Patent Publication Number: US-2021162946-A1

Title: Device and method for detecting whether a seatbelt is being worn

Description:
RELATED APPLICATIONS 
     This application corresponds to PCT/EP2019/058467, filed Apr. 4, 2019, which claims the benefit of German Application No. 10 2018 108 275.4, filed Apr. 9, 2018, the subject matter of which are incorporated herein by reference in their entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     The invention relates to a device for detecting a belted condition for a seat belt system of a motor vehicle and to a method for detecting a belted condition for such seat belt system. 
     For correctly adjusting an airbag safety system, it is important whether or not a vehicle occupant is correctly belted, i.e. whether, in the case of crash, the seat belt restrains the vehicle occupant in defined manner. For example, when a vehicle occupant is belted, the airbag safety system is not released before the vehicle is significantly accelerated. In addition, a gas filling amount of the airbag safety system by which an airbag of the airbag safety system is inflated may depend on whether or not the vehicle occupant is belted. 
     When the vehicle occupant passes the seat belt behind his/her body or behind the vehicle seat, for example, and inserts a latch tongue of the seat belt into the associated belt buckle, it is not sufficient to merely detect the latch tongue inserted in the belt buckle for detecting correct fastening of the seat belt and actually efficient belting of the vehicle occupant, respectively, for which the seat belt provides the desired restraining function. 
     Also, the vehicle occupant can bypass belt buckle detection by inserting a wrong latch tongue, for example a latch tongue of a different seat belt that is not associated with the belt buckle (especially in the uncoded case) or a (possibly coded) latch tongue that is separately configured. 
     SUMMARY OF THE INVENTION 
     Therefore, it is the object of the invention to provide a device and a method for detecting a belted condition by means of which it can be reliably detected whether a vehicle occupant has correctly fastened the seat belt. 
     According to the invention, the object is achieved by a device for detecting a belted condition for a seat belt system of a motor vehicle, comprising at least one first transceiver for electromagnetic waves as well as a transponder and a controller, wherein the first transceiver, when viewed in the vehicle longitudinal direction, is disposed in front of or behind the seated position of a vehicle occupant and is connected to the controller so as to transmit signals, wherein the transponder is disposed on webbing of the seat belt system associated with the vehicle seat and is configured to receive and automatically respond to scanning signals of the transceiver, and wherein the controller is configured to detect, based on output signals of the first transceiver, whether the vehicle occupant has correctly fastened the seat belt. The transponder, sometimes also referred to as radio tag, and the transceiver especially are an RFID (radio-frequency identification) system. The transponder responds to the scanning signals of the transceiver in a predefined manner only when the vehicle occupant has correctly fastened the seat belt. By means of the device according to the invention, it can thus be reliably detected whether the seat belt is correctly fastened. 
     The device according to the invention is based on the fundamental idea to exploit the absorption of electromagnetic waves by the human body for detecting a belted condition. Accordingly, the transceiver and the transponder are transmitting in a wavelength range in which electromagnetic waves are properly absorbed by the human body that primarily consists of water. The transceiver and the transponder are arranged so that the transponder will respond only when the seat belt is correctly fastened (or else will not respond). For example, the transceiver is arranged in the area of the instrument panel. The transponder disposed in the seat belt responds to a scanning signal of the transceiver only when the vehicle occupant has passed the seat belt in front of the body, which corresponds to correct fastening of the seat belt. If the vehicle occupant had passed the seat belt behind his/her body, then the vehicle occupant would absorb the scanning signals. Alternatively, the transceiver may also be disposed in the vehicle seat. In such case, the transponder would respond to the scanning signal of the transceiver when the seat belt is not correctly fastened (i.e. is passed behind the vehicle occupant), although this should definitely not be possible when the seat belt is correctly fastened. Thus, in both cases, a correctly fastened seat belt can be detected from whether or not the transponder responds. 
     The transceiver is provided especially directly in front of or directly behind the sitting position, for example in or at the vehicle seat or in the area of the instrument panel. The sitting position may be the sitting position of the driver, the passenger or else a sitting position on a rear bench seat of the motor vehicle. In particular, the at least one transceiver and/or the transponder is/are designed so that a main emitting and/or receiving direction for electromagnetic waves is substantially orientated in the vehicle longitudinal direction. 
     One aspect intends a second transceiver for electromagnetic waves to be provided which faces the first transceiver, the second transceiver being connected to the controller so as to transmit signals. The controller is especially configured to detect, on the basis of output signals of the second transceiver, whether the vehicle occupant has correctly fastened the seat belt. Preferably, the two transceivers are located on different sides of the sitting position relating to the vehicle longitudinal direction. Thus, the term facing in this case means that between the two transceivers the vehicle occupant is located, if he/she takes a seat in the respective vehicle seat. In this variant, the response signals of the transponder to the scanning signals of the two transceivers allow to detect especially reliably whether the vehicle occupant has correctly fastened the seat belt. Especially in this configuration of the invention, also a situation can be detected in which the seat belt is not extended and a latch tongue is inserted in the belt buckle which actually is not associated with said belt buckle. This may be a separate latch tongue (“cheating tongue”) or a latch tongue associated with a different seat. Since the transponder in the non-extended seat belt does not respond either to the scanning signal of the first transceiver or to the scanning signal of the second transceiver, such situation can be detected especially reliably by means of the two transceivers. 
     According to another aspect, the first transceiver and the second transceiver are disposed in the vehicle seat and, resp., in the area of the instrument panel. The first transceiver may also be arranged on the vehicle seat. Especially, the second transceiver is provided in the area of a steering wheel. 
     In one configuration of the invention, a belt buckle of the seat belt system is configured to detect an inserted latch tongue, especially wherein the belt buckle is connected to the controller so as to transmit signals. Especially, the controller is configured to detect, based on output signals of the belt buckle, whether the driver has correctly fastened the seat belt. In connection with the output signals of the first and/or the second transceiver, it can be determined particularly reliably whether the vehicle occupant has correctly fastened the provided seat belt. 
     In another configuration of the invention, the transponder is configured as an active transponder. Especially, the transponder and/or the at least one transceiver is/are configured to carry out a changing code method. Alternatively, the transponder may also be a passive transponder. 
     The transponder can be accommodated in a button cap on the webbing, the button cap being associated with a latch tongue. Since the button cap is provided on the webbing anyway, the transponder thus can be arranged especially easily on the webbing. 
     According to another aspect, the driver-side or the passenger-side latch tongue comprises a further transponder. Also, each of the driver-side and the passenger-side latch tongue may comprise a further transponder. A belt buckle of the seat belt system can be configured to transmit scanning signals and to receive corresponding response signals of the associated transponder. In this way, it can be directly detected whether the correct latch tongue is inserted in the associated belt buckle. Alternatively, a different coding can be provided. This helps reliably prevent a different latch tongue of the seat belt system which is not associated with the respective seat from being inserted in the belt buckle to deceive the detection of a belted condition. In addition, even the use of latch tongues not belonging to the seat belt system can thus be identified. 
     In one configuration of the invention, at least one further transceiver and one further transponder associated to a further vehicle seat are provided. Preferably, at least one transceiver and one transponder are associated with both of the driver seat and the passenger seat. Especially, the transceiver and the transponder can be analogously arranged at both seats. 
     Another aspect provides that at least one seat occupancy mat associated with the vehicle seat or the further vehicle seat is connected to the controller so as to transmit signals. In this way, it can be reliably detected whether the respective seat is occupied, thus allowing to further justify a conclusion of detecting a belted condition. 
     Furthermore, according to the invention, the object is achieved by a method for detecting a belted condition for a seat belt system of a motor vehicle comprising a seat belt. Initially, an electromagnetic scanning signal is generated by at least one transceiver. Now it is detected whether at least one transponder provided on webbing of the seat belt responds to the electromagnetic scanning signal. On the basis of whether the at least one transponder responds, it is detected whether the vehicle occupant has correctly fastened the seat belt. Then the transponder responds to the scanning signals of the transceiver, if the vehicle occupant is not located between the transceiver and the seat belt and absorbs the signal. Depending on the arrangement of the transceiver, when the seat belt is correctly fastened, a response signal is or is not to be given. By means of the method according to the invention, it can therefore be reliably detected whether the vehicle occupant has correctly fastened the seat belt. As to the further advantages, the foregoing explanations shall be referred to. 
     One aspect provides that the response of the at least one transponder is received by the transceiver and, on the basis of the response, it is established whether the vehicle occupant has correctly fastened the seat belt. Accordingly, the response may be a predefined response or a response that is established in a changing code method. In other words, it is either merely established whether the transponder responds at all, or also the content of the response signal is established and considered for detecting a belted condition. 
     According to another aspect, it is additionally established whether a latch tongue is located in a driver-side belt buckle or in a passenger-side belt buckle. When the latch tongue(s) is/are provided with a transponder, also a scanning signal can be generated and the response of the transponder(s) can be evaluated. 
     In another configuration of the invention, it is established by means of a seat occupancy mat whether a further vehicle seat is occupied. This helps further justify a conclusion of detecting a belted condition. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further advantages and characteristics of the invention will be evident from the following description and the drawings which are referred to, wherein: 
         FIG. 1  shows a schematic top view of a device according to the invention for detecting a belted condition; 
         FIG. 2  shows the device for detecting a belted condition of  FIG. 1  comprising a modified guidance of a seat belt; 
         FIG. 3  shows a schematic top view of a second variant of a device according to the invention for detecting a belted condition; 
         FIG. 4  shows the device for detecting a belted condition of  FIG. 3  comprising a modified guidance of a seat belt; and 
         FIG. 5  shows a schematic flow chart of the steps of a method according to the invention for detecting a belted condition. 
     
    
    
     DESCRIPTION 
       FIG. 1  illustrates a first variant of a device  10  for detecting a belted condition for a seat belt system  12  of a motor vehicle  14 . 
     In the situation shown there, a vehicle occupant  16  has incorrectly fastened a seat belt  18 , and in particular webbing of the seat belt  18  extends incorrectly. More exactly speaking, the seat belt  18  is passed, with respect to a vehicle longitudinal direction L, behind the vehicle occupant  16  (between the back of the vehicle occupant  16  and a vehicle seat  19 ), wherein a latch tongue  20  associated with the seat belt  18  is correctly inserted in an associated belt buckle  22 , however. 
     The device  10  includes a first transceiver  24  and, in the shown variant, additionally a second transceiver  26 . The first and second transceivers  24 ,  26  are arranged, when viewed in the vehicle longitudinal direction L, behind and, resp., in front of a sitting position of the vehicle occupant  16 , i.e. facing each other. 
     More exactly speaking, the first transceiver  24  is associated with, especially integrated in, a backrest of a vehicle seat  19 . The second transceiver is disposed in the area of an instrument panel  27 , especially in the area of a steering wheel. 
     In the seat belt  18 , a transponder  28  is provided, for example integrated in a button cap of the seat belt  18  which button cap is associated with the latch tongue  20 . The transponder  28 , sometimes also referred to as radio tag, and the transceivers  24 ,  26  are especially parts of an RFID system (“radio frequency identification system”). 
     The two transceivers  24 ,  26  are connected to a controller  30  so as to transmit signals, especially by means of electric wiring or wirelessly. The controller  30  is, for example, part of the vehicle control system or a control system configured separately herefrom which may be communicated with the higher vehicle control system. 
     The controller  30  is configured to control the transceivers  24 ,  26  as well as to receive and evaluate output signals therefrom. Furthermore, the controller  30  is configured to carry out a method for detecting a belted condition described hereinafter by way of  FIG. 5 . 
     To start with, a scanning signal is generated by means of at least one of the transceivers  24 ,  26  (step S 1 ). 
     If the transponder  28  responds to the scanning signal, the response is received by means of at least one of the transceivers  24 ,  26  and a respective output signal is transmitted to the controller  30  (step S 2 ). 
     On the basis of the output signals, it is detected whether the vehicle occupant  16  has correctly fastened the seat belt  18  (step S 3 ). 
     The detection of a belted condition is based on the principle of absorption. The wavelength of the electromagnetic waves emitted by the transceivers  24 ,  26  is within a range in which the human body properly absorbs the same, as the human body consists primarily of water. 
     When the seat belt  18  is correctly fastened, the transponder  28  should appropriately respond to a scanning signal of the second transceiver  26  rather than to a scanning signal of the first transceiver  24 . 
     In the case shown in  FIG. 1 , the transponder  28  responds to the scanning signal of the first transceiver  24  rather than to that of the second transceiver  26 . The controller  30  therefrom detects that the seat belt  18  is not correctly fastened. 
     It may be provided to output a warning signal when the controller  30  detects that the seat belt  18  is not correctly fastened, similarly to the warning signal for the latch tongue  20  not being inserted. 
     This applies mutatis mutandis to the situation shown in  FIG. 2  in which the seat belt  18  is passed behind the backrest of the vehicle seat  19 . 
     In this case, too, the transponder  28  would respond to the scanning signal of the first transceiver  24  rather than to that of the second transceiver  26 , wherefrom the controller  30  establishes that the seat belt  18  is not correctly fastened. 
     In accordance with one variant, the transponder  28  can be an active transponder. Especially, the transponder  28  then is configured to carry out a changing code method. In this respect, the response signal appropriately changes to impede deliberate bypassing of the detection of the belted condition. 
     In order to further improve the quality of detecting the belted condition, the belt buckle  22  may be provided for being configured to detect an inserted latch tongue  20  (step S 4 ), for example by means of a corresponding coding of the associated latch tongue  20 . 
     Accordingly, the belt buckle  22  can be connected to the controller  30  so as to transmit a signal. The controller  30  is especially configured to detect, on the basis of output signals of the belt buckle  22 , whether the vehicle occupant  16  has correctly fastened the appropriate seat belt  18 . 
     The latch tongue  20  may (equally) be provided with a transponder. Preferably, the belt buckle  22  then is configured to transmit scanning signals and to receive corresponding response signals of the associated transponder of the latch tongue  20 . 
       FIGS. 3 and 4  illustrate further situations in which a latch tongue  20  of another seat belt  32  associated with a different place or vehicle seat is inserted in the belt buckle  22  ( FIG. 3 ) or, resp., in which a separate latch tongue  33  (“cheating tongue”) is inserted in the belt buckle  22  ( FIG. 4 ). 
     In this case, too, the afore-described device  10  helps detect that the seat belt  18  is not correctly fastened, as the transponder  28  does not respond either to the scanning signal of the first transceiver  24  or to that of the second transceiver  26 . 
     As illustrated in  FIGS. 3 and 4 , there may also be provided further transceivers  34 ,  36  associated with another vehicle seat  37 , in this case the passenger seat. The further transceivers  34 ,  36  are connected to the controller  30  so as to equally transmit signals. 
     Moreover, the further seat belt  32 , i.e. the seat belt  32  associated with the passenger seat, may comprise a further transponder  38 . 
     In this variant, the incorrect guidance of the seat belt shown in  FIG. 3  is doubtlessly evident, as the further transponder  38  responds to the signals of the two further transceivers  34 ,  36  which are associated with the further vehicle seat  37  or, resp., the passenger seat. 
     The fact that additionally no latch tongue is inserted in a belt buckle  40  associated with the further vehicle seat  37  is further indicative of situation of incorrect belting. 
     Furthermore, in this variant the afore-illustrated incorrect belting situations can also be identified for a further vehicle occupant. 
     For further justifying the results of the detecting a belted condition, output signals of at least one seat occupancy mat  42  associated with the vehicle seat  19  and/or the further vehicle seat  37  can be forwarded to and evaluated by the controller  30  (step S 5 ). 
     The situations shown in  FIGS. 1 to 4  in which the seat belt  32  associated with the vehicle operator&#39;s seat is not correctly fastened can be detected already by one transceiver only, for example the second transceiver  26 , as the latter should receive a response signal when the seat belt  32  is correctly fastened. Consequently, if the second transceiver  26  receives no response signal, the controller  30  can conclude an incorrectly fastened seat belt  32 . 
     In this respect, it can be detected sufficiently safely already by one transceiver whether or not the seat belt is correctly fastened. 
     This determination can be further justified, however, by a second transceiver, further transceivers associated with other vehicle seats, a belt buckle identification and/or a seat occupancy mat. 
     Especially, thus the way in which the seat belt is incorrectly fastened can be detected.