Patent Publication Number: US-9414680-B2

Title: Flexible tilt adjustment device for a chair back

Description:
BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The invention relates to chairs, particularly to back tilt adjustment of chairs. 
     2. Related Art 
     Some office chairs are provided with a back tilt adjustment function. Such a function is typically accomplished by a spring between a cushion and a back. However, this spring tends to elastic fatigue. 
     Some chairs adopt a flexible tilt adjustment structure as shown in  FIG. 1 . The structure is fixed to a seat  61  through an adjustment rod  60 . An end of the adjustment rod  60  connects a driving block  62 . The seat  61  is provided with a transmission rod  63 . The transmission rod  63  is pivotally connected to the driving block  62 . A spring  64  is passed by the transmission rod  63 . The seat  61  is provided with a sway element  66  connected to a back. The sway element  66  is pushed by the spring  64 . Thus the back can be adjusted by moving the transmission rod  63  flexibly pushed by the spring  64 . 
     In above structure, rotating the adjustment rod  60  to move the transmission rod  63  by hand needs a larger force. This causes inconvenience in operation. The adjustment rod  60  and transmission rod  63  need a link set  65  to change the direction of force. When the link set  65  has jammed, the whole adjustment structure cannot work. Furthermore, the single-sided transmission from the link set  65  to the transmission rod  63  is easy to be unbalanced. This will cause damage of the transmission rod  63 . 
     SUMMARY OF THE INVENTION 
     An object of the invention is to provide a flexible back tilt adjustment device, which can adjust back tilt without effort. 
     To accomplish the above object, the back tilt adjustment device of the invention includes a seat connected to a back by a first rod and an elasticity set. The elasticity has a base connected to the first rod. A pressing rod is connected to the base. A first spring is passed through by the pressing rod and stopped by the base. A pushing block is connected to the pressing rod and the first spring. A rotating rod passes through the seat. Two pressing blocks with a threaded hole are passed by the rotating rod and separately screwed with the rotating rod. Two second springs are passed through by the rotating rod and nipped between the pressing blocks and the edge plates. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view of a conventional back tilt adjustment structure; 
         FIG. 2  is a perspective view of the invention; 
         FIG. 3  is an exploded view of the invention; 
         FIG. 4  is a top plan view of the invention showing the unforced first spring; 
         FIG. 5  is a schematic view of the invention in operation; 
         FIG. 6  is a top plan view of the invention showing the forced first spring; and 
         FIG. 7  is a schematic view of the invention assembled in a chair. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Please refer to  FIGS. 2-4 . The flexible adjustment device of the invention includes a hollow seat  1 . Two sides of the seat  1  are formed with two parallel and symmetric edge plates  11 ,  12 . The two edge plates  11 ,  12  are separately provided with two long holes  111 ,  121 . In this embodiment, these long holes  111 ,  121  are arc-shaped. The two edge plates  11 ,  12  are separately provided with two through holes  112 ,  122  and two fixing holes  113 ,  123 . A fixing rod  13  passes through the fixing holes  113 ,  123 . One end of the fixing rod  13  is provided with a plug  131  for allowing to remove the fixing rod  13 . 
     The long holes  111 ,  121  of the seat  1  is passed through by a first rod  2  connected to a chair back. A length of the long holes  111 ,  121  is greater than a diameter of the first rod  2  to make the first rod  2  movable therein. A second rod  3  passes through the seat  1  near the first rod  2 . In this embodiment, the second rod  3  is placed above the first rod  2 . The second rod  3  is used for connecting a chair cushion. 
     The first rod  2  connects an elasticity set  4 . The elasticity set  4  includes a base  41  with a trough  411  abutting against the first rod  2  and a connecting hole  412  receiving an end of a pressing rod  42 . The pressing rod  42  is a telescopic tube. The elasticity set  4  further includes a first spring  43 . The first spring  43  is axially passed through by the pressing rod  42 . An end of the first spring  43  is stopped by the base  41 . The other end of the first spring  43  connects a pushing block  44 . The pushing block  44  is formed with a connecting tube  441  for connecting the other end of the pressing rod  42 . The other end of the first spring  43  presses the pushing block  44 . The pushing block  44  is formed with a recess  442  and two arc-shaped shoulders  443  beside the recess  442 . 
     The elasticity set  4  further includes a rotating rod  45  passing through the through holes  112 ,  122 . The rotating rod  45  is formed with two thread sections  451  for separately fastening two pressing blocks  46 . Each pressing block  46  has a threaded hole  461  for screwing with the thread section  451 . The pressing blocks  46  will linearly move along the rotating rod  45  when the rotating rod  45  is rotated. When the pressing blocks  46  near the center of the rotating rod  45 , their protrusions  460  just abut against the shoulders  443  of the pushing block  44 . The protrusions  460  are arc-shaped for corresponding to the shoulders  433 . Each pressing block  46  is formed with a sliding trough  462  engaging with the fixing rod  13  for supporting the pressing blocks  46  to slide. 
     The rotating rod  45  passes through two second springs  47 . Each second spring  47  is nipped between one of the pressing blocks  46  and one of the edge plates  11 ,  12  so that the pressing blocks  46  can be pressed by the second springs  47 . Finally, the rotating rod  45  further connects a control module  5 . The control module  5  includes a chassis  511  with a first link  512  connecting the rotating rod  45 . The first link  512  axially connects a first gear  513 . The chassis  511  is further disposed with a second link  514 . The second link  514  axially connects a second gear  515 . The second gear  515  is less than the first gear  513  in diameter. The second gear  515  engages with the first gear  513 . The chassis  511  is fastened to the edge plate  12  by screws  516 . The chassis  511  is assembled with a cover  517  to cloak the first and second gears  513 ,  515 . The second link  514  connects an adjustment rod  52 . The elasticity set  4  can be controlled by rotating the adjustment rod  52 . 
     Please refer to  FIGS. 5 and 6 . To adjust tilt of a chair back, a user can rotate the adjustment rod  52  to drive the control module  5 . The adjustment rod  52  drives the second gear  515 , the first gear  513  and the rotating rod  45 . Because the second gear  515  is less than the first gear  513  in diameter, a user can obtain an effort-saving effect. When the rotating rod  45  begins rotating, the pressing blocks  46  move toward and press the pushing block  44  and then the pressing rod  42  and the first spring  43  are compressed. Thus the compressed first spring  43  will generate stronger elasticity. Meanwhile, the second springs  47  are also compressed by the moving pressing blocks  46  so that the elasticity of the second springs  47  can help a user to save his/her effort. Also, the arc-shaped touch between the protrusions  460  and the shoulders  443  can promote smoothness and reduce friction in operation. 
     On the contrary, when the adjustment rod  52  is reversed to move the pressing blocks  46  away from the pushing block  44 , the first spring  43  will be loosen. As shown in  FIG. 7 , when a user presses a back A 1  of a chair A, the first rod  2  slides in the long holes  111 ,  112  to tilt the back A 1  under control to the first spring  43 .