EP0960586B1 - Chair, particularly office chair - Google Patents

Description

The present invention relates to a chair according to the preamble of claim 1.

A chair of the type mentioned is known from EP-A-0 277 474 known.

In this known chair form the seat plate (2), the seat carrier (5) and two links (9, io) a parallelogram arrangement. In unloaded Condition of the seat plate (2) extend the handlebars (9, 10) approximately vertically and with a slight inclination forward, that is to the front edge of the seat plate (2). at a load on this seat plate (2) by a user, the seat plate (2) under Maintaining its horizontal alignment along a section of a circular path initially essentially forward and then increasingly moved downwards, only when a significant downward movement of the associated spring (16) increasing is tense.

A disadvantage is considered in this known chair that the movement of the seat plate (2) when loaded, initially substantially forward and then only after down below. This leads to an undesirable increase in the distance of the Rear end of the seat plate (2) of the backrest (3) of the chair. Another disadvantage is seen in the fact that a significant movement of the seat plate (2) forward required is, before a noticeable downward movement, which then only one Increasing the tension of the spring (16) leads. When moving the seat plate (2) when loaded by a user, the rear end of the seat plate (2) not only towards the front of the backrest (3) away, but relative to the backrest (3) also lowered downwards. This lowering of the rear end of the seat plate (2) leads undesirably increasing the vertical distance between the trailing edge the seat plate (2) and the backrest (3), what is known as the so-called "shirt pull-out effect" is. A final disadvantage is finally seen in that in the known Chair for the parallelogram mechanics a total of four pivot points are needed what correspondingly many items and a correspondingly complex production and assembly results.

For the chair according to the present application and according to the newly presented claim Fig. 1 presents the prior art with respect to the prior art known from EP-A-0 277 474 Task, a displacement of the seat plate when loaded by a user forward away from the back, and at the same time the so-called "shirt pull-out effect" to avoid and moreover a simplified and less items requiring To allow construction. At the same time, however, the automatic automatic Adjustment of the preload force of the backrest to different degrees of difficulty Users of the chair are fully preserved.

The solution of this problem is achieved with the chair according to the newly presented claim 1.

With the construction according to the invention is achieved that in cooperation between the front Sitztragarm and the forward facing first lever arm of Levers each load of the seat plate of the chair by a chair user directly to a predominantly vertical lowering of the front portion of the seat plate without displacement leads to the front and that while the tension of the Spring is increased immediately. At the same time a lowering of the rear part of the Seat plate avoided because here the rear Sitztragarm means of the seat joint directly is connected to the teaching support. This provides two advantages. The first Advantage is that the seat plate when loaded by a user not be removed from the back to the front. The second advantage is that the seat panel does not sink under load from a user in its rear part and so is not removed in the vertical direction downwards from the backrest, which the unpleasant "shirt pull-out effect" is safely avoided. simultaneously is saved in the construction according to the invention a joint, because here on a Parallelogram construction is omitted, reducing the number of items smaller is and the assembly is less expensive. At the same time remains in the inventive Chair but the function of automatic adjustment of the backrest preload force to differently heavy users of the chair alone by their Weight that acts on the seat plate obtained. In addition, the chair also offers today usual synchronous mechanism, in which a synchronous pivoting of the seat plate and Backrest in a certain ratio to each other takes place.

In a first embodiment of the invention Chair is as spring arrangement at least one tension spring provided, with the front end of the tension spring connected second lever arm of the pivot lever to the rear and wherein the connection of the rear end of the Tension spring with the backrest support from the backrest swivel joint is offset upwards. With this version of the Spring arrangement is technically simple and reliable Way the desired function is achieved. In addition Manufacturing costs are kept low and it Only relatively little space will be available for the accommodation Spring arrangement needed.

Furthermore, it is preferably provided that the pivot lever as straight or up to 45 ° angled Lever is executed. This design of the pivot lever has the advantage that the lever is easy to produce and that a flat construction arranged under the seat plate Parts of the chair mechanism is possible. This reduces the space required for the chair mechanism under the Seat plate and improves the visual appearance of the chair, especially when viewed from the side.

In an alternative embodiment of the invention Chair is at least one as a spring arrangement Compression spring provided, with the front end the compression spring connected second lever arm of the pivot lever pointing down or angled and where the connection of the rear end of the compression spring with the Backrest support from the backrest swivel joint down is offset. Also with this embodiment of the spring arrangement is done in a technically simple and reliable way ensures the desired function. By the changed Lever effects is due to the spring arrangement also at This chair on the seat plate an upward-acting and on the backrest, a forward biasing force exercisable.

Preferred is in the last described embodiment the chair of the pivot lever as an angle lever with in between about 70 and 110 ° to each other angled lever arms executed. With a so executed pivoting lever can use the preload forces from the compression spring favorable leverage on the seat transferred while maintaining a compact design remains.

To the from the backrest to the back of a chair user additionally exercised supportive force In addition to being able to influence and change the force exerted by the tension spring on the backrest force be adjustable.

In a further embodiment, preference is given in this regard provided that the connection point of the rear end the spring assembly on the backrest support in its distance adjustable by the backrest swivel joint. hereby is the lever arm between the spring assembly and changed the length of the backrest in his length, what a desired Lehnenkraftveränderung ensures.

Next is preferably provided that the rear End of the spring arrangement via a pivotable and lockable adjustment lever connected to the backrest support is. By this design, the bias of the Spring arrangement hardly changed, but the changes Leverage between the spring assembly and the backrest support depending on the respective position of the adjusting lever.

Preferably, as a spring arrangement at least one screw, Thigh, torsion bar, gas pressure, rubber or elastomer spring provided, such springs are cost-effective and in the market in the most diverse Models represent easily available component.

To use the chair when not in use in at least one Basic position to be able to fix and in the event that the user of the chair in a fixed position use and on e.g. abandon the reclined position wants, it is envisaged that the order of the backrest swivel joint pivotable backrest supports in stepless or graduated Verschwenkungs positions locked is.

A first embodiment of the chair with the aforementioned Lockability of the backrest support provides that at least a pivotable about a horizontal pivot axis one-arm locking lever on the backrest support in vertical Distance from the backrest pivot articulated joint is substantially in the horizontal direction to Seat support extends and in a first, automatically assumed release position in its longitudinal direction is freely displaceable relative to the seat support and in a second, by adjusting an actuating element assumed blocking position in arresting Engagement with at least one arranged on the seat support Blocking element occurs, which is a shift of Lock lever prevents relative to the seat support. If the Locking lever is in its release position, the movements of seat plate and backrest are relative not obstructed to the seat carrier; only when the locking lever by adjusting the actuator its Is a further movement of the Seat plate and the backrest relative to the seat support and prevented relative to each other.

A preferred embodiment provides that the blocking element there is at least one bolt passing through a slot runs in the locking lever, wherein the slot at least a downward recess to the blocking Recording of the bolt has. In release position of the locking lever, the bolt passes through the slot, so that the bolt and the locking lever unhindered can move relative to each other. When the locking lever is raised and the bolt passes into the recess is, this movement is no longer possible and the seat plate and the backrest are then fixed. It will this blocking position by the spring force of the spring assembly and the friction between the bolt and the recess fixed, so that the fixation of seat plate and Backrest is automatically maintained. Only when the Seat plate and the backrest again by a user be loaded, the spring force is influenced, that the lock is released by the locking lever around its pivot axis falls down and again got into his release position.

An alternative version of the chair provides that the blocking element by several protruding, parallel to each other on a radius about the pivot axis of the Locking lever extending teeth is formed with the opposite Teeth attached to the locking lever, can be brought into and out of engagement. With this version of locking element and locking lever will be the same Function achieved, as described above has been; In addition, it is advantageous with this second Execution a finer graduation of the fixing positions possible.

Alternatively to the two previously described versions The chair can be used as a spring arrangement in a stepless or graduated positions detectable gas pressure spring be provided. This detectable gas pressure spring Brings the desired spring force and allows at the same time a fixation of the backrest carrier and the associated backrest in a desired Standing within the total range of motion of the backrest carrier can be selected. When the gas pressure spring is solved, the chair has the entrance described mobility of the backrest, in which case a Swiveling the backrest backwards in conjunction with a lowering of the rear end of the seat plate solely by shifting the weight of the chair user is possible.

The ratio of the movements on the one hand the rear end the seat plate and on the other hand, the backrest is determined by the distance of the rear seat joint from the backrest swivel joint. In a simple version The chair can be a solid, for most User made appropriate positioning. alternative is provided that the rear seat hinge in its position relative to the backrest and thus in its distance from the backrest swivel joint in backrest longitudinal direction adjustable and fixable. To this Way, the ratio of the movements of the rear end the seat plate and the backrest changed specifically Be sure to put the rear seat hinge in position relative to the backrest either forward, i. closer to the backrest swivel joint, or to the rear, i.e. further away from the backrest swivel joint, moved and then set in a desired position becomes. When the rear seat hinge is closer to the backrest pivot is positioned, results in the same Lowering the rear end of the seat plate a larger pivotal movement of the backrest; vice versa results in the rear positioned behind Seat joint with fixed lowering of the seat plate lower swing angle of the backrest.

Finally, in the chair according to the invention are preferred two front and two rear seat arms, two Backrest support and two springs in the chair longitudinal mid-plane mirror-symmetrical arrangement provided. To this Way is the chair, especially its seat plate and its backrest, insensitive to overturning moments, but at the same time a cost-effective manufacturability the chair is preserved because all the parts, which are used in pairs, identically executed could be.

Figur 1

einen Stuhl in Seitenansicht bei Belastung durch einen leichtgewichtigen Benutzer in aufrechterHaltung,

Figur 2

den Stuhl aus Figur 1, nun bei Belastung durch einen schwergewichtigen Benutzer,

Figur 3

den Stuhl aus Figur 1 bei Belastung durch einen leichtgewichtigen Benutzer in zurückgelehnter Haltung,

Figur 4

den Stuhl aus Figur 1, nun bei Belastung durch einen schwergewichtigen Benutzer in zurückgelehnter Haltung,

Figur 5

eine geänderte Ausführung des Stuhls aus den Figuren 1 bis 4 in einer vergrößerten ausschnittsweisen Seitenansicht,

Figur 6

den Stuhl gemäß den Figuren 1 bis 4 in Unteransicht,

Figur 7

den Stuhl gemäß Figur 1, zusätzlich mit einer Arretierung in Freigabe-Stellung,

Figur 8

den Stuhl aus Figur 7 in einer vergrößerten Ausschnitts-Darstellung, nun mit der Arretierung in Sperrstellung, und

Figur 9

den Stuhl gemäß den Figuren 1 bis 4 mit einer geänderten Ausführung der Arretierung in Freigabe-Stellung, in gleicher Darstellungsweise wie in Figur 8.

In the following, embodiments of the chair according to the invention will be explained with reference to a drawing. The figures of the drawing show:

FIG. 1

a chair in side view under load by a light-weight user in the upright position,

FIG. 2

the chair of Figure 1, now under load from a heavyweight user,

FIG. 3

FIG. 1 shows the chair of FIG. 1 under load by a lightweight user in a reclined position;

FIG. 4

the chair of Figure 1, now under load from a heavyweight user in a reclined position,

FIG. 5

1 shows a modified embodiment of the chair from FIGS. 1 to 4 in an enlarged partial side view,

FIG. 6

the chair according to the figures 1 to 4 in bottom view,

FIG. 7

the chair according to FIG. 1, additionally with a lock in release position,

FIG. 8

the chair of Figure 7 in an enlarged detail view, now with the lock in the locked position, and

FIG. 9

the chair according to the figures 1 to 4 with a modified version of the lock in the release position, in the same representation as in Figure 8.

In the embodiment shown in Figures 1 to 4 a chair 1 is an office swivel chair. The chair 1 comprises a seat plate 10 as well one behind this, i. arranged in the drawing on the right Backrest 20. From the underside of the seat plate 10 extends a front Sitztragarm 11 and a rear Sitztragarm 12 down. From the backrest 20 runs a backrest support 21 first down and then forward under the seat plate 10. The backrest 20 is by means of a backrest bearing 22 with a horizontally and transversely to the chair 1 extending pivot axis hingedly connected to the backrest support 21.

Below the seat plate 10, a seat support 30 is provided, the fixed at the upper end of a central chair column 31 is attached. The chair column 31 is only in represented in its upper part; closes down a common base, as it is known, on. In addition, as is well known, the chair column 31 height adjustable and suspension.

The seat support 30 extends with its predominant Part of the seat support 30 forward in the direction to the front Sitztragarm 11. At its front end is a two-armed pivot lever 40 is mounted on the seat carrier 30, the running around a horizontal and across the chair 1 Pivot axis 43 is pivotable. The front Lever arm 41 of the pivot lever 40 is via a hinge pin 11 'to the lower end of the front Sitztragarms 11 articulated. With the rear lever arm 42 of the pivot lever 40 is in a connection point 45 the front end of a tension spring 50, here a helical tension spring, connected.

Behind the chair column 31, i. in the drawing on the right from this, the seat support 30 is by means of a backrest pivot joint 23 with the lower front end the backrest 21 connected. This backrest swivel joint 23 also has a horizontal and transversely to the chair 1 extending pivot axis.

Above the backrest pivot joint 23 is at a distance from this the rear end of the tension spring 50 with the backrest support 21 in another connection point 25 connected.

The rear Sitztragarm 12 is by means of a rear Seat joint 13 hinged to the backrest support 21, wherein the rear seat hinge 13 from the backrest pivot 23 spaced in the rearward direction is. This rear seat hinge 13 has a horizontal and transverse to the chair 1 pivot axis on.

In FIG. 1, the chair 1 is shown in a state as he puts him through a lightweight Occupants with upright sitting posture, wherein the user of the chair 1 is not shown here is. In this case acts on the seat plate 10 a relatively low force, which causes the Pivoting lever 40 only by a relatively small amount the pulling force of the spring 50 is pivoted counterclockwise is, by the front Sitztragarm 11 the front lever arm 41 with a correspondingly low force pushes down. The backrest support 21 is located in this low-load position of the chair 1 to a not specifically shown stop, the a further pivoting of the backrest 20 over the 1 position shown in FIG. 1.

Figure 2 of the drawing shows the chair 1 in the same representation like the figure 1, but now in a position he is under stress from a heavyweight User in upright posture occupies. In this Trap acts a greater weight on the seat plate 10, which causes the front Sitztragarm 11th with a greater force on the front lever arm 41st the pivot lever 40 acts. This greater power has As a result, the pivot lever 40 to a larger Swivel angle as in Figure 1 counterclockwise is pivoted about the pivot axis 43. This larger one Verschwenkungsbewegung of the pivot lever 40 has a stronger tension of the tension spring 50 result. hereby is achieved that over the rear end of the spring 50th and the connection point 25 on a stronger leverage the backrest support 21 in the sense of pivoting the Backrest 20 is applied to the front. It is herewith So causes when using the chair 1 by a heavy user the backrest 20 with a greater forward force by the spring 50 is preloaded, which is an automatic adjustment to the represents each occurring load.

Figures 3 and 4 of the drawing show the chair 1 in a state like he is in a reclined posture the user enters, wherein Figure 3 shows the state a lightweight user and Figure 4 shows the state in a heavyweight user of the chair 1 shows. The difference between the two in Figure 3 and FIG 4 states of the chair 1 is to that in Figure 3, the pivot lever 40 by a lesser degree pivoted counterclockwise than this at the pivot lever 40 in Figure 4 is the case. The different one Degree of pivoting of the pivot lever 4th results here again from the different Weight, which the user respectively on the seat plate 10 and the smaller in the case of Figure 3 is as in the case according to the figure 4. Also in this Position of the chair 1 is that of the backrest 20 force applied to the back of the user to the body weight adapted to the user, because in the case of the Figure 3, the tension spring 50 is less strained than in the case of Figure 4. The stronger the tension spring 50 is tensioned is, the larger is the one of the backrest 20 exerted, forward acting force on the Back of the chair user. Also and especially with the leaning back Pose of chair 1 user fits So the backrest force to the by the body weight user's needs.

As a measure of the spring tension in each case the distance between the connecting points 25, 45 of the two spring ends of the tension spring 50 is shown in Figures 1 to 4. In comparison between Figure 1 and Figure 2, the spring length X _{1 is} smaller than the spring length X ₂ . Thus, in Figure 1, the tension of the tension spring 50 is smaller than in the state shown in Figure 2. In the comparison of Figures 3 and 4, the length of the tension spring 50 in one case X ₁ and in the other case X ' _2nd Where X ' _{1 is} smaller than X' ₂ .

As further apparent from the figures 1 to 4, runs in the chair 1 in the upright posture of the user according to Figures 1 and 2, the seat plate 10 forward down with a slight downward slope. This passion is ergonomically favorable and desired, because thereby a hindrance of the blood circulation in the legs of the Chair user is avoided. Leaning the user the chair 1, however, back, occurs in addition to a pivoting the backrest 20 to the rear at the same time one Lowering the rear part of the seat plate 10 what For this reclined posture as particularly pleasant is felt and what a relaxed sitting posture allows and at the same time perceived as unpleasant Pushing the backrest 20 on the back of the user Chair 1 avoids.

In Figure 5 is a modification of the chair with additional Facilities shown, with only a section here of the chair shown below the seat plate is.

A first additional feature in the execution of the Chair according to Figure 5 is that the backrest pivot joint 23 fixed in desired positions is. For this purpose, on the backrest support pivot 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 support pivot joint 23rd is freely movable and being in the other position of the Locking lever 24, the backrest pivot joint 23 in a previously set position locked and then immovable. In this way, the user of the Chair pivotal movement of the backrest carrier 21 and the Prevent backrest 20.

Furthermore, an additional feature is that the connection point 25 of the rear end of the spring 50th relative to the backrest pivot joint 23 in its position changeable and fixable in a desired position is, where the means for positional change and fixing here by a swiveling and lockable adjusting lever 25 'are formed. The Pivot axis 26 'of the adjusting lever 25' is parallel to the pivot axis of the backrest pivot joint 23rd moved back to this by the backrest support 21. To adjust a handwheel threaded spindle 26th on the backrest 21. By this measure is the leverage the tension spring 50 adjustable in advance to a default setting that of the backrest 20 on the back of a User to exercise force applied. The Adjustment of the connection point 25 takes place along here an arcuate path on a radius around the Pivot axis 26 'around.

Finally, it is shown on the far right in FIG. 5 that the rear seat hinge 13 in its position relative to Backrest support 21 in the longitudinal direction adjustable and lockable. For this purpose, in the backrest support 21 a Guide 15 is provided along which the rear seat hinge 13 adjustable in the longitudinal direction of the backrest carrier 21 is. With the rear seat hinge 13 is a locking mechanism connected, via a second locking lever 14 as needed solved and after reaching the desired Position of the rear seat joint 13 again can be determined. Due to this adjustability of the rear seat joint 13 becomes the gear ratio between the Absenkwinkel of the rear end of the seat plate 10 and the pivot angle of the backrest carrier 21 with the backrest 20 is changed, creating an adaptation to the individual needs of the chair user in an even wider scope is made possible.

With regard to the further reference numerals entered in FIG and items will be on the previous one Description, in particular of Figure 1, referenced.

FIG. 6 of the drawing shows a bottom view of a Chair, with the seat plate and the backrest not are shown. In the center of Figure 6 is in section the chair column 31 recognizable, on the upper, here from Viewer facing away from the end of the seat support 30 attached is. At the upper end of the seat support 30, the backrest support pivot joint extends 23, by means of which two are parallel mutually extending backrest support 21 pivotally are connected to the seat support 30. By means of the Rear seat joint 13, two are also parallel mutually extending rear seat support arms 12 with the Back support 21 articulated connected.

At the lower end of the seat support 30 is the pivot axis 43 recognizable, about the two-armed pivot lever 40 pivotally are. In addition to each pivot lever 40 is ever a front Sitztragarm 11, which together with the two rear seat support arms 12 not shown here Wear seat plate. The respective front lever arm 41 each Pivoting lever 40 is connected via a hinge pin 11 'with the front Sitztragarm 11 hinged. At the respective other lever arm 42 of the pivot lever 40 engages one end of a helical tension spring 50 in a spring connection point 45 on. The other, rear end the spring 50 is at a spring connection point 25 on Back support 21 fixed.

Particularly clear in Figure 6, the symmetry of the individual Parts of the mechanics of the chair are mirror-symmetrical to a longitudinal median plane P, as a dot-dash line Line is drawn. Due to this symmetrical design The moving parts of the chair become special stable, giving a reliable function over a long time guaranteed.

In FIGS. 7 and 8, an embodiment of the chair 1 is shown illustrated in which a locking of the backrest 20th and the seat plate 10 in two predetermined positions is possible. This is at the front, in the drawing left end of the backrest support 21 above the backrest pivot joint 23 by means of a pivot axis 63rd a locking lever 60 articulated, which is parallel to the seat support 30 forward, i. in the drawing to the left, extends. The locking lever 60 is freely pivotable to the pivot axis 63 and takes under gravity its position shown in Figure 7 a. Furthermore owns the locking lever 60 in its free front part 61 two substantially in the horizontal direction and thus in the longitudinal direction of the locking lever 60 extending slots 66, each at its front and rear End have a downwardly extending recess 66 '. Through each slot 66 extends transversely to this one Locking element 36 in the form of a bolt fixed to the Seat support 30 is connected. Furthermore, in the seat carrier 30, an operating lever 62 is provided without exercising an actuating force in its visible in Figure 7 Position falls down.

In this self-assumed position of the locking lever 60, the backrest support 21 without hindrance move forwards and backwards, with the locking lever 60 relative to the seat support 30 and attached thereto Locking elements 36 in the horizontal direction back and forth emotional.

To the seat plate 10 and the backrest 20 in a desired Locking position, a user pulls the Chair 1, the operating lever 62 upwards, whereby the Lock lever 60 in its position shown in Figure 8 arrives. By leaning or preventing the user of the Chair 1 enters the backrest 20 either in her rear or front end position, in which the front or the rear of the recesses 66 'engaged with the blocking element 36 can occur. So that the locking lever 60th enters this position, the user must the operating lever 62 move up and one up load acting force until the recesses 66 'of the two slots 66 in one of the two possible positions with the associated locking element 36 into engagement to step. After reaching this blocking position of the locking lever 60, the user can get up from the chair 1 and release the operating lever 62. The catch remains obtained because of the force of the in Figure 7 and 8 not shown spring assembly 50 of the locking lever 60 its position due to the friction on the Locking elements 36 reserves.

A user sits down again on the chair 1 and moves on this slightly forward or backward, the backrest 20 is pivoted accordingly and the Locking the chair will be without further action lifted, because the friction between the locking lever 60 and the locking elements 36 is omitted. Thereby the locking lever 60 falls down again and takes again his drawn in Figure 7 release position.

Figure 9 of the drawing finally shows a modified Execution of the chair 1 with a modified design the lock. Also in the example of FIG 9, a pivotable locking lever 60 is used, the in the same way as in Figures 7 and 8 about the pivot axis 63 is pivotable and by means of an actuating lever 62 from its drawn in Figure 9 release position pivoted upwards into its blocking position can be.

Instead of slots and bolts are included In this example, teeth facing away from the viewer Side of the locking lever 60 and gegengleiche teeth 36 at the viewer facing side of the seat support 30th provided, which are engageable with each other. The teeth 66 and 36 are each with a light Curvature running on a radius around the Swivel axis 63 runs. The operation of the lock according to Figure 9 corresponds to that according to the figures 7 and 8, the only difference being that that in the example of Figure 9 is a finer Gradation of possible locking positions achieved becomes. To the other reference numerals in Figures 7, 8 and 9 Reference is made to the preceding parts of the description.

Claims (16)

1. Chair (1), in particular office chair, comprising a seat plate (10), comprising a seat base (30) connected to a central chair column (31) or several chair legs in a non-removable manner, and comprising a backrest (20) that is arranged on a backrest base (21) first extending underneath the seat plate (10) in a backward direction and then in an upward direction and mounted to the seat base (30) by means of a backrest base swivel joint (23) that extends horizontally in a transverse direction, wherein the seat plate (10), at its front end, is pin-connected to the seat base (30) via an at least double-armed rocking lever (40) comprising first and second lever arms (41, 42) and pivoted to the seat base (30) about a swivel axix (43) that extends horizontally in a transverse direction, wherein the seat plate (10), at its rear end, is pin-connected to the backrest base (21) by means of a rear seat joint (13) that extends horizontally in a transverse direction, wherein the seat plate (10), also at its rear end, is offset from the backrest base swivel joint (23) in a backward direction, and wherein a spring arrangement (50) that is provided underneath the seat plate (10) exerts a preload force acting on the seat plate (10) in an upward direction and acting on the backrest (20) in a forward direction, this being achieved by one end of the spring arrangement (50) being connected to the second lever arm (42) of the lever (40) and the other end of the spring arrangement (50) being connected to the backrest base (21) at a distance from the backrest base swivel joint (23),
   characterized in that
   at least one front seat-supporting arm (11) and at least one rear seat-supporting arm (12) project from the bottom side of the seat plate (10),
   the first lever arm (41) of the lever (40), being the front lever arm, points forwards and is pin-connected to the lower end of the front seat-supporting arm (11) and can be swivelled in a downward direction by the front seat-supporting arm (11) when a load is exerted on the seat plate (10), and
   the seat plate (10), at its rear end, is directly connected to the backrest base (21) via the rear seat-supporting arm (12) by means of the seat joint (13).
2. Chair according to claim 1, characterized in that at least one helical tension spring is provided as spring arrangement (50), that the second lever arm (42) of the rocking lever (40) that is connected to the front end of the helical tension spring (50) points backwards, and that the connection of the rear end of the helical tension spring (50) to the backrest base (21) is offset from the backrest base swivel joint (23) in an upward direction.
3. Chair according to claim 2, characterized in that the rocking lever (40) is designed as a lever that either extends in a straight line or is angled by no more than 45 degrees.
4. Chair according to claim 1, characterized in that at least one compression spring is provided as spring arrangement (50), that the second lever arm (42) of the rocking lever (40) that is connected to the front end of the compression spring (50) points downwards or is angled, and that the connection of the rear end of the compression spring (50) to the backrest base (21) is offset from the backrest base swivel joint (23) in a downward direction.
5. Chair according to claim 4, characterized in that the rocking lever (40) is designed as elbow lever with two lever arms (41, 42) that are angled in relation to each other by approximately 70 to 110 degrees.
6. Chair according to one of the preceding claims, characterized in that the force the spring arrangement (50) exerts on the backrest (20) is adjustable.
7. Chair according to claim 6, characterized in that the distance between the point (25) where the rear end of the spring arrangement (50) is connected to the backrest base (21) and the backrest base swivel joint (23) is adjustable.
8. Chair according to claim 7, characterized in that the rear end of the spring arrangement (50) is connected to the backrest base (21) via a swivelling and securable adjustment lever (25').
9. Chair according to one of the preceding claims, characterized in that at least one coil spring, spring clip, torsion spring, gas pressure spring, rubber spring, or elastomeric spring is provided as spring arrangement (50).
10. Chair according to one of the preceding claims, characterized in that the backrest base (21) that can be swivelled about the backrest base swivel joint (23) can be locked in continuously or discontinuously variable swivel positions.
11. Chair according to claim 10, characterized in that at least one single-arm locking lever (60) that can be swivelled about a horizontal swivel axis (63) is pivoted to the backrest base (21) at a vertical distance from the backrest base swivel joint (23) and extends, in essence, to the seat base (30) in horizontal direction and, in a first automatically taken release position, is free to slide along its longitudinal direction in relation to the seat base (30) and, in a second locking position taken by adjustment of an actuation element (62), comes into locking engagement with at least one locking element (36) that is arranged at the seat base (30) and prevents the locking lever (60) from shifting in relation to the seat base (30).
12. Chair according to claim 11, characterized in that the locking element (36) is at least one bolt that extends through an elongated hole (66) in the locking lever (36), with the elongated hole (66) comprising at least one recess (66') that extends in a downward direction and is provided for receiving the bolt in a locking manner.
13. Chair according to claim 11, characterized in that the locking element (36) is formed by several projecting teeth that are arranged in parallel to each other on a radius about the swivel axis (63) of the locking lever (60) and can be brought into and out of engagement with counterpart teeth that are attached to the locking lever (60).
14. Chair according to claim 9, characterized in that a gas pressure spring forming the spring arrangement (50) can be secured in continuously or discontinuously variable positions.
15. Chair according to one of the preceding claims, characterized in that the rear seat joint (13) can be adjusted and defined in its position in relation to the backrest base (21) along the latter's longitudinal direction.
16. Chair according to one of the preceding claims, characterized in that two front and two rear seat-supporting arms (11, 12), two backrest bases (21) and two springs (50) are provided in an arrangement mirror-symmetrical about the longitudinal middle plane of the chair.

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