Patent Publication Number: US-9894999-B2

Title: Mechanism for an office chair

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The invention relates to a mechanism for an office chair, in which the pivoting resistance of the backrest support can be altered. As a rule, it is possible in this respect to select a setting between “hard” and “soft”, depending on whether the user of the office chair is a heavy or light person. 
     EP 2244605 A1 discloses a mechanism for an office chair, having a spring mechanism that has at least one spring element, said spring mechanism being operatively connected to a backrest support of the office chair and determining the pivoting resistance of the backrest support during pivoting from a starting position into a pivoted position, having a movable functional element that is operatively connected to the spring mechanism, and having an actuating element that is operatively connected to the functional element, the position of said actuating element being altered during pivoting of the backrest support. 
     BRIEF SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a mechanism for an office chair, in which a small adjustment travel is sufficient to realize a large adjustment range of the pivoting resistance of the backrest. 
     This object is achieved by a mechanism as claimed. Advantageous embodiments of the invention are specified in the dependent claims. 
     Accordingly, provision is made to configure the mechanism such that the actuating element has a supporting and/or guide track for the functional element, the position of which on the supporting and/or guide track is altered during a change in position of the actuating element during pivoting of the backrest support. Provision is furthermore made of a movable control arm for the coupling connection of the functional element to a further structural element of the mechanism, wherein the control arm determines the type of change in position of the functional element on the supporting and/or guide track during pivoting of the backrest support. 
     In other words, it is a core idea of the invention that the actuating element itself provides the supporting and/or guide track for the functional element, said functional element bringing about a change in the spring tension during pivoting. Since the actuating element always moves during pivoting of the backrest support, the supporting and/or guide track thus also executes at the same time a corresponding movement and therefore influences the change in position of the functional element, without further structural measures being necessary for this purpose. At the same time, the position and the movement of the functional element on the supporting and/or guide track are forced during pivoting by a control arm, said control arm being arranged between the functional element and a further structural element of the mechanism. 
     Such an arrangement makes it possible, with the aid of an easy-to-realize variable-location connection of the control arm to the further structural element of the mechanism, to realize a large adjustment range of the pivoting resistance of the backrest with a small adjustment travel. Therefore, the mechanism according to the invention requires particularly little space for setting the spring force. 
     A structural embodiment of the invention that is particularly simple in design terms is possible when the actuating element is firmly connected to the backrest support. It then follows the pivoting movement of the backrest support 1:1. 
     An embodiment of the invention in which the functional element is a rolling or sliding body, preferably in the form of a cylindrical pin, that is mounted in a variable position and is acted upon directly by the actuating element, has proved to be very particularly advantageous. In such an embodiment, during the pivoting of the backrest support, the dynamic automatic positioning, characterizing the invention, of the functional element can be realized in a particularly simple manner under the influence of the actuating element and simultaneous guidance of the control arm. 
     The functional element preferably comprises a bearing, wherein the latter is a roller bearing, in particular in the form of a ball bearing or needle bearing. However, it is of course also possible for other bearing devices, for example plain bearings, to be used. 
     In one embodiment of the invention, the control arm is supported only on the further structural element of the mechanism, without being fixedly connected to the further structural element. In the simplest case, the control arm is located as an inherently rigid component between the functional element and the further structural element of the mechanism, automatically maintaining its position in the process. In this respect, in one embodiment of the invention, the control arm is articulated on the functional element with its one end and clamped against a receptacle in the further structural element with its opposite end. In another case, the position of the control arm supported on the further structural element is maintained in that an additional connecting element that cooperates with the control arm and is preferably attached directly to the control arm is provided, said connecting element forming a releasable connection, locking the support, with the further structural element. 
     If the control arm is supported only on the further structural element, then it is possible in a particularly simple manner to embody the connection of the control arm to the further structural element in a variable location. A variable-location connection of the control arm to the further structural element is also possible, however, when the control arm is connected to the further structural element in some other way. 
     The fact that the control arm is connected to the further structural element in a variable location means, in the case of a non-variable-position, i.e. fixed further structural element, that the position of the connection location is variable in that the control arm can be connected to the structural element at different points. In other words, the control arm can be supported at various locations on the further structural element and/or be connected to the structural element at these locations. 
     According to the invention, a change in the connection location brings about in all cases an altered change in position of the functional element on the supporting and/or guide track during pivoting of the backrest support, and thus an alteration in the pivoting resistance of the backrest from “soft” to “hard” or vice versa. 
     In one embodiment, the further structural element has a number of mutually adjoining receptacles into which that end of the control arm that is assigned to the further structural element can be successively moved. As a result, an adjustment device for the non-continuous, discrete changing of the pivoting resistance is created. In one embodiment of the invention, a pulling means, preferably in the form of a Bowden cable, which is connected to that end of the control arm that is assigned to the further structural element, serves as adjusting element. 
     In one embodiment of the invention, the receptacles provided on the further structural element are arranged such that the control arm can be pivoted on a circular path about its articulation point on the functional element, without the connection between the control arm and the further structural element being released. Therefore, during the change in position of the control element with the aid of the adjustment device, the coupling between the functional element and the further structural element is always maintained. Furthermore, the spring force which is applied by the spring mechanism to the movable functional element that is operatively connected to the spring mechanism preferably acts in a perpendicular manner on the supporting and/or guide track provided by the actuating element. As a result, the location of the connection of the control arm to the further structural element of the mechanism can be altered without a substantial change in the position of the functional element on the supporting and/or guide track occurring. Therefore, during the setting of the spring force in the non-pivoted state of the backrest, it is not at all necessary, or necessary only to a very small extent, to work against the force of the at least one spring element of the spring mechanism. Therefore, particularly smooth spring force setting is possible. 
     In an alternative embodiment of the invention, an adjustment device for the non-continuous, discrete changing of the pivoting resistance is created in that the control arm, supported on the further structural element of the mechanism, is releasably connected to the further structural element via an additional connecting element. In addition to a preferably straight supporting surface, on which the control arm is supported, the further structural element has a number of locking elements in which an additional connecting element can successively engage in order to form a lock, wherein this connecting element is connected to that end of the control arm that is supported on the further structural element. Such an attachment of the control arm to the further structural element is preferably configured such that the control arm, together with its point of articulation on the functional element, is moved in a linear manner during a change in the pivoting resistance that occurs with the aid of the adjustment device. Preferably, the functional element is supported on the further structural element throughout the change in position of the control arm. 
     In this embodiment of the invention, a change in the connection location of the control arm to the further structural element results in a simultaneous change in the position of the functional element on the supporting and/or guide track. As a result, the distance between the functional element and the main pivot axis of the mechanism changes. This preferably takes place such that this distance increases in the case of a change from a “soft” to a “hard” setting of the pivoting resistance. As a result, the active lever arm, which is determined by the distance between the axis of the functional element and the main pivot axis of the mechanism, said lever arm being essential for the subsequent pivoting movement of the backrest support, lengthens during the setting of the pivoting resistance from “soft” to “hard”. As a result, this brings about a greater initial resistance, which needs to be overcome at the start of pivoting when the backrest is pivoted by a user of the chair. In other words, on account of the structural configuration of this embodiment of the invention, the magnitude of the initial resistance of the backrest pivoting movement is adapted to the magnitude of the pivoting resistance. A “hard” setting of the pivoting resistance is assigned a matching higher initial resistance. As a result, in particular heavy persons find structural support on leaning against the backrest. Too light a start of the pivoting movement and thus “collapsing” are prevented. Again, the position of the functional element on the supporting and/or guide track preferably changes in such a way that, during the setting of the spring force in the non-pivoted state of the backrest, it is not at all necessary, or necessary only to a very small extent, to work against the force of the at least one spring element of the spring mechanism. Therefore, in this case, too, particularly smooth spring force setting is possible. 
     A structural embodiment of the invention that is particularly simple in design terms is possible when the further structural element of the mechanism is part of the base support. 
     As a result of the change in position of the actuating element during pivoting of the backrest and the change in position, caused thereby, of the functional element, the tension in the at least one spring element is altered according to the invention. In the spring mechanism, any desired types of spring elements for the purposes of the present invention can be used. On account of their simplicity and robustness, helical springs, in particular in the form of helical compression springs, have proved to be particularly advantageous. If a helical compression spring is used, the functional element is preferably a component that acts indirectly or directly on one end of the spring, preferably on a spring seat. 
     In the simplest case, the supporting and/or guide track can have the form of a circular arc segment. Variations in the concavity of the bearing face, for example initially flat, subsequently becoming steeper etc., are possible and result in different dynamic spring behaviour. 
     The spring mechanism operatively connected to the backrest support of the office chair can be connected either directly or indirectly to the backrest support. In the case of an indirect connection, the spring mechanism is preferably connected to the backrest support via the seat support as coupling element. The specific structural configuration is dependent on the structure of the office chair and the type of mechanism (synchronous mechanism, asynchronous mechanism). 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
       Two exemplary embodiments of the invention are explained in more detail in the following text with reference to the drawings, in which: 
         FIG. 1  shows a sectional illustration of a first mechanism with a “soft” setting of the pivoting resistance in a starting position, 
         FIG. 2  shows a sectional illustration of the mechanism from  FIG. 1  with a “soft” setting of the pivoting resistance in a pivoted position, 
         FIG. 3  shows a sectional illustration of the mechanism from  FIG. 1  with a “hard” setting of the pivoting resistance in a starting position, 
         FIG. 4  shows a sectional illustration of the mechanism from  FIG. 1  with a “hard” setting of the pivoting resistance in a pivoted position, 
         FIG. 5  shows a perspective illustration of the mechanism from  FIG. 1  with a “hard” setting of the pivoting resistance, 
         FIG. 6  shows a sectional illustration of a second mechanism with a “soft” setting of the pivoting resistance in a starting position, 
         FIG. 7  shows a sectional illustration of a second mechanism with a “hard” setting of the pivoting resistance in a starting position. 
     
    
    
     DESCRIPTION OF THE INVENTION 
     All of the figures show the invention merely in a schematic manner and with its essential constituent parts. Identical reference signs in this case correspond to elements with an identical or comparable function. 
     The figures show parts of a pivoting mechanism  1  for an office chair, wherein only the structural elements that are absolutely necessary for understanding the present invention are illustrated. 
     The pivoting mechanism  1  comprises a base support  2  having a conical receptacle  3  for the upper end of a chair column, a seat support  4  and a backrest support  5 . In this case, the side pieces of the backrest support  5 , which is fork-shaped in plan view, are arranged on either side of the base support  2 . 
     The front end  6  of the base support  2  is connected to the front end  7  of the substantially horizontally arranged seat support  4  via a rotary/sliding joint  8  (not depicted in detail). The rear end  12  of the seat support  4  is furthermore connected pivotably to the backrest support  5 , to be more precise to an upper side-piece part of the backrest support  5 , at bearing points  13 . Just as the seat support  4  can be provided with a seat, the backrest support  5  can also be provided with a backrest, wherein neither the type of seat nor the type of backrest is important for the invention. The backrest support  5  is furthermore articulated on the base support  2  with its front end  14 , thereby forming the main pivot axis  9 , extending transversely to the chair longitudinal direction  11 , of the mechanism  1 . The bearing points  13  are located behind the main pivot axis  9 , as seen in the chair longitudinal direction  11 . 
     When a user leans against the backrest, the backrest support  5  can be transferred from its starting position, illustrated in  FIGS. 1 and 3 , into a pivoted position, as is illustrated for example in  FIGS. 2 and 4 . In order to set the restoring force of the backrest support  5 , provision is made of a spring mechanism  15 , the functioning of which is explained in detail in the following text. 
     The spring mechanism  15  comprises a helical compression spring  16  arranged centrally in the mechanism  1 . In the figures, this compression spring  16  is illustrated only in part for reasons of clarity. A guide device  17 , in the form of a hollow cylinder having a guide rod  18  running through it, is inserted in a parallel manner in the compression spring  16 , said guide rod  18 , as anti-kink protection, preventing the compression spring  16  from bending during compression. The guide device  17  forms a spring seat  19  at the fixed end  21  of the compression spring  16 . This spring seat  19  is mounted in an articulated manner at the front end  6  of the base support  2 . The guide rod  18  is connected to a spring seat  20  at the movable end  23  of the compression spring  16 . This spring seat  20  is connected to a variable-position functional element  22  in the form of a pin-shaped rolling and/or sliding body. The axis  24  of this rolling and/or sliding body  22  extends in this case parallel to the main pivot axis  9  of the mechanism  1 . In the starting position of the backrest, the axis  24  of the functional element  22  is located in front of the main pivot axis  9  of the mechanism  1 , as seen in the chair longitudinal direction  11 . The functional element  22  has two needle bearings  27  for supporting the functional element  22  in a rotational manner on a supporting and/or guide track  25  which is formed by a concave bearing face of a pivot lever  28 , said bearing face being open towards the front, as seen in the chair longitudinal direction  11 . The pivot lever  28 , acting as actuating element, is embodied as part of the backrest support  5  and is connected to the front end  14  of the backrest support  5  in a rotationally fixed manner beneath the main pivot axis  9  of the mechanism  1 . The main pivot axis  9  of the mechanism  1  is at the same time the rotation axis of the pivot lever  28 . 
     A lower, fixed end  29  of a coupler  31  that serves as a control arm is pivotably connected to the functional element  22 . A lug  32  provided at the end  29  of the coupler  31 , said lug  32  surrounding the functional element  22 , serves for this purpose. 
     The exemplary embodiment illustrated in  FIGS. 1 to 5  is described in more detail in the following text. 
     Attached to the upper, movable end  33  of the coupler  31  is a cylindrical clamping pin  34 , the longitudinal centre axis  35  of which extends parallel to the main pivot axis  9  of the mechanism  1 . Here, too, a lug  36  provided at the end  33  of the coupler  31  serves to guide the clamping pin  34 . The clamping pin  34  is supported in a correspondingly shaped receptacle  37  on the underside  38  of the base support  2 , such that the coupler  31  is clamped between the functional element  22  and the base support  2 . 
     The receptacle  37  is part of a receiving plate  39  which, together with a Bowden cable  41  that serves as an adjusting element and is illustrated only in part in  FIGS. 1 and 2 , forms an adjustment device  42  for the coupler  31 . For this purpose, the receiving plate  39  has a number of mutually adjoining receptacles  37 , into which the free end  33  of the coupler  31  can be successively moved. The Bowden cable  41 , which is embodied such that it can move the coupler  31  from one receptacle  37  to the next receptacle  37  and back again, is connected to the free end  33  of the coupler  31  and is supported at suitable points of the base support  2 . 
     The receptacles  37  are arranged on the receiving plate  39  such that the coupler  31  can be pivoted on a circular path about its articulation point  44  on the functional element  22 , without the connection between the coupler  31  and the underside  38  of the base support  2  being lost. The articulation point  44 , which is indicated in  FIGS. 1 and 5 , is determined by the connection of the lug  32  to the functional element  22 . The compression spring  16  is perpendicular or substantially perpendicular to the supporting and/or guide track  25  in the non-pivoted state of the backrest. Therefore, when the clamping pin  34  is moved from one receptacle  37  to the next, essentially only the force which is necessary to overcome the separating strips that separate the individual hollow-like receptacles  37  from one another needs to be applied. 
     When the backrest support  5  is pivoted downwards and to the rear in the pivoting direction  46 , the pivot lever  28  connected to the backrest support  5  likewise pivots in the same manner, with the result that the functional element  22 , held at a defined distance from the base support  2  by the coupler  13 , is moved on the supporting and/or guide track  25 . This results in a defined movement of the functional element  22  depending on the pivoting movement of the backrest support  5 . 
     In the example shown in  FIGS. 1 and 2 , the free end  33  of the coupler  31  is located in the rearmost receptacle  37 , as seen in the chair longitudinal direction  11 , of the receiving plate  39 , with the result that the “softest” setting of the spring force setting is defined. In the starting position of the backrest, the longitudinal centre axis  35  of the clamping pin  34  is located behind the main pivot axis  9  of the mechanism  1 , as seen in the chair longitudinal direction  11 . When the backrest support  5  is pivoted, the functional element  22  moves upwards in the direction of the main pivot axis  9  and at the same time forwards in the direction of the front end  6  of the base support  2 . As a result, the distance between the spring seats  19 ,  20  decreases, and the compression spring  16  is compressed. 
     If the free end  33  of the coupler  31  is moved, with the aid of the Bowden cable  41 , from the rearmost receptacle  37 , as seen in the chair longitudinal direction  11 , into the front receptacle  37 ′, as shown in  FIGS. 3 and 4 , the “hardest” setting is carried out as a result. The supporting and/or guide track  25  remains unaltered in this case, and in particular the gradient of the track  25  does not change. In the starting position of the backrest, the longitudinal centre axis  35  of the clamping pin  34  is then located in front of the main pivot axis  9  of the mechanism  1 , as seen in the chair longitudinal direction  11 , and just behind the axis  24  of the functional element  22 . As a result of the adjustment device  42  being actuated, the position of the coupler  31  changes relative to the position of the compression spring  16 , to be more precise relative to the spring longitudinal direction  47 , but not the length of the coupler  31 . Therefore, when the backrest support  5  is pivoted, an altered ratio of the acting forces arises, this being expressed in an altered movement of the functional element  22 . 
     When the backrest support  5  is pivoted, the functional element  22  moves downwards away from the main pivot axis  9  and at the same time forwards in the direction of the front end  6  of the base support  2 . As a result, the distance between the spring seats  19 ,  20  decreases much more greatly and the compression spring  16  is compressed more strongly than in the case of the above-described “soft” setting. At the same time, the active lever arm (not shown) which is essential for the pivoting movement of the backrest support  5  is enlarged, said lever arm being determined by the distance between the axis  24  of the functional element  22  and the main pivot axis  9  of the mechanism  1 . At the same time, on account of the changed position of the compression spring  16 , coupler  31  and pivot lever  28  with respect to one another, the sum of the forces effectively acting on the pivot lever  28  increases. Overall, this results in considerably increased pivoting resistance. 
     Overall, in spite of the only small adjustment travel between the rearmost receptacle  37  and the front receptacle  37 ′ of the adjustment device  42 , a large adjustment range of the spring force adjustment arises. In other words, as a result of a comparatively small change in the position of the free end  33  of the coupler  31 , a spring force adjustment from a very soft to a very hard setting and vice versa can take place. 
     In the following text, the exemplary embodiment illustrated in  FIGS. 6 and 7  is described in more detail. This exemplary embodiment differs from the above-described exemplary embodiment primarily by the manner in which the upper end  33  of the coupler  31 ′ is connected to the base support  2 . Instead of a self-locking configuration, locking that is establishable with the aid of an additional connecting element  48  is provided. This results, in addition to an altered adjustment device  42 ′, in particular in an altered change in position of the functional element  22  on the supporting and/or guide track  25  during pivoting of the backrest support  5 . All further essential features, in particular the resulting functional advantages of the mechanism  1 , remain the same, however, or result in a corresponding manner. 
     The additional connecting element  48  is articulated on the upper, movable end  33  of the coupler  31 ′. The connecting element  48  comprises a pawl  49 . The connecting element  48 , which is pivotable about a locking pivot axis  50  extending parallel to the main pivot axis  9  of the mechanism  1 , is supported on a planar supporting face  52  by way of its one side  51  facing the base support  2 . This supporting face  52  is provided on the underside  38  of the base support  2 , rigidly connected to the base support  2 , and defines a rectilinear guide track for the upper end  33  of the coupler  31 ′ when the pivoting resistance is adjusted. 
     The position of the coupler  31 ′ between the functional element  22  and base support  2  is maintained in that the pawl  49  provided on the opposite side  53  of the connecting element  48 , that is to say the side facing away from the supporting face  52 , engages in locking elements in the form of locking teeth  54  and thus locks the connecting element  48  and thus the coupler  31 ′ on the base support  2 , forming a ratchet. The locking teeth  54  are arranged in the form of a rectilinear tooth strip extending parallel to the supporting face  52  and, together with the supporting face  52  to which they are firmly connected, form the further structural element within the meaning of the invention. Every time the backrest support  5  is pivoted in the pivoting direction  46 , the coupler  31 ′ is urged in the direction of the supporting face  52 . As a result, the coupler  31 ′, to be more precise the top side  51  of the connecting element  48  of the coupler  31 ′, is supported on the supporting face  52 . Displacement of the connecting element  48  on the flat supporting face  52  in the direction of a “softer” setting, upwardly to the right in the figures, is prevented, however, in that the pawl  49  locks in the locking teeth  54 . 
     In the example shown in  FIG. 6 , the connecting element  48  is supported on the rearmost abutment point, as seen in the chair longitudinal direction  11 , of the supporting face  52 , and the pawl  49  is located next to the rearmost locking tooth  54 , as seen in the chair longitudinal direction  11 , in the tooth strip, with the result that the “softest” setting of the spring force setting is defined. In the starting position of the backrest, the locking pivot axis  50  of the connecting element  48  is located behind the main pivot axis  9  of the mechanism  1 , as seen in the chair longitudinal direction  11 . 
     In order to alter the pivoting resistance from “soft” to “hard”, provision is made of a first Bowden cable  56  (indicated merely symbolically and away from its actual position in the figures for the sake of clarity) as adjusting element, said first Bowden cable  56  acting on a first engagement point  57  of the connecting element  48  and being supported at suitable points on the base support  2 . This first engagement point  57  is provided on the connecting element  48  such that the connecting line between the first engagement point  57  and the locking pivot axis  50  of the connecting element  48  extends parallel to the supporting face  52 . In the event of a pull in the first pulling direction  58  defined thereby, the pawl  49  is unlocked and the locking brought about by the pawl  49  is overcome. The ratchet formed by the pawl  49  and locking teeth  54  acts in this case as a type of limit-force ratchet, in which the locking forces can be overcome by a pull in the first pulling direction  58 . An increase in the pivoting resistance, i.e. an alteration in the position of the coupler  31 ′ into a respectively “harder” position, is possible in each case by renewed actuation of the first Bowden cable  56 . 
     On the other hand, if the pivoting resistance is intended to be reduced, that is to say the coupler  31 ′ moved into a “softer” position, this is not possible with the aid of the first Bowden cable  56 . This is because, on account of the connecting element  49  being supported on the supporting face  52  with simultaneous engagement of the pawl  49  in the locking teeth  54 , the ratchet formed by the pawl  49  and locking teeth  54  acts as a kind of directional ratchet, which does not allow a movement of the connecting element  48  counter to the first pulling direction  58 . Therefore, in order to alter the pivoting resistance from “hard” to “soft”, provision is made of a second Bowden cable  59  (indicated merely symbolically and away from its actual position in the figures for the sake of clarity) as adjusting element, said second Bowden cable  59  acting at a second engagement point  60 , different from the first engagement point  57 , of the connecting element  48  and being supported at suitable points on the base support  2 . This second engagement point  60  is provided on the connecting element  48  such that it is not located on the connecting line between the first engagement point  57  and the locking pivot axis  50  of the connecting element  48 . Instead, the second engagement point  60  is arranged on a lever arm  61 , acting on the pawl  49 , of the connecting element  48  such that in the event of a pull in the second pulling direction  62 , which is different from the first pulling direction  58 , a torque acts on the pawl  49  such that the latter is unlocked. In other words, the pawl  49 , which is embodied as part of the connecting element  48 , is raised and pivoted out of the locking teeth  54  in that the entire connecting element  48  is pivoted about its locking pivot axis  50  on the coupler  31 ′. A reduction in the pivoting resistance, i.e. an alteration in the position of the coupler  31 ′ into an in each case “softer” position, is then possible in each case by renewed actuation of the second Bowden cable  59 . 
     If the upper end  33  of the coupler  31 ′ was moved, with the aid of the first Bowden cable  56 , from the rearmost engagement point, as seen in the chair longitudinal direction  11 , of the supporting face  52  to the front engagement point, as shown in  FIG. 7 , the “hardest” setting is carried out as a result. In the starting position of the backrest, the locking pivot axis  50  of the connecting element  48  is then located again in front of the main pivot axis  9 , as seen in the chair longitudinal direction  11 , of the mechanism  1  and just behind the axis  24  of the functional element  22 . 
     During the setting of the pivoting resistance, an alteration in the position of the coupler  31 ′ always takes place such that the upper end  33  of the coupler  31 ′ is moved in a linear manner corresponding to the guide track defined by the supporting face  52 . The position of the functional element  22 , connected to the fixed end  29  of the coupler  31 ′, on the supporting and/or guide track  25  is likewise altered in the process. In other words, not only does the upper end  33  move on the supporting face  52  but the fixed end  29  of the coupler  31 ′ also moves on the supporting and/or guide track  25  when the pivoting resistance is increased towards the front in the chair longitudinal direction  11  and when the pivoting resistance is reduced towards the rear in the chair longitudinal direction  11 . Thus, the coupler  31 ′ is always moved as a whole when the pivoting resistance is changed. 
     During the setting of the pivoting resistance, the functional element  22  moves in a defined, constant relationship with respect to the movement of the upper end  33  of the coupler  31 ′. While the upper end  33  of the coupler  31 ′ moves in each case in the first pulling direction  58  or counter to the first pulling direction  58 , the fixed end  29  of the coupler  31 ′ moves with the functional element  22  on a circular path around the fixed point  21  of the helical compression spring  16 . On account of this movement path, when the pivoting resistance is set, the helical compression spring  16  is not compressed or is only compressed to an insignificant extent. The pivoting resistance is therefore particularly easy to set. 
     All of the features represented in the description, the following claims and the drawings can be essential to the invention both individually and in any desired combination with one another. 
     LIST OF REFERENCE SIGNS 
     
         
           1  Pivoting mechanism 
           2  Base support 
           3  Conical receptacle 
           4  Seat support 
           5  Backrest support 
           6  Front end of the base support 
           7  Front end of the seat support 
           8  Rotary/sliding joint 
           9  Main pivot axis 
           10  (not used) 
           11  Chair longitudinal direction 
           12  Rear end of the seat support 
           13  Bearing point 
           14  Front end of the backrest support 
           15  Spring mechanism 
           16  Helical compression spring 
           17  Guide device 
           18  Guide rod 
           19  Spring seat 
           20  Spring seat 
           21  Fixed end of the spring 
           22  Functional element, rolling and/or sliding body 
           23  Movable end of the spring 
           24  Axis of the functional element 
           25  Supporting and/or guide track 
           26  (not used) 
           27  Needle bearing 
           28  Pivot lever 
           29  Fixed end of the coupler 
           30  (not used) 
           31  Coupler 
           32  Lug 
           33  Movable end/free end of the coupler 
           34  Clamping pin 
           35  Longitudinal centre axis 
           36  Lug 
           37  Receptacle 
           38  Underside of the base support 
           39  Receiving plate 
           40  (not used) 
           41  Bowden cable 
           42  Adjustment device 
           43  (not used) 
           44  Articulation point 
           45  (not used) 
           46  Pivoting direction 
           47  Spring longitudinal direction 
           48  Connecting element 
           49  Pawl 
           50  Locking pivot axis 
           51  Top side of the connecting element 
           52  Supporting face 
           53  Underside of the connecting element 
           54  Locking tooth 
           55  (not used) 
           56  First Bowden cable 
           57  First engagement point 
           58  First pulling direction 
           59  Second Bowden cable 
           60  Second engagement point 
           61  Lever arm 
           62  Second pulling direction