chair

Abstract

To provide a chair having excellent design flexibility in which an upper frame is rotatably supported for a lower frame.SOLUTION: A back support medium D of a chair includes: a lower frame p1 having a shank J; and an upper frame p2 having a bearing part K and rotatably supported for the lower frame p1. The shank J extends in a horizontal direction and has a width dimension wj in a longitudinal direction which is structured shorter than a width dimension in a vertical direction. In an upper part in the shank J, there is formed a curve surface jm which is partially shaped as a cylindrical curved surface and can be indirectly engaged through an intermediate member S with the bearing part K.SELECTED DRAWING: Figure 12

Description

Technical Field

[0001] The present invention relates to a chair used in an office or the like.

Background Art

[0002] Conventionally, various chairs have been known in which a backrest is rotatably supported on a support base via a back support rod (see, for example, Patent Document 1).

[0003] In Patent Document 1, an upper back frame is rotatably supported in the front-rear direction on a lower back frame that constitutes the back support rod. A metal support shaft (so-called steel shaft) extending in the left-right direction is provided between the lower back frame and the upper back frame.

[0004] In such a configuration, a structure for providing a metal support shaft between the lower back frame and the upper back frame is essential. For this reason, the degree of freedom in design for reducing the number of parts and suppressing the assembly man-hours has been restricted.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] The present invention has been made paying attention to the above circumstances, and an object thereof is to provide a chair excellent in the degree of freedom in design for rotatably supporting an upper frame with respect to a lower frame at least.

Means for Solving the Problems

[0007] That is, the chair of the present invention has the following configuration.

[0008] The invention described in claim 1 is a chair in which a backrest is rotatably supported on a support base via a back support, wherein the back support comprises a lower frame having either a shaft portion or a bearing portion that receives the shaft portion, and an upper frame having the other of the shaft portion and the bearing portion and being rotatably supported with respect to the lower frame, wherein the shaft portion extends in the horizontal direction, and its width in the front-to-back direction is shorter than its width in the up-to-down direction, and an axial curved surface is formed on either the upper or lower part of the shaft portion, which has a partial cylindrical curved surface shape and can engage directly or indirectly with the bearing portion via another member.

[0009] The invention described in claim 2 is the chair according to claim 1, wherein the lower frame is provided with the shaft portion having the axial curved surface formed on its upper part, and the upper frame is provided with the bearing portion.

[0010] The invention described in claim 3 is the chair according to claim 1, wherein the upper frame or the lower frame, which includes the shaft portion, is integrally formed from synthetic resin.

[0011] The invention described in claim 4 is the chair according to claim 2, wherein the lower frame is provided with an upper frame engaging portion including the shaft portion, and the upper frame engaging portion comprises a lower frame base, left and right support arms extending in pairs in the vertical direction from the left and right of the lower frame base, and a horizontal frame portion installed between these left and right support arms and including the shaft portion.

[0012] The invention described in claim 5 is the chair according to claim 4, wherein the horizontal frame comprises shaft portions arranged in pairs on the left and right sides, each outer portion of which is integrally connected to the left and right support arms, and connecting portions connecting these shaft portions.

[0013] The invention described in claim 6 is the chair according to claim 2, wherein the lower part of the upper frame is provided with a bearing recess that includes the bearing portion and is open downward.

[0014] The invention described in claim 7 is the chair according to claim 6, wherein the other member is an intermediate member disposed in the bearing recess, which is made of a resin having better sliding properties than the upper frame, and the axial curved surface formed on the upper part of the shaft engages with the bearing via the intermediate member.

[0015] The invention described in claim 8 is the chair according to claim 7, wherein the resin is polyoxymethylene (POM) resin.

[0016] The invention described in claim 9 is the chair according to claim 6, wherein the bearing recess comprises a front wall portion, a rear wall portion disposed behind the front wall portion, and a connecting portion connecting the upper parts of the front wall portion and the rear wall portion, and the bearing portion is configured to be a downward C shape including the front wall portion, the rear wall portion, and the connecting portion.

[0017] The invention described in claim 10 is the chair according to claim 9, wherein a reinforcing connecting portion is provided that connects the left-right intermediate portion at the upper part of the front wall portion and the rear wall portion. [Effects of the Invention]

[0018] As described above, the present invention provides a chair that offers excellent design freedom in at least the ability to rotatably support the upper frame with respect to the lower frame. [Brief explanation of the drawing]

[0019] [Figure 1] A perspective view showing one embodiment of the present invention. [Figure 2] Front view of the same embodiment. [Figure 3] Right side view of the same embodiment. [Figure 4] Right side view of the same embodiment. [Figure 5] Right side view of the same embodiment. [Figure 6] An exploded perspective view of the same embodiment. [Figure 7] A perspective view of the same embodiment. [Figure 8] Front view in the same embodiment. [Figure 9] Rear view in the same embodiment. [Figure 10] Exploded perspective view in the same embodiment. [Figure 11] Exploded perspective view in the same embodiment. [Figure 12] Exploded front view in the same embodiment. [Figure 13] Exploded rear view in the same embodiment. [Figure 14] Right side view in the same embodiment. [Figure 15] Exploded perspective view in the same embodiment. [Figure 16] Exploded perspective view in the same embodiment. [Figure 17] Exploded side view in the same embodiment. [Figure 18] Cross-sectional view taken along line A-A in FIG. 8. [Figure 19] Cross-sectional view taken along line B-B in FIG. 8. [Figure 20] Cross-sectional view taken along line C-C in FIG. 8. [Figure 21] Cross-sectional view of the reclined posture corresponding to the cut location in FIG. 18. [Figure 22] Front view in the same embodiment. [Figure 23] Rear view in the same embodiment. [Figure 24] Exploded perspective view in the same embodiment. [Figure 25] Cross-sectional view taken along line D-D in FIG. 3. [Figure 26] End view taken along line E-E in FIG. 2. [Figure 27] Right side view for explaining the assembly in the same embodiment. <​​​​​​​​​A front view illustrating the assembly in the same embodiment. [Figure 32] Cross-sectional view of the mounting position corresponding to the cutting point in Figure 18. [Figure 33] A front view illustrating the assembly in the same embodiment. [Figure 34] An exploded perspective view of the same embodiment. [Figure 35] An exploded perspective view of the same embodiment. [Modes for carrying out the invention]

[0020] Hereinafter, one embodiment of the present invention will be described with reference to Figures 1 to 35.

[0021] The chair comprises legs A, a support base B that is rotatably supported relative to legs A, a seat C positioned on the support base B, and a backrest E that is rotatably supported relative to the support base B via a back support D.

[0022] The chair is equipped with a tilt setting mechanism I between the support base B and the back support D, which allows the user to set the degree of tilt of the backrest E using a tilt setting lever 5, which is an operating lever.

[0023] The following describes in detail each component of the chair in this embodiment.

[0024] <<Legs A>> Leg A comprises multiple leg blades a1 arranged radially and having casters at their tips, and a leg support column a2 erected at the base end of the leg blades a1 and capable of extending and retracting in the vertical direction.

[0025] <<Support base B>> Support base B is mounted on leg A. Support base B is made of a material with excellent rigidity. Support base B is, for example, integrally molded from metal or synthetic resin. Support base B has a box shape that is open to the top.

[0026] The support base B is provided with a main shaft j1 extending in the left-right direction for rotatably supporting the back support D. A reaction spring F is disposed in the space within the support base B to provide a reaction force against the backward tilting movement of the back support D.

[0027] The space within the support base B houses a support shaft j4 that receives the rear end of the reaction spring F, a support shaft support member m3 that supports the support shaft j4, and the base end of the reaction force adjustment lever G that acts on the front end of the reaction spring F.

[0028] <<Location C>> The seat C is mounted on the support base B. The seat C comprises a seat support c1 and a seat body c2 which has a seating surface that contacts the occupant and is positioned so as to be able to change its front-to-back position relative to the seat support c1.

[0029] The front portion of seat C is supported so as to be movable vertically relative to the support base B via a front axis j2. The front-to-rear middle portion of seat C is supported by a seat engagement axis j3 provided on the back support D.

[0030] <<Back support D>> The back support D is interposed between the support base B and the backrest E. The back support D is capable of supporting the backrest E in a tiltable manner.

[0031] The lower part of the back support D is composed of a back support base M and a lower frame p1. The back support base M and the lower frame p1 that constitute the lower part of the back support are fixed to each other. The lower part of the back support is supported so as to be rotatable around the main axis j1 with respect to the support base B between the initial state (N) and the reclined state (H).

[0032] As shown in Figure 5, the upper frame p2 constituting the back support D is supported by the lower part of the back support D so as to be able to tilt between an upright position (ps) and a reclined position (pr).

[0033] The back support D is constantly biased in a direction that allows the backrest E to assume its initial state (N) by a reaction spring F provided on the support base B. A tilt adjustment lever 5, which allows the degree of tilt of the backrest E to be selectively set, is rotatably supported on the back support D.

[0034] The back support D comprises a back support base M rotatably supported on a support base B via a main shaft j1, and a back support body P connected to the rear of the back support base M.

[0035] <Back support base M> The back support base M is a metal structure interposed between the support base B and the backrest E, and between the support base B and the seat C.

[0036] The back support base M comprises left and right arms m1 arranged in pairs on the left and right and rotatably supported with respect to the support base B via a main shaft j1, a connecting member m2 connecting the rear ends of the left and right arms m1, a seat engagement shaft j3 supported on the front ends of the left and right arms m1, left and right receiving shaft support members m3 arranged in pairs on the left and right and their upper ends connected to the seat engagement shaft j3, and a receiving shaft j4 connected between the lower ends of the left and right receiving shaft support members m3.

[0037] The lower part of the back support base M is covered by a front cover body 6 made of synthetic resin.

[0038] [Left and right arms m1] The left and right arms m1 are in the shape of upright plates extending in the front-to-back direction. The left and right arms m1 are positioned outside the support base B.

[0039] Each left and right arm m1 has left and right arm bodies m4 that extend in the front-rear direction and can support the main spindle j1 at their front ends, left and right front arm portions m5 that extend integrally from the front ends of the left and right arm bodies m4 diagonally forward and upward and support the seat engagement shaft j3 at their upper ends, and a main spindle insertion hole (not shown) that penetrates in the left-right direction and can hold the main spindle j1, provided between the left and right arm bodies m4 and the left and right front arm portions m5.

[0040] The rear ends of the left and right arm bodies m4 are rigidly connected by a connecting member m2. The left and right arm bodies m4 are provided with rearward protruding portions mt that extend further back than the connecting member m2. The left and right rearward protruding portions mt are fitted into fitting holes 111 of the back support base connecting portion 11, which is provided at the base end (front end) of the lower frame p1 that constitutes the back support body P.

[0041] [Connection member m2] The connecting member m2 is shaped like an upright plate extending in the left-right direction. Both the left and right ends of the connecting member m2 are welded to the inner parts of the left and right arm bodies m4. The connecting member m2 is provided with a pair of nut portions n1 on the left and right sides, to which screws v1 for attaching the lower frame p1 are screwed.

[0042] A back support base connecting portion 11, which has a screw insertion hole h1, engages with the connecting member m2. The lower frame p1 is then fixed to the back support base M by screwing a screw v1, which is inserted through the screw insertion hole h1, into the nut portion n1 of the connecting member m2.

[0043] [Seat engagement axis j3] The seat engagement shaft j3 extends in the left-right direction and is capable of engaging with the seat C. The seat engagement shaft j3 is positioned in front of and above the main shaft j1. The seat engagement shaft j3 extends in the left-right direction and is held by a shaft holding portion (not shown) provided on the seat receiver c1.

[0044] [Support member m3] The receiving shaft support members m3 are arranged in pairs on the left and right sides, inside the left and right front arm portions m5. The receiving shaft support members m3 are in the shape of upright plates extending in the front-rear and up-down directions. The upper part of the receiving shaft support member m3 is connected to the seat engagement shaft j3. The receiving shaft j4 is connected to the lower part of the receiving shaft support member m3.

[0045] [Receiving axis j4] The support shaft j4 is positioned in front of and below the main shaft j1. The support shaft j4 is biased towards the rear by a reaction spring F.

[0046] <Back support body P> The back support body P supports the backrest E. The back support body P is connected to the upper and lower parts of the center in the left-right direction of the backrest E. In a side view, the back support body P and the backrest E are spaced apart, except for the upper connection part, the backrest engagement part 32, and the lower connection part, the backrest connecting part 22a.

[0047] The back support body P comprises a lower frame p1 having a shaft portion J, an upper frame p2 having a bearing portion K that receives the shaft portion J and being supported on the lower frame p1 so as to be rotatable in the front-rear direction between an upright position (ps) and a reclined position (pr), a coil spring V which is a biasing member interposed between the lower frame p1 and the upper frame p2, and an intermediate member S interposed between the lower frame p1 and the upper frame p2.

[0048] In this embodiment, the lower part of the chair's back support is composed of a back support base M and a lower frame p1. The lower part of the back support is rotatable with respect to the support base B between the initial state (N) shown in Figure 2 and the reclined state (H) shown in Figure 4, and, as shown in Figure 5, it can rotatably support the upper frame p2 so that it can assume both an upright position (ps) and a reclined position (pr).

[0049] [Bottom frame p1] The lower frame p1 is fixed to the back support base M. In other words, the lower frame p1 operates integrally with the back support base M.

[0050] The lower frame p1 is attached to the back support base M by screws v1. The lower frame p1 is fixed to the back support base M. The lower frame p1 can support the upper frame p2 so that it can rotate in the front-to-back direction. The lower frame p1 is connected to the lower part of the back side of the backrest E.

[0051] The lower frame p1 comprises a base structure 1 with a back support base connecting portion 11 at its front that connects to the back support base M, and an upper frame engaging portion 2 provided at the rear of the base structure 1.

[0052] (Foundation structure part 1) The foundation structure 1 comprises a back support base connecting portion 11 facing forward, and left and right side wall portions 12 extending linearly forward from both the left and right sides of the back support base connecting portion 11.

[0053] The back support base connecting portion 11 includes a pair of left and right fitting holes 111 that are open to the front and fit into left and right rearward protruding portions mt that protrude from the rear end of the back support base M, a connecting wall 112 disposed between the pair of left and right fitting holes 111 and attached to the connecting member m2 of the back support base M, and an arm engaging wall 113 that extends forward from the outer sides of each of the left and right fitting holes 111 and has portions that engage with the upper and lower edges of the left and right arm bodies m4.

[0054] The connecting wall 112 is provided with a pair of screw insertion holes h1 on the left and right sides that penetrate in the front-to-back direction. The lower frame p1 is fixed to the back support base M by screwing a screw v1 inserted from the rear through the screw insertion holes h1 of the connecting wall 112 into a nut n1 provided on the connecting member m2.

[0055] The left and right side wall portions 12 are in an upright position and are provided at the left and right front ends of the lower frame p1. The left and right side wall portions 12 are arranged along the outer rear portions of the left and right arm bodies m4. The front portions of the left and right side wall portions 12 are provided with forward-opening notches 121.

[0056] The notch 121 has a partially circular shape (C-shape in side view) with an end face into which the base end (near the flange portion 523) of the cylindrical portion 521 of the rearward tilt setting lever 5 can engage. The flange portion 523 of the lever body 52 engages with the inner peripheral edge of the notch 121 in the left and right side wall portions 12.

[0057] (Upper frame engagement part 2) The upper frame engagement portion 2 is connected to the rear of the foundation structure portion 1. The upper frame engagement portion 2 extends vertically as a whole. The upper frame engagement portion 2 is formed to be positioned gradually upward toward the rear as a whole.

[0058] The upper frame engagement portion 2 comprises a lower frame base portion 21 with a front spring receiving portion 211 provided in the center in the left-right direction, left and right support arms 22 extending in pairs in the vertical direction from the left and right of the lower frame base portion 21, a horizontal frame portion 23 that is installed between the vertical center portions of the left and right support arms 22 and includes a shaft portion J, and a restricting portion 24 that engages with the attitude deformation portion s2 of the intermediate member S attached to the upper frame p2 and is provided protruding from the inner side of the left and right support arms 22.

[0059] The lower frame base 21 is interposed between the foundation structure 1 and the left and right support arms 22. The front spring support portion 211 receives the front part of the coil spring V. The front spring support portion 211 faces rearward so as to face the space sp between the base ends of the left and right support arms 22 on which the coil spring V is arranged.

[0060] The left and right support arms 22 are rectangular columnar in shape, formed such that their front-to-back dimensions gradually decrease towards the top. The left and right support arms 22 are provided with an engaging portion 221 having a forward-facing surface 22m that engages with the upper frame p2 which is located at the top and is in a reclined position (pr), and a backrest connecting portion 22a disposed below the engaging portion 221 and connected to the lower part of the left-right central portion of the backrest E.

[0061] Between the left support arm 22 and the right support arm 22, there is a space sp in which a bearing recess 4, which is a lower frame engagement portion that protrudes downward from the upper frame p2, can be installed.

[0062] The engaging portion 221 is positioned above the shaft portion J. The engaging portion 221 can position the upper frame p2 in a backward tilted position (pr). The front wall portion 311 that constitutes the recessed portion 31 of the upper frame p2 in a backward tilted position (pr) abuts against the front surface 22m of the engaging portion 221.

[0063] The lower part of the backrest base e1, which constitutes the backrest E, is screwed into the backrest connecting portion 22a. The backrest connecting portion 22a protrudes forward of the engaging portion 221. The backrest connecting portion 22a is provided with a nut n2 into which a screw (not shown) that has passed through a screw insertion hole (not shown) provided in the backrest base e1 is screwed.

[0064] The horizontal section 23 is positioned below the backrest connecting section 22a. The horizontal section 23 is arranged in pairs on the left and right sides, and comprises left and right shaft sections J, the outer parts of which are integrally connected to the inner parts of the left and right support arms 22, and a connecting section 231 that integrally connects the lower parts of the left and right shaft sections J.

[0065] In the left-right central part of the horizontal section 23, a recessed area 232 is formed that is recessed downwards to avoid the reinforcing connecting portion 44 which is provided in a rib-like manner in the bearing recess 4.

[0066] The shaft portion J has an axial curved surface jm that extends in the left-right direction. The upper part of the shaft portion J has an axial curved surface jm that is partially cylindrical in shape. In other words, the shaft portion J has an axial curved surface jm that can indirectly engage with the bearing portion K of the upper frame p2 via the bearing cover portion s4 of the intermediate member S, which is another member.

[0067] The axial curved surface jm formed on the upper part of the shaft portion J engages with the bearing portion K via the bearing cover portion s4 of the intermediate member S.

[0068] The shaft portion J has a shape that is longer in the vertical direction than in the front-to-back width dimension. The front-to-back width dimension of the shaft portion J (the thickness dimension of the shaft portion J, wj) is shorter than the vertical width dimension. The entire lower frame p1, including the shaft portion J, is integrally formed from synthetic resin.

[0069] The restricting portion 24 is located adjacent to the shaft portion J. The restricting portion 24 is provided on the inner surfaces of the left and right support arms 22. The restricting portion 24 is a part that can engage with the attitude deformation portion s2 of the intermediate member S. The restricting portion 24 is block-shaped and is provided on the front and lower parts of each of the left and right shaft portions J.

[0070] The regulating portion 24 comprises a forward-facing surface 242 that faces forward and an inner surface 241 that is located behind the forward-facing surface 242 and faces inward.

[0071] An inclined surface portion km is provided on the upper part of the inward-facing inner surface 241, which is sloped downwards and gradually towards the left-right central part of the lower frame p1 (gradually approaching the direction of the base portion s1 in the intermediate member S). The inclined surface portion km is provided at the front of the shaft portion J. The portion of the inner surface 241 below the inclined surface km extends in a substantially vertical direction.

[0072] The forward-facing surface 242 of the restricting portion 24 is configured such that the posture deformation portion s2, which forms the second posture (Y) of the intermediate member S, comes into contact with the upper frame p2 when it is in an upright posture (ps).

[0073] The attitude deformation portion s2 of the intermediate member S engages with the inner surface 241 of the regulating portion 24. The attitude deformation portion s2 deforms from a second attitude (Y) to a first attitude (X) as the upper frame p2 in the mounting attitude (T) approaches the lower frame p1.

[0074] In other words, as the bearing portion K of the upper frame p2 approaches the shaft portion J of the lower frame p1, which is the part to be assembled, the posture deformation portion s2 of the intermediate member S is guided by the inner surface 241 which has an inclined surface portion km, and its tip portion s22 approaches the base portion s1, that is, it is elastically deformed from the second posture (Y) to the first posture (X).

[0075] The upper and lower parts of the lower frame p1, which has the above configuration, are covered by an upper cover body 7 and a lower cover body 8 made of synthetic resin.

[0076] [Top frame p2] The upper frame p2 is supported so as to be rotatable around the shaft J relative to the lower frame p1. The upper frame p2 is provided with a bearing portion K configured to indirectly receive the shaft J of the lower frame p1 via the bearing cover portion s4 of the intermediate member S. The upper frame p2 is a single column extending in the vertical direction and is positioned behind the left-right intermediate portion of the backrest E.

[0077] The upper frame p2 is configured to be rotatable around the shaft J so that it can assume an assembled position (T) in which a coil spring V can be attached between it and the lower frame p1, and a normal position (U) which is different from the assembled position (T).

[0078] The assembly position (T) is a position that can only be adopted when attaching the upper frame p2 to the lower frame p1 and when detaching it. The assembly position (T) of the upper frame p2 is set to a more forward-leaning position than the normal position (U).

[0079] The assembly position (T) of the upper frame p2 can only be adopted when assembling it to the lower frame p1 and when detaching it from the lower frame p1.

[0080] In other words, the upper frame p2 is configured such that, after transitioning from the assembled position (T) to the normal position (U) (after the assembly of the upper frame p2 to the lower frame p1 is completed), it cannot return to the assembled position (T) unless a special operating force for disassembly is applied to the positional deformation part s2 of the intermediate member S.

[0081] The upper frame p2 is configured to be tiltable (capable of tilting) between an upright position (ps) and a reclined position (pr) that is more backward than the upright position (ps) in the normal position (U).

[0082] The upper frame p2 comprises an upper frame body 3 that extends vertically and constitutes a part visible to the user, and a downward projection (base end structure) disposed below the upper frame body 3, which includes a bearing portion K and a bearing recess 4 that is open downward and outward.

[0083] (Upper frame main body 3) The lower part of the upper frame body 3 is provided with recessed portions 31 that are open downwards on both the left and right sides. The upper part of the upper frame body 3 is provided with a backrest engagement portion 32 that can engage with the backrest E in a manner that allows for vertical movement.

[0084] The upper parts of the left and right support arms 22, which are provided on the lower frame p1, are positioned inside the left and right recessed portions 31. The front wall portion 311 that constitutes the recessed portion 31 engages with the forward-facing surfaces 22m of the engaging portions 221 provided on the left and right support arms 22, thereby defining the backward tilting posture (pr) of the upper frame p2.

[0085] (Bearing recess 4) The bearing recess 4 is located at the lower part of the upper frame p2. The bearing recess 4 is positioned so as to protrude downward relative to the upper frame body 3 in both front and rear views. In other words, the left-right dimension of the bearing recess 4 in both front and rear views is set to be shorter than the left-right dimension of the upper frame body 3.

[0086] The bearing recess 4 comprises a front wall portion 41, a rear wall portion 42 positioned behind the front wall portion 41, and a connecting portion 43 that connects the upper parts of the front wall portion 41 and the rear wall portion 42.

[0087] The front wall portion 41 is a wall-like structure that extends in the vertical and horizontal directions.

[0088] A rear spring support portion 411 is provided on the lower front side of the front wall portion 41. The rear spring support portion 411 faces forward so as to face the space sp in which the coil spring V (tilt spring) located between the base ends of the left and right support arms 22 is installed.

[0089] The lower end of the front wall portion 41 is provided with a lower mounting portion 412 to which the front mounting portion s3 of the intermediate member S is attached. The lower mounting portion 412 has a plurality of protrusions that extend downward at different vertical positions. The lower mounting portion 412 has a central protrusion 41a and left and right side protrusions 41b that are located above the central protrusion 41a. The front mounting portion s3 of the intermediate member S is fitted onto the lower mounting portion 412.

[0090] On the rear side (rear-facing side) of the front wall portion 41, a plurality of positioning ribs 413 are provided, extending in the vertical direction and positioned horizontally relative to the base portion s1 of the intermediate member S.

[0091] The rear wall portion 42 is a wall-like structure that extends in the vertical and horizontal directions. The rear wall portion 42 is set to have a width dimension that is approximately the same as or shorter than the horizontal distance between the left support arm 22 and the right support arm 22. The rear wall portion 42 has approximately the same horizontal width dimension as the front wall portion 41. The rear wall portion 42 is shorter in the vertical direction than the front wall portion 41. The rear wall portion 42 as a whole (excluding the forward protruding portion 42b) is provided so as to gradually move away from the front wall portion 41 toward the downward direction.

[0092] The rear wall portion 42 is provided with a rear mounting portion 421 to which the rear mounting portion s5 of the intermediate member S is attached. The rear mounting portion 421 of the rear wall portion 42 comprises a projection engagement portion 42a that can engage with a plurality (four) of engagement projections s51 arranged in parallel on the rear mounting portion s5 of the intermediate member S, and a forward projection portion 42b that fits into a fitting recess s52 provided on the rear mounting portion s5 of the intermediate member S.

[0093] The protruding engagement portion 42a is provided in through holes that are arranged in a row (four) in the left-right direction and penetrate in the front-to-back direction.

[0094] The forward-projecting portion 42b is provided to protrude forward from the left-right center of the lower end of the rear wall portion 42.

[0095] The connecting portion 43 connects the upper parts of the front wall portion 41 and the rear wall portion 42 in the front-rear direction. The bearing recess 4 is configured to be open downwards and outwards by the front wall portion 41, the rear wall portion 42, and the connecting portion 43.

[0096] Furthermore, a reinforcing connecting portion 44 is provided in the left-right intermediate portion below the connecting portion 43 in the bearing recess 4, connecting the upper parts of the front wall portion 41 and the rear wall portion 42.

[0097] The bearing recess 4 is provided with left and right bearing portions K that receive the shaft portion J of the lower frame p1. The bearing portion K is a part that engages with the shaft portion J so as to be rotatable relative to it. The bearing portion K has a downward C-shape and is composed of a front wall portion 41, a rear wall portion 42, and a connecting portion 43. The left and right bearing portions K are provided on the left and right sides of the reinforcing connecting portion 44.

[0098] The bearing recess 4 is provided with an axial passage Z that allows the shaft portion J of the lower frame p1 to enter toward the bearing portion K, but only in the assembled position (T).

[0099] In this embodiment, the size of the axial passage Z, i.e., the passage width wz, is determined by the cooperation of the front wall portion 41 of the bearing recess 4 having a positioning rib 413 and the base portion s1 and rear mounting portion s5 (forward protrusion portion / lateral mounting portion retaining portion) of the intermediate member S disposed in the bearing recess 4.

[0100] [Coil spring V (biasing member)] The coil spring V biases the upper frame p2 in the direction of the upright position (ps). The coil spring V is a compression spring type. The coil spring V generates a reaction force to return the upper frame p2 from the reclined position (pr) to the upright position (ps).

[0101] The front portion of the coil spring V is supported by a front spring support portion 211 provided on the lower frame p1 so as to be located below the shaft portion J and the bearing portion K.

[0102] The rear portion of the coil spring V is supported by a rear spring support portion 411 provided on the upper frame p2 so as to be located below the shaft portion J and the bearing portion K.

[0103] In this embodiment, as shown in Figure 32, the coil spring V is configured to be positioned between the front spring support portion 211 and the rear spring support portion 411 only when the upper frame p2 is in the assembled position (T).

[0104] In other words, the worker can easily position the coil spring V in the designated location using only their fingers, without the need for any tools.

[0105] In other words, in this embodiment, the back support body P is set such that the rear spring support portion 411 on the upper frame p2 and the front spring support portion 211 on the lower frame p1 are spaced further apart in the front-rear direction than in the normal position (U).

[0106] [Intermediate member S] The intermediate member S is positioned between the lower frame p1 and the upper frame p2. The intermediate member S is attached to the bearing recess 4 of the upper frame p2. Specifically, the main part of the intermediate member S is attached to the inner surface of the front wall portion 41, the rear wall portion 42, and the connecting portion 43 that constitute the bearing recess 4.

[0107] The intermediate member S is made of polyoxymethylene (POM) resin, which has superior rigidity and sliding properties compared to the upper frame p2.

[0108] The intermediate member S is designed to improve sliding properties with respect to the shaft J. Furthermore, the intermediate member S can restrict the rotation of the upper frame p2, preventing it from returning to the assembled position (T) once its orientation has been changed from the assembled position (T) to the normal position (U).

[0109] The intermediate member S comprises a base portion s1 positioned in the center in the left-right direction, a posture deformation portion s2 extending in a cantilever arm shape in pairs to the left and right of the base portion s1, a front mounting portion s3 extending below the base portion s1 and fitting onto the lower mounting portion 412 of the front wall portion 41, a bearing cover portion s4 connected to the base portion s1 and covering the inner circumferential surface of the bearing portion K while adhering to it, and a rear mounting portion s5 extending downward from the rear end of the bearing cover portion s4 and mounted on the front side (inner side) of the rear wall portion 42.

[0110] In a side view, the intermediate member S has a V-shape with its vertical direction reversed overall. That is, the intermediate member S comprises a front portion Sf including a base portion s1, a posture deformation portion s2, and a front mounting portion s3; a rear portion Sr including a rear mounting portion s5; and an upper portion Su including a bearing cover portion s4.

[0111] The intermediate member S, which has an inverted V-shape in side view, can temporarily undergo elastic deformation so that its front portion Sf and rear portion Sr come together when mounted in the bearing recess 4 of the upper frame p2, in side view.

[0112] In this embodiment, the temporary movement of the front portion Sf and the rear portion Sr moving toward each other is mainly achieved by the elastic deformation of the ends of the vertically elongated left and right connecting arm portions s12, i.e., the portions near the bearing cover portion s4.

[0113] (base s1) The base portion s1 is attached to the inner surface of the front wall portion 41 in the bearing recess 4. The base portion s1 comprises a base body s11 which is substantially rectangular in shape when viewed from the front and rear, and left and right connecting arm portions s12 which extend integrally upward from the upper part of both the left and right sides of the base body s11, with their extended ends continuous with the bearing cover portion s4.

[0114] The base body s11 is provided with reinforcing ribs rv in pairs on the left and right sides, extending in the vertical direction, at the center of the front side. The reinforcing ribs rv are connected between the base body s11 and the front mounting part s3 in order to increase the overall rigidity of the front part Sf.

[0115] The reinforcing rib rv interacts with the positioning rib 413 provided on the front wall portion 41 of the bearing recess 4, and also performs a positioning function in the left-right direction relative to the front wall portion 41.

[0116] The left and right connecting arm portions s12 are thin, plate-like structures extending in the vertical direction, except for the portions near the bearing cover portion s4. Only the portions of the left and right connecting arm portions s12 near the bearing cover portion s4 are relatively thin, columnar in shape, and are easily elastically deformable in the front-to-back direction.

[0117] (Posture deformation part s2) The posture deformation section s2 extends outward from both the left and right sides of the lower end of the base body s11.

[0118] The posture deformation section s2 comprises a base end portion s21 extending outward from both the left and right sides of the base portion s1, and a tip portion s22 connected to the upper end of the base end portion s21, which is a block-like or solid-shaped tip portion with a larger width dimension than the base end portion s21.

[0119] The base portion s21 is plate-shaped and easily elastically deformable. The base portion s21 extends diagonally from both the left and right sides of the lower part of the base portion s1, gradually moving upward outwards.

[0120] The base portion s21 is the main part that undergoes elastic deformation in the left-right direction when the attitude deformation portion s2 engages with the restricting portion 24 during the assembly of the lower frame p1 and the upper frame p2.

[0121] The posture deformation section s2 is configured to adopt a first posture (X) in the assembled posture (T) and a second posture (Y) that is different from the first posture (X) in the normal posture (U).

[0122] In other words, in the first posture (X), the posture deformation part s2 engages with the inner surface 241 of the restricting part 24 provided on the inner side of the left and right support arms 22, causing the tip portion s22 to be elastically deformed in a direction that brings it closer to the base portion s1.

[0123] Furthermore, in the second posture (Y), the posture deformation section s2 is positioned at a location where it can engage with the forward-facing surface 242 of the restricting section 24 provided on the inner side of the left and right support arms 22.

[0124] In other words, the tip portion s22 of the attitude deformation portion s2 is positioned in front of the restricting portion 24 in the second attitude (Y). In the second attitude (Y), the attitude deformation portion s2 can restrict the rearward rotation range of the portion of the upper frame p2 below the bearing portion K (the lower part of the front wall portion 41) in order to define the upright attitude (ps) of the upper frame p2.

[0125] In the second posture (Y), the attitude deformation section s2 is configured such that the engagement relationship with the inner surface 241 of the restricting section 24, which was performed in the first posture (X), is released.

[0126] As the upper frame p2 transitions from the assembled position (T) to the normal position (U), the posture deformation section s2 transitions from the first position (X) to the second position (Y). At this time, the tip portion s22 of the posture deformation section s2 elastically returns to a position away from the base portion s1 in the left-right direction in accordance with the elastic deformation of the base portion s21, and is positioned at a location (in front of the restricting section 24) where it can engage with the forward-facing surface 242 of the restricting section 24.

[0127] The posture deformation section s2, which forms the second posture (Y), is positioned forward and separated from the forward-facing surface 242 of the restricting section 24 in the reclined posture (pr), and is in contact with the forward-facing surface 242 of the restricting section 24 in the upright posture (ps).

[0128] In other words, the posture deformation section s2, which forms the second posture (Y), is designed to intersect (support) between the restricting section 24 and the front wall section 41 when the upper frame p2 takes the upright posture (ps).

[0129] (Front mounting part s3) The front mounting portion s3 includes a central fitting recess s31 located in the center in the left-right direction, and side fitting recesses s32 provided to the left and right of the central fitting recess s31 so as to be located above the central fitting recess s31.

[0130] The central fitting recess s31 is designed to accommodate the central protrusion 41a of the lower mounting portion 412 on the front wall portion 41. The left and right side protrusions 41b of the lower mounting portion 412 on the front wall portion 41 are designed to accommodate the side fitting recess s32.

[0131] (Bearing cover section s4) The bearing cover portion s4 is a partially cylindrical shape attached to each of the left and right bearing portions K. The bearing cover portion s4 is interposed between the shaft portion J provided on the lower frame p1 and the bearing portion K provided on the upper frame p2.

[0132] The bearing cover portion s4 is supported by a backing on the bearing portion K. The bearing cover portion s4 is in direct contact with the shaft portion J and is capable of sliding in conjunction with the rotation of the upper frame p2.

[0133] The entire intermediate member S, including the bearing cover portion s4, is made of polyoxymethylene resin (POM), which has excellent sliding properties and rigidity. Therefore, by interposing the bearing cover portion s4 between the shaft portion J and the bearing portion K, the upper frame p2 can be rotated smoothly without the need to apply grease or the like to the lower frame p1.

[0134] Alternatively, the bearing portion K and the shaft portion J may be configured to directly engage with each other without interposing a bearing cover portion s4 between them.

[0135] (Rear mounting part s5) The rear mounting portion s5 comprises a wall-like portion sw extending in the vertical and horizontal directions, an engaging projection s51 projecting rearward from the lower part of the wall-like portion sw, a fitting recess s52 provided on the rear side of the lower part of the wall-like portion sw so as to be recessed forward, and a protruding portion st projecting forward from the lower part of the wall-like portion sw, i.e., in the direction of the base portion s1, and capable of engaging with the horizontal frame portion 23.

[0136] The wall-like portion sw is integrally connected to the rear end of the bearing cover portion s4. A flange sg is integrally provided on the outer ends of the bearing cover portion s4 and the wall-like portion sw to improve the connection strength. A notch sk is provided in the left-right center of the bearing cover portion s4 and the wall-like portion sw to avoid interference with the reinforcing connecting portion 44.

[0137] Multiple (four) engaging projections s51 are arranged side by side in the left-right direction. The engaging projections s51 are designed to engage with the engaging projections 42a provided in the through holes of the rear wall portion 42 of the upper frame p2.

[0138] The fitting recess s52 is provided on the rear side of the center of the wall-like portion sw in the left-right direction. The forward projection portion 42b, which protrudes from the rear wall portion 42 of the upper frame p2, engages with the fitting recess s52.

[0139] The protruding portion st is provided to project forward from the lower part of the wall-like portion sw. The protruding portion st is provided to project forward at approximately perpendicular to the wall-like portion sw.

[0140] The protruding portion st works in cooperation with the base portion s1 and the positioning rib 413 to define the passage width wz of the axial passage Z through which the horizontal portion 23 of the lower frame p1 can pass toward the bearing portion K.

[0141] In other words, when the upper frame p2 is in the assembled position (T), the horizontal section 23 of the lower frame p1 is configured to pass through the axial passage Z, which includes the protruding section st, and reach the bearing section K (bearing cover section s4).

[0142] The protruding portion st is positioned to prevent the horizontal section 23 from coming off the bearing section K when the upper frame p2 is in its normal position (U). In other words, when the upper frame p2 is in its normal position (U), the protruding portion st is positioned to engage with the lower edge of the horizontal section 23.

[0143] In other words, the protruding portion st engages with the lower frame p1, thereby preventing the upper frame p2 from detaching (moving upward) in its normal position (U).

[0144] <<Rear tilt degree setting mechanism I>> The reclining degree setting mechanism I is configured to allow the user to select one of two or more (four reclining degrees in this embodiment) from the reclining degree of the backrest E, which is supported on the support base B via the back support D so as to be able to tilt backward, by rotating the reclining degree setting lever 5.

[0145] The rear tilt setting mechanism I comprises a rear tilt setting lever 5 rotatably supported on a back support D, a rotating member Q integrally rotatably attached to the rear tilt setting lever 5, a damper member (not shown) disposed on a support base B to which the rotating member Q can abut, and a stopper engagement member R attached to the back support D that can stopper engage the rotating member Q.

[0146] <Lean degree setting lever 5 (operating lever)> The backward tilt setting lever 5 comprises a lever shaft portion 51 that extends in the left-right direction and is pivotally supported in shaft holes ma provided in the left and right arm bodies m4, and a lever body 52 that is mounted so as not to rotate relative to the lever shaft portion 51 without the use of fasteners and has a portion that can be gripped by the user.

[0147] [Lever shaft portion 51] The lever shaft portion 51 is made of metal. The lever shaft portion 51 is a cylindrical shaft that extends in the left-right direction as a whole. A projection portion 511 is provided at the protruding end of the lever shaft portion 51, projecting in a direction perpendicular to the axis.

[0148] The lever shaft portion 51 is provided with a disc-shaped (donut-shaped) positioning plate 512 whose inner surface is in contact with the outer surface of the right arm body m4. The positioning plate 512 is welded to the lever shaft portion 51.

[0149] The positioning plate 512 provided on the lever shaft portion 51 contacts the outer surface of the right arm body m4, thereby restricting the leftward movement of the lever shaft portion 51 relative to the right arm body m4.

[0150] Furthermore, the flange portion 523 provided on the lever body 52 abuts against the outer surface of the positioning plate 512 provided on the lever shaft portion 51. In other words, the positioning plate 512 is interposed between the left arm body m4 and the flange portion 523 of the lever body 52.

[0151] [Lever body 52] The lever body 52 is made of synthetic resin. In this embodiment, the lever body 52 does not have a screw insertion hole for fixing it to the lever shaft portion 51.

[0152] The lever body 52 comprises a cylindrical portion 521 that extends in the left-right direction and has a housing hole 52a formed inside in which the lever shaft portion 51 is disposed, a flange portion 523 integrally formed at the base end of the cylindrical portion 521, and a lever piece 522 that cantilevered out from the cylindrical portion 521.

[0153] The cylindrical portion 521 is provided with a housing hole 52a into which the lever shaft portion 51 is fitted. The housing hole 52a is provided with a keyway portion 52b that can engage with a projection 511 provided on the lever shaft portion 51.

[0154] The flange portion 523 extends outward from the base end of the cylindrical portion 521. The flange portion 523 is positioned between the right arm body m4 on the back support base M and the side wall portion 12 of the lower frame p1 on the back support body P.

[0155] The flange portion 523 is provided around the entire circumference of the base end of the cylindrical portion 521. Of the entire circumference of the flange portion 523, only a specific portion extends significantly outward, corresponding to the rotation range of the rearward tilt setting lever 5. That is, only the rear upper portion 52c of the flange portion 523, which can particularly engage with the peripheral edge of the notched hole 121 in the side wall portion 12, is provided to protrude significantly outward.

[0156] In other words, in this embodiment, since the lever body 52 is fitted onto the lever shaft portion 51 without using a fastener, the relative movement of the lever body 52 with respect to the lever shaft portion 51 in the axial direction (left-right direction) is restricted by the flange portion 523 provided on the lever body 52 directly or indirectly engaging with the components of the back support D.

[0157] The flange portion 523 is positioned between the right arm body m4 on the back support base M and the side wall portion 12 on the lower frame p1 in a manner that prevents lateral displacement, thereby ensuring that the lever body 52 is favorably supported with respect to the lever shaft portion 51.

[0158] In this embodiment, the flange portion 523 is indirectly engaged with the right arm body m3, which is a component of the back support base M, via the positioning plate 512.

[0159] In other words, the flange portion 523 is positioned by being sandwiched between the positioning plate 512 of the lever shaft portion 51, which is in contact with the outer surface of the right arm body m4, and the peripheral portion of the notched hole 121 in the side wall portion 12 of the lower frame p1.

[0160] The lever piece 522 is provided projecting from the tip of the cylindrical portion 521 in a direction perpendicular to the longitudinal direction of the cylindrical portion 521. The lever piece 522 is a protruding piece designed to make it easier for the user's fingers to grip it.

[0161] <Rotating member Q> The rotating member Q is made of synthetic resin and is configured to rotate integrally with the rearward tilt setting lever 5. The rotating member Q is positioned between the left and right arm bodies m4 on the back support base M. The rotating member Q is biased by a spring qs in the direction of the joint engagement member R attached to the inner surface of the right arm body m4.

[0162] <<Backrest E>> The backrest E is supported by the back support D. The backrest E comprises a shell-shaped backrest base e1 located on the back side and a backrest body e2 attached to the front side of the backrest base e1.

[0163] The lower part of the backrest base e1 is screwed to the upper part of the lower frame p1. The upper part of the backrest base e1 is supported so as to be able to move relative to the upper frame p2 in the vertical direction.

[0164] The backrest body e2 has an inner shell and a back cushion (not shown), which are covered with a surface material.

[0165] <<Regarding the attachment of the upper frame p2 to the lower frame p1>> In this embodiment, the back support body P is configured such that the lower frame p1 and the upper frame p2 can be assembled in a one-touch manner and cannot be separated, after manually positioning the coil spring V between the lower frame p1 and the upper frame p2.

[0166] In other words, although the back support body P requires the interposition of a coil spring V between the lower frame p1 and the upper frame p2, it is configured to be easily assembled by providing an intermediate member S that can perform a function of restricting the rotation range of the upper frame p2 relative to the lower frame p1.

[0167] An example of the process of assembling the upper frame p2 to the lower frame p1 will be explained primarily with reference to Figures 27 to 32. Note that in Figures 28 to 31 and 33, the upper frame p2 is omitted for the sake of clearly illustrating the operation of the intermediate member S. Furthermore, a portion (the lower part) of the intermediate member S is also omitted from the illustration.

[0168] <Preparation process> First, the lower frame p1, coil spring V, upper frame p2, and intermediate member S that constitute the back support body P are prepared. The process of assembling the upper frame p2 to the lower frame p1 can be performed by hand only, without the use of tools.

[0169] Furthermore, there is no need to prepare grease. The intermediate member S is made of polyoxymethylene (POM) resin, which has excellent sliding properties and rigidity, so assembly can be carried out without applying grease between the members.

[0170] <Attachment of intermediate member S to upper frame p2> Next, the intermediate member S is attached to the bearing recess 4 of the upper frame p2. The mounting structure of the intermediate member S to the bearing recess 4 has already been explained, so it will be omitted here.

[0171] In this explanation of the process of assembling the upper frame p2 to the lower frame p1, for the sake of convenience, the upper frame p2 with the intermediate member S attached may be simply referred to as "upper frame p2".

[0172] <Movement of upper frame p2 etc. in the assembled position (T)> Next, as shown in Figure 27, the upper frame p2 and the intermediate member S are changed to an assembled position (T) that is tilted forward by approximately 15° compared to the normal position (U) relative to the lower frame p1 [tilted forward by approximately 15° relative to the upright position (ps)].

[0173] Then, as shown in Figures 27 and 28, the upper frame p2 and the lower frame p1 are moved relative to each other so that the horizontal portion 23 (shaft portion J) of the lower frame p1 is positioned within the bearing recess 4 of the upper frame p2 in a predetermined assembly position (T).

[0174] When the upper frame p2 is in the assembled position (T), the axial passage Z of the bearing recess 4, which is set to have a passage width wz that is approximately the same as or slightly longer than the thickness dimension (short side thickness dimension) of the lateral section 23 (shaft section J), is configured so that the lateral section 23 (shaft section J) of the lower frame p1 can move from the outside towards the bearing section K.

[0175] As shown in Figure 29, in the initial stage in which the horizontal section 23 (shaft section J) moves toward the back of the bearing recess 4 where the bearing section K is provided (bearing section K), the outer surface of the base end portion s21 of the attitude deformation section s2 that forms the second attitude (Y) provided on the intermediate member S comes into contact with the inner surface 241 of the restricting section 24 that protrudes from the lower frame p1.

[0176] As shown in Figures 29 and 30, the base end portion s21 of the attitude deformation portion s2, which is in contact with the inner surface 241 of the regulating portion 24, is pressed inward due to its interaction with the inner surface 241 of the regulating portion 24 which is fixed to the lower frame p1, and its attitude is gradually changed from the second attitude (Y) to the first attitude (X).

[0177] An inclined surface portion km is provided on the upper part of the inner surface 241 of the regulating portion 24. Therefore, the base end portion s21 of the attitude deformation portion s2 of the intermediate member S is guided by the inclined surface portion km in the initial stage, and its attitude is deformed smoothly and without force from the second attitude (Y) to the first attitude (X).

[0178] As shown in Figure 31, when the horizontal section 23 (shaft section J) moves into the inner part of the bearing recess 4 (bearing section K) and finally reaches a position where it is supported by the bearing section K (bearing cover section s4), the upper frame p2 becomes rotatable around the shaft section J relative to the lower frame p1. In addition, the attitude deformation section s2 takes on a first attitude (X) that is elastically deformed by the inner edge 241 of the regulating section 24 so as to be close to the base section s1.

[0179] <Placement of coil spring V> At this stage, as shown in Figure 32, while maintaining the assembled position (T) of the upper frame p2, the coil spring V is positioned between the front spring support portion 211 on the lower frame p1 and the rear spring support portion 411 on the upper frame p2.

[0180] When the upper frame p2 is in the assembled position (T), the space sp between the front spring support portion 211 and the rear spring support portion 411 provides sufficient space in the front-to-back direction to allow the coil spring V to be positioned in the correct position solely by the worker's manual labor.

[0181] <Change of posture to normal posture (U) in upper frame p2> Subsequently, after the coil spring V is positioned between the front spring support portion 211 and the rear spring support portion 411, the upper frame p2 is rotated around the shaft portion J (tilting the upper frame p2 backward) in order to change the orientation of the upper frame p2 from the assembled position (T) to the normal position (U).

[0182] As shown in Figure 33 (Figures 18 and 20), when the upper frame p2 is rotated from the assembled position (T) to the normal position (U), the position deformation section s2, which was in the first position (X), moves forward relative to the restricting section 24. As a result, the elastic engagement with the inner surface 241 of the restricting section 24 is released, and the s2 is positioned on the forward-facing surface 242 side of the restricting section 24.

[0183] In other words, the attitude deformation part s2, which was in the first attitude (X), moves outward due to elastic deformation (elastic return) as a result of the engagement relationship with the inner surface 241 of the restricting part 24 being released, and its attitude is changed to the second attitude (Y).

[0184] The tip portion s22 of the attitude deformation section s2, which forms the second posture (Y), is positioned to engage with or be in close proximity to the inner surface portions of the left and right support arms 22. As a result, the tip portion s22 of the attitude deformation section s2 in the second posture (Y) is positioned in front of the regulating section 24.

[0185] In other words, the posture deformation part s2 in the second posture (Y) is positioned to be able to intersect (support) between the lower frame p1 and the upper frame p2. As the upper frame p2 changes its posture from the assembled posture (T) to the normal posture (U), the posture deformation part s2 automatically changes its posture from the first posture (X) to the second posture (Y).

[0186] Furthermore, in the second posture (Y), the posture deformation part s2 is positioned to move forward and away from the restricting part 24 when the upper frame p2 is in a reclined posture (pr). On the other hand, in the second posture (Y), the posture deformation part s2 is positioned to rest (support) between the front wall part 41 and the restricting part 24 when the upper frame p2 is in an upright posture (ps).

[0187] In other words, the upper frame p2 is configured such that when it assumes an upright posture (ps), it is obstructed by the posture deformation part s2 of the second posture (Y), preventing it from adopting a more forward-leaning posture relative to the lower frame p1.

[0188] In the normal position (U), the upper frame p2 is prevented from rotating backward by the thickness dimension in the front-to-back direction of the tip portion s22 of the attitude deformation section s2.

[0189] In the normal position (U), the upper frame p2 cannot return to the assembled position (T) in which the lateral section 23 can be disengaged from the bearing recess 4 unless a special operating force is applied to the attitude deformation section s2 of the second position (Y), which is an obstructing member.

[0190] In other words, when the upper frame p2 is in its normal position (U), the protruding portion st of the intermediate member S cannot escape the positional relationship in which it can engage with the lower edge of the horizontal section 23 (it is located below the horizontal section 23), and the upper frame p2 cannot detach from the lower frame p1.

[0191] After completing the above steps, the attachment of the upper frame p2 to the lower frame p1 is complete.

[0192] To remove the upper frame p2 from the lower frame p1, the posture deformation part s2 in the second posture (Y) can be forcibly changed to the first posture (X) using fingers or a rod-shaped member.

[0193] In this embodiment, the coil spring V constantly biases the front wall portion 41 that constitutes the bearing recess 4 toward the rear. Therefore, by forcibly changing the posture deformation portion s2 in the second posture (Y) to the first posture (X) using fingers or a rod-shaped member, it is possible to change the posture of the upper frame p2 from the normal posture (U) to the assembled posture (T) relatively easily.

[0194] In other words, in this embodiment, the back support body P, in its normal position (U), always has the coil spring V biasing the upper frame p2 in the assembled position (T) direction (the direction that tends to tilt it forward).

[0195] Therefore, if the posture deformation part s2, which is stuck (supported) between the restricting part 24 of the lower frame p1 and the front wall part 41 of the upper frame p2, is forcibly moved from the second posture (Y) to the first posture (X), the coil spring V assists the rotation so that the upper frame p2 can transition to the assembled posture (T).

[0196] With the embodiment described above, it is possible to realize a configuration in which the upper frame p2 is rotatably supported by the lower frame p1 without applying a single steel shaft as in the conventional method.

[0197] Therefore, with the chair of this embodiment, not only is it easier to design in a way that contributes to improved aesthetics, but it also offers excellent design freedom in rotatably supporting the upper frame p2 relative to the lower frame p1.

[0198] In the embodiment described above, even if it is necessary to interpose a coil spring V, which is a biasing member, between the lower frame p1 and the upper frame p2, the assembly of the upper frame p2 of the back support D, which is the second member and is configured to be rotatable with respect to the lower frame p1 of the back support D, which is the first member, the back support D can be suitably carried out.

[0199] In the embodiment described above, not only can the number of parts constituting the reclining degree setting lever 5, which is the operating lever, be reduced, but it is also possible to provide a chair with excellent design freedom that can form a suitable appearance for the reclining degree setting lever 5.

[0200] As described in detail above, the chair of this embodiment has a backrest E rotatably supported on a support base B via a back support D. The back support D comprises a lower frame p1 having a shaft portion J, and an upper frame p2 having a bearing portion K that receives the shaft portion J and being rotatably supported relative to the lower frame p1.

[0201] The shaft portion J extends horizontally, and its width in the front-to-back direction is shorter than its width in the up-to-down direction. An axial curved surface jm is formed on the upper part of the shaft portion J, which has a partially cylindrical curved shape and can indirectly engage with the bearing portion K via an intermediate member S, which is another member.

[0202] Therefore, it is possible to provide a chair with excellent design flexibility, where the upper frame p2 is rotatably supported by the lower frame p1.

[0203] In other words, this embodiment makes it possible to achieve a configuration in which the upper frame p2 is rotatably supported by the lower frame p1 without using a separate steel shaft. Therefore, it is easier to design in a way that reduces the number of parts and improves the aesthetics.

[0204] The lower frame p1 is provided with a shaft portion J having an axial curved surface jm formed on its upper part, and the upper frame p2 is provided with a bearing portion K.

[0205] Therefore, the shaft portion J and the bearing portion K can be suitably engaged via the intermediate member S.

[0206] The lower frame p1, which includes the shaft portion J, is integrally formed from synthetic resin.

[0207] Therefore, compared to conventional configurations that use a single steel shaft, this design allows for a reduction in the number of parts.

[0208] The lower frame p1 is provided with an upper frame engagement portion 2 which includes a shaft portion J. The upper frame engagement portion 2 comprises a lower frame base portion 21, left and right support arms 22 extending in pairs in the vertical direction from the left and right sides of the lower frame base portion 21, and a horizontal frame portion 23 which is installed between the left and right support arms 22 and includes a shaft portion J.

[0209] Therefore, the shaft portion J included in the upper frame engagement portion 2 is provided in a manner that offers excellent rigidity.

[0210] The horizontal section 23 is arranged in pairs on the left and right sides, and each outer part is integrally connected to the left and right support arms 22, comprising shaft sections J and connecting sections 231 that connect these shaft sections J.

[0211] Therefore, the left and right shaft portions J included in the upper frame engagement portion 2 are provided in a manner that offers excellent rigidity.

[0212] The lower part of the upper frame p2 is provided with a bearing recess 4 that includes a bearing section K and is open downwards.

[0213] Therefore, the upper frame p2 has a configuration in which the bearing portion K is suitably engaged with the shaft portion J which is integrally provided with the lower frame p1.

[0214] Another component, the intermediate member S, is made of a resin that has better sliding properties than the upper frame p2 and is disposed in the bearing recess 4. The axial curved surface jm formed on the upper part of the shaft J engages with the bearing K via the intermediate member S.

[0215] Therefore, the intermediate member S can slide smoothly against the shaft J without the use of a lubricant such as grease.

[0216] The resin is polyoxymethylene (POM) resin. Therefore, the intermediate member S has excellent strength and can slide smoothly against the shaft J without the use of lubricants such as grease.

[0217] The bearing recess 4 comprises a front wall portion 41, a rear wall portion 42 positioned behind the front wall portion 41, and a connecting portion 43 that connects the upper parts of the front wall portion 41 and the rear wall portion 42. The bearing portion K is formed in a downward C shape, including the front wall portion 41, the rear wall portion 42, and the connecting portion 43.

[0218] Therefore, the bearing recess 4 has a suitable configuration for receiving the shaft portion J.

[0219] A reinforcing connecting portion 44 is provided that connects the left-right intermediate portions at the upper parts of the front wall portion 41 and the rear wall portion 42.

[0220] Therefore, the front wall portion 41 and the rear wall portion 42 have a structure with excellent strength due to the reinforcing connecting portion 44.

[0221] However, the present invention is not limited to the embodiments described in detail above.

[0222] The lower frame may be provided with a bearing section to receive the shaft, and the upper frame may be provided with the shaft.

[0223] The lower part of the shaft may have a partially cylindrical curved surface formed on it.

[0224] The shaft and the bearing can engage directly or indirectly through other components. In other words, the configuration does not require an intermediate member to be interposed between the shaft and the bearing.

[0225] The shaft portion may be formed separately from the upper or lower frame.

[0226] The entire lateral region of the horizontal section may constitute the shaft.

[0227] The intermediate member that can provide the rotation-restricting function may be provided between the support base and the back support.

[0228] In other words, the chair has a backrest that is rotatably supported on a support base via a back support, and either the support base or the back support has a shaft portion, and the other has a bearing portion that receives the shaft portion, and a biasing member is interposed between the support base and the back support, and the back support is configured to be rotatable around the shaft portion so that it can take an assembled position in which the biasing member can be attached to the support base and a normal position which is a different position from the assembled position, and an intermediate member may be provided between the support base and the back support that can restrict the rotation of the back support so that it cannot return to the assembled position when its position has been changed from the assembled position to the normal position.

[0229] A more specific configuration of the above-described invention is one in which the back support is configured to be tiltable between an upright position and a backward-tilted position that is more backward than the upright position in the normal posture, and the biasing member biases the back support in the direction of the upright position.

[0230] Furthermore, the intermediate member may be provided between the first and second members that constitute the chair. The first and second members can be any type of components that make up the chair.

[0231] In other words, the chair is configured such that a second member is rotatably supported by a first member, and either the first member or the second member has a shaft portion, and the other has a bearing portion that receives the shaft portion, and a biasing member is interposed between the first member and the second member, and the second member is configured to be rotatable around the shaft portion so that it can take an assembled position in which the biasing member can be attached to the first member, and a normal position which is a different position from the assembled position, and an intermediate member is provided between the first member and the second member that can restrict the rotation of the back support so that it cannot return to the assembled position when its position has been changed from the assembled position to the normal position.

[0232] A more specific configuration of the invention described above is one in which the second member is configured to be tiltable between an initial position and a shifted position different from the initial position in the normal position, and the biasing member biases the second member in the direction of the initial position.

[0233] Furthermore, the specific configuration of each part is not limited to the above embodiments, and various modifications are possible without departing from the spirit of the present invention. [Explanation of symbols]

[0234] 4...Bearing receiving recess B...Support base D...back support E...backrest J…Shaft part jm…axis curved surface K...Bearing part P…back support body p1... Lower frame (first component) p2…Upper frame (second component) V... Coil spring (biasing member)

Claims

1. A chair in which the backrest is rotatably supported by a back support at the support base, The back support comprises a lower frame having either a shaft portion or a bearing portion that receives the shaft portion, and an upper frame having the other of the shaft portion and the bearing portion and being rotatably supported with respect to the lower frame. The aforementioned shaft portion extends horizontally, and its width in the front-to-back direction is shorter than its width in the up-to-down direction. A chair having a partially cylindrical curved surface formed on either the upper or lower part of the shaft, which can engage directly or indirectly with the bearing portion via another member.

2. The lower frame is provided with the shaft portion having the axial curved surface formed on its upper part, The chair according to claim 1, wherein the bearing portion is provided on the upper frame.

3. The chair according to claim 1, wherein the upper frame or the lower frame, which includes the shaft portion, is integrally formed from synthetic resin.

4. The lower frame is provided with an upper frame engagement portion which includes the shaft portion, The chair according to claim 2, wherein the upper frame engagement portion comprises a lower frame base, left and right support arms extending in pairs in the vertical direction from the left and right of the lower frame base, and a horizontal frame portion that is installed between these left and right support arms and includes the shaft portion.

5. The chair according to claim 4, wherein the horizontal section comprises shaft sections arranged in pairs on the left and right sides, with each outer section integrally connected to the left and right support arms, and connecting sections connecting these shaft sections.

6. The chair according to claim 2, wherein the lower part of the upper frame is provided with a bearing recess that includes the bearing portion and is open downwards.

7. The other member is an intermediate member disposed in the bearing recess, which is made of a resin having better sliding properties than the upper frame. The chair according to claim 6, wherein the curved axial surface formed on the upper part of the shaft engages with the bearing portion via the intermediate member.

8. The chair according to claim 7, wherein the resin is polyoxymethylene (POM) resin.

9. The bearing recess comprises a front wall portion, a rear wall portion disposed behind the front wall portion, and a connecting portion connecting the upper parts of the front wall portion and the rear wall portion. The chair according to claim 6, wherein the bearing portion is configured to be a downward C-shape including the front wall portion, the rear wall portion, and the connecting portion.

10. The chair according to claim 9, wherein a reinforcing connecting portion is provided that connects the left-right intermediate portion at the upper part of the front wall portion and the rear wall portion.

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