Abstract:
In order to provide an office chair having a comparatively low constructive effort and expense, a degree of comfort comparable with that of a synchronization mechanism, the chair has a seating element with a seating surface and a back element pivotable around a lateral axis and linked in a jointed manner to the seating element. The seating surface of the seating element is configured in a way that a user performs a movement, which follows the movement of the back element, when the back element is pivoting to a rear position. As a result, a synchronous movement of the body of the user with the movement of the back element is facilitated, without the whole seating element performing the synchronous movement.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This is a continuing application, under 35 U.S.C. § 120, of copending international application PCT/EP2006/003909, filed Apr. 27, 2006, which designated the United States; this application also claims the priority, under 35 U.S.C. § 119, of German patent application DE 10 2005 020 247.0, filed Apr. 28, 2005; the prior applications are herewith incorporated by reference in their entirety. 
     
    
     BACKGROUND OF THE INVENTION  
     Field of the Invention  
       [0002]     The invention relates to a chair, in particular an office chair. So-called synchronization mechanisms are known from the prior art. They constitute assemblies in the substructure of an office chair seat that facilitate a correlated movement of a seat and a backrest. For this purpose, the seat support and the backrest support are flexibly coupled so that a backward tilt of the backrest, caused e.g. by a chair user leaning against the backrest, induces a lowering of the rear edge of the seat. This brings with it a considerable degree of comfort and is desirable for orthopaedic reasons. A disadvantage of such synchronization mechanisms is their comparatively complicated mechanical structures. This makes synchronization mechanisms relatively expensive to produce as well.  
       BRIEF SUMMARY OF THE INVENTION  
       [0003]     It is accordingly an object of the invention to provide seating furniture, in particular office chairs which overcomes the above-mentioned disadvantages of the prior art devices of this general type, which has comparatively low constructive effort and expense and provides an advantage in comfort comparable with that of a synchronization mechanism.  
         [0004]     With the foregoing and other objects in view there is provided, in accordance with the invention, a chair. The chair contains a fixed seating element having a seating surface, and a back element being pivotable around a lateral axis and linked in a jointed manner to the fixed seating element. The seating surface of the seating element is configured such that a user, when pivoting the back element towards a rear position, executes a movement that follows a movement of the back element.  
         [0005]     It features a chair that is formed of only two principal structural assemblies, namely a preferably fixed seating element and a back element, whereby the seating element has a seating surface and the back element is pivotable around a lateral axis and linked in a jointed manner to the seating element. According to the invention, the seating surface is configured in a way that a user, when the backrest pivots backwards, such as happens when the user leans against it, performs a movement, which follows the movement of the back element. In other words, due to the configuration of the seating surface, a backward tilt of the backrest leads to the user sinking down towards the back, without the seating element itself moving. As a result, a synchronous movement of the body of the user with the movement of the back element is facilitated, without the whole seating element imitating the synchronous movement. Consequently, there is a shift of the user&#39;s center of gravity as well as a shift of movement in the sense that the invention allows the user to accomplish a movement resembling, to a large extent, the movement a user would make if an appropriate synchronization mechanism were employed. In a constructively simple and therefore also very economical manner the invention thus facilitates a degree of comfort to be achieved similar to that achievable with a significantly more expensive synchronization mechanism. A particular advantage is that the so-called “shirt stripping effect” is effectively prevented.  
         [0006]     In a particularly advantageous embodiment of the invention the seating surface contains at least two different seating areas disposed behind one another in longitudinal direction of the seat, such seating areas differing with regard to the way they are upholstered. The term ‘upholstery’ is understood to mean any type of flexible design of the seating surface, regardless of the material employed. Apart from formed foams, basically any other elastic materials may be used, such as spring packets, or combinations of materials, such as e.g. foam in conjunction with silicon cushions. The use of e.g. dual zone foam is possible as well.  
         [0007]     It is of particular advantage if at least one of the rear seating areas contains a type of upholstery, which, compared with a front seating area, permits the user to sink in to a greater extent. Thus, when the user moves backwards and by doing so is putting weight on the rear section of the seat, there is a simultaneous “yielding” of the seat. In other words, the seating area is configured so that when pressure is put on the backrest, the user&#39;s pelvis glides into the upholstery in the form of rolling. The result is a highly synchronized sequence of movements between the back element and the user.  
         [0008]     In addition, it is of particular advantage when the back element is linked with the seating element via a swivel axis, which, seen in a longitudinal direction of the chair, is positioned in front of the attachment of the chair post to the seating element. The position of the swivel axis contributes greatly to facilitating an ergonomically beneficial seating position.  
         [0009]     A particularly flat configuration can be achieved where spring elements, arranged in a generally horizontal position in the seating element, are provided for pre-stressing the back element. Depending on the design of the model, any type of springs, e.g. tension springs or compression springs, can be used to serve as the spring elements.  
         [0010]     Other features which are considered as characteristic for the invention are set forth in the appended claims.  
         [0011]     Although the invention is illustrated and described herein as embodied in seating furniture, in particular office chairs, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.  
         [0012]     The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING  
       [0013]      FIG. 1  is a diagrammatic, perspective view of a seating element without a seating surface (first spring position) according to the invention;  
         [0014]      FIG. 2  is a diagrammatic, cross-sectional view through the seating element (first spring position);  
         [0015]      FIG. 3  is a diagrammatic, cross-sectional view through the seating element (second spring position);  
         [0016]      FIG. 4  is a diagrammatic, cross-sectional view through the seating element (first spring position), with a seating pad; and  
         [0017]      FIG. 5  is a diagrammatic, cross-sectional view through the seating element (second spring position). 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0018]     Referring now to the figures of the drawing in detail and first, particularly, to  FIGS. 1-2  thereof, there is shown an office chair of the invention that contains a seating element  1  and a back element  2 . As shown in  FIG. 2 , the seating element  1  disposed in a generally horizontal position is hinged to the back element  2  at a bearing point  3 . In other words, the back element  2  is hinged to an underside  4  of the seating element  1  so that if, for instance, the user leans against the back element  2 , it performs a tilting movement  5  around a swivel axis  6  that runs at a right angle to a longitudinal direction  7  of the chair.  
         [0019]     In the context of the invention it is immaterial what type of back element  2  is used. The back element  2  can for example have the shape of a shell or a net or similar.  
         [0020]     The back element  2  can be moved from its normal position as shown in the drawings to a position further back and returned again. To vary the backward tilting resistance of the back element  2 , a spring tension adjustment facility  8  is provided, the exact functioning of which will be explained later.  
         [0021]     The seating element  1  includes, on the one hand, the actual seat bearing with the hinge attachment for the back element  2 , as well as the spring tension adjustment facility  8 . Due to the pivotal point of the mechanism being positioned closely below a seating surface  9 , the sequence of movements in connection with a backward tilt of the back element  2  is similar to that facilitated by a synchronization mechanism. It reduces, in particular, the so-called “shirt-stripping effect”. In other words, the horizontal and vertical positions of the swivel axis  6  relative to the seating element  1  and the back element  2 , respectively, are decisive for the achievable sequence of movements.  
         [0022]     Moreover, all other mechanical components are integrated in the seating element  1 , including e.g. receptacles  10  for the non-illustrated armrests. In other words, the functional components of the seat bearing and the mechanism form a single structural unit. The integrated and compact construction of the seating element  1  is particularly evident from  FIG. 1 . A special advantage of the configuration is that production costs are low. In addition, the number of separate components required is significantly reduced, which further reduces the manufacturing costs and also increases the safety from failure.  
         [0023]     The seating element  1  features a more or less centrally positioned taper socket  11  serving for receiving an upper end of a non-illustrated chair post, for example a gas spring.  
         [0024]     A base element  12  of the seating element  1  is formed generally of a plastic base plate with a number of wall elements  14  in both longitudinal direction  7  and transverse direction  13  of the chair. The wall elements  14  serve not only for providing the necessary stability of the seating element  1 . At the same time, considerable savings in material can be achieved. Furthermore, some of the wall elements  14  have additional functions. Thus they provide e.g. guide or retaining elements for a release bar  15  that serves for a height adjustment of the gas spring, with the release bar  15  being operated by a key  16  also integrated in the base element  12 . Another function of the wall elements  14  is to guide or retain a driving axle  17  of the spring tension adjustment  8 , whereby an operating element, e.g. in the form of a hand wheel, not shown in  FIG. 1 , is attached to a free end  18  of the driving axle  17 .  
         [0025]     A spring configuration serves to return the back element  2  from a position further back to its normal position. The spring configuration contains two compression springs  19  of circular cross section sitting in corresponding spring holders  20  provided in the base element  12 .  
         [0026]     Apart from the fact that the spring angle can be altered by a movement of the spring hinge when the spring tension adjustment  8  is operated, compression springs  19  are disposed in a generally horizontal position in the seating element  1 , which permits a fairly flat configuration. The shallow construction height facilitates, on the one hand, an optically particularly attractive design of the chair. Furthermore, it permits the use of various chair posts, or gas springs, so that even unusual requirements in respect of the seating height, can be met.  
         [0027]     The position of the two compression springs  19  is altered by a U-shaped round iron  21 , the U-shanks  22  of which are inserted in the two round-bar spiral springs  19 . By moving a “U-base”  23  of the round iron  21  in the direction of a lateral deflection  24 , the compression springs  19  are lifted or lowered on one side, while the opposite ends of the compression springs  19  remain in their original positions, due to ends  25  of the round iron  21  being fixed to the base element  12 . For this purpose, the rounded ends  25  sit in a type of ball cup  26  in the base element  12 .  
         [0028]     When pressure is put on the back element  2 , i.e. when it tilts to a position further back, hinged nozzles  28 , which are fitted to an axle  27  and reach through the base element  12  from below to the round iron  21 , press against the compression springs  19  and thereby establish an effective connection between the compression springs  19  and the back element  2 . The hinged nozzles  28  are configured as U-shaped guides in an appropriate form to accept the U-shanks  22  of round iron  21 .  
         [0029]     An alteration of the spring tension adjustment leads, via a rotation of the driving axle  17 , to a rotation of a worm gear  29  attached to it, which, in turn, leads to a rotation of a cogwheel  30  engaging in the worm gear  29 . The cogwheel  30  is mounted on a threaded shaft  31 , which is disposed in the direction of lateral deflection  24 , i.e. vertically, and to which a cantilever  32  is fitted via a coil. The cantilever  32  features a U-shaped cam  33 , which takes along the round iron  21  either upwards or downwards, depending on the direction of rotation of the driving axle  17 . As a result, the position of the compression springs  19  is adjusted from a lower first spring position ( FIGS. 1, 2 ,  4 ) to an upper second spring position ( FIGS. 3, 5 ). In other words, a “forceless” spring tension adjustment is possible in this way. Only the position of the compression springs  19  and thus the hinge angle are changed. Expressed differently, the spring tension adjustment is effected by incorporating the laws of the lever principle in that the compression springs  19  engage in different locations of the hinged nozzles  28 . By shifting the pivotal points in outward lateral direction  24 , the lever arm is lengthened or shortened, respectively, so that the round-bar spiral springs  19  are compressed to a greater or lesser extent.  
         [0030]     Upholstery  34  of the seating area  9 , see  FIG. 4 , is formed of formed foam and is attached to a seating base plate  39  that can be fitted to suitable receptacles  40  on the base element  12 . As a result of the special configuration of the upholstery  34 , the user more or less rolls down towards the back when the back element  2  is moved. He/she glides into the foam. The foam should therefore be free towards the seating surface end  35  so as to be able to expand backwards. To achieve this, an open configuration of the upholstery  34  without any bordering elements at the back is preferred.  
         [0031]     The seating surface  9  is divided into two different seating areas  36 ,  37 , disposed behind one another in longitudinal direction  7  of the seat and differing with regard to the way they are upholstered. With the form of seating surface  9  of the present example, the front seating area  36 , which constitutes about 30% to 40% of the total length of the upholstery  34 , is fitted with “standard” upholstery thickness, while the rear seating area  37  (between 70% and 60% of the total length) is fitted with variable upholstery  34  that permits the user to sink down towards the back. In the example shown, the upholstery thickness of the rear seating area  37  is higher by at least 20 mm compared with the upholstery thickness of the front seating area  36 . The transition from the front seating area  36  to the rear seating area  37  is preferably very soft and smooth without any ridges. Particularly good results are achieved with a transition area  38  in the form of an elongated horizontal S. The transition from the front seating area  36  to the rear seating area  37  is so disposed that the user in a normal (“average”) seating position will put his weight predominantly on the front seating area. When pressure is put on the backrest, the user&#39;s pelvis rolls over the horizontal S into the rear seating area. The user thus follows the movement of the backrest downwards to the back