Abstract:
A variable firmness motorcycle seat that includes a bottom plate, a cushion stuffing placed on the bottom plate and a seat skin that covers the cushion stuffing and is secured to the bottom plate. In order to improve sitting comfort, a portion with a greater firmness than surrounding portions is incorporated into the seat so as to provide riding comfort and prevent permanent seat deformation problems. The location of the greater firmness portion corresponds to the area where seat pressure produced by a rider is greatest.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to vehicle seats that have varied levels of firmness, especially vehicle seats with a saddle-type construction. 
     Vehicle seats with a saddle-type construction are commonly found on vehicles that require a rider to sit astride for balancing purposes, such as motorcycles, snowmobiles, and water jet propulsion units. Saddle-type vehicle seats typically have a construction that includes a hard bottom plate made of metal or hard plastic, a stuffing cushion made of expanded urethane, and a seat skin made of synthetic leather. The firmness or rigidity of the seat when a rider sits on it is altered by changing the thickness of the seat skin or by changing the material or density of the cushion stuffing. 
     The inherent design of a straddle-type seat makes the seat conducive to permanent deformation caused by repeated sitting in a commonly-used seat position. Over time, the commonly-used seat portion recedes and takes a permanent set. This permanent deformation of the seat causes riding discomfort and may cause the rider&#39;s line of vision to be at an unsafe altitude for operating the vehicle. 
     In the past, receding and deformation of the seat was corrected by increasing the entire seat firmness. The entire seat firmness could be increased by using a thicker seat skin stretched over the entire seat surface or changing the material or density of the cushion stuffing. Increasing the entire seat firmness improved comfort in a rider&#39;s less sensitive buttocks region but impaired comfort in the sensitive thigh and coccyx region, small bone at end of spine. Additionally, stretching the uniformly thick seat skin over the entire seat surface tended to produce wrinkles and affect the seat appearance. 
     The object of the present invention is to provide a saddle-type seat with a greater firmness portion that eliminates the disadvantages of permanent deformation found in conventional seats. 
     Another object of the present invention is to improve sitting comfort by providing greater firmness in the buttocks region of a rider and less firmness in the thigh and coccyx region of a rider. 
     A further object is to provide a seat skin that can be stretched over the entire seat surface and maintain a nice appearance without wrinkles. 
     Further objects and advantages of the present invention will become apparent from a consideration of the drawings and ensuing description. 
     SUMMARY OF THE INVENTION 
     A variable firmness vehicle seat that includes a bottom plate, a cushion stuffing placed on the bottom plate and a seat skin that covers the cushion stuffing and is secured to the bottom plate. In order to improve sitting comfort, a portion with a greater firmness than surrounding portions is incorporated into the seat so as to provide riding comfort and prevent permanent seat deformation problems. The location of the greater firmness portion corresponds to the area where seat pressure produced by a rider is greatest. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic side view of a motorcycle that includes the seat of the present invention. 
     FIG. 2 is a longitudinal cross section of a bottom plate of a tandem seat as an embodiment of the present invention. 
     FIG. 3 is a lateral cross section of the seat taken along line A—A on FIG.  2 . 
     FIG. 4 is a plan view of the seat shown in FIG. 3 showing the greater firmness portion of the seat. 
     FIG. 5 is a plan view of an alternative design of the greater firmness portion of the seat. 
     FIG. 6 is a three-dimensional diagram of pressure produced by a motorcycle rider. 
     FIG. 7 is partially enlarged cross section of a the greater firmness portion of the embodiment shown in FIG.  3 . 
     FIG. 8 is a partially enlarged cross section of a second embodiment of the greater firmness portion. 
     FIG. 9 is a partially enlarged cross section of a third embodiment of the greater firmness portion. 
     FIG. 10 is a partially enlarged cross section of a fourth embodiment of a greater firmness portion. 
     FIG. 11 is a partially enlarged cross section of a fifth embodiment of the greater firmness portion. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 is a schematic side view of the vehicle seat according to the present invention on a motorcycle. The present invention may be used with a motorcycle, but its application is not limited thereto. A vehicle seat  10  is a saddle type comprising a front seat portion  10   a  for a rider and a rear seat portion lob for a co-rider. Seat  10  is continuous and forms a stepped shape between front seat portion  10   a  and rear seat portion lob. The seat  10  is located behind a fuel tank  12  above a main frame  14  and is secured on a pair of seat frames (not shown) extending from a rear middle point on the main frame  14 . Both sides of the seat frame below the seat; are covered with seat cowls  16 . 
     FIG. 2 is a longitudinal cross section of a bottom plate  20  constituting the bottom portion of seat  10 . The bottom plate  20  comprises a planar member made of metal or hard plastic and is formed in an integral, stepped shape with bottom plates  20   a  and  20   b . Bottom plate  20   a  is connected to bottom plate  20   b  through a step portion  20   c . Bottom plates  20   a  and  20   b  correspond to front seat portion; and rear seating portion  10   b , respectively. An engagement portion  20   d  is integrally formed on the underside of the front portion  20   a  of the bottom plate  20  for engagement with a seat securing portion (not shown) of a vehicle body. 
     FIG. 3 is a lateral cross section taken along line A—A of FIG. 2 of the seat  10 . A cushion stuffing  22  is placed on the bottom plate  20  and is covered with a seat skin  24 , with the periphery of the seat skin  24  secured to the periphery of the bottom plate  20 . The cushion stuffing  22  is constructed of urethane foam. The seat skin  24  is constructed of a surface skin made of polyvinyl chloride synthetic leather, and a backing sheet made of wooly nylon. 
     FIG. 4 is a plan view of the seat shown in FIG. 3 showing the greater firmness portion  30  of the seat  10 . Greater firmness portion  30  has a greater firmness than other surrounding portions of seat  10 . The design of the greater firmness portion  30  of the seat  10  corresponds to the areas where seat pressure produced by a rider is greatest, shown generally as  31  in the seating pressure distribution diagram in FIG.  6 . The arrow shows the forward direction of the vehicle and rider when the rider sits on the seat  10 . 
     The greater firmness portion  30  is located in the areas of greatest seat pressure  31  and repeated use. The inherent design of a straddle-type seat makes the seat conducive to permanent deformation in a repeatedly-used area. The greater firmness portion  30  is located in this area. By making the seat  10  more rigid in the areas of greatest seat pressure  31  and repeated use, improved riding comfort is provided and permanent deformation problems are prevented. 
     FIG. 5 is a plan view of an alternative design of the greater firmness portion  30 . In FIG. 5, the greater firmness portion  30  is not continuous, allowing for less firmness and greater comfort in a rider&#39;s genital region. 
     As shown in FIGS. 4 and 5, the greater firmness portion  10  is more longitudinally elongated than the seating pressure distribution diagram in FIG. 6 in order to account for longitudinal shifts in riding position. Recesses  30 A and  30 B allow for less firmness and greater comfort in a rider&#39;s thighs and coccyx, respectively. 
     Numerous embodiments exist for creating the greater firmness portion  30  in seat  10 . The greater firmness portion  30  may be created by varying the seat skin condition, cushion stuffing condition, or changing the interaction between the seat skin and cushion stuffing. 
     In FIGS. 7 and 8, the greater firmness portion is created by varying the seat skin condition. FIG. 7 is a partially enlarged cross section of the greater firmness portion of the embodiment shown in FIG.  3 . In FIG. 7, a thicker seat skin  24   a  is provided in the greater firmness portion  30 . Thicker seat skin  24   a  has a greater thickness than the seat skin  24  in the surrounding portions of seat  30 . The thicker seat skin  24  makes the greater firmness portion  30  firmer and less elastic than surrounding portions of seat  30 , providing greater riding comfort and preventing permanent seat deformation problems. 
     In FIG. 8, a different less elastic material  24   b  is provided in the greater firmness portion  30 . The less elastic material  24   b  has a lower elasticity than the seat skin  34  in the surrounding portions of seat  10 . The less elastic material  24   b  makes the greater firmness portion  30  firmer and less elastic than surrounding portions of seat  10 . In an alternative embodiment, a different less elastic and thicker material  24   b  is provided in the greater firmness portion  30  to produce the same advantages mentioned above. 
     Alternatively, as also shown in FIG. 8, the greater firmness of portion  30  is created by varying the cushion stuffing condition. The great firmness portion  30  is created by increasing the density of the cushion stuffing  12  or using a less elastic cushion stuffing  22  in the greater firmness portion  30 . 
     In FIGS. 9-11, the greater firmness portion  30  is created by changing the interaction between the seat skin  24  and the cushion stuffing  22 . An impact absorbing member  32  in the shape of the greater firmness portion  10  is disposed between the seat skin  24  and cushion stuffing  22 . Along with increasing firmness in the greater firmness region  30 , the impact absorbing member  32  attenuates vibrations transmitted to the vehicle during operation. The impact absorbing member  32  is constructed of rubber or urethane. By bonding the impact absorbing member  32  to the underside of the seat skin  24  prior to the assembly of seat  10 , manufacturing time of the seat decreases and productivity improves. 
     In FIG. 10, the greater firmness portion  30  is created by bonding the underside of the seat skin  24  directly to the cushion stuffing  22  with an organic solvent in the greater firmness portion  30 . 
     In FIG. 11, the greater firmness portion is created by bonding the underside of the seat skin  24  to the cushion stuffing  22  with a double-sided adhesive sheet  34  in the shape of the greater firmness portion  30 . Bonding the seat skin  24  to the cushion stuffing  22  with the double-sided adhesive sheet  15  instead of an organic solvent improves production efficiency because less time is spent applying the bond and no drying time is required. Bonding with a double-sided adhesive sheet  34  instead of an organic solvent also improves the workplace environment. 
     The variable firmness motorcycle seat is not limited to the specific embodiments described above and may be created by any combination of the above embodiments.