Chair with a pivoting backrest

A chair having a fixed support structure including two side uprights, a backrest having two side portions, and a pair of elastic joints connecting said side portions of the backrest to said side uprights, wherein each of said elastic joints comprises: a bushing fixed to a respective side upright, a helical spring having a longitudinal axis, the helical spring having an upper end resting against a front wall of the bushing, a compression member resting against a lower end of the spring, an upper attachment fixed to a corresponding side portion of the backrest, and a rigid connecting rod having an upper end and a lower end.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit of Italian patent application number TO2013A000650, filed Jul. 31, 2013, which is herein incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a chair with a pivoting backrest capable of tilting backwards under a thrust applied by the user's back.

2. Description of Prior Art

In the state of the art, there are various known solutions of chairs in which the backrest is connected to a fixed support structure by a pair of elastic joints, each of which comprises an upper support inserted into a tubular portion of the backrest, a lower support inserted into a tubular element of the fixed support structure and an elastic element, which allows an inclination between the upper support and the lower support.

For example, the document EP2183997 of the same applicant describes a chair comprising a base structure including two rear tubular elements, a backrest having two tubular portions and two elastic devices, each of which has an upper support inserted into a tubular portion of the backrest, a lower support inserted into the corresponding tubular element of the base structure and an elastic element deformable by bending to allow pivoting between the upper support and the lower support, wherein each of the elastic devices comprises a plurality of stacked sectors, arranged between the upper support and the lower support.

The elastic elements that are deformable by bending have the drawback of a limited elastic force for opposing the backward thrust applied by the user.

In principle, with elastic elements in compression formed, for example, by helical compression springs, it would be possible to increase the force provided by the elastic joints that contrast the backward thrust applied by the user on the backrest of the chair. However, with helical compression springs arranged coaxially to the side uprights of the backrest, the lever arm for the compression of the springs is limited.

SUMMARY OF THE INVENTION

The present invention aims to provide a chair with a pivoting backrest equipped with simple and robust elastic joints, capable of providing a high elastic force that counteracts the backward thrust applied by the user on the backrest of the chair.

According to the present invention, this object is achieved by a chair having the characteristics forming the subject of claim1.

The claims form an integral part of the disclosure provided in relation to the invention.

DETAILED DESCRIPTION

With reference toFIGS. 1 and 2, numeral10indicates a chair according to the present invention. The chair10comprises a fixed support structure12including a pair of front legs14and a pair of rear legs16. The front legs14and the rear legs16are connected together by means of upper connecting elements18. A seat20is fixed to the upper connecting elements18of the fixed support structure12.

The fixed support structure12comprises two tubular side uprights22extending upwards. The two side uprights22are fixed with respect to the support structure12. For example, the side uprights22can be fixed to the upper connecting elements18.

The seat10comprises a backrest24pivotally connected to the fixed support structure12. The backrest24comprises a backrest panel26having an arcuate shape, and two side portions28located laterally on opposite sides with respect to the backrest panel26. The side portions28can be formed in a monolithic manner with the backrest panel26. The side portions28of the backrest24are connected to the respective side uprights22of the fixed support structure12by means of respective elastic joints30.

With reference toFIG. 5, each elastic joint30comprises a bushing32having a cylindrical wall34having an open lower end and an upper end fitted with a front wall36. The bushing32can be equipped with a projecting appendage38that projects upwards from the front wall36.

The elastic joint30comprises a helical spring40housed within the cylindrical wall34of the bushing32. The helical spring40has a longitudinal axis A coaxial to the axis of the cylindrical wall34of the bushing32. The helical spring40has an upper end42and a lower end44. The upper end42rests against the front wall36of the bushing32. The lower end44of the helical spring40rests on a compression member46. In the illustrated example, the compression member46comprises a body of plastic material48and a metal washer50. The body of plastic material48has a cylindrical portion52that couples, in a sliding manner, with the lower end of the bushing32. At the bottom of the cylindrical portion52, a radially-projecting shoulder54is formed. The body48of the compression member46has a through hole56with a rectangular section. The washer50rests against a lower surface of the body48. The washer50has a through hole58with a rectangular section aligned with the hole56of the body48. Preferably, the washer50has a convex deformed portion60that couples with a corresponding concave seat62formed on the lower surface of the body48. The washer50has a concave seat64on the surface opposite to the convex projection60.

The elastic joint30comprises a rigid connecting rod66preferably made of metal. The connecting rod66preferably has a rectangular cross section. The connecting rod66has a lower end68and an upper end70equipped with respective holes72,74, engaged by respective pins76,78. The axes of the pins76,78, indicated with B and C, are parallel to each other, and transverse relative to the axis A of the spring40.

The elastic joint30comprises an upper attachment80having a shank82, which is fixed into a hole formed at the lower end of the respective side portion28of the backrest24. The upper attachment80has a groove84into which the upper end70of the connecting rod66is inserted. The upper attachment80has a transverse hole86, through which the upper pin78is inserted, which connects the upper end70of the connecting rod66to the upper attachment80, in an articulated manner.

The elastic joint30is preferably provided with a ring of plastic material88fitted on the appendage38of the bushing32. The ring88has a lower front surface, which rests on the front surface36of the bushing32, and an upper surface90against which a lower surface92of the upper attachment80rests. As is illustrated inFIGS. 3 and 4, the upper surface90of the ring88and the lower surface92of the upper attachment80may have respective projecting and receding profiles in order to establish a shape coupling.

As is visible inFIGS. 3 and 4, the bushing32of each elastic joint30is fixed, for example by hammering, to the upper end of the corresponding tubular upright22of the fixed support structure12.

The lower portion of the connecting rod66extends through the holes56and58of the body48and of the washer50of the compression member46. The first pin76connects the lower end68of the connecting rod66to the compression member46in an articulated manner. The pin76is housed in the concave seat64of the washer50. The central portion of the connecting rod66included between the ends68,70extends through the helical spring40and through a through hole94formed in the upper part of the bushing32.

The upper end70of the connecting rod66that projects above the ring88is bent forwards. In this way, the articulation axis C, between the upper end70of the connecting rod66and the upper attachment member80, is moved forward by a distance d (FIG. 3) with respect to the longitudinal axis A of the spring40. The articulation axis B of the lower end68of the connecting rod66of the compression member46is essentially located on the longitudinal axis A of the spring40.

The effect of the forward displacement of the axis C with respect to the longitudinal axis A of the spring40is that of increasing, all other conditions being equal, the elastic torque applied by the springs40to the backrest24. When a backward thrust is applied to the backrest24by the user's back, the upper attachment80pivots backwards about a fulcrum point, indicated with F inFIGS. 3 and 4. The fulcrum point F is defined by the point of mutual rotation between the contact surfaces of the upper attachment80and the ring88. The rotation of the upper attachment80about the fulcrum point F compresses the spring40by means of the connecting rod66. The return elastic force of the spring40has a lever arm of dimension d1, with respect to the pivot fulcrum F. The lever arm d1is increased thanks to the forward displacement of the articulation axis C. Consequently, at a constant axial force exerted by the spring40, thanks to the forward displacement of the articulation axis C, a higher torque on the backrest24is achieved, which counteracts the backward thrust applied by the user.

In the position of maximum backward inclination of the backrest, illustrated inFIG. 4, the radial shoulder54of the compression member46rest against the lower end of the bushing32and forms a stroke end, which prevents further backward inclination of the backrest.

To stiffen the fixing area between the side portions28of the backrest24and the corresponding upper attachments80, each elastic joint30may be fitted with a stiffening pin96(FIGS. 3 and 4) having an upper portion driven into a hole98of the side portion28of the backrest24, and a lower portion driven into a hole100of the respective upper attachment80.

Each elastic joint30can also be fitted with an protective elastic element102arranged coaxially around the contact area between the upper attachment80and the ring88, in order to avoid pinching of garments or parts of the body between the contact surfaces of the upper attachment80and the ring88.

Of course, without prejudice to the principle of the invention, the details of construction and the embodiments may vary widely with respect to those described and illustrated without departing from the scope of the invention as defined by the following claims.