Tilting spring mechanism for a chair, especially an office- or working chair

The invention relates to a rocking swing mechanism for a chair, particularly an office or a working chair where the mechanism is provided between a stem part and movable part of the chair that can be tilted about one transversal tilting axe in the stem part, the mechanism is comprises of a torsion spring providing an increasing gripping of rocking of the movable part of the chair.

A rocking spring mechanism of this type is for e.g. known from the Norwegian Patent Application No. 1992 0470. This known mechanism comprises a torsion spring arrangement connected between the chairs foot or stem part and the seat part of the chair, the seat part being tillable about transversal tilting axes and by an increasing tilting angle causing an increasing resilience of the spring. The spring has side parts in the form of a so-called torsion shaft pivotal mounted in supporting parts connected to the seat part. Further, the spring has front torsion parts connected to a torsion device for adjusting the pretension in the spring and a rear part being connected to a pivotal supported intermediate part which extend towards the rear, to which the back part of the chair is fastened. The reconnecting part of the torsion spring is connected to the intermediate part via an articulated joint. To obtain synchronized movement of the back part in relation to the seat part by the rocking movement of the seat part.

The bias of the torsion spring may, as mentioned above, be adjusted by means of mentioned tension bias; however, the spring characteristic is not adjustable.

The object of the present invention is to provide a rocking spring mechanism which makes possible both an adjustment of the spring bias and the spring characteristic, the mechanism at the same time having a simple and robust construction.

De above said objects are achieved by means of rocking spring mechanism of the initially mentioned type, which according to this invention is characterised by that the torsion spring mainly is square formed and comprises of two longitudinal side parts and two front transversal parts facing each other, the transversal parts and pieces rest on an abutment device on a back part of the chair, so that the torsion spring can be tensioned according to the tilting angle of the back part and where the side parts are actually movable supported in the stem part transversal to the rocking shaft, so that the distance between the rocking shaft and the torsion springs transversal parts can be changed by the moment of the spring and adjust the spring characteristics. An advantageous embodiment of this invention is characterised by the abutment device for the transversal parts and pieces having an abutment piece sloping upwards in a direction away from the rocking shaft in order to increase bias of the torsion spring by increasing the distance between the rocking shaft and the torsion springs front transversal parts.

As apposed to the known rocking spring mechanism as mentioned above, the mechanism according to this invention is designed for use in a chair having a fixed seat part and a movable back part. The spring is movable mounted in the chairs stem part in order to adjust the spring characteristic, but is permanent in relation to the stem part and the seat by tilting the back part. A progressive spring is thus achieved and a uniform or soft changing power due to the movement of the users gravity/weight on the seat.

The invention will be described further by means of an exemplary embodiment and the drawings, where Fig. 1 shows a view in perspective of a rocking spring mechanism according to the invention mounted in connection with a stem part of a chair,

Fig. 2-4 show a side view, front view and a view from the under side of the rocking spring mechanism of Fig. 1 , respectively, and

Fig. 5-8 further show similar view as Fig. 4, but with the torsion spring in another functional position.

As it appears from the drawings, these show only elements of a chair in which a rocking spring mechanism according to the invention has been mounted. The figures show an office or a working chair in which a rocking spring mechanism is mounted to work between the fixed stem part 1 and a movable back part 2 of the chair. A seat part (not shown) is fixed mounted to the stem part 1.

The stem part is in its central region provided with a hole 3 for mounting to a chair column (not shown) which as usual can be height adjustable by means of conventional gas spring.

Only the lower part 2 of the chair's back part is shown. The real back supporting part which is not shown will be securely fasten to the back part 2 at it's rear end. The back part is pivotably mounted about supporting points in the stem part 1, so that it can be tilted about a transversal rocking shaft AA under influence of a torsion spring 4.

The torsion spring 4 is mainly a ring formed or square formed body by a rod of springs of preferably round cross section. The spring 4 comprises two longitudinal side parts 4a, 4b, two forward facing transversal parts 4c, 4d and a rear transversal part 4e connecting the side parts 4a, 4b.

As shown the end pieces 5 of the forward transversal parts 4c, 4d rest against an abutment arrangement on the back part 2 by its forward end so that the torsion spring 4 is tensioned depending of the back parts tilting angle. In the shown embodiment the abutment arrangement consists of two rod parts 6, 7 with a round cross section which extend transverse of the spring transversal parts 4c, 4d and is supported by a sloping plate part 8 of the back part 2. The abutment arrangement has thus an

abutment part sloping in the directional away from the rocking shaft and the forward transversal parts 4c, 4d of the torsion springs.

Since the abutment arrangement consists of rod parts we a round cross section, a stable abutment point will be achieved between the rod parts and the transversal parts of the spring and thus an even relative change of movement and uniform changing of the spring tension by tilting the back part of a chair.

The side parts 4a, 4b of the torsion spring are rotating and axially slidingly supported in their respective groove parts 9 and 10 which are suitably fixed to the under side of the stem part 1 and runs transversely of the shaft A-A in a mainly horizontal plan. The rotary support allows for the turning of the springs side parts by varying the tension of the spring the chair is in use. Since the side parts of the spring also are axially movably supported, the distance between these rocking shaft A-A and the transversal parts 4c, 4d of the spring can be changed by a sliding spring in the channel parts 9, 10 for thus to adjust the spring characteristic and set the tension of the spring individually according to the weight of the actually use of the chair.

Once the spring is suitably set according to the rocking shaft A-A, it will be fixed in relation to the stem part by use of the chair.

As would appear from the drawings the rocking spring mechanism in fig. 1-4 is shown in a first functional position while it in fig. 5-8 is shown in another functional torsion where the torsion spring is offset in the stem part causing a larger distance between the chair's rocking shaft A-A and the forward transversal parts 4c, 4d of the torsion spring. In order to obtain the desired adjustment of the offset position of the torsion spring, an operating device is provided, which in the shown embodiment comprises an operating lever 11 which is pivotally supported in the stem part 1 and is operative connected to the torsion spring 4 via a rotary joint 12 and a connecting rod 13 connected to the spring so the spring can be offset by manually turning of the operating lever. The operating lever is carried through a suitable hole (not shown) in the channel part 9 and is axially fixed in this at the same time as it can be turned about its longitudinal axes. Further the operating lever is connected to the rotary joint 12 via a thread connection (not shown), so that the rotary joint by turning the operating lever can be turned between the two outer positions shown in fig. 4 and 8 respectively. Said thread connection has rather coarse threads so that the rotary joint can be rotated between the outer positions by relatively few turnings of the operating lever.