chair

Abstract

To provide a chair with enhanced workability for which a spring member to be used for return of a backrest can be easily compressed and assembled due to a simple constitution.SOLUTION: A backrest is rotatably engaged around a third shaft center C3 in the width direction relative to the rear part of a compression coil spring 60; a fourth shaft center C4 is arranged in front of a rear side attachment part 53, above the third shaft center C3; a seat 5 is supported to be rotatable around the fourth shaft center C4 relative to the front side of the compression coil spring 60; and a first distance L1 between the third shaft center C3 and the fourth shaft center C4 is designed to be longer than the natural length of the compression coil spring 60, in a post-assembly state.SELECTED DRAWING: Figure 5

Description

[Technical Field]

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

[0002] Conventionally, a chair back used for office work, etc., has been known that includes a back supported on a support structure so as to be rotatable about an axis along the width direction of the support structure, and a spring member that biases the back in a direction returning the back to an upright position.

[0003] The chairs described in Patent Documents 1 and 2 have a backrest that is tiltably supported on a support structure, and a spring member that is disposed behind the backrest's position relative to the support structure. In Patent Document 1, a compression spring is disposed in a compressed state between the backrest and the support structure. Patent Document 2 describes a configuration in which the compression spring is disposed within a strength member that constitutes part of the seat, and when the compression spring is assembled, an initial reaction force of the compression spring is applied to the backrest when the compression spring is positioned in the correct position. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 4848099 [Patent Document 2] Patent No. 5724063 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the chair described in Patent Document 1 requires an assembly process in which the compression spring is manually pressed and placed between the two members, leaving room for improvement in terms of workability. Furthermore, in the case of the chair described in Patent Document 2, the compression spring is disposed inside the seat, which causes a problem in that the component configuration of the seat becomes complicated.

[0006] Therefore, the present invention has been made in consideration of the above circumstances, and provides a chair that can be assembled easily by compressing the spring member used to return the backrest with a simple structure, thereby improving workability. [Means for solving the problem]

[0007] In order to achieve the above object, the present invention employs the following means. That is, the chair according to the present invention comprises a support structure, a backrest rotatably supported on the support structure around a first axis in the chair width direction and displaceable in the front-rear direction between an upright state and a tilted state, a front supported portion supported so as to be movable relative to the front of the support structure in the front-rear direction, and a rear supported portion supported at a position above the first axis, and displaceable in the front-rear direction as the backrest displaces relative to the support structure, and a seat provided in a compressed state between the support structure or the seat and the backrest, and deforming in accordance with the displacement of the backrest in the front-rear direction to move at least the backrest in the upright state. and a spring member that biases the seat in a direction to return the seat to its original position, wherein the rear supported portion of the seat is supported relative to the backrest so as to be rotatable about a second axis in the chair width direction, the support structure or the backrest is engaged with a rear portion of the spring member so as to be rotatable about a third axis in the chair width direction, a fourth axis in the chair width direction is disposed forward of the rear supported portion and above the third axis, and the seat is engaged with a front portion of the spring member so as to be rotatable about the fourth axis, and a first distance between the third axis and the fourth axis is set to be smaller than a natural length of the spring member in an assembled state. In a pre-assembly state in which the seat is rotated about the second axis so that the front supported portion of the seat is opened above the front portion of the support structure, the seat is set to open to a position where the first distance is greater than the natural length of the spring member. . The chair according to the present invention comprises: a support structure; a backrest rotatably supported on the support structure around a first axis in the chair width direction and displaceable in the front-rear direction between an upright state and a tilted state; a seat having a front supported portion supported so as to be movable in the front-rear direction relative to a front part of the support structure and a rear supported portion supported at a position above the first axis, and displaceable in the front-rear direction as the backrest displaces relative to the support structure; and a spring member provided in a compressed state between the support structure or the seat and the backrest, which deforms as the backrest displaces in the front-rear direction, thereby biasing at least the backrest in a direction returning to the upright state, and the rear supported portion of the seat is the seat is rotatably supported relative to the backrest around a second axis in the chair width direction, the support structure or the backrest is rotatably engaged with a rear portion of the spring member around a third axis in the chair width direction, and a fourth axis in the chair width direction is disposed forward of the rear supported portion and above the third axis, the seat is rotatably engaged with a front portion of the spring member around the fourth axis, and in an assembled state, a first distance between the third axis and the fourth axis is set to be smaller than a natural length of the spring member, and in an unassembled state, the fourth axis is disposed at a position higher than a front end of the support structure, and in an assembled state, the fourth axis is disposed at a position lower than the front end of the support structure. .

[0008] In a chair configured in this manner, the rear supported portion of the seat rotates about the second axis relative to the backrest, and the front supported portion of the seat can be opened upward relative to the front of the support structure. When attaching the spring member in a compressed state to a predetermined position in the spring assembly space between the support structure and the seat, the seat is rotated about the second axis to separate the front portion of the seat upward from the front portion of the support structure, opening the seat, and the spring member is inserted into the spring assembly space through the separated opening. The rear portion of the spring member is then engaged with the backrest via the third axis, and the front portion of the spring member at its natural length is supported by the seat via the fourth axis. The front side of the seat is then tilted downward around the second axis as a fulcrum, moving toward the front of the support structure, and the front supported portion of the seat is supported by the front of the support structure, thereby attaching the spring member in a compressed state to the predetermined position. In this case, in the attached state in which the front portion of the seat is supported by the support structure, the first distance becomes shorter than the natural length of the spring member, and the spring member is in a compressed state. In this way, in the present invention, the seat can be opened around the second axis to engage the spring member, and then rotated to close it, which is a simple operation, eliminating the need for an operation to apply an initial reaction force to the spring member before assembly, and allowing efficient assembly with a compressed force applied to the spring member. In a chair configured in this manner, in the pre-installation state in which the first distance between the third axis and the fourth axis is greater than the natural length of the spring member, the spring member can be engaged with the seat in its natural length, making assembly easy.

[0009] In addition, in the chair according to the present invention, the first distance may be smaller than a second distance between the second axis and the fourth axis.

[0010] In a chair configured in this manner, the first distance is smaller than the second distance between the second axis and the fourth axis, so that the spring member can be easily compressed by rotating and closing the seat.

[0013] In addition, the chair of the present invention may be characterized in that a front engagement portion is provided at the front of the spring member, and the seat has a front spring support portion that rotatably engages with the front engagement portion around the fourth axis, and one of the front engagement portion and the front spring support portion forms a first recess that opens into the other, and the other has an axis portion coaxial with the fourth axis that engages with the first recess.

[0014] In a chair configured in this manner, for example, a first recess is formed in the front engagement portion of the spring member, and in the pre-installation state in which the front spring bearing portion of the seat has an axle, the spring member can be easily engaged with the axle of the seat by simply fitting the first recess into the axle of the seat. In this case, even when a compressive force is applied to the spring member, the axle will not come out of the first recess, and the spring member can be supported stably against the seat regardless of the pre-assembly or post-assembly state of the spring member.

[0015] In the chair according to the present invention, it is preferable that the front spring receiving portion is disposed rearward of the front supported portion.

[0016] In a chair configured in this manner, the first distance, which corresponds to the length of the spring member in its assembled state relative to the seat, can be made smaller, thereby increasing the amount of compression of the spring member compressed by the seat and increasing the spring force provided by the spring member.

[0017] Furthermore, the chair of the present invention may be characterized in that the support structure or the backrest is provided with a rear spring support portion that supports the rear of the spring member rotatably around the third axis, and the rear spring support portion is arranged on a forward-facing inclined surface that faces upward and forward and is formed on the support structure or the backrest.

[0018] In a chair configured in this way, the forward-facing inclined surface of the backrest faces upward and forward, so the rear spring bearing portion disposed on this forward-facing inclined surface can also be disposed so as to face upward and forward, which makes it easier to attach the rear portion of the spring member to the rear spring bearing portion, improving work efficiency.

[0019] Furthermore, the chair according to the present invention may be characterized in that the rear spring receiving portion is provided on the backrest, and the support structure has a lower shielding surface located below the rear spring receiving portion.

[0020] In a chair configured in this manner, the lower side of the rear spring bearing portion is shielded by the lower shielding surface provided on the support structure, which prevents the spring member from falling downward during the assembly work of engaging the rear portion of the spring member with the rear spring bearing portion, thereby improving the work efficiency involved in assembling the spring member.

[0021] In addition, the chair of the present invention may be configured such that the support structure includes a lower wall that constitutes the lower shielding surface and a pair of side walls that rise upward from both sides of the lower wall in the chair width direction, and the backrest includes a pair of side pieces that face the pair of side walls from the inside in the chair width direction and are supported rotatably around the first axis, and an intermediate piece that supports the rear spring support portion is arranged between the pair of side pieces in the chair width direction.

[0022] In a chair configured in this manner, the side walls of the support structure and the side pieces of the backrest are supported rotatably about the first axis on each side of the chair width, thereby ensuring a large space between the pair of side pieces for arranging the rear spring bearings supported by the intermediate pieces.

[0023] In addition, in the chair of the present invention, a rear engagement portion is provided at the rear of the spring member, which is rotatably engaged with the support structure or the backrest around the third axis, and the rear engagement portion may be configured to form a second recess that opens to the rear.

[0024] In a chair configured in this manner, the second recess formed in the rear engagement portion of the spring member can be easily engaged by simply fitting it into a shaft portion or the like provided on the support structure or the backrest. In this case, the second recess will not come off the shaft portion even when a compressive force is applied to the spring member, and the spring member can be stably supported on the seat regardless of the pre-assembly or post-assembly state of the spring member. [Effects of the Invention]

[0025] According to the chair of the present invention, the spring member used to return the backrest to its original position can be easily compressed and assembled with a simple structure, thereby improving workability. [Brief explanation of the drawings]

[0026] [Figure 1] 1 is a perspective view of a chair according to an embodiment of the present invention, seen obliquely from the front. [Figure 2] 1 is a perspective view of a chair according to an embodiment of the present invention with upholstery removed, seen obliquely from the rear. FIG. [Figure 3] 1 is an exploded perspective view of a chair according to an embodiment of the present invention. [Figure 4] 1 is a partially exploded side view showing the configuration of a seat, a backrest, and a support base of a chair according to an embodiment of the present invention. [Figure 5] 11 is a vertical cross-sectional view of the configuration in FIG. 4, taken along the line X1-X1 in FIG. 10. [Figure 6] FIG. 2 is a perspective view of the seat support member as seen from diagonally above the front. [Figure 7] FIG. 4 is a plan view of the seat support member as viewed from above. [Figure 8] FIG. 6 is an enlarged view of the main part shown in FIG. 5. [Figure 9] FIG. 10 is a perspective view of a support base provided with a compression coil spring and a portion of a backrest, viewed obliquely from above and in front. [Figure 10] FIG. 10 is a plan view of the configuration shown in FIG. 9 as seen from above. [Figure 11] 11 is a cross-sectional view taken along the line X2-X2 shown in FIG. 10. [Figure 12] 11 is a cross-sectional view taken along the line X3-X3 shown in FIG. 10. [Figure 13] FIG. 2 is a perspective view of the adjustment means and the operating means as seen obliquely from behind. [Figure 14] 1A and 1B are diagrams showing the rotational states of the backrest, in which (a) is a diagram showing the upright state and (b) is a diagram showing the tilted state. [Figure 15] 1(a) to 1(c) are diagrams illustrating the assembly process of a compression coil spring. DETAILED DESCRIPTION OF THE INVENTION

[0027] Hereinafter, a chair according to an embodiment of the present invention will be described with reference to the drawings. In the following explanation, for the sake of convenience, the direction in which a seated person sitting in a normal posture on seat 5 faces forward will be referred to as "forward," and the opposite direction will be referred to as "rear." Furthermore, the up / down and left / right directions in the following explanation refer to directions that match the direction of the seated person when sitting in a normal posture on seat 5 with the seated person at the center. In the following explanation, the left / right direction in this case will also be referred to as the width direction (chair width direction). Note that an arrow FR pointing forward, an arrow UP pointing upward, and an arrow LH pointing to the left are shown in appropriate places in the drawings.

[0028] As shown in Figure 1, the chair 1 of this embodiment comprises legs 10 placed on the floor surface F, a box-shaped support base 40 placed on top of the legs 10, a seat 5 attached to the top of the support base 40, a backrest 20 attached to the rear of the support base 40 to support the back of the seated person, and armrests 19 extending from both sides of the lower side of the seat 5 to the upper side of the seat 5 on which the seated person's elbows and arms can be rested.

[0029] The leg 10 has a multi-leg 11 with casters 11a, and a base 12 that stands up from the center of the multi-leg 11 and has a built-in gas spring (not shown) that serves as a lifting mechanism. The base 12 has an outer cylinder 13 and an inner cylinder 14. The outer cylinder 13 is fitted and supported on the multi-leg 11 so as not to rotate. The lower part of the inner cylinder 14 is supported on the outer cylinder 13 so as to be rotatable in the horizontal direction. The upper part of the inner cylinder 14 is fixed to a support base 40. The support base 40 has a built-in lift adjustment mechanism for the base 12 and a tilting mechanism for the backrest 20.

[0030] The backrest 20 has a backrest structure 20A (see FIG. 2) and an upholstery material 26 that covers the backrest structure 20A. The backrest structure 20A supports the back of a seated occupant. As shown in FIG. 2, the backrest structure 20A has a backrest support 21 and a backrest main body 23 supported by the backrest support 21.

[0031] The backrest support 21 supports the back of the seated occupant. The backrest support 21 has a backrest support member 30 and a rear extension member 22.

[0032] 3, the backrest support member 30 has an inner member 31 and an outer member 32. The inner member 31 has a shape that is elongated in the vertical direction. The inner member 31 is formed in a flat plate shape.

[0033] The plate surface of the inner member 31 faces substantially in the front-to-rear direction. The inner member 31 has an inner vertical extension portion 33 and an inner upper protruding portion 34. The inner vertical extension portion 33 has an inner curved upper portion 331, an inner curved lower portion 332, an inner lower portion 333, and an inner lower fixing portion 334.

[0034] The outer member 32 has an outer vertical extension portion 35 and an outer upper protruding portion 36. The outer vertical extension portion 35 has an outer curved upper portion 351, an outer curved lower portion 352, and an outer lower portion 353. The inner member 31 and the outer member 32 are connected by screws.

[0035] The backrest support member 30 of the backrest 20 is fixed to the inner member 31 and the outer member 32, and is provided with a rotating member 38 at the rear of the support base 40 that is rotatable around a first axis C1 in the width direction (left-right direction) via a rotating main shaft 42 (see Figures 4 and 5). The inner member 31 and the outer member 32 are integrated and fixed to the rotating member 38 by inserting a bolt 38a from the mounting recess 353a of the outer lower part 353 of the outer member 32 to the mounting hole 353b, through the mounting hole 334a of the inner lower fixing part 334 of the inner member 31, and through the mounting hole formed in the rotating member 38, and tightening a nut (not shown) onto this bolt 38a.

[0036] As shown in FIG. 3, the rotating member 38 and the outer lower portion 353 of the outer member 32 are covered from behind by a rear cover 37.

[0037] The backrest 20 configured in this manner is supported rotatably around the first axis C1 (main pivot axis 42) relative to the support base 40, as shown in Figures 1 and 2, and is displaceable in the front-to-rear direction from an upright state P1 (see Figure 14(a)) in which the upper end 20a is positioned relatively forward to a tilted state P2 (see Figure 14(b)) in which the upper end 20a is positioned relatively backward.

[0038] 4 and 5, the seat 5 is provided so as to be displaceable in the front-to-rear direction in accordance with the displacement of the backrest 20 relative to the support base 40. The seat 5 includes a seat body 51 and a seat support member 50 that supports the seat body 51 from below.

[0039] The seat support member 50 is formed in a rectangular shape in plan view from above, so that the seat body 51 can be attached to the upper edge. The seat support member 50 is a strong member made of a metal material such as drawn sheet metal or aluminum die-cast, and has a saucer shape that is open on the top in the vertical direction.

[0040] As shown in Figures 5 and 6, the seat support member 50 has an elongated hole 52 (front supported portion) that is supported so as to be movable relative to the front part of the support base 40 in the front-to-rear direction, a rear mounting portion 53 (rear supported portion) that is supported so as to be movable relative to the front part at a position above the first axis C1, and a front spring support portion 55 that rotatably engages with the front part of the compression coil spring 60 described later. The seat support member 50 is positioned forward of the rear mounting portion 53 and above the third axis C3 described later, and is rotatably engaged with the front portion of the compression coil spring 60 around the fourth axis C4 described later.

[0041] 5 to 7, the seat support member 50 has a bottom wall 501 and a side wall 502 standing upright from the periphery of the bottom wall 501. The above-mentioned seat body 51 (see FIG. 4) is attached to the upper end of the side wall 502. The bottom wall 501 extends in the front-rear direction along the outer shape of the compression coil spring 60, which is disposed below, so as not to interfere with the compression coil spring 60, which will be described later, and has a protruding convex portion 503 formed on the upper side.

[0042] 5 and 8, the rear attachment portion 53 is rotatably connected to the rotating member 38 of the backrest support member 30 around a shaft member 39 that extends in the width direction, which will be described later. Here, the central axis of the shaft member 39 is defined as a second axis C2.

[0043] As shown in FIG. 8, the rear attachment portion 53 protrudes downward from the lower rear end of the seat support member 50 and has a rotation shaft hole 531 penetrating in the width direction. The shaft member 39 is rotatably inserted into the rotation shaft hole 531. The rear attachment portion 53 (i.e., the seat support member 50) is rotatable around the shaft member 39 relative to the rotating member 38 (see FIG. 5). That is, as shown in FIG. 5, the seat support member 50 moves rearward relative to the support base 40 when the backrest 20 changes from the upright position P1 (see FIG. 14(a)) to the tilted position P2 (see FIG. 14(b)). Here, an arrow E1 shown in FIG. 5 indicates the movement direction of the seat support member 50 when changing from the upright position P1 to the tilted position P2.

[0044] As shown in Figures 6 and 7, a pair of elongated holes 52 are provided at a distance from each other on both sides in the width direction in the front portion of the bottom wall portion 501. An engaging protrusion 43 (see Figures 9 and 10) protruding upward from the front portion of the support base 40 is slidably engaged with each of the pair of elongated holes 52 along the longitudinal direction (front-rear direction) of the elongated hole 52 while its downward movement is restricted so that it does not slip out of the elongated hole 52. When the backrest 20 tilts, the elongated hole 52 slides rearward relative to the engaging protrusion 43 provided on the support base 40, and the seat support member 50 moves rearward. In other words, when the seat support member 50 moves rearward, the position of the engaging protrusion 43 in the front-rear direction relative to the elongated hole 52 moves from the rearward side to the frontward side.

[0045] 9 to 12, the front spring bearing portion 55 has a pair of fixing portions 551 provided on both sides in the width direction and fixed to the underside of the bottom wall portion 501 of the seat bearing member 50, and a front spring reaction force receiving shaft 552 that connects the pair of fixing portions 551 to each other in the width direction and receives the spring reaction force. Here, the central axis of the front spring reaction force receiving shaft 552 is defined as a fourth axis C4. The front spring bearing portion 55 is provided between a pair of elongated holes 52 that are spaced apart in the width direction.

[0046] The fixed portion 551 is a member formed by bending a plate material into a U-shape and has a pair of reinforcing walls 551A facing each other in the width direction. The reinforcing walls 551A are disposed so that their surfaces are perpendicular to the fourth axis C4 and extend in the up-down direction. A front spring reaction force receiving shaft 552 penetrates each pair of reinforcing walls 551A of the pair of fixed portions 551. The front spring reaction force receiving shaft 552, which is positioned between the pair of reinforcing walls 551A of the fixed portion 551, supports the front portion (front engagement portion 62) of the compression coil spring 60, which will be described later. In this manner, in this embodiment, the reinforcing wall 551A is disposed between the front spring receiving portion 55 and the elongated hole 52.

[0047] The front spring reaction force receiving shaft 552 is a rod member with a circular cross section. The front spring reaction force receiving shaft 552 is inserted through multiple (four) reinforcing walls 551A and is fixed so as not to move in the left-right direction relative to these reinforcing walls 551A. The front engagement portion 62 of a compressed compression coil spring 60 is supported on the front spring reaction force receiving shaft 552 of each fixing portion 551.

[0048] As shown in Figure 3, the support base 40 comprises a support base body 41 (support structure) fixed to the upper part of the leg pillar 12 (see Figure 1), a pivot main shaft 42 that supports the pivot member 38 of the backrest support member 30 rotatably around the first axis C1 in a direction that tilts the pivot member 38 relative to the support base body 41, and an engaging protrusion 43 (see Figures 9 and 10) that supports the seat support member 50 slidably in the front-to-rear direction.

[0049] 5, the support base body 41 has a bottom wall 411 that forms a bottom shielding surface 411a, and a pair of side walls 412 that extend upward from both the left and right sides of the bottom wall 411, and is formed into a bowl shape that opens upward as a whole. In other words, a space (first internal space S1) is formed above the bottom wall 411 and between the pair of left and right side walls 412. The bottom shielding surface 411a is located below the rear engagement portion 63. Two compression coil springs 60 (spring members) are arranged in parallel in the width direction and housed in a first internal space S1 (see FIG. 9) above the support base body 41. The rear end 41a of the support base body 41 protrudes rearward beyond the rear upper parts 412a of the side walls 412. The support base body 41 has rotation main shafts 42 mounted on the rear upper parts 412a of the side walls 412 located on both the left and right sides so as not to rotate relative to each other.

[0050] The front part of the rotating member 38 of the backrest support member 30 is rotatably supported by a rotating shaft 42 on the inside rear part of the support base body 41. As shown in Fig. 10, the rotating shafts 42 provided on each of the side walls 412 on both sides in the width direction are coaxial with each other on a first axis C1. Note that the rotating shafts 42 may be provided so as not to be rotatable relative to the rotating member 38.

[0051] 9 and 10, the engaging protrusions 43 are provided on the front upper ends 412b of the side walls 412 on both the left and right sides of the support base body 41 so as to protrude upward. The engaging protrusions 43 have a protruding portion 431 and a sliding portion 432 that is provided on the upper end of the protruding portion 431 and has a larger diameter than the protrusion. The protruding portion 431 is formed in a circular cross section with a diameter that is approximately the same as the width of the elongated hole 52 (see FIGS. 6 and 7) of the seat receiving member 50. The protruding portion 431 of the engaging protrusion 43 is inserted into the elongated hole 52, and the sliding portion 432 is disposed inside the seat receiving member 50.

[0052] The sliding portion 432 of the seat support member 50 is located on the upper surface of the bottom wall portion 501 and between the pair of side wall portions 502. The sliding region of the sliding portion 432 in the inner portion of the seat support member 50 is located at a position that avoids the convex portion 503 (see FIG. 5) that protrudes upward in a shape that follows the outer shape of the compression coil spring 60 described above, and provides a space where the sliding portion 432 does not interfere with other portions. In other words, the position of the elongated hole 52 and the sliding region of the sliding portion 432 are located at positions on both the left and right sides that avoid the pair of compression coil springs 60 when viewed from above.

[0053] The support base body 41 of the support base 40 and the pivoting member 38 are provided with a compression coil spring 60 (spring member) that biases the backrest 20, which is in the tilted state P2 (see Figure 14(b)), and the seat 5, which is displaced in the direction indicated by the arrow E1 in conjunction with the tilting of the backrest 20, in a direction returning to the upright state P1 (see Figure 14(a)), an adjustment means 70 that adjusts the biasing force of the compression coil spring 60, and an operating means 80 that is connected to the adjustment means 70 and operates the adjustment means 70.

[0054] 8 to 10, the rotating member 38 has a rear wall 381 and a pair of side walls 382 (side pieces) extending perpendicularly from both left and right ends of the rear wall 381 and spaced apart in the width direction. A second internal space S2 is formed between the pair of side walls 382. The second internal space S2 on the front side of the rotating member 38 accommodates the adjustment means 70 and the operating means 80. In addition, the rear end of the compression coil spring 60 is supported in the front part of the second internal space S2.

[0055] A pair of side walls 382 of the rotating member 38 are rotatably supported by the main rotating shaft 42 relative to the rear upper portion 412a of the side wall 412 of the support base portion 41. An adjustment means 70 and an operating means 80 are disposed in a second internal space S2 located rearward of the main rotating shaft 42 in the rotating member 38. The rotating member 38 supports the main rotating shaft 42 at its front portion. The rotating member 38 also includes a shaft member 39 at its rear portion to which the rear mounting portion 53 of the seat receiving member 50 is attached. The rotating member 38 supports an operating shaft 81 of the operating means 80 at a portion intermediate between its front and rear portions.

[0056] 8, the shaft member 39 that constitutes the second axis C2 extends in the width direction. Both sides of the shaft member 39 in the width direction are supported by the side walls 382. A rear attachment portion 53 of the seat support member 50 is rotatably supported by the shaft member 39. In other words, the rear portion of the seat support member 50 is rotatably supported with respect to the rotating member 38.

[0057] 5 and 9 to 12, the compression coil spring 60 is disposed with its biasing direction facing the front-to-rear direction. The compression coil spring 60 is provided in a compressed state between the backrest 20 and the seat 5 (seat support member 50), and is deformed in accordance with the displacement of the seat support member 50 in the front-to-rear direction, thereby biasing the backrest 20 and the seat 5 in a direction returning them to the upright state P1. In other words, the compression coil spring 60 has a restoring force that, by its biasing force, returns the backrest 20 and the seat 5 to their original positions (the upright state P1 shown in FIG. 8) after they have been tilted by a load input from the front to the backrest main body 23 (a load input when the seated person leans their back against the backrest main body 23). The compression coil spring 60 has a front engaging portion 62 provided at one end (front portion) of the compression coil spring 60, and a rear engaging portion 63 provided at the other end (rear portion).

[0058] When the compression coil spring 60 is compressed in the front-to-rear direction, the front engagement portion 62 is displaced rearward and the rear engagement portion 63 is displaced forward. Two compression coil springs 60, with their biasing direction facing the front-to-rear direction, are housed side by side in the width direction in the first internal space S1 of the support basic body portion 41. The pair of compression coil springs 60 are attached in a constantly compressed and biased state whether the backrest 20 is in the upright position P1 (see FIG. 14(a)) or the tilted position P2 (see FIG. 14(b)). More specifically, the compression coil spring 60 is arranged in a state compressed from its natural length (symbol L3 shown in FIG. 15(a)) (a state compressed by symbol L4 shown in FIG. 15(c)) between the front spring bearing portion 55 and the rear spring bearing portion 65 with the engaging protrusion 43 positioned at the rear end of the elongated hole 52.

[0059] The front engagement portion 62 has an outer cylinder 62b that extends toward the rear engagement portion 63 in the axial direction of the compression coil spring 60. The compression coil spring 60 is fitted onto the spring shaft 64. A front portion 64a of the spring shaft 64 is slidably inserted into the outer cylinder 62b of the front engagement portion 62, and a rear portion 64b is engaged with a spring bearing portion 64A that is fixed to the rear engagement portion 63. The rear end of the spring bearing portion 64A has a flange portion 64d that supports the rear end of the compression coil spring 60 from the rear. The peripheral surface of the spring shaft 64 on the rear portion 64b side is provided with a protrusion 64c that protrudes radially outward. The protrusion 64c abuts against a front end 64e of the spring bearing portion 64A from the front side, thereby restricting rearward movement of the spring shaft 64. The front portion of the compression coil spring 60 is fitted onto the outer cylinder 62b of the front engagement portion 62, and the rear portion is fitted onto the spring receiving portion 64A. As the compression coil spring 60 compresses and expands, the outer cylinder 62b of the front engagement portion 62 and the spring receiving portion 64A on the rear engagement portion 63 side move closer to or farther away from each other, thereby changing the distance between them.

[0060] The front engagement portion 62 abuts against the front end of the compression coil spring 60 from the front. The front engagement portion 62 is formed in a U-shape that opens forward when viewed in the width direction. The U-shaped recess 62a (first recess) engages with the front spring reaction force receiving shaft 552 of the front spring receiving portion 55 provided on the seat receiving member 50, pressing it from behind. In other words, the front spring reaction force receiving shaft 552 bears the reaction force of the compression coil spring 60 whether the backrest 20 is in the upright position P1 or the tilted position P2. The front spring receiving portion 55 is positioned rearward of an appropriate position within the front-rear direction range of the elongated hole 52.

[0061] The rear engagement portion 63 abuts against the rear end of the compression coil spring 60 from behind. The rear engagement portion 63 has a through-hole 63a (see FIG. 5) that penetrates in the width direction. A shaft portion 712 of an operating shaft 71 that extends in the direction of a third axis C3 in the width direction of an adjustment means 70 (described later) is inserted into and supported in the through-hole 63a. The backrest 20 is engaged with the rear engagement portion 63 of the compression coil spring 60 so as to be rotatable about the third axis C3. The rear engaging portion 63 may have a second recessed portion that opens rearward instead of the through hole 63a. In this case, the second recessed portion is engaged with the shaft portion 712 from the front in a rotatable state.

[0062] The rear engagement portion 63 is in a state in which a spring force is applied from the front to the operating shaft 71. In other words, the operating shaft 71 bears the reaction force of the compression coil spring 60 whether the backrest 20 is in the upright position P1 or the tilted position P2.

[0063] 5, 8, and 9, the rotating member 38 of the backrest 20 is provided with a rear spring bearing portion 65 that supports the compression coil spring 60 rotatably about the third axis C3 relative to the rear engagement portion 63 at the rear of the compression coil spring 60 via the shaft portion 712 of the operating shaft 71. In other words, the rear engagement portion 63 of the compression coil spring 60 and the rear spring bearing portion 65 are provided rotatably about the third axis C3, with the shaft portion 712 serving as the common third axis C3.

[0064] The rear spring receiving portion 65 is disposed in surface contact with a forward inclined surface 38c (forward surface) facing upward and forward, which is formed on the rotating member 38 of the backrest 20. The rear spring receiving portion 65 is provided so that its position can be adjusted in the vertical direction with respect to the forward inclined surface 38c by an adjustment means 70, which will be described later, and has a receiving surface 65a that is in surface contact with the forward inclined surface 38c.

[0065] The forward inclined surface 38c may have a vertically extending groove formed therein for engaging the receiving surface 65a. The receiving surface 65a is in surface contact with the bottom surface of the groove. In this case, the rear spring receiving portion 65 is movable in the vertical direction but is restricted from moving in the width direction. In other words, the groove allows the rear spring receiving portion 65 to be positioned in the width direction.

[0066] 8, the rear spring receiving portion 65 includes a spring engaging portion 651 that engages with the rear engaging portion 63 of the compression coil spring 60 so as to be relatively movable in response to vertical displacement, and a receiving portion 652 that is disposed rearward of the spring engaging portion 651 and has the above-mentioned receiving surface 65a. Both widthwise side surfaces of the spring engaging portion 651 are disposed at a distance in the widthwise direction from the side walls 382 of the pivoting member 38 of the support structure or backrest 20.

[0067] 9 and 10, the adjustment means 70 has the function of adjusting the biasing force of the compression coil spring 60 and adjusting the restoring force of the backrest 20 in the tilted state P2 (see FIG. 14(b)). The adjustment means 70 is housed in the second internal space S2 between the side walls 382 of the rotating member 38 of the backrest 20. The adjustment means 70 adjusts the position of the rear engagement portion 63 of the compression coil spring 60 in the vertical direction. 9 to 13, the adjustment means 70 includes an action shaft 71 that acts on the biasing force of the compression coil spring 60, an adjustment shaft 72 that movably supports the action shaft 71, and a support member 73 that rotatably supports the adjustment shaft 72 with respect to the operating means 80. The adjustment shaft 72 (central portion, intermediate piece) is located in the center in the width direction.

[0068] A second transmission gear 721 consisting of a bevel gear is integrally provided at the upper end of the adjustment shaft 72. This second transmission gear 721 meshes with a first transmission gear 83 of the operating means 80, which will be described later, so that by operating the operating means 80, a rotational force is transmitted from the first transmission gear 83 to the second transmission gear 721, causing the adjustment shaft 72 to rotate in both forward and reverse directions. A male thread is formed on the adjustment shaft 72 along the entire axial direction, with which the operating shaft 71 is threadedly engaged.

[0069] 11, in the upright position P1, the adjustment shaft 72 is disposed such that its axial direction is angled obliquely so that the length gradually increases from the front to the rear as it moves from the lower shaft end 72b to the upper shaft end 72a in a side view. The lower shaft end 72b is located below the rotation main shaft 42 (first axis C1). The upper shaft end 72a is located above and rearward of the rotation main shaft 42. In other words, the operating shaft 71, which moves along the adjustment shaft 72, i.e., the rear engagement portion 63 provided at the rear end of the compression coil spring 60 connected to the operating shaft 71, is configured to move between a position below the rotation main shaft 42 (indicated by the two-dot chain line in FIG. 14(a)) and a position above and rearward of the rotation main shaft 42 (indicated by the solid line in FIG. 14(a)).

[0070] The adjustment means 70 is configured so that, as the adjustment shaft 72 rotates, the action shaft 71, which is threaded onto the male screw, moves in the axial direction of the adjustment shaft 72 according to the rotational position of the adjustment shaft 72. That is, the adjustment means 70 can adjust the position of the action shaft 71 by moving the action shaft 71 along the adjustment shaft 72. When the action shaft 71 moves on the adjustment shaft 72, the compression coil spring 60 rotates around the front engagement portion 62 (first axis C1), and therefore only the angle viewed from the width direction changes.

[0071] 8 and 13, the support member 73 extends in the vertical direction and includes a fixed plate 731 fixed to the rear wall 381 of the rotating member 38 with screws (not shown), and an upper support plate 732 and a lower support plate 733 extending forward from the upper and lower ends of the fixed plate 731. The adjustment shaft 72 is disposed between the upper support plate 732 and the lower support plate 733. As shown in FIG. 11, the adjustment shaft 72 has an upper end 72a rotatably supported by the upper support plate 732 and a lower end 72b rotatably supported by the lower support plate 733.

[0072] The action shaft 71 includes a nut portion 711 having a female thread that screws onto the adjustment shaft 72, and a shaft portion 712 that extends to both the left and right sides of the nut portion 711. The nut portion 711 moves along the adjustment shaft 72 as the adjustment shaft 72 rotates. As shown in FIG. 10 , the rear engagement portion 63 of the spring member 60 is connected to the shaft portion 712.

[0073] 9, the operating means 80 is provided on the rotating member 38. The operating means 80 has an operating shaft 81 extending in the left-right direction, an operating lever 82 provided at the tip (one end) of the operating shaft 81 that protrudes outward from a side wall 382, ​​and a first transmission gear 83 made of a bevel gear provided in the middle of the operating shaft 81 and located in the second internal space S2. That is, the operating means 80 has an outer end portion of the operating shaft 81 in the width direction that protrudes widthwise from the side wall 382, ​​while the inner end portion in the width direction is positioned within the second internal space S2 and connected to the adjustment means 70.

[0074] The operating shaft 81 is disposed in a state where it protrudes outward from the upper part of the side wall 382 of the rotating member 38. The operating shaft 81 is disposed above the adjustment shaft 72 so that the axis of the operating shaft 81 and the axis of the adjustment shaft 72 are positioned in the same plane.

[0075] A first transmission gear 83 provided in the axial middle of the operating shaft 81 meshes with a second transmission gear 721 provided on the adjustment shaft 72. In other words, the rotation of the operating shaft 81, i.e., the rotation of the first transmission gear 83 around its axis in the left-right direction, is converted into the rotation of the second transmission gear 721 around the axis of the adjustment shaft 72.

[0076] The operating lever 82 is located to the side in the width direction of the side wall 382 of the rotating member 38, and behind the seat support member 50. In other words, the operating lever 82 is located above and behind the seat support member 50, and is in a position that is easily accessible by the hands of an occupant sitting on the seat 5 on the seat support member 50.

[0077] In the chair 1 configured in this manner, when adjusting the reaction force (returning force) of the backrest 20, first, the operating lever 82 of the operating means 80 is rotated, and the action shaft 71 located at the rear engagement portion 63 of the compression coil spring 60 moves up and down along the adjustment shaft 72. For example, by rotating the operating lever 82 in one direction, the adjustment shaft 72 rotates in one direction via the first transmission gear 83 and the second transmission gear 721, and the nut portion 711 that screws onto the adjustment shaft 72, i.e., the action shaft 71, moves up along the adjustment shaft 72.

[0078] 14(a) and 14(b), the operating shaft 71 moves on the adjustment shaft 72, which changes the distance between the front engagement portion 62 and the rear engagement portion 63 of the spring member 60, thereby adjusting the compression amount of the compression coil spring 60, i.e., the biasing force (reaction force) of the compression coil spring 60. In other words, the return force when the backrest 20 returns from the tilted state P2 to the upright state P1 can be adjusted.

[0079] 14(a) shows the backrest 20 in an upright position P1, and FIG. 14(b) shows the backrest 20 in a tilted position P2. The compression coil spring 60 shown by the solid line in FIG. 14(a) and (b) indicates the upper limit position T1 when the adjustment means 70 is used, and the compression coil spring 60 shown by the two-dot chain line indicates the lower limit position T2 when the adjustment means 70 is used.

[0080] The upper limit position T1 of the rear engagement portion 63 (third axis C3) of the compression coil spring 60, which is adjusted by the adjustment means 70, is set to a position above the first axis C1. As shown in Fig. 5, the upper limit position T1 of the rear engagement portion 63 (third axis C3) is set forward and below the rear attachment portion 53 (second axis C2). Furthermore, the distance L5 between the first axis C1 and the rear engagement portion 63 (third axis C3) at the upper limit position T1 is set to be shorter than the distance between the first axis C1 and the rear attachment portion 53 (second axis C2).

[0081] In this way, the adjustment means 70 of this embodiment is configured so that the position of the action shaft 71, i.e., the position of the rear engagement portion 63 of the compression coil spring 60, is changed by moving the action shaft 71 on the adjustment shaft 72, thereby adjusting the biasing force of the compression coil spring 60 (the return force of the backrest 20). In this embodiment, the action shaft 71, which moves on the adjustment shaft 72, can be adjusted to a position above the rotation main shaft 42 in the vertical direction.

[0082] Next, the positional relationship between the above-mentioned axes C1, C2, C3, and C4 will be described in more detail. As shown in Figures 14(a) and (b), in the chair 1 of this embodiment, the first distance L1 between the third axis C3 and the fourth axis C4 is set to be smaller than the second distance L2 between the second axis C2 and the fourth axis C4.

[0083] 15(a), in the chair 1, in the pre-assembly state where the seat receiving member 50 is opened upward with the elongated hole 52 of the seat 5 relative to the front part (engaging protrusion 43) of the support base part 41 of the support base 40, the seat receiving member 50 is configured to open up to a first position N1 where the first distance L1 is greater than the natural length L3 of the compression coil spring 60. In other words, when the seat receiving member 50 is in the first position N1, the front engaging part 62 of the compression coil spring 60, whose natural length L3 is engaged with the rear engaging part 63 of the backrest 20, can be engaged with the front spring receiving part 55 of the seat receiving member 50.

[0084] 15(c), in the assembled state where the seat receiving member 50 is engaged and closed with the elongated hole 52 of the seat 5 against the front part (engaging protrusion 43) of the support base 41 of the support base 40, the first distance L1 is set to a second position N2 where it is shorter than the natural length L3 of the compression coil spring 60. In other words, in the assembled state, the compression coil spring 60 is attached in a state where it has an initial reaction force where a compressive force (symbol F1 shown in FIG. 15(c)) is applied from the front engaging part 62.

[0085] 15(b) shows the state before assembly of the compression coil spring 60, which is at a third position N3 between the first position N1 and the second position N2, where the first distance L1 is shorter than the natural length L3 of the compression coil spring 60. Even in this third position N3, a compressive force (denoted by symbol F1 in FIG. 15(c)) acts on the compression coil spring 60 from the front engagement portion 62.

[0086] In the chair 1 configured in this manner, the rear mounting portion 53 of the seat support member 50 of the seat 5 rotates about the second axis C2 relative to the backrest 20, and the front portion of the seat support member 50 can be opened upward relative to the front portion of the support base 40. When the compression coil spring 60 is attached in a compressed state to a predetermined position in the spring assembly space between the support base 40 and the seat support member 50, as shown in Figure 15(a), the seat support member 50 is rotated about the second axis C2 to move the front portion of the seat support member 50 upward away from the front portion of the support structure, opening the seat support member 50, and the compression coil spring 60 is inserted into the spring assembly space through the opened opening. Then, the rear engagement portion 63 of the rear part of the compression coil spring 60 engages with the rear spring support portion 65 provided on the backrest 20 via the third axis C3, and the front part (front engagement portion 62) of the compression coil spring 60 in its natural length is supported on the seat support member 50 via the fourth axis C4.

[0087] Then, as shown in Figure 15(b), the seat support member 50 is tilted downward at its front side with the second axis C2 as a fulcrum and moved in a direction approaching the front of the support base 40, and the long hole 52 of the seat support member 50 is supported by the engaging protrusion 43 of the support base 40, whereby the compression coil spring 60 is attached in a compressed state to a predetermined position.

[0088] 14(a), in a pre-assembly state in which the first distance L1 between the third axis C3 and the fourth axis C4 is greater than the natural length L3 of the compression coil spring 60, the compression coil spring 60 can engage with the seat support member 50 at its natural length. In an assembled state in which the first distance L1 is smaller than the second distance L2 between the second axis C2 and the fourth axis C4 and the front portion of the seat support member 50 is supported by the support base 40, as shown in FIG. 15(c), the first distance L1 becomes a compressed length L4 that is smaller than the natural length L3 of the compression coil spring 60 (see FIG. 15(a)), and the compression coil spring 60 is in a compressed state.

[0089] In this way, in this embodiment, the seat support member 50 is opened around the second axis C2 to engage the compression coil spring 60 with a natural length L3, and then the seat support member 50 is rotated to close it, which is a simple operation. This eliminates the need for an operation to apply an initial reaction force to the compression coil spring 60 before assembly, and allows efficient assembly with a compression force applied to the compression coil spring 60.

[0090] Furthermore, in this embodiment, the first recess 62a is formed in the front engagement portion 62 of the compression coil spring 60, and in a pre-assembly state in which the front spring reaction force receiving shaft 552 is provided in the front spring receiving portion 55 of the seat receiving member 50, the compression coil spring 60 can be engaged with the front spring reaction force receiving shaft 552 of the seat receiving member 50 by a simple operation of simply fitting the first recess 62a of the front engagement portion 62 of the compression coil spring 60 onto the front spring reaction force receiving shaft 552 of the seat receiving member 50. In this case, even when a compressive force is applied to the compression coil spring 60, the front spring reaction force receiving shaft 552 will not come off the first recess 62a, and the compression coil spring 60 can be stably supported by the seat receiving member 50 regardless of the pre-assembly state or the assembled state of the compression coil spring 60.

[0091] Furthermore, in this embodiment, the front spring support portion 55 is positioned rearward of the elongated hole 52, and the first distance L1, which corresponds to the length of the compression coil spring 60 in its assembled state relative to the seat support member 50, can be made smaller. This increases the amount of compression of the compression coil spring 60 compressed by the seat support member 50, thereby applying a large spring force to the compression coil spring 60.

[0092] In addition, in this embodiment, since the forward inclined surface 38c of the pivoting member 38 of the backrest 20 faces forward and upward, the rear spring bearing portion 65 disposed on this forward inclined surface 38c can also be disposed so as to face forward and upward. This makes it easier to attach the rear portion of the compression coil spring 60 to the rear spring bearing portion 65, improving work efficiency.

[0093] In this embodiment, the lower side of the rear spring bearing portion 65 is shielded by the lower shielding surface 411a provided on the support base 40. This prevents the compression coil spring 60 from falling downward during the assembly work of engaging the rear portion of the compression coil spring 60 with the rear spring bearing portion 65, thereby improving the work efficiency involved in assembling the compression coil spring 60.

[0094] In this embodiment, the support base 40 includes a lower wall that forms the lower shielding surface 411a and a pair of side walls that rise upward from both sides of the lower wall in the chair width direction. The backrest 20 has a pair of side pieces that face the pair of side walls from the inside in the width direction and are supported rotatably around the first axis C1, and an intermediate piece that supports the rear spring bearing portion 65 is disposed between the pair of side pieces in the width direction. As a result, on both sides in the width direction, the side walls of the support base 40 and the side pieces of the backrest 20 are supported rotatably around the first axis C1 as a rotation axis. Therefore, a large space can be secured between the pair of side pieces to accommodate the rear spring bearing portion 65 supported by the intermediate piece.

[0095] In this embodiment, the second recess formed in the rear engagement portion 63 of the compression coil spring 60 may be easily engaged with the shaft portion 712 or the like provided on the backrest 20. In this case, even when a compressive force is applied to the compression coil spring 60, the second recess will not come off the shaft portion 712, and the compression coil spring 60 can be stably supported by the seat support member 50 regardless of the pre-assembly or post-assembly state of the compression coil spring 60.

[0096] The technical scope of the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention.

[0097] For example, in the embodiment described above, the rear engaging portion 63 of the compression coil spring 60 is provided on the backrest 20, but it may also be configured to be provided on the support base body portion 41 (support structure).

[0098] In addition, in this embodiment, a compression coil spring 60 is used as the spring member, but this is not limited to this and other spring members such as a torsion coil spring can also be applied. Furthermore, the spring is not limited to a compression spring and a tension spring such as a tension coil spring can also be used.

[0099] In addition, in this embodiment, a first recess 62a is formed in the front engagement portion 62 of the compression coil spring 60, and the front spring support portion 55 has a front spring reaction force receiving shaft 552 that is coaxial with the fourth axis C4 and engages with the first recess 62a, but the first recess may also be provided in the front spring support portion 55.

[0100] In addition, in this embodiment, the rotating member 38 of the backrest 20 has a pair of side walls 382 spaced apart in the width direction, and the adjustment means 70 is arranged in the space between the side walls 382 (second internal space S2), but the rotating member 38 may be configured without a pair of side walls 382.

[0101] Furthermore, in this embodiment, the second internal space S2 is part of the first internal space S1, but this is not limited to this, and the first internal space S1 and the second internal space S2 may be separate and not overlap each other.

[0102] Furthermore, it is possible to appropriately change the specific configurations and arrangements of the spring member 60, the adjustment means 70, and the operating means 80. For example, although the pair of compression coil springs 60 are used as the spring members in this embodiment, other biasing members may also be used.

[0103] In addition, within the scope of the spirit of the present invention, the components in the above-described embodiments may be replaced with well-known components as appropriate, and the above-described modifications may be combined as appropriate. [Explanation of symbols]

[0104] 1 chair 20 Backrest 20A Backrest structure 30 Backrest support member 38 Rotating member 39 Shaft member 40 base 41 Support body (support structure) 42 Rotating shaft 50 Seat support member 51 Seat body 53 Rear mounting portion (rear supported portion) 55 Front spring support 60 Compression coil spring (spring component) 62 Front engagement part 62a First recess 63 Rear engagement part 65 Rear spring support 70 Adjustment means 71 Axis of action 72 Adjustment axis 80 Operating means 411a Lower shielding surface 552 Front spring reaction bearing shaft C1 First axis center C2 Second axis C3 3rd axis C4 Fourth Axis

Claims

1. a support structure; a backrest supported by the support structure so as to be rotatable about a first axis in the chair width direction and displaceable in the front-rear direction between an upright state and a tilted state; a seat having a front supported portion supported so as to be movable relative to the front portion of the support structure in the front-rear direction, and a rear supported portion supported at a position above the first axis, the seat being displaceable in the front-rear direction in accordance with displacement of the backrest relative to the support structure; a spring member that is provided in a compressed state between the support structure or the seat and the backrest, and that deforms in accordance with the displacement of the backrest in the front-rear direction to bias at least the backrest in a direction to return it to the upright state; The rear supported portion of the seat is supported rotatably around a second axis in the chair width direction relative to the backrest, the support structure or the backrest is rotatably engaged with the rear portion of the spring member around a third axis in the chair width direction, A fourth axis in the chair width direction is disposed forward of the rear supported portion and above the third axis, the seat is engaged with the front portion of the spring member so as to be rotatable about the fourth axis; In an assembled state, a first distance between the third axis center and the fourth axis center is set to be smaller than a natural length of the spring member, The chair is configured so that, in a pre-assembly state in which the seat is rotated about the second axis to open the front supported portion of the seat above the front of the support structure, the seat opens to a position where the first distance is greater than the natural length of the spring member.

2. a support structure; a backrest supported by the support structure so as to be rotatable about a first axis in the chair width direction and displaceable in the front-rear direction between an upright state and a tilted state; a seat having a front supported portion supported so as to be movable relative to the front portion of the support structure in the front-rear direction, and a rear supported portion supported at a position above the first axis, the seat being displaceable in the front-rear direction in accordance with displacement of the backrest relative to the support structure; a spring member that is provided in a compressed state between the support structure or the seat and the backrest, and that deforms in accordance with the displacement of the backrest in the front-rear direction to bias at least the backrest in a direction to return it to the upright state; The rear supported portion of the seat is supported rotatably around a second axis in the chair width direction relative to the backrest, the support structure or the backrest is rotatably engaged with the rear portion of the spring member around a third axis in the chair width direction, A fourth axis in the chair width direction is disposed forward of the rear supported portion and above the third axis, the seat is engaged with the front portion of the spring member so as to be rotatable about the fourth axis; In an assembled state, a first distance between the third axis center and the fourth axis center is set to be smaller than a natural length of the spring member, A chair in which, in a pre-assembled state, the fourth axis is positioned at a higher position than the front end of the support structure, and in a post-assembled state, the fourth axis is positioned at a lower position than the front end of the support structure.

3. 3. The chair of claim 1, wherein the first distance is less than a second distance between the second axis and the fourth axis.

4. 3. The chair of claim 2, wherein in a pre-assembly state in which the seat is rotated about the second axis so that the front supported portion of the seat is opened above the front of the support structure, the seat is set to open to a position where the first distance is greater than the natural length of the spring member.

5. a front engaging portion is provided at a front portion of the spring member; the seat includes a front spring receiving portion that is rotatably engaged with the front engagement portion around the fourth axis, A chair as described in any one of claims 1 to 4, wherein one of the front engagement portion and the front spring support portion forms a first recess that opens into the other, and the other has an axis portion coaxial with the fourth axis that engages with the first recess.

6. The chair according to claim 5, wherein the front spring receiving portion is disposed rearward of the front supported portion.

7. a rear spring bearing portion that supports the spring member rotatably around the third axis relative to a rear portion of the spring member, the rear spring bearing portion being provided on the support structure or the backrest; The chair according to any one of claims 1 to 6, wherein the rear spring bearing portion is disposed on a forward-facing inclined surface that is formed on the support structure or the backrest and faces forward and upward.

8. The rear spring receiving portion is provided on the backrest, 8. The chair of claim 7, wherein the support structure has a lower shielding surface located below the rear spring seat.

9. The support structure includes: a lower wall that constitutes the lower shielding surface; a pair of side walls rising upward from both sides of the lower wall in the chair width direction, The backrest is A pair of side pieces that face the pair of side walls from the inner side in the chair width direction and are supported rotatably around the first axis; The chair according to claim 8, wherein an intermediate piece supporting the rear spring bearing portion is disposed between the pair of side pieces in the chair width direction.

10. a rear engaging portion that is rotatably engaged with the support structure or the backrest around the third axis is provided at a rear portion of the spring member; The chair according to any one of claims 1 to 9, wherein the rear engagement portion forms a second recess that opens rearward.

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