the switching states of the electrical sensor switches 112-t, 1122, 1123.

[0054] The resistances R, of the electrical resistors 114i, 1142, 1143 of the plurality of electrical resistors 114i, 1142, 1143 are chosen according to (1) for i = 1, 2, .... n-1, n wherein Ro denotes a selectable constant resistance value that is preferably selected to lie in a range between and including 100 Ω and 100 kO. In this specific embodiment a constant resistance value Ro of 300 Ω is chosen. It is worth noting that by choosing the resistance values R, of the plurality of electrical resistors 114i, 1142, 1143 in this way, levels of the total electrical resistance Rtotai can be achieved for the eight different switching state configurations that are set in an equidistant manner, separated by the resistance value Ro. By this, an easy and robust evaluation of the measurable total electrical resistance Rtotai is facilitated.

[0055] Those of skills in the art will appreciate that a distinction between the total electrical resistances Rtotai of the eight switching state configurations is possible with little hardware effort.

[0056] In reality, the electrical resistance of the force-sensitive sensor switches in the closed switching state is close to but not exactly 0 Ω. Indeed, the largest electrical resistance of the force-sensitive sensor switches in the closed switching state is about 0.5 Ω. By that, a ratio of the smallest of the electrical resistances R, of the plurality of electrical resistors 114i, 1142, 1143 and the largest of an electrical resistance of the force-sensitive sensor switches in a closed switching state is 300 Ω/0.5 Ω = 600, a ratio that can be considered sufficient for

distinguishing between the total electrical resistances Rtotai indicating the potential switching combinations.

[0057] Fig. 2 schematically illustrates a vehicle sensor unit 120 including the vehicle sensor circuit 110 pursuant to Fig. 1. Further, the vehicle sensor unit 120 comprises an electronic control unit 122 that includes electrical resistance measurement means (not shown) for determining the total electrical resistance Rtotai of the vehicle sensor circuit 110. Electrical resistance measurement means are well known in the art and therefore need not be discussed in detail herein.

[0058] The first output line 116 is connected to a ground connection 140 formed by the car body. The second output line 118 is connected to an input line 128 of the electronic control unit 122. The electronic control unit 122 comprises a ground connection 140 as a return line of the electrical resistance measurement means, besides other purposes.

[0059] The electronic control unit 122 is configured to determine a total electrical resistance Rtotai of the vehicle sensor circuit 110 and to compare the determined total electrical resistance Rtotai with a plurality of predetermined thresholds for the total electrical resistance Rtotai. The predetermined thresholds are given by endpoints of intervals about the values of the total electrical resistance Rtotai presented in the last column of Table 1 as center values of these intervals. Each interval has a width of ±100 Ω about its center value. The electronic control unit 122 is configured to identify switching states of the plurality of electrical sensor switches 112i, 1122, 1123, depending on a result of the comparison, such that a specific switching state is identified if the determined total electrical resistance Rtotai lies within the interval about the value of the total electrical resistance Rtotai of the specific switching state.

[0060] To this end, the electronic control unit 122 comprises a processor unit 124 and a digital data memory unit 126 to which the processor unit 124 has data access. The plurality of predetermined thresholds for the total electrical resistance Rtotai resides in the digital data memory unit 126.

[0061] The processor unit 122 is configured to consecutively execute steps, in a periodic manner, of determining the total electrical resistance Rtotai of the vehicle sensor circuit 110, of comparing the determined total electrical resistance Rtotai with the plurality of predetermined thresholds for the total electrical resistance Rtotai, and of identifying switching states of the plurality of electrical sensor switches 112i, 1122, 1123, depending on a result of the comparison.

[0062] Eventually, the processor unit 122 is configured to output an information, for instance a case number, representing the identified switching states of the plurality of electrical sensor switches 112i, 1122, 1123 to a higher-level vehicle control unit 138.

[0063] If the determined total electrical resistance Rtotai does not lie in any one of the described intervals, the electronic control unit 122 is configured to output an error message to the higher-level vehicle control unit 138.

[0064] It will be readily appreciated by those skilled in the art that Fig. 1 can as well be interpreted as an embodiment of an embodiment of the vehicle sensor circuit in accordance with the invention for a vehicle seat belt buckle monitoring system, wherein each electrical sensor switch of the plurality of three electrical sensor switches is formed by a buckle switch member that is configured to detect a vehicle seat belt fastening status. Each one of the three buckle switch members is disposed at a seat buckle that is assigned to one of the three juxtaposed seating positions of the rear seat bench cushion of the vehicle designed as a passenger car (not shown). In contrast to the vehicle sensor circuit pursuant to Fig. 1, the electrical sensor switches are not arranged on a common carrier.

[0065] For the vehicle sensor circuit for vehicle seat belt buckle monitoring, the resistance values of the plurality of electrical resistors may be the same or they may be chosen differently.

[0066] A first output line of this vehicle sensor circuit is connected to a ground connection formed by the car body. A second output line is connected to another input line of the electronic control unit. The identification of a switching state of the three buckle switch members is conducted by the electronic control unit in the same way as described for the force-sensitive sensor switches. So, one vehicle sensor circuit for vehicle seat occupancy detection of the seating positions of the three-seat rear bench is connected to a first input line of the electronic control unit, and another vehicle sensor circuit for detection of vehicle seat belt fastening statuses at the seating positions of the three-seat rear bench is connected to a second input line of the electronic control unit. In this manner, a complete seat belt reminder system can be realized for the seating positions of the three-seat rear bench of the vehicle requiring just two input lines of the electronic control unit.

[0067] Fig. 3 schematically illustrates another vehicle sensor unit 220 including an alternative vehicle sensor circuit 210 in accordance with the invention. Only those features that differ from the first embodiment will be described. As for features that are common to both embodiments, reference is made to the description of the first embodiment [0068] The vehicle sensor circuit 210 is designed for a seat belt reminder system, i.e. a combination of a vehicle seat occupancy detection system and a vehicle seat belt buckle monitoring system.

[0069] The vehicle sensor circuit 210 comprises a plurality of six electrical sensor switches 212, (i = 1 to 6) electrically connected in series. The plurality of electrical sensor switches 212, (i = 1 to 6) includes three identical force-sensitive sensor switches 212i, 2122, 2123 designed as foil-type switching members that are configured to detect a vehicle seat occupancy status, and three buckle switch members 2124, 2125, 2126 that are configured to detect a vehicle seat belt fastening status.

[0070] Each one of the three force-sensitive sensor switches 212i, 2122, 2123 is disposed at a center of a B-surface of one of three juxtaposed seating positions 232, 234, 236 of a rear seat bench cushion of a vehicle designed as a passenger car (not shown). The three force-sensitive sensor switches 212^ 2122, 2123 may be arranged on a common carrier. As in the first embodiment, the force-sensitive sensor switches 212^ 2122, 2123 are configured to change a switching state in a reversible manner from a first switching state to a second switching state if a mechanical load corresponding to a pre-determined threshold value is applied to the force-sensitive sensor switch 2121( 2122, 2123. The first switching state of the force-sensitive sensor switches 212i, 2122, 2123 is the open switching state. The second switching state of the force-sensitive sensor switches 212i, 2122, 2123 is the closed switching state.

[0071] Each one of the three buckle switch members 2124, 2125, 2126 is disposed at a seat buckle that is assigned to one of the three juxtaposed seating positions 232, 234, 236. The buckle switch members 2124, 2125, 2126 are formed by reed switches and are configured to change a switching state in a reversible manner from a first switching state to a second switching state if a physical quantity given by a magnetic field corresponding to at least a pre-determined threshold value is applied to the reed switch. The magnetic field is generated at the location of the reed switch by inserting a latch into the seat belt buckle, by which a permanent magnet is displaced in a direction towards the reed switch. The first switching state of the buckle switch members 2124, 2125, 2126 is the closed switching state. The second switching state of the buckle switch members 2124, 212δ, 2126 is the open switching state.

[0072] The vehicle sensor circuit 210 further includes a plurality of six electrical resistors 214, (i = 1 to 6) having mutually distinct resistance values R, and are selected according to formula (1) with a constant resistance value Ro of 300 Ω. Thus, the electrical resistors 214, (i = 1 to 6) have the following electrical resistance values R, (i = 1 to 6):

Ri = 300 Ω R2 = 600 Ω Η3= 1200Ω R4 = 2400 Ω R5 = 4800 Ω R6 = 9600 Ω [0073] Again, the resistance value R, of each one of the electrical resistors 214, is distinct from any arithmetic sum of any potential combination of the other electrical resistors 214k (k = 1 to 6; k # i) of the plurality of electrical resistors 214, (i = 1 to 6).

[0074] The vehicle sensor circuit 210 is equipped with a first output line 216 and a second output line 218. The first output line 216 is electrically connected to an open connection of the electrical sensor switch 212θ of the plurality of electrical sensor switches 212, (i = 1 to 6) that is arranged at one end of the series-connected plurality of electrical sensor switches 212, (i = 1 to 6). The second output line 218 is electrically connected to an open connection of the electrical sensor switch 212i of the plurality of electrical sensor switches 212j (i = 1 to 6) that is arranged at an opposite end of the series-connected plurality of electrical sensor switches 212, (i = 1 to 6).

[0075] The total electrical resistance Rtotai that is measurable between the first output line 216 and the second output line 218 is provided in Table 2 for the 26 = 64 possible switching state configurations (cases). The electrical resistance of a force-sensitive sensor switch 212i, 2122l 2123 in the closed switching state and the one of a buckle switch member 2124, 212s, 212β in the closed switching state is assumed to be 0 Ω.

Table 2 [0076] As shown in Table 2, equidistant levels of the total electrical resistance Rtotai are achieved for the 64 different switching state configurations, separated by the resistance value Ro, and an easy and robust evaluation of the measurable total electrical resistance is facilitated.

[0077] The predetermined thresholds are given by endpoints of intervals about the values of the total electrical resistance Rtotai presented in the last column of Table 2 as center values of these intervals. Each interval has a width of ±100 Ω about its center value.

[0078] An electronic control unit 222 forms part of the vehicle sensor unit 220. The electronic control unit 222 is identically designed to the electronic control unit 122 of the first embodiment and is configured to execute the functions of determining the total electrical resistance Rtotai of the vehicle sensor circuit 210, of comparing the determined total electrical resistance Rtotai with the plurality of predetermined thresholds for the total electrical resistance Rtotai> of identifying switching states of the plurality of electrical sensor switches 212, (i = 1 to 6), depending on a result of the comparison, and of outputting an information representing the identified switching states of the plurality of electrical sensor switches 212, (i = 1 to 6) to a higher-level vehicle control unit 238 in the same manner as electronic control unit 122.

[0079] The case of unoccupied seating positions and unbuckled seat belts corresponds to case # 57 and will be identified if the measured total electrical resistance Rtotai lies between 2000 and 2200 Ω.

[0080] For instance, a correctly buckled seat occupancy at seating position 232 (case # 50) will be identified if the measured total electrical resistance Rtotai lies between 4100 Ω and 4300 Ω. A correctly buckled seat occupancy at seating position 234 (case # 43) will be identified if the measured total electrical resistance Rtotai lies between 6200 Ω and 6400 Ω. A correctly buckled seat occupancy at seating position 236 (case # 29) will be identified if the measured total electrical resistance Rtotai lies between 10400Ω and 10600 Ω. A correctly buckled seat occupancy at seating positions 232 and 236 (case # 22) will be identified if the measured total electrical resistance Rtotai lies between 12500 Ω and 12700 Ω, and so forth.

[0081] Again, if the determined total electrical resistance Rtotai does not lie in any one of the described intervals, the electronic control unit 222 is configured to output an error message to the higher-level vehicle control unit 238.

[0082] 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.

[0083] 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 vehicle sensor circuit 12 electrical sensor switch 14 electrical resistor 16 first output line 18 second output line 20 vehicle sensor unit 22 electronic control unit 24 processor unit 26 digital data memory unit 28 input line 30 common carrier 32 seating position 34 seating position 36 seating position 38 vehicle control unit 40 ground connection

Claims

A vehicle sensor circuit (110; 210) for at least one of a seat occupancy detection system in a vehicle and a seatbelt monitoring system in a vehicle, the vehicle sensor circuit (110; 210) comprising: a plurality of electrical sensor switches (112; 212) electrically connected in series wherein each electrical sensor switch (112; 212) of the plurality of electrical sensor switches (112; 212) is adapted to reversibly change a switching state from a first switching state to a second switching state when a physical quantity corresponding to at least a predetermined threshold for the physical quantity is applied to the electrical sensor switch (112; 212); a plurality of electrical resistances (114; 214) having resistance values different from each other and selected such that the resistance of each electrical resistor (114; 214) is an arithmetic sum of each possible combination of the other electrical resistances (114; and wherein an electrical resistance (114; 214) of the plurality of electrical resistors (114; 214) is connected in parallel with each electrical sensor switch (112; 212) of the plurality of electrical sensor switches (112; 212), a first output line (116; 216) electrically connected to an open connection of the electrical sensor switch (112; 212) of the plurality of electrical sensor switches (112; 212) connected to one end of the series connected plurality of electrical sensor switches (112; ), a second output line (118; 218) electrically connected to an open connection of the electrical Sen sensor switch (112; 212) of the plurality of electrical sensor switches (112; 212) disposed at an opposite end of the series-connected plurality of electrical sensor switches (112; 212), wherein a total electrical resistance (Rtotai) connected between the first output line (116 216) and the second output line (216; 218) is unambiguously representative of the switching states of the electrical sensor switches (112; 212) of the plurality of electrical sensor switches (112; 212).

The vehicle sensor circuit (110; 210) of claim 1, wherein the plurality of electrical resistors (114; 214) comprise a total of n electrical resistors (114; 214), where n is a natural number greater than or equal to two, and wherein the resistors R of resistors (114; 214) of the plurality of electrical resistors (114; 214) are selected according to R, = 21'1 Ro at i = 1,2, ..., n-1, n where Ro is a selectable constant resistance value designated.

The vehicle sensor circuit (110; 210) according to claim 2, wherein the selectable constant resistance value Ro is in a range between 100Ω and 100 KΩ inclusive.

A vehicle sensor circuit (110; 210) according to any one of the preceding claims, wherein the plurality of electrical sensor switches (112; 212) comprise at least one force sensitive sensor switch (112- (1,122,1233,2121,221,221,223) adapted to: to recognize a seat occupancy state in a vehicle.

The vehicle sensor circuit (110; 210) of any of the preceding claims, wherein the plurality of electrical sensor switches (112; 212) comprise three force sensitive sensor switches (112 ^ 1122, 1123; 212i, 2122, 2123) for detecting a seat occupancy state in a vehicle, and wherein each of the three force sensitive sensor switches (112i, 1122, 1123; 212i, 2122i 2123) is adapted to be located at one of three juxtaposed seating positions (132, 134, 136; 232, 234, 236), and wherein the three force sensitive sensor switches (112-j, 1122, 1123, 212-i, 2122, 2123) are disposed on a common carrier (130).

The vehicle sensor circuit (110; 210) according to claim 4 or 5, wherein at least one of the force-sensitive sensor switches (112i, 1122, 1123; 212i, 2122, 2123) is formed as a film-type switching element.

The vehicle sensor circuit (210) of any one of the preceding claims, wherein the plurality of electrical sensor switches (212) include at least one buckle shift element (2124, 2125, 2126) configured to detect a state of seat belt application in a vehicle.

The vehicle sensor circuit (210) of any one of the preceding claims, wherein the plurality of electrical sensor switches (212) comprise three buckle shift elements (2124, 2125, 2126) for detecting a state of seatbelt application in a vehicle, and wherein each of the three buckle shift elements (2124, 2125, 2126) is adapted to be placed on a buckle associated with one of three juxtaposed positions (232, 234, 236).

A vehicle sensor unit (120; 220) comprising at least one vehicle sensor circuit (110; 210) according to any one of the preceding claims, an electronic control unit (122; 222) comprising electrical resistance measuring means for determining the total electrical resistance (Rtotai) of the vehicle sensor circuit (110; 210), wherein the electronic control unit (122; 222) is adapted to determine a total electrical resistance (Rtotai) of the vehicle sensor circuit (110; 210), the determined total electrical resistance (Rtotai) having a plurality of predetermined threshold values for the entire electrical To compare resistance (Rtotai), and to detect switching states of the plurality of electrical sensor switches (112; 212) depending on a result of the comparison.

The vehicle sensor unit (120; 220) of claim 9, wherein the electronic control unit (122; 222) comprises: a processor unit (124; 224) and a digital data storage unit (126; 226), the processor unit (124; 224) therefor is configured to sequentially periodically perform the steps of: determining the total electrical resistance (Rtotai) of the vehicle sensor circuit (120; 220); comparing the determined total electrical resistance (Rtotai) to a plurality of predetermined total electrical resistance (Rtotai) thresholds; Detecting switching states of the plurality of electrical sensor switches (112; 212) according to a result of the comparison, and wherein the plurality of predetermined total electrical resistance (Rtotai) thresholds are in the digital data storage unit (126; 226). The vehicle sensor unit (120; 220) of claim 9 or 10, wherein the processor unit (124; 224) is adapted to present information representative of the detected switching states of the plurality of electrical sensor switches (112; 212) to a vehicle control unit (138; 238 ) spend a higher level.