Abstract:
A safety arrangement in a motor vehicle comprises a seat to be occupied by a passenger of the vehicle. The seat is supported by a framework ( 32, 33 ). The framework is mounted on to a carriage ( 6 ) by four deformable members ( 5 ) each having sensor means responsive to deformation of the deformable members. The sensor can determine the weight of a person sitting on the seat and also the position of that person within the seat. The sensors are associated with controls adapted to initiate and control the inflation of an air-bag when an accident arises. The inflation characteristic of the air-bag can therefore be adapted to the weight and position of the occupant of the seat.

Description:
BACKGROUND OF THE INVENTION 
     THE PRESENT INVENTION relates to a safety arrangement in a motor vehicle. 
     It has been proposed to provide safety arrangements in a motor vehicle which incorporate an air-bag adapted to be inflated in the event that an accident should occur to provide protection for the driver or an occupant of a vehicle. It has been customary to mount an air-bag intended to provide protection for a front seat passenger of a motor vehicle in the event that a frontal impact should occur within the dashboard of the motor vehicle. The air-bag is associated with an appropriate sensor arrangement which initiates inflation of the air-bag in the event that a frontal impact should occur. 
     When the air-bag is inflated, the fabric of the air-bag may be given, at least initially, a very substantial velocity directed towards the occupant of the front seat. If the occupant of the front seat is not in an appropriate position, that is to say, is not sitting fully back in the seat, then difficulties may arise. If, for example, the occupant of the seat is leaning forwardly at the instant that the air-bag is inflated, the air-bag may impact severely with the occupant of the seat and may impart substantial injuries to the occupant of the seat. 
     If the occupant of the front seat is very heavy, then the occupant of the seat will require much more “cushioning” in the event that a frontal impact should arise than a very light occupant of the seat. Thus, it is desirable to be able to inflate an air-bag which has been provided to protect the occupant of a front seat in the event of a frontal impact, in dependence upon the weight of the occupant of the seat. 
     It has been proposed before to control the inflation of an air-bag provided to protect a front seat passenger in a motor vehicle. DE OS 2516185 discloses an arrangement in which a switch is provided within the squab of the seat. If the occupant is sitting on the seat, the switch is closed, and in the event that an accident should occur, the air-bag is fully inflated. However, if the switch is not closed, which is a situation which might obtain if the occupant of the seat is not actually sitting on the seat, but instead is standing in front of the seat, then the air-bag is only partially inflated. 
     DE 3809074 also discloses an arrangement in which sensors are located between the squab of the seat and the floor of the motor vehicle to determine the downward forces applied at the front and at the rear of the seat, to determine the position of the occupant of the seat and thus to control the inflation characteristic of an air-bag. 
     Sensors that have been utilised previously have been designed to resist the forces which may be applied to the sensors in an accident situation. These forces can be extremely high. It has proved to be extremely difficult to provide a sensor which has sufficient strength, but which can provide a reliable and accurate determination of the forces applied to the seat during ordinary driving conditions. Many of the sensors that have been used before are such that the measurement of the force is determined as a consequence of a movement of one part of the sensor relative to another part of the sensor. Any frictional effects between the two parts of the sensor causes the sensor to provide an incorrect reading and also, if the occupant of a seat changes position there may be a substantial time delay (at least relative to the time available to inflate an air-bag during an accident situation, which is usually measured as a few tens of milliseconds) before a correct output signal is provided. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention seeks to provide an improved safety arrangement. 
     According to this invention there is provided a safety arrangement in a motor vehicle, the safety arrangement comprising a seat to be occupied by a passenger of the vehicle, a plurality of sensors located between the seat and the floor of the vehicle, each adapted to provide an indication of the downward force applied to it, control means adapted to initiate and control the inflation of an air-bag and adapted to receive signals from the sensors, and adapted to control the inflation of the air-bag in dependence upon the nature of the said signals, the sensors comprising means which, at least in ordinary use of the seat, form the sole connection between the seat and the floor of the motor vehicle, each sensor comprising a first portion connected directly or indirectly to the floor of the motor vehicle, and a second portion connected directly or indirectly to the seat, said two portions being inter-connected by a deformable element having sensor means responsive to deformation thereof. 
     Preferably the first portion of each sensor is mounted on a carriage slideable along a rail mounted on the floor of a motor vehicle and the second portion of each sensor is connected to a sub-frame of the seat. 
     Conveniently the element inter-connecting the first and second portions of each sensor comprises a cantilever beam adapted to deflect when a downward force is applied to the portion connected to the seat. 
     In one embodiment the cantilever element has one end connected to a mounting block comprising said first portion, the mounting block having means securing the mounting block to part of the carriage, and has the other end connected to a mounting block, that other mounting block having means securing the mounting block to part of a sub-frame for the seat. 
     In an alternative embodiment each sensor comprises an integral element, the element having a first portion mounted to a carriage slidably mountable in a rail connected to the floor of the vehicle and a second portion connected to the sub-frame of a seat, the two portions being inter-connected by a cantilever element. 
     Preferably part of the carriage is located adjacent part of the sub-frame, one of said parts carrying a projection of a predetermined diameter, said projection being located within an aperture of slightly greater diameter formed in the other part, the arrangement being such that in the event that a substantial force is applied to the seat, the projection carried by the one part will engage the wall of the aperture carried by the other part. 
     Conveniently the said one part comprises a web carried by the carriage, and the other part comprises a flange carried by a support element forming part of the sub-frame, the carriage carrying a bolt having a threaded portion passing through a bore provided in the web and having a portion of enlarged diameter, defining a shoulder with the threaded portion, the portion of enlarged diameter extending through said aperture which is formed in a flange provided on a support element forming pail of the sub-frame of the seat. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In order that the invention may be more readily understood, and so that further features thereof may be appreciated, the invention will now be described, by way of example, with reference to the accompanying drawings in which: 
     FIG. 1 is a schematic illustration, which comprises a partial block diagram, illustrating a vehicle seat for a front seat passenger in a motor vehicle, and an associated air-bag, together with a control arrangement, 
     FIG. 2 is a perspective view of the sub-frame for the seat as shown in FIG. 1, and associated carriages on which the sub-frame is mounted for movement along rails (which are shown in phantom), 
     FIG. 3 is an enlarged view of a load cell forming a mounting element as shown in FIG. 2, 
     FIG. 4 is an enlarged view of an alternative form of load cell, and 
     FIG. 5 is an enlarged sectional view illustrating a bolt arrangement securing the sub-frame of FIG. 2 to the carriage of FIG.  2 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring initially to FIG. 1 of the accompanying drawings, a vehicle seat  1  is illustrated having a squab  2  and a back  3 . The squab  2  is connected by means of four sensors, (only two of which  4 ,  5 , are visible in FIG. 1) to two carriages, (only one of which,  6 , is visible in FIG.  1 ), which are mounted on a pair of rails (only one of which,  7 , is visible in FIG. 1) which are mounted on the floor of a motor vehicle. The seat is provided with two sensors  4 ,  5 , along each side of the seat, one sensor  4  being located at the front of the seat, and one sensor  5 , being located at the rear of the seat. 
     The sensors  4 ,  5  are connected to a control arrangement  8  which also receives signals from further sensors  9  which are responsive to an accident or a situation when an accident is likely to occur. Thus, the sensors  9  may comprise acceleration sensors or impact sensors. 
     The control device  8  is connected to an air-bag arrangement  10  mounted in the dashboard  11  in front of the seat  1 . The control arrangement  8  can initiate inflation of the air-bag  10 . The control arrangement  8  can also control the manner in which the air-bag is inflated. For example, the air-bag may be provided with two pyrotechnic gas generating charges. The control arrangement may activate either one of the charges, or the other of the charges, or both of the charges, thus providing three degrees of inflation of the air-bag. Alternatively the control arrangement may, in certain circumstances, activate neither of the charges and the air-bag will remain uninflated. The control arrangement  8  can, of course, also control the instant at which inflation of the air-bag is commenced. 
     Referring to FIG. 2, the squab  2  of the seat  1  is mounted on a sub-frame  20  which is illustrated in FIG.  2 . The sub-frame  20  is mounted on the carriages  6  which are mounted for axial sliding movement on the rails  7 . The sub-frame, the carriages and the rails are substantially symmetrical about the mid-point of the sub-frame. 
     In FIG. 2, the rails  7  are shown in phantom. Each rail is provided, at its forward end, with a clip  21  by means of which the forward end of the rail is secured to the floor of the motor vehicle. The rear part of each rail, as illustrated, is also provided with a clip  22  by means of which the rail is secured to the floor of the vehicle. Each rail  7  comprises an elongate extrusion defining a channel having an elongate open top  23 . 
     Each carriage  6  comprises a lower portion  24  adapted to be received within the channel defined by the rail. Appropriate ball bearings or other roller elements are located between the portion  24  of the carriage  6  which is received within the channel, and the channel itself to facilitate axial movement of the carriage along the rail. 
     The carriage  6  incorporates an up-standing web  25  which extends vertically upwardly through the open top  23  of the channel. Connected to the web  25  are the sensors  4 ,  5 , which act to support an elongate “L”-shaped support element  26  which forms part of the sub-frame  20 . The support element  26  comprises a vertical flange  27 , which is in alignment with and substantially adjacent the web  25  of the rail  6 . The vertical flange  27  supports, towards the rear of the seat, a horizontally extending pivot  28  and, towards the front of the seat, an upstanding movable link  29  which supports, at its upper end, a horizontally extending pivot  30 . The squab  2  of the seat may be mounted on the pivots  28 ,  30  and movement of the squab relative to the sub-frame may be controlled by a pair of gas springs  31  (shown in phantom) connected between the horizontally extending flange  32  of the support element  26  and the squab of the seat. The horizontally extending flange  32  also supports a plate  33  which extends transversely towards the other carriage. Two plates  33  are connected together to provide a rigid sub-frame. 
     It is to be appreciated, at this stage, that the sub-frame, which comprises the support elements  26  and the plates  33 , supports the squab of the seat, and the sub-frame itself is supported on the carriages by means of the sensors  4  and  5 . The sensors  4  and  5  thus form the sole connection between the sub-frame and the carriages. 
     The sensors  4  and  5  are of the same design, and the sensor  4  is illustrated in FIG.  3 . The sensor  4  comprises a lower mounting block  34  provided with two oppositely outwardly apertured lugs  35  by means of which the mounting block may be secured to the upstanding web  25  provided on the carriage  6 . The mounting block  34  presents a planar upper surface, and one end of a cantilever beam  36  rests upon that upper surface. Above that one end of the cantilever beam  36  is a keeper plate  37 , and two bolts  38  are provided which extend through the keeper plate  37 , through the end of the cantilever beam  36  and into appropriate threaded bores provided in the mounting block  34 . 
     The cantilever beam  36  extends substantially parallel with the axis of the rail  7 . The other end of the cantilever beam is sandwiched between a keeper plate  39  located beneath the end of the beam, and a horizontal face which forms the lower-most face of a mounting block  40 . The mounting block  40  is provided with two oppositely and outwardly directed apertured lugs  41  by means of which the upper mounting block  40  may be mounted to the vertical flange  27  of the support element  26 . A pair of bolts  42  are provided which extend upwardly through the keeper plate  39 , through the end of the cantilever beam  36  and into the mounting block  40 . 
     It will thus be understood that the entire sub-frame  20 , and the seat supported by the sub-frame  20 , is supported from the carriage by means of four cantilever beams  36 . The cantilever beams  36  are provided with sensors  43  provided on the surface of the cantilever beams  36  which are responsive to distortion or deformation of the cantilever beams  36 . The sensors may, for example, comprise resistive material, the resistance of which is dependent upon the tensile forces applied to the material. The sensors may comprise piezo electric material which provide a potential in dependence upon the stress or pressure applied to the piezo electric material. The cantilever beam  36  thus forms a load cell. 
     FIG. 4 illustrates a modified sensor where the mounting blocks and the cantilever element are all formed integrally. 
     Thus, referring to FIG. 4, an alternative sensor comprises an integral component  50  comprising a first substantially rectangular mounting block  51  having a substantial horizontal extent, the block  51  being provided with horizontal bores  52 ,  53  at the opposed ends thereof by means of which the block  51  may be secured to the upstanding web  25  provided on the carriage  6 . At one end of the mounting block  51  there is provided an upwardly directed extension  54  having a width which is substantially less than the length of the block  51 , the extension  54  merging into a second substantially horizontally extending cantilever block  55  which lies over the first block  51 . A substantial part of the cantilever block  55  is spaced from the block  51  by means of a gap  56 . A centrally located horizontal bore  57  extends through the cantilever block  55 . Sensor elements  58  are mounted on the side wall of the bore  57  of the cantilever block  55 . The sensor elements  58  may be of the same type as described with reference to FIG.  3 . The end of the cantilever block  55 , which is remote from the upwardly directed extension  54 , is itself provided with a second upstanding extension  59  which serves to connect that end of the cantilever block  55  to an upper-most horizontally extending mounting block  60 . The mounting block  60  is provided with a horizontal bore  61  by means of which the block  60  may be bolted to the vertical flange  27  of the support element  26 . There is a gap  62  between the mounting block  60  and the cantilever block  55 . 
     It will be appreciated that the central cantilever block  55  with the sensors  58  performs an equivalent function to the cantilever element  36  and the sensor elements  43  of the embodiment described with reference to FIG.  3 . 
     Turning now to FIG. 5 of the accompanying drawings, part of the carriage  6  is shown in cross-section, and the lower part  24  of the carriage is shown as part of a hollow extrusion supporting the web  25 . Located adjacent the web  25  is the upstanding flange  27  of the support element  26 . 
     A bore  70  is provided in the web  25  provided on the carriage  6 . A bolt  71  extends through the bore  70 . The bolt  71  is provided with a threaded portion  72  of a diameter which is slightly smaller than the diameter of the bore  70 , and this portion of the bolt passes through the bore  70 . The threaded portion  72  is connected to a non-threaded portion  73  of slightly greater diameter than the bore  70 , there thus being a discrete shoulder  74  between the threaded portion  72  and the non-threaded enlarged diameter cylindrical portion  73 . The shoulder  74  abuts one side face of the web  25  adjacent the bore  70 . The non-threaded cylindrical portion  73  carries an enlarged hexagonal head  75 . There is a clearance gap between the head  75  and the web  25  of the carriage  6 . 
     The threaded portion  72  carries a washer  76  which abuts against the other face of the web  25  and a nut  77  which holds the washer in place. 
     The cylindrical portion  73  of the bolt of enlarged diameter extends through an aperture  78  formed in the vertical flange  27  of the support element  26 . The aperture  78  is of greater diameter than that of the cylindrical portion  73 . 
     A bolt arrangement as illustrated in FIG. 5 is provided, as can be seen in FIG. 2, adjacent each sensor  4  and  5 . 
     When the seat is in use, with a person sitting on the seat, a downward force will be applied to each of the sensors  4  and  5 , causing the cantilever element of each sensor to bend. The degree of bending is dependent upon the downward force applied to the sensor. The degree of bending, and thus the downward force, applied to each sensor can readily be determined and, by comparing the forces applied to the sensors  4  provided at the front of the seat, and the sensors  5  provided at the rear of the seat, it is possible to determine the position of the centre of gravity of the occupant of the seat. It is possible to determine if the centre of gravity is located in a position equivalent to that of a person sitting fully back in the seat, or equivalent to that of a person leaning forwardly in the seat. Also, by determining the total sum of the downward forces applied to the four sensors, it is possible to determine the body weight of the occupant of the seat. The appropriate calculations are carried out in the control arrangement  8  which determines the manner in which the air-bag  10  will be inflated in the event that the sensors  9  provide signals indicative of the fact that an accident is likely to happen or an accident is happening. 
     In the event that an accident does arise, and if very substantial forces are applied to the sub-frame  20  of the seat, if the sensors permit a substantial movement of sub-frame relative to the carriages  6 , the cylindrical portions  73  of the bolts  71  of enlarged diameter will engage the apertures  78 , thus preventing the sub-frame moving by more than a relatively small predetermined distance, relative to the carriages  6 . It is to be appreciated, however, that the spacing between the exterior part of the enlarged diameter cylindrical portions  73  of the bolts  71 , and the apertures  78  is such that in ordinary use of the seat, and with persons of ordinary weight sitting upon the seat, the external periphery of the enlarged diameter cylindrical portion  73  of the bolts  71  do not come into contact with the interior of the apertures  78 , meaning that the sub-frame is supported solely by the sensors  4  and  5 .