Patent Publication Number: US-2022225770-A1

Title: Pivot fitting and piece of furniture

Description:
BACKGROUND AND SUMMARY OF THE INVENTION 
     Exemplary embodiments of the present invention relate to a pivot fitting, in particular for movable furniture parts on seating or reclining furniture, and to a piece of furniture. 
     A pivot fitting of the type is known, for example, from DE 10 2017 110 253 A1. In this pivot fitting, two levers can be fixed relative to each other by means of a clamping mechanism. One of these levers can be attached to a base body or seat part of an upholstered piece of furniture, while the second lever serves to fix a pivotably mounted headrest, armrest, footrest, or another furniture part pivotably mounted on the base body or seat part of the piece of furniture. 
     With the aid of the pivot fitting, the pivotable furniture part can be pivoted from an initial position into a predetermined pivot position and fixed in this pivot position. 
     The pivot fitting is designed in such a way that the furniture part to be adjusted can be moved from any pivot position without the two levers first having to be pivoted back into the initial position. 
     Such a pivot fitting has proven itself in practice. 
     The problem with such a pivot fitting is that if the pivot fitting is overloaded, damage to the pivot fitting or a furniture part can occur. 
     To prevent such damage, it is known, for example, from DE 10 2017 110 248 A1 to mount an overload clutch between the two levers of the pivot fitting, which is arranged as a structural unit between the first lever and the second lever. 
     The disadvantage here is that such overload clutches are relatively expensive to manufacture. Another disadvantage is that the overload clutch must be re-engaged at the point at which it is disengaged, or at least can only be re-engaged in a staggered grid. 
     Exemplary embodiments of the present invention are directed to further developing a pivot fitting of the generic type in such a way that the pivot fitting is also protected against an overload in a simple and inexpensive manner. 
     Exemplary embodiments of the invention are further directed to providing piece of furniture with which the operation of a piece of furniture with movable components is further improved. 
     The pivot fitting according to the invention comprises at least one first lever, which is mounted so as to be pivotable about a force-transmitting shaft serving as a pivot axis from an initial position through a predetermined angle thereto. 
     The pivot fitting further comprises a clamping mechanism for fixing the first lever in different angular positions within the predetermined angle relative to the force-transmitting shaft. 
     This clamping mechanism has a toothed-ring disc fitted onto the force-transmitting shaft with outer toothing structure formed on the outer edge, and a catch pivotably mounted on the first lever, is loaded in the direction of the outer toothing structure and is in engagement with the outer toothing structure of the toothed-ring disc in a latching position. 
     The clamping mechanism further comprises a first control disc rotatably mounted about the force-transmitting shaft and by means of which the at least one catch can be disengaged from the toothing in an adjustment direction after passing over the predetermined angle from the normal position, so that, when the catch is disengaged from the toothing, the first lever can be pivoted back into the normal position relative to the force-transmitting shaft by passing over the predetermined angle in a return direction. 
     At least one friction disc arranged on the force-transmitting shaft in a rotationally fixed and axially secured manner is pushed onto the toothed-ring disc, wherein the toothed-ring disc is retained on the at least one friction disc in a frictionally locking manner up to a predetermined torque against rotation about the axis of rotation. 
     With a pivot fitting designed in this manner, an overload safety device is made possible that is easy to install and inexpensive in its components, with which the force-transmitting shaft is decoupled from the toothed-ring disc and thus the force-transmitting shaft is decoupled from the first lever in the event of an overload. 
     This allows the first lever to be pivoted relative to the force-transmitting shaft without damaging the clamping mechanism. 
     If the overload is again undershot, the pivot fitting according to the invention is still fully functional. 
     According to an advantageous embodiment variant of the invention, an inner circumferential edge of the toothed-ring disc is conically shaped and slid onto a cone arranged on the force-transmitting shaft. 
     In this case, the at least one friction disc is in pressing contact with the toothed-ring disc on the side of the smaller diameter of the inner circumferential edge of the toothed-ring disc. 
     Due to the cone arranged on the force-transmitting shaft and the friction disc, the friction disc arranged on the force-transmitting shaft in a rotationally fixed manner and the toothed-ring disc are pressed against each other in such a way that the predetermined torque defining the limit for overload must be exceeded in order to rotate the friction disc relative to the toothed ring disc. 
     Friction is created on the cone and on the contact surface of the toothed-ring disc by the resilient contact force of the friction disc. 
     Depending on the selected contact pressure or friction value between the contact surface of the toothed-ring disc on the friction disc as well as the predefined cone angle, the predetermined torque can be defined. 
     According to an advantageous further development of the invention, the cone is integrally formed on the force-transmitting shaft, which enables extremely simple assembly. 
     According to an alternative embodiment variant, the cone is mounted on the force-transmitting shaft. 
     This means that the force-transmitting shaft itself and the cone, which is to be manufactured as an individual component, for example as a sheet metal element, can be produced very cost-effectively. 
     According to an advantageous further development, the cone is formed as a radially slotted clamping ring. 
     According to an advantageous embodiment variant, the cone angle of the cone is between 15° and 35°, particularly preferably between 20° and 30°. 
     According to an alternative embodiment variant, a friction disc is slid on both sides of the toothed-ring disc in a rotationally fixed and axially secured arrangement. 
     Accordingly, this variant does not require a cone on the force-transmitting shaft. 
     According to an alternative embodiment variant, a plurality of toothed-ring discs are placed on the force-transmitting shaft, with a friction disc held non-rotatably on the force-transmitting shaft being arranged between two toothed-ring discs. 
     Preferably, three toothed-ring discs and two friction discs arranged therebetween are used. 
     In an alternative embodiment variant, two toothed-ring discs are used with a friction disc arranged between them. 
     As a result of the force exerted by the friction discs fitted and/or pressed onto the force-transmitting shaft in a rotationally fixed manner, friction is thus generated at six contact points (in the case of three toothed-ring discs) or four contact points (in the case of two toothed-ring discs fitted), via which the torque provided for the overload protection can be adjusted. 
     The wear and the overload torque can be easily adjusted by means of the spring force and pressure depth of the friction discs used and the number of toothed-ring discs used. 
     According to a further advantageous embodiment variant, a tab is integrally formed on the first control disc that extends perpendicularly to the plane of the first control disc axially outwardly relative to the force-transmitting shaft into a recess provided for this purpose in a cutout of the first lever. 
     According to a further embodiment variant, a recess is formed on an outer edge of the friction disc, in which a changeover element is accommodated such that it can be pivoted through a changeover angle in the plane of the friction disc. 
     This changeover element also serves as an alternative to the combination of the control pin arranged on the first lever and the cutout in the first control disc. 
     The friction disc accommodating the changeover element has a thickness, in the axial direction of the force-transmitting shaft, which is greater than the thickness of the changeover element. 
     This is a simple way of ensuring that the forces applied by the friction discs cannot cause this changeover element to jam. 
     According to a preferred embodiment variant, the at least one friction disc is pressed onto the force-transmitting shaft against the toothed-ring disc with an interference fit. 
     This makes it possible to generate sufficient friction between the friction disc and the toothed-ring disc by means of the friction disc alone. 
     According to a further advantageous embodiment variant, the friction disc is designed as a disc spring. 
     According to a further preferred embodiment variant, a changeover contour is formed on an outer edge of the friction disc. 
     According to a further advantageous further development, the predetermined torque up to which the toothed-ring disc is frictionally held against rotation about the axis by the at least one friction disc is at least 70 Nm, preferably at least 80 Nm. 
     This ensures that at lower loads, where there is no risk of damage to the pivot fitting, the clamping mechanism does not react to lower torques, so that the levers remain in their position and can only be adjusted against each other from the predetermined torque, without using the actual function of the clamping mechanism. 
     A particular advantage arises in the arrangement according to the invention in that the pivot fitting allows a maximum angle of adjustment of approximately 250°. This is made possible by the arrangement of the control pins and the stops as well as the internal structure with the toothed-ring disc, the control disc and the catch. 
     According to one embodiment variant, a second lever is coupled in a rotationally fixed manner to the force-transmitting shaft. 
     The piece of furniture according to the invention is characterized by a pivot fitting as described above. 
     According to one embodiment variant, the second lever is part of the adjustable furniture part. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURES 
       Preferred embodiment variants are described in more detail below with reference to the accompanying drawings, wherein: 
         FIG. 1  shows a top view of an embodiment variant of a pivot fitting according to the invention, 
         FIG. 2  shows a perspective exploded view of the pivot fitting without representation of the second lever, 
         FIG. 3  shows an individual perspective view of the toothed-ring disc, the force-transmitting shaft, the friction disc, the cone and the first control disc, 
         FIG. 4  shows a partial sectional view of the force-transmitting shaft with overload components arranged on it, 
         FIG. 5  shows an exploded view of an embodiment variant of the toothed-ring disc, the cone and the force-transmitting shaft, 
         FIG. 6  shows a perspective view of the components shown in  FIG. 5  in the assembled state, 
         FIG. 7  shows a perspective view of an alternative embodiment variant of a friction disc mounted on the force-transmitting shaft, 
         FIG. 8  shows a top view of the pivot fitting showing a stop, 
         FIG. 9  shows a representation of the pivot fitting corresponding to  FIG. 8  in another pivot position, 
         FIG. 10  shows sectional view of the pivot fitting, 
         FIGS. 11 and 12  show top views of the pivot fitting with alternatively designed stops on the second lever, 
         FIG. 13  shows a side view of an alternative embodiment configuration of the overload protection, 
         FIGS. 14 to 19  show top views of the pivot fitting with the lever head omitted to illustrate the functional sequence of a pivoting and changeover movement, 
         FIG. 20  shows a perspective exploded view of an alternative embodiment variant of a clamping mechanism with overload protection with three toothed-ring discs and friction discs arranged between them, 
         FIG. 21  shows a side view of the embodiment configuration shown in  FIG. 20 , 
         FIG. 22  shows a perspective exploded view of a further alternative embodiment variant of a clamping mechanism with overload protection with two toothed-ring discs and friction discs arranged therebetween, 
         FIG. 23  shows a side view of the embodiment configuration shown in  FIG. 22 , 
         FIG. 24  shows a perspective exploded view of a further alternative embodiment variant of a clamping mechanism with overload protection with three toothed-ring discs and friction discs arranged therebetween and an alternative changeover element, 
         FIG. 25  shows a side view of the embodiment configuration shown in  FIG. 24 , 
         FIG. 26  shows a schematic top view of the embodiment configuration shown in  FIG. 24  to illustrate the arrangement of the changeover element, and 
         FIGS. 27 and 28  show schematic representations of a piece of furniture with a pivotable furniture part arranged thereon. 
     
    
    
     DETAILED DESCRIPTION 
     In the following figure description, terms such as top, bottom, left, right, front, rear, etc. refer exclusively to the exemplary representation and position of the pivot fitting, lever, toothed-ring disc, catch, force-transmitting shaft, cone, friction disc and the like selected in the respective figures. These terms are not to be understood restrictively, i.e., due to different working positions or the mirror symmetrical design or the like, these references may change. 
     In  FIG. 1 , the reference sign  1  altogether denotes an embodiment variant of a pivot fitting according to the invention. 
     Such a pivot fitting  1  serves in particular to enable a pivoting movement of movable furniture parts on pieces of furniture, such as for example an armrest  103  or a backrest  102 , headrest or footrest of a piece of furniture  100  designed as a piece of seating or reclining furniture, as shown by way of example in  FIGS. 27 and 28 . 
     As shown in  FIG. 1 , in the embodiment variant shown here, the pivot fitting  1  has a first lever  2  and a second lever  3 . The two levers  2 ,  3  are mounted so as to be pivotable relative to one another about a pivot axis D from an initial position through a predetermined angle in an adjustment direction V and a return direction R. 
     A clamping mechanism of the pivot fitting  1  arranged here between two lever heads  23   a  and  23   b  of the first lever  2  is designed in such a way that the two levers  2 ,  3  can be fixed in different angular positions within the predetermined angle relative to each other against a torque acting in the return direction R and can be pivoted in the return direction R when the clamping mechanism is deactivated. 
     This allows, for example, the adjustment of the armrest  103  of the piece of furniture  100 , in which the armrest  103  is connected to the second lever  3  while the first lever  2  is connected to the body  101  of the furniture, so as to pivot the armrest  103  to a position that is comfortable for the user and to latch it in the pre-desired position. 
     As shown in  FIGS. 2 and 3 , the clamping mechanism comprises a force-transmitting shaft  6  coupled to the second lever  3  in a rotationally fixed manner. 
     A toothed-ring disc  4  having outer toothing structure  41  formed on the outer edge is placed on this force-transmitting shaft  6 . 
     It is also conceivable to design the pivot fitting  1  without a second lever  3 . 
     The clamping mechanism acts between the lever  2  and the force-transmitting shaft  6 , thus allowing an angular adjustment between the lever  2  and the force-transmitting shaft  6 . 
     If the pivot fitting  1  comprises a second lever  3  mounted on the force-transmitting shaft  6 , the clamping mechanism thus also allows an angular adjustment between the first lever  2  and the second lever  3 . 
     It is expressly noted that the second lever  3  can also be part of a piece of furniture that is placed directly on the force-transmitting shaft  6 . 
     The shape of the lever  3  may therefore differ significantly from the flat and elongated shape shown in the figures, for example the use of tubes, in particular rectangular or square tubes, is also conceivable. 
     Furthermore, a catch  5  loaded by a spring element  10  in the direction of this outer toothing structure  41  of the toothed-ring disc  4  is pivotably mounted on the first lever  2 . The catch  5  is thereby in engagement with this outer toothing structure  41  in a latching position. 
     Furthermore, the clamping mechanism comprises a first control disc  7 , which is rotatably mounted about the common axis D and by means of which the catch  5  can be disengaged from the outer toothing structure  41  of the toothed-ring disc  4  after passing the predetermined angle from the initial position in an adjustment direction V. 
     In this out-of-engagement position, the second lever  3  can be pivoted back to the initial position relative to the first lever  2  by passing over the predetermined angle in a return direction R. 
     As further shown in  FIGS. 2 to 4 , at least one friction disc  8 , which is pushed onto the force-transmitting shaft  6  in a rotationally fixed and axially secured manner, is slid onto the toothed-ring disc  4 . 
     The toothed-ring disc  4  is frictionally held on the at least one friction disc  8  against rotation about the axis D up to a predetermined torque M. 
     Frictionally retaining the toothed-ring disc  4  relative to the force-transmitting shaft  6  up to a predetermined torque M thus represents a cost-effective overload safety device for such a pivot fitting  1 , which is less of a build-up compared to an overload safety device designed as a separate structural unit. 
     As shown in  FIGS. 3 to 5 , according to a preferred embodiment variant, an inner circumferential edge  42  of the toothed-ring disc  4  is pushed onto a cone  9  arranged on the force-transmitting shaft  6  in a conical shape. In this case, the one friction disc  8  is in pressing contact with the toothed-ring disc  4  on the side of the smaller diameter of the inner circumferential edge  42  of the toothed-ring disc  4 . 
     In one embodiment variant, the cone  9  may be integrally formed directly on the force-transmitting shaft  6 . 
     According to an alternative preferred embodiment variant, the cone  9  is mounted on the force-transmitting shaft  6 . 
     In particular, the cone  9  is designed as a radially slotted clamping ring, as shown in  FIG. 5 . The cone  9  shown there has an internally toothed inner diameter  92 , for rotationally fixed attachment to the force-transmitting shaft  6  provided with an outer toothing structure  61 . 
     The outer circumferential edge  91  of the cone  9  is conically shaped. 
     For easier application of the cone  9  to the force-transmitting shaft  6 , the cone  9  shown in  FIG. 5  is formed with a slot  93 . When the friction disc  8  is pressed onto the cone  9 , the internal toothing structure of the cone  9  is pressed onto the outer toothing structure of the force-transmitting shaft  6 , so that the cone  9  is axially clamped on the force-transmitting shaft  6 . 
     Preferably, the cone angle of the outer circumferential edge  91  of the cone  9  is between 15° and 35°. Particularly preferably, the cone angle is between 20° and 30°. 
     The friction disc  8  is preferably pressed onto the force-transmitting shaft  6  against the toothed-ring disc  4  with an interference fit. 
     Alternatively, other axial fixations of the friction disc  8  are conceivable, for example by applying a weld seam, a nut, or the like. 
     As an alternative to mounting the toothed-ring disc  4  via a cone  9  shown in  FIGS. 3 to 5 , it is also conceivable to slide such a friction disc  8  onto the force-transmitting shaft  6  on both sides of the toothed-ring disc  4 . 
     This also allows a sufficiently large friction between the friction discs  8  and the toothed-ring disc  4  to ensure the function of an overload protection. 
     As further shown in  FIG. 3 , the at least one friction disc  8  is preferably designed as a disc spring. 
     The predetermined torque M, up to which the toothed-ring disc  4  is frictionally held against rotation about the axis D by the at least one friction disc  8 , is preferably at least 70 Nm, particularly preferably at least 80 Nm. 
     As further shown in  FIG. 3 , the first control disc  7  is placed on the force-transmitting shaft  6  on the side of the toothed-ring disc  4  facing away from the friction disc  8 . 
     The first control disc  7  can be pivoted relative to the force-transmitting shaft  6  and is secured axially by a disc-spring-like spring element  13 . 
     The spring element  13  is thereby secured against rotation by teeth  132  on an inner circumference  131  of the spring element  13  on the force-transmitting shaft  6 . 
     As shown in  FIG. 2 , the second control disc  11  is arranged on the side of the friction disc  8  facing away from the toothed-ring disc  4  on the force-transmitting shaft  6 . The second control disc  11  has a switching arm  111  and an elongated hole  112 . A single tooth  113  engages the outer toothing structure of the force-transmitting shaft  6 . 
     As shown in  FIG. 7 , in place of the second control disc  11 , it is also conceivable to form on the friction disc  8  a changeover contour  82  which extends radially outwardly from the circumferential edge of the friction disc  8  through a predetermined angle. 
     The catch  5  has a plurality of teeth  52  at a first end of a catch arm  51 , which engage in use with the outer toothing structure  41  of the toothed-ring disc  4 . 
     At the opposite end of the catch arm  51 , pivot pins  53  protrude on both sides, with which the catch is pivotably fixed to pivot pin receptacles  27  of the lever heads  23  of the first cover  2   a  and the second cover  2   b.    
     On the side of the catch arm  51  facing the outer toothing structure  41  of the toothed-ring disc  4  in the assembled position, a recess  54  is formed between the toothing  52  and the pivot pin  53  for accommodating the changeover contour  71  of the first control disc  7 . 
     For limiting the pivoting angle between the two levers  2 ,  3 , control pins  12  are fixed or integrally formed on the covers  2   a ,  2   b  of the first lever  2 , which in the embodiment variant shown in  FIGS. 8 and 9  strike in respective end positions against stop edges of a disc-shaped stop  15 , wherein the disc-shaped stop  15  is connected in a rotationally fixed manner to the second lever  3  or the force-transmitting shaft  6 . 
     In an alternative embodiment variant, these stops are formed by lateral stops  34  on the second lever  3 , as shown in  FIGS. 11 and 12 . 
     The function of the pivot fitting  1  in normal operation is described below with reference to  FIGS. 14 to 19 . 
     In  FIG. 14 , an exemplary position of the pivot fitting  1  is shown that has already been pivoted slightly in the adjustment direction V, in which the catch  5  engages in the outer toothing structure  41  of the toothed-ring disc  4 . 
       FIG. 15  shows a position of the pivot fitting  1  pivoted further in the adjustment direction V. 
     Here, the catch  5  is always pressed against the outer toothing structure  41  of the toothed-ring disc  4  by the spring element  10 , which is in the form of a spring plate. The alignment of the outer toothing structure  41  of the toothed-ring disc  4  and the teeth  52  of the catch  5  is such that, in the adjustment direction V, the catch  5  can be displaced tooth by tooth of the outer toothing structure  41  of the toothed-ring disc  4 . 
     In the position shown in  FIG. 16 , the switching arm  111  of the second control disc  11  has reached the outermost tooth of the toothing of the catch  5 . 
     The outermost tooth  52  is thereby formed with a run-up chamfer  55 . As a result, upon further rotation of the force-transmitting shaft  6  and thus of the second lever  3  in the adjustment direction V, the switching arm  111  can be pushed onto the outer teeth  52  of the catch  5 , whereby the teeth  52  of the catch  5  disengage from the outer toothing structure  41  of the toothed-ring disc  4 , as shown in  FIG. 17 . 
     As further shown by dashed lines in  FIG. 17 , in this position, the changeover contour  71  of the first control disc  7  is engaged in the recess  54  of the catch  5 . 
     Furthermore, the control pin  12  rests in the recess  72  of the first control disc  7  at the right edge of this recess  72 . 
     If the second lever  3  or the force-transmitting shaft  6  is now moved in the opposite direction, i.e., in the return direction R, this causes the second control disc  11  to be pivoted about the switching arm  111  currently fixed on the teeth  52  of the catch  5  by the engagement of the control tooth  113  on the inner circumference of the second control disc  11  by the force-transmitting shaft  6  in the elongated hole  112  in the center of the second control disc  11 . 
     At the same time, during this rotation of the force-transmitting shaft  6  in the return direction, the control pin  12  reaches the left edge of the recess  72  of the first control disc  7 . 
     During the subsequent further rotation of the force-transmitting shaft  6  in the return direction R, the changeover contour  71  of the first control disc  7  is pushed onto a toothless plane of the arm  51  of the catch  5 , so that the teeth  52  of the catch  5  remain out of engagement with the outer toothing structure  41  of the toothed-ring discs  4  and the pivot fitting  1  can thus be pivoted back into the initial position. 
     In the event of an overload acting on the pivot fitting  1 , the function of the overload protection is such that, in the case or any pivot position or the levers  2 ,  3  of the pivot fitting  1  relative to one another, from a torque M caused by the friction between the friction disc  8  and the toothed-ring disc  4 , the toothed-ring disc  4  begins to slip relative to the friction disc  8  about the axis of rotation D and the two levers  2 ,  3  can thus be pivoted relative to one another, as long as the force exerted on the levers is greater than the predetermined torque M. 
     If the force exerted on the levers decreases and falls below the predetermined torque M, the frictional adhesion between the friction disc  8  and the toothed-ring disc  4  resumes, so that the normal function of the pivot fitting  1  resumes. 
     In the alternative embodiment variants of a pivot fitting according to the invention shown in  FIGS. 20 to 26 , the clamping mechanism has a plurality of toothed-ring discs  202 ,  302  arranged side by side on the force-transmitting shaft  6  instead of the one toothed-ring disc  4 . 
     A friction disc  203 ,  303 ,  304 , which is held in a rotationally fixed manner on the force-transmitting shaft  6 , is arranged between each of two such toothed-ring discs  202 ,  302 . 
     In the embodiment variant shown in  FIGS. 20 and 21 , three such toothed-ring discs  202  are provided. 
     Each of these toothed-ring discs  202 ,  302  has an annular inner circumferential edge  221 ,  321  and an outer toothing structure  222 ,  322  in which the catch  5  engages. 
     In both the embodiment variants shown in  FIGS. 20 and 21  and the embodiment variants shown in  FIGS. 22 and 23  and  FIGS. 24 to 26 , the friction discs  8  rest against the outer surfaces of the outer toothed-ring discs  202 ,  302 , pressing in the axial direction against the toothed-ring discs  202 ,  302 . 
     Analogous to the embodiment variant shown in  FIG. 13 , a first control disc  201 ,  301  is slid onto the force-transmitting shaft  6  on an outer side of one of the friction discs  8 . 
     This first control disc  201 ,  301  also has an annular inner circumferential edge  211 . 
     Extending from an outer circumferential edge, identically to the embodiment variant shown in  FIG. 3 , is a changeover contour  212  serving the same purpose as the changeover contour  71  of the first control disc  7  according to the embodiment variant shown in  FIG. 3 . 
     In contrast to the embodiment variant shown in  FIG. 3 , a tab  213  is formed here on the opposite circumferential edge of the first control disc  201 , which tab extends perpendicularly to the plane of the control disc  201  in the direction of the disc-spring-like spring element  13  on the side of the first control disc  201  facing away from the toothed-ring discs  202 . 
     In the installed state, this tab  213  protrudes into a recess provided for this purpose on the first lever  2 , which in this case has an elongated-hole-shaped recess instead of the control pin  12 , in which recess the tab  213  can be pivoted through a changeover angle in the circumferential direction of the first control disc  201 . 
     Similar to the friction disc  8  shown in  FIG. 7 , the friction discs  203  disposed between the toothed-ring discs  202  have a changeover contour  232  extending radially outwardly from the outer circumference of the friction discs  203 . 
     The friction discs  203  further comprise an inner circumferential edge with an internal toothing structure  231 , analogous to the friction discs  8 . 
     In contrast to the embodiment variant shown in  FIGS. 20 and 21 , in which three toothed-ring discs  202  are provided with two interposed friction discs  203 , in the embodiment variant shown in  FIGS. 22 and 23  two toothed-ring discs  202  are provided with one interposed friction disc  203 . In all other respects, the structure of the clamping mechanism of these two embodiments is identical. 
     The embodiment variant of a further alternative clamping mechanism shown in  FIGS. 24 to 26  preferably comprises three toothed-ring discs  302 , analogous to the embodiment variant shown in  FIGS. 20 and 21 , having a respective friction disc  303 ,  304  arranged between two of the toothed-ring discs  302 . 
     In contrast to the embodiment variants described with reference to  FIGS. 20 to 23 , in this embodiment variant one of the friction discs  304  has an elevation  343  on its outer circumference  342 , which is adjoined by a recess  344  for accommodating a changeover element  305 . 
     The changeover element  305  is thereby adapted to the inner contour of the recess  344  in such a way that it can be pivoted by a predetermined switching angle within the recess  344  about a pivot axis which is disposed coaxially to the pivot axis of the force-transmitting shaft  6 , but radially offset therefrom outside the force-transmitting shaft  6 , as can also be seen well in  FIG. 26 . 
     In this regard, the recess  344  has a substantially V-shaped receiving area for receiving a V-shaped partial section of the changeover element  305 . 
     In this regard, a neck of the changeover element  305  has a circumferential width such that it can pivot within the recess  344  through a predetermined switching angle. 
     The switching angle is preferably between 8° and 12°. The thickness of this changeover element  305 , viewed in the longitudinal direction of the force-transmitting shaft  6 , is thereby less than the thickness of the friction disc  304 . 
     In the embodiment variant shown herein, the friction disc  304  is larger than the thickness of the friction disc  303 . 
     The slightly smaller thickness of the changeover element  305  compared to the friction disc  304  makes it possible, in a simple manner, to prevent the changeover element  305  from being jammed by the friction discs  8  pressing against the toothed-ring discs  302  from the outside. 
     Although the invention has been illustrated and described in detail by way of preferred embodiments, the invention is not limited by the examples disclosed, and other variations can be derived from these by the person skilled in the art without leaving the scope of the invention. It is therefore clear that there is a plurality of possible variations. It is also clear that embodiments stated by way of example are only really examples that are not to be seen as limiting the scope, application possibilities or configuration of the invention in any way. In fact, the preceding description and the description of the figures enable the person skilled in the art to implement the exemplary embodiments in concrete manner, wherein, with the knowledge of the disclosed inventive concept, the person skilled in the art is able to undertake various changes, for example, with regard to the functioning or arrangement of individual elements stated in an exemplary embodiment without leaving the scope of the invention, which is defined by the claims and their legal equivalents, such as further explanations in the description. 
     LIST OF REFERENCE SIGNS 
     
         
           1  Pivot fitting 
           2  First lever 
           2   a  First cover 
           2   b  Second cover 
           21  Lever arm 
           22  Bending range 
           23   a  Lever head 
           23   b  Lever head 
           24  Bore 
           25  Receptacle 
           26  Bore 
           27  Pivot pin receptacle 
           3  Second lever 
           31  Lever arm 
           32  Lever head 
           33  Bore 
           34  Stop 
           4  Toothed-ring disc 
           41  Outer toothing structure 
           42  Inner circumferential edge 
           5  Catch 
           51  Catch arm 
           52  Teeth 
           53  Pivot pin 
           54  Recess 
           55  Run-up chamfer 
           6  Force-transmitting shaft 
           61  Outer toothing structure 
           62  Groove 
           7  First control disc 
           71  Changeover contour 
           72  Recess 
           8  Friction disc 
           81  Internal toothing structure 
           82  Changeover contour 
           9  Cone 
           91  Outer circumferential edge 
           92  Internal toothing structure 
           93  Slot 
           10  Spring element 
           101  Spring steel strip 
           102  Tooth 
           11  Second control disc 
           111  Switching arm 
           112  Elongated hole 
           113  Tooth 
           12  Control pin 
           13  Spring element 
           131  Inner circumference 
           132  Tooth 
           14  Disc 
           15  Stop 
           151  Stop edge 
           100  Piece of furniture 
           161  Furniture body 
           162  Backrest 
           163  Armrest 
           201  First control disc 
           211  Inner diameter 
           212  Changeover contour 
           213  Tab 
           202  Toothed-ring disc 
           221  Inner circumferential edge 
           222  Outer teething structure 
           203  Friction disc 
           231  Internal toothing structure 
           232  Changeover contour 
           301  First control disc 
           311  Inner diameter 
           312  Changeover contour 
           313  Angled region 
           314  Recess 
           302  Toothed-ring disc 
           321  Inner circumferential edge 
           322  Outer toothing structure 
           303  Friction disc 
           331  Internal toothing structure 
           304  Friction disc 
           341  Internal toothing structure 
           342  Outer circumference 
           343  Elevation 
           344  Recess 
           305  Changeover element 
         D Axis of rotation 
         V Adjustment direction 
         R Return direction 
         α maximum adjustment angle 
         M Torque 
         d R  Thickness of the friction disc 
         d U  Thickness of the changeover element