Patent Publication Number: US-7584667-B2

Title: Method and apparatus for sensing seat occupant weight

Description:
RELATED APPLICATION 
   This application is a continuation of U.S. Ser. No. 09/507,868 filed Feb. 22, 2000, which claims priority to U.S. Provisional Application No. 60/120,637 filed on Feb. 24, 1999. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates to a method and apparatus for measuring the weight of a seat occupant. Specifically, a sensor arrangement is mounted within a vehicle seat track to provide accurate seat occupant weight measurements. 
   2. Related Art 
   Most vehicles include airbags and seatbelt restraint systems that work together to protect the driver and passengers from experiencing serious injuries due to a high speed collision. It is important to control the deployment force of the airbags and the force of the seatbelt pretensioners based on the size of the driver or the passenger. One way to control these forces is to monitor the weight of the seat occupant. If a smaller person such as a child or infant in a car seat is in the passenger seat, the weight on the seat will be less than if an adult occupies the seat. 
   Current systems for measuring the weight of a seat occupant are complex and expensive. One type of system uses pressure sensitive foil mats mounted within the seat bottom foam. Another system uses sensors placed at a plurality of locations within the seat bottom. The combined output from the mats or the sensors is used to determine the weight of the seat occupant. These sensors experience a substantially vertical force, due to the weight of the seat occupant, but are also subject to longitudinal and lateral forces caused by acceleration, deceleration, or turning. The lateral and longitudinal forces picked up by the sensor incorporate an error component into the weight measurement. The sensors are very sophisticated using multiple strain gages and complicated bending elements to provide high measurement sensitivity in the vertical direction and low sensitivity to lateral and longitudinal forces in order to increase accuracy. 
   Mounting these sensors within the seat bottom can also be difficult and time consuming. It is difficult to find mounting locations for each the sensors that will accommodate all of the various positions of a seated occupant while still providing accurate measurements. Further, shifting of the occupant on the seat can dislodge or move the sensors out of their proper location. Because the sensors are mounted within the seat bottom, it is difficult to reposition the sensors after the seat is installed in the vehicle. 
   Thus, it is desirable to have a simplified seat occupant weight measurement system that is accurate and easily to install and overcomes the above references deficiencies with prior art systems. 
   SUMMARY OF THE INVENTION 
   In a disclosed embodiment of this invention, a system for measuring the weight of an occupant seated on a vehicle seat includes a track assembly that is used to support a vehicle seat. The track assembly includes a first track mounted to a vehicle structure and a second track supported for movement relative to the first track. The tracks are deflectable in a vertical direction due to an occupant weight force exerted on the seat. At least one sensor is mounted on the tracks for generating a signal representative of the occupant weight force. 
   In a preferred embodiment, the track assembly is comprised of an inboard track assembly and an outboard track assembly spaced apart from the inboard track assembly. A first sensor assembly is mounted to the inboard track assembly for generating a first signal in response to measuring deflection of the inboard track assembly due to seat occupant weight. A second sensor assembly is mounted to the outboard track assembly for generating a second signal in response to measuring deflection of the outboard track assembly due to seat occupant weight. The system uses a central processor to determine seat occupant weight based on the first and second signals. The system also preferably includes an airbag control module that is in communication with the processor. Deployment force of an airbag is controlled by the control module based on seat occupant weight. 
   A method for determining the weight of a seat occupant includes the following steps. An inboard seat track assembly is mounted to a vehicle structure and an outboard seat track assembly is spaced apart from the inboard seat track assembly and mounted to the vehicle structure. The inboard and outboard seat track assemblies are defined by a predetermined cross-sectional area and each track assembly has at least one track segment with a cross-sectional area that is less than the predetermined cross-sectional area. The method steps includes mounting a first sensor assembly in the track segment of the inboard seat track assembly, mounting a second sensor assembly in the track segment of the outboard seat track assembly, generating a first signal from the first sensor assembly in response to deflection of the inboard track assembly due to seat occupant weight, generating a second signal from the second sensor assembly in response to deflection of the outboard track assembly due to seat occupant weight, and combining the first and second signals to determine seat occupant weight. 
   Additional steps include providing a system controller for controlling deployment of an airbag and generating a seat occupant weight signal based on the combination of the first and second signal. The seat occupant weight signal is transmitted to the controller and the deployment force of the airbag is controlled based on the seat occupant weight. 
   These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view showing a vehicle with an airbag system and an occupant sitting in a seat with the airbag in an active state shown in dashed lines. 
       FIG. 2  is a side view of a seat assembly incorporating the subject weight measurement system. 
       FIG. 3  is a side view of the seat track assembly of  FIG. 2 . 
       FIG. 3A  is a magnified view of the section  3 A indicated in  FIG. 3 . 
       FIG. 4  is a cross sectional view of the track assembly taken along lines  4 - 4  of  FIG. 3 . 
       FIG. 5  is a schematic view of a control system for the subject weight measurement system. 
       FIG. 6  is a schematic view of the sensors mounted within the subject track assembly. 
       FIG. 7  is a schematic view representing a full bending bridge. 
       FIG. 8  is a schematic view of the sensors mounted within the subject track assembly having an overload mechanism. 
   

   DETAILED DESCRIPTION OF AN EXEMPLARY EMBODIMENT 
   A vehicle includes a vehicle seat assembly, shown generally at  12  in  FIG. 1 , and an airbag system  14 . The seat assembly  12  can be either a driver or passenger seat and includes a seat back  16  and a seat bottom  18 . When a vehicle occupant  20  is seated on the seat  12  a vertical force Fv is exerted against the seat bottom  18 . The vertical force Fv represents the weight of the seat occupant  20 . 
   The airbag system  14  deploys an airbag  24  under certain collision conditions. The deployment force for the airbag  24 , shown in dashed lines in  FIG. 1 , varies according to the weight of the occupant  20 . The vehicle includes a unique system for measuring the weight of the seat occupant  20 . This unique system is installed within a seat track assembly, generally indicated at  26  in  FIG. 2 . 
   The seat track assembly  26  includes a first track member  28  mounted to a vehicle structure  30  such as a floor, frame, or riser, for example. A second track member  32  is supported for movement relative to the first track member  28  along a longitudinal axis  34 . First  38  and second sensors  40  are mounted on one of the track members  28 ,  32 . The sensors  38  and  40  are used to generate a signal representative of the occupant weight. The first sensor  38  is preferably positioned rearwardly and the second sensor  40  positioned forwardly on the track assembly  26 . The first  38  and second  40  sensors are used to measure deflection of the track assembly  26  to generate the signal. 
   The first track member  28  includes a forward end  42  and a rearward end  44  with a central track portion  46  extending between the ends  42 ,  44 . The forward  42  and rearward  44  ends are mounted to the vehicle structure  30  such that the central track portion  46  remains unsupported to form gap  48  between the vehicle structure  30  and the central track portion  46 . Preferably, the first track member  28  is mounted to a riser  50  having upwardly extending supports  52  at each end for attachment to the forward  42  and rearward  44  ends of the first track member  28 . 
   Thus, the central track portion  46  of the seat track assembly  26  is deflectable under load. When the occupant is seated on the seat  12 , a vertical force Fv is exerted against the track assembly  26 , as shown in  FIG. 3 . Reaction forces Fr are exerted in the opposite direction. The forces cause the central track portion  46  to deflect and reflect full bending beam behavior, shown generally at  54  in  FIG. 3A . The sensors are preferably strain gages  38 ,  40  that are positioned along the central track portion  46 , however, other types of sensors known in the art could also be used. For example, fiber optic or magneto elastic sensors could be used. 
   The sensors  38 ,  40  are preferably positioned in the first track member  28  such that the sensors  38 ,  40  remain positioned in the unsupported track section as the second track member  32  adjusts horizontally along axis  34 . As shown in  FIG. 4 , a plurality of ball bearings  56  are installed between the track members  28 ,  32  such that the second track member  32  can slide easily relative to the first track member  28 . The bearings  56  also transfer the forces applied to the second track member  32  to the rigid central track portion  46  between the two (2) sensor locations. 
   As shown in  FIG. 5 , the seat  12  is mounted to the vehicle structure  30  on an inboard track assembly  26   a  and an outboard track assembly  26   b  that is spaced apart from the inboard track assembly  26   a  by a predetermined distance. The inboard  26   a  and outboard  26   b  track assemblies are mounted to have similar bending behavior, i.e. both track assemblies  26   a ,  26   b  are deflectable in a vertical direction due to an occupant weight force. Both the inboard  26   a  and outboard  26   b  track assemblies include first  28  and second  32  track members. 
   In one embodiment, first  38  and second  40  sensors are installed in the inboard track assembly  26   a  and third  58  and fourth  60  sensors are installed in the outboard track assembly  26   b . The first  38  and second  40  sensors generate a first signal  62  representative of the portion of occupant weight on the inboard track assembly  26   a  and the third  58  and fourth  60  sensors generate a second signal  64  representative of the portion of occupant weight on the outboard track assembly  26   b . The signals  62 ,  64  are transmitted to an electronic control unit (ECU)  66 , which combines the signals to determine the weight of the occupant  20 . The ECU then sends a control signal  68  to a system controller  70 . Preferably, the system controller  70  is an airbag control module that is in communication with the ECU  66  such that the deployment force of the airbag  24  is controlled based on seat occupant weight. The system controller  70  could also be used to control the force of seat belt pretensioners based on occupant weight. 
   While the above configuration is preferred, an option configuration could utilize one sensor assembly mounted to the inboard track assembly for generating the first signal  62  in response to measuring deflection of the inboard track assembly  26   a  due to seat occupant weight and a second sensor assembly mounted to the outboard track assembly  26   b  for generating the second  64  signal in response to measuring deflection of the outboard track assembly  26   b  due to seat occupant weight. 
   As shown in greater detail in  FIG. 6 , the track assembly  26  has a predetermined cross-sectional area defined by height H 1 . A track portion, generally indicated at  72 , of each track assembly  26  has a cross-sectional area defined by H 2  that is less than the predetermined cross-sectional area H 1 . Each track assembly  26   a ,  26   b  has two (2) track portions  72  with this decreased cross-sectional area. One sensor assembly  38 ,  40 ,  58 ,  60  is mounted in each track portion  72 . Only the first sensor assembly  38  is shown in  FIG. 6 . As the track assembly  26  deflects under load, the sensor assembly  38  measures full bending beam behavior  54 , shown in  FIG. 7 . Each of the sensors  38 ,  40 ,  58 ,  60  at the four (4) locations thus serves as a Wheatstone Bridge for measuring deflection. The operation of a Wheatstone Bridge is well known in the art. 
   Preferably, the reduced cross-sectional area track portions  72  are created by forming square shaped holes within the first track member  28 . The holes create dual-beam spring elements. With such elements located on the inboard  26   a  and outboard  26   b  track assemblies, it is possible to measure the vertical force Fv applied on the area between the two sets of tracks  26   a ,  26   b.    
   The method for determining the weight of a seat occupant includes the following steps. An inboard seat track assembly  26   a  is mounted to a vehicle structure  30  and an outboard seat track assembly  26   b  is spaced apart from the inboard seat track assembly  26   a  and mounted to the vehicle structure  30 . The inboard  26   a  and outboard  26   b  seat track assemblies are defined by a predetermined cross-sectional area H 1  and each track assembly  26   a ,  26   b  has at least one track portion  72  with a cross-sectional area H 2  that is less than the predetermined cross-sectional area H 1 . The method steps include mounting a first sensor assembly in the track portion  72  of the inboard seat track assembly  26   a  and mounting a second sensor assembly in the track portion  72  of the outboard seat track assembly  26   b . A first signal  62  is generated from the first sensor assembly in response to deflection of the inboard track assembly  26   a  due to seat occupant weight. A second signal  64  is generated from the second sensor assembly in response to deflection of the outboard track assembly  26   b  due to seat occupant weight. The first  62  and second  64  signals are used to determine seat occupant weight. 
   Additional steps include providing a system controller  70  for controlling deployment of an airbag  24  and generating a seat occupant weight signal based on the combination of the first  62  and second  64  signals. The seat occupant weight signal is transmitted to the controller and the deployment force of the airbag is controlled based on the seat occupant weight. 
   Other steps include providing the inboard  26   a  and outboard  26   b  track assemblies with forward ends  42  and rearward  44  ends interconnected by the central track portion  46  and fixing the forward  42  and rearward  44  ends to the vehicle structure  30  such that the central track portion  46  of each track assembly  26   a ,  26   b  remains unsupported. The track portion  72  is preferably located in the central track portion  46 . 
   As discussed above, the first sensor assembly is preferably comprised of first  38  and second  40  sensors that are mounted in the first track member  28  of the inboard track assembly  26   a . The second sensor assembly is preferably comprised of third  58  and fourth  60  sensors that are mounted in the first track member  28  of the outboard track assembly  26   b.    
   A seat track assembly  26  with integrated weight sensors  38 ,  40 ,  58 ,  60  is provided to determine the weight of an occupant  20  seated on a vehicle seat  12 . It is preferable to integrate the sensors  38 ,  40 ,  58 ,  60  into the seat track assembly  26  because it is a common component for most vehicle seats  12 . The subject weight measurement system is easily incorporated into any type of seat track configuration. The weight sensors  38 ,  40 ,  58 ,  60  are mounted within reduced size track portions  72  to measure deflection of the track material caused by the weight of the occupant  20 . The measured weight is independent of seat positions and is accurately provided in various occupant positions on the seat  12 . 
   By measuring the deflection in all four (4) locations in the inboard  26   a  and outboard  26   b  track assemblies, it is possible to calculate the occupant weight, which is proportional to the sum of the output of all of the sensors  38 ,  40 ,  58 ,  60 . The center of gravity of the upper part of the seat and the occupant can be calculated by subtracting the sum of the sensor signals in the front from the sum of the sensor signals in the rear and dividing the result by the sum of all four (4) signals. The electronics for signal conditioning can be housed within the track assemblies  26   a,    26   b  as is well known in the art. 
   Under high overload conditions, the track assembly  26  experiences high vertical Fv and horizontal Fh forces. These forces cause the track to experience an overload resultant force Fre that will try to separate the track  26  from the floor  30 . In applications, with heavy overload conditions, like seats having integrated or all-belts-to seat configurations, it is beneficial to integrate an active overload protection. One such method of protection utilizes an overload bolt  74 , shown in  FIG. 8 , extending through the track members  28 ,  32  to the vehicle floor  30 . Under high vehicle impact forces, the bolt  74  prevents the track assembly  26  from separating from the floor  30 . Thus, the reduced cross-sectional areas of track portion  72  do not have to sustain the full impact forces. 
   Although a preferred embodiment of this invention has been disclosed, it should be understood that a worker of ordinary skill in the art would recognize many modifications come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.