Backrest and chair

Abstract

This backrest comprises a back frame which has an opening that is open in the front-rear direction and which is in the form of a frame. The back frame is provided with a pair of side frame members which are provided on both sides in the left-right direction and a connecting member which extends in the left-right direction and which connects the pair of side frame members together. The side frame members are each provided with a first side frame portion which forms the upper part of the corresponding side frame member and which extends in the vertical direction, a second side frame portion which extends from the lower end of the first side frame portion downward and inward in the left-right direction, and a lower part side frame portion which extends from the lower end of the second side frame portion downward, outward in the left-right direction, and forward.

Description

Backrest and chair

[0001] The present disclosure relates to a backrest and a chair.

[0002] For example, Patent Document 1 discloses a backrest with a back frame formed in a generally rectangular frame shape when viewed from the front. The back frame includes a pair of rods extending vertically, a lower frame section spanning between the lower ends of the pair of rods, and a connecting frame provided between the upper ends of the pair of rods. The back frame is attached to the chair base via a support base attachment section formed below and in front of the lower frame section.

[0003] Japanese Patent No. 6765182

[0004] To improve comfort, it is desirable for the back frame of a chair to bend to some extent in the front-to-rear direction when a seated person leans against it. In this case, stress is applied to the back frame due to the load from the seated person in the front-to-rear direction. This stress may place a load on the support base mounting part.

[0005] In contrast, if the rigidity of the back frame is increased to reduce the load on the support base mounting portion of the back frame, the back frame will be less likely to flex when the seated person leans against it, impairing the seating comfort. The present disclosure has been made to solve the above problem, and aims to provide a backrest and chair that can provide good sitting comfort while reducing the load on the support base mounting portion and other parts of the back frame.

[0006] In order to solve the above problems, the present disclosure employs the following aspects: (1) A backrest according to one aspect of the present disclosure is a backrest for a chair, comprising: a frame-shaped back frame having an opening that opens in the front-rear direction; and a load support surface that covers the back frame from at least the front and supports the upper body of a seated occupant, the back frame comprising a pair of side frame members provided on both left and right sides, and a connecting member that extends in the left-right direction and connects the pair of side frame members, the side frame members constituting upper parts of the side frame members comprising a first side frame portion that extends in the up-down direction, a second side frame portion that extends downward and inward in the left-right direction from a lower end of the first side frame portion, and a third side frame portion that extends downward and forward in the left-right direction from the lower end of the second side frame portion.

[0007] According to this aspect, when a seated person leans against the backrest, the load from the seated person's upper body (mainly the back) acts diagonally downward from front to rear on the first side frame portion of a pair of side frame members provided at the top of the back frame via the upholstery material. The pair of side frame members then elastically deform, centering around the lower end of the second side frame portion, so that the upper end of the first side frame portion displaces rearward. At this time, the load acting on the side frame members is transmitted downward. Therefore, in this aspect, the second side frame portion extends inward in the left-right direction as it extends downward, while the third side frame portion extends outward in the left-right direction and forward as it extends downward. With this configuration, the second and third side frame portions are connected via a shape-changing portion (bent portion). Therefore, the load transmitted to the third side frame portion can be reduced compared to, for example, when the second and third side frame portions are connected in a straight line. Therefore, for example, when sitting, the stress acting on the structural parts of the chair connected to the backrest due to the front-to-rear load acting on the first side frame and the second side frame can be reduced. In this way, it is possible to provide a backrest that provides a comfortable sitting experience while reducing the load on the attachment parts to the support base at the bottom of the back frame. Moreover, because a portion of the side frame member of the second side frame extends inward in the left-to-right direction, it is easy to set the angle of the third side frame relative to the vertical direction so that the load is not easily transmitted to the third side frame while keeping the left-to-right dimension of the backrest as a whole small. This also improves design freedom.

[0008] (2) In the backrest according to the above aspect (1), the connecting member preferably includes a first connecting portion that connects the upper ends of the first side frame portions. According to this aspect, for example, a load acting on one side frame member is easily transmitted to the other side frame member via the first connecting portion. Therefore, the seating load can be distributed and supported across the entire back frame. Therefore, stress acting on the boundary between the second and third side frame portions can be reduced.

[0009] (3) In the backrest according to the above-described (1) or (2), the connecting member preferably includes a second connecting portion that connects the boundary between the second and third side frame portions of the pair of side frame members. According to this aspect, a load transmitted to the second side frame portion due to, for example, a seating load is also transmitted to the second connecting portion, thereby reducing stress acting on the boundary between the second and third side frame portions. As a result, the effect of stress on the lower side frame portion below the second connecting portion can be reduced.

[0010] (4) In the backrest according to the above aspect (3), it is preferable that the second connecting portion has a thickness that gradually increases in the up-down direction from the rear to the front. According to this aspect, compared to when the second connecting portion is a thin plate with a constant thickness in the up-down direction from the rear to the front, the thickness of the second connecting portion gradually increases in the up-down direction from the rear to the front, thereby improving the torsional rigidity of the second connecting portion. This makes it possible to effectively resist stress acting on the boundary between the second side frame portion and the third side frame portion and on the second connecting portion, for example, due to seating load.

[0011] (5) In the backrest according to either of the above (3) or (4), the connecting member preferably includes a third connecting portion that connects the lower ends of the third side frame portions. According to this aspect, the pair of third side frame portions, the second connecting portion, and the third connecting portion form a strong loop at the bottom of the back frame. This allows the load transmitted to the third side frame portions to be transmitted to the third connecting portion as well, thereby distributing and supporting the load transmitted to the third side frame portions to the bottom of the back frame. As a result, stress acting on the structural parts of the chair connected to the backrest can be reduced.

[0012] (6) In the backrest according to the above aspect (5), the third connecting portion preferably includes a base connecting portion that is connected to the base of the chair that supports the backrest. According to this aspect, as described above, the load transmitted to the third side frame portion can be distributed and supported at the lower part of the back frame, thereby reducing stress acting on the structural portion of the chair connected to the backrest.

[0013] (7) In the backrest according to any one of the above aspects (1) to (6), it is preferable that the third side frame portion includes an armrest attachment portion to which an armrest can be attached. According to this aspect, the load acting from the occupant's back, among the seating load, can be supported by the first side frame portion and the second side frame portion, while the load acting from the occupant's elbow can be supported by the third side frame portion. This reduces the rigidity required for the first side frame portion and the second side frame portion compared to, for example, when an armrest is connected to the first side frame portion and the second side frame portion.

[0014] (8) In the backrest according to any one of the above aspects (1) to (7), it is preferable that the first side frame portion extends diagonally forward from its upper end to its lower end, and the second side frame portion extends diagonally backward from its upper end to its lower end. According to this aspect, the first side frame portion extends diagonally forward from its upper end to its lower end, thereby supporting the upper part of the occupant's upper body from both the left and right sides, providing a comfortable seating experience. The second side frame portion connected to the lower end of the first side frame portion extends diagonally backward from its upper end to its lower end, thereby enabling the extension direction of the second side frame portion to be appropriately positioned relative to the direction of load acting from the occupant's upper body in a side view.

[0015] (9) A chair according to this aspect includes a backrest according to any one of the above aspects (1) to (8). According to this aspect, it is possible to provide a chair with a backrest that can provide a comfortable sitting experience while reducing the load on the attachment portion to the support base at the bottom of the back frame.

[0016] According to each of the above aspects, it is possible to provide a comfortable sitting experience while reducing the load on the attachment portion to the support base at the bottom of the back frame.

[0017] Fig. 2 is a perspective view of a chair according to an embodiment of the present disclosure, as seen from the left rear; Fig. 3 is a rear view of the chair; Fig. 4 is a perspective view of a back frame according to the present embodiment; Fig. 5 is a cross-sectional view taken along the line II in Fig. 2; Fig. 6 is a view of the lower part of the back frame as seen from the front;

[0018] Next, embodiments of the present disclosure will be described with reference to the drawings. In the embodiments and modified examples described below, corresponding components may be designated by the same reference numerals, and their description may be omitted. In the following description, expressions indicating relative or absolute arrangements, such as "parallel," "orthogonal," "center," and "coaxial," not only strictly refer to such arrangements, but also refer to a state in which the components are relatively displaced by an angle or distance to a degree that allows tolerance or the same function to be obtained. In this embodiment, "facing" does not only refer to a case in which the orthogonal directions (normal directions) of two surfaces are aligned with each other, but also includes a case in which the orthogonal directions intersect with each other.

[0019] [Chair 1] Fig. 1 is a perspective view of chair 1 as seen from the left rear. Fig. 2 is a rear view of chair 1. As shown in Figs. 1 and 2, chair 1 has a support structure 2, a seat 3, a backrest 4, and armrests 5. In the following description, directions such as front-to-back, up-down, left-to-right, etc. are assumed to be the same directions as those of a person (seat occupant) sitting in the chair 1 in a normal posture. In this case, in the drawings, arrow UP indicates upward, arrow FR indicates forward, and arrow LH indicates left. In the following description, in the front-to-back, up-down, and left-to-right directions, the side away from the center of chair 1 may be referred to as the outside, and the side toward the center of chair 1 may be referred to as the inside.

[0020] <Support structure 2> The support structure 2 includes a leg body 11 and a support base 12. The leg body 11 includes a multi-leg 13 and a pedestal 14. A caster 15 capable of running on a floor surface F is attached to each leg of the multi-leg 13.

[0021] The leg pillar 14 extends upward from the center of the multi-legged leg 13. A gas spring 16, which is a lifting mechanism for the chair 1, is built into the leg pillar 14. The gas spring 16 is configured such that an inner cylinder 16a is supported by an outer cylinder (not shown) provided inside the leg pillar 14 so as to be able to move up and down and rotate relative to the outer cylinder.

[0022] The support base 12 is connected to the upper end of the leg pillar 14 (inner cylinder 16a). The support base 12 supports the seat 3 from below. The support base 12 supports the backrest 4 so that it can tilt.

[0023] <Seat 3> The seat 3 is formed in a downwardly protruding arc shape when viewed from the front, and supports the portion of the seated person from the buttocks to the thighs from below. As shown in Figure 1, the seat 3 comprises a seat shell 30 and a seat main body 31. The seat shell 30 is a resin-molded plate-like member that forms the framework of the seat 3. The seat shell 30 is attached to the support base 12 in a state where it covers the entire support base 12 from above. The seat main body 31 is supported by the seat shell 30 from below. The seat main body 31 comprises a cushioning material placed on the upper surface of the seat shell 30 and a cover material that covers the cushioning material from above.

[0024] <Backrest 4> The backrest 4 supports the seated occupant's lower back and back from behind. The backrest 4 is connected to the support base 12 so as to be tiltable around an axis along the left-right direction. However, the backrest 4 may also be connected to the support base 12 so as not to be tiltable.

[0025] FIG. 3 is a perspective view of the back frame 41 according to this embodiment. As shown in FIGS. 1 and 3 , the backrest 4 includes a back frame 41 and an upholstery member 42. The back frame 41 is a reinforcing member that defines the outer shape of the backrest 4. The back frame 41 is integrally molded from a resin material or the like. The back frame 41 is formed in a rearwardly convex arc shape in a plan view and an S-shape in a side view. As shown in FIGS. 1 to 3 , the back frame 41 is formed in an eight-shape in a front view, with the upper frame portion 41A and the lower frame portion 41B connected vertically. Specifically, the back frame 41 includes a pair of side frame members 43, a first connecting portion (connecting member) 51, a second connecting portion (connecting member) 52, a third connecting portion (connecting member) 53, a base connecting portion 56 (see FIG. 3 ), and an armrest mounting portion 57.

[0026] Each of the pair of side frame members 43 has an upper side frame portion 44 and a lower side frame portion 45. The upper side frame portion 44 has a first side frame portion 46 and a second side frame portion 47. The first side frame portion 46 forms the upper portion of the side frame member 43 and extends in the up-down direction. The first side frame portion 46 extends diagonally forward from its upper end to its lower end in a side view. The second side frame portion 47 extends downward from the lower end of the first side frame portion 46. The second side frame portion 47 extends diagonally rearward from its upper end to its lower end in a side view. The second side frame portion 47 has a shorter length in the up-down direction than the first side frame portion 46. As a result, at the portion where the lower end of the first side frame portion 46 and the upper end of the second side frame portion 47 are connected, the upper side frame portion 44 has a bent portion located below the center in the up-down direction.

[0027] 2 and 3 , the first side frame portions 46 extend downward and outward in the left-right direction. The second side frame portions 47 extend downward and inward in the left-right direction from the lower end portions of the first side frame portions 46. As a result, in a front view, the left-right distance between the pair of first side frame portions 46 gradually increases downward. Furthermore, the left-right distance between the pair of second side frame portions 47 gradually decreases downward.

[0028] The lower frame portion (third frame portion) 45 extends downward from the boundary between the upper frame portion 44 and the second connecting portion 52. The upper end of the lower frame portion 45 is connected to straddle the lower end of the upper frame portion 44 and the lower wall portion 52d of the second connecting portion 52. The lower frame portion 45 extends downward and forward from the lower end of the second frame portion 47 in a side view. That is, the lower frame portion 45 extends diagonally forward from its upper end to its lower end. As a result, in a side view, the connection portion between the lower end of the second frame portion 47 and the upper end of the lower frame portion 45 is bent so as to protrude rearward. As shown in FIG. 1 , in a side view, the angle θ1 formed between the lower end of the second frame portion 47 and the upper end of the lower frame portion 45 is preferably an obtuse angle.

[0029] The lower frame portions 45 extend downward and outward in the left-right direction from the lower ends of the second frame portions 47. As a result, the left-right spacing between the pair of lower frame portions 45 gradually increases downward in a front view. In a front view, the connection between the lower ends of the second frame portions 47 and the upper ends of the lower frame portions 45 is bent so as to protrude inward in the left-right direction. As shown in FIG. 2, the angle θ2 formed between the lower ends of the second frame portions 47 and the upper ends of the lower frame portions 45 in a front view is preferably an obtuse angle. As shown in FIGS. 1 and 2, the vertically intermediate portion of the lower frame portion 45 overlaps the outer left-right end of the seat 3 in a front view. The lower end of the lower frame portion 45 is located below the seat 3. The front end of the lower frame portion 45 is located forward of the bent portion of the upper frame portion 44.

[0030] As shown in Figures 1 to 3, the first connecting portion 51 constitutes the upper end of the back frame 41. The first connecting portion 51 connects the upper ends of the first side frame portions 46 together. In a plan view, the first connecting portion 51 extends in the left-right direction in an arc shape that convex toward the rear. The vertical dimension of the first connecting portion 51 gradually increases toward the front.

[0031] FIG. 4 is a cross-sectional view taken along the arrows I-I in FIG. 2. The second connecting portion 52 connects the boundary between the lower end of the second side frame portion 47 and the lower side frame portion 45. In a plan view, the second connecting portion 52 extends in the left-right direction in a circular arc shape that convex toward the rear. As shown in FIG. 4, the vertical thickness of the second connecting portion 52 gradually increases from the rear to the front. In a cross-sectional view, the second connecting portion 52 is formed into a C-shape that opens forward, with the rear ends of the upper wall portion 52t and the lower wall portion 52d connected to each other. The upper surface of the upper wall portion 52t of the second connecting portion 52 is formed into an inclined surface that slopes upward toward the front. Meanwhile, the lower surface of the lower wall portion 52d of the second connecting portion 52 is formed so that the vertical distance between the upper surface of the upper wall portion 52t and the lower surface of the lower wall portion 52d gradually increases toward the front. However, the lower surface of the second connecting portion 52 may be inclined upward toward the front as long as the angle (elevation angle) between the lower surface and the horizontal plane is smaller than the angle (elevation angle) between the upper surface and the horizontal plane.

[0032] FIG. 5 is a view of the lower part of the back frame 41 as viewed from the front. As shown in FIGS. 4 and 5 , the second connecting portion 52 has a forward-facing recess 52a formed on its front end surface. Specifically, the front-end opening of the forward-facing recess 52a faces diagonally downward toward the front. In a side view, the forward-facing recess 52a is formed in a triangular shape whose vertical dimension gradually decreases toward the rear. In this embodiment, the forward-facing recess 52a is formed across the entire left-right direction of the second connecting portion 52. The formation of the forward-facing recess 52a in the second connecting portion 52 improves moldability and reduces weight.

[0033] As shown in FIG. 5 , a plurality of vertical ribs 58 are formed inside the forward-facing recess 52a. The vertical ribs 58 are provided at intervals in the left-right direction within each forward-facing recess 52a. Each vertical rib 58 connects a downward surface 52c facing downward on the upper wall portion 52t and an upward surface 52b facing upward on the lower wall portion 52d, which are opposed to each other in the vertical direction, on the inner surface of the forward-facing recess 52a. The vertical ribs 58 extend throughout the entire length of the forward-facing recess 52a in the front-to-rear direction. These vertical ribs 58 reinforce the second connecting portion 52 in which the forward-facing recess 52a is formed.

[0034] As shown in Figure 4, a tension material holding member 70 is fitted into the forward-facing recess 52a. The tension material holding member 70 has an upper contact surface 70a that contacts the downward surface 52c of the forward-facing recess 52a and a lower contact surface 70b that contacts the upward surface 52b. In a side view, the tension material holding member 70 is formed so that the vertical distance between the upper contact surface 70a and the lower contact surface 70b gradually decreases toward the rear. The tension material holding member 70 extends in the left-right direction and is fitted from the front into the entire left-right area of ​​the forward-facing recess 52a, and is fixed to the second connecting portion 52 by bolts or the like (not shown).

[0035] The lower end of the front edge of the upholstery material holding member 70 protrudes forward beyond the downward surface 52c of the second connecting portion 52. The upholstery material holding member 70 has an engagement groove 71 that engages with part of the peripheral edge of the upholstery material 42 along the second connecting portion 52. The engagement groove 71 is formed across the entire left-right direction of the upholstery material holding member 70. The engagement groove 71 opens downward at the lower end of the front edge of the upholstery material holding member 70. In a side view, the engagement groove 71 opens diagonally downward and toward the rear. By attaching such a upholstery material holding member 70 to the forward-facing recess 52a, the second connecting portion 52 is reinforced.

[0036] 1 to 3, the upper frame portion 41A is configured by the first connecting portion 51, the upper side frame portion 44, and the second connecting portion 52. The upper frame portion 41A has an opening 41p that opens in the front-rear direction.

[0037] As shown in Figures 2, 3, and 5, the third connecting portion 53 extends in the left-right direction and connects the lower ends of the lower side frame portions 45 together. In a front view, the third connecting portion 53 is formed in a downwardly convex arc shape. In a side view, the third connecting portion 53 is located forward of the second connecting portion 52. As shown in Figures 3 and 5, the vertical thickness of the third connecting portion 53 gradually increases from the rear to the front. The upper surface 53t of the third connecting portion 53 is formed as an inclined surface that slopes downward toward the front. Meanwhile, the lower surface 53d of the third connecting portion 53 slopes downward toward the front, and the vertical distance between the lower surface 53d and the upper surface 53t gradually increases toward the front.

[0038] The third connecting portion 53 has a forward-facing recess 53a formed on its front end surface. The forward-facing recess 53a improves moldability and reduces weight of the third connecting portion 53. Specifically, the front end opening of the forward-facing recess 53a faces diagonally downward and forward. In a side view, the forward-facing recess 53a is formed in a triangular shape whose vertical dimension gradually decreases toward the rear. In this embodiment, the forward-facing recess 53a is formed on both sides of the third connecting portion 53, excluding the center portion in the left-right direction.

[0039] A plurality of vertical ribs 59 are formed inside the forward-facing recess 53a. The vertical ribs 59 are provided at intervals in the left-right direction within each forward-facing recess 53a. Each vertical rib 59 connects the inner surfaces of the forward-facing recess 53a that face each other in the vertical direction (the upward surface 55b facing upward and the downward surface 55c facing downward). The vertical ribs 59 extend the entire length of the forward-facing recess 53a in the front-to-rear direction. These vertical ribs 59 reinforce the third connecting portion 53 in which the forward-facing recess 53a is formed.

[0040] The base connecting portion 56 is provided in the center of the third connecting portion 53 in the left-right direction. The base connecting portion 56 is formed integrally with the third connecting portion 53. The base connecting portion 56 is connected to the base 12. The base connecting portion 56 protrudes upward from the third connecting portion 53 and is formed in a box shape that opens forward. The inside of the base connecting portion 56 forms an insertion groove 56a into which a part of the base 12 is inserted.

[0041] The armrest attachment portions 57 are provided at the lower end portions of the lower side frame portions 45. The armrest attachment portions 57 protrude on both the left and right sides of the third connecting portion 53.

[0042] As shown in Figures 1 and 2, the upholstery material 42 forms a load-bearing surface 42f that supports the upper body of the seated occupant, specifically, the seated occupant's lower back and back. The upholstery material 42 is provided to cover the opening 41p of the upper frame portion 41A from the front. The upholstery material 42 is configured to be elastically deformable, for example, by a membrane-like material such as mesh or cloth. The outer periphery of the upholstery material 42 is fixed to the outer surface of the upper frame portion 41A (the first connecting portion 51, the upper side frame portion 44, and the second connecting portion 52) so as to wrap around the upper frame portion 41A. Note that the backrest 4 may be configured so that the back frame 41 is covered with a cushion and a cover material instead of the upholstery material 42.

[0043] <Armrests 5> The armrests 5 are connected to the back frame 41. The armrests 5 are attached to the armrest mounting portions 57 and support the portion of the seated occupant's elbows through to their forearms from below. The armrests 5 include an armrest support member 80 and an armrest body 81.

[0044] The armrest support member 80 is a member that connects the armrest attachment portion 57 and the armrest main body 81, and functions as a strength member of the armrest 5. The armrest support member 80 is formed in an L-shape when viewed from the front. The lower end of the armrest support member 80 is attached to the armrest attachment portion 57 from the outside in the left-right direction.

[0045] The armrest main body 81 is supported on the armrest support member 80 so as to be able to move up and down. The armrest main body 81 comprises an armrest support pillar 82 and an armrest rest portion 83. The armrest support pillar 82 is inserted from above the armrest support member 80 into an insertion hole 80a that passes through the armrest support member 80 in the up and down direction. The armrest support pillar 82 is configured so as to be able to move up and down along the insertion hole 80a.

[0046] The armrest 83 is provided on the upper end of the armrest support 82. The armrest 83 is formed, for example, by covering a shell and padding with a skin material. The upper surface of the armrest 83 forms an armrest surface that supports the elbows of the seated occupant. The armrest 83 covers the armrest support 82 from above and is attached to the armrest support 82 in a state where it protrudes in the front-to-back and left-to-right directions relative to the armrest support 82. The armrest 5 may be attached to the seat 3 or the support base 12. The armrest 5 may also be configured not to move up and down.

[0047] <Lumbar support 100> A lumbar support 100 that supports the lower back of a seated person is provided in the center of the second connecting portion 52 in the left-right direction. The lumbar support 100 protrudes upward from the second connecting portion 52 so as to be visible within the upper frame portion 41A. Note that the lumbar support 100 is not an essential component of the chair 1 of this embodiment, and the lumbar support 100 may be omitted. The chair includes a lumbar support main body 101 and an attachment portion 130.

[0048] The lumbar support body 101 abuts against the back of the seated occupant through the upholstery 42, supporting the weight of the seated occupant from behind. The attachment portion 130 is a member that attaches the lumbar support body 101 to the chair body 1A. The attachment portion 130 is attached to the center of the second connecting portion 52 in the left-right direction.

[0049] In the backrest 4 of this embodiment, the pair of side frame members 43 of the back frame 41 are configured to include a first side frame portion 46, a second side frame portion 47 extending downward and inward in the left-right direction from the lower end of the first side frame portion 46, and a lower side frame portion 45 extending downward and outward in the left-right direction from the lower end of the second side frame portion 47 and forward. With this configuration, when a seated person leans against the backrest 4, the load (seating load) from the seated person's upper body (mainly the back) acts diagonally downward from the front to the rear on the first side frame portions 46 of the pair of side frame members 43 provided at the top of the back frame 41 via the upholstery material 42. This elastic deformation of the pair of side frame members 43 causes the upper ends of the first side frame portions 46 to be displaced rearward around the lower ends of the second side frame portions 47. At this time, the load acting on the side frame members 43 is transmitted downward. Therefore, in this embodiment, the second side frame portion 47 extends inward in the left-right direction as it extends downward, while the lower side frame portion 45 extends outward in the left-right direction and forward as it extends downward. With this configuration, the second side frame portion 47 and the lower side frame portion 45 are connected via a shape-changing portion (bent portion). Therefore, compared to, for example, a case in which the second side frame portion 47 and the lower side frame portion 45 are connected in a straight line, the load transmitted to the lower side frame portion 45 can be reduced. Therefore, for example, when sitting, stress acting on the structural parts of the chair 1 connected to the backrest 4 due to a front-to-rear load acting on the upper frame portion 41A (the first side frame portion 46 and the second side frame portion 47) can be reduced. In this way, it is possible to provide a backrest 4 that provides a comfortable sitting experience while reducing the load on the structural parts of the chair 1 connected to the backrest 4 at the bottom of the back frame 41. Furthermore, since a portion of the side frame member 43 of the second side frame portion 47 extends inward in the left-right direction, it is easy to reduce the overall left-right dimension of the backrest 4 and set the angle of the lower side frame portion 45 relative to the vertical direction at an angle that makes it difficult for load to be transmitted to the lower side frame portion 45. This also improves the degree of freedom in design.

[0050] In the backrest 4 of this embodiment, the upper ends of the first side frame portions 46 are connected to each other by the first connecting portion 51. With this configuration, for example, a load acting on one side frame member 43 is easily transmitted to the other side frame member 43 via the first connecting portion 51. This allows the seating load to be distributed and supported across the entire back frame 41. This reduces stress acting on the boundary between the second side frame portion 47 and the lower side frame portion 45.

[0051] In the backrest 4 of this embodiment, the boundary between the second side frame portion 47 and the lower side frame portion 45 is connected by the second connecting portion 52. With this configuration, a load transmitted to the second side frame portion 47 due to, for example, a seating load is also transmitted to the second connecting portion 52, thereby reducing stress acting on the boundary between the second side frame portion 47 and the lower side frame portion 45. As a result, the effect of stress on the lower side frame portion 45 below the second connecting portion 52 can be suppressed.

[0052] In the backrest 4 of this embodiment, the second connecting portion 52 is configured so that its thickness in the up-down direction gradually increases from the rear to the front. With this configuration, compared to when the second connecting portion 52 is a thin plate with a constant thickness in the up-down direction from the rear to the front, the thickness of the second connecting portion 52 in the up-down direction gradually increases from the rear to the front, thereby improving the torsional rigidity of the second connecting portion 52. This allows the second connecting portion 52 to effectively resist stress acting on the boundary between the second side frame portion 47 and the lower side frame portion 45 and on the second connecting portion 52, for example, due to seating load.

[0053] The backrest 4 of this embodiment is configured to include a third connecting portion 53 that connects the lower ends of the lower side frame portions 45. With this configuration, the pair of lower side frame portions 45, the second connecting portion 52, and the third connecting portion 53 form a strong loop at the bottom of the back frame 41. As a result, the load transmitted to the lower side frame portions 45 is also transmitted to the third connecting portion 53, so that the load transmitted to the lower side frame portions 45 can be distributed and supported by the bottom of the back frame 41. As a result, stress acting on the structural portions of the chair 1 connected to the backrest 4 can be reduced.

[0054] In the backrest 4 of this embodiment, the third connecting portion 53 is configured to include the support base connecting portion 56. With this configuration, as described above, the load transmitted to the lower side frame portion 45 can be distributed and supported at the lower portion of the back frame 41 (lower frame portion 41B), thereby reducing the stress acting on the structural portion of the chair 1 connected to the backrest 4.

[0055] In the backrest 4 of this embodiment, the lower side frame portion 45 is configured to include an armrest attachment portion 57. With this configuration, the load acting from the back of the seated occupant, part of the seating load, can be supported by the upper frame portion 41A (the first side frame portion 46 and the second side frame portion 47), while the load acting from the elbows of the seated occupant can be supported by the lower frame portion 41B (the lower side frame portion 45). This reduces the rigidity required for the upper frame portion 41A compared to, for example, a case in which an armrest is connected to the upper frame portion 41A.

[0056] In the backrest 4 of this embodiment, the first side frame portion 46 extends diagonally forward from its upper end to its lower end, and the second side frame portion 47 extends diagonally backward from its upper end to its lower end. With this configuration, the first side frame portion 46 extends diagonally forward from its upper end to its lower end, so that the upper part of the occupant's upper body is supported on both the left and right sides via the upholstery material 42, providing a comfortable seating experience. The second side frame portion 47, connected to the lower end of the first side frame portion 46, extends diagonally backward from its upper end to its lower end, so that the extension direction of the second side frame portion 47 can be appropriately positioned relative to the direction of load acting from the occupant's upper body when viewed from the side.

[0057] The chair 1 of this embodiment includes the above-described backrest 4. This configuration makes it possible to provide a chair 1 equipped with a backrest 4 that can provide a comfortable sitting experience while reducing the load on the attachment portion to the support base at the bottom of the back frame 41.

[0058] (Other Modifications) Although preferred embodiments of the present disclosure have been described above, the present disclosure is not limited to these embodiments. Additions, omissions, substitutions, and other modifications to the configuration are possible without departing from the spirit of the present disclosure. The present disclosure is not limited by the above description, but is limited only by the appended claims. In the above-described embodiment, the first side frame portion 46 extends downward and outward in the left-right direction, but this is not limited thereto. The first side frame portion 46 may simply extend downward (vertically downward) in a front view, as long as it extends in the up-down direction. The first side frame portion 46 may also extend downward and inward in the left-right direction. However, the angle at which the first side frame portion 46 slopes downward and inward in the left-right direction is preferably smaller than the angle at which the second side frame portion 47 slopes downward and inward in the left-right direction. In the above-described embodiment, the second side frame portion 47 extends diagonally rearward from the upper end to the lower end in a side view, but this is not limited thereto. The second side frame portion 47 may extend vertically downward or diagonally forward from the upper end to the lower end in a side view.

[0059] In the above-described embodiment, a configuration including the first connecting portion 51, the second connecting portion 52, and the third connecting portion 53 as connecting members has been described, but this configuration can be modified as appropriate. For example, although the description is given with , at least one of the first connecting portion 51, the second connecting portion 52, and the third connecting portion 53 may be omitted. Furthermore, other connecting members may be provided in addition to the first connecting portion 51, the second connecting portion 52, and the third connecting portion 53. Furthermore, the vertical position, shape, etc. of the connecting members can be modified as appropriate.

[0060] In the above-described embodiment, the configuration of each part of the chair body 1A has been described, but the configuration can be changed as appropriate. In the above-described embodiment, the configuration in which the chair 1 includes the armrests 5 has been described, but the armrests 5 are not an essential component.

[0061] In addition, within the scope of the present disclosure, the components in the above-described embodiments may be replaced with well-known components as appropriate, and the above-described modified examples may be combined as appropriate.

[0062] REFERENCE SIGNS LIST 1 Chair 4 Backrest 5 Armrest 41 Back frame 41p Opening 42f Load support surface 43 Side frame member 46 First side frame portion 47 Second side frame portion 51 First connecting portion (connecting member) 52 Second connecting portion (connecting member) 53 Third connecting portion (connecting member) 56 Support base connecting portion 57 Armrest mounting portion

Claims

1. A backrest for a chair comprising: a frame-shaped back frame having an opening that opens in the front-to-rear direction; and a load support surface that covers the back frame from at least the front and supports the upper body of a seated occupant, wherein the back frame comprises: a pair of side frame members provided on both left and right sides; and a connecting member extending in the left-right direction and connecting the pair of side frame members, wherein the side frame members comprise: a first side frame portion that forms an upper portion of the side frame members and extends in the up-down direction, a second side frame portion that extends downward and inward in the left-right direction from a lower end of the first side frame portion, and a third side frame portion that extends downward and forward in the left-right direction from the lower end of the second side frame portion.

2. A backrest as described in claim 1, wherein the connecting member has a first connecting portion that connects the upper ends of the first side frame portions together.

3. A backrest as described in claim 1 or 2, wherein the connecting member has a second connecting portion which connects the boundary portions between the second side frame portion and the third side frame portion of the pair of side frame members.

4. The backrest according to claim 3, wherein the second connecting portion has a thickness that gradually increases in the vertical direction from the rear to the front.

5. The backrest according to claim 3, wherein the connecting member comprises a third connecting portion that connects the lower ends of the third side frame portions together.

6. The backrest according to claim 5, wherein the third connecting portion comprises a base connecting portion that is connected to a base of the chair that supports the backrest.

7. A backrest as claimed in claim 1 or 2, wherein the third side frame portion is provided with an armrest mounting portion to which an armrest can be attached.

8. A backrest as claimed in claim 1 or 2, wherein the first side frame portion extends diagonally forward from the upper end to the lower end, and the second side frame portion extends diagonally backward from the upper end to the lower end.

9. A chair equipped with a backrest according to claim 1 or 2.

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