Abstract:
Tilting seat chair, comprising: a base structure ( 16 ) bearing a transverse tilting axis ( 24 ), a seat support structure ( 14 ), tiltably mounted about the transverse tilting axis ( 24 ), an elastic arrangement for opposing the seat tilting motion, and an adjustment device ( 42 ) for varying the force opposing the elastic arrangement. The aforesaid elastic arrangement comprises a torsion bar ( 32 ) connecting the seat support structure ( 14 ) to the base structure ( 16 ) in a tilting manner about the transverse tilting axis ( 24 ). The torsion bar ( 32 ) has at least a first portion ( 32   a ) rotatably connected to the seat support structure ( 14 ) and at least a second portion ( 32   b ) connected to the base structure ( 16 ) through the aforesaid adjustment device.

Description:
FIELD OF THE INVENTION 
     This invention relates to a chair with a tilting seat, of the type comprising: 
     a base structure bearing a transverse tilting axis, 
     a seat support structure, tiltably mounted about the said transverse tilting axis, 
     elastic means capable of opposing the seat tilting motion, and 
     means of adjustment for varying the force opposing the said elastic means. 
     SUMMARY OF THE INVENTION 
     The purpose of this invention is to provide a chair with a tilting seat of the type described above, provided with elastic means and adjustment means having a particularly simple or robust and compact structure. A further object of this invention is to provide a device for adjustment of the elastic means which opposes the tilting of the seat, which device does not require a large operating force. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     This invention will now be described in detail with reference to the appended drawings, given purely by way of a non-restrictive example, in which: 
     FIG. 1 is a diagrammatical side view of a chair according to the invention, 
     FIG. 2 is a perspective view of the mechanism for tilting the seat of the chair in FIG. 1, 
     FIG. 3 is a plan view along the arrow III in FIG. 2, 
     FIGS. 4 and 5 are cross sections along the line IV—IV in FIG. 3 in two different working positions, 
     FIG. 6 is a partial cross section along the line VI—VI in FIG. 3, 
     FIG. 7 is a cross section along the line VII—VII in FIG. 4, 
     FIG. 8 is a cross section similar to that in FIGS. 4 and 5, illustrating a variant of this invention, and 
     FIG. 9 is a diagrammatical cross section along the line IX—IX in FIG.  8 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 illustrates a chair provided with a seat  10  and a back  12 . Seat  10  is fixed to a seat supporting structure  14  which is tiltably mounted about a transverse axis with respect to a base structure  16  mounted at the top of a central support  18 , of a type which is in itself known, which can be adjusted for height. 
     With reference to FIG. 2, from the point of view of its construction, seat support structure  14  comprises two longitudinal members  20  of bent sheet, which are spaced apart in a transverse direction and connected together by a rear plate  22 . Base structure  16  is formed of a body of substantially a box shape which has a transverse tilting axis  24  about which is tiltably mounted seat supporting structure  14 . A pair of tubular members  26  are fixed to longitudinal members  20  and are arranged coaxially with tilting axis  24 . 
     In FIG. 2,  28  indicates a supporting structure for the back. This supporting structure is tiltably mounted on base structure  16  about a second transverse tilting axis  30  parallel to tilting axis  24  and set at a slight distance from the latter towards the rear of the chair. Back support structure  28  is connected by means of a pair of tie bars (not illustrated) to seat supporting structure  14 , so that the tilting movements of the seat and back are synchronized. A mechanism for immobilizing the seat and the back in a plurality of operating positions is described in detail in a simultaneous patent application by the same applicant. 
     With reference to FIGS. 4,  5  and  6 , tilting axis  24  of seat supporting structure  14  comprises a torsion bar  32  which extends coaxially with axis  24 . From the point of view of its construction, torsion bar  32  comprises a plurality of extended rods  34  having a transverse cross section of flattened rectangular shape. The various rods  34  are placed on top of each other and fixed together in such a way as to form a bar of quadrangular transverse cross section with an extension in the transverse direction which is slightly greater than the distance between longitudinal side members  20  of seat supporting structure  14 . As can be seen in particular in FIG. 6, end portions  32   a  of torsion bar  32  project laterally outside the two longitudinal side members  20 . End portions  32   a  of torsion bar  32  are fixed to tubular members  26  forming part of seat support structure  14 . This attachment may for example be achieved by means of a pair of washers  35  welded to tubular members  26  which have quadrangular holes engaged by end portions  32   a . A pair of transverse pins  36  prevents torsion bar  32  from moving in an axial direction. The portions of torsion bar  32  which project at the side are covered by corresponding caps  38 . A central portion  32   b  of torsion bar  32  is rotatably connected to a lever  40 . In the example illustrated in FIGS. 4 and 5, the rotatable connection between lever  40  and central portion  32   b  is achieved by the fact that lever  40  has a hole with a quadrangular cross section within which the central portion  32   b  of torsion bar  32  is inserted. With reference to FIGS. 4 and 5, lever  40  acts together with an adjustment device  42 , supported by base structure  16 , which is capable of varying the angular position of lever  40  with respect to the axis of torsion bar  32 . In the embodiment illustrated in FIGS. 4 and 5, adjustment mechanism  42  comprises a wedge  44  which can slide in a longitudinal direction on a guide wall  46  of base structure  16 . Wedge  44  has an inclined guide surface  48  along which is slidably mounted a shoe  50  having a concave seat  52  which supports a rounded end  54  of lever  40  (see also FIG.  7 ). Wedge  44  can be moved in a longitudinal direction by causing a knob  56  located outside base structure  16  in a central position on the front of the chair to rotate. Knob  56  is rotatably connected to a threaded rod  58  which is axially attached to base structure  16  and is free to rotate around its own longitudinal axis. Threaded bar  58  engages a threaded nut  60  which is fixed with respect to wedge  54 . The elastic action of torsion spring  32  tends to hold lever  40  pressed against shoe  50 . Thus movement of wedge  44  which is controlled manually by the user through knob  56  can vary the angular position of lever  40  which consequently alters the angular position of central section  32   b  of the torsion spring about its own axis. FIGS. 4 and 5 illustrate the two end-of-travel positions of wedge  44  which define the field of adjustment for device  42 . Each angular position of lever  40  corresponds to a particular amount of preloading on torsion spring  32 . Given that seat support structure  14  is fixed to the end of torsion bar  32 , preloading of the torsion bar opposes tilting of the seat in the direction indicated by arrow  62  in FIGS. 4 and 5. The user therefore has the possibility of continuously adjusting the elastic force opposing the tilting movement of the seat between a minimum value and a maximum value. From the description above it will be understood that torsion bar  32  performs both the function of the elastic member which opposes the tilting movement of the seat and back, and that of the pivot member between the seat supporting structure and base structure  16 . This arrangement renders the tilting mechanism for the seat particularly compact in that the space which is normally necessary to house the shaft providing the joint between the seat support structure and the base structure also incorporates the elastic member. Adjustment mechanism  42  makes it possible to achieve an extensive gearing down of the operating force, as a result of which knob  56  can be operated easily without having to apply excessive force. 
     FIGS. 8 and 9 illustrate a variant of the adjustment mechanism according to this invention. The details corresponding to those previously described are indicated by the same reference numbers. In this variant threaded rod  58  is replaced by a shaft  64  which has teeth  66  at one end which engage with a wheel  68  which can rotate with and is incorporated with a threaded rod  70 . Threaded rod  70  is free to rotate about its own longitudinal axis and engages a nut  72 . Lever  40  fixed in central section  32   b  of torsion bar  32  has a fork-shaped end with two limbs  74  which support nut  72  on opposite sides with respect to threaded bar  70 . The elastic reaction force of torsion bar  32  exerts a downward force on nut  72  and prevents the latter from rotating about the axis of threaded rod  70 . Therefore rotation of shaft  64  controlled by manually operated knob  56  (not visible in FIGS. 8 and 9) can be used to move nut  72  upwards and downwards and as a consequence to vary the angular position of lever  40 . In this case too the user can vary the elastic force opposing the oscillating movement of the seat between a minimum value and a maximum value by rotating knob  56 .