Patent Publication Number: US-RE46717-E

Title: Chair with a pivoting backrest

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims benefit of Italian patent application number TO2013A000650, filed Jul. 31, 2013, which is herein incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a chair with a pivoting backrest capable of tilting backwards under a thrust applied by the user&#39;s back. 
     2. Description of Prior Art 
     In the state of the art, there are various known solutions of chairs in which the backrest is connected to a fixed support structure by a pair of elastic joints, each of which comprises an upper support inserted into a tubular portion of the backrest, a lower support inserted into a tubular element of the fixed support structure and an elastic element, which allows an inclination between the upper support and the lower support. 
     For example, the document EP2183997 of the same applicant describes a chair comprising a base structure including two rear tubular elements, a backrest having two tubular portions and two elastic devices, each of which has an upper support inserted into a tubular portion of the backrest, a lower support inserted into the corresponding tubular element of the base structure and an elastic element deformable by bending to allow pivoting between the upper support and the lower support, wherein each of the elastic devices comprises a plurality of stacked sectors, arranged between the upper support and the lower support. 
     The elastic elements that are deformable by bending have the drawback of a limited elastic force for opposing the backward thrust applied by the user. 
     In principle, with elastic elements in compression formed, for example, by helical compression springs, it would be possible to increase the force provided by the elastic joints that contrast the backward thrust applied by the user on the backrest of the chair. However, with helical compression springs arranged coaxially to the side uprights of the backrest, the lever arm for the compression of the springs is limited. 
     SUMMARY OF THE INVENTION 
     The present invention aims to provide a chair with a pivoting backrest equipped with simple and robust elastic joints, capable of providing a high elastic force that counteracts the backward thrust applied by the user on the backrest of the chair. 
     According to the present invention, this object is achieved by a chair having the characteristics forming the subject of claim  1 . 
     The claims form an integral part of the disclosure provided in relation to the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will now be described in detail with reference to the accompanying drawings, given purely by way of non-limiting example, wherein: 
         FIG. 1  is a side view of a chair according to the present invention in the rest position; 
         FIG. 2  is a side view corresponding to  FIG. 1 , illustrating the backrest in the backwardly-inclined position; 
         FIG. 3  is an axial section of the part indicated by the arrow III in  FIG. 1  in the rest position; 
         FIG. 4  is an axial section analogous to  FIG. 3  in the position of maximum backward-inclination; and 
         FIG. 5  is an exploded perspective view of certain components of the elastic joint indicated by the arrow III in  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     With reference to  FIGS. 1 and 2 , numeral  10  indicates a chair according to the present invention. The chair  10  comprises a fixed support structure  12  including a pair of front legs  14  and a pair of rear legs  16 . The front legs  14  and the rear legs  16  are connected together by means of upper connecting elements  18 . A seat  20  is fixed to the upper connecting elements  18  of the fixed support structure  12 . 
     The fixed support structure  12  comprises two tubular side uprights  22  extending upwards. The two side uprights  22  are fixed with respect to the support structure  12 . For example, the side uprights  22  can be fixed to the upper connecting elements  18 . 
     The seat  10  comprises a backrest  24  pivotally connected to the fixed support structure  12 . The backrest  24  comprises a backrest panel  26  having an arcuate shape, and two side portions  28  located laterally on opposite sides with respect to the backrest panel  26 . The side portions  28  can be formed in a monolithic manner with the backrest panel  26 . The side portions  28  of the backrest  24  are connected to the respective side uprights  22  of the fixed support structure  12  by means of respective elastic joints  30 . 
     With reference to  FIG. 5 , each elastic joint  30  comprises a bushing  32  having a cylindrical wall  34  having an open lower end and an upper end fitted with a front wall  36 . The bushing  32  can be equipped with a projecting appendage  38  that projects upwards from the front wall  36 . 
     The elastic joint  30  comprises a helical spring  40  housed within the cylindrical wall  34  of the bushing  32 . The helical spring  40  has a longitudinal axis A coaxial to the axis of the cylindrical wall  34  of the bushing  32 . The helical spring  40  has an upper end  42  and a lower end  44 . The upper end  42  rests against the front wall  36  of the bushing  32 . The lower end  44  of the helical spring  40  rests on a compression member  46 . In the illustrated example, the compression member  46  comprises a body of plastic material  48  and a metal washer  50 . The body of plastic material  48  has a cylindrical portion  52  that couples, in a sliding manner, with the lower end of the bushing  32 . At the bottom of the cylindrical portion  52 , a radially-projecting shoulder  54  is formed. The body  48  of the compression member  46  has a through hole  56  with a rectangular section. The washer  50  rests against a lower surface of the body  48 . The washer  50  has a through hole  58  with a rectangular section aligned with the hole  56  of the body  48 . Preferably, the washer  50  has a convex deformed portion  60  that couples with a corresponding concave seat  62  formed on the lower surface of the body  48 . The washer  50  has a concave seat  64  on the surface opposite to the convex projection  60 . 
     The elastic joint  30  comprises a rigid connecting rod  66  preferably made of metal. The connecting rod  66  preferably has a rectangular cross section. The connecting rod  66  has a lower end  68  and an upper end  70  equipped with respective holes  72 ,  74 , engaged by respective pins  76 ,  78 . The axes of the pins  76 ,  78 , indicated with B and C, are parallel to each other, and transverse relative to the axis A of the spring  40 . 
     The elastic joint  30  comprises an upper attachment  80  having a shank  82 , which is fixed into a hole formed at the lower end of the respective side portion  28  of the backrest  24 . The upper attachment  80  has a groove  84  into which the upper end  70  of the connecting rod  66  is inserted. The upper attachment  80  has a transverse hole  86 , through which the upper pin  78  is inserted, which connects the upper end  70  of the connecting rod  66  to the upper attachment  80 , in an articulated manner. 
     The elastic joint  30  is preferably provided with a ring of plastic material  88  fitted on the appendage  38  of the bushing  32 . The ring  88  has a lower front surface, which rests on the front surface  36  of the bushing  32 , and an upper surface  90  against which a lower surface  92  of the upper attachment  80  rests. As is illustrated in  FIGS. 3 and 4 , the upper surface  90  of the ring  88  and the lower surface  92  of the upper attachment  80  may have respective projecting and receding profiles in order to establish a shape coupling. 
     As is visible in  FIGS. 3 and 4 , the bushing  32  of each elastic joint  30  is fixed, for example by hammering, to the upper end of the corresponding tubular upright  22  of the fixed support structure  12 . 
     The lower portion of the connecting rod  66  extends through the holes  56  and  58  of the body  48  and of the washer  50  of the compression member  46 . The first pin  76  connects the lower end  68  of the connecting rod  66  to the compression member  46  in an articulated manner. The pin  76  is housed in the concave seat  64  of the washer  50 . The central portion of the connecting rod  66  included between the ends  68 ,  70  extends through the helical spring  40  and through a through hole  94  formed in the upper part of the bushing  32 . 
     The upper end  70  of the connecting rod  66  that projects above the ring  88  is bent forwards. In this way, the articulation axis C, between the upper end  70  of the connecting rod  66  and the upper attachment member  80 , is moved forward by a distance d ( FIG. 3 ) with respect to the longitudinal axis A of the spring  40 . The articulation axis B of the lower end  68  of the connecting rod  66  of the compression member  46  is essentially located on the longitudinal axis A of the spring  40 . 
     The effect of the forward displacement of the axis C with respect to the longitudinal axis A of the spring  40  is that of increasing, all other conditions being equal, the elastic torque applied by the springs  40  to the backrest  24 . When a backward thrust is applied to the backrest  24  by the user&#39;s back, the upper attachment  80  pivots backwards about a fulcrum point, indicated with F in  FIGS. 3 and 4 . The fulcrum point F is defined by the point of mutual rotation between the contact surfaces of the upper attachment  80  and the ring  88 . The rotation of the upper attachment  80  about the fulcrum point F compresses the spring  40  by means of the connecting rod  66 . The return elastic force of the spring  40  has a lever arm of dimension d 1 , with respect to the pivot fulcrum F. The lever arm d 1  is increased thanks to the forward displacement of the articulation axis C. Consequently, at a constant axial force exerted by the spring  40 , thanks to the forward displacement of the articulation axis C, a higher torque on the backrest  24  is achieved, which counteracts the backward thrust applied by the user. 
     In the position of maximum backward inclination of the backrest, illustrated in  FIG. 4 , the radial shoulder  54  of the compression member  46  rest against the lower end of the bushing  32  and forms a stroke end, which prevents further backward inclination of the backrest. 
     To stiffen the fixing area between the side portions  28  of the backrest  24  and the corresponding upper attachments  80 , each elastic joint  30  may be fitted with a stiffening pin  96  ( FIGS. 3 and 4 ) having an upper portion driven into a hole  98  of the side portion  28  of the backrest  24 , and a lower portion driven into a hole  100  of the respective upper attachment  80 . 
     Each elastic joint  30  can also be fitted with an protective elastic element  102  arranged coaxially around the contact area between the upper attachment  80  and the ring  88 , in order to avoid pinching of garments or parts of the body between the contact surfaces of the upper attachment  80  and the ring  88 . 
     Of course, without prejudice to the principle of the invention, the details of construction and the embodiments may vary widely with respect to those described and illustrated without departing from the scope of the invention as defined by the following claims.