Patent Publication Number: US-6669294-B2

Title: Chair

Description:
CROSS REFERENCE TO RELATED APPLICATIONS: 
     This is a U.S. National Phase Application under 35 U.S.C. §371 and applicant herewith claims the benefit of priority of PCT/JP01/08733 filed Oct. 3, 2001, which was published Under PCT Article 21(2) in Japanese, which claims priority to Japanese Application No. P2000-315767, filed Oct. 16, 2000, the entire contents of which are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates to chair structures and, more specifically, to a chair made more comfortable to sit. 
     BACKGROUND ART 
     Among chairs presently used in offices and the like, there exist chairs of the type which is capable of bending an upper portion of its back rearwardly. Such a chair, which allows the backbone of a person sitting thereon to bend backwardly thereby refreshing the sitting person, is generally of a construction having a shaft for rotation mounted intermediate between upper part and lower part of the backrest portion to allow a back portion above the shaft for rotation to incline rearwardly about the shaft for rotation. 
     With such a conventional construction having a shaft for rotation intermediate between the upper and lower parts of the backrest portion, however, the radius of gyration with which the upper back portion is inclined rearwardly is small and, hence, the upper end side of the upper back portion largely leans rearwardly. Consequently, when the upper back portion thus constructed is inclined rearwardly, it cannot support the shoulders or parts therearound of the sitting person and, hence, this condition is substantially the same as the absence of the upper back portion, making the sitting person unstable. Further, the provision of the shaft for rotation intermediate between the upper and lower parts of the backrest portion raises a problem that the load of the sitting person is concentrated on the shaft for rotation because the backrest portion steeply bends about the shaft, thus making the sitting person feel uncomfortable or giving him or her a sense of incongruity or the like. 
     With a view to solving the aforementioned problems, the present invention intends to provide a chair which is capable of inclining its back portion rearwardly while offering improved comfortableness to sit. 
     DISCLOSURE OF INVENTION 
     With a view to solving the foregoing problems, the present invention provides a chair wherein a back portion located rearwardly of a seat portion is divided into an upper back portion and a lower back portion, at least the upper back portion being capable of inclining rearwardly, characterized in that a fulcrum for rearwardly inclining the upper back portion is located below a seating surface, the upper back portion being allowed to incline rearwardly about the fulcrum. 
     Since the fulcrum for rearwardly inclining the upper back portion is located below the seat portion, the upper back portion can be moved rearwardly while rearwardly inclining gently, whereby the shoulders and parts therearound of a person sitting on the chair can be contacted and supported by the upper end side of the upper back portion. 
     The angle of rearward inclination of the upper back portion may vary depending upon the build, posture or preference of the sitting person. In such a case, it is sufficient to provide a plurality of fulcrums for rearwardly inclining the upper back portion below the seating surface for the sitting person to select any one of the fulcrums so that switching of rearwardly inclining modes of the upper back portion can be made. With the chair thus constructed, the sitting person is capable of selecting a desired one of modes including, for example, a mode of rearwardly inclining the upper back portion largely and a mode of rearwardly inclining it with a smaller radius of gyration. Thus, the chair can be more suited to the preference and the like of a person sitting thereon. 
     Further, the chair may be constructed such that the seat portion or the like is moved in cooperation with the switching of rearwardly inclining modes of the upper back portion. With this construction, it is possible to select a desired mode including movement of the seat portion. 
     If the chair having the back portion divided into the upper back portion and the lower back portion is constructed to allow the upper back portion to incline rearwardly with the lower back portion being maintained at a predetermined angle, the chair allows the sitting person to bend his or her backbone backwardly thereby refreshing the sitting person. 
     In the case where the upper back portion is inclined rearwardly relative to the lower back portion, the distance between the upper back portion and the lower back portion changes. To absorb this change in the distance, it is preferred that an upholstery member be attached to a body contacting part of the back portion. The provision of such an upholstery member makes it possible not only to absorb changes in the distance between the upper back portion and the lower back portion but also to make the surface of the whole back portion smooth. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a perspective view showing a principal part of a chair representing one embodiment of the present invention. 
     FIG. 2 is a side elevational view of the chair representing the same embodiment in an upright position. 
     FIG. 3 is a side elevational view representing the same embodiment in a first position. 
     FIG. 4 is a side elevational view representing the same embodiment in a second position. 
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     Hereinafter, one embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a perspective view showing a principal part of a chair  1  representing one embodiment of the present invention. The chair  1  includes a support base  3  mounted on a base leg  2 , links  6  and  7  attached to the support base  3 , a seat frame  4  forming a seat portion and attached to the links  6  and  7 , and a backrest frame  5  comprising a backrest upper frame  55  forming an upper back portion and a backrest lower frame  50  forming a lower back portion. The chair  1  further comprises an upholstery member  9  of cloth or the like mounted to extend between the backrest upper frame  55  and the backrest lower frame  50 , and a seat cushion  41  having a seating surface  41   a  on the obverse side thereof and mounted on an upper portion of the seat frame  4 . 
     The support base  3  is constructed of an aluminum member shaped into an inverted triangle and has a lower side attached to the base leg  2  and a front end portion fitted with the links  6  through shafts  61 . The links  6  are configured to be rotatably movable by means of shaft  40  and shafts  61  located on opposite sides of a front portion of the seat frame  4 . Between the shaft  40  extending between the upper ends of the links  6  and a central portion of the support base  3  is provided a gas spring  90  which can be switched between a fixed state and a free state to vary the inclination of the backrest frame  5  by means of a lever not shown. A torsion bar  72  is provided in a substantially central portion of the support base  3  and each link  7  is fixed at its one end to a shaft  71  extending in the direction of an extension of the torsion bar  72 . Each link  7  is constructed of a metal member extending obliquely rearwardly from the shaft  71  and is rotatably attached at its other end to a part flanking a rear portion of the seat frame  4 . The spring force of the torsion bar  72  urges shafts  8  located below the seating surface  41 a to rotate forwardly of the chair  1  (toward the side B). 
     On the underside of an upper end portion of the links  7  is provided a gas spring  91  connected to the backrest upper frame  55 , the gas spring  91  constantly pressing the backrest upper frame  55  forwardly (toward the side B) by means of its gas pressure. In the vicinity of the gas spring  91  is provided a mechanism for pinching a shaft of the gas spring  91  to fix the same and, hence, the gas spring  91  can be switched between a free state and a fixed state when a lever not shown is operated. 
     Inside the backrest upper frame  55  is rotatably mounted the backrest lower frame  50  through shafts  70  attached to the links  7 . The backrest lower frame  50  comprises ischium-corresponding frames  51  each extending substantially in the direction of an extension of the corresponding link  7 , an interconnecting member  53  located on an upper portion of the ischium-corresponding frames  51 , and hipbone-corresponding frames  52  located on opposite ends of the interconnecting member  53  to extend substantially perpendicularly upward therefrom. The hipbone-corresponding frames  51  (sic) each have an end portion formed with an arcuately curved portion  52   a  curved toward the rear side of the chair  1  (toward the side A). A gas spring  92  is provided between the interconnecting member  53  and a rear frame of the seat frame  4  located below the interconnecting member  53  for fixing at a predetermined angle. In this embodiment, the gas spring  92  is constantly kept in a fixed state. 
     On the other hand, the backrest upper frame  55  attached to the shafts  8  becomes rotatable about the shafts  71  together with the links  7  as an integral part when the gas spring  91  located on the underside of the backrest upper frame  55  is switched to the fixed state. Alternatively, when the gas spring  91  is switched to the free state, the backrest upper frame  55  becomes rotatable about the shafts  8 . Like the backrest lower frame  50 , the backrest upper frame  55  is bent behind the seat frame  4  and extends behind the backrest lower frame  50  from the bent portion to terminate in a curved portion  55   a  at a level adjacent the shoulders of a person sitting on the chair  1 . 
     Over the curved portion  55   a  of the backrest upper frame  55  and the curved portion  52   a  of the backrest upper frame  55  is provided a cantilever elastic piece  93  (see FIG. 2) which is bendable over these curved portions, and further the upholstery member  9  is mounted over the elastic piece  93  to cover the backrest upper frame  55  and the backrest lower frame  50 . 
     Next, description is directed to switching between backrest states of the chair  1  thus constructed. Described first is the case where a first state (shown in FIG. 3) is to be assumed which allows the backrest lower frame  50  and the backrest upper frame  55 , as an integral part, to incline rearwardly in the direction A with the seat frame  4  rearwardly inclining interlockingly therewith. 
     In switching a state (shown in FIG. 2) where the backrest lower frame  50  and the seat frame  4  are in the upright position of the chair  1  (namely, a state where a person does not sit on the chair  1  while the gas spring  90  is made free) to the first state (shown in FIG. 3) allowing the whole backrest frame  5  to incline rearwardly, the gas spring  91  is turned into a fixed state, while the gas spring  90  is made free. By so doing, the backrest upper frame  55  together with the links  7 , as an integral part, becomes capable of largely rotating about the shafts  71 . Interlockingly therewith, a four-member link mechanism comprising the support base  3 , links  6 , seat frame  4  and links  7  causes the seat frame  4  to incline rearwardly since the gas spring  90  assumes a free state. The backrest lower frame  50  also inclines rearwardly as the links  7  rotate and, hence, the seat frame  4  and the backrest frame  5  move synchronously as a whole. 
     Alternatively, in switching the state (shown in FIG. 2) where the backrest lower frame  50  and the seat frame  4  are in the upright position of the chair  1  to the second state (shown in FIG. 4) allowing the backrest upper frame  55  to rearwardly incline with a smaller radius of gyration, the gas spring  91  is turned into the free state, while the gas spring  90  located below the seat frame  4  is turned into the fixed state. By so doing, the seat frame  4  and the backrest lower frame  50  are fixed, while only the backrest upper frame  55  becomes capable of rotating about the shafts  8  toward the side A. In this case, the distance between the upper end position of the backrest upper frame  55  and the upper end position of the backrest lower frame  50  changes. However, the upholstery member  9  and elastic piece  93  bend to absorb this change in the distance thereby maintaining the whole backrest portion smooth. 
     According to this embodiment of the present invention, the chair  1  wherein the backrest frame  5  is divided into the backrest upper frame  55  and the backrest lower frame  50 , at least the backrest upper frame  55  being capable of inclining rearwardly, is of the construction that: the shafts  71  and shafts  8  for rearwardly inclining the backrest upper frame  55  with different radii of gyration are located below the seating surface  41   a ; and switching between the shafts  71  and the shafts  8  allows selection of any desired one of plural rearwardly inclining modes (shown in FIGS.  3  and  4 ). By this construction, the upper back portion is allowed to move rearwardly while rearwardly inclining gently. Thus, the shoulders and parts therearound of a person sitting on the chair  1  can be stably supported by the upper end side of the upper back portion. Further, the construction allows selection of any desired one of plural rearwardly inclining modes and, hence, the chair can be suited to the preference of a person sitting thereon. Since this embodiment is constructed to allow the backrest upper frame  55  to incline rearwardly with the backrest lower frame  50  being maintained at a predetermined angle, a person sitting on the chair is capable of bending his or her backbone backwardly whereby the person can be refreshed. 
     Further, since the chair is constructed such that in rearwardly inclining the whole backrest frame  5 , the seat frame  4  also rearwardly inclines interlockingly therewith, the hip part of the sitting person can be prevented from slipping when the backrest frame  5  is wholly inclined rearwardly, whereby the chair is made more comfortable to sit. 
     Furthermore, since the chair  1  has the elastic piece  93  allowing its bending which is mounted to extend between the backrest upper frame  55  and the backrest lower frame  50 , and the upholstery member  9  disposed over the elastic piece  93 , the bending of the elastic piece  93  and upholstery member  9  can absorb a change in the relative distance between the backrest upper frame  55  and the backrest lower frame  50  if it occurs. 
     It should be noted that though the backrest lower frame  50  is located inside the backrest upper frame  55 , this arrangement may be reversed. Further, though the axis of rotation of the backrest upper frame  55  is changed through switching of the gas spring  91  between the fixed state and the free state, the present invention is not limited to this arrangement and may employ any arrangement which can switch the coupling between the backrest upper frame and the links  7 . 
     Industrial Applicability 
     The present invention is practiced in the embodiment described above and provides the following effects. 
     That is, the chair of the present invention wherein the back portion located rearwardly of the seat portion is divided into the upper back portion and the lower back portion, at least the upper back portion being capable of inclining rearwardly, is of the construction that the fulcrum for rearwardly inclining the upper back portion is located below the seating surface, the upper back portion being allowed to incline rearwardly about the fulcrum. By this construction, the upper back portion is allowed to move rearwardly while rearwardly inclining gently, whereby the shoulders and parts therearound of a person sitting on the chair can be contacted and supported by the upper end side of the upper back portion.