Chair With Adjustable Backrest

Chairs are known which have frames in the form of a curved backplate to which a backrest cushion is secured. The backrest cushion stretches from the seat cushion to the top edge of the backplate. When the backplate is moved back and forth, the backrest cushion moves with it, being displaced to a greater extent in the upper region than in the lower because of the chosen position of the pivot at the base. The movement achieves only a slight change in the depth of the seat in the lower region, and the user is obliged to incline the body according to the position of the backrest. Consequently, the optimal body inclination is not possible in all backrest positions. For example, when the backrest is pivoted to its most forward position, it is not possible to adopt a relaxed upright posture because the edge of the backrest extends too far forward at the top.

An object of the invention is to avoid the disadvantages of the known chairs and to provide a chair of the type mentioned above in which a relaxed, upright posture is possible in all backrest positions. This object is achieved according to the invention in that an adjusting means is provided on the backplate, which is arranged to simultaneously adjust the horizontal distance of at least one zone of the backrest relative to the backplate depending upon the backplate angle of inclination. With such an arrangement, the lower portion of the backrest padding automatically experiences a greater forward movement than the mere angular movement of the backplate itself in this zone as the backplate moves forwardly. Similarly, a backward movement of the backplate results in greater backward displacement of the backrest lower portion than that of the backplate in this zone. The backrest effects a forward positioning of the pelvis, thus supporting the sacrolumbar area of the back in a manner beneficial to the health of the user. In a preferred embodiment of the invention, the lower end of the backrest is provided with a means which draws this portion against the backplate.

This invention can be used to special advantage when the supporting frame is of the known, curved-plate type.

The adjusting means of one suitable embodiment of the invention is provided with at least one substantially vertically rod pivoted to a fixed point and secured at its upper end to a crossbar, arranged at right-angles to the plane of pivot, and in contact with a guide means which is mounted on the backplate, so that the crossbar is moved relative to the backplate, taking with it at least one portion of the backrest whenever the backplate is pivotally adjusted.

A variety of shapes and angles can be used for the guide means. The desired support and movement of the backrest in relation to the inclination of the backplate may be attained by selecting a suitable form and location for the guide means. An especially simple construction provides a guide means having a downwardly sloping guide surface.

It has proved advantageous to arrange the pivot point of the rod behind that of the backplate.

With one suitable embodiment, the means of adjustment comprises two parallel rods, connected by a crossbar with bent-over ends which support the backrest, whereby the guide means are arranged between the two rods. The rods may be pivoted to a lug on the seat frame.

Principally, two different embodiments of the backrest are possible. With the first embodiment, the backrest is provided with a rigid backboard. The result of providing a rigid backboard is that the horizontal curvature of the backrest remains unchanged during adjustment. In a second embodiment, the backrest is in itself flexible. With such an embodiment, the curvature is altered during adjustment in that the zone affected by the bow of the crossbar is moved to a greater extent than the other zones of the backrest.

The upper edge is pivoted to provide pivotal movement between the backrest and the backplate. A suitable means for drawing back the base of the backrest is an elastic tape.

In the following, preferred embodiments of the invention are described in detail with the aid of the drawings which show:

FIG. 1 is a longitudinal section through a first embodiment of the invention with two inclinations of the backrest and the backplate, the backrest having a rigid backboard; and

FIG. 2 is a view, analogous to FIG. 1 of a second embodiment in which the backrest is flexible.

Referring to FIG. 1, a supporting frame 3 in the form of a curved backplate is shown as being pivoted at pivot point 2 to the seat 1. The backrest cushion 4 is mounted on the curved backplate 3 at pivot point 5. The backrest 4 is backed by a curved, rigid backboard 4". Two lugs 13, arranged next to each other, are provided on the frame of the seat 1, of which only one is visible in the drawing. Two parallel rods 7 are vertically pivoted to the lugs at pivot point 6. The two rods 7 are connected by means of a crossbar 7' the bent-over ends of which contact the backboard 4". The crossbar 7' rests upon the guide surface 9 which is connected to the backplate 3 and, in the depicted example, slopes downwardly towards the front.

The uppermost point of the guide surface 9 on the backplate 3 describes the arc indicated by arrow 10, when the backrest is pivotally moved. The center of this arc is the pivot 2. The crossbar 14 describes the arc shown by arrow 11 having as its center the pivot 6 of the rod 7.

In the position shown in full lines, the crossbar 7' is at its nearest point to the backplate 3. When the broken-line position is assumed, the crossbar 7' slides down the guide surface 9 and, simultaneously, moves forward a distance, thus increasing the space between the backboard 4" and the backplate 3. When this happens, the elastic tape 8 which draws the lower zone 4' of the backrest 4 towards the backplate, is extended.

The adjusting means, comprising rods 7, crossbar 7', and guide surface 9 has thus displaced the lower zone 4' of the backrest 4 to a greater extent than the mere pivoting of the backplate would achieve. This provides an especially beneficial supporting of the lower spinal zone, and a healthy posture for the user due to the forward positioning of the pelvis.

Displacement of the lower zone 4' of the backrest 4 occurs over the entire pivotal arc of the backplate 3 and can be influenced by the shape and position of the guide surface to perform in a desired manner.

When the backplate 3 is pivoted rearwardly, the elastic tape 8 draws the backrest into its original position. The adjusting means is thereby also urged into the original position depicted in full lines.

The embodiment shown in FIG. 2 differs from the embodiment according to FIG. 1 in that there is no rigid backboard 4". The rest of the mechanism, however, is unchanged. Instead of the rigid backboard 4" the backrest 4 is provided with a flexible backboard 4"'. Thus the whole backrest 4 is flexible.

When the backplate 3 of this embodiment is pivotally moved, the base 4"' of the backrest 4 is held by the connection 8, and the forward displacement of the crossbar 14 affects only the zone where the bow 15 contacts the backrest 4. The curvature of the zone 16 increases when the backplate is pivoted forwards, becoming more defined. Rearward movement of the backplate reduces the curvature of the zone 16 so that it becomes gradually flatter.