Abstract:
A chair is provided in which the position and movement of the backrest, which is pivotally carried on a backrest carrier, is effected by movement of the seat top, which, in turn, is subjected to the weight of the seat user. The amount of the user&#39;s weight differently affects the position of the backrest through the use of pivoting linkages and a tension spring.

Description:
This application is a continuation-in-part of application Ser. No. 09/133,209, filed Aug. 13, 1998 now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to a chair, in particular an office chair comprising a seat top with at least one front seat support arm and at least one rear seat support arm projecting at the underside of the seat top, a seat carrier which is securely connected to a central chair column or several chair legs, and a backrest which is arranged at a backrest carrier firstly extending under the seat top backwards and thereafter upwards with the backrest carrier supported by means of a crosswise horizontally extending backrest carrier swivelling joint with the front seat support arm articulately connected to the seat carrier through at least one lever wherein the rear seat support arm offset backwards from the backrest carrier swivelling joint is articulately connected to the backrest carrier by means of a crosswise horizontally extending rear seat joint, and wherein a spring arrangement is provided under the seat top with the spring arrangement exerting a biasing force upwards upon the seat top and forwardly upon the backrest. 
     A chair of the type mentioned is known from DE 43 13 301 C2. The spring arrangement provided for this chair consists of a pressure spring which is arranged between the seat carrier and the seat top. By the arrangement of the single parts of this chair as explained above the chair offers the user the opportunities to selectively sit upwards on this chair or in a reclined position. In the reclined position the seat top will lower in the rear part, whereby at the same time the backrest with the backrest carrier will pivot backwards. 
     It is a disadvantage of this known chair that it offers no possibility to adapt the force acting upon the back of the user to the user, in particular to the body weight thereof. Therefore the known chair is only a compromise regarding the force acted upon the back of the user by the backrest, which in many cases is not optimal, in particular when the chair is used by light weight or heavy weight users. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the invention to provide a chair of the type mentioned above which avoids the disadvantages mentioned, and wherein the force acted upon the back of the user by the backrest may be adapted to the body weight of the user, wherein an automatic adaption must be possible. 
     For attaining this object, a chair of the type mentioned above is proposed characterized in that the lever connecting the front seat support arm with the seat carrier is designed as a two-arm swivelling lever, pivotable around a crosswise horizontally extending swivelling axis, and supported at the seat carrier, with the one lever arm of the swivelling lever articulately connected to the front seat support arm, and with the other lever arm of the swivelling lever connected to one end of the spring arrangement. The other end of the spring arrangement is connected to the backrest carrier in spaced relation from the backrest carrier swivelling joint. 
     It is essential for this novel chair that the single pressure spring acting directly onto the seat top used in the state of the art is replaced by a spring arrangement with the biasing force thereof variable by means of the two-arm swivelling lever, wherein the variation is automatically attained by the weight load of the seat top by the user of the chair. Without a manual operation it is thereby attained that with light weight users of the chair, the backrest exerts only a smaller force upon the back of the user, and that with heavy weight users of the chair, the backrest exerts a larger force upon the back of the user, such that depending upon the weight of the user of the chair, the back of the user is always supported with an adequate and suitable force by the backrest. At the same time, the mechanical effort for realizing this adaption of the force of the backrest is relatively small, such that the chair according to the invention may be manufactured at low cost, and may be produced in a stable, safe, and durable way without much effort. 
     In the first embodiment of the chair according to the invention it is provided that at least one tension spring is the spring arrangement, wherein the second lever arm of the swivelling lever connected to the front end of the tension spring points backwards, and wherein the connection of the rear end of the tension spring with the backrest carrier is offset upwards from the backrest carrier swivelling joint. With this arrangement of the spring arrangement the required function is attained in a technically simple and reliable fashion. Furthermore the production costs are kept low, and it is only relatively little space required for the accommodation of the spring arrangement. 
     Furthermore, it is preferably provided that the swivelling lever is designed as a strain lever or as a lever angled up to 45° at maximum. This design of the swivelling lever has the advantage that the lever may be easily manufactured, and that a flat construction of the parts of the chair mechanism arranged under the seat top is possible. This will reduce the room requirement for the chair mechanism under the seat top, and improves the optical appearance of the chair, in particular when viewed from the side. 
     In order to willingly influence and vary the support force acted upon the back of the user of the chair by the backrest, optionally the force of the tension spring acted upon the backrest may be adjustable. 
     For this reason, in a further embodiment it is provided that the connection point of the rear end of the spring arrangement at the backrest carrier is adjustable in the distance from the backrest carrier swivelling joint. By this means, the lever arm between the spring arrangement and the backrest carrier may be varied in the length thereof, which takes care of the required change of the backrest force. 
     Furthermore, it is preferably provided that the rear end of the spring arrangement is connected to the backrest carrier through a pivotable adjusting lever which may be locked. By this design, the biasing force of the spring arrangement is hardly changed, however, the lever effect between the spring arrangement and the backrest carrier is varied in dependence from the corresponding position of the adjusting lever. 
     Preferably at least one helical leg, torsion bar, gas pressure, rubber or elastomer spring is provided as the spring arrangement wherein such springs are cheap and easily accessible construction members which may be purchased in the market without any problems. 
     To lock the chair in at least one base position when not in use, and in case that the user of the chair wants to use it in a fixed position, and e.g., does not want the reclined position, it is provided that the backrest carrier pivotable around the backrest carrier swivelling joint may be locked in continuous or stepped swivelling positions. 
     A first embodiment of the chair with the locking capability of the backrest carrier mentioned before provides that at least one one-arm catch lever pivotable around a horizontal swivelling axis is connected to the backrest carrier in vertically spaced relationship from the back-rest carrier swivelling joint with the catch lever substantially extending horizontally to the seat carrier, and freely displaceable in its longitudinal direction in relation to the seat carrier in a first, automatically occupied release position, and in a locking fashion engaging a locking element in a second locking position occupied by adjusting an actuating element, wherein the locking element prevents a displacement of the catch lever in relation to the seat carrier. When the catch lever is in its release position the movements of the seat top and the backrest in relation to the seat carrier are not hindered, only when the catch lever takes its locking position by adjusting the actuating element a further movement of the seat top at the backrest in relation to the seat carrier and in relation to each other is prevented. 
     A preferred further development provides that the locking element is at least one bolt extending through an elongated hole in the catch lever, wherein the elongated hole comprises at least one indentation extending downward for receiving the bolt in a locking position. In the release position of the catch lever, the bolt extends through the elongated hole such that the bolt extends through the elongated hole such that the bolt and the catch lever may freely move in relation to each other. When the catch lever is raised, and the bolt gets into the indentation, this movement is no longer possible and the seat top and the backrest are locked. This locking position is secured by the spring force of the spring arrangement, and the friction between the bolt and the indentation is such that the locking of the seat top and the backrest carrier are automatically maintained. Only when the seat top and the backrest again are loaded by a user is the spring force influenced such that the locking is released, wherein the catch lever will fall downwards around its swivelling axis and again attains its release position. 
     Thereto an alternate embodiment of the chair provides that the locking element is formed by several projecting teeth extending in parallel at a radius around the swivelling axis of the catch lever with the teeth engageable and disengageable with corresponding teeth attached to the catch lever. With this embodiment of the locking element and catch lever, the same function is attained as has been described above. Moreover with this second embodiment a finer stepping of the locking positions is possible. 
     As an alternate to the two embodiments described before. the spring arrangement may be a gas pressure spring which may be locked in continuous or stepped positions. This gas pressure spring to be locked offers the desired spring force and at the same time enables a locking of the backrest carrier, and the backrest connected therewith, in a desired position which may be selected within the total range of movement of the backrest carrier. When the gas pressure spring is released, the chair has the movability of the backrest which was described before, wherein a swivelling of the backrest backwards in connection with a lowering of the rear part of the seat top is possible solely by displacing the load of the user of the chair. 
     The ratio of the movements of the rear end of the seat top on the one hand, and the backrest on the other hand is fixed by the distance of the rear seat joint from the backrest carrier swivelling joint. In a simple embodiment of the chair, a fixed positioning may be selected which is suitable for most users. Alternately it is provided that the rear seat joint is adjustable and may be locked in its position in relation to the backrest carrier in the longitudinal direction thereof. In this way the ratio of the movements of the rear end of the seat top and the backrest may be changed at will, wherein the rear seat joint is pushed in its position in relation to the seat carrier either frontally, i.e., closer to the backrest carrier swivelling joint, or backwards, i.e., further away from the backrest carrier swivelling joint, and then locked in the desired position. When the rear seat joint is positioned closer to the backrest carrier swivelling joint, a larger swivelling movement of the backrest will result with a simultaneous lowering of the back end of the seat top, vice versa with a further backwards positioned rear seat joint, a smaller swivelling angle of the backrest will result with a fixed lowering of the seat top. 
     Finally, it is provided that the chair according to the invention that two front and two rear seat support arms, two backrest carriers, and two springs are provided symmetrical in relation to the chair longitudinal middle plane. In this way the chair, in particular the seat top and the backrest thereof, is not susceptible against tilting forces, wherein simultaneously an economical production of the chair remains because all parts which are used in pairs may be identical. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the following embodiments of the chair according to the invention are explained referring to a drawing. 
     FIG. 1 shows a chair in a side elevational view, when used by a light weight user, in an upright position. 
     FIG. 2 shows the chair of FIG. 1 in a side elevational view when used by a heavy weight user. 
     FIG. 3 shows the chair of FIG. 1 in a side elevational view when used by a light weight user, in a reclined position. 
     FIG. 4 shows the chair of FIG. 1 in a side elevational view when used by a heavy weight user, in reclined position. 
     FIG. 5 shows a changed embodiment of the chair of FIGS. 1-4 in an enlarged partial side elevational view. 
     FIG. 6 shows the chair according to FIGS. 1-4 in a bottom elevational view. 
     FIG. 7 shows an embodiment of the chair according to FIG. 1 in a side elevational view additionally with a locking in a release position. 
     FIG. 8 shows the chair of FIG. 7 in an enlarged partial side elevational view, now with the locking in a locking position. 
     FIG. 9 shows an embodiment of the chair according to FIGS. 1-4 in an enlarged partial side elevational view with a changed design of the locking in a release position. 
     FIG. 10 shows a further embodiment of the chair of FIG. 1 in a side elevational view. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In FIGS. 1-4, embodiments of a chair  1  are shown which, in this case, is an office swivelling chair. The chair  1  comprises a seat top  10  and a backrest  20  which is behind the seat top, which is at the right side of the figure. From the underside of the seat top  10  a front seat support arm  11  extends downwardly and a rear seat support arm  12  extends downwardly. From the backrest  20  a backrest carrier  21  extends firstly downwardly and then forwardly below the seat top  10 . The backrest  20  is articulately connected with the backrest carrier  21  by means of a backrest bearing  22  with a horizontally and crosswise extending swivelling axis in relation to the chair  1 . 
     Below the seat top  10  a seat carrier  30  is provided which is securely connected to the upper end of a central chair column  31 . The chair column  31  is only illustrated in the upper part thereof. At its lower part a standard and known foot arrangement is provided. Furthermore, the chair column  31  may be adjustable in its height and spring loaded, as well known. 
     The seat carrier  30  extends with the most part of it forwardly of the chair column  31  in the direction of the front seat support arm  11 . At the front end, a two-arm swivelling lever  40  is supported at the seat carrier  30 , with the swivelling lever pivotable around a swivelling axis  43  extending horizontally and crosswise in relation to the chair  1 . A front lever arm  41  of the swivelling lever  40  is articulately connected to the lower end of the front seat support arm  11  through a joint bolt  11 ′. A front end of a tension spring  50 , in this case a helical tension spring, is connected with a rear lever arm  42  of the swivelling lever  40  at a connection point  45 . The arms  41 ,  42  are angled from each other between 0° and 45°. 
     Rearwardly of the chair column  31 , to the right in the drawing, the seat carrier  30  is connected with the lower front end of the backrest carrier  21  by means of a backrest carrier swivelling joint  23 . This backrest carrier swivelling joint  23  also comprises a swivelling axis extending horizontally and crosswise in relation to the chair  1 . 
     Above the backrest carrier swivelling joint  23 , and spaced therefrom, a rear end of the tension spring  50  is connected to the backrest carrier  21  at a further connection point  25 . 
     The rear sear support arm  12  is articulately connected with the backrest carrier  21  by means of a rear seat joint  13 , wherein the rear seat joint  13  is spaced rearwardly from the backrest carrier swivelling joint  23 . Also, this rear seat joint  13  comprises a swivelling axis extending horizontally and crosswise in relation to the chair  1 . 
     In FIG. 1 the chair  1  is illustrated in the position wherein the user has an upright sitting position and sits on it, wherein the user of the chair is not illustrated. In this case only a relatively small force acts upon the seat top  10 . The result is that the swivelling lever  40  is swivelled counterclockwise only a relatively small distance against the tension force of the spring  50 , wherein the front seat support arm  11  presses the front lever arm  41  downwards with a correspondingly small force. In this position of the chair when the load is small, the backrest carrier  21  presses against a stop, which is not illustrated, with the stop preventing a further forwardly swivelling of the backrest  20  beyond the position shown in FIG.  1 . 
     FIG. 2 of the drawing illustrates the chair  1  in the same way as in FIG. 1, however, in a position when a heavy weight user sits on it. In this case a larger weight load acts upon the seat top  10 , which leads to the fact that the front seat support arm  11  acts with a larger force upon the front lever arm  41  of the swivelling lever  40 . This larger force has the consequence that the swivelling lever  40  is pivoted counterclockwise in a larger swivelling angle around the swivelling axis  43  than shown in FIG.  1 . This larger swivelling movement of the swivelling lever  40  results in a larger tension of the tension spring  50 . Hereby it is attained that a larger lever force is acted upon the backrest carrier  21  by the rear end of the spring  50  and the connection point  25 , leading to a forwardly pivoting of the backrest  20 . Thereby it is attained, that when the chair  1  is used by a heavy weight user, the backrest  20  is biased with a larger frontal force by the spring  50  leading to an automatic adaption to the occurring load. 
     FIGS. 3 and 4 of the drawing illustrate the chair  1  in a position which occurs in a reclined position of the user, wherein FIG. 3 illustrates the position with a light weight user, and FIG. 4 illustrates the position with a heavy weight user of the chair  1 . The difference of the positions of the chair  1  in FIG.  3  and FIG. 4 is that in FIG. 3, the swivelling lever  40  is pivoted counterclockwise to a smaller degree than is the case with the swivelling lever  40  in FIG.  4 . The different degree of swivelling lever  4  results from the different weight load acting upon the seat top  10  by the user, which is smaller in FIG. 3 as compared with the case in FIG.  4 . Also in this position of the chair  1 , the weight exerted upon the back of the user by the backrest  20  is adapted to the body weight of the user because in the case of FIG. 3, the tension spring  50  is tensioned to a lesser degree than in FIG.  4 . The greater the tension spring  50  is biased, the larger is the forward force acting upon the back of the user of the chair by the backrest  20 . Also, and more so in the reclined position of the chair user, the backrest force will adapt to the requirements of the body weight of the user. 
     As a measure for the spring tension in FIGS. 1-4, the distance of the connection points  25 ,  45  of the two spring ends of the tension spring  50  is illustrated. When comparing FIGS. 1 and 2, spring length X 1  is smaller than spring length X 2 . Therefore, in FIG. 1 the tension force of the tension spring  50  is smaller than shown in FIG.  2 . When comparing FIGS. 3 and 4 the length of the tension spring  50  in the one case is X 1 ′, and in the other case X 2 ′, with X 1 ′ smaller than X 2 ′. 
     FIGS. 1-4 illustrate that with a chair  1  in an upright position of the user according to FIGS. 1 and 2, the seat top extends forwardly with a small downward directed inclination. This inclination is ergonomicly favorable and desired because the blood circulation in the user&#39;s legs is not hindered. When the chair user reclines, in addition to besides a pivoting of the backrest  20  backwards at the same time, a lowering of the rear part of the seat top  10  will occur which in this reclined position is sensed as pleasant. This enables a relaxed sitting position, and at the same time avoids a shifting of the backrest  20  at the chair user&#39;s back which is sensed as unpleasant. 
     In FIG. 5 a variation of this chair with additional devices is illustrated, wherein in this case, only a section of the chair below the seat top is illustrated. 
     A first additional feature with this embodiment of the chair according to FIG. 5 is that the backrest carrier swivelling joint  23  may be locked in desired position. For this reason, at the backrest carrier swivelling joint  23 , a locking mechanism with a manually adjustable locking lever  24  is provided, wherein in the one position of the locking lever  24 , the backrest carrier swivelling joint  23  is freely movable, and wherein in the other position of the locking lever  24 , the backrest carrier swiveling joint  23  may be locked in a previously selected position and then is stationary. In this way the chair user may prevent a swivelling movement of the backrest carrier  21  with the backrest  20 . 
     A further additional feature is that the connection point  25  of the rear end of the spring  50  is variable in its position in relation to the backrest carrier swivelling joint  23 , and may be locked in a desired position, wherein the means for changing the position and locking it in this case are provided by a pivotable adjustment lever  25 ′ which may be locked. A swivelling axis  26 ′ of the adjustment lever  25 ′ extends parallel to the swivelling axis of the backrest carrier swivelling joint  23 , and offset rearwardly therefrom through the backrest carrier  21 . A hand wheel threaded spindle  26  at the backrest carrier  21  provides the adjustment. By this means, the lever effect of the tension spring  50  is preselectable in order to provide a base position of the force acted by the backrest  20  upon the back of a user. The adjustment of the connection point  25  is attained along an arcuate course at a radius around the swiveling axis  26 ′. 
     Finally it is illustrated at the right side of FIG. 5 that the rear seat joint  13 , in its position in relation to the backrest carrier  21 , is adjustable in longitudinal direction thereof and may be locked. For this reason, a guide slot  15  is provided in the backrest carrier  21  along which the rear seat joint  13  is adjustable in longitudinal direction of the backrest carrier  21 . A locking mechanism is connected to the rear seat joint  13  with the locking mechanism to be released if desired through a second locking lever  14 , and to be secured after reaching the desired position of the rear seat joint  13 . By this adjustability of the rear seat joint  13 , the transfer ratio between the lowering angle of the rear end of the seat top  10  and the swivelling angle of the backrest carrier  21  with the backrest  20  is changed, whereby an adaption to the individual requirements of the chair user is possible in an even greater range. 
     Regarding the numerals in FIG.  5  and further details, reference is made to the above description in particular to FIG.  1 . 
     FIG. 6 of the drawing illustrates a bottom view of a chair wherein the seat top and the backrest are not shown. In the middle of FIG. 6 in a section the chair column  31  is visible with the seat carrier  30  secured at the upper end which is facing away from the viewer. At the upper end of the seat carrier  30  the backrest carrier swivelling joint  23  extends by means of which two backrest carriers  21  extending in parallel with each other are articulately connected to the seat carrier  30 . By means of the rear seat joint  13  two seat support arms  12  running also in parallel with each other are articulately connected to the backrest carriers  21 . 
     At the lower end of the seat carrier  30  the swivelling axis  43  is visible whereabout the two one-armed swivelling levers  40  are pivotable. Beside each swivelling levers  40  are pivotable. Beside each swivelling lever  40  a front seat support arm  11  is positioned which together with the two rear seat support arms  12  support the seat top which is not illustrated. The front lever arm  41  of each swivelling lever  40  is articulately connected with the front seat support arm  11  through a joint bolt  11 ′ The one end of the helical tension spring  50  at a spring connection point  45  engages the correspondingly other lever arm  42  of the swivelling lever  40 . The correspondingly other rear end of the spring  50  is secured at a spring connection point  25  at the backrest carrier  21 . 
     In FIG. 6 the symmetrical arrangement of the single part of the mechanics of the chair is clear to be symmetrical in relation to a longitudinal middle plane P shown as a dash-dotted line. By this symmetrical arrangement the movable parts of the chair are particularly stable ensuring a reliable function over a long period of time. 
     In FIGS. 7 and 8 an embodiment of the chair  1  is illustrated wherein a locking of the backrest  20  and the seat top  10  is possible in two preselected positions. For this end a catch lever  60  is connected to the front end of the backrest carrier  21  (at the left end in the drawing) above the backrest carrier swivelling joint  23  by means of a swivelling axis  63  with the catch lever extending in parallel with the seat carrier  30  forward, i.e., to the left in the drawing. The catch lever  60  is freely pivotable around a swivelling axis  63  and under influence of gravity takes the position illustrated in FIG.  7 . Furthermore the catch lever  60  comprises two elongated holes  66  in its free front part  61  with the elongated holes substantially extending in horizontal direction, which is the longitudinal direction of the catch lever, with the elongated holes comprising a downwards extending indentation  66 ′ at its front end, and at its rear end. Through each elongated hole  66  a locking element  36  designed as a bolt extends crosswise to the elongated hole, with the locking element secured to the seat carrier  30 . Furthermore, an actuating lever  62  is provided in the seat carrier  30 , with the actuating lever  62  falling downwards in a position visible in FIG. 7 without exerting an actuating force. 
     In this automatically occupied position of the catch lever  60 , the backrest carrier  21  may freely move forward and backwards, wherein the catch lever  60  will move forward and backwards in horizontal direction in relation to the seat carrier  30  and the locking element  36  secured thereto. 
     In order to lock the seat top  10  in the backrest  20  in a required position, the user of the chair will pull the actuating lever  62  upwards, whereby the catch lever will take its position as shown in FIG.  8 . By a backwards or forward leaning by the user of the chair  1 , the backrest  20  will move into its rear or front end position, wherein the front or rear one of the indentations  66 ′ will engage the locking element  36 . To move the catch lever  60  into this position the user has to move the actuating lever  62  upwards and load it with an upwards directed force until the indentations  66 ′ of the two elongated holes  66  will engage one of the two possible positions of the associated locking elements  36 . After attaining this locking position of the catch lever  60 , the user of the chair  1  may stand up and release the actuating lever  62 . Thereby the locking is maintained because the catch lever  60  will maintain its position because of the force of the spring arrangement  50  not illustrated in FIGS. 7 and 8 and the friction at the locking elements  36 . 
     When a user again will take a seat at the chair  1  and will slightly move to the front or to the back, the backrest  20  will be pivoted correspondingly, and the locking of the chair is released without further actuating means as the friction between the catch lever  60  and the locking elements  36  is no longer there. Thereby the catch lever  60  will fall downwards and take its release position illustrated in FIG.  7 . 
     Finally, FIG. 9 of the drawing illustrates a changed embodiment of the chair  1  in a changed design of the locking means. Also in the example according to FIG. 9 a pivotable catch lever  60  is used which in the same way as in FIGS. 7 and 8 is pivotable around the swivelling axis  63 , and which may be pivoted from its release position illustrated in FIG. 9 upwards into its locking position by means of an actuating lever  62 . 
     Instead of elongated holes and bolts, in this example teeth are provided at the side of the catch lever  60  facing away from the viewer, and corresponding teeth  36  at the side of the seat carrier  30  facing the viewer, with both sets of teeth engageable with each other. The teeth  36  and  66  are each designed with a slight curve which extends at a radius around the swivelling axis  63 . The function of the locking according to FIG. 9 corresponds with that according to FIGS. 7 and 8, wherein the difference is only that in the example according to FIG. 9 a finer stepping of the possible locking positions is attained. Regarding the remaining numerals in FIGS. 7,  8  and  9 , reference is made to the preceding description. 
     In FIG. 10 a chair  1   a  is illustrated which is substantially similar to the chair of FIG. 1, except that a compression or pressure spring  50   a  is provided instead of the extension spring  50  shown in FIG. 1. A slight modification of the mounting location for the spring  50   a  is provided on an angle lever  40   a  and a backrest carrier  21   a  as illustrated to accommodate the opposite force provided by the spring  50   a . In all other respects, the chairs are the same and similar modifications can be made as discussed with respect to FIGS. 6-9. 
     That is, the second or rearward lever arm of the swivelling lever  40   a  connected to a front end of the pressure spring  50   a  points downwards or is angled downwards, and a connection of a new end of the pressure spring with the backrest carrier  21   a  is offset downwards and spaced away from the backrest carrier swivelling joint  23   a . The lever arms of the angle lever  40   a  form an angle of between 70° and 110° with each other. 
     As is apparent from the foregoing specification, the invention is susceptible of being embodied with various alterations and modifications which may differ particularly from those that have been described in the preceding specification and description. It should be understood that we wish to embody within the scope of the patent warranted hereon all such modifications as reasonably and properly come within the scope of our contribution to the art.