Abstract:
A method of providing a seat back ( 17 ) of a seat assembly including shape defining steps that involve the use of a design manikin ( 14 ). A contour of the centerline ( 15 ) for the seat back is determined according to a hip point ( 10 ), or ‘h-point,’and a torso line ( 12 ) of the manikin. The determination includes definition of a lumbar apex reference point ( 16 ) above the hip point along the torso line, a lumbar shape reference circle ( 40 ) defined as being behind the torso line and spaced apart therefrom, a forward lumbar prominence line ( 30 ) which is parallel to the torso line and tangential to the lumbar shape reference circle, and a rearward lumbar prominence ( 20 ) line which is parallel to and rearward of the forward lumbar prominence line.

Description:
1. FIELD OF THE INVENTION  
       [0001]     This invention relates to a method of designing seating assemblies, and more particularly, to a process for designing the contours for the seat back of a seating assembly for maximum occupant support and comfort.  
       2. DESCRIPTION OF THE RELATED ART  
       [0002]     Seat design has become increasingly important with respect to the design of automobiles as engineers attempt to design seating assemblies that are both safe and comfortable, however, consumers are commonly dissatisfied with automobile seat comfort, or lack thereof. Upon close analysis, the most highly ranked dissatisfaction is with poor or uncomfortable lumbar support. These dissatisfactions refer to either the lumbar mechanism or the lower back seating contour or both.  
         [0003]     The greatest challenge engineers face when designing seats has to do with the multitudes of different body sizes and shapes. When designing seats, a supplier typically samples the complete population with respect to both morphology (shape) and anthropometry (structure), in order to have representative models for use in seat design. It is important when designing seat backs to also consider the specific structure of the spinal column, since the inherent structure of the spinal column is consistent over the entire population.  
         [0004]     The spinal column has a specific number of vertebrae—a taller person does not have more vertebrae, but instead has bigger vertebrae. The placement of a person&#39;s vertebrae dictates that person&#39;s lumbar curve, or lordosis. The length of this curve depends on the torso length of the particular individual, meaning the apex of this curve can vary from person to person by an amount up to about 120 mm. This means that designing a seat back to accommodate such a varying population becomes challenging at best. There is a need in the art for a method of better designing the curvature of a seat back to accommodate and be comfortable for a significant portion of the population.  
         [0005]     The invention uses an inside-out design methodology, which considers an occupant to the seat rather than the seat to the occupant, and anatomical landmarks of the occupant to support the lower back. This is an alternate approach to the more common lumbar support concept. This alternate approach allows a designer to design a seat back based on cross-sectional human dimensions (transverse plane), rather than longitudinal dimensions (saggital plane). This design also offers a larger surface contact area (the pelvis) rather than the traditional lumbar (lumbar spine area). In addition, the present invention assists in controlling dynamic effects (micro motions) transferred to the spinal muscles (erector spinae) that are associated with road vibration transmissions. These vibration transmissions elicit a rapid firing of the spinal muscles ultimately leading to muscle fatigue condition and thus, discomfort.  
       SUMMARY OF THE INVENTION  
       [0006]     According to one aspect of the invention, a method for shaping a centerline for a seat back of a seat assembly is provided. The process involves the use of a design manikin having a hip point and a torso line. The method defines a lumbar apex reference point above the hip point along the torso line. A lumbar shape reference circle defined as being behind the torso line and spaced apart therefrom. A forward lumbar prominence line is created parallel to the torso line and tangential to the lumbar shape reference circle. A rearward lumbar prominence line, which is parallel to the forward lumbar prominence line, is created and spaced reward from the forward lumbar prominence line. A centerline is then shaped for the seat back, wherein the centerline incorporates the forward and rearward lumbar prominence lines and the lumbar shape reference circle. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]     Advantages of the present invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:  
         [0008]      FIG. 1  is a plan view of a design manikin with the hip point and torso line determined as explained in the process below;  
         [0009]      FIG. 2  is a plan view of the torso of a design manikin with various construction shapes used to determine the contours of a seat back as described in the process;  
         [0010]      FIG. 3  is a plan view of the construction of a apex horizontal contour;  
         [0011]      FIG. 4  is a plan view of the construction of a lower horizontal seat back contour;  
         [0012]      FIG. 5  is a plan view of the construction of an upper horizontal contour;  
         [0013]      FIG. 6  is a plan view of the construction of the middle seat back bolster contour;  
         [0014]      FIG. 7  is a plan view of the construction of the upper seat back bolster contour;  
         [0015]      FIG. 8  is a plan view of the overall seat back contours as constructed in the process as described herein; and  
         [0016]      FIG. 9  is a perspective view of a seat assembly inside a motor vehicle, partially cut away. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0017]     Referring to  FIG. 1 , the process of developing seat contours incorporates a design process taken from the perspective of the occupant. To this end, parameters of a design manikin  14  are required. More specifically, a hip point  10  (“Hpt”) and a torso line  12  of the design manikin  14  must be known. The parameters of the design manikin  14  are chosen based on a particular vehicle environment in which the seat assembly is to be located. Once these reference parameters have been defined, the method can then begin the construction of the seat back contour that will optimally support the full range of intended occupants.  
         [0018]     The first main step of the method is to determine a centerline  15  of a seat back  17 , best seen in  FIG. 9 . The centerline  15  is the relatively vertical line (usually rotated rearward relative to vertical based on the intended design recline angle of the seat, which varies according to the goal of the design, and is generally parallel to the design manikin torso line) of the seat back  17 . The centerline  15  will determine a contour of the seat back  17  which will be the basis of how a seat assembly  19  incorporating the seat back  17  will support its occupants.  
         [0019]     Determining the Lumbar Support Shape with a Lumbar Centerline Contour  
         [0020]     Referring to  FIG. 2 , and because the Hpt  10  and torso line  12  of the design manikin  14  have been defined, the next step is to create the proper lumbar support shape based on the proper lumbar apex location and surface radius in this region. This is accomplished by constructing a lumbar apex reference point  16  vertically upward from the Hpt  10  along the torso line  12  a specified distance based on anthropometric landmarks. Using the lumbar apex reference point  16  as the origin, a rearward lumbar apex reference line  18  is extended rearward and perpendicular to the torso line  12  in such a manner that the end of the lumbar apex reference line  18  is substantially distant from the origin. This rearward lumbar apex reference line  18  is then used as a reference to establish the desired amount of lumbar support prominence. In order to achieve this, two lines perpendicularly related to the rearward lumbar apex reference line must be created.  
         [0021]     The first perpendicularly related line, the rearward lumbar prominence line  20 , extends between a rearward origin  22  and a rearward endpoint  24 . The rearward origin  22  is located along the rearward lumbar apex reference line  18  at a specified distance forward of an intersection of a rearward surface  25  of the design manikin  14  and the rearward lumbar apex reference line  18 . The rearward lumbar prominence line  20  extends from the rearward origin  22  in a relatively vertical sense parallel with the torso line  12  to the rearward endpoint  24 , which is distant from the rearward origin  22 .  
         [0022]     The second perpendicularly related line, the forward lumbar prominence line  30 , extends between a forward origin  32  and a forward endpoint  34 . The forward origin  32  is located along the rearward lumbar apex reference line  18  at a specified distance forward of the rearward origin  22 . The specified distance is representative of a total lumbar deflection desired. The forward lumbar prominence line  30  extends from the forward origin  32  in a relatively vertical sense, parallel with the torso line  12  to the forward endpoint  34  which is distant from the forward origin  32 .  
         [0023]     A lumbar shape reference circle  40  is then created having its center  42  located along the rearward lumbar apex reference line  18  and wherein the rearward lumbar prominence reference line  20  is tangent thereto. The radius of the lumbar shape reference circle  40  is representative of the desired shape of the lumbar support region and is determined based on anthropometric dimensions of the human body.  
         [0024]     Determining the Overall Seat Back Shape with an Overall Centerline Contour  
         [0025]     Using the rearward lumbar prominence reference line  20 , an upper seat back contour transition reference point  50  is created along the rearward lumbar prominence reference line  20  a distance above the rearward origin  22  based on anthropometric landmarks of the human body. A lower seat back contour transition reference point  52  is created at the tangency location of the lumbar shape reference circle  40  and the forward lumbar prominence reference line  30 . A transition shape  54  extending between the lower seat back contour transition reference point  52  and the upper seat back contour transition reference point  50  is created by means of a shaping function. The shaping function is a spline function. It should be appreciated by those skilled in the art that functions other than the spline function may be used without changing the scope of the invention. A lower seat back contour endpoint  60  is identified by an intersection of the lumbar shape reference circle  40  and a seat cushion contour  62 , representing a contour of a seat cushion  63 .  
         [0026]     The centerline  15 , which is used to determine the overall shape of the seat back  17 , is identified as the shape extending from the lower seat back contour endpoint  60  generally vertically extending along the lumbar shape reference circle  40  to the lower seat back contour transition reference point  52 , from the lower seat back transition reference point  52  along the transition shape  54 , accomplished by means of the mathematical shaping function, to the upper seat back contour transition reference point  50 , from the upper seat back contour transition reference point  50  along the rearward lumbar prominence line  20  to an upper seat back contour end point  66 , determined by the required design height of the seat back  17 , which can vary depending on the seat assembly  19  being designed.  
         [0027]     Determining the Horizontal (Cross-Car) Seat Back Contours  
         [0028]     The second main step of this method is the cross-car (horizontal) contour of the seat back  17 . This is the relatively horizontal shape of the seat back  17  and is perpendicularly related to the centerline  15  at specific locations along the seat back  17 . The specific locations of the specified cross-car contours are determined based on specific anthropometric landmarks of the human body. These have been translated to specific locations of the design manikin  14  to ensure a consistent design methodology. This design feature provides proper support to the occupant&#39;s back while not exerting excessive load onto the spinal processes (vertebral bodies of the spine). Minimizing load to these bodies improves both physical and perceived occupant comfort.  
         [0029]     Referring to  FIGS. 3-5 , two copies of the centerline  15  are made. These two copies, are referred to as outer contour lines  70  (the first outer contour  70   a  and the second outer contour  70   b , respectively) and are located horizontally outward and parallel to the centerline  15 . The distance between each of the outer contour lines  70  and the centerline  64  is determined by the anthropometry of the human body. Each outer contour line  70  shall be adjusted perpendicularly forward of the torso line  12 , such that each outer contour  70  is forward of the centerline  15 . Two additional copies of the centerline  15  are constructed. These two copies are inner contour lines  72 . The inner contour lines  72  are horizontally located outward and parallel to the centerline  15 . The distance between the centerline  15  and each of the inner contour lines  72  is determined by the anthropometry of the human body. Each inner contour line  72  shall be forwardly adjusted along a line perpendicular to the torso line  12 , such that it is forward of the centerline  15  and rearward of the outer contour lines  70 .  
         [0030]     Referring to  FIG. 3 , an apex horizontal contour  74  is constructed to define a portion of the horizontal contour. The apex horizontal contour  74  spans across the middle of the seat back  17 . An apex contour point  76  located at the intersection of a plane perpendicular to the torso line  12  and containing the lumbar apex reference point  16  and the centerline  15  is constructed. Then, an apex circle  78  is constructed having a radius defined based on the anthropometry of the human body. The apex circle  78  resides in a plane that is perpendicular to the centerline  15 , intersects each outer contour line  70 , intersects each inner contour line  72 , and contains the apex contour point  76 . The apex horizontal contour  74  is the line having a first outer point  80  defined by the intersection of the apex circle  78  and the first outer contour  70   a , intersection points  82  and  84  defined by the intersection of the apex circle  78  and each of the inner contour lines  72 , a center point  86  defined by the intersection of the apex circle  74  and the centerline  15 , and a second outer point  88  defined by the intersection of the apex circle  78  and the second outer contour  70   b.    
         [0031]     Referring to  FIG. 4 , a lower horizontal contour  174  is constructed to define a portion of the horizontal contour. A lower horizontal construction point  176  located at the intersection of a plane perpendicular to the design manikin torso line  12  and containing the design manikin Hpt  10  and the centerline  15  is constructed. Then, a lower circle  178  is constructed, having a radius one and half times the radius of the apex circle  78 , and residing in a plane perpendicular to the centerline  15 , intersects each outer contour line  70 , intersects each inner contour line  72 , and contains the lower horizontal construction point  176 . The lower horizontal contour  174  is the line having a first outer point  180  defined by the intersection of the lower circle  178  and the first outer contour  70   a , intersection points  182  and  184  defined by the intersection of the lower circle  178  and each of the inner contour lines  72 , a center point  186  defined by the intersection of the lower circle  174  and the centerline  15 , and a second outer point  188  defined by the intersection of the lower circle  178  and the second outer contour  70   b.    
         [0032]     Referring to  FIG. 5 , an upper horizontal contour  274  is constructed to define a portion of the horizontal contour. An upper horizontal seat back contour reference point  90  located vertically above the lumbar apex reference point  16  at a desired distance based on the anthropometry of the human body is constructed. Then, an upper horizontal construction point  276  located at the intersection of a plane perpendicular to the torso line  12  and containing the upper horizontal seat back contour reference point  90  and the centerline  15  is constructed. Next, an upper circle  278  is constructed, having a radius twice the size of the radius of the apex circle  78 . The upper circle  278  resides in a plane perpendicular to the centerline  15 , intersecting each outer contour line  70  (adjusted 10 mm outward from the location when constructing the lower and apex horizontal contours), intersecting each inner contour line  72  (adjusted 10 mm outward from the location when constructing the lower and apex horizontal contours), and containing the upper horizontal construction point  276 . The upper horizontal contour  274  is the line having a first outer point  280  defined by the intersection of the upper circle  278  and the first outer contour  70   a , intersection points  282  and  284  defined by the intersection of the upper circle  278  and each of the inner contour lines  72 , a center point  286  defined by the intersection of the upper circle  274  and the centerline  15 , and a second outer point  288  defined by the intersection of the upper circle  278  and the second outer contour  70   b.    
         [0033]     The overall seat back contour  92  as shown in  FIG. 8 , is defined by the shape resulting from connecting the outer points  180 ,  188  and the center point  184  of the lower horizontal contour  174  to the outer points  80 ,  88  and the center point  84  of the apex horizontal contour  74 , respectively, by means of a mathematical shaping formula. The overall seat back contour  92  is further defined by the shape resulting from the surface connecting the outer points  80 ,  88  and center point  84  of the apex horizontal contour  74  to the outer points  280 ,  288  and the center point  284  of the upper horizontal contour  274 , respectively, using the spline function, which includes a mathematical shaping formula. A mathematical shaping function is necessary to connect the contours into a single, consistent, smooth contour is necessary to connect the contours, as the shape will not be consistent.  
         [0034]     Determining the Seat Back Bolster Contours  
         [0035]     The final main step of this method is the bolster contours for the bolsters  96  of the seat back  17 . The bolsters  96  are the relatively extended portions along the lateral edges of the seat back  17  designed to hold the occupant in the seat during cornering as well as to provide stabilizing support of the occupant during standard driving (straight driving). The shape of the bolster  96  is angularly related to the centerline contours at specific horizontal (width) locations. The proper placement in the horizontal direction as well as the proper angular relationship allows the seat back  17  to accommodate a full range of intended users.  
         [0036]     Referring to  FIG. 6 , apex bolster contours  98  are constructed to define a portion of the bolsters  96 . First, an apex bolster line  100  is constructed by connecting the outer points  80 ,  88  of the apex horizontal contour  74 . Then, apex bolster reference lines  102 , lines having their origin at each outer point  80 ,  88  of the apex horizontal contour  74  and extending substantially forward and rotated outwardly 30 degrees from a respective pair of planes perpendicular to the apex bolster line  100  and containing the apex horizontal contour  74  are constructed. An inner apex bolster point  104  for each apex bolster contour  98  is defined by the intersection of the apex bolster reference line  102  and a first line  107  perpendicularly forward 60 mm and parallel to the apex bolster line  100 . Next, an outer apex bolster point  106  for each apex bolster contour  98  is defined by the intersection of the apex bolster reference line  102  and a second line  108  perpendicularly forward 115 mm and parallel to the apex bolster line  100 . The apex bolster contours  98 , respectively inboard  98   a  and outboard  98   b , are the segments  109  of each apex bolster reference line  102  extending between the inner apex bolster point  104  and the outer apex bolster point  106 .  
         [0037]     Referring to  FIG. 7 , upper bolster contours  298  are constructed to define a portion of the bolsters  96 . First, an upper bolster line  200  is constructed between the outer points  280 ,  288  of the upper horizontal contour  274 . Then, upper bolster reference lines  202 , lines having their origin at each outer point  280 ,  288  of the upper horizontal contour  247  and extending substantially forward and rotated outwardly 30 degrees from a respective pair of planes perpendicular to the upper bolster line  200  and containing the upper horizontal contour  274 , are constructed. An inner upper bolster point  204  for each upper bolster contour  298  is defined by the intersection of the upper bolster line  200  and the upper horizontal contour  274 . Next, an outer upper bolster point  206  for each apex bolster contour  98  is defined by the intersection of the upper bolster reference line  202  and a third line  207  perpendicularly forward 60 mm and parallel to the upper bolster line  200 . The upper bolster contours  298 , respectively inboard  298   a  and outboard  298   b , are the segments  209  of each upper bolster reference line  202  extending between the inner upper bolster point  104  and the outer upper bolster point  106 .  
         [0038]     Next, overall bolster contours  110 , a pair of surfaces inboard  110   a  and outboard  110   b  respectively, are constructed by connecting the bolster points  204 ,  204  of the upper bolster contour  298  to the bolster points  104 ,  106  of the apex bolster contour  98 , respectively, by means of a mathematical shaping formula. Each seat back bolster surface inboard  110   a  and outboard  110   b , are located relatively in space such that they do not necessarily make contact with the overall seat back contour  92 .  
         [0039]     The invention has been described in an illustrative manner, and it is to be understood that the terminology that has been used, is intended to be in the nature of words of description rather than of limitation. Accordingly, any measurements used were for one particular application of the process and one skilled in the art will recognize that such measurements may be varied depending on the goals of the particular application.  
         [0040]     Many modifications and variations of the present invention are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced other than as specifically described.