Chair mechanisms of the above-mentioned type, in which both the seat height and the seat/backrest rake can be adjusted by means of a single operating lever, are known.

US-A-3,756,654, for example, discloses such a mechanism.

For safety reasons, a requirement has recently been introduced that adjustment of the seat/backrest rake should be possible only when the seat is loaded by the weight of a person sitting on the chair. Chair mechanisms that fulfil this requirement are also known.

The object of the present invention is to produce a chair mechanism of the aforementioned type, which has relatively few parts, which can be manufactured rationally and of which only a small number are moving parts and which are therefore cost effective to manufacture and assemble.

This object is achieved in that the chair mechanism according to the invention has the features specified in the characterising part of claim 1.

Further details of the chair mechanism according to the invention are set out in the subordinate claims and the following description, making reference to the drawing attached, in which: Fig. 1 in a diagrammatic side view shows a chair having a chair mechanism according to the invention. Fig. 2 shows an oblique view of the chair mechanism from beneath, and fig. 3 shows an exemplary embodiment of the structure of a frame part, forming part of the chair mechanism and having a locking element, by means of which the seat rake and seat height can be adjusted by means of a single operating lever. Fig. 4 shows the frame part in fig. 3 from a different perspective to that in fig. 3.

In the drawing, 1 generally denotes a chair having a seat la and backrest lb, which in this instance is rigidly connected to the seat la, as will be explained below. 2 generally denotes a chair mechanism according to the invention, having an operating lever 3 for adjusting the seat rake and seat height, it being possible to adjust the seat rake by moving the lever 3 backwards, that is towards the backrest lb, provided, however, that the seat la is loaded by the weight of a person sitting thereon. The seat height can be adjusted by moving the operating lever 3 upwards.

The chair mechanism 2 is connected to a chair stand comprising a gas-filled spring, only an upper part 4 of the chair stand, in which the gas-filled spring is located, being visible in figures 1 and 2.

The exterior structure of the chair mechanism can be seen from fig. 2, in which the upper part 4 of the chair stand is to be found. A first inner frame part 2a is connected to the chair stand.

A second, outer frame part 2b is connected to the chair seat by way of a fixing plate 2c. It will be noted from fig. 1 that the rigid connection between the seat 1 a and the backrest lb consists of two arms lc, which are fixed into the backrest and fitted to the frame part 2b.

The frame parts 2a, 2b are to a limited extent rotatable in relation to one another about an axis 2d, which lies across the chair mechanism. It will be appreciated from the above that this relative rotation involves an adjustment of the rake of the chair seat 1 a in relation to the horizontal plane.

A catch mechanism that can be actuated by means of the operating lever 3 and is designed to lock the frame parts 2a, 2b relative to one another in a number of selectable chair seat rakes, acts between the frame parts 2a, 2b. Also acting between the frame parts 2a, 2b is a spring element 5 (see fig. 3) which in the embodiment shown in the drawing is a rubber cylinder, but which obviously may alternatively be a helical coil spring. The spring element 5 endeavours to turn the frame parts 2a, 2b away from one another, but is designed to be compressed when a person sits on the chair. The catch mechanism comprises a locking element 2e operatively connected to the operating lever 3. By means of the operating lever 3, this locking element 2e can be displaced transversely to the direction of the axis 2d in and out of engagement with openings 2bl arranged in a wall 2b2 in the frame part 2b aligned transversely to the locking element 2e.

The tendency of the spring element 5 to turn the frame parts 2a, 2b away from one another produces a frictional engagement between the locking element 2e and the opening 2bl into which it is introduced, a frictional engagement great enough to allow the locking element 2e to be drawn out of the opening by means of the operating lever 3 only when the force of the spring element 5 is overcome by the weight of a person sitting on the chair seat la ; the gravitational force exerted by the person in question naturally tends to turn the frame parts 2a, 2b towards one another.

The operating lever 3 is articulated in a wall 2al in the frame part 2a running transversely to the axis 2d, in such a way that it can be moved horizontally for adjustment of the seat rake and vertically for adjustment of the seat height, as will be explained later.

As can be seen from fig. 4, after the support in the wall 2al, the inner end 3 a of the operating lever 3 is bent in a U-shape, passes through an oblong opening 2el in the locking element 2e and is terminated by a part 6, fixed to the end 3a, widening out across the locking element 2e, as can be seen from fig. 3. A helical coil spring 7, which extends essentially in the longitudinal direction of the locking element 2e, acts between the part 6 and the locking element 2e. The spring force of the spring 7 is here selected so that when the operating lever 3 is actuated and the seat la is not under load, it is overcome by the frictional engagement between the locking element 2e and the opening 2bl, into which the remote end of the locking element is introduced. The operating lever 3 can consequently be moved forwards against the spring force but nothing further happens. When the seat la is loaded by the weight of a person sitting thereon, the spring is able to transmit the movement of the operating lever 3 to the locking element 2e and draw the latter out of engagement with the opening 2bl. Another chair seat rake may now be selected ; the remote end of the locking element 2e automatically snaps in the corresponding opening 2bl under the action of the spring 7 without the need to move the operating lever 3.

According to the invention, the locking element 2e takes the form of an element to which torsion can be applied about. its longitudinal axis, such as a leaf spring, which at its edge 2e2 situated nearest the wall 2al of the frame part 2a is supported by the operating lever 3, but which, when the said lever is raised, is acted upon by the part 6, so that the opposite edge 2e3 is forced downwards by the turning of the locking element 2e. The locking element 2e is thereby brought into engagement with an operating pin 8 belonging to the gas-filled spring, see fig. 4, which permits adjustment of the seat height. When the operating lever 3 is released, the locking element 2e returns to its original shape and the engagement with the pin 8 ceases.