Patent Publication Number: US-6659555-B1

Title: Spring unit for weight adjustment of a chair

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The invention relates to a spring unit for the weight setting of a chair, in particular an office chair, having a first spring element and at least one further spring element. In this case, weight setting is understood to mean the setting of the opposing force to be applied by the spring unit to the weight of the person using the chair. 
     For the weight setting of a chair, DE 38 34 614 A1 discloses the provision of a spring unit which has a gas spring and a spiral spring which surrounds the latter coaxially and is borne by the gas spring, which is held on the chair frame at one end such that it can rotate. The construction and the mode of action of a gas spring of this type is described, for example, in DE 42 37 495 A1. 
     In the known spring unit, the prestress of the spiral spring, which acts as a compression spring, is set manually by means of a rotary knob coupled to a sleeve-like driver. The drawback in this case is that, on the one hand, in particular in the case of a permanent maximum weight setting, the spiral spring serving as a compression spring is often kept in the prestressed state to an undesirably high extent and/or over an impermissibly long time period. On the other hand, with a high expenditure of force, which at the same time is undesirable, a large number of revolutions of the rotary knob are needed for the weight setting, so that in the event of a bodily posture which is generally unfavorable, said setting is very time-consuming, because of the often poor accessibility of the rotary knob. 
     SUMMARY OF THE INVENTION 
     The invention is therefore based on the object of specifying a spring unit of the type mentioned at the beginning which, while avoiding the aforementioned disadvantages, permits a particularly suitable weight or force setting of a chair over the greatest possible force range. The spring unit is in particular to be suitable for an easy-to-handle weight setting of an office chair provided, for example, with a synchronizing mechanism for adjusting the inclination of a backrest/seat unit. 
     According to the invention, this object is achieved by the features of claim  1 . To this end, provision is made that at a basic setting, preferably for a minimum opposing force to be applied by the spring unit to the weight, only the first spring element is effective. In order to increase the opposing force of the spring unit adjustably, a number of further spring elements can be connected up, individually or in combination in steps, to the first spring element, which is preferably a gas spring. As a result, depending on the set weight—and therefore as a function of the opposing force to be applied by the spring unit to the weight—at least one of the further spring elements is effective in addition to the gas spring. At the same time, both the gas spring and the connected-up spring elements are effective only under load, that is to say when a compressive force or weight is exerted on the spring unit. In other words: when the spring unit is not loaded, in particular none of the connected spring elements is prestressed. 
     In an advantageous refinement of the spring unit, both the first spring element and the or each further spring element are a gas spring. In this case, the gas springs are jointly held on one side by their housing-side spring ends. Their piston-side spring ends can then expediently be brought into operative engagement, individually or in combination, with an adjusting slotted guide. The gas springs of the spring unit can be arranged beside one another both in a row and in a circle. The adjusting slotted guide can be designed as a perforated slide or as a perforated, rotatable disk. Both the perforated slide and the perforated disk can be provided with a latching mechanism. In this case, the slide or the disk latches in various positions in such a way that the respectively inactivated gas springs slide with their piston-side ends through the holes which are aligned with the latter when no weight is acting on the spring unit. 
     In an alternative embodiment, the or each further spring element is a spiral spring surrounding the gas spring coaxially. In this case, a first spiral spring surrounding the gas spring and a second spiral spring surrounding the first are expediently provided, between which a distance sleeve can be arranged. The inner, first spiral spring is in this case preferably weaker than the outer, second spiral spring. 
     In order to connect up the spiral springs to the gas spring, their movable piston end is guided on a cross-shaped arm, on which two plunger arms are arranged such that they can be displaced synchronously and transversely with respect to the spring axis. Depending on the set position of the plunger arms, these either slide past the outer spiral springs—only the gas spring then being effective—or are in an active position with the outer spiral spring, with the inner spiral spring or with both spiral springs. 
     The advantages achieved with the invention consist in particular in that, as a result of the use of a spring unit expediently having one gas spring as a first spring element for the basic weight setting and having a number of further spring elements which can be connected up individually or in combination to the gas spring, a stepwise setting of the opposing force of the spring unit, and therefore a stepwise weight setting of a chair is possible in a particularly simple way. 
     The spring unit is particularly suitable for the weight setting of an office chair having a synchronizing mechanism for adjusting the inclination of the backrest or of the latter in a unit with the seat. In this application, the spring unit is expediently arranged between a seat carrier that is connected to a rotary column, and the seat. Alternatively, the spring unit can also be arranged between the seat carrier and a backrest link which extends at least approximately parallel to the seat or to the seating area and belongs to the backrest. 
    
    
     Exemplary embodiments of the invention will be explained in more detail below using a drawing, in which: 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a side view of an office chair with a spring unit according to the invention for the weight setting as part of a synchronizing mechanism of an office chair, 
     FIGS. 2 a-d  show a first variant of the spring unit with a first gas spring, to which a second, a third and a fourth gas spring are connected up, and 
     FIGS. 3 a-e  show a second embodiment of the spring unit, having a central gas spring and two spiral springs surrounding the latter coaxially, of which the outer, the inner, both or no spiral spring is connected up. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Mutually corresponding parts are provided with the same reference symbols in all the figures. 
     FIG. 1 shows a chair  1  having a so-called synchronizing mechanism for adjusting the inclination of a backrest  2 , which is connected to a rotary frame  5  via a backrest link  4  which extends underneath a seating area or a seat  3 , at least approximately parallel to the latter. For this purpose, the backrest link  4  has a hinged connection, approximately in the area of the front edge of the seat  3 , via a rotary joint  6  to a seat carrier  7  which, for its part, is firmly connected to a rotary column  8  of the rotary frame  5 . The rotary frame  5  has a frame foot  9 , for example one of star shape, having rollers  10  fastened at the ends. A spring unit  11  provided for the weight setting is held on the housing side on the seat carrier  7  and on the piston side on the backrest link  4 , such that it can be rotated or pivoted. 
     FIGS. 2 a  to  2   d  show a preferred embodiment of the spring unit  11  at various weight or opposing-force settings. The spring unit  11  comprises a gas spring  12 , which is fastened to a holding element  13  at its holding or spring end  12   a  on the housing side. Within a pressure housing  14  of the gas spring  12 , a piston rod  15  connected at the end to a piston is guided such that it can be moved axially in a manner not specifically illustrated. At its spring end  12   b  on the piston side, the gas spring  12  is guided in an adjusting slotted guide  16  and, by means of the latter, is prestressed in the illustrated position. 
     Arranged adjacent to this gas spring  12  are three further spring elements  17 ,  18 ,  19 , again in the form of a gas spring in each case. The further gas springs  17  to  19  are likewise fastened to the holding element  13  by their housing-side spring ends  17   a ,  18   a  and  19   a . In addition, the further spring elements  17  to  19  are guided on the adjusting slotted guide  16  by their piston-side spring ends  17   b ,  18   b  and  19   b.    
     At the basic setting illustrated in FIG. 2 a , the further spring elements  17  to  19  are not connected up to the gas spring  12 , by their piston rods  20 ,  21 ,  22  being led through passage holes or openings  23 ,  24  and  25  provided in the adjusting slotted guide  16 . At this basic setting, the further spring elements  17  to  19  are therefore not prestressed. The basic setting corresponds, for example, to a weight of 50 kg of a person occupying the chair  1 , so that the opposing force F G  of the spring unit  11 , to be applied only by the gas spring  12  and counteracting the weight of the person, is 50 kN in this example. 
     For the purpose of the weight setting or adjustment, the further spring elements  17  to  19  of the gas spring  12  can be connected up individually or in combination. To this end, the adjusting slotted guide  16  is adjusted manually—in the exemplary embodiment, transversely with respect to the spring longitudinal axis  26 —for example is displaced or rotated. Thus, in FIGS. 2 b  to  2   c  of the gas spring  12 , the spring element  18 , the spring element  19  and, in addition, the spring element  17  are connected up by appropriate adjustment of the adjusting slotted guide  16 . The pistons  20 ,  22  of the spring elements  17  and  19 , respectively, are led through the corresponding passage openings  23  and  25  in the adjusting slotted guide without being blocked. 
     Given a spring or opposing force F 1 , F 2  and F 3  (FIG. 2 d ) of the further spring elements  17 ,  18 ,  19  of, for example, 10 kN, 20 kN and 40 kN, the opposing force F can be set in steps and therefore in a time-saving manner in 10 kN steps from F=50 kN to F=120 kN. For this purpose, the spring elements  17  to  19  are connected up to the gas spring  12  individually or in an appropriate combination. A continuous and therefore necessarily time-consuming and complicated weight setting is therefore avoided in a simple way. 
     FIGS. 3 a  to  3   e  show a further embodiment of the spring unit  11 , again having a central gas spring  12  for the basic setting of the opposing force F G , and having two further spring elements. These are designed in the form of two spiral springs  27  and  28  surrounding the gas spring  12  coaxially, the inner, first spiral spring  27  being designed to be weaker than the outer, second spiral spring  28 . While the inner spiral spring  27  is guided by the pressure housing  14  of the gas spring  12 , the outer spiral spring  28  is guided by a positioning and distance sleeve  29  provided between the two spiral springs  27  and  28 . In this case, the sleeve  29  at the same time serves as a spacer between the two spiral springs  27  and  28 . 
     In this embodiment of the spring unit  11 , the piston rod  15  of the gas spring  12  is guided at the ends on a cross-shaped arm  30 , on whose arms  30   a  and  30   b , extending transversely with respect to the spring longitudinal axis  26 , in each case a plunger arm  31   a  and  31   b  of an adjusting plunger  31  is arranged such that it can be displaced. Lever arms  32   a  and  32   b  attached to the plunger arms  31   a  and  31   b  are guided at the ends in a slot  33  which is common to the latter and is provided in the cross-shaped arm  30 . Depending on the position of the lever arms  32   a  and  32   b  within the slot  33 , the plunger arms  31   a  and  31   b  assume an active position (FIGS. 3 a  and  3   b ) in which they are aligned with the outer spiral spring  28 , an active position (FIG. 3 c ) in which they are aligned with the inner spiral spring, an active position (FIG. 3 d ) in which they are aligned with both spiral springs  27  and  28 , or an active position (FIG. 3 e ) which projects laterally beyond both spiral springs  27  and  28 . 
     In the last-mentioned active position according to FIG. 3 e , neither of the two spiral springs  27 ,  28  is connected up to the gas spring  12 . In this active position, the plunger arms  30 ,  31   a  and  31   b  slide past the outer spiral spring  28  without actively engaging the latter or the inner spiral spring  27 , so that the spiral springs  27 ,  28  are prestressed neither in the loaded nor in the unloaded state of the spring unit  11 . This adjustment or slotted-guide setting corresponds to the basic setting of the spring unit  11 , with an opposing force F G  of, for example, 50 kN, which corresponds to a weight setting of 50 kg. 
     In the active position illustrated in FIG. 3 a  of the plunger or adjusting arrangement  30 ,  31 ,  32 , only the outer spiral spring  28  is connected up to the gas spring  12 . However, the outer spiral spring  28  becomes effective only when the spring unit  11  is loaded. In this loading state of the spring unit  11 , which can be seen from FIG. 3 b , the outer spiral spring  28  is used to connect up an additional opposing force F′ 1  of, for example, 30 kN to the gas spring  12 . This would correspond to a weight setting of 80 kg. In the unloaded state (FIG. 3 a ), the outer spiral spring  28  is unstressed, just like the gas spring  12 , and is thus inactive. 
     In the active position illustrated in FIG. 3 c  of the adjusting or plunger arrangement  30 ,  31 ,  32 , only the inner, comparatively weak spiral spring  27  is connected up to the gas spring  12 , analogously to FIG. 3 a . In the loaded state of the spring unit  11 , the inner spiral spring  27  is used to connect up an additional opposing force F′ 2  or, for example, 20 kN to the gas spring  12 , which would correspond to a weight setting of 70 kg. Here, too, the inner spiral spring  27  is not prestressed in the illustrated, unloaded state of the spring unit  11 . By contrast, in the active position illustrated in FIG. 3 d  of the plunger or adjusting arrangement  30 ,  31 ,  32 , both the outer spiral spring  28  and the inner spiral spring  27  are connected up to the gas spring  12 . This corresponds to a weight setting of 100 kg.