Patent Publication Number: US-7216933-B2

Title: Backrest, particularly for an office chair

Description:
BACKGROUND OF THE INVENTION 
     FIELD OF THE INVENTION 
     The invention relates to a backrest having a lordosis support comprising supporting ribs arranged in a manner such that they run parallel to one another, and having an adjusting element, which can be actuated via an adjusting member and is intended for setting the lordosis curvature. It furthermore relates to a chair, in particular an office chair, having a backrest of this type and a seat surface which is movable synchronously thereto. 
     DE 29 47 472 C2 discloses a backrest, in particular for a motor vehicle seat, which has a lordosis support with a number of supporting ribs. The lordosis support is fitted into a backrest frame by means of spring elements and can be set with regard to its lordosis curvature by means of an adjusting member. For this purpose adjusting elements, which can be actuated by the adjusting member, on the rear side of the backrest, which side faces away from a backrest cushion, engage on the lordosis support in the manner of a bowstring. Actuation of the adjusting member causes the adjusting elements to be subjected to a tensile load in such a manner that the lordosis curvature increases as a consequence of the adjusting elements decreasing in length. 
     SUMMARY OF THE INVENTION 
     The invention is based on the object of specifying a backrest having a particularly suitable lordosis support. Furthermore, a chair having a backrest of this type and a particularly suitable synchronizing mechanism is to be specified. 
     With regard to the backrest, the abovementioned object is achieved according to the invention by the features of claim  1 . For this purpose, the supporting ribs are precurved in a flexurally elastic manner in their starting position. The adjusting element is guided on the curvature side of the lordosis support, which side faces a cushion side of the backrest, in such a manner that the lordosis curvature decreases during a tensile loading of the adjusting element. The tensile loading of the adjusting element by means of the adjusting member therefore causes the backrest in the lordosis region to be increasingly straightened out starting from the maximum possible lordosis curvature in the starting position. 
     According to one particularly preferred variant, the supporting ribs are an integral part of a backrest shell which extends over at least a substantial part of the backrest. A number of horizontal longitudinal slots have been made in the lordosis region of this backrest shell, forming the supporting ribs. In this case, the backrest shell expediently consists of a synthetic material, with, as a consequence of it being weakened in the lordosis region by the longitudinal slots, supporting ribs which are integral with the backrest shell, but are flexurally elastic, being formed. The unslotted edge region of the backrest or backrest shell forms lateral lordosis edges, which are likewise flexurally elastic transversely with respect to the backrest height, which extends in the vertical direction, and, in the starting position, are likewise precurved toward the cushion side of the backrest. 
     The adjusting element may be guided in the central region of the lordosis support. However, the adjusting elements are expediently guided on the lordosis edge or on each lateral lordosis edge via guide elements, which are expediently integrally formed on the backrest shell. In the case of a preferred guidance on both sides of two adjusting elements in the transverse direction to the supporting ribs and therefore in the longitudinal direction of the backrest, when an individual adjusting member in the form of a worm gear, which can be actuated by means of a rotary knob and has a driven coil, is used, the adjusting element, which is guided on the lordosis edge facing the adjusting member, is guided directly to the adjusting member. The adjusting element guided on the opposite lordosis edge is then guided to the adjusting member via return guides provided in the lower region of the backrest. 
     The or each adjusting element, which is preferably designed in the form of a draw-in wire, is fastened on the upper side of the lordosis support, which side faces away from the adjusting member, to the backrest, expediently to the backrest shell thereof. 
     With regard to the chair having a backrest of this type, the abovementioned object is achieved according to the invention by the features of claim  7 . For this purpose, the backrest is connected at its lower backrest end, which faces a seat surface which can be moved synchronously therewith, via a draw-in element, which is designed in an articulated manner, to the rear seat end of the seat surface, which end faces the backrest. 
     In an expedient refinement, the draw-in element is integrally formed on the backrest. In this case, the articulated connection of the backrest to the seat surface preferably takes place via a film hinge. 
     When the backrest is inclined to the rear, the draw-in element causes the lower side of the backrest to be drawn onto the seat surface, which is moved synchronously to the rear and downward together with the backrest. In order to enable, in a particularly simple and reliable manner, a relative movement between the backrest or, if appropriate, the backrest shell thereof relative to the backrest carrier carrying it, the backrest or the backrest shell is connected at the upper backrest end, which faces away from the seat surface, via a pendulum and/or rotary joint to the backrest carrier. 
     The advantages achieved by the invention are, in particular, that, firstly, the provision of a lordosis support which, in the starting state is precurved in a flexurally elastic manner on the cushion side and therefore in the cushioning direction of the backrest and, secondly, the guidance of the adjusting elements along the lordosis curvature again on the cushion side of the backrest mean that the adjusting elements can already be completely covered by the backrest cushion. As a result, the rear side of the backrest, which side faces away from the cushion side, is free of adjusting elements or adjusting members, so that the rear side of the backrest does not have to be concealed by additional screens. 
     By means of the provision of a backrest shell, which consists of plastic and the lordosis region of which is weakened in a targeted manner by means of longitudinal slots, with supporting ribs being formed, such that a flexurally elastic deformation of the lordosis region, which deformation can be obtained by means of the adjusting elements, is achieved, particularly simple manufacturing of the backrest for a chair with, at the same time, a reliable and virtually infinitely variably adjustable lordosis curvature, is made possible. 
     The connection of the lower backrest end via a draw-in element designed in an articulated manner has the advantage that the backrest, during the synchronizing movement, in addition to the movement about the pivot point between the seat surface and backrest carrier, at the same time oscillates about the connecting point between the backrest and the upper end of the backrest carrier. This gives rise to a combined movement which, relative to the seat or the seat surface, resembles a rotation about an assumed point that, in a ergonomically advantageous manner, is situated higher than the pivot point between the seat surface and backrest carrier. 
     Exemplary embodiments of the invention will be explained in more detail below with reference to a drawing, in which: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows, in a perspective illustration, a backrest according to the invention having a lordosis support which can be adjusted via an adjusting member 
         FIGS. 2   a  and  2   b  show, in a side view, the backrest according to  FIG. 1  respectively having a precurved and straightened-out lordosis support, 
         FIG. 3  shows the adjusting member in an enlarged exploded illustration, and 
         FIGS. 4   a  and  4   b  show a chair with a seat surface and a backrest according to  FIG. 1 , connected thereto via a draw-in element, in the starting position and in the end position inclined to the rear. 
     
    
    
     Mutually corresponding parts are provided with the same reference numbers in all of the figures. 
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The backrest  1  illustrated in  FIGS. 1 and 2  has a lordosis or lordosis support  3  formed from supporting ribs  2  arranged in a manner such that they run horizontally and parallel to one another. The lordosis support  3  is provided between an upper side  4  of the backrest and a lower side  5  of the backrest in the central to lower region of the backrest  1  and therefore in the region of a user&#39;s spinal column that is in the vicinity of the chest and pelvis. 
     In the region of the lower side  5  of the backrest, an adjusting member  6  which can be actuated by a rotary knob  7  is fastened to the backrest  1 . Rotation of the rotary knob  7  in the rotational direction  8  causes an adjusting element  9 , which is designed as draw-in wire in the present case, to be wound or unwound. The draw-in wire  9  is guided via a number of guide elements  10 ,  11 . The guide elements  10 ,  11  are connected fixedly to the backrest  1  on the cushion side, which is referred to below as the curvature or front side  12  and faces a backrest cushion  13 , which is illustrated by dashed lines in  FIGS. 2   a  and  2   b . The guide elements  11  are also used for retaining the draw-in wire  9  in the region of the lower side  5  of the backrest. 
     The guide elements  10  are arranged—with reference to FIG.  1 —one above or below another in the longitudinal direction  16  of the backrest on the left backrest edge or lordosis edge  14  and on the right backrest edge or lordosis edge  15 . In these edge regions, the supporting ribs  2  are connected to one another via the particular lordosis edge or backrest edge  14 ,  15 . In this case, these backrest edge regions  14 ,  15 , like the supporting ribs  2 , are precurved in a flexurally elastic manner in the curvature or convex direction  17 , i.e. toward the backrest cushion  13 . 
     The drawing-in wire  9  is guided on the cushion side or front side  12  of the backrest  1 . Rotation of the rotary knob  7  in the rotational direction  8  causes the draw-in wire  9  to be subjected to an increasing tensile load. In this case, starting from the starting position illustrated in  FIG. 2   a  with, for example, maximum lordosis curvature of the convexly precurved lordosis support  3  the adjusting element  9  is increasingly shortened. As a result, the lordosis curvature  18  decreases from the starting position illustrated in  FIG. 2   a  as far as the end position, which is shown in  FIG. 2   b , is comparatively slightly precurved and in which the backrest  1  is at least approximately straightened out. In this case, the or each draw-in wire  9  is fixed in the region of the lordosis upper side  19  by its wire end  9   a  which is there to the backrest  1 . 
     As can be seen from  FIG. 3 , the respective opposite wire end  9   b  of the draw-in wire  9  is wound up onto a coil  20  of the adjusting member  6 . The coil  20  is connected fixedly to a toothed wheel or wormwheel  21  which engages in a worm  22 . The rotary knob  7  can be placed in a form-fitting and frictional manner onto a worm shaft  23 , which is designed as an extension of the worm  22 . The worm gear formed by the wormwheel  21  and the worm  22  is fixed to the backrest  1  by means of a covering flange  24 . 
     The lordosis support  3  is integrated integrally into the backrest  1 . For this purpose, the backrest  1  is formed from a backrest shell  25 , which consists of synthetic material and in the region of which which is assigned to the lordosis support  3  longitudinal slots  26  running horizontally are made. In each case one of the supporting ribs  2  of the lordosis support  3  is formed between in each case two of these longitudinal slots  26 . The backrest  1  with the integrated lordosis support  3  can therefore be produced in a particularly simple manner, for example by injection molding. In the edge region  14 ,  15  of the lordosis support  3 , the guide elements  10 ,  11  are also integrally formed on the backrest shell  26 . 
     As is apparent from  FIGS. 2 and 4 , the backrest  1  or the backrest shell  25  is held on the edge side by backrest carriers  27 . In this case, the mounting on the upper side  4  of the backrest is realized via a pendulum joint and/or rotary joint  28  between the upper carrier end  29  which is there and the backrest  1 . On the opposite lower side  5  of the backrest, a draw-in element  30  is integrally formed on the backrest shell  26 , preferably via a joint or a hinge  31 . In this case, the joint  31  is expediently designed as a film hinge. 
     Via this draw-in element  30 , the backrest  1  or the backrest shell  26  can be connected fixedly by its lower backrest side  5  to the rear seat end  32  of a seat surface  33  of the chair illustrated in  FIGS. 4   a  and  4   b . The backrest carrier  27  merges at its lower carrier end or carrying limb  34 , which faces away from the pendulum/rotary joint  28 , into a backrest guide bar  35  or is connected, for example integrally, to the latter. The backrest guide bar  35 , which constitutes an extension of the backrest carrier  27 , is connected to a seat carrier  36  which, for its part, is connected to a static foot  37  (only part of which is illustrated). The connection of the backrest carrier  27  in its extension via the backrest guide bar  35  to the seat carrier  36  takes place via a first rotary joint  38 . A second rotary joint  39  is provided between the backrest guide bar  35  and the seat surface  33 . A seat guide bar  40 , which is provided in the front region of the seat surface  33 , produces a rotatable and slidable connection between the seat carrier  36  and the seat surface  33 . 
     When the backrest is inclined from the starting position illustrated in  FIG. 4   a  into the inclination position illustrated in  FIG. 4   b , the seat surface  33  is moved at the same time rearward and downward synchronously with the backrest  1 . At the same time, the lower side  5  of the backrest  1  is drawn forward in the direction of the seat surface  33  via the draw-in element  30 . The oscillating or rotational movement required for this takes place via the pendulum/rotary joint  28  between the backrest carrier  27  and the backrest  1 , on the upper side  4  thereof. The setting of the lordosis support  3 , i.e. the degree of its lordosis curvature  18 , can be set here in every synchronizing position of the chair. 
     As a consequence of the articulated connection of the lower backrest end or carrier end  34  via the draw-in element  31  to the seat surface  33 , the backrest  1 , during the synchronizing movement, in addition to the movement about the pivot point  39  between the seat surface  33  and the backrest carrier  27 , at the same time oscillates about the connecting point in the form of the joint  28  between the backrest  1  and the upper end of the backrest carrier  27 . The resultant combined movement resembles a rotation about an assumed point  29  relative to the seat surface  33 . This virtual pivot point  29  is situated, in an ergonomically advantageous manner, higher than the pivot point  39  between the seat surface  33  and the backrest carrier  27 . 
     It is particular advantageous here for the adjusting element  9  of the lordosis support  3  in the form of the draw-in wires (illustrated by way of example) and the guide elements  10 ,  11 , which are provided for guiding them, to be completely covered by the backrest cushion  13  in the final installation state. Additional covering elements, in particular on the rear side  41  of the backrest  1 , which side faces away from the front side  12 , are therefore not required, since no adjusting elements of the lordosis support  3  whatsoever are to be provided there.