Seat with a tubular base and method for mounting same

Abstract

The invention relates to a seat comprising a squab (300), a backrest (100) separate from the squab (300), and a base (1) comprising a leg assembly and a tubular frame supporting the backrest (100) and the squab (300), comprising: a tubular frame configured as a trapezium; a backrest (100) which comprises a groove for positioning on a rear crossmember (3) of the frame, and channels (102) for elastic clip-fastening on longitudinal members (4, 5) of the frame; a squab (300) resting on the tubular frame and comprising, on the lower face thereof, a part (350) for centring and reversible fastening on the tubular frame.

Description

[0001] SEAT WITH TUBULAR BASE AND MOUNTING METHOD.

[0002] The present invention relates to a seat comprising, in a very conventional manner, a seat, a backrest and the base of which comprises a base surmounted by a tubular frame used as a support for the backrest and the seat. The backrest and the seat are based on plastic shells fixed to the base, and consequently designed to adapt to the tubular configuration of the support frame, which surmounts the legs of the chair.

[0003] In many long-known structures, for example for chairs, the plate forming the seat and the backrest are fixed to the base frame by conventional mechanical means such as horizontal bolting or riveting. In this case, assembly / disassembly operations can be tedious and time-consuming. For simpler chairs, this type of attachment can also appear on the visible surface of the backrest or seat, or even protrude if the design or assembly is poorly done. At worst, this can cause damage to clothing when sitting or standing up. In some cases, such as the solution described in KR200493744Y1, the attachment mechanisms are provided under the seat, manipulated with tools in a horizontal direction, and are therefore invisible from above.

[0004] Tool-free assembly structures also exist, allowing the seat and backrest to be fixed to a structure comprising the seat base, often quickly but with disassembly that is not always easy or possible. Thus, CN205568392U discloses a solution in which the seat and backrest are formed from a single shell that unfolds in two directions, the fixing means being located at the seat. This has reliefs capable of sliding on side members of a tubular structure of the base and fixing parts of said structure in contact with the lower face of the seat. W02011029161A1 also discloses a configuration in which the backrest and the seat are in one piece, and fixed to the base using a fixing / locking mechanism placed centrally under the seat, which must therefore be positioned correctly in relation to said base to secure them to each other.Such designs are intended for single-shell seat models, which do not allow for the seat configuration to be modulated since the seat and backrest are a single piece. Since the attachment is generally made at the seat, the question of securing the backrest does not arise. Assembly / disassembly, which depends on this single, bulky part that is not always easy to handle, can be difficult to carry out.

[0005] There are also configurations in which the seat and backrest are made as two separate shells, which must then be installed separately on a base with a leg. The seat described in GB2587463 thus has a backrest separate from the seat, with grooves oriented towards the seat, by means of which the backrest is fixed to the sides of the seat. During assembly, the seat is therefore first fixed to a leg structure, then the backrest is secured to the seat. The backrest is therefore not directly connected to the leg, which represents a design constraint on the seat, the configuration of which must be planned to be able to receive the backrest via a rigid connection. There is no modularity possible in the assembly, the backrest and the seat being dependent on each other.

[0006] The configuration of the invention overcomes these drawbacks by proposing a modular seat design whose parts to be mounted on the tubular base structure comprising the base are designed to be assembled without tools and very easily. The sequence of their assembly also guarantees precise relative positioning, the assembly allowing the implementation of a locking of the backrest and the seat on the base presenting the base.

[0007] To this end, the seat of the invention, conventionally comprising a seat, a backrest separate from the seat and a base comprising a base and a tubular frame supporting the backrest and the seat, is such that:

[0008] - the tubular frame is shaped like a trapezoid and has a rear cross member, two side members and a front cross member constituting the large base of the trapezoid;

[0009] - the backrest has a positioning groove on the rear cross member and elastic clip-on fixing channels on the side members, housing the upper part respectively of the rear cross member and a portion of the side members proximal to said rear cross member; and

[0010] - the seat rests on the tubular frame and has on its lower face a reversible centering and fixing part on the tubular frame, said part having means for clipping the seat onto the front cross member and fixing it to the side members.

[0011] As will be seen in more detail below, the backrest is first mounted by elastic clipping, its attachment to the rear crosspiece and to the side members ensuring its immobilization in relation to the tubular frame of the base fitted with the base. In a second step, the seat is placed on the tubular frame and slid towards the backrest already secured to the frame until it reaches contact with said backrest, this position corresponding on the one hand to a mutual locking with the side members of the frame and on the other hand to a clipping of the seat on the tubular frame. There is only one possible positioning for the two parts forming respectively the backrest and the seat, achieved in both cases very easily and intuitively by tool-free connections, including in particular elastic clips.

[0012] Furthermore, preferably, the elastic clipping channels of the backrest on the side members can be locked relative to the tubular frame. The seat then comprises a member for locking each channel on a side member. The clipping from above as already carried out, participating in practice in the desired positioning of the backrest on the tubular frame, can in fact be disassembled by a reverse operation in a substantially vertical direction if it remains in the state. According to the invention, it is therefore supplemented by a locking means in this direction.

[0013] More specifically, according to one possible configuration, the locking member of each backrest channel on a frame rail may consist of a half-sleeve with a U-shaped section, which can slide axially in the channel to complete surrounding the rail. This U-shaped component completes the covering of the rail, the upper part of which is covered by the clip-on channel. The respective dimensions and shapes allow axial sliding but no relative radial movement, which is consistent with the objective of locking in a vertical direction.

[0014] The half-sleeve constituting the locking member is also preferably provided at one end with at least one flexible tab intended to be fixed by elastic clipping to the chute, by cooperation between a recess and a relief of corresponding shapes of the tab and a portion of the internal wall of the proximal chute of the rear cross member. The locking member is therefore itself immobilized axially relative to the chute when it is completely slid into the chute and clipping has occurred, said clipping signaling that its positioning relative to said chute is finalized.

[0015] According to the invention, the groove for positioning the backrest on the rear crossmember comprises a plurality of ribs integral with the backrest, each having a semicircular opening capable of housing said crossmember, as well as at least two hooks capable of being inserted into openings made in the rear face of the rear crossmember. When the backrest is placed on the tubular frame, these ribs conform to the rear crossmember on which they rest, sharing the support on this crossmember. In such a configuration, the groove is somewhat discontinuous, materialized by a few discreet inverted arches. The seat itself comprises means for installation / positioning on the tubular frame of the base, and the centering and fixing part of the seat present on its lower face may, according to the invention, comprise:

[0016] - two lateral rails parallel to the side members having rectilinear internal conduits with semi-cylindrical recesses opening into a vertical plane opposite each other and open at their axial ends, capable of accommodating the side members and sliding in contact with them;

[0017] - said rails being able to be inserted between the side members when their distal end of the backrest is in the vicinity of the front cross member, and housing said side members when their proximal end of the backrest comes against the chutes; and

[0018] - a housing for the front crossmember, comprising a channel opening towards the side rails and with a flexible wall to allow the insertion of said crossmember into the channel by elastic deformation of said flexible wall when the axial ends of the proximal rails of the backrest come against the backrest chutes.

[0019] The seat can therefore be placed on the tubular frame when it is initially placed at a distance from the backrest, since the side rails can then freely insert themselves between the side members. It is then brought closer to the backrest, gradually causing a rail and a side member to come closer on each side, the latter penetrating as it moves inside a semi-cylindrical conduit, which it fills at the end of sliding, upon arrival in contact with the backrest channels. This movement in practice achieves self-centering of the seat in the tubular frame. In this final position, the front cross member is positioned in the housing channel, which for this purpose has a hollow shape capable of housing the cylindrical cross member over a part of its periphery slightly greater than half the cylinder of the cross member, which implies an axial opening of the channel of width slightly less than the diameter of the cross member.The elastic flexible wall of the housing channel allows the passage and positioning of one inside the other.

[0020] According to one possibility, the wall of the housing includes clip-on protrusions in slots made in the front cross member, said protrusions being manually operable by tabs on said wall. These tabs may, for example, consist of extensions of sections of the wall separated from the rest of the housing. Their manipulation only occurs to remove the protrusions from the slots in the front cross member, with a view to disassembling the seat from the tubular frame during a movement in the opposite direction.

[0021] According to one possible configuration, the side rails and the front crossbar housing are part of a U-shaped piece fixed to the underside of the seat. This piece, which manages the connection of the seat to the tubular frame of the base equipped with the chair legs, is separate from the seat, to which it is fixed before carrying out said connection. The underside of the seat has for this purpose means for positioning and clipping the U-shaped piece. No tools are therefore necessary to assemble them.

[0022] The invention further relates to a method of mounting a seat as described previously, comprising the following steps:

[0023] - Positioning the backrest on the rear cross member of the tubular frame and clipping the channels onto the side members;

[0024] - Locking of the chutes on the side members by the locking devices;

[0025] - Fixing the centering and fixing piece on the underside of the seat;

[0026] - Inserting the seat between the side members so that it rests on the tubular frame;

[0027] - Moving the seat towards the backrest until the front crosspiece is clipped into the centering and fixing part of the seat on the tubular frame of the base.

[0028] Other aims and advantages of the present invention will become apparent during the description which follows, relating to an embodiment which is given only as an indicative example. The understanding of this description will be facilitated in particular by reference to the figures attached in the appendix and in which:

[0029] - Figure 1 shows an exploded perspective view of a seat model according to the invention;

[0030] - Figure 2 shows a partial perspective view of the method of fixing the backrest to the tubular frame of the seat base by means of the clipping channels;

[0031] - Figures 3a and 3b show the means of positioning the backrest on the rear cross member of the tubular frame;

[0032] - Figures 4a and 4b show cross-sectional views of the cooperation between a clipping chute of the backrest to a side member and a locking member;

[0033] - Figures 5a to 5c illustrate, in a view from below, the backrest chute clipped onto a side member, then equipped with a locking member respectively seen from the outside then in section;

[0034] - Figure 6 shows a perspective view of the seat shell, from the side of its lower face equipped with the means of fixing to the U-shaped part, with enlarged detailed views of said means of fixing;

[0035] - Figure 7 shows the base consisting of the shell and the U-shaped part secured to each other, with enlarged detailed views of the operation of the means of fixing one to the other;

[0036] - Figure 8 shows, in a view from below, the seat being installed on the frame; and

[0037] - Figure 9 shows, in side view, the seat secured to the frame, with an enlarged detailed view of the elastic clip connection of the front cross member in a housing in the U-shaped part of the seat.

[0038] With reference to Figure 1, the seat of the invention comprises a tubular base 1 comprising a base formed of four legs 2 and a tubular upper frame comprising a rear cross member 3, two side members 4 and 5 and a front cross member 6 and, optionally, armrest frames 7 and 8. A backrest 100 is fixed to this tubular base 1, at and in the vicinity of the rear cross member 3. It is locked to the base 1 by means of locking members 200. A seat 300 formed of a shell 310 and a U-shaped part 350 is fixed to the tubular frame, more precisely to the side members 4, 5 and to the front cross member 6 of said frame.

[0039] The backrest 100 is fixed to the tubular frame via protrusions 101 provided with channels 102 (see figure 2) which clip elastically onto the side members 4, 5 near the cross member 3. These channels 102 with a partial cylindrical recess of circular section surround the top of the side members 4, 5 over a fraction of their periphery which is greater than half a cylinder. The side walls 103, 104 of the chute 102 (see figures 4a, and 4b) are consequently flexible, to allow them to be clipped onto the tubing of the side member 4, 5. The backrest 100 also rests on the rear cross member 3, as illustrated in figures 3a and 3b, via ribs 130 each having a semi-circular opening housing said cross member 3. These aligned ribs 130 in reality constitute a discontinuous groove; they structurally perform substantially the same function as a continuous groove.To ensure correct positioning, said openings of the ribs 130 have an internal diameter which corresponds to the external diameter of the crosspiece 3, with a tight tolerance, so that said openings fit the crosspiece 3. Furthermore, hooks 140, in this case two in number, are provided to be inserted into openings 31 made in the rear face of the rear crosspiece 3. These hooks 140 make it possible in particular to prevent the backrest 100 from tilting forward. They are particularly visible in figure 3b.

[0040] The protuberances 101 comprising the chutes 102 have, in the configuration shown, an inverted U-shaped section encompassing the circular section of the chutes 102 themselves, having an upper wall 110 and side walls 111, 112 of vertical appearance. The residual space between these walls 111, 112 and the side walls 103, 104 of the chute 102 facing them is used in particular for fixing the locking member 200. This takes the form of a portion of sleeve with a very generally U-shaped section which completes from below the covering of the spar 4, 5, the upper part of which is already inserted into the chute 102. The sleeve portion has been described as a half-sleeve, considering its U-shaped section.

[0041] Figure 4a shows an axial end of the locking member 200 which closes the residual spaces between the walls 111, 112 and the side walls 103, 104 of the chute 102, and which fits the portion of spar 4, 5 not covered by the chute 102. Figure 4b represents a section of an intermediate part of this locking member 200, illustrating the existence of external or internal ribs on its walls. Thus, the ends of the branches of the U are provided with external ribs 201, 202 which ensure contact with the walls 111, 112 of the protrusion 101. The curvilinear wall forming the base of the U is provided with ribs 203 coming into contact with the cylindrical lower portion of the spar 4, 5.All these axial ribs 201, 202, 203 ensure a tightening which does not, however, hinder the sliding movement of the locking member 200 relative to the chute 102, also ensured by their respectively internal and external faces which have a corresponding shape, the sliding also being guided by these faces which match.

[0042] More precisely, each locking member 200 is installed by sliding in said residual spaces between the walls 103, 104 of the chute 102 and the side walls 111, 112 of the protuberance 101. This sliding is notably guided by the end edges 105, 106 of the walls 103, 104 of the chute 102 which cooperate with shoulders 204, 205 placed between the branches of the U of the locking member 200 and the curvilinear wall forming its base.

[0043] In the bottom view of Figure 5a, the outlet of the residual spaces placed between the walls 103, 111 and 104, 112 respectively appears, limited by the edges 105, 106. Figure 5b is equivalent to Figure 5a in the presence of the locking member 200, the bottom view showing said locking member 200 fixed at the end of sliding, preventing any vertical movement of said member 200 which would then allow the backrest 100 to be unclipped from the tubular frame of the base 1. Figure 5c is a section which shows the axial fixing of the half-sleeve 200 when the sliding in the chute 102 is completed. In addition to the vertical locking mentioned, there is therefore also a horizontal locking of the locking member 200 in the chute 102 of the protuberance 101.This is carried out, in the example shown in figure 5c, via flexible tabs 206 protruding axially from the end of the locking member 200 located in the vicinity of the lower crosspiece 3. These tabs 206 each comprise a hollow or recess capable of housing a relief 113, 114 of corresponding shape protruding from the internal face of the protuberance 101, beyond the chute 102. Their cooperation and the axial locking which follows is carried out by elastic clipping at the end of sliding.

[0044] The backrest 100 is initially led towards the tubular frame of the base 1 from above, in the direction of the rear crosspiece 3, in contact with which it can be correctly positioned by inserting said crosspiece 3 into the circular openings of the discontinuous groove formed by the ribs 130 of the backrest 100, ensuring the insertion of the hooks 140 into the openings 31 (see in particular figure 3b) by a slight tilting of the backrest 100 towards the rear before verticalizing it again. This verticalization leads to clipping of the chutes 102 with elastic walls 103, 104 onto the sections of the side members 4, 5 proximal to the rear cross member 3. The locking members 200 are then installed by sliding along the axis of said side members 4, 5 in the direction of the rear cross member 3, until the tabs 206 are clipped onto the reliefs 113, 144 which in practice lock them to the backrest 100.This clipping, and consequently the locking implemented by the locking members 200, is reversible.

[0045] The seat 300 is, as mentioned, composed of two parts: a shell 310 of flat appearance and a U-shaped part 350, attachable to the shell 310 and designed to manage the fixing of the seat 300 to the tubular frame surmounting the legs 2 of the chair 1. The shell 310, on its lower face, comprises means for fixing the U-shaped part 350, visible in figure 6. Their location roughly outlines the location of the tubular frame of the base 1. Two bars 311, 312 in a single piece with the shell 310 and in directions parallel to those of the side members protrude from this lower face. They comprise, towards the outside of the shell 310, reinforcing ribs framing reliefs for centering and fixing the U-shaped part 350 to the shell 310. Two hooks 313, 314 are arranged on a line perpendicular to said bars 311, 312. These hooks 313 and 314 are shown in enlarged detail in the left circular window of figure 6.Each bar 311, 312 has at its two ends a relief with a chamfered semicircular arch 315, said relief being connected to the bar. A canal recess 316 separates the arch 315 from the contiguous wall of the bar 311, 312. The free ends of the piles extending the semicircular arch are flat, provided with appendages 318, 319 also chamfered on the arch side. In the middle, a cylindrical stud 317 protrudes from the bars 311, 312.

[0046] The U-shaped part 350 comprises, on the two branches of the U, a lateral rail 360 having an internal conduit 351 with a semi-cylindrical recess open at its axial ends. The two rails 360 are slightly convergent, the convergence angle being the same angle as the angle between the side members 4, 5. The ducts of the rails 351 are oriented so as to open radially opposite one another, in this case towards the outside of the hull 310. The bottom of these rails 360 has openings capable of cooperating with the aforementioned reliefs 315, 317 for the purpose of fixing the U-shaped part 350 on the bars 311, 312. Thus, as visible in figure 7, in the enlarged detail placed on the left, the semicircular arch reliefs 315 cooperate with two orifices placed in the vicinity of the ends of the duct 351.The fixing is carried out by elastic clipping, at least one flexible relief 352 protruding from the inner wall of these orifices being provided to clip into the aforementioned canal recess 316 separating the arch 315 from the contiguous wall of the bar 311, 312. These orifices also comprise an inner tab 353 capable of being inserted between the piles of the arch 315, serving for guidance - as does the flat surface of the appendages 318, 319 of the piles of the arch - at the time of insertion of the branches of the U-shaped part 350 comprising the rails 360 in contact with the bars 311, 312 of the shell 310. The cooperation between the studs 317 and the corresponding orifices placed in the center of the rails 351 helps in the relative positioning of the two elements.

[0047] The U-shaped part 350 also comprises, at the base of the U, a housing comprising an internal channel 354 provided to house the front crossmember 6, opening towards the center of the U, that is to say towards the rails 351. Two openings 355 are made at the base of this housing channel 354, in order to allow the passage of the hooks 313, 314 protruding from the lower face of the shell 310 to ensure the positioning and fixing of the U-shaped part 350 and the shell 310 at the base of the U. The housing 354 comprises a flexible wall, in particular radially, surrounding a hollow volume also of cylindrical appearance provided to allow elastic insertion of the crossmember 6 in a substantially horizontal direction into the channel 354, as shown in figures 8 and 9. It should be noted that the U-shaped part comprises a U-shaped frame 356 of flat appearance, connecting the rails 360 and the channel housing 354, and intended to be positioned in contact with the lower face of the shell 310.It is from this U-shaped frame 356 that the lateral rails 360 and the housing channel 354 develop downwards. The U-shaped part 350 is made of a flexible material, which in particular allows mutual adaptations / fixings between it and the shell 310 by elastic clipping.

[0048] When the seat 300, composed of the integral shell 310 / U-shaped piece 350 assembly, is in the position shown in figure 8 relative to the base and in particular relative to the tubular frame composed of the rear 3 and front 6 crosspieces and the side members 4 and 5, a movement is given to it in the direction of the arrow F. In this first position, the width between the side members 4, 5 is slightly greater than the width between the rails 351.Given the converging direction of the axes respectively of the side members 4, 5 and the rails 360 and the positioning of the semi-cylindrical conduits 351 opposite the side members 4, 5 when the shell 310 is placed on the tubular frame, said side members 4, 5 gradually penetrate into the conduits 351 of the rails 360, until they are housed inside them, resting on their bottoms, when the free ends of the proximal rails 360 of the backrest 100 arrive in the immediate vicinity of the chutes 102, leaving a functional clearance between them. The converging orientations of the side members 4, 5 and the rails 360 allow in practice a self-centering of the seat 300 inside the tubular frame of the base 1. The corresponding circular section of the side members 4, 5 and the conduits 351 furthermore causes, in this final position of insertion of one into the other, a securing of the seat 300 to the tubular frame of the base 1 in a vertical direction.In the last part of the path according to arrow F, before the butting, the crosspiece 6 is housed elastically in the channel of the housing 354. The clipping occurs as shown in figure 9, at the end of movement in the direction F. More precisely, the opening of the channel 354 in a plane of vertical appearance substantially perpendicular to the direction of this movement being less wide than the diameter of the tube of the front crosspiece 6, a first elastic clipping takes place during the insertion of one into the other, guided at the entrance by the tabs 357. These tabs 357 are further provided with protrusions 358 which are intended to be housed, according to a second elastic clipping, in slots 61, 62 made in the front crosspiece 6. These tabs 357 are extensions of portions of the wall of the channel 354 themselves separated by radial cutting from the rest of the housing.

[0049] The assembly of such a chair, once one has its components, namely the tubular base 1, the backrest 100, the locking members 200, the seat shell 310 and the U-shaped part 350, is simple and quick. The operator in charge of assembly begins by fixing the backrest 100 on the base, as explained previously. Then, he proceeds to lock them by placing the locking members 200. Next, he assembles the seat 300 by securing the U-shaped part 350 to the shell 310 of the seat. Finally, he places the seat 300 relative to the tubular base 1 as shown in figure 8, a little distance from the backrest 100.A movement towards said backrest 100 allows the sliding of the rails 360 and their conduits 351 in contact with the side members 4, 5, until the horizontal clipping of the protrusions 358 in the slots 61, 62 of the front cross member 6, the proximal axial ends of the backrest 100 of the rails 360 then being in proximity - only separated by a functional clearance - of the chutes 102, with the side members 4, 5 resting on the bottom of the rails 351, seat 300 centered. This proximity leads to a second axial blocking of the locking members 200, in addition to that which results from the flexible tabs 206 and which has been explained above. Said members 200 can in fact no longer slide in a direction which separates them from the rear cross member 3. There is therefore in practice a safety redundancy for the locking of the backrest.

[0050] The configuration examples which are the subject of the figures should not be considered as exhaustive of the invention, which includes for example variants of shape in the clipping systems, or in the shapes of the constituent elements of the chair such as the backrest 100, the tubular base 1, the seat shell 310, etc.

Claims

Claims 1. Seat comprising a seat (300), a backrest (100) separate from the seat (300) and a base (1) comprising a base and a tubular frame supporting the backrest (100) and the seat (300), characterized in that: - the tubular frame is shaped like a trapezoid and has a rear cross member (3), two lateral side members (4, 5) and a front cross member (6) constituting the large base of the trapezoid; - the backrest (100) comprises a positioning groove on the rear cross member (3) and chutes (102) for fixing by elastic clipping on the side members (4, 5), housing the upper part respectively of the rear cross member (3) and of a portion of the side members (4, 5) proximal to said rear cross member (3); and - the seat (300) rests on the tubular frame and comprises on its lower face a centering and fixing part (350) reversible on the tubular frame, said part (350) comprising means for clipping the seat (310) onto the front cross member (6) and fixing it to the side members (4, 5).

2. Seat according to the preceding claim, characterized in that it comprises a locking member (200) for each chute (102) on a side member (4, 5).

3. Seat according to the preceding claim, characterized in that the locking member (200) consists of a half-sleeve with a U-shaped section, which can slide axially in the channel (102) to finish surrounding the side member (4, 5).

4. Seat according to the preceding claim, characterized in that the locking member (200) is provided with one end of at least one flexible tab (206) intended to be fixed by elastic clipping to the chute (102), by cooperation between a recess and a relief (113, 114) of corresponding shapes of the tab (206) and of a portion of the internal wall of the chute (102) proximal to the rear cross member (3).

5. Seat according to one of the preceding claims, characterized in that the positioning groove of the backrest (100) on the rear crossmember (3) comprises a plurality of ribs (130) integral with the backrest (100) each having a semicircular opening capable of housing said crossmember (3) as well as at least two hooks (140) capable of being inserted into openings (31) made in the rear face of the rear crossmember (3).

6. Seat according to one of the preceding claims, characterized in that the part (350) for centering and fixing the seat (300) comprises: - two side rails (360) parallel to the side members (4, 5) having rectilinear internal conduits (351) with semi-cylindrical recesses opening into a vertical plane opposite one another and open at their axial ends, capable of housing the side members (4, 5) and sliding in contact with them; - said rails (360) being able to be inserted between the side members (4, 5) when their distal end of the backrest (100) is in the vicinity of the front cross member (6), and housing said side members (4, 5) when their proximal end of the backrest (100) comes against the chutes (102); and - a housing for the front cross member, comprising a channel (354) opening towards the side rails (360) and with a flexible wall to allow the insertion of said crosspiece (6) into the channel (354) by elastic deformation of said flexible wall when the axial ends of the proximal rails (360) of the backrest (100) come against the chutes (102) of the backrest (100).

7. Seat according to the preceding claim, characterized in that the wall of the housing comprises projections (358) for clipping into slots (61, 62) made in the front crosspiece (6), said projections (358) being manually operable by tabs (357) of said wall.

8. Seat according to one of claims 6 and 7, characterized in that the side rails (360) and the housing of the front crosspiece (6) are part of a U-shaped part (350) fixed to the lower face of the seat (300).

9. Seat according to the preceding claim, characterized in that the lower face of the seat (300) comprises means for positioning and clipping the U-shaped part (350).

10. Method for mounting a seat according to the preceding claims, characterized by the following steps: - positioning the backrest (100) on the rear cross member (3) of the tubular frame and clipping the chutes (102) onto the side members (4, 5); - locking the chutes (102) on the side members (4, 5) by the locking members (200); - fixing the centering and fixing part (350) on the lower face of the seat (300); - inserting the seat (300) between the side members (4, 5) so that it rests on the tubular frame; - moving the seat (300) towards the backrest (100) until the front crosspiece (6) is clipped into the part (350) for centering and fixing the seat (300) to the tubular frame of the base (1).

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