Height-adjustable swivel chair equipped with gas-pressure spring, especially office chair or office armchair

In the swivel chair, a seat frame and a backrest frame are joined by articulation and movable with a rocking motion synchronously against spring force, and the tilt of seat and backrest can be locked in several positions. The entire mechanical system for the tripping, adjustment, and locking of the tilt of seat frame and backrest frame, for triggering the height adjustment, and for setting the rocking spring force is accommodated in a supporting tube that is bent at an obtuse angle. This supporting tube surrounds in a rotatable and displaceable fashion a base tube at the lower end, this base tube being seated on a compound base and accommodating the gas-pressure spring, and is connected at the upper end with a horizontal transverse tube extending perpendicularly to the supporting tube, this transverse tube housing the swivel axles of the seat frame as well as of the backrest frame. The pivot axle of the backrest frame is constituted by two torsion springs which are respectively fixed with a longer, angled spring leg within a tube of the bottom part of the backrest frame and are in contact, with a shorter spring leg, against an adjustably designed abutment in the upper end of the supporting tube.

The invention relates to a swivel chair of the type set forth in the 
preamble of claim 1. 
In such chairs or armchairs wherein seat and back are separately pivotably 
supported for the execution of rocking motions, the so-called "undressing 
effect" occurs as a rule, i.e. during rocking or during tilt adjustment a 
change results in the distance between the seating center and the backrest 
center; as a consequence, the clothing of the person occupying the chair 
or armchair is displaced in the back region, for example the shirt is 
pulled out of the trousers. 
German Utility Model No. 84 17 429 discloses, for example, a 
"center-synchronized adjusting device" which is to avoid this 
disadvantageous effect. However, for this purpose, an expensive and, above 
all, voluminous mechanism is arranged underneath the seat which, in 
addition, does not exactly render the design of the chair or armchair 
esthetic. 
The invention is based on the object of overcoming the above-discussed 
problem of the "undressing effect" by means of a relatively simple and 
compactly accommodated rocking and tilting adjustment mechanism. 
This object has been attained according to this invention by characterizing 
features (a) and (b) of claim 1. Advantageous further embodiments of the 
invention can be derived from the dependent claims as well as from the 
subsequent description of embodiments illustrated in the drawings. 
The swivel chair of this invention affords, due to the far forwardly 
displaced rocking axes of the seat and the backrest, an optimum 
synchronous movement to avoid the "undressing effect" with a space-saving 
accommodation of the total mechanism, making it possible to provide an 
entirely novel and additionally rugged chair design, wherein no bellows is 
required to cover any pinch or shear zones. The supporting structure, 
consisting exclusively of economical steel tubing, serves as a basic frame 
for an entire family of models, i.e. from a steno chair up to the heavy 
executive armchair.

The lower end of a supporting tube (3), bent at an obtuse angle, is guided 
displaceably and rotatably on a base tube (2) fixedly connected to a 
multi-strut base (1) of the swivel chair; between the base tube (2) and 
the supporting tube (3), a synthetic resin bushing (4) is provided for 
guidance and additional support. The base tube (2) accommodates, in its 
interior in a guide bushing (5) of a synthetic resin, a gas-pressure 
spring (6) resting at the bottom in the base tube (2) on an axial thrust 
bearing (7) and being mounted at the top with a cone (8) in a conical 
bushing (9) which latter is welded at (10) via a bore to the supporting 
tube (3) and at (11) to an insert tube (12) welded into the lower end of 
the supporting tube (3). A transverse tube (13) is fixedly connected with 
the upper end of the supporting tube (3). In this arrangement, the 
supporting tube (3) and the transverse tube (13) are cut out and welded 
together in such a way that the inside cross section of both tubes (3, 13) 
is not constricted by this connection at any location. The transverse tube 
(13) extends perpendicularly to the supporting tube (3) and lies 
horizontally. 
As shown in FIG. 1, the entire mechanism for chair adjustment is 
accommodated in the upper end of the supporting tube (3). In this 
arrangement, a guide block (14) is mounted by means of screws (15) in the 
supporting tube (3). A detent (16) is displaceably arranged in the guide 
block (14) and engages, for determining a tilt position of a seat frame 
(17) and of a backrest frame (18), into a toothed rack (19) which latter, 
in the embodiment of FIGS. 1 and 2, is attached to a cross strap (20) of 
the seat frame (17) and projects by way of an opening (21) into the 
supporting tube (3). The toothed rack (19) exhibits a longer tooth (22) at 
the free inner end, this tooth abutting the detent (16) when the latter is 
retracted so that the toothed rack (19) cannot be pulled entirely out of 
the opening (21) of the supporting tube (3). For this purpose, the 
tripping movement of the detent (16) is restricted by a leaf spring (23) 
which can be forced out of the way during the disassembly of the mechanism 
by means of a screw driver or the like. 
The detent (16) is connected via a connecting rod (24) to a lever (25) at a 
shaft (26), this shaft being supported in small bearing blocks (27, 28) 
within the left-hand side of the cross tube (13) and carrying on the outer 
end an operating lever (not illustrated herein), this lever being 
accessible at the front on the left-hand side beneath the seat frame (17). 
Additional small bearing blocks (29, 30) are provided in the right-hand 
side of the transverse tube (13), an additional shaft (31) in alignment 
with the shaft (26) being supported therein; this shaft (31) pertains to 
the operating mechanism for the height adjustment of the chair. A lever 
(32) on the inner end of the shaft (31) is connected, via a connecting rod 
(33), with an angle lever (34) supported at the rear end of the guide 
block (14). This angle lever, upon actuation of an operating lever (35) 
(FIG. 2) accessible from the right-hand side at the front underneath the 
seat, exerts pressure on a plunger (36) of the valve of the gas-pressure 
spring (6) in order to release the spring for height adjustment. 
The seat frame (17) exhibits bearing lugs (37) on both sides at the front 
end; pivots (38) that can be threaded into the outer small bearing blocks 
(27, 29) serve for the rotatable support of these lugs. The axle for the 
pivotal support of the backrest frame (18) in the small bearing blocks 
(27-30) is constituted by two torsion springs (39) fixed in place with 
respectively one long spring leg (40) in an associated tube of the lower 
portion of the backrest frame (18). For this purpose, these tubes include 
bushings (41) (see FIG. 2), and the spring legs (40) have bevels (42) 
engaged by clamping screws (not shown). 
In the region of the connecting point between the supporting tube (3) and 
the transverse tube (13), the torsion springs (39) have shorter spring 
legs (43) pressing against a stop block (44) fashioned as an adjusting 
nut; this block is adjustable at the front end of the supporting tube (3) 
by means of a knurled disk (45) in order to set the spring force of the 
torsion springs (39). The seat frame (17) and the backrest frame (18) are 
joined on both sides by means of joint fishplates (46). 
Additional spring elements (47) are inserted in both lateral tubes of the 
upper part of the backrest frame (18); flexible synthetic resin sheaths 
(48) are threaded onto the free lengths of these spring elements, 
supplementing the diameter of the tubes of the backrest frame (18). 
The embodiment illustrated in FIG. 4 differs from the embodiment of FIG. 1 
merely in that the toothed rack (19) is in this arrangement attached to a 
cross strap (49) of the lower part of the backrest frame (18), and the 
latter is joined to the seat frame (17) by way of rubber-metal buffers 
(50). 
The torsion springs (39) are preferably made of steel rods, but they can 
also consist of leaf-spring packs. The padding of the chair, not shown, 
can be of any desired type since the disclosed chair frame and its 
mechanical components serve, as mentioned in the foregoing, as a basic 
framework for an entire family of models. 
FIG. 5 shows, in a partially sectional view, a further embodiment of the 
swivel chair. The detent (16') is under the force of a spring (51) which 
has the tendency to insert the detent (16') in the toothed rack (19). A 
key (not shown herein) for triggering the detent (16') is fashioned as an 
indexing key, i.e. during the first depression of the key, the detent 
(16') is pulled out of the toothed rack (19) and then is again released 
upon the second depressing of the key. For this purpose, a locking device 
is utilized with a pawl (54) pivotable in two planes under the action of a 
spring (53), as is customary in click-stop switching keys of electrical or 
electronic appliances and thus needs no detailed explanation. The pawl 
(54) cooperates with a pin (55) at the detent (16'). 
In the embodiment of FIGS. 6 and 7, larger effective spring lengths are 
available for the torsion springs (39'). For this purpose, the extreme 
ends of the torsion springs (39') are mounted in shape-mating connection 
with tubes (57) by way of coupling bushings (56) (see FIGS. 7 and 8); 
these tubes transmit the torsion force in the direction toward a spindle 
nut (44'). Beveled ends (58) of the torsion springs (39') are isnerted in 
corresponding shallow bores (59) of the coupling bushings (56). Hooks (60) 
are attached to the inner ends of the tubes (57), these hooks engaging 
into hook-shaped extensions (61) at the spindle nut (44'). By adjustment 
of an adjusting spindle (62) seated in the spindle nut (44') by means of a 
rotary knob (63), the pretensioning of the torsion springs (39') can be 
set. 
FIGS. 9-11 show, on a somewhat enlarged scale, the adjusting mechanism for 
the pretensioning of the torsion springs (39'). A forwardly projecting, 
rectangular, housing-type extension (64) is attached to the transverse 
tube (13') and accommodates the adjusting spindle (62) and the spindle nut 
(44'). The adjusting spindle (62) exhibits an annular collar (65) in 
contact with an axial ball bearing (66) which latter abuts, at the other 
end, against an essentially rectangular counterpressure disk (67); the 
latter, as indicated in dot-dash lines in FIG. 10, makes it possible to 
install the spindle (62) with nut (44') and to effect its own installation 
without screws and any tool, since the counterpressure disk (67) exhibits 
a widened bore (68). In the assembled condition, the counerpressure disk 
(67) is seated with a flat indentation (69) in a recess (70) of the 
housing-like extension (64). In a round crimp (71) of the indentation 
(69), a race (72) for the ball bearing (66) is disposed, this race having 
a bore adapted to the spindle (62) and thus fixing the adjusting spindle 
(62) in place concentrically to the flaring bore (68) of the 
counterpressure disk (67), namely under the constant pressure of the 
torsion springs (39'). 
FIG. 12 shows, inter alia, the arrangement and structure of an operating 
key (73) which is supported on one end (here on the right-hand end) of the 
transverse tube (13'), is connected via a lever (74) to the shaft (31) 
already mentioned in the description of FIG. 2, and pertains to the 
operating mechanism for the height adjustment of the swivel chair. The 
lever (74) projects out of the transverse tube (13') through a slot (75), 
and the operating key (73) exhibits toward the top a beak-like extension 
(76) covering the slot (75) in the rest position of the lever (74) and 
preventing pinch injuries to fingers. 
According to FIG. 12, the seat frame (17) is furthermore tiltable about an 
axle (77) within limits once this tilting movement has been released by 
the detent (16). The seat frame (17) is, for this purpose, supported on 
cantilevers (78) in front of the forward, top rim of the transverse tube 
(13').