chair

Abstract

To provide a chair having an excellent design degree of freedom which can have a weight sensing rocking mechanism disposed while maintaining a suitable configuration for a seat and a leg.SOLUTION: A chair comprises a back support body D having a rear shaft jk3 rotatably supported by a support base via a main shaft, disposed in front of the main shaft, and capable of engaging with a seat receiver c1 of a seat; a weight sensing rocking mechanism is configured and disposed so as to lift a front part of the seat upward by interlocking it with back tilting operation of the back support body D; the seat receiver c1 comprises a recess cw opened downward, in which the rear shaft jk3 is stored; and the recess cw comprises a recess top wall part cw1 with a lower surface facing the recess space cs and an upper surface constituting an upper surface of the seat receiver c1.SELECTED DRAWING: Figure 83

Description

[Technical field]

[0001] The present invention relates to a chair. [Background technology]

[0002] 2. Description of the Related Art There has been known a chair equipped with a weight-sensing rocking mechanism that is configured so that the entire seat can be lifted upward in conjunction with the backward tilting of the backrest (see, for example, Patent Document 1).

[0003] In this type of chair, in order to realize a suitable rocking action of the backrest and the seat, at least the seat support shaft for lifting the seat must be arranged above and spaced apart from the main shaft that is the rotation center of the back support. In other words, a certain area in the vertical direction is essential for the chair to have a weight-sensing rocking mechanism including the main shaft and the seat support shaft.

[0004] On the other hand, under the assumption that the distance from the seating surface of a chair to the floor of an office, etc. is limited, it is desirable for the seat to have a vertical dimension that provides a comfortable seating experience for the user, and it is desirable for the legs to have a constant vertical dimension that gives the impression of being slim to the viewer.

[0005] For these reasons, there is a demand for chairs that have seats and legs that ensure the required vertical dimensions within a limited area from the floor to the seating surface, and that are equipped with weight-sensing rocking mechanisms that allow for optimal operation. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 5789753. Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention has been made in light of the above-mentioned circumstances, and its object is to provide a chair with excellent design freedom that can accommodate a weight-sensing rocking mechanism while maintaining at least a suitable configuration for the seat and legs. [Means for solving the problem]

[0008] That is, the present invention has the following configuration.

[0009] The invention described in claim 1 is a chair comprising legs, a support base attached to the upper end of the legs, a seat disposed on the support base, and a back support rotatably supported on the support base via a main shaft and having a seat engagement shaft disposed ahead of the main shaft and capable of engaging with the seat, and provided with a weight-sensing rocking mechanism configured to lift the front of the seat upward as the back support tilts backward, wherein the seat comprises a seat support having an axis holding portion capable of holding the seat engagement shaft, and a seat body supported by the seat support, the seat support having a recess having a recessed space that is open downward and receives the seat engagement shaft, and the recess has a recess top wall portion whose lower surface faces the recessed space and whose upper surface constitutes the upper surface of the seat support. The back support can movably support the backrest between a normal position and a backward tilted position tilted further backward than the normal position, the back support is biased in a direction in which the backrest can take the normal position by a reaction force generating part provided on the support base, the back support has a bearing shaft pressed backward by the reaction force generating part, the bearing shaft is supported by the seat engagement shaft and the main shaft via a bearing shaft support member, and the bearing shaft is disposed in front of the main shaft and below the main shaft. It's a chair.

[0010] The invention described in claim 2 is A chair comprising legs, a support base attached to the upper end of the legs, a seat disposed on the support base, and a back support rotatably supported on the support base via a main shaft and having a seat engagement shaft disposed ahead of the main shaft and capable of engaging with the seat, the chair being provided with a weight-sensing rocking mechanism configured to lift the front of the seat upward as the back support tilts backward, the seat comprising a seat support having an axis holding portion capable of holding the seat engagement shaft, and a seat body supported by the seat support. the seat holder is provided with a recess having a recessed space that is open downward and that houses the seat engagement shaft, the recess has a lower surface facing the recessed space and a recess top wall portion whose upper surface constitutes the upper surface of the seat holder, the seat is supported movably relative to the support base via the front shaft, the support base has a front shaft support portion in the form of an elongated hole that can support the front shaft so as to be slidable, and the seat holder has front shaft holding portions that can hold both ends of the front shaft. It's a chair.

[0011] The invention described in claim 3 is A chair comprising legs, a support base attached to the upper end of the legs, a seat disposed on the support base, and a back support rotatably supported on the support base via a main shaft and having a seat engagement shaft disposed ahead of the main shaft and capable of engaging with the seat, the chair being provided with a weight-sensing rocking mechanism configured to lift the front of the seat upward as the back support tilts backward, the seat comprising a seat support having an axis holding portion capable of holding the seat engagement shaft, and a seat body supported by the seat support, the seat support comprising a recess having a recessed space that is open downward and in which the seat engagement shaft is housed, the recess comprising a recess top wall portion whose lower surface faces the recessed space and whose upper surface constitutes the upper surface of the seat support, the axis holding portion being disposed in the center of the seat support in the front-rear direction and the center of the seat support in the left-right direction. It's a chair.

[0012] The invention described in claim 4 is A chair comprising legs, a support base attached to the upper ends of the legs, a seat disposed on the support base, and a back support rotatably supported on the support base via a main shaft and having a seat engagement shaft disposed ahead of the main shaft and engageable with the seat, and provided with a weight-sensing rocking mechanism configured to lift a front part of the seat upward as the back support tilts backward, the seat comprising a seat support having a shaft holding part capable of holding the seat engagement shaft, and a seat body supported by the seat support, the seat support comprising a recess having a recessed space that is open downward and receives the seat engagement shaft, the recess comprising a recess top wall portion whose lower surface faces the recessed space and whose upper surface constitutes the upper surface of the seat support, and the recess top wall portion is provided with left and right shaft end engagement parts capable of engaging with upper parts of both left and right ends of the seat engagement shaft. It's a chair.

[0013] The invention described in claim 5 is A chair comprising legs, a support base attached to the upper end of the legs, a seat disposed on the support base, and a back support rotatably supported on the support base via a main shaft and having a seat engagement shaft disposed in front of the main shaft and capable of engaging with the seat, and provided with a weight-sensing rocking mechanism configured to lift a front portion of the seat upward as the back support tilts backward, wherein the seat comprises a seat support having a shaft holding portion capable of holding the seat engagement shaft, and a seat body supported by the seat support, the seat support having a recess having a recessed space that is open downward and in which the seat engagement shaft is housed, the recess having a recess top wall portion whose lower surface faces the recessed space and whose upper surface constitutes the upper surface of the seat support, and the shaft holding portion comprises a first holding member that protrudes into the recessed space and has a portion that can engage with at least a front portion of the seat engagement shaft, and a second holding member that protrudes into the recessed space and has a portion that can engage with at least a rear portion of the seat engagement shaft. It's a chair.

[0014] The invention described in claim 6 is A chair comprising legs, a support base attached to the upper end of the legs, a seat disposed on the support base, and a back support rotatably supported on the support base via a main shaft and having a seat engagement shaft disposed ahead of the main shaft and capable of engaging with the seat, the chair being provided with a weight-sensing rocking mechanism configured to lift the front of the seat upward as the back support is tilted backward, the seat comprising a seat support having an axis holding portion capable of holding the seat engagement shaft, and a seat base supported by the seat support. and a body, the seat receiver having a recess that is open downward and has a recessed space in which the seat engagement shaft is housed, the recess having a recess top wall portion whose lower surface faces the recessed space and whose upper surface constitutes the upper surface of the seat receiver, the recess having the recess top wall portion, a recess front wall portion and a recess rear wall portion respectively extending downward from the front and rear of the recess top wall portion, and left and right recess side wall portions respectively extending downward from the left and right side portions of the recess top wall portion.It's a chair.

[0015] The invention described in claim 7 is A chair comprising legs, a support base attached to the upper end of the legs, a seat disposed on the support base, and a back support rotatably supported on the support base via a main shaft and having a seat engagement shaft disposed ahead of the main shaft and capable of engaging with the seat, and provided with a weight-sensing rocking mechanism configured to lift the front of the seat upward as the back support tilts backward, the seat comprising a seat support having a shaft holding part capable of holding the seat engagement shaft, and a seat body supported by the seat support, the seat support comprising a recess having a recessed space that is open downward and in which the seat engagement shaft is housed, the recess comprising a recess top wall portion whose lower surface faces the recessed space and whose upper surface constitutes the upper surface of the seat support, the seat body being supported on the seat support so as to be slidable in the front-rear direction, and the upper surface of the seat support constituting a lower support area capable of contacting the lower surface of the seat body. It's a chair.

[0016] The invention described in claim 8 is The seat is supported movably relative to the support base via a front shaft. Claim 1, 3, 4, 5, 6 or 7 This is the chair described.

[0017] The invention described in claim 9 is The bearing shaft is disposed behind the seat engagement shaft. Claim 1 This is the chair described.

[0018] The invention described in claim 10 is The rocking mechanism is configured to lift the front part of the seat upward and move the rear part of the seat downward in association with the backward tilting movement of the back support. A chair according to claim 1, 2, 3, 4, 5, 6, 7, 8 or 9.

[0019] The invention described in claim 11 is The recess includes the recess top wall portion, and a recess front wall portion and a recess rear wall portion extending downward from the front and rear portions of the recess top wall portion, respectively. The first holding member is a wall extending in the front-rear direction and is integrally connected to the recess top wall portion and the recess front wall portion. The second holding member is a wall extending in the front-rear direction and is integrally connected to the recess top wall portion and the recess rear wall portion. Claim 5 This is the chair described.

[0020] The invention described in claim 12 is The first holding members are arranged in a plurality of positions spaced apart in the left-right direction, and the second holding members are arranged in a plurality of positions spaced apart in the left-right direction. Claim 5 or 11 This is the chair described.

[0021] The invention described in claim 13 is Between the first holding member and the second holding member, a shaft passage through which the seat engagement shaft can pass when the seat engagement shaft is attached to the shaft holding portion is provided. Claim 5 , 11 or 12 This is the chair described.

[0022] The invention described in claim 14 is The seat body includes a seat cushion. Claims 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 or 13 is a chair as described above.

[0023] The invention described in claim 15 is a chair comprising legs, a support base attached to the upper end of the legs, a seat movably arranged on the support base via a front axle, and a back support rotatably supported on the support base via a main axle and having a seat engagement axle arranged in front of and above the main axle and capable of engaging with the seat, and is provided with a weight-sensing rocking mechanism based on a configuration in which the front and front-to-rear central parts of the seat can be lifted upward as the back support is tilted backward, wherein the back support is given a reaction force against the backward tilting movement by a reaction force generating section including a coil spring provided on the support base, the degree of compression of the coil spring can be adjusted by operating a reaction force adjustment lever, and the amount of compression of the coil spring by operating the reaction force adjustment lever is set to approximately half the value of the amount of compression of the coil spring by the backward tilting movement of the back support. Effect of the Invention

[0027] As described above, according to the present invention, it is possible to provide a chair with excellent design freedom, which can accommodate a weight-sensing rocking mechanism while maintaining at least a suitable configuration for the seat and legs. [Brief description of the drawings]

[0028] [Figure 1] FIG. 1 is a perspective view showing an embodiment of the present invention. [Diagram 2] FIG. [Diagram 3] FIG. [Figure 4] FIG. [Diagram 5] FIG. [Figure 6] FIG. [Figure 7] FIG. [Figure 8] FIG. [Figure 9] FIG. [Figure 10] FIG. [Figure 11] FIG. [Figure 12] FIG. 4 is a plan view of an adjustment lever (reaction force adjustment lever) in the embodiment. [Figure 13] Cross-sectional view taken along line AA in FIG. 9(a). [Figure 14] FIG. [Figure 15] FIG. [Figure 16] FIG. [Figure 17] FIG. [Figure 18] FIG. [Figure 19] Cross-sectional view of line BB in Figure 2. [Figure 20] Cross-sectional view taken along line CC in FIG. 2. [Figure 21] Cross-sectional view of line DD in Figure 2. [Figure 22] FIG. [Figure 23] FIG. [Figure 24] FIG. [Diagram 25] FIG. [Figure 26] An enlarged view of part E in FIG. [Figure 27] 20 is a cross-sectional view taken along line FF in FIG. 19. [Figure 28] FIG. [Figure 29] FIG. [Diagram 30] FIG. [Diagram 31] 31 is a view taken in the direction of arrow G in FIG. 30 . [Diagram 32] FIG. [Diagram 33] FIG. [Diagram 34] FIG. [Diagram 35] FIG. [Diagram 36] Cross-sectional view of line JJ in Figure 2. [Figure 37] FIG. [Figure 38] FIG. [Figure 39] FIG. [Diagram 40] FIG. [Diagram 41] FIG. [Diagram 42] Cross-sectional view of line HH in Figure 41. [Diagram 43] Cross-sectional view of line II in Figure 41. [Diagram 44] Cross-sectional view of line LL in Figure 3. [Diagram 45] FIG. 45 is a cross-sectional view for explaining the operation corresponding to FIG. 44 . [Diagram 46] FIG. 45 is a cross-sectional view for explaining the operation corresponding to FIG. 44 . [Figure 47] FIG. [Figure 48] FIG. [Figure 49] FIG. [Figure 50] Cross-sectional view taken along line KK in FIG. [Figure 51] FIG. 4 is a perspective view of a support base main body in the embodiment. [Figure 52] FIG. [Diagram 53] FIG. [Figure 54] FIG. 4 is a right side view of the support base main body in the embodiment. [Figure 55] FIG. 4 is a left side view of the support base main body in the embodiment. [Figure 56] FIG. [Figure 57]FIG. 4 is a bottom view of the support base main body in the embodiment. [Figure 58] FIG. [Figure 59] Cross section along line MM in Figure 58. [Figure 60] Cross section taken along line NN in Figure 52. [Figure 61] FIG. 2 is a perspective view showing a support base, a back support, and the like in the embodiment. [Figure 62] FIG. [Figure 63] FIG. [Figure 64] FIG. [Figure 65] FIG. [Figure 66] FIG. [Figure 67] Cross-sectional view of line OO in Figure 66. [Figure 68] Cross-sectional view of line PP in Figure 66. [Figure 69] FIG. [Figure 70] FIG. [Figure 71] FIG. [Figure 72] Cross-sectional view of line QQ in Figure 71. [Figure 73] Cross-sectional view of line RR in Figure 71. [Figure 74] FIG. [Figure 75] FIG. [Figure 76] 4 is a central cross-sectional view of a main part of the rearward tilt degree setting mechanism in the embodiment. FIG. [Figure 77] 4 is a central cross-sectional view of a main part of the rearward tilt degree setting mechanism in the embodiment. FIG. [Figure 78] 4 is a central cross-sectional view of a main part of the rearward tilt degree setting mechanism in the embodiment. FIG. [Figure 79] 4 is a central cross-sectional view of a main part of the rearward tilt degree setting mechanism in the embodiment. FIG. [Figure 80]FIG. [Figure 81] FIG. [Figure 82] Cross section of line SS in Figure 80. [Figure 83] FIG. [Figure 84] FIG. [Figure 85] Cross-sectional view of line TT in Figure 81. [Figure 86] 5 is a schematic diagram for explaining a rocking operation in the embodiment. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] Hereinafter, one embodiment of the present invention will be described with reference to FIGS.

[0030] In this embodiment, the present invention is applied to a swivel chair for business use (hereinafter simply referred to as a "chair") suitable for use in an office or the like.

[0031] The chair comprises legs A, a support base B which is a support member supported rotatably relative to the legs A, a seat C disposed on the support base B, a backrest E supported so as to be able to tilt backward relative to the support base B via a back support body D, a lumbar support R attached to the backrest E, and a backrest surface extension member F and a hanger G which are options which can be selectively attached to the backrest E.

[0032] The chair is provided with a backward tilt degree setting mechanism X between the support base B and the back support D, which can set the backward tilt degree of the backrest E.

[0033] The chair of this embodiment is provided with a so-called weight-sensing rocking mechanism V that moves the seat C upward and backward in response to the backward tilting of the backrest E.

[0034] The weight-sensing rocking mechanism V is configured to lift the front and front-to-rear central parts of the seat C upward and move the rear end part Ce of the seat C downward in response to the backward tilting movement of the back support D linked to the backrest E.

[0035] In other words, the rocking mechanism V is associated with a back support body D which is supported rotatably around the main axis jk1 relative to the support base B, and is configured to enable the backrest E to move between an upright normal position (ES) which it can assume when not under load, and a rearward tilted position (EK) which is tilted further back than the normal position (ES), and to enable the seat C to move between a normal position (CJ) and a rearward tilted position (CK) which is positioned further back than the normal position (CJ) and tilted further back.

[0036] In other words, the backrest E and the seat C can be changed in position between the normal position (ES) (CJ) and the backward leaning positions (EK) (CK) in conjunction with the movement of the back support D.

[0037] <<Legs A>> The leg A includes a plurality of leg blades a1 arranged radially, each having a caster a11 at its tip, and a leg support a2 erected at the base end of the leg blade a1.

[0038] The leg support a2 is configured to be extendable and retractable in the vertical direction. The leg support a2 is capable of supporting the support base B by a gas spring (not shown) so that the vertical position can be changed.

[0039] <<Support base B>> The support base B is mainly composed of a support base main body 1 which is integrally formed from synthetic resin. The support base B is attached onto the leg A.

[0040] <Support base body 1> The support base body 1 is integrally molded from synthetic resin. The support base body 1 has an internal storage space sp and is box-shaped with an open top. The support base body 1 is designed not to be covered by a cover body that is a separate member.

[0041] The support base main body 1 not only performs the function of supporting the seat C and the backrest E, but also exhibits design properties such as acting as a cover that does not spoil the aesthetic appearance.

[0042] At least a portion of the outer surface of the support base body 1, i.e., a portion of the downward surface 11s of the foundation bottom structure 11, the downward surface 12s of the inclined bottom wall 12, the downward surface 13s of the front bottom wall 13, and a portion of the outward surfaces 14s of the left and right side walls 14, are exposed to the outside and can be directly seen by the user.

[0043] The support base main body 1 comprises a foundation bottom structure 11 having a downward surface 11s and attached to the leg support a2, an inclined bottom wall 12 having a downward surface 12s facing diagonally downward and rearward and extending diagonally downward and forward from the front end of the foundation bottom structure 11, a front bottom wall 13 having a downward surface 13s and extending forward from the front end of the inclined bottom wall 12 and inclined so as to gradually position upward as it moves forward, the foundation bottom structure 11, the inclined bottom wall 12, and left and right side walls 14 having outward surfaces 14s and extending upward from both left and right ends of the front bottom wall 13, respectively, and a front wall 15 having a forward surface 15s and in an upright position connecting the front ends of the left and right side walls 14.

[0044] In other words, the support base main body 1 comprises a bottom wall component 10 composed of a foundation bottom structure 11, an inclined bottom wall 12, and a front bottom wall 13, left and right side walls 14 which are in an upright position and connected upward from both left and right end portions of the bottom wall component 10, and a front wall 15 which connects the front ends of the left and right side walls 14.

[0045] The support base main body 1 is surrounded by a foundation bottom structure 11, an inclined bottom wall 12, a front bottom wall 13, left and right side walls 14, and a front wall 15, and is provided with a storage space sp that accommodates the reaction force generating part HG, a bearing shaft d4 that engages with the reaction force generating part HG, a bearing shaft support member d3 that supports the bearing shaft d4, and the lever base shaft part k3 of the reaction force adjustment lever K.

[0046] [Foundation bottom structure 11] The foundation bottom structure 11 comprises a bottom wall portion 111 having a downward surface 11s, a boss portion 112 erected on the bottom wall portion 111, a rear curved wall 113 erected on the bottom wall portion 111, located behind the boss portion 112 and curved along the boss portion 112, a side upright wall 114 erected on the bottom wall portion 111, extending in the front-rear direction, and positioned between the boss portion 112 and the left and right side walls 14, a rear connecting wall 115 erected on the bottom wall portion 111 and extending in the front-rear direction connecting between the left-right central portion of the rear of the boss portion 112 and the left-right central portion of the rear curved wall 113, and a rear connecting wall 115 erected on the bottom wall portion 111 and extending in the front-rear direction connecting between the left-right central portion of the rear of the boss portion 112 and the left-right central portion of the rear curved wall 113. the side connecting wall 116 which is inclined in plan view and connects between the side portion of the boss portion 112 and the side upright wall 114; a front connecting wall 117 which is erected on the bottom wall portion 111 and connects between the front portion of the boss portion 112 and the side upright wall 114 and which is inclined in plan view; an outer connecting wall 118 which is erected on the bottom wall portion 111 and connects between the side upright wall 114 and the right and left side walls 14 and which is inclined in plan view; and an undershaft connecting portion 119 which is erected on the bottom wall portion 111 and connects between the side upright wall 114 and the right and left side walls 14 and is disposed below the main shaft jk1 inserted in the shaft hole 1b.

[0047] The shaft lower connecting portion 119 is provided at its upper portion with a shaft holding recess 1e that constitutes a shaft holding portion JH capable of holding the main shaft jk1. The shaft holding portion JH will be described in detail later.

[0048] The foundation bottom structure 11 has a fitting hole 11a that is provided so as to penetrate the bottom wall portion 111 and the boss portion 112 and serves as a connection portion for fitting externally onto the leg support a2.

[0049] A mounting seat 111a is provided at the rear end of the bottom wall 111 for mounting a damper member XM, which is a buffer attachment that can engage with the rotating member Re attached to the rearward tilt degree setting lever H. The mounting seats 111a are provided in pairs on the left and right sides of a partition wall 111d. The mounting seat 111a is provided with a hole 111b for mounting the damper member XM, which is an attachment that penetrates in the vertical direction. A recess 111c is formed on the underside of the bottom wall 111 corresponding to the mounting seat 111a.

[0050] A nut portion n7 is provided on the boss portion 112 for mounting a gas spring operating mechanism (not shown) that can be operated by transmitting an operating force to the operating piece L disposed on the seat receiver c1.

[0051] [Sloped bottom wall 12] The inclined bottom wall 12 has a downward surface 12s facing diagonally downward and rearward, and is in a rearward inclined position extending diagonally downward and forward from the front end of the bottom wall portion 111 of the foundation bottom structure 11. A pair of left and right intermediate connecting walls 121 extending in the front-to-rear direction and connected to the front part of the foundation bottom structure 11 and the rear part of the front bottom wall 13 are provided on the inner surface of the inclined bottom wall 12.

[0052] On the inclined bottom wall 12, side upright walls 122 extending in the front-rear direction are provided so as to be continuous with the side upright walls 114 of the foundation bottom structure 11. In other words, the side upright walls 122 are provided on the inside of the left and right side walls 14.

[0053] The upper surface side of the inclined bottom wall 12 facing the storage space sp is provided with a pair of left and right intermediate connecting walls 121 which act as movement restricting parts that can engage with the receiving shaft d4 biased by the reaction force generating part HG and restrict the rearward movement of the receiving shaft d4.

[0054] The intermediate connecting wall 121 is provided with bearing shaft abutment parts 121e that face forward and extend in the vertical direction. A groove part mv recessed backward is provided in the center part in the horizontal direction of the left and right bearing shaft abutment parts 121e, so that the impact sound with the bearing shaft d4 is reduced.

[0055] [Front bottom wall 13] The front bottom wall 13 has a downward surface 13s, extends forward from the front end of the inclined bottom wall 12, and is inclined so as to be positioned gradually higher as it moves forward.

[0056] The front bottom wall 13 has a curved shape that is convex downward so that the left-right center is located lower than both the left and right sides. A reaction force generating part HG that is mainly made of a coil spring HG1 and can expand and contract in the front-rear direction is disposed above the left-right center of the front bottom wall 13, i.e., in the storage space sp of the support base main body 1.

[0057] The front bottom wall 13 is provided with a side upright wall 131 extending in the front-rear direction and continuing from the side upright wall 122 of the inclined bottom wall 12. That is, the side upright wall 131 is provided on the inside of the left and right side walls 14. In addition, the front bottom wall 13 is provided with a plurality of connecting walls 132 connecting the side upright wall 131 and the left and right side walls 14.

[0058] The front part of the front bottom wall 13 is provided with a plurality of bearing portions 133a, 133b, 133c which receive a plurality of retained shaft portions k31a, k31b, k31c provided on the lever base shaft portion k3 of the reaction force adjustment lever K, i.e., the right bearing portion 133a on one side, the central bearing portion 133b, and the left bearing portion 133c on the other side.

[0059] The radius of curvature of the central bearing portion 133b is set to be larger than the radius of curvature of the right bearing portion 133a, and the radius of curvature of the left bearing portion 133c is set to be larger than the radius of curvature of the central bearing portion 133b.

[0060] The right bearing portion 133a and the left bearing portion 133c are each in an upwardly open position. The right bearing portion 133a and the left bearing portion 133c are provided on the upper portion of the side upright wall 131. The right bearing portion 133a and the left bearing portion 133c are provided with a grease retaining groove 1j on their recessed surfaces.

[0061] The central bearing portion 133b is open toward the rear. The central bearing portion 133b is provided on the back support portion 13a that supports, from the back side, the reaction force adjustment lever K that is erected in the center of the front bottom wall 13 in the left-right direction and is constantly pressed by the reaction force generating portion HG. The central bearing portion 133b also has a grease retaining groove 1j on its recessed surface.

[0062] [Left and right side walls 14] The left and right side walls 14 have outward surfaces 14a facing outward and are in an upright position extending upward from both left and right ends of the bottom wall portion 111 of the foundation bottom structure 11, the inclined bottom wall 12, and the front bottom wall 13, respectively.

[0063] The left and right side walls 14 are provided with an axle hole 1b penetrating in the left-right direction, which is provided at a front-to-rear position corresponding to the front of the bottom wall portion 111 of the foundation bottom structure 11 and which can rotatably hold the main shaft jk1, which is an axis, a recess 1a provided on the periphery of the axle hole 1b and recessed in the thickness direction of the side wall 14, a long hole 1c penetrating in the left-right direction, which is provided at the front end and can hold the front axle jk2 for supporting the front part of the seat C so that it can move forward and backward, an annular protrusion 141 protruding outward so as to surround the opening edge of the axle hole 1b in a side view, and a lever insertion hole 142 provided on the rear side of the long hole 1c in the left side wall 14 and through which the reaction force adjustment lever K is inserted.

[0064] The shaft hole 1b is capable of rotatably supporting the main shaft jk1 that is installed between the left and right arms d1 of the back support body D. In this embodiment, the shaft holes 1b provided in the left and right side walls 14 are parts that constitute the shaft holding portion JH for suitably holding the main shaft jk1 in the support base main body 1 made of synthetic resin.

[0065] That is, the shaft retaining portion JH is composed of a shaft hole 1b, which is a through hole formed in the left and right side walls 14 corresponding to the size of the main shaft jk1, and a shaft retaining recess 1e connected to the inner side of the left and right side walls 14 and provided on the upper part of the side upright wall 114 and the undershaft connecting portion 119 of the foundation bottom structure 11.

[0066] The shaft retaining recess 1e is formed at a position corresponding to the shaft hole 1b. The shaft retaining recess 1e is open upward. The shaft retaining recess 1e has a recessed surface 1f formed continuous with the inner peripheral surface of the lower part of the shaft hole 1b.

[0067] The shaft holding recess 1e is recessed so as to rotatably hold the lower part of the main shaft jk1. The shaft holding recess 1e is provided with a plurality of grease holding grooves 1g spaced apart in the left-right direction and extending in the front-rear direction along the recessed surface 1f.

[0068] The recess 1a is formed on the periphery of the shaft hole 1b, more specifically, below the shaft hole 1b. The recess 1a is provided approximately directly below the shaft hole 1b. The recess 1a is provided on the outer surface side of the left and right side walls 14. The recess 1a forms a space se that is approximately rectangular prism-shaped and open outward.

[0069] A resin portion JN is interposed between the recess 1a and the shaft hole 1b. The vertical dimension w4 of the resin portion JN is set to be shorter than the diameter w2 of the shaft hole 1b. The resin portion JN is formed by the portions of the left and right side walls 14 below the shaft hole 1b and the undershaft connecting portion 119 of the foundation bottom structure 11.

[0070] The inner dimension w1 in the front-rear direction of the recess 1a is set to be approximately equal to or shorter than the diameter w2 of the shaft hole 1b. The inner dimension w3 in the up-down direction of the recess 1a is set to be shorter than the diameter w2 of the shaft hole 1b. The recess 1a is covered and hidden by the seat support c1 of the seat C in a side view.

[0071] The long hole 1c extends obliquely so that its lower end is located forward of its upper end in side view. A sleeve member SL made of a material that easily slides on the front shaft jk2 is fitted into the long hole 1c. The front shaft jk2 is supported by the long hole 1c via the sleeve member SL.

[0072] The annular projection 141 is configured so that the protruding end surface facing outward can come into contact with the inner surfaces of the left and right arms d1 of the back support D.

[0073] [Front wall 15] The front wall 15 has a front surface s15 and is in an upright position connecting the front ends of the left and right side walls 14. The upper part of the front wall 15 is provided with a horizontally extending protruding wall 151 that is a rib extending in the left-right direction, and a plurality of vertically extending protruding walls 152 that are disposed on the horizontally extending protruding wall 151 and spaced apart in the left-right direction and extend in the up-down direction.

[0074] A reaction force generating unit HG is disposed inside the support base main body 1, i.e., in the storage space sp, for generating a reaction force of the backrest E that can tilt backward. The reaction force generating unit HG is disposed between a reaction force adjusting lever K pivotally supported on the support base B and a back support body D pivotally supported on the support base B and connected to the backrest E.

[0075] The reaction force generating section HG is mainly composed of a metallic coil spring HG1, which is a spring material. In this embodiment, the body weight of the seated person assists the reaction force in the normal position ES direction against the backward tilting of the backrest E based on the structure of the weight-sensing rocking mechanism V in which the seated person presses the rear axle jk3 forward and downward through the seat C. For this reason, a relatively small and lightweight coil spring HG1 is applied to the reaction force generating section HG in this embodiment.

[0076] The reaction force generating part HG is arranged so as to be extendable and contractible in the front-rear direction, and is inclined within the accommodation space sp of the support base main body 1 so that the front part is positioned higher than the rear part.

[0077] The reaction force generating part HG comprises a coil spring HG1 made of metal, a front member HG2 attached to the front part of the coil spring HG1, a rear member HG3 attached to the rear part of the coil spring HG1, and a posture holding shaft HG4 whose front part is inserted into a holding hole of the front member HG2 and whose rear part is inserted into a holding hole of the rear member HG3, thereby holding the posture of the front member HG2 and the rear member HG3.

[0078] The front end of the front member HG2 is connected to the rear end of the pressing block BL. The rear member HG3 holds a receiving shaft d4 at its rear end.

[0079] A pressing block BL is interposed between the front member HG2 of the reaction force generating part HG and the reaction force adjusting lever K. The pressing block BL is positioned by the cover body Ba and the support base main body 1 so as to be movable in the front-rear direction. The pressing block BL is constantly biased forward by the reaction force generating part HG. The front end of the pressing block BL engages with the cam portion k33 of the reaction force adjusting lever K.

[0080] The reaction force generating part HG is capable of biasing the receiving shaft d4 backward using the support base B (support base main body 1 / cover body Ba) as a foothold to which the biasing force is transmitted via the pressing block BL and the reaction force adjusting lever K.

[0081] The pressing block BL can be changed in its front-rear position by rotating the reaction force adjustment lever K having a cam portion k33. That is, by changing the front-rear position of the reaction force adjustment lever K in the pressing block BL, the initial compression state of the reaction force generating portion HG can be changed, and the degree of reaction force against the backward tilting motion of the backrest E can be adjusted.

[0082] A reaction force adjustment lever K, which is an adjustment lever for adjusting the reaction force of the backrest E, is rotatably supported on the support base B. The reaction force adjustment lever K is rotatably held between the support base main body 1 and a cover body Ba which covers the upper side of the lever base shaft part k3 of the reaction force adjustment lever K and is attached to the support base main body 1 by a screw v8. The screw v8, which passes through a screw insertion hole (not shown) provided in the cover body Ba, is screwed into a nut part n8 provided in the front bottom wall 13.

[0083] <<Reaction force adjustment lever K>> The reaction force adjustment lever K is rotatably supported on the support base 1. The reaction force adjustment lever K is pivotally supported on the support base 1 so that its longitudinal axis is in the left-right direction. The reaction force adjustment lever K is rotated by the user's hand, and as the lever is rotated, the degree of compression of the coil spring HG1, which is the spring material that constitutes the reaction force generating part HG, can be adjusted.

[0084] The reaction force adjustment lever K is provided with an operating part k1 which is provided at one end, i.e., the tip, and is gripped by a user to apply a rotational operating force, an intermediate connecting part k2 which is connected to the operating part k1 with its axis js aligned and has a shape in which the outer diameter dimension becomes shorter as it moves away from the operating part k1, and a lever base shaft part k3 which is connected to the intermediate connecting part k2 with its axis js aligned and has multiple, i.e., left, right and central, retained shaft parts k31a, k31b, k31c which are pivotally supported on the support base main body 1.

[0085] The reaction force adjusting lever K is made up of an operating portion k1, an intermediate connecting portion k2, and a lever base shaft portion k3 which are integrally formed from synthetic resin.

[0086] <Operation section k1> The operation unit k1 includes an operation unit body k11 having a generally cylindrical shape that is open to the outside, and a protruding portion k12 that is a mark portion provided at an end of the operation unit body k11 and extends toward the center of the operation unit body k11. The protruding portion k12 is a single portion that protrudes from the inner peripheral surface of the operation unit body k11 toward the center of the operation unit body k11.

[0087] [Operation unit body k11] The operation unit body k11 can form a substantially cylindrical space s1 inside. The operation unit body k11 is configured such that the outer peripheral surface of the tip portion k111 is positioned in a direction that gradually approaches the tip. In addition, a plurality of grooves k112 for preventing finger slippage are provided along the axis js on the outer peripheral surface of the tip portion k111 of the operation unit body k11.

[0088] A mark recessed portion k114 having a width dimension substantially equal to the thickness dimension of the protruding portion k12 is formed on the outer peripheral surface of the tip portion k111 of the operation portion main body k11 corresponding to the protruding portion k12. That is, the recessed portion k114 is provided on the outer peripheral surface of the tip portion k111 located directly behind the inner peripheral surface of the operation portion main body k11 from which the protruding portion k12 is protruded.

[0089] [Protruding part k12] The protrusion k12 protrudes from the inner circumferential surface of the operation unit main body k11 toward the axis js. The protrusion k12 is in the form of an upright wall extending along the longitudinal direction of the reaction force adjustment lever K. When viewed from the axis js direction, the protrusion k12 has a tip k121 which is a shaped portion that gradually narrows toward the axis js. In this embodiment, the gradually narrowing shaped portion is only present at the tip k121 of the protrusion k12. More specifically, the tip k121 of the protrusion k12 is in the form of a semicircular arc in a side view.

[0090] The protruding portion k12 has an outwardly facing end surface k122 for use as a marker on the outwardly facing end edge of the operation portion main body k11, that is, on the outer side of the opening edge k113 of the operation portion main body k11.

[0091] <Intermediate connection part k2> The intermediate connecting part k2 has a shape in which the outer diameter dimension gradually decreases from the side having the operating part k1 toward the side having the lever base part k3. That is, the intermediate connecting part k2 has a partial cone shape interposed between the operating part k1 and the lever base part k3.

[0092] A substantially conical inner space s2 is formed inside the intermediate connecting part k2, which is continuous with the cylindrical space s1 of the operating part main body k11. A protrusion k12 provided on the operating part main body k11 is connected to the inner peripheral surface of the tip side part of the intermediate connecting part k2, i.e., the inner peripheral surface on the operating part k1 side.

[0093] <Lever base part k3> The lever base shaft portion k3 is provided with a plurality of retained shaft portions k31a, k31b, k31c which are connected to the intermediate connecting portion k2 with their axis js aligned and journaled relative to the support base B, an engaging protrusion k32 which can engage with a protrusion for regulating the rotation range (not shown) provided on the cover body Ba of the support base B, and a cam portion k33 which can engage with the reaction force generating portion HG arranged inside the support base B.

[0094] A plurality of the held shaft portions k31a, k31b, and k31c are arranged on the lever base shaft portion k3. Among the left, right, and central held shaft portions k31a, k31b, and k31c arranged on the lever base shaft portion k3, the diameter of the base end (right) held shaft portion k31a is set to be the smallest, and the left held shaft portion k31c, i.e., the held shaft portion k31c on the tip side (operation portion k1 side), is set to be the largest.

[0095] In other words, the lever base shaft portion k3 is provided with a plurality of held shaft portions k31a, k31b, k31c having different diameters from the base end toward the tip end, and the diameter is set larger on the tip end side than on the base end side. More specifically, the diameter of the central held shaft portion k31b is set larger than the diameter of the right held shaft portion k31a, and the diameter of the left held shaft portion k31c is set larger than the diameter of the central held shaft portion k31b.

[0096] The engaging protrusions k32 are disposed at two positions on the left and right of the lever base shaft k3, spaced apart from each other. The engaging protrusions k32 are adapted to engage with a protrusion (not shown) for restricting the rotation range provided on the cover body Ba of the support base B, thereby restricting the rotation range of the reaction force adjusting lever K, which receives the operating force from the user, around the axis js.

[0097] The cam portions k31 are disposed at two positions on the left and right sides of the lever base shaft portion k3, spaced apart from each other.

[0098] <<Location C>> The seat C is disposed on the support base B. The seat C includes a seat support c1, which is also called an outer shell, and a seat body c2 having a seat surface and provided on the seat support c1 so that the front-rear position can be changed.

[0099] The seat C is supported movably relative to the support base B via the front axle jk2. The support base B is equipped with a long hole-shaped front axle support portion MS capable of supporting the front axle jk2 so that it can slide. The seat receiver c1 of the seat C is equipped with front axle holders ca4 capable of holding both ends of the front axle jk2. The front axle support portion MS is composed of a long hole 1c provided in the front portions of the left and right side walls 14 of the support base main body 1 at an incline so as to be positioned gradually upward toward the rear, and a sleeve member SL attached to the long hole 1c.

[0100] That is, the seat C has a seat body c2 supported on a seat receiver c1 so as to be slidable in the front-rear direction between a front position (i1) and a rear position (i2). The seat body c2 has a support member c21 made of synthetic resin, which is also called an inner shell.

[0101] The seat C is equipped with a shell-shaped seat support c1 made of synthetic resin, a seat body c2 arranged on the seat support c1 and supported so as to be slidable in the front-to-rear direction relative to the seat support c1, and an operating member ct supported so as to be movable up and down between an upper position and a lower position relative to the seat body c2, and which can cause the seat body c2 to be slidable in the front-to-rear direction when it is in the upper position.

[0102] <Zauke c1> The seat support c1 has a shell-like shape large enough to support the seat body c2 at its upper part. The seat support c1 has a curved shape that is convex backward when viewed from the bottom, and the four corners are rounded, forming a substantially rectangular shape overall.

[0103] The seat support c1 is capable of supporting the seat body c2 so that it can slide in the front-to-rear direction between a front position (i1) where the front part of the seat body c2 protrudes significantly forward from the front end edge of the seat support c1 when viewed from the bottom, and a rear position (i2) which is located rearward of the front position (i1).

[0104] The front part of the seat support c1 engages with the front shaft jk2. In other words, the front part of the seat support c1 is supported by the support base B via the front shaft jk2. In addition, the center part of the seat support c1 in the front-rear direction engages with the rear shaft jk3. In other words, the center part of the seat support c1 in the front-rear direction is supported by the support base B via the back support D having the rear shaft jk3.

[0105] The seat support c1 is provided with a seat support body ca constituting a shell-shaped main part capable of supporting the seat body c2 at the upper part, and four approximately T-shaped retaining projections cb protruding upward from the seat support body ca. The seat support body ca and the retaining projections cb are integrally formed from synthetic resin.

[0106] [Base body ca] The seat support main body ca comprises a seat support base c10 having a lower support area c13 formed on its upper surface which can be attached to the underside of the support member main body c211, a front lower extension wall c11 provided in the left-right center of the front part of the underside of the seat support base c10, left and right lower extension walls c12 provided in a pair on the left and right sides of the left and right center of the underside of the seat support base c10 and extending downward from both ends of the front lower extension wall c11 toward the rear, and a rear lower extension wall c14 provided in the left-right center of the rear part of the underside of the seat support base c10 and connecting the rear parts of the left and right lower extension walls c12.

[0107] The seat support base c10 has a plurality of exposed ribs (not shown) extending in the front-rear and left-right directions on the upper surface thereof to ensure rigidity. The seat support base c10 has a lower support region c13 formed by the upper ends of the ribs erected on the upper surface thereof, which can be brought into contact with and slide against the lower surface of the support member main body c211 of the support member c21.

[0108] The lower surface of the support member main body c211 can be brought into contact with the lower support area c13 of the seat support base c10. Also, when the seat body c2 slides in the front-rear direction, the lower surface of the support member main body c211 can be brought into sliding contact with the lower support area c13. The lower support area c13 has a curved shape such that the center is located lower than the outer parts when viewed from the front and rear.

[0109] Both side edges of the seat support body ca, i.e., both side edges of the seat support base c10, extend substantially linearly in the front-rear direction. The upper end portions c101 of both side edges of the seat support base c10 form the uppermost portion of the seat support body ca.

[0110] When the seat body c2 is in the rear position (i2), substantially the entire upper ends c101 of both side edges of the seat receiving base c10 are disposed in a position facing the left and right peripheral wall portions c213 of the support member c21 and the space sr.

[0111] On the other hand, when the seat body c2 is in the front position (i1), the rear portions of the upper ends c101 of both side edges of the seat support base c10 are arranged at a position intersecting with the support walls c214 located at the left and right side portions c21p at the rear of the support member c21, when viewed from the bottom.

[0112] The vertical portion c221 of the seat cushion c22 corresponding to the intersecting position is provided with a notch c221k for avoiding the upper end portion c101 of the seat support base c10. That is, the vertical portions c221 located on both left and right side portions c22p at the rear of the seat cushion c22 and disposed adjacent to the support walls c214 of the support member c21 have a shape in which the bottom is cut out so as not to interfere with the seat support c1 when the seat main body c2 is in the front position (i1).

[0113] The seat base c10 has a seat slit ca1 extending in the front-rear direction, which penetrates the seat base c10 in the up-down direction and in which an operating member ct is disposed, on the left and right sides of the lower surface of the seat base c10. An armrest attachment portion ca2 having a screw insertion hole h7 for screwing an armrest (not shown) is provided on each of the left and right sides of the lower surface of the seat base c10.

[0114] A recess ca6 is provided in the left-right center of the rear underside of the seat base c10 to avoid interference with the lower frame material 4 of the backrest E. An operating piece L that acts on a gas spring (not shown) to vertically expand and contract the leg support a2 is pivotally supported in a flapable manner on the lower part of the seat base c10.

[0115] A rear axle holding portion ca3 capable of holding the rear axle jk3 is provided in the center of the lower surface of the seat base c10 in the front-rear direction. The rear axle holding portion ca3 is provided in a portion located between the left and right lower extension walls c12 of the seat base c10 in a bottom view.

[0116] [Recess cw and rear axle retaining portion ca provided in seat base c10] The seat base c10 of the seat c1 is provided with a recess cw having a recessed space cs that is open downward and that accommodates the rear axle jk3 that is the seat engagement shaft. In this embodiment, a rear axle holder ca3 that is a shaft holder that can rotatably hold the rear axle jk3 is disposed in the recessed space cs of the recess cw.

[0117] In other words, the seat support c1 in this embodiment is designed so that the rear axle jk3 can be positioned as high as possible in the center of the seat support c1 in the front-rear direction and the left-right direction. In other words, the rear axle jk3 is disposed in a position that is recessed upward into the seat support c1.

[0118] The recess cw comprises a recess top wall portion cw1, the lower surface of which faces the recess space cs and the upper surface of which constitutes the upper surface of the seat support c1, a recess front wall portion cw2 and a recess rear wall portion cw3 extending downward from the front and rear parts of the recess top wall portion cw1, respectively, and left and right recess side wall portions cw4 extending downward from both the left and right side parts of the recess top wall portion cw1. Note that the upper surface of the recess top wall portion cw1 constitutes the center part of the upper surface of the seat support c1, but substantially the entire upper surface of the seat support c1 constitutes the lower support area c13 that can abut against the lower surface of the seat main body c2. The recess cw has a recess space cs surrounded by a recess top wall portion cw1, a recess front wall portion cw2, a recess rear wall portion cw3, and left and right recess side wall portions cw4. The rear axle retaining portion ca3 is provided in the recess space cs.

[0119] The distance between the inner surfaces of the left and right recess side walls cw4 is set to be longer than the longitudinal dimension, i.e., the left-right dimension, of the rear axle jk3. Also, the distance between the outer surfaces of the left and right side walls 14 of the support base main body 1 is set to be shorter than the longitudinal dimension of the rear axle jk3.

[0120] The inner surfaces of the left and right recess side wall portions cw4 are set to be approximately flush with the inner surfaces of the left and right lower extension walls c12 provided on the seat support main body ca.

[0121] The rear axle retaining portion ca3 is disposed in the center of the seat c1 in the front-rear direction and in the left-right direction. The rear axle retaining portion ca3 includes a first retaining member ca31 that protrudes into the recessed space cs and has a portion that can engage with at least an upper half including a front portion of the rear axle jk2, a second retaining member ca32 that protrudes into the recessed space cs and has a portion that can engage with at least a lower half including a rear portion of the rear axle jk2, and left and right shaft end engaging portions cf that are connected to the recess top wall portion cw1 and the recess side wall portion cw4 and can engage with upper portions of both left and right ends of the rear axle jk3, i.e., the upper halves.

[0122] The first holding member CA31 is disposed at two locations with a gap in the left-right direction. The first holding member CA31 is in the form of an upright plate extending in the front-rear direction. The first holding member CA31 is in the form of an upright wall extending in the front-rear direction and is integrally connected to the recess top wall portion CW1 located above and the recess front wall portion CW2 located in front.

[0123] The first retaining member CA31 is configured to engage only with the upper half of the rear axle JK3. In other words, the first retaining member CA31 is configured to barely engage with the lower half of the rear axle JK3. In other words, the first retaining member CA31 is not configured to restrict movement of the rear axle JK3 in a direction away from the recessed top wall portion CW1. Note that the second retaining member CA32 is responsible for restricting movement of the rear axle JK3 in a direction away from the recessed top wall portion CW1.

[0124] The second holding member CA32 is disposed at multiple locations, i.e., four locations, spaced apart in the left-right direction. The second holding member CA32 is in the form of an upright plate extending in the front-rear direction. The second holding member CA32 is provided at a different left-right position relative to the first holding member CA31. The second holding member CA32 is in the form of an upright wall extending in the front-rear direction, and is integrally connected to the recess top wall portion CW1 located above and the recess rear wall portion CW3 located behind.

[0125] The second retaining member CA32 is configured to be engaged with the lower half including the rear part of the rear axle JK3. That is, the second retaining member CA32 is configured to restrict the movement of the rear axle JK3 in a direction away from the recess top wall portion CW1.

[0126] The left and right shaft end engagement portions cf are configured to engage only with the upper halves of the left and right ends of the rear axle jk3. In other words, the left and right shaft end engagement portions cf are not configured to engage with the lower half of the rear axle jk3. In other words, the left and right shaft end engagement portions cf are not configured to restrict the movement of the rear axle jk3 in a direction away from the recess top wall portion cw1.

[0127] Between the first retaining member ca31 and the second retaining member ca32, there is provided an axle passage cg through which the rear axle jk3 can pass when the rear axle jk3 is attached to the rear axle retaining part ca3. In other words, even if the rear axle jk3 is rigidly connected in advance by welding or the like to the left and right arms d1 and bearing shaft support member d3 constituting the rear support body D, the rear axle jk3 can be held by the rear axle retaining part ca3 through the axle passage cg.

[0128] The front lower extension wall c11 is an upright wall. The front lower extension wall c11 extends downward from the seat base c10. The front lower extension wall c11 can cover the upper part of the front part of the support base main body 1. The front surface of the front lower extension wall c11 is exposed to the outside and can be seen by the user.

[0129] The left and right lower extension walls c12 are upright walls. The left and right lower extension walls c12 extend downward from the seat base c10 in pairs. The left and right lower extension walls c12 can cover the upper parts of both the left and right sides of the support base main body 1. The outer surfaces of the left and right lower extension walls c12 are exposed to the outside and can be seen by the user.

[0130] The left and right lower extending walls c12 are capable of covering and hiding the recessed portion 1a provided on the outer surface side of the support base main body 1 in a side view.

[0131] A front axle holding portion ca4 capable of holding the front axle jk2 is provided at the front of the left and right lower extending walls c12. The left and right lower extending walls c12 are configured to cover from the outside an outwardly opening recess 1a provided in the support base main body 1. Of the left and right lower extending walls c12, the left lower extending wall c12 is formed with a notch c121 so as to avoid the reaction force adjustment lever K protruding from the support base main body 1.

[0132] The rear lower extension wall c14 is an upright wall. The rear lower extension wall c14 is disposed between the rear portions of the left and right lower extension walls c12. A pair of slits ca5 extending in the vertical direction and opening downward are provided on the left and right sides of the rear lower extension wall c14 to avoid interference with the left and right arm bodies d11 of the back support D.

[0133] [Removal protrusion cb] The retaining projection cb is provided on the seat support body ca and has a generally T-shaped appearance in a front view. The retaining projection cb is engaged with a guide slit c211b provided in the support member c21 of the seat support body c2, thereby supporting the seat support body c2 against the seat support c1 so that the seat support body c2 cannot be separated from the seat support c1 and positioning the seat support body c2 so that the seat support body c2 can slide back and forth relative to the seat support c1.

[0134] <Seat body c2> The seat body c2 is configured to be able to slide in the front-rear direction relative to the seat support c1. The seat body c2 includes a shell-shaped support member c21 whose dimensions in the front-rear direction and the left-right direction are set larger than those of the seat support c1, a seat cushion c22 supported by the support member c21 and whose dimensions in the front-rear direction and the left-right direction are set larger than those of the support member c21, and a seat upholstery c23 that covers the peripheral portions of the seat cushion c22 and the support member c21 from the outside.

[0135] When the seat body c2 is in the rear position (i2), the entire peripheral edge of the seat receiver c1 is located more inward than the entire peripheral edge of the support member c21 in a bottom view.

[0136] When the seat body c2 is in the front position (i1), the rear part of the seat support c1 is located behind the rear part of the support member c21 in the bottom view. In other words, the rear end c21t of the support member c21 in the seat body c2 can be located in front of the rear end c1t of the seat support c1 in the front position (i1).

[0137] [Support member c21] The support member c21 is made of synthetic resin. The support member c21 is attached to the lower surface of the seat cushion c22 and serves to evenly support the weight of a seated person.

[0138] The support member c21 has a curved shape such that the central portion is located lower than the outer portions in front and rear views. The support member c21 has a curved shape such that the rear portion is convex backward in bottom view and has a generally rectangular shape. The outer edge shape of the support member c21 in bottom view is similar to the outer edge shape of the seat support c1.

[0139] The support member c21 comprises a support member main body c211 disposed in the center in the front-rear and left-right directions, a peripheral wall portion c213 extended outwardly via a step portion c212 on the peripheral portion of the support member main body c211 and whose lower surface is located higher than the lower surface of the support member main body c211, and a support wall c214 provided so as to protrude downwardly around the entire outer peripheral edge of the peripheral wall portion c213.

[0140] The support member main body c211 is provided with a plurality of seat center slits c211a arranged in the left-right direction corresponding to the recesses c222 of the seat cushion c22, the guide slits c211b extending in the front-rear direction with which the anti-detachment protrusions cb provided on the seat support c1 can engage, and an operating member retaining hole c211c extending in the vertical direction and capable of supporting the operating member ct so that it can move up and down but cannot slip out downward.

[0141] The peripheral wall portion c213 is located outside the support member main body c211 and disposed above the support member main body c211. The step portion c212 interposed between the support member main body c211 and the peripheral wall portion c213 is for positioning the peripheral wall portion c213 above the support member main body c211. In this embodiment, the step portion c212 is mainly constituted by a wall portion erected on the outer peripheral edge of the support member main body c211.

[0142] The peripheral wall portion c213 is disposed so as to surround the outer side of the support member main body c211 in a bottom view. Below the peripheral wall portion c213, i.e., on the lower surface side of the peripheral wall portion c213, an edge c23e of the seat upholstery c23 is disposed.

[0143] In other words, the support member c21 is surrounded by the peripheral wall portion c213, the step portion c212, and the support wall c214 in a roughly downward U-shape, forming a downwardly open space sr capable of accommodating the edge c23e of the seat upholstery c23.

[0144] In addition, hook pieces c21h for hooking the edge c23e of the seat upholstery c23 are provided at the four corners of the peripheral wall portion c213 and at the left-right center portions of the front and rear parts of the peripheral wall portion c213.

[0145] The support wall c214 is provided around the entire outer peripheral edge of the support member c21 and has a downwardly protruding shape. The support wall c214 is a wall extending downward from the outer peripheral edge of the peripheral wall portion c213. The support wall c214 plays a role in stably holding the peripheral portion c22e of the seat cushion c22 in cooperation with the seat upholstery c23, and the outer surface c21s can be attached to the inner surface c22s of the hanging portion c221, which is the inner surface of the seat cushion c22.

[0146] In this embodiment, the support wall c214 located at the rear of the support member c21 is set to have a vertical dimension that does not interfere with the seat support c1. More specifically, the vertical dimension of the support wall c214 formed on both left and right side portions c21p at the rear of the support member c21 is set to be shorter than the vertical dimension of the support wall c214 in other portions. More specifically, the support wall c214 in other portions may be the support wall c214 located at the left-right center portion at the front and rear of the support member c21, or the support wall c214 located at the front-rear center portion at both left and right side portions of the support member c21.

[0147] The left and right side portions c21p at the rear of the support member c21 (i.e., the left and right corner portions at the rear of the support member c21) are set at left and right positions that match the both side ends of the seat support main body ca in the rear view. The upper end portions c101 at the both side ends of the seat support main body ca constitute the uppermost portion of the seat support main body ca.

[0148] In other words, the support wall c214 of the support member c21 extends in the vertical direction as a whole in order to stably hold the peripheral portion c22e of the seat cushion c22 in cooperation with the seat upholstery c23, but in order to prevent interference with the upper end portion c101 at both side ends of the seat support body ca when the seat body c2 slides in the front-rear direction, the vertical dimension is set extremely short only in the portions located on both left and right side portions c21p at the rear.

[0149] In addition, the height of the support wall c214 located on both the left and right side portions c21p and set to have a relatively short vertical dimension compared to other portions, gradually returns to its original height so as to become gradually higher toward the central portion in the front-to-rear direction at both the left and right side portions of the support member c21, and also gradually returns to its original height so as to become gradually higher toward the central portion in the left-to-right direction at the rear of the support member c21.

[0150] For this reason, even when the seat body c2 is slid forward and backward while the seat occupant is seated on the seat C, the support wall c214 is unlikely to impede the sliding movement of the seat body c2. In addition, the support walls c214 located on both the left and right side portions c21p and corresponding to the area that is gently cut out as a whole can smoothly abut against the seat receiver c1, so that the seat body c2 that receives the weight of the seat occupant can be suitably supported by the seat receiver c1.

[0151] [Seat cushion c22] The seat cushion c22 is made mainly of a urethane foam material. A shell-shaped support member c21 is attached to the underside of the seat cushion c22. When viewed from the bottom, the outer edge shape of the seat cushion c22 is similar to the outer edge shape of the support member c21.

[0152] The seat cushion c22 is shaped so as to be fitted onto the support member c21 from above.

[0153] The seat cushion c22 is larger than the support member c21 in bottom view. In other words, the dimensions of the seat cushion c22 in the front-rear and left-right directions are set to be longer than the dimensions of the support member c21 in the front-rear and left-right directions.

[0154] The seat cushion c22 is provided at its periphery with a hanging portion c221 having an inner surface c22s that is an inner surface that can be brought into contact with the outer surface of the support wall c214. The hanging portion c221 is a portion that hangs downward at the periphery of the seat cushion c22. The hanging portion c221 is disposed outside the support wall c214.

[0155] The peripheral edge portion c22e of the seat cushion c22, including the vertical portion c221, is shaped to protrude outward beyond the support member c21. In other words, the peripheral edge portion c22e of the seat cushion c22 overhangs the support member c21.

[0156] Further, in the center of the lower surface side of the seat cushion c22 in the front-rear direction, a plurality of recesses c222 that are open downward are provided in correspondence with the seat center slits c211a provided in the support member c21.

[0157] The rear part of the peripheral part c22e of the seat cushion c22, i.e., the rear part including both left and right parts c22p of the seat cushion c22, is shaped to be lowered upward compared to the front part of the peripheral part c22e of the seat cushion c22 in order to avoid interference with the rear part and upper end part c101 of the seat support base c10. That is, the rear part of the seat cushion c22 including the both left and right parts c22p is also set to a suitable shape to avoid interference with the seat support c1, similar to the support member c21.

[0158] [Zahari c23] The seat upholstery c23 is mainly made of a stretchable fabric and is capable of covering the upper surface, outer surface, and lower surface of the peripheral portion c22e (lower surface of the hanging portion c221) of the seat cushion c22 from the outside, and also covering the support wall c214 provided to hang down from the peripheral edge of the support member c21 from the space sr side.

[0159] The seat upholstery c23 wraps around the underside of the peripheral portion of the seat cushion c22 and the support member c21, and the end edges c23e are tightened by a string member not shown, so that the seat upholstery c23 is attached to the seat cushion c22 and the support member c21 in an overall tensed state.

[0160] That is, the edge c23e of the seat upholstery c23 is narrowed in a direction in which the opening formed by the edge c23e becomes smaller (in a direction in which the diameter becomes smaller). After the worker has finished narrowing the edge c23e of the seat upholstery c23, the edge c23e is disposed under the peripheral wall portion c213 of the support member c21 and is hooked onto the hook piece c21h.

[0161] The peripheral portion c22e of the seat cushion c22, particularly the vertical portion c221 of the seat cushion c22 located outside the support wall c214, is subjected to a pulling force in the direction of the edge c23e by the tensioned seat upholstery c23, and is stably supported against the support wall c214.

[0162] <Operating parts ct> The operating member ct is supported on the seat body c2 so as to be movable up and down between an upper position and a lower position. The lower end portion, which is the operating end of the operating member ct, is exposed below the seat support c1 through the seat support slit ca1.

[0163] The operating member ct is adapted to be located at a lower position by receiving the biasing force of the seat cushion c22 when no load is applied. The operating member ct is adapted to be moved to an upper position by receiving an operating force from a user against the biasing force of the seat cushion c22.

[0164] When the operating member ct is in the lower position, it can position the seat body c2 at a predetermined position on the seat support c1. On the other hand, when the operating member ct is in the upper position, it can release the restriction on the movement of the seat body c2 in the front-rear direction relative to the seat support c1, and can slide the seat body c2 in the front-rear direction relative to the seat support c1.

[0165] <<Back support D>> The back support D is interposed between the support base B and the backrest E, and between the support base B and the seat C. The back support D has a rear shaft jk3 extending in the left-right direction that engages with a bearing portion (not shown) provided in the seat support c1 of the seat C. In other words, the back support D also functions as a seat support interposed to support the seat C on the support base B.

[0166] A rearward tilt degree setting lever H that can selectively set the rearward tilt degree of the backrest E is rotatably supported on the back support D.

[0167] The back support D is covered and concealed by a cover body I which is integrally formed from a synthetic resin.

[0168] The back support body D comprises a pair of left and right arms d1 pivotally supported on the support base main body 1 of the support base B via the main shaft jk1, which is an axis extending in the front-to-rear direction and is shaped like an upright plate, a connecting member d2 shaped like an upright plate that connects the rear portions of the pair of left and right arms d1, a rear shaft jk3 extending in the left-right direction and supported at a position forward of the main shaft insertion hole d13 in the pair of left and right arms d1, a pair of left and right bearing shaft support members d3 arranged inside the pair of left and right arms d1, i.e., toward the center in the left-right direction, and whose upper portions are connected to the rear shaft jk3, and a bearing shaft d4 connected between the lower portions of the pair of left and right bearing shaft support members d3.

[0169] The back support D can movably support the backrest E between a normal position (ES) and a backward tilted position (EK) tilted further backward than the normal position (ES). The back support D is biased by a reaction force generating part HG provided on the support base B so as to rotate in a direction in which the backrest E can take the normal position (ES).

[0170] The back support D is provided with a bearing shaft d4 that is pressed rearward by a reaction force generating portion HG, and the bearing shaft d4 is supported by the front shaft jk3 and the main shaft jk1 via a bearing shaft supporting member d3.

[0171] <Left and right arms d1> The left and right arms d1 are made of metal. The left and right arms d1 are in the form of upright walls having left and right arm bodies d11 that are portions extending in the front-rear direction. The left and right arms d1 are disposed outside the left and right side walls 14 of the support base body d1.

[0172] The left and right arms d1 include left and right arm bodies d11 extending in the front-to-rear direction and capable of supporting the main shaft jk1 at their front ends, left and right front arm portions d12 extending diagonally upward and forward from the front ends of the left and right arm bodies d11 and supporting the rear shaft jk3 whose upper end engages with the seat C, and a main shaft insertion hole d13 that is provided between the left and right arm bodies d11 and the left and right front arm portions d12 and penetrates in the left-right direction and is capable of holding the main shaft jk1.

[0173] [Left and right arm body d11] The left and right arm bodies d11 extend in a substantially straight line in the front-rear direction. The rear portions of the left and right arm bodies d11 are connected by a connecting member d2. The rear ends of the left and right arms d11 protrude rearward beyond the connecting member d2, and the protruding portion d111 can be fitted into the back support body connecting portion 41 of the lower frame material 4 of the backrest E.

[0174] A shaft hole d112 is provided in the left and right arm bodies d11 at a portion located forward of the portion where the connecting member d2 is attached, penetrating in the left and right direction. A rearward tilt degree setting lever H is rotatably supported in the shaft hole d112, which can selectively set one of a plurality of rearward tilt degrees of the backrest 5.

[0175] [Left and right front arm parts d12] The left and right front arm portions d12 are integrally extended obliquely upward and forward from the front ends of the left and right arm bodies d11. A rear shaft jk3 extending in the left-right direction and capable of engaging with the seat C is rigidly connected to the tip ends of the left and right front arm portions d12.

[0176] [Spindle insertion hole d13] The spindle jk1 is inserted through the spindle insertion hole d13. The spindle insertion hole d13 is provided at the front ends of the left and right arm bodies d11 and the base ends of the left and right front arm portions d12, i.e., in the dogleg-shaped bent portions of the left and right arms d1.

[0177] <Connection member d2> The connecting member d2 is made of metal. The connecting member d2 is in the form of an upright plate extending in the left-right direction. The left and right ends of the connecting member d2 are rigidly connected to the inner parts of the left and right arms d1 by welding.

[0178] The connecting member d2 is provided with a nut portion n6 to which a screw v6 for attaching the backrest E is screwed. In other words, the back support D is provided at its rear with a backrest attachment portion da to which the backrest E is attached.

[0179] The backrest attachment portion da is constituted by a portion formed in an H-shape in a plan view or bottom view by rear portions of left and right arms d1 and a connecting member d2 connecting the rear portions of the left and right arms d1.

[0180] <Rear axis jk3> The rear axle jk3 extends in the left-right direction and is connected to the front ends of the left and right arms d1, i.e., the upper ends of the left and right front arm portions d12. The rear axle jk3 is located above the support base main body 1 and extends outward beyond both sides of the support base main body 1.

[0181] <Left and right bearing shaft support members d3> The left and right bearing shaft support members d3 support the bearing shaft d4 that is pressed by the reaction force generating portion HG. The left and right bearing shaft support members d3 rigidly connect both ends of the bearing shaft d4 at their lower ends.

[0182] The left and right bearing shaft support members d3 are plate-shaped and arranged parallel to each other. The left and right bearing shaft support members d3 are arranged inside the left and right arms d1 and inside the side walls 14 of the support base main body 1. In other words, the left and right bearing shaft support members d3 are arranged closer to the center in the left-right direction than the left and right side walls 14 of the support base main body 1.

[0183] The upper portions of the left and right bearing shaft support members d3 are connected to the left-right central portion of the rear axle jk3. The rear portions of the left and right bearing shaft support members d3, which are located below the upper portions of the left and right bearing shaft support members d3, are provided with a spindle insertion hole d31 through which the spindle jk1 can be inserted. In other words, the rear portions of the left and right bearing shaft support members d3 are engaged with the spindle jk1.

[0184] <bearing axis d4> The receiving shaft d4 extends in the left-right direction and is disposed inside the support base main body 1. The receiving shaft d4 is connected to a reaction force generating part HG disposed in the support base B, and receives a biasing force generated by the reaction force generating part HG for biasing the backrest E in the direction of the normal posture. In this embodiment, the receiving shaft d4 is supported by the receiving shaft support member d3 so as to be located substantially directly below the rear axle jk3.

[0185] More specifically, the bearing shaft d4 is disposed behind the rear axle jk3, and in front of and below the main shaft jk1.

[0186] The back support body D described above has a bearing shaft d4 supported at the lower end of the left and right bearing shaft support members d3, and is connected at its upper end to the rear shaft jk3 and engaged at its rear end with the main shaft jk1. Therefore, the back support body D is configured such that the biasing force transmitted from the reaction force generating part HG to the bearing shaft d4 can be smoothly transmitted to the left and right arms d1 rotating around the main shaft jk1 via the left and right bearing shaft support members d3 and the rear shaft jk3 while avoiding interference with the support base main body 1 that is open upward.

[0187] <Reaction force transmission structure from reaction force generating part HG to backrest E> The reaction force generating part HG housed in the housing space sp of the support base B urges the receiving shaft d4 held by the rear member HG3 of the reaction force generating part HG backward, using the support base B as a foothold. When the backrest E is in the normal position (ES), that is, in a no-load state where the backrest E is not subjected to the backward tilt load of the seated person, the receiving shaft d4 urged by the reaction force generating part HG engages with the intermediate connecting wall 121, which is a movement restricting part of the support base main body 1, and its backward movement is restricted.

[0188] The bearing shaft d4 constitutes the back support body D and is disposed near the bottom of the accommodation space sp of the support base body 1, i.e., in a position close to the front bottom wall 13. The back support body D is rotatably supported with respect to the support base body 1 via the main shaft jk1. The bearing shaft d4 is connected to the rear shaft jk3, which is disposed above and in front of the main shaft jk1, via the bearing shaft support member d3 so as to be operable integrally therewith.

[0189] The bearing shaft support members d3 are plate-shaped extending in the vertical direction and are arranged in pairs on the left and right so as to be generally parallel to each other. The left and right ends of the bearing shaft d4 are supported by the lower ends of the bearing shaft support members d3 arranged in pairs on the left and right. The rear ends of the left and right bearing shaft support members d3 in the vertical center are engaged with the spindle jk1 inserted into the spindle insertion hole d31.

[0190] The rear axle jk3 extends in the left-right direction and engages with the rear axle retaining portion ca, which is an axle retaining portion provided on the seat receiver c1 of the seat C, and is disposed above the left and right side walls 14 of the support base main body 1. The longitudinal dimension of the rear axle jk3 is set to be longer than the width dimension of the support base main body 1. The rear axle jk3 is connected to left and right arms d1 that are disposed outside the left and right side walls 14 of the support base main body 1. More specifically, both ends of the rear axle jk3 are connected to upper portions of the left and right front arm portions d12. The left and right front arm portions d12 extend diagonally upward and forward from the portion where the main axle jk1 is disposed.

[0191] When the backrest E tilts backward, the back support D that supports the backrest E rotates around the main shaft jk1. At this time, the left and right arm bodies d11 of the back support D move downward and forward, and the left and right front arm sections d12 move upward and backward. Furthermore, the rear shaft jk3 connected to the upper parts of the left and right front arm sections d12 also moves upward and backward in the same manner as the left and right front arm sections d12 move. As a result, the rear shaft jk3 moves upward and backward, lifting the seat C upward against the seating weight of the seated person.

[0192] The bearing shaft support member d3, which is supported by the rear shaft jk3 and the main shaft jk1, rotates around the main shaft jk1. The bearing shaft d4, which is supported on the lower end of the bearing shaft support member d3, is located in front of and below the main shaft jk1, so that the bearing shaft d4 moves upward and forward while compressing the reaction force generating portion HG against the biasing force.

[0193] In other words, the rearward tilt reaction force received by the reaction force generating part HG arranged in the storage space sp of the support base main body 1 on the receiving axis d4 also arranged in the storage space sp is transmitted in the following order: the receiving axis support member d3 extending in the vertical direction, the rear axis jk3 arranged above the support base main body 1, and the left and right arms d1 arranged on the left and right outer sides of the support base main body 1, and reaches the backrest E.

[0194] In other words, the biasing force of the reaction force generating part HG is transmitted across the inside and outside of the left and right side walls 14 of the support base main body 1 using the rear axis jk3, and is ultimately transmitted to the backrest E.

[0195] In this embodiment, a reaction force transmission structure based on the above-mentioned configuration is adopted from the reaction force generating unit HG to the backrest E. Therefore, the shape of the support base main body 1 can be formed into a box shape that is open upward and has excellent rigidity.

[0196] <<Spindle jk1>> The spindle jk1 is held by the shaft holding portion JH of the support base main body 1. The spindle jk1 is equipped with a spindle body jk11 extending in the left-right direction, a flange portion jk12 that is integrally provided at one end of the spindle body jk11 and can engage with the outer surface of either the left or right arm d1 of the back support body D, and a retaining ring jk13 that is attached to the other end of the spindle body jk11 and can engage with the outer surface of the other of the left and right arms d1.

[0197] <<Rearward tilt degree setting mechanism X>> The backward tilt degree setting mechanism X allows the user to select from two or more different backward tilt degrees of the backrest E, which is supported so as to be able to tilt backward relative to the support base B via the back support body D, by operating the mechanism.

[0198] In this embodiment, the tilting action setting mechanism X can set the degree of tilt of the backrest E to four different degrees of tilt, namely, first, second, third and fourth degrees of tilt (x1), (x2), (x3) and (x4).

[0199] In addition, the first backward tilt degree (x1) is such that the backrest E is maintained in the basic position and hardly tilts backward. The second backward tilt degree (x2) is such that the backrest E can tilt backward within a certain range by rotating from the basic position around the main axis jk1. The third backward tilt degree (x3) is such that the backrest E can tilt backward within a wider range than the second backward tilt degree (x2) by rotating from the basic position around the main axis jk1. The fourth backward tilt degree (x4) is such that the backrest E can tilt backward within a wider range than the third backward tilt degree (x3) by rotating from the basic position around the main axis jk1.

[0200] In other words, the backward tilt degree setting mechanism X is configured to be able to set the backward tilt degree of the backrest E to gradually increase from the first backward tilt degree (x1), which is the smallest backward tilt degree of the backrest E, to the second, third, fourth backward tilt degrees (x2), (x3), and (x4), in that order.

[0201] The rearward tilt degree setting mechanism X includes a rearward tilt degree setting lever H which is an operating lever rotatably supported on the back support D, a rotating member Re which is rotatably attached to the rearward tilt degree setting lever H and has a plurality of contact surfaces corresponding to the first, second, third and fourth rearward tilt degrees (x1), (x2), (x3) and (x4), i.e., the first, second, third and fourth contact surfaces at1, at2, at3 and at4 which are arranged at intervals in the rotational direction, a damper member XM which is arranged on the support base B and with which a specific contact surface among the first, second, third and fourth contact surfaces at1, at2, at3 and at4 can selectively come into contact, and a detent mechanism XD which detentatively engages the rotating member Re at one of a plurality of rotation positions corresponding to the first, second, third and fourth rearward tilt degrees (x1), (x2), (x3) and (x4).

[0202] In the present embodiment, the rearward tilt degree setting mechanism X has the first, second, third and fourth rearward tilt degrees (x1), (x2), (x3) and (x4) determined by the first, second, third and fourth contact surfaces at1, at2, at3 and at4 abutting against a common contact member, the damper member XM.

[0203] The rearward tilt degree setting mechanism X is covered by a cover body I except for the operation end of the rearward tilt degree setting lever H. In other words, most of the rearward tilt degree setting mechanism X is covered by the cover body I and cannot be seen from the outside.

[0204] <Rear lean setting lever H> The rearward tilt degree setting lever H comprises a lever shaft portion ha pivotally supported in an axial hole d112 provided in the left and right arms d1 constituting the back support body D, which extend in the left-right direction, and a handle portion hb attached to the right end portion, which is one end of the lever shaft portion ha.

[0205] [Lever shaft ha] The lever shaft ha is made of metal. A pair of projections hat projecting in a direction perpendicular to the axis are formed in the left-right central portion of the portion of the lever shaft ha located between the left and right arms d1. The projections hat on the lever shaft ha are adapted to engage with a groove e12 provided in the base end portion e1 of the rotating member Re. The projections hat on the lever shaft ha engage with the groove e12 of the rotating member Re, allowing the entire rotating member Re to rotate integrally with the rearward tilt degree setting lever H.

[0206] A retaining member han is attached to the tip of the lever shaft ha and is disposed on the outside of the left arm d1, thereby preventing the lever shaft ha from being removed from the left and right arms d1.

[0207] [Handle part hb] The handle portion hb is made of synthetic resin and includes a cylindrical shaft connection portion hb1 that is fitted onto the lever shaft portion ha, and a lever piece hb2 that protrudes from the shaft connection portion hb1 in a cantilever manner.

[0208] <Rotating member Re> The rotating member Re is made of synthetic resin and configured to be able to rotate integrally with the rearward tilt degree setting lever H. The rotating member Re includes a base end e1 in which an insertion hole e11 through which the lever shaft ha is inserted is formed, left and right rotating member bodies e2 which are integral with the base end e1 and have a plurality of contact surfaces, i.e., first, second, third and fourth contact surfaces at1, at2, at3 and at4, which are provided in pairs on the left and right sides, a connecting wall e3 which extends from the base end e1 in a wall shape and connects the left and right rotating member bodies e2 to each other, and a moderation engaging portion e4 which extends in a direction perpendicular to the longitudinal direction of the base end e1 and has an engaging protrusion e41 formed on its outer end.

[0209] [Proximal end e1] The base end e1 forms a portion that is connected to the lever shaft ha of the rearward tilt degree setting lever H. The base end e1 is shaped to rotate the rotating member Re integrally with the lever shaft ha and to support the rotating member Re so as to be movable relative to the lever shaft ha in the longitudinal direction, i.e., the axial direction, of the lever shaft ha. A groove e12 that extends in the left-right direction is provided at the left-right center of the insertion hole e11 in the base end e1 and can be engaged with a protruding piece hat of the lever shaft ha.

[0210] The left end portion, which is one end of the base end portion e1, is provided with a spring housing portion e13 that is cylindrical with a larger diameter than other portions and can house a coil spring xd2, which is a biasing spring, inside. The spring housing portion e13 can house a part of the coil spring xd2 that is wound around the lever shaft portion ha and can bias the rotating member Re in the direction of the right arm d1.

[0211] The outer end of the coil spring xd2 elastically contacts the inner surface of the left arm d1, and the inner end of the coil spring xd2 elastically contacts a spring receiving portion (not shown) formed inside the spring accommodating portion e13.

[0212] [Rotating member body e2] The rotating member body e2 is a block-shaped body that is cantilevered from the base end portion e1. The rotating member bodies e2 are arranged in pairs on the left and right sides with a certain distance between them.

[0213] The rotating member main body e2 includes a quadrangular column-shaped portion e20 which is approximately rectangular in side view and abuts against the damper member XM of the support base B, a first mountain-shaped portion e21 which is located closer to the base end e1 than the quadrangular column-shaped portion e20, is approximately triangular in side view, and abuts against the damper member XM of the support base B, a second mountain-shaped portion e22 which is located closer to the base end e1 than the first mountain-shaped portion e21, is approximately triangular in side view, and abuts against the damper member XM of the support base B, and a third mountain-shaped portion e23 which is located closer to the base end e1 than the second mountain-shaped portion e21, is approximately triangular in side view, and abuts against the damper member XM of the support base B.

[0214] The quadrangular prism portion e20 is provided with a first contact surface at1 having a substantially rectangular shape that faces downward when it contacts the damper member XM attached to the support base main body 1.

[0215] The first mountain-shaped portion e21 is provided with a second contact surface at2 that has a substantially rectangular shape and faces downward when it contacts the damper member XM attached to the support base main body 1.

[0216] The second mountain-shaped portion e22 is provided with a third contact surface at3 that has a substantially rectangular shape and faces downward when it contacts the damper member XM attached to the support base main body 1.

[0217] The third mountain-shaped portion e23 is provided with a fourth contact surface at4 that has a substantially rectangular shape and faces downward when it contacts the damper member XM attached to the support base main body 1.

[0218] The first, second, third and fourth contact surfaces at1, at2, at3 and at4 are provided on the rotating member main body e2 in correspondence with the first, second, third and fourth backward inclination degrees.

[0219] The first contact surface at1 is provided at a position farther from the base end e1 than the second contact surface at2. The second contact surface at2 is provided at a position farther from the base end e1 than the third contact surface at3. The third contact surface at3 is provided at a position farther from the base end e1 than the fourth contact surface at4.

[0220] When the first contact surface at1 contacts the damper member XM, the backrest E is set to a first backward tilt degree (x1) at which the backrest E hardly tilts backward.

[0221] [Connecting wall e3] The connecting wall e3 connects the left and right rotating member bodies e2. The connecting wall e3 plays a role in increasing the rigidity of the entire rotating member e1. The connecting wall e3 extends from the base end e1 and connects the left and right rotating member bodies e2 at portions close to the base end e1.

[0222] [Moderation engagement part e4] The moderation engagement portion e4 has an engagement protrusion e41 that can engage with an engagement recess xd11 of an adapter xd1 attached to the right arm d1, which is one of the left and right arms d1.

[0223] The moderation engagement portion e4 and the right-side rotation member main body e1 are connected by a reinforcing wall e5 extending from the base end portion e1 in the same direction as the connecting wall e3.

[0224] <Damper material XM> The damper members XM are formed from a synthetic resin that is softer than the support base main body 1. The damper members XM are arranged in pairs on the left and right at the rear of the support base B, which is the fixed side portion. In other words, the support base B includes the support base main body 1 that is integrally formed from synthetic resin, and the left and right damper members XM that are separate from the support base main body 1 and attached to the rear end of the support base main body 1.

[0225] The damper member XM is block-shaped and comprises a damper member main body xm1 whose bottom surface is attached to a mounting seat 111a of the support base main body 1, and a mounting protrusion xm2 which protrudes downward from the damper member main body xm1 and is inserted into a hole 111b provided in the mounting seat 111a.

[0226] The damper member XM is a part that does not move in conjunction with the backward tilting movement of the backrest E.

[0227] [Damper material body xm1] The damper member main body xm1 is in the shape of a substantially rectangular block. The upper surface of the damper member main body xm1 is curved. That is, the upward surface of the damper member main body xm1 is curved so that the left-right center is located higher than both left-right ends.

[0228] [Mounting protrusion xm2] The mounting projection xm2 is provided integrally with the damper member main body xm1. A flange portion xm3 is formed in the vicinity of the lower end portion, which is the protruding end of the mounting projection xm2. The mounting projection xm2 is configured so that the flange portion xm3 is caught on the support base main body 1, making it difficult for the mounting projection xm2 to slip out of the hole 111b.

[0229] <Moderation mechanism XD> The moderation mechanism XD is intended to allow the user to conveniently operate the rearward tilt degree setting lever H to set the first, second, third and fourth rearward tilt degrees (x1), (x2), (x3) and (x4) relative to the backrest E.

[0230] The moderation mechanism XD is mainly composed of a moderation engagement portion e4 provided at the right end, which is one end of a rotating member Re that is supported rotatably integrally with the rearward tilt degree setting lever H, an adapter xd1 made of synthetic resin that is attached to the right arm d1 of the left and right arms d1 and has multiple, i.e., four, recesses xd11 with which the moderation engagement portion e4 can be moderatedly engaged, and a coil spring xd2 that biases the moderation engagement portion e4 toward the adapter ed1.

[0231] The left and right arms d1 are formed with fitting holes d113 into which the mounting protrusions x12 provided on the adapter xd1 can fit. In this embodiment, the protrusion xd2 of the adapter xd1 fits into the fitting hole d113 of the right arm d1.

[0232] <<Backrest E>> The backrest E comprises a backrest base, a back frame M, which has a screw insertion hole h6 and is attached to the backrest mounting portion da of the back support body D with a screw v2, a back frame cap T, which is a concealing member that is removably attached to the back frame M and can cover the storage space sd of the recess U formed in the lower frame material 4 of the back frame M, and a mesh-like tension member P that is stretched over the back frame M.

[0233] The backrest E has a backrest surface pm that supports the back of a seated person from behind, and is formed from an upholstery member P that is mainly made of mesh fabric.

[0234] The chair of this embodiment is configured so that an optional backrest surface extension member F and a hanger G can be selectively attached to the upper frame material 3 of the backrest E.

[0235] In the chair of this embodiment, a lumbar support R capable of supporting the lower back of a seated person from behind is attached to the left and right side frame members 2 of the backrest E.

[0236] <Back frame M> The back frame M comprises left and right side frame members 2 each having a tension member mounting groove mz opening outward, an upper frame member 3 having a tension member mounting groove mz opening upward and connecting the upper parts of the left and right side frame members 2, a lower frame member 4 connecting the lower parts of the left and right side frame members 2, and an intermediate connecting frame member 5 having a tension member mounting groove mz opening downward and connecting the left and right side frame members 2 together while forming an upper cavity sa between the upper frame member 3 and a lower cavity sb between the lower frame member 4.

[0237] The left and right side frame members 2, the upper frame member 3, and the lower frame member 4 are integrally molded from synthetic resin. The intermediate connecting frame member 5 is attached to the left and right side frame members 2 with screws v5.

[0238] The back frame M comprises an upper frame-shaped portion w1 which is formed with an upper cavity sa therein by left and right side frame members 2, an upper frame member 3, and an intermediate connecting frame member 5, and a lower frame-shaped portion w2 which is formed with a lower cavity sb therein by left and right side frame members 2, a lower frame member 4, and an intermediate connecting frame member 5.

[0239] The backrest E in this embodiment is configured such that a tension member P capable of forming a backrest surface pm is tensioned to an upper frame portion w1 which is a frame portion provided on a back frame M.

[0240] The lower frame-shaped portion w2 is not provided with a tension member P. In other words, a cavity sb is formed between the lower frame member 4 and the intermediate connecting frame member 5, which is a horizontal member, and in which no tension member P is provided.

[0241] [Left and right side frame 2] The left and right side frame members 2 extend in the vertical direction. A tension member mounting groove mz is formed on the outer surface of the left and right side frame members 2, which continues from the upper end of the side frame member 2 to a height position that approximately corresponds to the lower edge of the intermediate connecting frame member 5. A tension member P is tensioned between the left and right side frame members 2 that extend in the vertical direction.

[0242] Each of the left and right side frame members 2 has an extension portion 23 that extends toward each other and connects the intermediate connecting frame member 5. The extension portion 23 has a base end portion 231 that extends inwardly in a columnar shape, and a tip end portion 232 that extends inwardly from the extended end of the base end portion 231, has an upright plate shape, and is set to have a thickness dimension in the front-to-rear direction shorter than that of the base end portion 231.

[0243] The front surface of the tip portion 232 is substantially flush with the front surface of the base portion 231. Meanwhile, the back surface of the tip portion 232 is located forward of the back surface of the base portion 321. In other words, a recessed portion 233 that is recessed forward is formed on the back surface side of the tip portion of the extension portion 23. The side end portion of the intermediate connecting frame member 5 is arranged in the recessed portion 233 when the intermediate connecting frame member 5 is attached.

[0244] The tip portion 232 has a screw insertion hole h5a penetrating therethrough in the front-rear direction, and is formed with a rectangular recessed portion 232a on the front side for arranging a nut n5.

[0245] The left and right side frame materials 2 have an outer frame portion 21 having a tension member mounting groove mz that is open outward, and an inner frame portion 22 located inside the outer frame portion 21 and with its front portion located rearward of the front portion of the outer frame portion 21.

[0246] On the outer surfaces of the left and right side frame members 2, tension member mounting grooves mz are formed which continue from the upper ends of the side frame members 2 to a height position which approximately corresponds to the upper edges of the base ends 231 of the extension portions 23.

[0247] Additionally, a step 2a is formed on the front surface of each of the left and right side frame materials 2, extending inwardly and approximately horizontally from near the lower end of the tensile member mounting groove mz. The step 2a is formed on the front surface at a height position that approximately corresponds to the upper edge of the extension portion 23 of the side frame material 2. The step 2a has a shape in which the lower side protrudes further forward than the upper side, and the step dimension approximately corresponds to the thickness dimension of the tensile member P.

[0248] A lumbar support holding portion N is disposed in the vertical middle portion of the left and right side frame members 2, more specifically, in the vertical middle portion of the inner frame portion 22 of the left and right side frame members 2, which is at a height position corresponding to the waist of a seated person, and is capable of holding the lumbar support R so that its vertical position can be changed.

[0249] The lumbar support holding portions N are provided on the left and right side frame members 2 at portions bent so as to convex forward in side view (portions bent in a dogleg shape in side view).

[0250] The lumbar support holding portion N is capable of holding the held portions r22 provided at both the left and right ends of the lumbar support R. The lumbar support holding portion N is provided with an accommodation groove 221 that extends in the vertical direction and is open forward and that accommodates a plurality of, i.e., two, protrusions, an upper protrusion r221 and a lower protrusion r222, provided on the held portion r22 of the lumbar support R, and a holding member Q having a front restricting portion q1 that is disposed in front of the accommodation groove 22 and can restrict the forward movement of the upper protrusion r221 and the lower protrusion r222.

[0251] The accommodating groove 221 is mainly formed of a back groove forming wall 221a and a side groove forming wall 221b that engage with the held portion r22. The accommodating groove 221 includes a back groove forming wall 221a located on the rear side of the upper protruding portion r221 and the lower protruding portion r222, and a side groove forming wall 221b that extends forward from the inner side of the back groove forming wall 221a and is located on the inner side of the upper protruding portion r221 and the lower protruding portion r222.

[0252] The front surface of the rear groove forming wall 221a forms an abutment portion that contacts the protruding ends of the upper protruding portion r221 and the lower protruding portion r222. The front surface, which is the abutment portion of the rear groove forming wall 221a, is inclined so that the inner side is located behind the outer side.

[0253] The inner surface of the side groove forming wall 221b, i.e., the surface facing the front side of the back groove forming wall 221a, forms an abutment portion that contacts the inner portions of the upper protruding portion r221 and the lower protruding portion r222. The side groove forming wall 221b that can form the storage groove 221 is provided with an upper notch 221c and a lower notch 221d that are notches through which the upper protruding portion r221 and the lower protruding portion r222 can pass when the lumbar support R is attached to or detached from the backrest E.

[0254] That is, the side groove forming wall 221b has an upper notch 221c through which the upper protruding portion r221 can pass and a lower notch 221d through which the lower protruding portion r222 can pass when the lumbar support R is attached to or detached from the backrest E. The upper notch 221c and the lower notch 221d are formed spaced apart from each other above and below the side groove forming wall 221b. The upper notch 221c and the lower notch 221d are provided in the front half of the side groove forming wall 221b.

[0255] The shape of the upper cutout 221c is set to correspond to the upper protruding portion r221 of the lumbar support R so that the upper cutout 221c can pass through the upper protruding portion r221. Note that the upper cutout 221c has a protrusion 221e protruding from the center in the up-down direction in correspondence with the shape of the upper protruding portion r221.

[0256] The shape of the lower cutout 221d is set to a shape corresponding to the lower protruding portion r222 of the lumbar support R so that the lower cutout 221d can pass through the lower protruding portion r222 of the lumbar support R. Note that the shape of the upper protruding portion r221 and the shape of the lower protruding portion r222 of the lumbar support R are different from each other.

[0257] By making the shape of the upper cutout 221c corresponding to the upper protruding portion r221 and the shape of the lower cutout 221d corresponding to the lower protruding portion r222 different, the user can easily grasp the up-down position of the lumbar support R. In other words, the chair of this embodiment is designed so that the user cannot attach the lumbar support R to the backrest E by mistakenly placing it upside down.

[0258] The retaining member Q is made of synthetic resin and is configured as a separate member from the left and right side frame materials 2. In other words, the retaining member Q is separate from the left and right side frame materials 2. The retaining member Q is attached to each of the left and right side frame materials 2. The retaining member Q is attached to the inner frame portions 22 of the left and right side frame materials 2 via screws v3.

[0259] The retaining member Q extends in the vertical direction and includes a front regulating portion q1 that is arranged in front of the accommodating groove 221 and abuts against the upper protruding portion r221 and the lower protruding portion r222 of the lumbar support R to regulate the forward movement of the upper protruding portion r221 and the lower protruding portion r222, an attachment portion q2 that is connected to the upper and lower ends of the front regulating portion q1 and has a screw insertion hole h3 that penetrates in the front-to-rear direction, and a positioning wall q3 that extends from the outer portion of the front regulating portion q1 rearward, i.e., toward the inner frame portion 22, and is arranged between the accommodating groove 221 and the outer frame portion 21.

[0260] The front restricting portion q1 is shaped like a rail extending in the vertical direction. The front restricting portion q1 is capable of sandwiching the upper protruding portion r221 and the lower protruding portion r222 in the front-rear direction in cooperation with the inner groove forming wall 221a that can form the accommodation groove 221.

[0261] Between the front restricting portion q1 of the retaining member Q and the side groove forming wall 221 of the accommodating groove 221, there is formed a communication space sc extending in the vertical direction through which the retained portions r22 of the left and right arm materials r2 in the lumbar support R having an upper protruding portion r221, a lower protruding portion r222, and a protruding portion 220 at their tips can communicate.

[0262] In other words, the holding member Q is capable of sandwiching and holding the upper protruding portion r221 and the lower protruding portion r222 by cooperating with the left and right side frame materials 2. Therefore, the lumbar support R is sandwiched in the front-rear direction between the front-facing surfaces of the left and right side frame materials 2 and the rear-facing surface of the holding member Q, and can be appropriately held in a predetermined vertical position within the accommodation groove 221 without sliding downward due to gravity.

[0263] The mounting portion q2 has a screw insertion hole h3 for mounting the retaining member Q to the inner frame portion 22 of the left and right side frame members 2. In addition, the mounting portion q2 has an external fitting wall q21 protruding therefrom that can be externally fitted onto the peripheral edge of a nut portion n3 protruding from the inner frame portion 22 of the left and right side frame members 2.

[0264] The retaining member Q is attached to the inner frame portions 22 of the left and right side frame members 2 by screwing the screws v3 inserted through the screw insertion holes h3 into the nut portions n3 provided on the left and right side frame members 2.

[0265] [Top frame material 3] The upper frame material 3 extends in the left-right direction. The upper frame material 3 has an outer frame portion 31 in which a tension member mounting groove mz that opens upward for mounting a tension member P is formed, and an inner frame portion 32 disposed below the outer frame portion 31. The upper frame material 3 is provided with a nut holding recess nt in which a nut member J for mounting an option can be held, as will be described in detail later.

[0266] The outer frame portion 31 constitutes the upper portion of the upper frame material 3. The front surface of the outer frame portion 31 forms the portion that is attached to the rear surface of the tension member P, i.e., the portion that backs the tension member P.

[0267] The inner frame portion 32 constitutes the lower portion of the upper frame material 3. The inner frame portion 32 is located more inward than the outer frame portion 31. In other words, the inner frame portion 32 is provided in a location that is covered by the tension member P when viewed from the front.

[0268] The inner frame portion 32 includes a hanging wall 321 that is arranged to hang downward from the rear of the outer frame portion 31, a lower end wall 322 that extends forward from the lower end of the hanging wall 321, and a plurality of connecting walls 323 that form upright walls connecting between the lower end wall 322 and the outer frame portion 31, and between the lower end wall 322 and the hanging wall 321.

[0269] The back surface of the hanging wall 321 is substantially flush with the back surface of the outer frame portion 31. The bottom end wall 322 is provided at a distance in the up-down direction from the outer frame portion 31. The connecting walls 323 are provided to increase the connecting strength between the bottom end wall 322 and the outer frame portion 31, and a plurality of them are provided at regular intervals in the left-right direction.

[0270] The inner frame portion 32 is provided with a nut holding recess nt that is formed with an upper opening portion kh1 that is open upward, a lower opening portion kh2 that is open downward, and a front opening portion kh3 that is open forward and that can hold the nut member J. The nut holding recess nt is provided at a plurality of positions on the inner frame portion 32.

[0271] The nut retaining recess nt is provided in the lower end wall 322 of the inner frame portion 32. The nut retaining recess nt has left and right standing wall portions nt1 and a rear standing wall portion nt2 connecting rear portions of the left and right standing wall portions nt1. The nut retaining recess nt has a generally U-shaped hole shape that is open to the front when viewed from the bottom.

[0272] The nut retaining recess nt is formed by left and right upright wall portions nt1 and a rear upright wall portion nt2, which define an upper opening portion kh1 that is open upward, a lower opening portion kh2 that is open downward, and a front opening portion kh3 that is open forward.

[0273] In addition, the nut retaining recess nt forms a portion that can form an upper opening portion kh1 by the upper edges of the left and right upright wall portions nt1 and the upper edge of the rear upright wall portion nt2, and also forms a flange engagement portion nt3 that can engage with the underside of the flange portion j2 of the nut member J.

[0274] A gap sk capable of accommodating the flange portion j2 of the nut member J is formed between the nut holding recess nt and the outer frame portion 31.

[0275] In this embodiment, the inner frame portion 32 is provided with four nut holding recesses nt spaced apart in the left-right direction. The pair of nut holding recesses nt located on both the left and right outer sides are used when attaching a backrest surface extension member F for extending the backrest surface pm, and the pair of nut holding recesses nt located on both the left and right inner sides are used when attaching a hanger G for hanging clothes.

[0276] The nut member J held in the nut holding recess nt is made of metal. The nut member J includes a boss portion j1 ​​that is accommodated in the enclosed space of the nut holding recess nt and has a screw groove j11 on its inner peripheral surface, and a flange portion j2 that is connected to the boss portion j1 ​​and can engage with a flange portion engagement portion nt3 whose lower surface forms the upper open portion kh1.

[0277] The nut member J has a generally T-shape. That is, the flange portion j2 extends longitudinally outward in the left-right direction from the upper end of the generally cylindrical boss portion j1.

[0278] The method of holding the nut member J in the nut holding recess nt provided in the backrest E and attaching the optional backrest surface extension member F and optional hanger G will be described in detail later.

[0279] [Bottom frame material 4] The lower frame material 4 has a portion that connects the lower portions of the left and right side frame materials 2 and is connected to the back support body D. The lower frame material 4 is provided with a back support body connecting portion 41 that is recessed and open forward, for fitting externally to and connecting to the backrest mounting portion da provided on the back support body D.

[0280] The back side of the lower frame member 4 is provided with a recess U in which an accommodation space sd is formed that can accommodate the head v61 of the screw v6 for connecting the back frame M to the back support D. The recess U is recessed so that the accommodation space sd can be formed therein while opening to the rear. That is, the recess U has the accommodation space sd formed therein and is provided with an opening uk that is open to the rear.

[0281] The lower frame member 4 is provided with screw insertion holes h6 through which the screws v6 are inserted, penetrating in the front-rear direction. The screw insertion holes h6 are provided in pairs on the left and right. The screw insertion holes h6 are provided so as to communicate between the recess U that is open to the rear and the back support member connecting portion 41 that is open to the front.

[0282] The recess U is equipped with a screw engagement wall u1 which is a rear wall through which a screw insertion hole h6 is drilled and into which the head 61 of the screw v6 can engage, an upright wall u2 which is a front wall located rearward of the screw engagement wall u1 and forward of the opening uk, a peripheral wall u3 which extends in the front-to-rear direction and whose inner side faces the storage space sd, and an intermediate wall u4 which extends in the front-to-rear direction and has a surface facing the storage space sd and connects the outer end of the upright wall u2 and the inner end of the screw engagement wall u1.

[0283] The screw engagement walls u1 are provided in pairs on the left and right. The screw engagement walls u1 are circular when viewed from the rear, and have a screw insertion hole h6 formed in the center. The opposite surface of the screw engagement wall u1, that is, the front surface, is adapted to abut against the rear surface of the connecting member d2 of the back support body D. In other words, the screw engagement wall u1 also serves as an engagement wall with the connecting member d2 of the back support body D.

[0284] The standing wall u2 is provided inside the screw engagement walls u1 provided on the left and right sides when viewed from the rear. The standing wall u2 is elongated in the left-right direction and disposed in a position substantially parallel to the screw engagement walls u1. The standing wall u2 has a window hole u21 as an engagement portion with which the locking protrusion t31 formed on the fall-off prevention protrusion t3 of the back frame cap T can engage. The window hole u21 is substantially rectangular and provided in pairs on the left and right sides.

[0285] The peripheral wall u3 has an inner peripheral surface u31 that faces a direction substantially perpendicular to the front-rear direction, and an opening uk is formed by the inner peripheral surface u31 at the rear end of the peripheral wall u3. In other words, the opening uk does not have a portion that can restrict the cap body t1 of the back frame cap T from advancing too far back.

[0286] In other words, the opening uk has a shape that allows progression toward the depth of the cap body t1, and does not have any parts that could prohibit movement in the depth direction, such as steps, protrusions, ribs, etc.

[0287] <Back Frame Cap T> The back frame cap T is removably attached to the lower frame member 4 and can cover the storage space sd of the recess U. In this embodiment, the screw v6 can be confirmed based on the relative position of the back frame cap T with respect to the lower frame member 4.

[0288] The back frame cap T is equipped with a cap body t1 which is a concealing member body arranged in the opening uk of the recess U and capable of hiding the storage space sd from the outside, a screw head abutment protrusion t2 which protrudes from the cap body t1 and has a tip t21 which can abut against the head v61 of the screw v6, and a slip-off prevention protrusion t3 which protrudes from the cap body t1 and engages with the recess U to prevent the back frame cap T from coming off the back frame M.

[0289] [Cap body t1] The cap body t1 is an upright plate-like shape elongated in the left-right direction. That is, the cap body t1 has a flat outer surface 4a and is in the shape of a horizontally elongated plate that is in an upright position as a whole. The left and right side portions of the cap body t1 are formed in a semicircular shape when viewed from behind.

[0290] [Screw head contact protrusion t2] The screw head abutment protrusions t2 are provided so as to protrude forward from the cap body t1. The screw head abutment protrusions t2 are provided in pairs on the left and right in correspondence with the left and right screw insertion holes h6. The screw head abutment protrusions t2 are provided so as to protrude forward from both the left and right ends of the cap body t1.

[0291] The protruding dimension of the screw head abutment protrusion t2 is set to a length such that when the screw v6 has been properly screwed into the nut portion n6 of the back support D (i.e., when the head v61 of the screw v6 abuts against the screw engagement wall u1 and can no longer proceed forward), the outer surface t11 of the cap body t1 is approximately flush with the outer surface 4a of the peripheral portion at the recess U when the tip t21 engages with the head v61.

[0292] [Anti-fall protrusion t3] The anti-removal projections t3 are provided so as to project forward from the cap body t1. The anti-removal projections t3 are provided in pairs on the left and right. The pair of anti-removal projections t3 are disposed between the pair of screw head abutment projections t2 provided on the left and right.

[0293] The anti-removal protrusion t3 is generally arrow-shaped in side view. The anti-removal protrusion t3 has locking protrusions t31 protruding upward and downward near its tip. The anti-removal protrusion t3 is sized so that the part other than the locking protrusions t31 can pass through the window hole u21 in the front-rear direction.

[0294] The locking projection t31 of the fall-off prevention projection t3 is engaged with a window hole u21 provided in the upright wall u2 of the recess U, thereby restricting only the rearward movement of the back frame cap T. When the locking projection t31 is engaged with the window hole u21 and the rearward movement is restricted, the outer surface t11 of the cap body t1 is substantially flush with the outer surface 4a of the peripheral portion of the recess U.

[0295] [Verification function for screw v6 based on the position of the back frame cap T] In the chair of this embodiment, confirmation regarding the screw v6 can be performed based on the relative position of the back frame cap T with respect to the lower frame material 4.

[0296] More specifically, it is configured so that, based on the relative position between the outer surface t11 of the back frame cap T and the outer surface 4a of the lower frame material 4, it can be confirmed whether the screw v6 is properly screwed in as intended and whether any screw v6 has been forgotten to be screwed in.

[0297] The back frame cap T is configured so that the outer surface t11 of the cap body t1 can be approximately flush with the outer surface 4a of the peripheral portion at the recess U only when the screw v6 is inserted into the screw insertion hole h6 and has completed screwing into the nut portion n6 provided on the back support body D, i.e., when the screw v6 has been properly installed.

[0298] [If screw v6 is installed correctly] As shown in FIG. 44, the tip t21 of the screw head abutting protrusion t2 abuts against the head v61 of the screw v6, so that the back frame cap T is restricted from moving further forward.

[0299] In addition, since the locking projection t31 of the anti-detachment projection t3 engages with the window hole u21 of the upright wall u2 in the recess U, the rear frame cap T is restricted from moving backward.

[0300] In this state, the outer surface t11 of the cap body t1 in the back frame cap T is approximately flush with the outer surface 4a of the peripheral portion of the recess U, so that the assembly worker can see that the outer surfaces t11, 4a are approximately flush and confirm that the backrest E is properly attached to the back support body D using the screw v6.

[0301] [If the screw v6 is not properly threaded (threading is not yet complete)] As shown in FIG. 45, the tip t21 of the screw head abutting protrusion t2 abuts against the head v61 of the screw v6, so that the back frame cap T is restricted from moving further forward.

[0302] However, in the state shown in Figure 45, the screw v6 has not yet completely screwed in (the screw v6 is not sufficiently tightened or is not properly screwed in), and in this state, the outer surface t11 of the cap body t1 in the back frame cap T is positioned outside the outer surface 4a of the peripheral portion of the recess U.

[0303] Therefore, the assembly worker can see that the positions of the respective outer surfaces t11, 4a are not approximately flush and can confirm that the backrest E is not properly screwed to the back support body D.

[0304] [If screw v6 is not installed] As shown in Figure 46, after the back support body connection part 41 of the backrest E is temporarily supported by being externally fitted onto the protruding part d111 constituting the backrest mounting part da of the back support body D, it is possible that the worker will forget to screw in the screw v6.

[0305] In this case, since the head v61 of the screw v6 is not disposed in the recess U, the tip t21 of the screw head abutment protrusion t2 of the back frame cap T cannot abut against the head v61 of the screw v6. Furthermore, the back frame cap T continues to move forward as the locking projection t31 of the anti-removal protrusion t3 passes through the window hole u21 of the upright wall u2 in the recess U.

[0306] At this time, the locking projection t31 of the anti-detachment projection t3 can engage with the window hole u21 only at a specified position to restrict only rearward movement, but cannot restrict forward movement.

[0307] As shown in Figure 46, if the screw v6 for attaching the backrest E to the back support body D is not inserted into the screw insertion hole h6, the back frame cap T will penetrate deep into the recess U so that the outer surface t11 of the cap body t1 is not approximately flush with the outer surface 4a of the peripheral portion of the recess U.

[0308] As the anti-slip protrusion t3 continues to advance forward through the window hole u21, the tip t21 of the screw head abutment protrusion t2 of the back frame cap T hits the screw engagement wall u1, which is the rear wall that can form the recess U, and finally, its movement toward the rear of the back frame cap T is restricted.

[0309] The back frame cap T is configured such that, at least in this state, the outer surface t11 of the cap body t1 is positioned further back than the outer surface 4a of the peripheral portion of the recess U, so that the assembly worker can see that the positions of the respective outer surfaces t11, 4a are not approximately flush and can confirm that the backrest E is not properly screwed to the back support body D (the screw v6 is missing).

[0310] [Intermediate connection frame material 5] The intermediate connecting frame member 5, which is a cross member, extends in the left-right direction. The intermediate connecting frame member 5 is installed between the portions of the left and right side frame members 2 that are tilted forward when viewed from the side. The intermediate connecting frame member 5 is separate from the other frame members that make up the back frame M, i.e., the left and right side frame members 2, the upper frame member 3, and the lower frame member 4.

[0311] In this embodiment, the intermediate connecting frame member 5 is configured to be detachably attached to the left and right side frame members 2 via screws v5. Both left and right ends of the intermediate connecting frame member 5 are screwed to the left and right side frame members 2, respectively. The intermediate connecting frame member 5 has a curved shape that is convex toward the rear in a plan view. The intermediate connecting frame member 5 is formed with a tension member mounting groove mz that opens downward.

[0312] The intermediate connecting frame member 5 is capable of supporting the lower part of the tension member P. The intermediate connecting frame member 5 comprises an intermediate connecting frame member main body 51 in the form of an upright plate having a tension member mounting groove 5 that is open downward, and mounting parts 52 that are arranged at both ends of the intermediate connecting frame member main body 51 and have screw insertion holes h5b that penetrate in the front-to-rear direction.

[0313] The intermediate connecting frame member main body 51 constituting the intermediate connecting frame member 5 is provided with a tension member mounting groove mz that is open downward. A lower end portion pe of the tension member P is attached to the tension member mounting groove mz.

[0314] The left and right mounting portions 52 have screw insertion holes h5b formed therein, and are adapted to be attached with screws v5 to the extension portions 23 provided on the left and right side frame members 2. In other words, the intermediate connecting frame member 5 is adapted to be attached to the left and right side frame members 2 by screwing the screws v5 inserted through the screw insertion holes h5b, h5a into the nuts n5 of the extension portions 23.

[0315] The left and right mounting portions 52 are set to have a shorter thickness dimension in the front-to-rear direction than the intermediate connecting frame member main body 51. The rear surface of the mounting portions 52 is substantially flush with the rear surface of the intermediate connecting frame member main body 51. Meanwhile, the front surface of the mounting portions 52 is located rearward of the front surface of the intermediate connecting frame member main body 51. In other words, a recessed portion 53 recessed toward the rear is formed on the front surface side of both end portions of the intermediate connecting frame member 5. The tip portion 232 of the extension portion 23 is arranged in the recessed portion 53.

[0316] In this embodiment, the tension member P is wrapped around and supported by the intermediate connecting frame member 5 so as to cover the back surface of the intermediate connecting frame member 5, as shown in Figure 50. More specifically, the tension member P is wrapped around the intermediate connecting frame member 5 from the lower end portion pe side in the order of the back surface, top surface, front surface, bottom surface and back surface. Therefore, on the back surface side of the intermediate connecting frame member 5, the tension member P is arranged in two layers, front and back.

[0317] <Upholstery material P> The upholstery member P is mainly made of a mesh-like fabric capable of forming the backrest surface pm.

[0318] The tensile member P is adapted to be attached at its peripheral portion to a tensile member attachment groove mz provided in the upper frame-shaped portion w1 of the back frame M. The tensile member P is stretched over the front side of the upper frame-shaped portion w1 of the back frame M.

[0319] An inserted member ps is sewn to the end portion pe of the tensioning member P attached to the upper frame-shaped portion w1, and is inserted into the tensioning member mounting groove mz together with the tensioning member P. The inserted member ps of the end portion pe is of a size that allows it to be press-fitted into the tensioning member mounting groove mz of the upper frame-shaped portion w1 during assembly, and is, for example, a strip-shaped member made of synthetic resin.

[0320] An end portion pe of the lower edge of the tension member P is adapted to be attached to a tension member attachment groove mz of the intermediate connecting frame material 5. As shown in Fig. 50, the tension member P is wrapped around the intermediate connecting frame material 5 from the lower end portion pe side in the order of back surface, top surface, front surface, bottom surface, and back surface.

[0321] An example of how the intermediate connecting frame member 5 with the tension member P wrapped around it is attached to the extension portions 23 of the left and right side frame members 2 is as follows.

[0322] First, the portion of the tension member P that is wrapped around the mounting portion 52 is temporarily pressed and moved toward the intermediate connecting frame material main body 51, and the mounting portion 52 exposed to the outside is secured to the extension portion 23 with the screw v5.

[0323] Next, the portion that was temporarily pressed and moved toward the intermediate connecting frame member main body 51 is shifted and moved to a position where the mounting portion 52 and the extension portion 23 can be wound. As a result, the screws v5 for attaching the intermediate connecting frame member 5 to the left and right side frame members 2 are doubly covered with the tension member P when viewed from behind, which can provide a preferable appearance.

[0324] Thereafter, the end portions pe of the upper portion and both left and right sides of the tension member P are attached to the tension member mounting grooves mz of the upper frame material 3 and the left and right side frame materials 2, completing the attachment of the tension member P to the back frame M.

[0325] The above-mentioned mounting procedure is merely an example. For example, the tension member P may be wound around the intermediate connecting frame member 5 in a state in which the intermediate connecting frame member 5 is screwed to the left and right side frame members 2.

[0326] <<Lumbar Support R>> The lumbar support R is installed between the left and right side frame members 2. The lumbar support R is located behind the tension member P and is capable of supporting the lower back of a seated person. The lumbar support R is vertically changeable relative to the left and right side frame members 2 of the backrest E, and is provided so as to be attachable and detachable without the need to attach or detach fasteners such as screws.

[0327] In other words, in this embodiment, whether the lumbar support R is attached to the backrest E after the fact or detached from the backrest E, this can be done by temporarily bending the lumbar support R and inserting or detaching the held portion r22 into or from the lumbar support holding portion N without using fasteners such as screws.

[0328] The lumbar support R includes a lumbar support body r1 extending in the left-right direction, and left and right arm members r2 supported by the lumbar support body r1. The left and right arm members r2 are supported so as to be movable in the left-right direction relative to the lumbar support body r1.

[0329] <Lumbar support body r1> The lumbar support body r1 includes a front body member r11 and a rear body member r12 that is substantially the same size as the front body member r11 and is attached to the rear side of the front body member r11.

[0330] [Front body member r11] The front main body member r11 includes a front main body base r111 made of synthetic resin in the shape of a plate extending in the left-right direction, and a front cover material r112 that covers the front surface and peripheral edge portion of the front main body base r111.

[0331] The front body base r111 can be temporarily bent in the thickness direction. The front body base r111 has a horizontally long plate shape in an upright position as a whole. The left and right side portions of the front body base r111 are formed in a semicircular shape when viewed from the front.

[0332] The front main body base r111 is provided with claw receiving portions r113 at a plurality of positions for receiving engaging claws r123 provided on the rear main body base r121 of the rear main body member r12.

[0333] A triangular prism-shaped positioning protrusion r114 that can fit into a fitting recess r124 provided in the rear main body base r121 of the rear main body member r12 is provided at the center in the left-right and up-down directions of the front main body base r111 and protrudes rearward.

[0334] On the left and right sides of the front main body base r111, there are provided outwardly facing C-shaped guide walls r115 which engage with the outer edges of the arm base portions r21 that constitute the left and right arm materials r2 and can guide the left and right movement of the left and right arm materials r2 relative to the lumbar support main body r1.

[0335] [Rear body member r12] The rear main body member r12 includes a rear main body base r121 made of synthetic resin in the shape of a plate extending in the left-right direction, and a rear covering material r122 that covers the rear surface and peripheral edge portion of the rear main body base r121.

[0336] The rear main body base r121 is provided with engaging claws r123 at a plurality of positions, which can engage with claw receiving portions r113 provided on the front main body base r111 of the front main body member r11.

[0337] A fitting recess r124 into which a triangular prism-shaped positioning protrusion r114 provided on the front main body base r111 of the front main body member r11 can be fitted is formed in the center in the left-right and up-down directions of the rear main body base r121.

[0338] On the left and right sides of the rear main body base r121, there are provided outwardly facing C-shaped guide walls r125 which engage with the outer edges of the arm base portions r21 that constitute the left and right arm materials r2 and can guide the left and right movement of the left and right arm materials r2 relative to the lumbar support main body r1.

[0339] In the inner region surrounded by the guide wall r125 of the rear main body base r121, an upper convex portion r126 and a lower convex portion r127 which are first engagement portions are disposed toward the front, that is, toward the front main body base r111.

[0340] Furthermore, the upper convex portion r126 and the lower convex portion r127 are capable of engaging with the upper engagement hole r213 and the lower engagement hole r214, which are horizontally elongated holes and are second engagement portions provided in the inner plate-like portion r211 of the left and right arm materials r2.

[0341] <Right and left arm material r2> The left and right arm materials r2 are sandwiched between a front main body member r11 and a rear main body member r12. The left and right arm materials r2 have at their outer ends held portions r22 that are held by a lumbar support holding portion N provided on the backrest E. The left and right arm materials r2 are each integrally formed from synthetic resin.

[0342] The left and right arm materials r2 each have an arm base r21 having a rectangular plate-shaped portion extending in the left-right direction, and a held portion r22 connected to the outer end of the arm base r21 and held by the lumbar support holding portion N of the backrest E.

[0343] The arm base r21 and the held portion r22 that constitute the left arm material r2 are integrally formed from synthetic resin, and the arm base r21 and the held portion r22 that constitute the right arm material r2 are integrally formed from synthetic resin.

[0344] [Arm base r21] The arm base r21 has an inner plate-like portion r211 which is rectangular extending in the left-right direction and is located within the lumbar support main body r1, and an outer plate-like portion r212 which is plate-like and has a portion extending diagonally forward and outward from the outer edge of the inner plate-like portion r211.

[0345] The inner plate-like portion r211 has a generally rectangular shape with its upper and lower edges generally parallel to each other. An upper engagement hole r213 and a lower engagement hole r214 are provided at the upper and lower parts of the inner end of the inner plate-like portion r211, which are long hole-shaped second engagement parts extending in the left-right direction. In addition, an elongated interference avoidance hole r215 for avoiding the boss portion r128 having the screw insertion hole h4, and a rectangular interference avoidance hole r216 for avoiding the engagement claw r123 and the claw receiving portion r113, which are the connecting mechanism for connecting the front main body member r11 and the rear main body member r12, are provided at the left-right center of the inner plate-like portion r211.

[0346] The upper convex portion r126 and the lower convex portion r127, which are first engagement portions provided on the lumbar support main body r1, engage with the upper engagement hole r213 and the lower engagement hole r214, which are second engagement portions provided on the inner plate-like portion r211 of the left and right arm materials r2, so that the left and right arm materials r2 can move in the left and right direction relative to the lumbar support main body r1. The upper engagement hole r213 and the lower engagement hole r214 are set to be longer in the width direction than the upper convex portion r126 and the lower convex portion r127.

[0347] The outer plate-like portion r212 is disposed outside the lumbar support body r1. The outer plate-like portion r212 includes an inclined extending plate portion r217 extending diagonally forward and outward from the outer end edge of the inner plate-like portion r211, and a horizontal extending plate portion r218 extending outward from the extending end of the inclined extending plate portion r217.

[0348] [Holded part r22] The held portion r22 has an upper protruding portion r221 and a lower protruding portion r222 that protrude rearward and are arranged with a gap between them in the vertical direction.

[0349] The upper protruding portion r221 and the lower protruding portion r222 are provided to protrude rearward from the outer edge portion of the outer plate-like portion r212 constituting the arm base portion r21, i.e., the outer end portion of the horizontally extending plate portion r218 of the outer plate-like portion r212. The upper protruding portion r221 and the lower protruding portion r222 are bulged outwardly and obliquely rearward from the outer end portion of the arm base portion r21.

[0350] The upper protruding portion r221 and the lower protruding portion r222 are provided at their respective front ends with forward engaging surfaces r223, r227 which serve as front engaging portions that face forward and can engage with the front restricting portion q1 of the holding member Q constituting the lumbar support holding portion N.

[0351] The rear ends of the upper protruding portion r221 and the lower protruding portion r222 are provided with rearward engaging surfaces r224, r228 which serve as rear engaging portions and which face rearward and can engage with the groove forming wall 221a at the back of the accommodating groove 221 which constitutes the lumbar support holding portion N.

[0352] At each inner end of the upper protruding portion r221 and the lower protruding portion r222, lateral engagement surfaces r225, r226 are provided which face inward and serve as side engagement portions capable of engaging with the groove forming wall 221b on the side of the accommodating groove 221 which constitutes the lumbar support holding portion N.

[0353] In this embodiment, the shape of the upper protruding portion r221 is set to be different from the shape of the lower protruding portion r222. More specifically, the upper protruding portion r221 has a notch r226 at the vertical middle portion of the rear end portion, which is the protruding end portion, but the lower protruding portion r222 does not have a similar notch. In addition, the vertical dimension of the upper protruding portion r221 is set to be shorter than the vertical dimension of the lower protruding portion r222.

[0354] The chair of this embodiment is designed to prevent a user from attaching the lumbar support R to the backrest E with the wrong top and bottom. The upper cutout 221c formed in the accommodation groove 221 of the lumbar support holding portion N corresponds to the shape of the upper protruding portion r221 of the lumbar support R. That is, the upper cutout 221c is provided with a protrusion 221e that can pass through the cutout r226 of the upper protruding portion r221.

[0355] The held portion r22 of the lumbar support R is provided with a eave-shaped protrusion r220 that connects between the upper protrusion portion r221 and the lower protrusion portion r222 and protrudes outward from the outer end of the arm base r21 (i.e., the outer end of the horizontal extension portion r218 in the outer plate-like portion r212).

[0356] Furthermore, the upper notch and lower notch that allow the upper protruding portion r221 and the lower protruding portion r222 to pass through are not limited to those provided in the left and right side frame materials 2, but may be, for example, those provided in the front regulating portion q1 of the retaining member Q.

[0357] <<Backrest extension member F>> The backrest surface extension member F is for providing an extended backrest surface fm as a contact surface that can contact the user on the backrest surface pm formed by the backrest E. The backrest surface extension member F in this embodiment is called a "shoulder support" because the user's shoulders can mainly contact the extended backrest surface fm.

[0358] The backrest surface extension member F includes a pad body f1 having an extended backrest surface fm, the front surface of which is a contact surface that can come into contact with a user, and a base body f2 that can support the pad body f1.

[0359] The backrest surface extension member F has an upper frame material arrangement recess fu formed between the lower part of the base body f2 and the lower end part of the pad body f1, the upper frame material arrangement recess fu being open to the front and both the left and right sides.

[0360] The backrest surface extension member F is provided with a movement restricting portion ks, which is located on the rear side of the upper frame material 3 in the backrest E and can restrict forward movement by engaging with the rear portion of the upper frame material 3, at a position facing the upper frame material arrangement recess fu.

[0361] <Pad body f1> The pad body f1 includes a pad body main body f3 attached to a pad body attachment portion f6 provided on the base body f2, and a front skin f4 covering the front surface and peripheral edge portion of the pad body main body f3.

[0362] The pad body f1 has a generally rectangular shape with its elongated sides in the left-right direction when viewed from the front. The pad body f1 has a generally symmetrical shape when viewed from the front. The edges of both the left and right sides of the pad body f1 are gently curved so as to convex outward when viewed from the front. The extended backrest surface fm, which is the front surface of the pad body f1, is set to be generally flush with the backrest surface pm formed by the upholstery member P.

[0363] The vertical dimension of the pad body f1 is shorter than the vertical dimension of the base body f2. The position of the upper edge of the pad body f1 is approximately aligned with the position of the upper edge of the base body f2. The shape of the side edge of the pad body f1 in a front view is approximately aligned with the shape of the side edge at the same height position of the base body f2. The lower edge of the pad body f1 is set at a position that approximately abuts against the upper frame member 3.

[0364] [Pad body f3] The pad body f3 includes a pad base f31 formed of synthetic resin in the shape of a generally upright plate, and a cushion f32 made of urethane foam attached to the front surface of the pad base f31.

[0365] The pad base f31 has a pair of hook engaging portions f311 spaced apart from each other in the left-right direction at the center of the back side of the pad base f31 in the vertical direction. The hook engaging portion f311 has an engaging hole f314 that is open in the vertical direction.

[0366] The hook engaging portion f311 has an engaging hole f314 penetrating in the vertical direction, which is formed by left and right protruding walls f312 protruding rearward and a connecting wall f313 connecting the rear portions of the left and right protruding walls f312. The hook engaging portion f311 can engage with the base body f2 by inserting a hook f61, which is an engaging portion protruding from the pad body mounting portion f6 of the base body f2, into the engaging hole f314.

[0367] The lower part of the rear side of the pad base f31 is provided with left and right fitting protrusions f315 and a central fitting protrusion f316 as engagement parts at three locations on the left, right and center. Each fitting protrusion f315, f316 is substantially arrow-shaped and protrudes rearward. Each fitting protrusion f315, f316 can be engaged with a protrusion fitting part f62 as an engagement part provided on the pad body mounting part f6 of the base body f2. The left and right fitting protrusions f315 are set in a different position from the central fitting protrusion f316. More specifically, the left and right fitting protrusions f315 are set in a position rotated 90 degrees from the central fitting protrusion f316 in rear view.

[0368] [Front skin material f4] The front skin f4 is made of a fabric having an area larger than the front part of the pad body f3. The edge part f4e of the front skin f4 can be stored between the pad body f3 and the base body f2 so as not to be visible from the outside. The front skin f4 can form an extended backrest surface fm provided on the backrest surface pm of the upholstery member P.

[0369] <Base body f2> The base body f2 comprises a base plate-shaped portion f5 having an approximately upright plate shape, a pad body mounting portion f6 provided on the front side of the base plate-shaped portion f5 and to which the pad body f1 is attached, an upper frame member mounting portion f7 provided below the pad body mounting portion f6 and attached to the upper frame member 3 using a fastener screw v1, and a rear skin material f9 that covers the peripheral portion and rear portion of the base plate-shaped portion f5.

[0370] The base plate portion f5, the pad body mounting portion f6, and the upper frame member mounting portion f7 that constitute the base body f2 are integrally formed from synthetic resin.

[0371] In this embodiment, the backrest surface extension member F is configured so that only the rear skin material f9 covering the base plate portion f5 of the base body f2 can be seen in the rear view. In other words, the backrest surface extension member F is configured so that no members other than the rear skin material f9 can be seen in the rear view.

[0372] [Base plate part f5] The base plate portion f5 has a generally rectangular shape with its elongated sides in the left-right direction in rear view. The edges of the left and right sides of the base plate portion f5 are gently curved so as to convex outward in rear view. The rear surface of the base plate portion f5 is covered with a rear skin material f9.

[0373] The front side of the base plate-shaped portion f5 is provided with an upper horizontal rib f52 extending in the left-right direction, the tip of which can abut against the rear surface of the pad base f31, and a plurality of vertical ribs f53 extending in the up-down direction, the tip of which can abut against the rear surface of the pad base f31. The vertical ribs f53 are arranged at intervals in the left-right direction. A lower horizontal rib f54 extending in the left-right direction, the tip of which can abut against the upper frame material 3 of the backrest E, is provided at the lower part of the front side of the base plate-shaped portion f5.

[0374] In this embodiment, the movement restriction portion ks is mainly composed of the components located behind the upper frame material 3, i.e., the tip of the lower horizontal rib f54 and the tip of the vertical rib f53 located below the lower horizontal rib f54, and can restrict the forward movement of the backrest surface extension member F by engaging with the back surface of the upper frame material 3.

[0375] [Pad body mounting part f6] The pad body mounting portion f6 has a hook f61 protruding at a position corresponding to the hook engagement portion f311 of the pad base f31, and a protruding engagement portion f62 protruding at positions corresponding to the left, right and center engagement protrusions f316 of the pad base f31.

[0376] The pad body f1 is attached to the base body f2 by engaging the hook engagement portion f311 with the hook f61 provided on the pad body mounting portion f6, and then engaging the left, right and central engaging protrusions f315, f316 with the protrusion engaging portions f62 provided on the pad body mounting portion f6.

[0377] [Upper frame mounting part f7] The upper frame member mounting portion f7 is mainly composed of a portion protruding forward from the lower end of the base plate portion f5. The upper frame member mounting portion f7 has an upward surface f71 that extends in the left-right direction and serves as the mounting base surface for the upper frame member 3.

[0378] The upper frame member mounting portion f7 has two screw holes h1 that penetrate vertically at the left and right. The backrest surface expansion member F is configured to be mounted to the upper frame member 3 by screwing the screw v1 inserted through the screw hole h1 into the nut member J disposed in the nut holding recess nt in the upper frame member 3.

[0379] The upper frame material mounting portion f7 has a convex wall portion f72 at the upper end of the front part corresponding to the portion where the screw insertion hole h1 is formed, which can be positioned in the front opening portion kh3 of the nut retaining recess nt provided in the upper frame material 3.

[0380] A storage groove f8 that is open downward and outward and can store the edge portion f9e of the rear skin f9 is formed in the lower part of the base body f2, i.e., between the upper frame member mounting portion f7 and the base plate-shaped portion f5. Groove-forming walls f73 are erected at the rear ends of both sides of the upper frame member mounting portion f7 to form the storage groove f8 between them and the peripheral portion of the base plate-shaped portion f5.

[0381] In addition, the front surface of the groove forming wall f73 can abut against the rear surface of the upper frame material 3, and also serves as a movement restricting portion ks that can restrict the forward movement of the backrest surface extension member F.

[0382] [Back skin material f9] The rear skin f9 is made of a material having an area larger than the rear surface of the base plate portion f5. The edge portion f9e of the rear skin f9 can be accommodated between the base plate portion f5 and the pad body f1, and can also be accommodated in an accommodating groove f8 provided between the lower peripheral edge of the base plate portion f5 and the upper frame member mounting portion f7.

[0383] << Hanger G >> The hanger G is for hanging the user's clothes, etc. The hanger G is attached to the upper frame member 3 of the back frame M.

[0384] The hanger G comprises a hanger body g1 extending in the left-right direction for hanging clothes, etc., a pair of left and right hanger legs g2 extending downward from the underside of the hanger body g1 and extending forward at the lower part, and a base portion g3 which connects the lower ends of the left and right hanger legs g2 and is provided with an upper frame member mounting portion g7 which is attached to the upper frame member 3.

[0385] The base portion g comprises a base portion main body g4 having an upper frame material mounting portion g7, and an upright wall g5 serving as a movement restricting portion ks that is erected at the rear of the base portion main body g4 and can engage with the rear surface of the upper frame material 3.

[0386] The upper frame material mounting portion g7 extends in the left-right direction and has an upward surface g71 which serves as the mounting base surface for the upper frame material 3.

[0387] The upper frame member mounting portion g7 is provided with two screw insertion holes h2 penetrating in the vertical direction at the left and right positions. The hanger G is configured to be mounted to the upper frame member 3 by screwing the screw v2 inserted into the screw insertion hole h2 into the nut member J disposed in the nut holding recess nt in the upper frame member 3.

[0388] The upper frame material mounting portion g7 has a convex wall portion g72 at the upper end of the front part corresponding to the portion where the screw insertion hole h2 is formed, which can be positioned at the front opening portion kh3 of the nut retaining recess nt provided in the upper frame material 3.

[0389] <<How to install the option (backrest extension part F)>> The chair of this embodiment is applied with a mounting structure that makes it easy to mount options to the backrest E. Hereinafter, a method of mounting the options to the upper frame material 3 of the backrest E will be described using the backrest surface extension member F as a specific example.

[0390] First, the nut member J is held in the nut holding recess nt that is open forward and provided in the upper frame member 3. A tension member P is stretched and provided in advance on the front side of the upper frame-shaped portion w1 of the back frame M.

[0391] The worker passes the approximately T-shaped nut member J through the upper cavity sa surrounded by the upper frame-shaped portion w1 from the rear to the front, and then holds the nut member J in the nut holding recess nt which is open to the front.

[0392] The boss portion j1 ​​of the nut member J is accommodated in the nut holding recess nt through the front opening portion kh3. The flange portion j2 of the nut member J is accommodated in the gap sk between the nut holding recess nt and the outer frame portion 31. The flange portion j2 of the nut member J engages with the flange portion engagement portion nt3, which is the portion that forms the upper opening portion kh1 in the nut holding recess nt, and cannot move downward. In other words, the nut member J is provisionally positioned relative to the upper frame material 3 by having the boss portion j1 ​​accommodated in the nut holding recess nt and the flange portion j2 disposed in the gap sk.

[0393] Next, the backrest surface extension member F is moved from rear to front, and disposed at a position where the upper frame material disposition recess fu surrounds the upper frame material 3.

[0394] Then, a screw v1 is inserted from the bottom to the top through a screw insertion hole h1 provided in the upper frame member mounting portion f7 of the backrest surface extension member F, and the screw v1 is screwed into the boss portion j1 ​​of the nut member J. By screwing the screw v1 into the nut member J, the upper frame member mounting portion f7 of the backrest surface extension member F and the inner frame portion 32 of the upper frame member 3 are fastened together.

[0395] Using the above mounting method, the backrest surface extension member F can be attached to the upper frame material 3 of the backrest E.

[0396] The nut holding recess nt provided in the upper frame material 3 is open in the forward and vertical directions, making it easy for an operator to attach (temporarily place) the nut member J. The operator can properly hold the nut member J in the nut holding recess nt by simply feeling the inner frame portion 32 of the upper frame material 3 from the rear side of the backrest E without having to closely check the nut holding recess nt which is covered by the upholstery member P and difficult to see.

[0397] In addition, the backrest surface extension member F is provided with a movement restriction portion ks that can restrict forward movement. Therefore, even if the backrest surface extension member F is pressed forward, the nut member J cannot move forward from the nut holding recess nt that is open to the front side.

[0398] <<Locking mechanism V>> The locking mechanism V is for moving the seat C at a constant ratio in response to the tilting of the backrest E.

[0399] The rocking mechanism V of this embodiment has a so-called weight sensing structure that can appropriately tilt the backrest E in accordance with the weight of the seated person. That is, the rocking mechanism V is configured to move the seat C backward in association with the backward tilting of the backrest E, while lifting the seat C against the weight of the seated person.

[0400] In other words, since the rocking mechanism V includes a mechanism for lifting the seat C upward against the weight of the person seated, it is configured to require a backward tilting load proportional to the weight of the person seated in order to tilt the backrest E backward.

[0401] The locking mechanism V supports the front part of the seat support c1 so that it can move back and forth via a front axle jk2 on the front end of the support base B, and pivots the fore-and-aft middle part of the seat C on a rear axle jk3 connected to the front arm portion d12.

[0402] The rear axle jk3 is disposed in front of and above the main shaft jk1 on the left and right arms d1. In this embodiment, the rear axle jk3 is also connected to a bearing shaft d4 disposed in the accommodation space sp of the support base main body 1 via a bearing shaft support member d3.

[0403] The weight-sensing rocking mechanism V is mainly composed of a support base B attached to the upper end of the leg A, a seat C arranged on the support base B and having its front part slidably engaged with the front part of the support base B via a front axle jk2, a back support body D which is rotatably supported on the support base B via a main axle jk1 and has a rear axle jk3 which is a seat engagement axle arranged in front of the main axle jk1 and can engage with the fore-aft center of the seat C, and a receiving axle d4 which is biased by the reaction force generating part HG so as to be able to move together with the support base B, a backrest E supported by the back support body D, and a reaction force generating part HG which is arranged between the support base B and the back support body D and can apply a reaction force against the backward tilting movement of the backrest E.

[0404] In addition, the weight-sensing rocking mechanism V of this embodiment is based on a configuration that can lift the front and front-to-rear central parts of the seat C upward in conjunction with the backward tilting movement of the back support body D linked to the backrest E.

[0405] In other words, the weight-sensing rocking mechanism V is configured to be able to change the position of the backrest E and seat C between the normal position (ES) (CJ) and the backward position (EK) (CK) in conjunction with the movement of the back support D.

[0406] In the locking mechanism V of this embodiment, the positions of the front shaft jk2 and the rear shaft jk3, which is the seat engagement shaft, relative to the main shaft jk1 are set so that the rear end Ce of the seat C (i.e., the rear end Ce of the seat body c2 when the seat body c2 is in the rear position i2) can move downward in accordance with the backward tilting movement of the back support D. The rear end Ce of the seat C is located in front of the backrest E.

[0407] With the above-described embodiment, it is possible to provide a chair having an operating unit main body k11 with an approximately cylindrical outer shape that suppresses complexity, while having a reaction force adjustment lever K that can preferably perform an indicator function of indicating the rotation posture by means of the protrusion k12.

[0408] Furthermore, in the above-described embodiment, the nut member J can be held in the nut retaining recess nt which is open above, below and to the front, making it possible to provide a chair having a suitable configuration in which options such as a backrest surface extension member F can be attached to the backrest E.

[0409] In the above-described embodiment, the backrest surface extension member F is attached to the upper frame member 3 of the backrest E. The backrest surface extension member F is configured such that only the rear skin material f9 covering the base plate-shaped portion f5 can be seen in the rear view, so that a preferable appearance based on the rear skin material f9 can be achieved in the rear view.

[0410] In addition, with the above-described embodiment, it is possible to provide a chair having a suitable configuration in which the lumbar support R, which can support the lower back of a seated person, can be adjusted in position in the vertical direction relative to the backrest E and can be attached and detached without having to attach or detach a fastening device.

[0411] In addition, in the above-described embodiment, since the upholstery member P is wound and supported on the intermediate connecting frame member 5, which is a cross member, it is possible to provide a chair with excellent flexibility, which not only effectively prevents the back surface of the intermediate connecting frame member 5 from being exposed to the outside, but also enables the upholstery member P to be tensioned to an appropriate degree relative to the back frame M.

[0412] Furthermore, in the above-described embodiment, the tip t21 of the screw head abutment protrusion t2 can engage with the head v61 of the screw v6, so that not only can the screw v6 for attaching the backrest E be covered up to obtain a preferable appearance, but it is also possible to provide a chair having a configuration that makes it possible to check whether the screw v6 is properly attached to the backrest E based on the position of the back frame cap T, which serves as a concealing member.

[0413] Furthermore, in the above-described embodiment, at least the foundation bottom structure 11 and the left and right side walls 14 are provided with a support base body 1 which is integrally molded from synthetic resin, and the left and right side walls 14 of the support base body 1 are formed with recesses 1a which are recessed in the thickness direction of the side walls 14. This makes it possible to suitably suppress abnormal deformation during molding of the left and right side walls 14, and provides a chair having a suitable configuration for supporting the main axis jk1 which is an axis relative to the left and right side walls 14 of the support base body 1 made of synthetic resin.

[0414] In addition, the recesses 1a are formed in the left and right side walls 14, and the recesses 1a can be used to suitably position the support base body 1 during assembly and disassembly. Therefore, in this embodiment, in order to improve the design and strength of the support base body 1, a suitable outer shape having curved surfaces or the like can be designed without difficulty, without having to worry about the difficulty of positioning during the assembly and disassembly processes.

[0415] Furthermore, with the above-described embodiment, the seat body c2 can be suitably slid forward and backward relative to the seat support c1, and a chair can be provided with excellent design freedom for obtaining a seat body c2 having a stably mounted seat cushion c22 that is larger than the support member c21.

[0416] In the above-described embodiment, the degree of backward inclination of the backrest E can be selectively set from two or more, and each of the first, second, third and fourth backward inclination degrees (x1), (x2), (x3) and (x4) is determined by the first, second, third and fourth contact surfaces at1, at2, at3 and at4 contacting the damper member XM. Therefore, regardless of the selected backward inclination degree, a common bottoming sensation can be given to the seated person, and a chair having a backrest E that contributes to comfortable use by the seated person can be provided.

[0417] Furthermore, in the embodiment described above, the seat support c1 is provided with a recess cw having a recessed space cs that is open downwards and accommodates the rear axle jk3, which is the seat engagement axle, and the recess cw has a recess top wall portion cw1 whose lower surface faces the recessed space cs and whose upper surface forms the upper surface of the seat support c1, so that a chair with excellent design freedom can be provided for arranging the rear axle jk3, which constitutes the weight-sensing locking mechanism V, on the upper part of the seat support c1 so that it can be positioned as close as possible to the seating surface.

[0418] Furthermore, with the above-described embodiment, it is easy to design a support base body 1 made of synthetic resin with a shape having excellent strength, and it is possible to provide a chair in which a configuration can be easily realized in which the reaction force of the reaction force generating part HG contained in the support base body 1 against the backward tilting movement of the backrest E can be transmitted to the left and right arms d1 arranged on the left and right outer sides of the support base body 1.

[0419] As described above, the chair according to this embodiment includes a leg A, a support base B attached to the upper end of the leg A, a seat C disposed on the support base B, and a back support D which is rotatably supported on the support base B via a main shaft jk1 and has a rear shaft jk3 which is a seat engagement shaft disposed in front of the main shaft jk1 and can engage with the seat C. The chair is provided with a weight-sensing rocking mechanism V which is configured to lift the front part of the seat C upward as the back support D tilts backward.

[0420] The seat C comprises a seat support c1 having a rear axle retaining portion ca3 capable of retaining the rear axle jk3, and a seat body c2 supported by the seat support c1, and the seat support c1 comprises a recess cw having a recessed space cs that is open downward and receives the rear axle jk3. The recess cw has a bottom surface facing the recessed space cs and a recess top wall portion cw1 whose top surface constitutes the top surface of the seat support c1.

[0421] This makes it possible to provide a chair with excellent design freedom for disposing the rear axle jk3, which constitutes the weight-sensing locking mechanism V, on the upper part of the seat support c1. In this embodiment, the recess top wall part cw1 that forms the recess cw constitutes the upper surface of the seat support c1, so the rear axle holder ca, which is provided in association with the recess top wall part cw1, is provided on the upper part of the seat support c1. As a result, the rear axle jk3 is disposed at an upper position that seems to be recessed upward from the bottom into the seat support c1.

[0422] Moreover, since the rear axle jk3 can be disposed on the upper part of the seat receiver c1, the thickness dimension of the seat body c2 that can provide a comfortable seating feeling can be designed without difficulty. In other words, the seat body c2 can be easily configured to be thick by applying a cushioning material or the like.

[0423] Furthermore, when the back support D is tilted backward, the rear axis jk3 is unlikely to move excessively upward, providing excellent design freedom. Therefore, the weight-sensing rocking mechanism V, which is configured to lift the front part and the central part in the front-rear direction of the seat C upward in accordance with the backward tilting movement of the back support D, can be operated based on the natural backward tilt load on the backrest E.

[0424] In other words, conventional weight-sensing rocking mechanisms tend to give the occupant the sensation of consciously putting weight on the backrest in order to raise the seat, but the mechanism of this embodiment is less likely to give such a sensation.

[0425] Also, in a chair that is configured with a weight-sensing rocking mechanism V, it is easy to design the vertical dimension between the seat body c2 and the leg A to be short while ensuring the thickness dimension of the seat body c2 and the vertical dimension of the leg support a2 in the seat A. Therefore, it is possible to ensure a large visible vertical dimension of the leg A, and it is possible to provide a chair that is easy to obtain a slim and suitable appearance.

[0426] The seat C is supported movably relative to the support base B via a front shaft jk2.

[0427] Therefore, a configuration in which the front part of the seat C is movable relative to the support base B can be suitably realized.

[0428] The back support D can movably support the backrest E between a normal position (ES) and a backward tilted position (EK) tilted further backward than the normal position (ES). The back support D is biased by a reaction force generating part HG provided on the support base B in a direction in which the backrest E can take the normal position (ES).

[0429] Therefore, a reaction force against the backward tilting motion of the backrest E is ensured by the reaction force generating portion HG.

[0430] The back support D is equipped with a bearing shaft d4 that is pressed rearward by the reaction force generating part HG. The bearing shaft d4 is supported by the rear shaft jk3 and the main shaft jk1 via a bearing shaft support member d3. The bearing shaft d4 is disposed in front of the main shaft jk1 and below the main shaft jk1.

[0431] Therefore, the biasing force generated by the reaction force generating portion HG can be appropriately applied in a direction that enables the backrest E to assume the normal position (ES) (as a reaction force against the backward tilting motion).

[0432] The bearing shaft d4 is disposed behind the rear shaft jk3. This makes it easier to dispose the reaction force generating part HG in a position close to the main shaft jk1, which contributes to making the support base main body 1 more compact.

[0433] The seat C is movably supported on the support base B via the front axle jk2, and the support base B has a long hole-shaped front axle support portion MS capable of supporting the front axle jk2 so that it can slide. The seat receiver c1 has front axle holders ca4 capable of holding both ends of the front axle jk2.

[0434] Therefore, a suitable configuration in which the seat C can slide relative to the support base B is realized.

[0435] The rocking mechanism V is configured to be able to lift the front part of the seat C upward and move the rear part of the seat C downward in association with the backward tilting movement of the back support D. In other words, the chair is provided with a weight-sensing rocking mechanism V based on a configuration that can lift the front part and the central part in the front-to-rear direction of the seat C upward in association with the backward tilting movement of the back support D, and the positions of the front axis jk2 and the rear axis jk3 relative to the main axis Jk1 are set so that the rear end part Ce of the seat C can move downward in association with the backward tilting movement of the back support D.

[0436] Therefore, despite the use of a weight-sensing rocking mechanism V, the rear end portion Ce of the seat C moves downward in response to the backward leaning load applied by the occupant against the backrest E, thereby achieving a natural movement of the seat C.

[0437] The rear axle jk3 is disposed in the center of the seat c1 in the front-rear direction and in the left-right direction, so that the left-right dimension of the rear axle jk can be suitably designed to be unlikely to be excessively long.

[0438] The recess top wall portion cw1 is provided with left and right shaft end engagement portions cf that can engage with the upper portions of both left and right ends of the rear axle jk3. Because the shaft end engagement portions cf do not have a shape that embraces the entire circumference of the rear axle jk3, the rear axle holding portion ca3 can be easily held by the rear axle jk3 without moving the rear axle jk3 laterally during assembly.

[0439] The rear axle retaining portion CA3 includes a first retaining member CA31 that protrudes into the recessed space CS and has a portion that can engage with at least the front portion of the rear axle JK3, and a second retaining member CA32 that protrudes into the recessed space CS and has a portion that can engage with at least the rear portion of the rear axle JK3.

[0440] Therefore, the first and second retaining members CA31, CA32 work together to suitably retain the rear axle JK3.

[0441] The recess cw comprises a recess top wall portion cw1, a recess front wall portion cw2 and a recess rear wall portion cw3 extending downward from the front and rear portions, respectively, of the recess top wall portion cw1, and left and right recess side wall portions cw4 extending downward from both the left and right side portions, respectively, of the recess top wall portion cw1.

[0442] For this reason, the recess cw that can form the recess space cs is provided in a manner with excellent strength by the recess top wall portion cw1, the recess front wall portion cw2, the recess rear wall portion cw3, and the left and right recess side wall portions cw4.

[0443] The first retaining member CA31 is a wall extending in the front-to-rear direction and is integrally connected to the recess top wall portion CW1 and the recess front wall portion CW2, and the second retaining member CA32 is a wall extending in the front-to-rear direction and is integrally connected to the recess top wall portion CW1 and the recess rear wall portion CW3.

[0444] For this reason, the first holding member ca31 and the second holding member ca32 are arranged within the recess cw in a manner that provides excellent strength.

[0445] The first holding member ca31 is arranged in multiple locations, i.e., two locations, spaced apart in the left-right direction, and the second holding member ca32 is arranged in multiple locations, i.e., four locations, spaced apart in the left-right direction.

[0446] Therefore, the first and second holding members CA31 and CA32 arranged in plurality can hold the rear axle JK3 in a well-balanced manner. Moreover, interference with the plate-shaped bearing shaft support member C3 connected to the rear axle JK3 can be suitably avoided.

[0447] Between the first retaining member CA31 and the second retaining member CA32, an axle passage CG is provided through which the rear axle JK3 can pass when the rear axle JK3 is attached to the rear axle retaining portion CA3.

[0448] This makes it possible to easily attach the rear axle jk3 to the rear axle retaining portion ca3.

[0449] The seat body c2 is supported on the seat support c1 so as to be slidable in the front-rear direction, and the upper surface of the seat support c1 constitutes a lower support area c13 that can abut against the lower surface of the seat body c2. Therefore, the recess top wall portion cw1 of the recess cw is provided at the uppermost part in the center of the seat support c1 in the left-right direction and the front-rear direction.

[0450] The seat body c2 includes the seat cushion c22. Therefore, the seat C can easily realize a configuration that can provide a comfortable seating feeling to the seated person by providing comfortable cushioning.

[0451] The back support D is provided with a reaction force against the backward tilting action by a reaction force generating section HG including a coil spring HG1 provided on a support base B, the degree of compression of the coil spring HG1 can be adjusted by operating a reaction force adjusting lever K, and the amount of compression of the coil spring HG1 by operating the reaction force adjusting lever K is set to approximately half the amount of compression of the coil spring HG1 by the backward tilting action of the back support D.

[0452] In other words, the ratio of the amount of compression of the coil spring HG1 caused by the backward tilting of the back support D to the amount of compression of the coil spring HG1 caused by the operation of the reaction force adjustment lever K is set to a value of approximately 2:1.

[0453] For this reason, in the chair of this embodiment, the reaction force against the backward tilting movement of the backrest E can be easily and widely adjusted based on the operation of the reaction force adjustment lever K in order to appropriately respond to various physiques of the seated person, i.e., individual differences including the seated person's weight, height, muscle structure, etc.

[0454] In other words, many conventional weight-sensing locking mechanisms do not have a reaction force adjustment lever, or even if a reaction force adjustment lever is provided, the amount of compression that can be exerted on the coil spring in the reaction force generating section due to this lever is extremely small, less than one-fifth of the amount of compression that can be exerted on the coil spring due to the backward tilting action of the back support.

[0455] On the other hand, in the chair of this embodiment, the adjustment of the reaction force against the backward tilting movement of the backrest E is not left solely to the configuration of the weight-sensing rocking mechanism V, but the strength of the reaction force against the backward tilting movement can also be widely adjusted by operating the reaction force adjustment lever K.

[0456] It should be noted that the present invention is not limited to the embodiment described above in detail.

[0457] The recess may have a downwardly open recessed space in which the seat engagement shaft can be housed, and the specific shape of the recess is not limited to that shown in the above-described embodiment.

[0458] The seat body may be configured not to slide forward and backward relative to the seat support. For example, the seat cushion constituting the seat body may be directly placed on the seat support.

[0459] The top wall of the recess does not have to be an integral wall, that is, it is sufficient that the top wall of the recess is a wall made up of a plurality of parts intermittently arranged with slits or holes interposed therebetween.

[0460] The front portion of the seat may be movably supported relative to the support base via a link member.

[0461] Furthermore, the specific configuration of each part is not limited to the above embodiment, and various modifications are possible without departing from the spirit of the present invention. [Explanation of symbols]

[0462] A…feet B…support base C… Block D…Back support jk1…spindle jk3…Rear axle (seat system combined axle) V…ロッキング Organization ca3…Rear axle holding part (axle holding part) cs…Aomi Space cw… concave place cw1…A depression wall

Claims

1. A chair comprising legs, a support base attached to the upper ends of the legs, a seat disposed on the support base, and a back support rotatably supported on the support base via a main shaft and having a seat engagement shaft disposed ahead of the main shaft and capable of engaging with the seat, the chair being provided with a weight-sensing rocking mechanism configured to lift the front of the seat upward as the back support is tilted backward, The seat includes a seat bearing having a shaft holding portion capable of holding the seat engagement shaft, and a seat body supported by the seat bearing, The seat support has a recess that is open downward and has a recessed space in which the seat engagement shaft is housed, the recess has a bottom surface facing the recess space and a top surface forming an upper surface of the seat; The back support member can operably support the backrest between a normal position and a rearwardly inclined position that is inclined rearward from the normal position, The back support is biased in a direction in which the backrest can take the normal posture by a reaction force generating portion provided on the support base, The back support member is provided with a bearing shaft that is pressed rearward by the reaction force generating portion, and the bearing shaft is supported by the seat engagement shaft and the main shaft via a bearing shaft support member, The chair, wherein the support axis is disposed in front of and below the main axis.

2. A chair comprising legs, a support base attached to the upper ends of the legs, a seat disposed on the support base, and a back support rotatably supported on the support base via a main shaft and having a seat engagement shaft disposed ahead of the main shaft and capable of engaging with the seat, the chair being provided with a weight-sensing rocking mechanism configured to lift the front of the seat upward as the back support is tilted backward, The seat includes a seat bearing having a shaft holding portion capable of holding the seat engagement shaft, and a seat body supported by the seat bearing, The seat support has a recess that is open downward and has a recessed space in which the seat engagement shaft is housed, the recess has a bottom surface facing the recess space and a top surface forming an upper surface of the seat; The seat is supported movably relative to the support base via a front shaft, the support base includes a front shaft support portion having a long hole shape capable of supporting the front shaft so as to be slidable thereon, The chair, wherein the seat support is provided with a front axis holding portion capable of holding both ends of the front axis.

3. A chair comprising legs, a support base attached to the upper ends of the legs, a seat disposed on the support base, and a back support rotatably supported on the support base via a main shaft and having a seat engagement shaft disposed ahead of the main shaft and capable of engaging with the seat, the chair being provided with a weight-sensing rocking mechanism configured to lift the front of the seat upward as the back support is tilted backward, The seat includes a seat bearing having a shaft holding portion capable of holding the seat engagement shaft, and a seat body supported by the seat bearing, The seat support has a recess that is open downward and has a recessed space in which the seat engagement shaft is housed, the recess has a bottom surface facing the recess space and a top surface forming an upper surface of the seat; A chair in which the shaft retaining portion is disposed in the center of the seat support in the front-rear direction and the center of the seat support in the left-right direction.

4. A chair comprising legs, a support base attached to the upper ends of the legs, a seat disposed on the support base, and a back support rotatably supported on the support base via a main shaft and having a seat engagement shaft disposed ahead of the main shaft and capable of engaging with the seat, the chair being provided with a weight-sensing rocking mechanism configured to lift the front of the seat upward as the back support is tilted backward, The seat includes a seat bearing having a shaft holding portion capable of holding the seat engagement shaft, and a seat body supported by the seat bearing, The seat support has a recess that is open downward and has a recessed space in which the seat engagement shaft is housed, the recess has a bottom surface facing the recess space and a top surface forming a top surface of the seat; A chair in which left and right shaft end engagement portions are provided on the top wall portion of the recess and can engage with the upper portions of both left and right ends of the seat engagement shaft.

5. A chair comprising legs, a support base attached to the upper ends of the legs, a seat disposed on the support base, and a back support rotatably supported on the support base via a main shaft and having a seat engagement shaft disposed ahead of the main shaft and capable of engaging with the seat, the chair being provided with a weight-sensing rocking mechanism configured to lift the front of the seat upward as the back support is tilted backward, The seat includes a seat bearing having a shaft holding portion capable of holding the seat engagement shaft, and a seat body supported by the seat bearing, The seat support has a recess that is open downward and has a recessed space in which the seat engagement shaft is housed, the recess has a bottom surface facing the recess space and a top surface forming a top surface of the seat; The chair has a shaft retaining portion including a first retaining member protruding into the recessed space and having a portion capable of engaging with at least the front portion of the seat engaging shaft, and a second retaining member protruding into the recessed space and having a portion capable of engaging with at least the rear portion of the seat engaging shaft.

6. A chair comprising legs, a support base attached to the upper ends of the legs, a seat disposed on the support base, and a back support rotatably supported on the support base via a main shaft and having a seat engagement shaft disposed ahead of the main shaft and capable of engaging with the seat, the chair being provided with a weight-sensing rocking mechanism configured to lift the front of the seat upward as the back support is tilted backward, The seat includes a seat bearing having a shaft holding portion capable of holding the seat engagement shaft, and a seat body supported by the seat bearing, The seat support has a recess that is open downward and has a recessed space in which the seat engagement shaft is housed, the recess has a bottom surface facing the recess space and a top surface forming a top surface of the seat; The chair has a recess comprising the recess top wall portion, a recess front wall portion and a recess rear wall portion extending downward from the front and rear portions, respectively, of the recess top wall portion, and left and right recess side wall portions extending downward from both the left and right side portions, respectively, of the recess top wall portion.

7. A chair comprising legs, a support base attached to the upper ends of the legs, a seat disposed on the support base, and a back support rotatably supported on the support base via a main shaft and having a seat engagement shaft disposed ahead of the main shaft and capable of engaging with the seat, the chair being provided with a weight-sensing rocking mechanism configured to lift the front of the seat upward as the back support is tilted backward, The seat includes a seat bearing having a shaft holding portion capable of holding the seat engagement shaft, and a seat body supported by the seat bearing, The seat support has a recess that is open downward and has a recessed space in which the seat engagement shaft is housed, the recess has a bottom surface facing the recess space and a top surface forming a top surface of the seat; The seat body is supported so as to be slidable in the forward and backward directions relative to the seat support, and the upper surface of the seat support constitutes a support area that can abut against the lower surface of the seat body.

8. 8. The chair according to claim 1, 3, 4, 5, 6 or 7, wherein the seat is supported movably relative to the support base via a front shaft.

9. 2. The chair according to claim 1, wherein the bearing axis is disposed behind the seat engaging axis.

10. 10. The chair according to claim 1, 2, 3, 4, 5, 6, 7, 8 or 9, wherein the rocking mechanism is configured to lift the front part of the seat upward and move the rear part of the seat downward in association with the backward tilting movement of the back support.

11. the recess includes the recess top wall portion, and a recess front wall portion and a recess rear wall portion respectively extending downward from a front portion and a rear portion of the recess top wall portion, the first holding member is a wall extending in the front-rear direction and is integrally connected to the recess top wall portion and the recess front wall portion, 6. The chair according to claim 5, wherein the second holding member is a wall extending in the front-rear direction and is integrally provided and connected to the top wall portion of the recess and the rear wall portion of the recess.

12. The first holding member is a plurality of members arranged at intervals in the left-right direction, 12. The chair according to claim 5 or 11, wherein the second holding members are a plurality of members arranged at intervals in the left-right direction.

13. A chair as claimed in claim 5, 11 or 12, wherein a shaft passage is provided between the first retaining member and the second retaining member, through which the seat engagement shaft can pass when the seat engagement shaft is attached to the shaft retaining portion.

14. 14. The chair according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 or 13, wherein the seat body includes a seat cushion.

15. A chair comprising legs, a support base attached to the upper ends of the legs, a seat movably disposed on the support base via a front shaft, and a back support rotatably supported on the support base via a main shaft and having a seat engagement shaft disposed in front of and above the main shaft and capable of engaging with the seat, the chair being provided with a weight-sensing rocking mechanism based on a configuration in which the front and front-to-rear central portion of the seat can be lifted upward as the back support is tilted backward, The back support is provided with a reaction force against a backward tilting motion by a reaction force generating unit including a coil spring provided on the support base, The degree of compression of the coil spring is adjustable by operating a reaction force adjustment lever, The amount of compression of the coil spring caused by operation of the reaction force adjustment lever is set to approximately half the amount of compression of the coil spring caused by the backward tilting movement of the back support.

Images