Patent Publication Number: US-2005140199-A1

Title: Padding for the seat proper of a vehicle seat and a seat proper equipped with such padding

Description:
FIELD OF THE INVENTION  
      The present invention relates to padding for the seat proper of a vehicle seat.  
      More particularly, the invention relates to padding for the seat proper of a vehicle seat, the padding extending in a longitudinal direction between a front portion and a rear portion serving to receive the pelvis of an occupant sitting on the seat, and in a vertical direction, between a bottom surface designed to face towards a vehicle floor, and a top surface designed to face towards the body of the occupant, said padding comprising at least: 
          a comfort foam that is soft both when the seat is in normal use, and when the vehicle decelerates suddenly; and     a visco-elastic foam that is stiffer when the vehicle decelerates suddenly than when the vehicle is in normal use;     said visco-elastic foam extending from the bottom surface, and said comfort foam, secured to said visco-elastic foam, extending to the top surface of the padding.        

     BACKGROUND OF THE INVENTION  
      Use of such visco-elastic foams is known, in particular from Patent Application FR 2 795 371 which describes a seat proper or another seat element in which the padding is made up in part of visco-elastic foam. In the event of frontal impact, an occupant sitting on a seat provided with such padding has the pelvis braked progressively, thereby preventing “submarining”, i.e. sliding under the lap-belt, while also reducing compression of the lumbar region of the occupant. Various mounting configurations for mounting visco-elastic foams in the padding are described, such foam extending, for example, in the front portion of the padding, or even occupying the entire volume of the padding. In order for the restraining effect procured by the visco-elastic foam to be fully advantageous, it is also necessary for the occupant to be able to enjoy normal use of the vehicle without being inconvenienced by the presence of such a visco-elastic foam in the seat. The presence of visco-elastic foam degrades the degree of comfort offered by the seat. Thus, none of the embodiments presented in FR 2 795 371 really optimizes both the comfort of the occupant during normal use of the vehicle and also the anti-submarining effect.  
      WO 00/36951 also describes such a type of padding, in which the comfort and visco-elastic foams extend from the rear portion to the front portion. However, the padding described in that document similarly does not make it possible to optimize the comfort and the anti-submarining effect, e.g. in a manner adapted to the geometrical shape of the seat proper.  
     OBJECTS AND SUMMARY OF THE INVENTION  
      A particular object of the present invention is to mitigate those drawbacks.  
      To this end, according to the invention, in padding of the type in question, said visco-elastic foam presents a stiffening thickness that varies between said rear end and said front end.  
      By means of these provisions, occupant safety is improved relative to the safety procured with known padding, without the improvement being achieved to the detriment of comfort.  
      In preferred embodiments of the invention, it is optionally possible to use one or more of the following provisions: 
          said rear portion presents a rear end, and said front portion presents a front end;     said comfort foam presents a comfort thickness that varies between said rear end and said front end; and     a ratio between the comfort thickness and the sum of the comfort thickness and of the stiffening thickness varies in said longitudinal direction;     said ratio decreases from said rear end to said front end;     said rear portion extends from said rear end towards the front end over a distance corresponding substantially to one third of the distance between the front end and the rear end, and, in the rear portion, said ratio lies in the range 40% to 80%, and preferably in the range 50% to 70%;     said front portion extends from said front end towards the rear end over a distance corresponding substantially to one third of the distance between the front end and the rear end; and     in the front portion, said comfort foam presents a comfort thickness smaller than 0.05 meters (m), and preferably smaller than 0.03 μm;     said visco-elastic foam presents a stiffening coefficient R greater than 10, the stiffening coefficient R being defined as the ratio between dynamic lift and quasi-static lift, lift being the ratio between the compression force to be exerted on the surface of a portion of foam in order to deform said portion by 50% and the area of said surface of the portion, dynamic lift being obtained for a deformation rate of not less than 10 per second (s −1 ); and     the padding further comprises an intermediate portion between said front portion and said rear portion, and a rigid element which is mounted on the bottom surface of said intermediate portion.        

      In another aspect, the invention provides a seat proper having a rigid structure on which such padding is mounted, said padding being covered with a cover.  
      In yet another aspect, the invention provides a seat proper having a rigid structure on which such padding is mounted, said padding further comprising an intermediate portion between said front portion and said rear portion, and said rigid structure further comprising a rigid element disposed facing said intermediate portion of said padding. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
      Other characteristics and advantages of the invention appear from the following description of one of the embodiments thereof, given by way of non-limiting example and with reference to the accompanying drawing.  
      In the drawing:  
       FIG. 1  is an overall view of a motor vehicle seat comprising a seat proper provided with padding of the invention, a seat back, and a headrest; and  
       FIG. 2  is a longitudinal section view of the padding of the seat proper of the seat of  FIG. 1 . 
    
    
     MORE DETAILED DESCRIPTION  
      In the various figures, like references designate elements that are identical or similar.  
       FIG. 1  shows a motor vehicle seat  1  that, in a manner known per se, is made up of a seat proper  2  supporting a seat back  3  that itself supports a headrest  4 .  
      The seat back  3  is, for example, mounted to pivot about the pivot axis A ( FIG. 2 ) on the seat proper  2 .  
      The seat proper  2  is itself constituted by a framework (not shown) over which elastic suspension webbing  5  is tensioned. The webbing supports padding  6  which is itself covered with a trim cover  7  suitable for being sat upon by a passenger of the motor vehicle on board which the seat  1  is installed.  
      The padding  6  extends longitudinally along the axis (x) relative to the direction in which the seat extends between a front end  8  remote from the seat back  3  and a rear end  9  close to said seat back. The seat proper can thus be subdivided into three portions, namely a rear portion  6   a , an intermediate portion  6   b , and a front portion  6   c , along the axis (x) between the rear end  9  and the front end  9  of the seat. Each of the portions is of length approximately equal to one third of the total length of the seat proper.  
      As shown in  FIG. 2 , the padding has, in particular, a top face  12  covered with the cover  7  and serving to receive the occupant by facing mainly upwards in the normal in-use position. The top face  12  is opposite from a bottom face  13  which faces towards the floor of the vehicle and is generally retained by the rigid structure of the seat and/or the suspension webbing  5 , at least when an occupant is seated on the seat.  
      The padding  6  comprises two portions of foam  10  and  11 , each of which is made of a respective type of foam. The two portions are superposed, portion  11  overlying portion  10 . At the junction between the two structures, an intermediate level  15  thus exists in the padding. Thus, at a given point of the padding along the longitudinal axis (x), said padding presents a given thickness or “comfort thickness” h c  of foam  11  above a given thickness or “stiffening thickness” h r  of foam  10 . In the embodiment shown, each of the two portions extends from the rear end to the front end of the seat along the longitudinal axis (x) of the seat proper.  
      The portion  11  of the padding  6  is made of a soft “comfort” foam, e.g. made of polyurethane. The portion  10  is made of a visco-elastic foam. Such a visco-elastic foam stiffens as a function of the speed at which it is compressed by the passenger in the seat when the vehicle is subjected to an impact against an external obstacle. It is thus soft under quasi-static conditions, at low deformation speeds, and hard at high speeds such as those imposed by the occupant during an impact.  
      The behavior of visco-elastic foam can be characterized by a stiffening coefficient R. This coefficient is defined as being the ratio of dynamic lift to static lift, lift being the ratio between the force to be exerted on the surface of a sample of the foam in order to obtain 50% deformation of said sample and the area of the surface of said sample. Dynamic lift is measured for deformation rates of about 100 s −1 , and quasi-static lift is measured for deformation rates of less than 0.1 s −1 . The deformation rate is obtained by dividing the instantaneous speed of the surface of the foam by the initial thickness of the sample.  
      A visco-elastic foam used in the context of the invention can have a stiffening coefficient R greater than 10. For example, it is a foam of density in the vicinity 100 kilograms per cubic meter (kg/m 3 ) manufactured by Aero E.A.R. Specialty Composites™ under the name CONFOR CF-42 Pink.  
      The make-up of the padding is shown in particular in  FIG. 2 . The portion  10  that is made of the visco-elastic foam extends under the portion  11  that is made of conventional soft foam, from the rear end  9  to the front end  8  of the seat proper. The block of visco-elastic foam is relatively thin in the rear portion of the seat proper, with a comfort height h c  representing in the range 40% of the combined thickness of the two foams to 80% of said combined thickness, and preferably in the range 50% to 70% and even more preferably about 60%. Firstly, the presence of visco-elastic foam in said rear portion makes it possible, by means of the intrinsic properties of said foam, to restrain the occupant as of the beginning of the impact. Secondly, the presence of conventional flexible foam superposed on said visco-elastic foam makes it possible to guarantee comfort for the occupant during normal occupancy.  
      In the front portion, the visco-elastic foam is in the majority. The conventional foam presents a thickness h c  of less than 3 centimeters (cm) therein, and even more preferably less than 2 cm. Such an arrangement provides sufficient comfort for the legs of the occupant while also making it possible to restrain the occupant optimally in the event the vehicle is subjected to frontal impact.  
      The two foams thus have different relative thicknesses depending on whether they are measured in the front portion or in the rear portion of the seat proper. In an intermediate portion  6   b  between the front portion and the rear portion, the intermediate level  15  between the conventional foam and the visco-elastic foam thus presents a rising slope so as to have a face that is almost normal to the movement of the pelvis of the occupant in the seat when the vehicle is subjected to a front impact. This considerably reduces pivoting of the pelvis and therefore reduces the forces acting on the lumbar region. Since movement of the occupant in the seat is minimized, other biomechanical criteria (head, chest, lower limbs) are also reduced.  
      Such a seat proper can be implemented in various manners.  
      For example, each of the foams could be made independently, and then be assembled together by adhesive bonding. Alternatively, the conventional foam could be overmolded onto the visco-elastic foam, which would enable the adhesion between the two components to be improved.  
      It is also possible to mold the visco-elastic foam to the appropriate shape first and then to fasten the cover  7  to the opposite side of the mold, and finally to inject the conventional foam. A cover molded directly over the filling  6  is thus obtained. In which case, in order to guarantee that the molding method proceeds properly, it is possible to check that the comfort foam  11  presents at least a minimum thickness, e.g. about 2 cm, along the axis (x).  
      Or else, the visco-elastic foam could be bonded by adhesive directly to the seat structure, whereupon the seat proper is filled with conventional foam in conventional manner.  
      It is optionally possible to add a rigid metal plate  14  to the bottom face of the padding, in its intermediate portion. Such a configuration further improves restraint of the occupant by increasing the reaction area. Alternatively, said plate is a component element of the seat proper structure. For example, the plate  14  is secured suitably to the rigid structure of the seat proper and, in this embodiment, the suspension webbing  5  can then be tensioned between the rear portion of the framework and the rear portion of the plate  14 , as shown in  FIG. 2 , as in a half-bucket structure.