Abstract:
A seat mechanism for an item of seating furniture, in particular a chair, has a movable seat carrier and a backrest carrier, which are mounted on a main carrier. The backrest carrier can be pivoted about a horizontal pivot axis counter to the action of a force accumulator, and the seat carrier and the backrest carrier are coupled to each other. A lifting mechanism is provided. The lifting mechanism converts pivoting of the backrest carrier into a lifting movement of the seat carrier. A seat mechanism is provided with a weight-dependent resetting force for the backrest. The seat mechanism is distinguished by a simple construction in which the weight can be utilized efficiently. To increase the comfort, the seat is lowerable in the rear region and the resetting force is adjustable by means of a second force accumulator.

Description:
BACKGROUND 
       [0001]    This disclosure relates to a seat mechanism, in particular for a chair. 
         [0002]    A seat mechanism of this type is disclosed, for example, in DE 198 23 632 C1. In said known chair, the force accumulator is designed in the form of a tension spring which is prestressed upon loading of the seat, and therefore, the prestressing is dependent on the weight of the seated person. Since the backrest carrier and therefore the backrest are inclined counter to the action of the force accumulator, the resetting force for the backrest is therefore likewise dependent on the weight. 
         [0003]    On the other hand, the weight is not utilized effectively in the known device since, in the device, the force accumulator is loaded via the front region of the seat, i.e. the thigh region of the seated person. 
         [0004]    By contrast, a seat mechanism herein employs a weight-dependent resetting force for the backrest, which seat mechanism is distinguished by simple construction and with which the weight can be utilized efficiently. 
       SUMMARY 
       [0005]    Briefly stated, a deviation is made from the known principle of prestressing the force accumulator by means of the weight of the seated person, and it is accordingly proposed to convert an inclination movement of the backrest and therefore of the backrest carrier into a lifting movement for the seat. Therefore, upon inclination of the backrest, the entire seat with the person seated thereon is raised, and therefore all of the weight can be utilized to apply the resetting force for the backrest. 
         [0006]    In this case, the conversion can take place, for example, via a lever mechanism or via a slotted guide mechanism of the seat or of the seat carrier. 
         [0007]    A space-saving construction is produced in particular by using helical springs as the force accumulator. 
         [0008]    Dynamic seating can be assisted if the seat is of flexible design and has a web in the central region. 
         [0009]    The rear region of the seat is preferably designed such that it can be lowered. In order to permit the lowering in the rear region of the seat, a flexible seat cushion carrier can have, in the side region, slots which run from the edges toward the center, wherein the slots are preferably arranged in the center to rear region of the seat cushion carrier, and the slots preferably become shorter in length with increasing distance from the rear edge of the seat cushion carrier. 
         [0010]    The flexibility of the seat cushion carrier can be increased by, for example, perforations being provided in the region of the ischial tuberosities, wherein the perforations are formed by slots which run parallel to the rear edge of the seat cushion carrier, and/or slots which run parallel to the side edges. 
         [0011]    In particular in the case of heavy/light people, the resetting force, which is purely weight-dependent, may be perceived to be too great/small. The use of a second force accumulator is therefore proposed and this, when the need arises, assists/obstructs the lifting movement such that the resetting force is reduced/increased. 
         [0012]    For this purpose, the second force accumulator is preferably adjustable. 
         [0013]    In a preferred embodiment, the force accumulator is mounted pivotably and can be prestressed when the backrest is pivoted or moved. 
         [0014]    In particular when working at computer screens, it is considered comfortable if the seat of the item of seating furniture can be lowered forward. The inventors have discovered that, when leaning back in the inclined position of the seat, an unpleasant sensation of “sliding” out of the seat may arise. It is therefore proposed to provide a resetting device which inevitably cancels the lowering upon a lifting movement of the seat carrier, wherein the resetting device preferably has a lever mechanism. 
         [0015]    Depending on the specific configuration, the force accumulators used may be, for example, tension springs, compression springs, gas-filled compression elements, torsion springs, leg springs, etc. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    An exemplary embodiment is explained with reference to the attached drawings, in which 
           [0017]      FIG. 1  shows an exploded illustration of the basic elements of a seat mechanism; 
           [0018]      FIG. 2  shows a perspective top view of the assembled seat mechanism; 
           [0019]      FIGS. 3-6  show various side and side section illustrations; 
           [0020]      FIG. 7  shows a central section of the office swivel chair; 
           [0021]      FIG. 8  shows a side illustration of the office swivel chair without a seat cushion; 
           [0022]      FIG. 9  shows a perspective illustration of the frame construction of the office swivel chair; and 
           [0023]      FIG. 10  shows a top view of the frame construction. 
       
    
    
     DETAILED DESCRIPTION 
       [0024]    In the above text, the definitions of “forward”, “rearward”, “at the top”, etc., arise from the normal position of the chair. 
         [0025]      FIG. 4  shows a side illustration of a seat mechanism with a seat carrier  1  on which a seat (not illustrated) is mounted, with a panel  10 , wherein a backrest carrier  3  is mounted pivotably on the seat carrier  1  via a coupling spindle  7 . The backrest carrier  3  carries a backrest (not illustrated), wherein, in the illustration of  FIG. 4 , the seat mechanism is in the normal position, i.e. the backrest is upright. 
         [0026]      FIG. 1  shows a perspective exploded illustration and, in addition to the backrest carrier  3  and the seat carrier  1 , shows a main carrier  9  and a front link and a central link  17 . 
         [0027]    The main carrier  9  carries the entire seat mechanism and is connected to a chair pillar in a manner known per se via a bore  11 . 
         [0028]    In the assembled state, the seat carrier  1  is connected to the main carrier  9  via the front link  15 , specifically via bearing bores  19 , which are aligned with bearing bores  21  on the main carrier, and via bearing bores  23  which are aligned with corresponding bearings (not illustrated) on the seat carrier. Furthermore, in the assembled state, the backrest carrier  3  is fastened pivotably to the main carrier  9 , specifically via bearing bores  25  which are aligned with bearing bores  27  on the main carrier, wherein said bearing bores define a main axis  13  (compare  FIG. 4 ). 
         [0029]    Furthermore, the backrest carrier  3  is fastened to the seat carrier via bearing eyes  26  on corresponding bearings such that the backrest carrier is pivotable with respect to the seat carrier. The bearing eyes  26  are offset with respect to the bearing bores  25  such that the backrest carrier  3  itself forms a rear link. 
         [0030]      FIG. 2  shows the seat carrier  1  and the backrest carrier  3  in the assembled state. Helical springs  33  are additionally illustrated. The helical springs are mounted in the backrest carrier  3  and the legs of the helical springs are supported in an abutment  35  of the backrest carrier  3 , wherein the legs at the other end of the helical springs are supported on the main carrier (not illustrated). 
         [0031]    Spring assemblies  37  are accommodated pivotably in the seat carrier  1 , wherein the spring assemblies act at one end on a displaceable spindle  39  and at the other end on an abutment  43  of the main carrier  9  ( FIG. 6 ). The displaceable spindle  39  is mounted at both ends on curved tracks  47  and can be displaced on the curved track via an actuating lever  41 . The curved track  47  runs at different distances with respect to the abutment  43 . Therefore, the spring assemblies  37  are loaded differently in different positions, for example in three positions, i.e. without loading in a first position, with average loading in a second position and with high loading in a third position. The spring assemblies here act as tension springs, and, under loading, tension forces act between the seat carrier and the main carrier. It should also be mentioned in this respect that the spring assemblies  37  are designed in terms of internal construction in such a manner that spring elements in the form of compression springs are formed, since a higher load-bearing capacity and longer service life can be achieved with this design. 
         [0032]    As already explained,  FIG. 4  shows the seat mechanism in the normal state, i.e. with the backrest upright. By contrast,  FIG. 6  shows the position of the seat mechanism with the backrest inclined at maximum to the rear, wherein the seat carrier  1  is raised parallel in relation to  FIG. 4 , specifically in the rear region via the rear link, as is evident from the position of the axis  13  and spindle  7 , and in the front region via the front link  15 , as is evident from the position of the latter. In this case, the helical springs  35  are loaded and subject the backrest carrier  3  to a resetting force which is additionally reinforced via the front and the rear links by the weight acting on the seat, wherein, as mentioned, the resetting force can be changed via the spring assemblies  37 . 
         [0033]    As is apparent in particular from  FIG. 5 , which shows the same position of the seat mechanism as  FIG. 6 , the front link  15  is mounted in elongated holes  49  on the seat carrier. In the normal position according to  FIG. 4  and in positions in which the seat carrier  1  is raised, the position of the link  15  in the elongated holes  49  is locked in the lower position of the elongated holes. In the normal position of  FIG. 4 , the locking can be canceled, and the seat carrier can be inclined forward, as illustrated in  FIG. 3 . The seating position is suitable particularly for people working at computer screens, etc. Since the position of the seat carrier is unfavorable when the backrest is inclined rearwards, the seat carrier is inevitably displaced into the horizontal position when the backrest carrier is pivoted. For this purpose, levers  51  are provided. The levers act at one end on the main carrier  9  and at the other end on the seat carrier  1  and cause the front edge of the seat carrier to be inevitably raised. In this case, the front link can be locked in the lower region of the elongated holes  49 . 
         [0034]    As is apparent in particular from  FIG. 1 , the central link  17  has one lever  51  in each case. The central link  17  is mounted in fastening tabs  31  which are fastened to the seat carrier. At the end facing away from the fastening tabs  31 , the levers  51  each bear bearing pins  29 , which are mounted in the main carrier. 
         [0035]    The seat mechanism illustrated here is suitable in particular for office swivel chairs but may also be used in other items of seating furniture, such as 4-legged chairs, armchairs, sofas and the like. 
         [0036]    According to  FIG. 7 , an office chair comprises the seat mechanism described, a seat  61  with a seat cushion carrier  65  and a seat cushion  63 , and a backrest frame  67 . The seat  61  is mounted on the seat carrier  1  such that it can be displaced forward or rearward, wherein the backrest frame  67  is connected via the backrest carrier to the main carrier  9 , which is fastened to a chair pillar  73 . 
         [0037]    A lower backrest frame  77  is mounted pivotably on the backrest frame  67 . the lower backrest frame is connected at the lower end thereof to the rear edge of the seat  61 . Furthermore, a lumbar support  75  is provided. The lumbar support is mounted on a lumbar support carrier comprising a transverse carrier  81  and a longitudinal carrier  83 . 
         [0038]    The arrangement of the last-mentioned elements is apparent in particular from the perspective illustration of  FIG. 9 , which shows the frame construction of the chair without a seat cushion. It is apparent from the illustration that the transverse carrier  81  extends between two struts of the backrest frame  67 . The longitudinal carrier  83 , which extends as far as a traversely running strut of the lower backrest frame  77 , is fastened in the center of the transverse carrier  81 . Furthermore, the longitudinal carrier  89  has a telescopic connection  85 . 
         [0039]    The backrest frame  77 , for its part, is connected to the backrest frame  67  via an articulated connection  89  comprising lamellas. 
         [0040]      FIG. 9  furthermore shows that the seat cushion carrier  65  is designed as a plate which is manufactured from flexible material and has a web  91  extending from the front rearward in the center. The web  91  rests on the seat carrier  1  ( FIG. 7 ) but may also be connected to the latter and to the seat mechanism  79 . The resting action and the flexibility promote dynamic seating when the right/left loading changes. 
         [0041]    In the region of the ischial tuberosities, the seat cushion carrier is provided with slots  95  which extend parallel to the side edges of the seat cushion carrier, and with slots  97  which extend parallel to the rear edge of the seat cushion carrier, in order to further increase the flexibility. 
         [0042]    In the region of the side edges, the seat cushion carrier  65  is provided with slots  99  which extend from the side edge toward the web  91 . The length of the slots  99  increases the closer the slots are arranged to the rear edge of the seat cushion carrier  65 . 
         [0043]    As illustrated by the double arrow in  FIG. 8 , which shows the chair without a seat cushion, the seat cushion carrier  65  is mounted displaceably in the depth direction of the chair. In this case, the lower backrest frame  77  follows a movement of the seat cushion carrier  65  such that a horizontal gap cannot be produced.  FIG. 8  shows the seat cushion carrier  5  in a central position. 
         [0044]    In this regard, it should also be noted that, in the use state of the chair, the backrest carrier is provided with a fabric covering, upholstery or the like. 
         [0045]    The seat cushion carrier  65  is mounted displaceably on the seat mechanism on lateral guides  105  ( FIG. 1 ), wherein, in the normal position, i.e. with the backrest not inclined, the web  91  rests on the seat mechanism  79 . 
         [0046]    It is apparent in particular from  FIG. 9  that the seat cushion carrier  65  is not designed as a flat plate but rather as a curved plate, wherein in particular the side regions of the seat cushion carrier  65  are curved upward in the normal position. If the seat cushion carrier is raised by the seat mechanism  79 , the web  91  is raised from the surface of the seat mechanism  79 , and the regions of curvature are pressed downward, and therefore compensated for, in dependence on the bodyweight of the seated person. This is assisted by the arrangement of the slots  99  and the shaping thereof such that the compensation takes place in particular in the rear region of the seat, and therefore the seat surface is lowered in particular in the rear region, as a result of which the seating comfort is increased when the seated person leans back.