Chair, in particular office chair

A chair, especially an office chair, has a base and a seat disposed thereon as well as a backrest. The seat and the backrest are supported such that they can be pivoted about horizontal axes in a coordinated manner, and at least one gas spring is provided for damping the pivoting movement and for attaining a restoring action. In such a chair, in order to attain an anatomically appropriate adjustment of the inclination which is perceived by the user as pleasant, and to attain the simplest and most effective possible construction, the chair includes a seat carrier (4) and a backrest support part (7), which is joined to the seat carrier such that it is pivotable about an axis (6), for securing a backrest supporting column (9); a supporting column (2) of the base (1) is rigidly fixable on the seat carrier (4); a seat holder (19) projecting upward beyond the seat carrier (4) and being pivotable thereon is provided on the seat carrier (4); the seat (3), in the vicinity of a front section, is rigidly joined to the seat holder (19); the seat (3), in the vicinity of a section located behind the axis (6), is elastically joined to the backrest support part (7); and a gas spring (33) is disposed between the backrest support part (7) and the seat carrier (4), extending obliquely with respect to the seat (3).

FIELD OF THE INVENTION 
The invention relates to a chair, in particular an office chair, generally 
having a base, a seat disposed on it, and a backrest. The seat and the 
backrest are supported such that they pivot about horizontal axes in a 
coordinated manner in accordance with the weight shifts of a person using 
the chair; at least one gas spring is provided in order to damp the 
pivoting movement and to attain a restoring effect. 
BACKGROUND OF THE INVENTION 
In a chair of this kind, a mechanism is provided which assures that when 
the user shifts his weight, for instance when leaning back in the chair, 
an anatomically adapted shift in the relative inclination of the seat 
surface and the backrest is effected in a coordinated manner. Such 
mechanisms are therefore known as synchronizing mechanisms. 
A chair of this general type, provided with this kind of synchronizing 
mechanism, is known from German patent document A 27 57 349. However, like 
other comparable chairs known previously (see, for instance, German patent 
documents C 27 33 322 and C 28 36 216 which correspond to U.S. Pat. No. 
4,200,332), this chair has the disadvantage that because of the relative 
movement in shifting the inclination of the seat and the backrest, a pull 
is exerted on the clothes of the user, which is perceived as unpleasant. 
This is due, among other factors, to the fact that in the previously known 
construction, an adjusting device is supported on the supporting column of 
the chair base such that it is pivotable about a horizontal axis, with the 
pivoting movement of the seat and backrest being coordinated via a 
triangular swinging arm. The posterior end of the seat is connected via a 
toggle joint to the lower end of the backrest support column, and this 
articulation point of the toggle joint is connected to the lower 
articulation point of the triangular swinging arm via a gas spring. This 
means that the backrest support column, in the final analysis, is 
pivotably joined to a section of the seat via a parallelogram linkage 
embodied by the triangular swinging arm, the toggle joint, the gas spring 
and this section of the seat. A further parallelogram linkage is embodied 
between the triangular swinging arm and a toggle joint which with one end 
engages the vicinity of the front edge of the seat and the other end of 
which is joined to a further gas spring. 
The known embodiment has not only the inherent disadvantage of a pushing or 
pulling effect on the user's clothes but also has the disadvantage that in 
order to attain a damping effect on the inclination shifting movement on 
the one hand and to attain a sufficiently great restoring moment on the 
other, two springs that are independent of one another must be provided, 
which makes construction relatively complicated and increases the cost of 
manufacture. 
SUMMARY OF THE INVENTION 
It is accordingly an object of the present invention to embody a chair of 
the general type described above in such a way that a synchronized 
movement which is properly adapted anatomically nd is perceived as 
pleasant by the user is attained between the backrest and the seat when 
the user shifts his weight, and such that the chair, intermsof its 
construction, functions reliably and can be manufactured at a favorable 
cost. 
This object is attained in accordance with the inventioon by providing a 
chair including a seat carier and a backrest support part, which is joined 
to theseat carrier such that it is poivotable about an axis, for securing 
a backrest supporting column; a supporting column of the base is rigidly 
fixable on the seat carrier; a seat holder projecting upward beyond the 
seat carrier and being pivotable thereon is provided on the sat carrier; 
the seat, in the vicinity of a front section, is rigidly joined to the 
seat holder; the seat, in the vicinity of a section located behind the 
axis is elastically joined to the backrest support part; and a gas spring 
is disposed between the backrest support part and the seat carrier, 
extending obliquely with respect to the seat. 
As a result of the associatino of the individual structural jparts with one 
another as provided by the invention, the user's clothing is not subjected 
to undersirable pushign and pulling, since the downward movement of the 
backrest does not lag behind the downward movement of the end of the seat; 
quite the contrary, the distance between the upper edge of the seat and 
the lower edge of the back rest in fact decreases. It is also possible in 
accordance with the invention to provide only a single gas spring, which 
both damps the inclination movement and also exerts the necessary 
restoring moments for restoring the backrest whenever the user again 
shifts his weight forward. 
The elastic buffers, of rubber or the like, provided by the invention act 
on the one hand as resilient spacers between the rear section of the seat 
and the supporting part of the backrest, and on the other hand enable a 
complicated relative movement between the seat and the backrest portion, 
which because of the construction according to the invention is imposed on 
the backrest part when the user leans back. At this time, not only does 
the distance between the seat and the backrest support part vary, but a 
translational movement of the parts approximately parallel to one another 
takes place as well. 
Preferably the pivot axis between the backrest support part and seat 
carrier is disposed approximately in the middle between the front end of 
the seat carrier and the rear end of the backrest support part; then the 
course of movement can be influenced by means of the precise location of 
the pivot axis. 
The construction according to the invention makes it possible in principle 
for merely one gas spring to suffice. Disposing the gas spring so that one 
of its articulation axes is disposed on the seat carrier below the pivot 
axis of the backrest support to seat carrier, and spaced from the seat 
carrier, and so that the other of its articulation axes is disposed on the 
backrest support in the vicinity of its upper and back edges, assures that 
in a particularly advantageous manner, a sole gas spring such as this 
becomes effective both for damping the tilting movements and for the 
restoring movements. 
It is particularly advantageous if the distance between the pivot axis of 
the seat holder and the pivot axis between the seat carrier and backrest 
support part is at a ratio of approximately 2:1 to the distance between 
the pivot axis and the articulation axis of the gas spring on the seat 
carrier; and/or if the angle of inclination of the gas spring with respect 
to the seat is approximately 30 to 45.degree.. 
By embodying the seat carrier and the backrest support part with a U-shaped 
cross section, with the side walls of the backrest support part 
overlapping the side walls of the seat carrier at intervals, bearings are 
provided in a simple manner for the pivot shafts that are required. 
Furthermore, the functional interlocking of these parts becomes 
unproblematic; a high degree of static stability is attained; and finally 
this construction also pays appropriate attention to esthetic 
considerations. 
The pivot shafts are particularly simple if the pivot axis between the 
backrest support part and the seat carrier is embodied by a bolt passing 
through the side walls, and the articulation axis of the gas spring on the 
seat carrier is embodied by a bolt secured to its side walls and the 
articulation axis of the gas spring on the backrest support part is 
embodied by a bolt passing through its side walls. 
Providing gas springs used in office chairs with a locking device is known 
per se. However, when the gas spring is disposed as provided by the 
invention, the locking device according to the invention can be embodied 
particularly simply and effectively, especially in the form of a 
relatively inexpensive, purely mechanical locking device. 
Further characteristics, advantages and details of the invention will 
become apparent from the ensuing description of a preferred form of 
embodiment, taken in conjunction with the drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
An office chair shown in FIG. 1 includes a base 1 having a supporting 
column 2, which is joined to a seat carrier 4 receiving the cushioned seat 
3. In FIG. 1, only the outer covering 5 of the seat carrier 4 is shown. 
A backrest support part 7 is connected to the seat carrier 4 such that it 
is pivotable about a pivot axis 6, and the backrest supporting column 9 
that supports the backrest 8 is connected to the backrest support part 7. 
The seat 3 is connected in an articulated manner, not shown in detail in 
the drawing, to the front end of the seat carrier 4 on the one hand and to 
the backrest support part 7 on the other. The articulated connection 
between the seat carrier 4 and the backrest support part 7 is furnished by 
means of a pivot bolt 10, which passes through the side walls 11, 12 and 
13, 14 of the backrest support part 7 and the seat carrier 4. Each of the 
seat carrier 4 and one backrest support 7 has a U-shaped cross section, of 
which the transverse parts 15, 16 of the U point toward the top, that is, 
toward the seat, and the side walls 11, 12 of the backrest support part 7 
partially overlap the side walls 13, 14 of the seat carrier 4. 
At the front end of the seat carrier 4, a seat holder 19 is pivotably 
supported by means of a pivot bolt 18, which defines a pivot axis. The 
seat holder 29 has a substantially L-shaped profile 20 having a bearing 
box 21 receiving the pivot bolt 18 and spacers 22 to which the seat 3 is 
rigidly secured. 
A cone 23 for receiving the supporting column 2 is rigidly secured to the 
seat carrier 4, and an actuating lever 25 for adjusting the height of the 
seat, by means of a corresponding device not shown in detail, passes 
through a recess 24 in the vicinity of the cone 23. 
Beginning at an angled edge 26 (See FIG. 3), the backrest support part 7 
tapers toward the back, where a guide element 27 for the backrest 
supporting column 9 is welded in place. A clamping screw 28 having an 
actuating lever 29 engages a bore 30 of the guide element 27, thereby 
making it possible to clamp the arms of the guide element 27, which is 
U-shaped in this embodiment, so as to fix the backrest supporting column 
in position. Two rubber buffers 32 (see FIG. 2) are secured at one end to 
the transverse part 15 of the U of the backrest support part 7 and at the 
other to the rigid seat bottom 31 of the seat 3. 
A gas spring 33 is articulated at one end on a pivot bolt 34 which extends 
through bores 35 in the side walls 11, 12 of the backrest support part 7 
and at the other end on a pivot bolt 36, which extends through a bore 37 
of the side walls 13, 14. 
The side wall 11 of the backrest support part 7 has a slit 39 extending in 
the form of a section of a circle, through which an actuating lever 40 for 
a locking device 38 passes so as to engage the slit. 
If the seat 3 is urged in the direction of the arrow 41 (see FIG. 2), or 
the backrest 8 is urged in the direction of the arrow 42, when a user 
shifts his weight backward, then the backrest support part 7 is pivoted 
about the pivot axis 6 counter to the spring force of the gas spring 33 
about an angle .gamma. until a state of equilibrium is attained. At the 
same time, the seat holder 19 connected to the seat 3 is pivoted about the 
pivot axis 18 by the angle .beta.. Because the rubber buffer 32 joining 
the seat 3 and the backrest support part 7 is spaced farther from the 
pivot axis 18 of the seat 3 than from the pivot axis 6 of the backrest 
support part 7, the angle .gamma. is larger than the angle .beta.. 
As a result of this movement of the user, the backrest 8 and the seat 3 
move out of the position shown in solid lines in FIG. 2 and assume the 
position shown in broken lines in FIG. 2. During this pivoting movement, 
the distance a between the lower edge 43 of the backrest 8 and the upper 
edge 44 of the cushion 43 of the seat 3 varies in such a manner that the 
corresponding new distance a' is smaller than the original distance; that 
is, in contrast to previously known constructions, the original distance a 
is not increased, and accordingly no tension is exerted upon the user's 
clothing. 
If the user shifts his weight forward again, this does not as a rule 
suffice to assure that the backrest 8 will at each moment remain reliably 
in contact with the user's back. This return movement of the backrest 8 is 
assured in this phase, however, by the gas spring 33, which has engagement 
points on the backrest support part 7, on the one hand, and the seat 
carrier 4 on the other, such that a reliable return of the backrest 8 even 
from a severely backward-pivoted position to the original position is 
assured without requiring further springs. 
The above advantages which are attainable in principle as a result of the 
embodiment according to the invention are optimized by dimensioning the 
chair as follows: 
The pivot axis 6 is disposed approximately in the middle between the pivot 
axis 18 and the pivot axis 34, which is embodied by the pivot bolt 35. 
The distance between the lower articulation axis (pivot bolt 36) of the gas 
spring 33 and the pivot axis 6 is approximately half as long as the 
distance between the pivot axis 6 and the pivot axis 18. 
The angle .gamma. between the longitudinal axis of the gas spring 33 and 
the transverse part 15 of the U of the backrest support part 7 is 
approximately 30.degree.. 
The distance between the rubber buffers 32 and the pivot axis 18 is 
approximately 21/2 times as long as the distance between them and the 
pivot axis 6. 
The locking device 38 can be particularly simply embodied, in the context 
of the construction according to the invention, by providing that it 
includes a sheath part 46 and a piston part 47, the piston part being 
disposed such that it is longitudinally displaceable in the sheath part. 
This device is disposed parallel to the gas spring 33; that is, the sheath 
part 46 is pivotably supported on the bolt 34 and the piston part 47 is 
pivotably supported on the bolt 36. On its free end, the actuating lever 
40 has a threaded bolt 48 which passes through a threaded sheath 49, which 
is joined to the side wall 13 of the seat carrier 4. When the actuating 
lever 40 is tightened, the front end of the threaded bolt 48 presses 
against the telescoped piston and sheath parts 46 and 47 and clamps them 
together over a large surface area. Thus, despite the ease of 
manipulation, a high degree of surface pressure and thus reliable locking 
are attained, so that the seat 4 and backrest can be pivoted upon demand. 
It is to be understood that the present invention is not limited to the 
embodiments disclosed which are illustratively offered and that 
modifications may be made without departing from the invention.