CHAIR

[0001] The present invention relates to a chair and, in particular, treats an office-use chair as a preferred object.

[0002] The first factor to be owned by a chair is comfort to a user. In particular, in a chair used in an office, a person continues sitting down for a long time and hence comfort is an important factor. There are some factors damaging comfort. Typically, such factors include a feeling of oppression caused by a situation that the portion hitting the body is hard and a feeling of tightness that the body cannot easily be moved. Thus, countermeasures are taken in order to reduce the feeling of oppression and the feeling of tightness.

[0003] The problem of the feeling of oppression is handled such that a cushion is arranged in the seat or the backrest, the seat or the backrest is constructed from a mesh, or the like. Adoption of a deformable structure in the seat plate or the backrest plate is also effective in improving softness.

[0004] On the other hand, in order that the feeling of tightness may be prevented or reduced, it is sufficient that the movement of the body in a state of sitting down is permitted. Imparting a rocking function to the chair is effective means for alleviating the feeling of tightness. Nevertheless, a simple rocking function alone has merely a limited effect in improving comfort. This is because a person takes various attitudes in a state of sitting down and hence the simple rocking function cannot follow the changes in the attitude of the person.

[0005] For example, it is usual that a seat occupant twists the body so as to turn aside. Nevertheless, in a case that the backrest has a rigid structure, when the person twists the body, the contact area with the backrest decreases so that the user receives a feeling of oppression and hence comfort is degraded.

[0006] Thus, designs have been performed for improving the follow-up property of the backrest for the movement of the body. As examples of these, as a structure that the backrest can be deformed by the body pressure of a seat occupant, Documents 1 to 4 describes a configuration that a backrest is supported by the back frame at three positions consisting of two right and left positions in the upper end part and of the right-left middle part of the lower end part.

[0007] In a case that the backrest is freely deformed by the body pressure of the seat occupant, the stability of the body is degraded and hence comfort is degraded on the contrary. That is, the backrest is required to have a function of firmly supporting the body. In particular, in a case that a person sits on the chair and performs various kinds of desk work, when the person slouches, the internal organs are pressed and hence an intense stress acts on the body. Thus, a high necessity is concluded that even in a non-rocking state, the body (especially, the lumbar) of the person is supported and held in a state that the back is straightened.

[0008] When the individual publicly known documents are viewed from the perspective of such a function of stably supporting the body, the backrest of the individual publicly known documents is supported at three positions consisting of two right and left positions at the upper end and of the right-left middle part of the lower end part. Thus, it is concluded that excessive deformation is avoided. Nevertheless, since the lower part of the backrest is easily deformed, a high function of firmly supporting the body in a non-rocking state and holding a state that the back is straightened is not expected. That is, in the individual publicly known documents, there is the possibility of an insufficient function of stably supporting the body in a non-rocking state.

[0009] Further, as a use mode of a chair, it is usual that in a rocking state, the body is twisted right or left or, alternatively, the shoulder is deviated right or left. In this case, the load is concentrated on the left side or the right side of the upper part of the backrest. Nevertheless, in the individual publicly known documents, the upper part of the backrest cannot easily be deformed. Thus, a high follow-up property for the attitude change of the body is not expected and hence, also in this perspective, there is room for improvement of comfort.

[0010] Further, in many cases, the backrest of a chair is provided with a back plate fabricated from resin. Then, as means for alleviating the feeling of oppression and improving the cushioning property and the fit property, a configuration is employed that the back plate has a flexible structure. For example, in Document 5, the applicant of the present application has disclosed that a large number of elongated grooves horizontally elongated in the right and left directions are provided in the back plate so that the body support part is constructed from the multi-stage band plate group. In this Document 5, in each band plate, in order that deformation may easily occur, a thin trimming groove is provided in the right and left end parts.

[0011] On the other hand, Document 6 discloses a back plate having a configuration similar to a honeycomb structure. Further, Document 7 discloses a backrest in which cross-shaped holes and straight-line-shaped holes are arranged regularly so that a structure similar to a mesh is formed.

[0012] In Documents 6 and 7, the body support part of the backrest is formed in a mesh structure. Then, a group of thin lines constituting the body support part are individually bent and hence the thin lines are allowed to perform extensional deformation in accordance with the body pressure. Thus, the entire body support part can be deformed such as to become concave rearward.

[0013] Here, the function of supporting the body achieved by the backrest is considered below. A high flexibility alone is not sufficient and the function of stably supporting the body is also important. For example, when there is a tendency that the body shakes in a rocking state, in some cases, comfort is degraded on the contrary.

[0014] Further, in a case that the seat occupant performs desk work like PC operation in a non-rocking state, when the lumbar is firmly supported, an appropriate attitude in which the back is straightened is maintained and hence this situation is preferable. In contrast, when the flexibility of the backrest is excessively high, the body cannot stably be supported.

[0015] Then, in Documents 6 and 7, a kind of mesh structure is employed and hence this structure is easily deformed in the entirety. Thus, although a high cushioning property is obtained, room for improvement in stably supporting the body is concluded. On the other hand, the band plate of Document 5 does not excessively perform extensional deformation and hence excels in the stability of supporting the body. Nevertheless, since there is a limit in the elongation of each band plate, room for improvement in the perspective of flexibility is concluded.

[0016] Patent Document 1: JP-A-2002-119366

[0017] Patent Document 2: JP-A-2004-129966

[0018] Patent Document 3: JP-A-2010-063831

[0019] Patent Document 4: U.S. Pat. No. 7,249,802

[0020] Patent Document 5: JP-A-2011-041615

[0021] Patent Document 6: Japanese Patent No. 4015673

[0022] Patent Document 7: U.S. Pat. No. 5,934,758

[0023] The invention of the present application has been devised in view of such present situations and is intended to provide a chair in which value in use has been enhanced and improvement has been achieved. Further, the present application includes a large number of improved configurations and hence to provide these may be an object.

[0024] Further, the invention of the present application has been devised in view of such present situations. An object thereof is to provide a more improved backrest.

[0025] The present application is constructed from a group of inventions having hierarchical and areal broadening. Then, typical modes thereof are identified as a first to a fifteenth invention.

[0026] Among these, the first invention constitutes a generic concept. The basic configuration thereof includes: a seat; a backrest; and a back frame having a rigid structure and arranged behind the backrest with an interval in between. Then, the backrest is attached to the back frame by a first support device arranged at a height position close to an upper end of the backrest and by a second support device arranged at a position lower than the first support device and higher than the seat surface. Further, the first support device is attached to a part close to a right-left middle part of the upper end part in the backrest.

[0027] Here, it is sufficient that the first support device is attached to the upper end of the backrest or a vicinity thereof. Thus, the backrest may run off over the first support device. That is, the attaching position of the first support device has a vertical width. The second support device is similar.

[0028] In the present invention, so to speak, the backrest is supported at three positions consisting of the right-left middle part of the upper end part and of two right and left positions thereunder. Then, in a case that the user sits down in a state of not leaning on the backrest in order to perform desk work like PC operation, the lumbar and the like can stably be supported by the portion supported at the two right and left positions within the backrest. Thus, the state that the back is straightened can appropriately be maintained and hence the user is allowed to take an appropriate working attitude.

[0029] On the other hand, the first support device is close to the right-left middle part of the backrest and hence the upper end part (or the upper part) of the backrest runs off to the outside in the right and left directions of the first support device so as to constitute free ends. That is, both right and left ends of the upper end part (the upper part) of the backrest serve as free ends not supported from the rear. Thus, when a configuration is employed that the upper part of the backrest can be deformed by the body pressure, the backrest can be deformed such as to follow the twist of the body in a state of leaning on the backrest. This contributes to improvement in comfort in a leaning-on state.

[0030] The second invention is an example of expansion of the first invention. In this invention, the first support device has such an elastic strength that, when the body pressure of a seat occupant acts on the backrest, permits warp deformation and thereby allows an upper part of the backrest to move and deviate rearward, whereas the second support device has such a rigidity that, even when the body pressure of a seat occupant acts, bending deformation does not substantially occur or, alternatively, although elastic deformation is caused by the body pressure of the seat occupant, the second support device has the elastic strength with which a magnitude of the elastic deformation of the second device is lower than that of the first support device.

[0031] In this second invention, the first support device has a spring property. Thus, in a state that a person leans on the backrest, the upper part of the backrest is allowed to move such as to approach the back frame. That is, a reaction force of the first support device acts on the upper part of the backrest from the rear and then this reaction force provides a cushion effect and, hence, comfort to the user. Further, the deformation in the first support device permits twist deformation in the backrest and hence also improves follow-up deformability in a case that the body is twisted in the right or left direction in a state that the person leans on the backrest.

[0032] Further, the second support device is hardly deformed by the body pressure of a seat occupant or, alternatively, even in a case that deformation occurs, the magnitude thereof is smaller than that in the first support device. Thus, the function of supporting the body in a leaning-on state is appropriately achieved. Further, when the lower part of the backrest is excessively deformed in a leaning-on state such as a rocking state, the stability of the body is degraded so that, in some cases, comfort is degraded on the contrary. However, in the second invention, even in a leaning-on state, the body is stably supported by the lower part of the backrest and hence excessive movement of the body is prevented so that comfort can be improved.

[0033] The third invention is an example of expansion of the first invention or the second invention. In this invention, the first support device is in an attitude elongated in up and down directions in side view, whereas the second support device is separated into two right and left parts and then the right and left second support devices are in such an inclined attitude that an interval of the right and left second support devices becomes wider as going to a nearer side in plan view.

[0034] In the present invention, the first support device and the second support device may employ various modes. However, when the third invention is employed, in both of the first support device and the second support device, the portion extending between the back frame and the backrest may be in a simple plate-shape configuration. This provides an advantage of simplified structure. Further, the first support device 12 is elongated in the up and down directions and hence can easily be deformed and bent rearward by the body pressure of a seat occupant. Thus, the follow-up property and the cushioning property against a change of the body can be improved.

[0035] The fourth invention is an example of expansion of the first invention or the second invention. In this invention, the back frame includes a pair of right and left vertically elongated members, these right and left vertically elongated members being inclined such that an interval becomes narrow as going upward, and upper ends being connected integrally through a linkage part, and the first support device is attached to the linkage part of the back frame and the second support device is attached to the right and left vertically elongated members. Here, the matter specific to the fourth invention may be applied also to the third invention.

[0036] For example, the back frame may be constructed from one member located in the right-left middle part of the backrest or, alternatively, may employ a configuration of inverted U-shape having a right and a left vertical part. However, when the configuration (the configuration of inverted V-shape) of the fourth invention is employed, an advantage is obtained that a high strength can be ensured by employing a simple configuration.

[0037] The fifth invention is an example of expansion of the first invention or the second invention. In this invention, the backrest includes a main member fabricated from resin and attached to the back frame, the main member includes a framework having a loop shape and constituting an outer periphery and a body support part located in an inner side thereof, and the body support part is provided with a large number of slits or holes so as to have such a strength that deformation is easily caused by the body pressure of a seat occupant. Here, the matter specific to the fifth invention may be applied also to the third invention or the fourth invention. The backrest may employ various configurations. However, in the fifth invention, the main member is composed of an integrally molded article. Thus, in comparison with a configuration that the framework and the body support part are constructed as separated members, the time and effort in manufacturing can be saved and variation in the quality can also be prevented.

[0038] Here, in the fifth invention, the body support part is provided at constant to the framework. However, as described above, a configuration may also be employed that the body support part is constructed from a flexible raw material such as a mesh material and then the flexible raw material is attached to the framework. In either case, it is preferable that the framework performs warp deformation in accordance with the body pressure of a seat occupant.

[0039] In the fifth invention, the backrest may be constructed from the main member alone and then the body pressure of the seat occupant may be received directly by the main member. In contrast, in the sixth invention serving as an example of expansion of the fifth invention, a cushion is arranged in the front face of the main member and then at least the cushion is covered by a skin material. In this configuration of the fifth invention, softness to the body can be ensured by the cushion.

[0040] The seventh invention also is an example of expansion of the fifth invention. In this invention, a lower end of the main member is located close to the seat surface, a lumbar support member for supporting the lumbar of a seat occupant is arranged on the front face or the rear face of the main member and, further, the main member is attached to the second support device at a position slightly higher than the lumbar support member. Here, the matter specific to the seventh invention may be applied also to the first to the fourth invention or the sixth invention.

[0041] When the lumbar support member is provided like in the seventh invention, the lumbar of the seat occupant can appropriately be supported. Thus, this can contribute to maintaining of an appropriate attitude by the seat occupant. Then, since the first support device is attached to the main member on the lumbar support member, this can avoid a situation that the width in the right and left directions of the main member becomes excessively large. Further, since the attaching part of the second support device and the attaching part of the lumbar support member are close to each other, the rigidity of the portion of the attaching part of the lumbar support member within the main member can also be improved and hence this can contribute to the further stability of the body of the user.

[0042] The eighth invention is an example of expansion of the first invention or the second invention. In this invention, when the body pressure of a seat occupant acts, the backrest is inclined rearward. The eighth invention is applied to a rocking chair. However, obviously, the eighth invention may be applied also to the third to the seventh invention. In rocking chairs, a configuration is widely employed that the seat is linked to the backrest. Obviously, the present invention may be applied also to such a chair of synchronous type.

[0043] Warp deformation in the backrest appears remarkably in a rocking state. Thus, the effect of the present invention is utilized especially under the eighth invention.

[0044] Among these, in a backrest of the ninth invention: a body support part on which a body pressure of a seat occupant acts is constructed from a plurality of areas divided into right and left with a certain amount of interval in between; each area is constructed from a large number of stays horizontally elongated in the right and left directions; the stays in adjacent areas are arranged in a manner of being deviated in the up and down directions; adjacent stays in adjacent areas are linked together by a linkage piece in an inclined attitude in front view; and thereby the inclined attitudes of linkage pieces adjacent in the up and down directions are opposite to each other.

[0045] In the ninth invention, each stay is in an attitude horizontally elongated in the right and left directions. Thus, basically, the body support part deforms such as to extend in the right and left directions alone. Thus, the configuration excels in the stability of supporting the body. That is, the deformation in the body support part has directivity and hence a situation is avoided that the body support part excessively follows the movement of the body so as to be deformed. Thus, the configuration excels in the stability of supporting the body.

[0046] Further, the linkage pieces are in an inclined attitude. Thus, when the attitudes of the linkage pieces vary so that the angle formed by linkage pieces adjacent in the up and down directions becomes small, the interval of stays adjacent in the right and left directions becomes wide. This realizes substantially the same state as a situation that the body support part has performed extensional deformation in the right and left directions. By virtue of this, a high cushioning property can be ensured. Further, each stay is deformed such as to be bent, twisted, or like. Thus, the configuration excels also in the fit property to the body.

[0047] In a backrest of the tenth invention, a group of stays are in a longitudinal orientation. That is, in the tenth invention: a body support part on which the body pressure of a seat occupant acts is constructed from a plurality of areas divided into up and down with a certain amount of interval in between; each area is constructed from a large number of stays elongated vertically; the stays in adjacent areas are arranged in a manner of being deviated in the right and left directions; adjacent stays in adjacent areas are linked together by a linkage piece in an inclined attitude in front view; and thereby the inclined attitudes of linkage pieces adjacent in the right and left directions are opposite to each other.

[0048] In the eleventh invention, the body support part easily performs extensional deformation in the right and left directions. However, basically, the same effect as that of the ninth invention is obtained.

[0049] The eleventh invention is a preferable example of expansion of the first invention or the second invention. In this invention, the width of the linkage piece is smaller than the width of the stay in front view. According to this configuration, in a state that the supporting area for the body is enlarged so that the stability of supporting the body is improved, deformation in the linkage pieces is made easy so that the cushion can be improved.

[0050] The twelfth invention is a detailed example of the ninth invention. In this invention, bases of linkage pieces adjacent in the up and down or the right and left directions are close to each other so that the linkage pieces adjacent in the up and down or the right and left directions are formed in a V-shape configuration.

[0051] The bases of linkage pieces adjacent in the up and down or the right and left directions may be separate from each other. Nevertheless, in this case, the number of linkage pieces is reduced so that a possibility arises that the strength is degraded. In contrast, in the configuration of the fourth invention, the linkage pieces are continuous to each other without a gap in between. Thus, the number of linkage pieces can be increased and hence the strength of the body support part also can be ensured.

[0052] The thirteenth invention is detailed and preferable implementation of the ninth invention. In this invention, the configuration includes: a center area located in a center in the right and left directions; and right and left side areas arranged on both right and left sides thereof, the center area being constructed from a group of center stays and the side area being constructed from side stays, wherein the group of linkage pieces for connecting together the group of center stays and the group of side stays is formed in a zigzag configuration.

[0053] The number of areas constructing the body support part can arbitrarily be set forth. Nevertheless, when an excessively large number of areas is employed, the number of linkage pieces also increases and hence a concern of excessively high flexibility is caused unless any means is taken. In contrast, like in the thirteenth invention, in a configuration constructed from one center area and two side areas, the stability of supporting the body and the cushioning property can be harmonized with each other in a satisfactory manner and hence this configuration is preferable.

[0054] The fourteenth invention is detailed and preferable implementation of the ninth invention. In this invention, in the portion of the lumbar support part for supporting a vicinity of the lumbar of a seat occupant, the density of stays is high. In this invention, the lumbar of the seat occupant is appropriately supported and hence this configuration is useful in improvement of the stability of the body of the user. Here, also in the tenth invention, it is preferable to employ means for improving the rigidity of the portion of the lumbar support part. In both the first invention and the second invention, as the means for improves the rigidity of the lumbar support part, different means from the fourteenth invention may be employed like the plate thickness of the stay is increased.

[0055] The fifteenth invention also is detailed and preferable implementation of the ninth invention. In this invention, each stay has a plate-shape configuration in which a plate thickness in the frontward and rearward directions is smaller than a vertical width, then a rib elongated in the right and left directions is formed in a rear face of each stay, and then the rib also is connected integrally to the linkage piece.

[0056] In this fifteenth invention, in a state that each stay is made as thin as possible, necessary bending strength can be ensured. Thus, this configuration is preferable for saving the material (the resin). Further, since the rib and the linkage piece are connected to each other, smooth deformation can be realized with avoiding a situation that bending is concentrated on the end part portion of the stay. Another advantage is also obtained that stress concentration is prevented and hence durability is improved. Here, the configuration that a rib is provided in the rear face of the stay may be applied also to the tenth invention.

[0057] By virtue of the present invention, comfort in a state of leaning on a chair is improved. Further, the strength of the chair can be ensured, the time and effort in manufacturing can be saved, and variation in the quality can be prevented.

[0069] Next, an embodiment of the present invention is described below with reference to the drawings. The present embodiment is applied to a swivel chair widely used in offices or the like. Here, in the embodiment and the claims given below, terms “frontward and rearward” and “right and left” are used for identifying the directions. Then, these directions are defined with reference to a person ordinarily sitting on the chair.

[0070] (1). Outlines of Chair

[0071] As shown in FIGS. 1A to 2B, a chair includes as main elements a leg device 1, a seat 2, and a backrest 3. The backrest 3 is attached to a back frame 4 arranged behind it. The leg device 1 includes: a leg pillar 5 in a vertical attitude; and a center tube 6 for supporting this. Five branched arms extend in radial directions from the center tube 6. Then, a caster is attached to the tip of each branched arm.

[0072] The leg pillar 5 is constructed from a gas cylinder of extendable type provided with an inner cylinder and an outer cylinder. As shown in FIG. 2B, a base 7 is attach to the upper end of the leg pillar 5 and then the back frame 4 is linked through a joint member 8 to the base 7 in a manner permitting rearward inclination. Here, the back frame 4 and the joint member 8 may be integrated together. The inner cylinder and the outer cylinder constituting the leg pillar 5 are freely rotatable relatively. Thus, the base 7 (and the seat 2 and the backrest 3) is freely rotatable horizontally.

[0073] Although illustration is omitted, a rocking spring for elastically supporting the rearward inclination of the back frame 4 is built in the base 7. In the seat 2, an intermediate member (not shown) provided in the base 7 is attached in a manner permitting rearward inclination and rearward movement about the front part serving as a center. The intermediate member and the joint member 8 are linked together in a manner permitting relative movement by a shaft horizontally elongated in the right and left directions. By virtue of this, the seat 2 performs rearward movement and rearward inclination in linkage with the rearward inclination of the backrest 3.

[0074] The backrest 3 includes a main member fabricated from a raw material of resin such as polypropylene by injection molding. In a case that the backrest 3 includes a cushion and a skin material, the backrest 3 and the main member need be distinguished from each other. However, in the present embodiment, the entirety of the backrest 3 is constructed from the main member and hence distinction of these does not provide a substantial advantage. Thus, for simplicity of description, the term “main member” is not used and the term “backrest 3” is used.

[0075] The backrest 3 is constructed from a framework 9 constituting the outer periphery and a body support part 10 located in the inside. As shown in FIG. 8, the framework 9 is formed in a shape substantially close to a quadrangle by: a pair of side members 9a constituting both right and left sides; an upper member 9b horizontally elongated in the right and left directions and constituting the upper end part; and a lower member 9c horizontally elongated in the right and left directions and constituting the lower end.

[0076] The lower end of the backrest 3 is located close to the seat surface. Within the backrest 3, a lumbar support member 11 for supporting the lumbar of a seat occupant is arranged in the front face at a height position corresponding to the lumbar of the seat occupant. The body height and the preference depend on the individual seat occupant. Thus, the lumbar support member 11 is in a height adjustable manner.

[0077] The backrest 3 of the present embodiment has such a constricted shape that the attaching part of the lumbar support member 11 is the narrowest. However, employable configurations need not be limited to this. That is, as the configuration of the backrest 3, an arbitrary shape may be employed like: a configuration that the width in the right and left directions is substantially fixed; the shape of an inverted trapezium in which the upper end is wide and the lower end is narrow; and the shape of an inverted trapezium in which the upper end is narrow and the lower end is wide.

[0078] For example, as shown in FIGS. 3A and 3B, the back frame 4 includes right and left vertically elongated members 4a inclined such that the interval between these becomes close as going upward. In the right and left vertically elongated members 4a, the upper ends are connected integrally through a linkage part 4b.

[0079] Thus, the right and left vertically elongated members 4a constitute a configuration of inverted V-shape. The lower ends of the right and left vertically elongated members 4a are connected integrally through a lower stay part 4c. Further, a frontward arm part 4d is provided integrally at the lower end of the right and left vertically elongated members 4a. The frontward arm part 4d and the lower stay part 4c are connected to the joint member 8 shown in FIG. 2A and 2B. For example, as clearly seen from FIG. 4B, the vertically elongated member 4a of the back frame 4 is formed in an L-shaped cross section having a back face plate and a side face plate. Thus, a light-weight structure is obtained that is strong in the frontward and rearward directions and the right and left directions as well as against twist.

[0080] In the back frame 4 of the present invention, a resin molded article or an aluminum die-cast article is employed. Instead, fabrication may be performed by employing a metal plate or a metallic pipe as the material. A composite article constructed from materials of different kinds may be employed. Further, an integral construction is not unavoidable. That is, for example, the right and left vertically elongated members 4a may be separately fabricated and then linked together at the upper ends, that is, may be constructed from a plurality of component parts. A shell-structured article also may be employed as the back frame 4.

[0081] Then, for example, as shown in FIGS. 3A and 3B, within the backrest 3, the right-left middle part of the upper member 9b is attached through a first support device 12 to the linkage part 4b of the upper end of the back frame 4. Then, in a part above the attaching part of the lumbar support member 11, the right and left side members 9a are attached through second support devices 13 to the vertically elongated member 4a of the back frame 4. This point is described below in detail.

[0082] (2). Attaching Structure of Backrest

[0083] As shown in FIGS. 4A and 4B, the first support device 12 includes two spring parts 12a arranged in a V-shape in front view. An upper attaching part 12b horizontally elongated in the right and left directions is connected integrally to the upper ends of the spring parts 12a. Then, a lower attaching part 12c protruding rearward is connected integrally to the lower ends of the right and left spring plate parts 12a. The first support device 12 is fabricated from a raw material of resin such as polypropylene by injection molding. The spring plate parts 12a are in an attitude elongated in the up and down directions, however, has a plate shape which is wide in front view and narrow in side view. Thus, bending deformation can easily be caused by a force from the front.

[0084] The lower attaching part 12c is formed in the shape of a block (the shape of a boss) horizontally elongated in the right and left directions. A rear-side first recess 15 serving as a frontward aperture into which the lower attaching part 12c is fitted is formed in the linkage part 4b of the back frame 4. The lower attaching part 12c is fixed with a first bolt 16 inserted into a rear-side first recess 15 from below. As shown in FIG. 4A, in the attaching part 12c of the first support device 12, a nut insertion hole 17 into which a nut for the first bolt 16 is set is opened rearward.

[0085] As shown in FIGS. 5A and 5B, the upper member 9b of the backrest 3 has a triple structure in the inside and outside having an outer wall, an inner wall 18, and an intermediate wall 19. Thus, two elongated grooves 20 opened rearward are formed. Then, the right-left middle part of the inner wall 19 is, for example, cut off so that a front-side first recess 21 into which the upper attaching part 12b of the first support device 12 is fitted is formed. The upper attaching part 12b of the first support device 12 is fixed to the upper member 9b with a second bolt 22 inserted from below.

[0086] A nut holding part 23 opened rearward is formed in the upper member 9b of the backrest 3. On the other hand, in the upper attaching part 12b of the first support device 12, a stopper piece 24 for abutting against the nut holding part 23 of the upper member 9b from the rear is provided such as to protrude upward.

[0087] The second support device 13 is fabricated from a raw material of resin such as nylon resin having a high rigidity. Then, as shown in FIGS. 5B and 5C, the second support device 13 includes an arm part 13a having a band plate shape gradually bent into a wave shape in plan view. At the rear end of the arm part 13a, a rear boss part 13b is provided integrally. Then, at the front end of the arm part 13a, a front boss part 13c is provided integrally. The arm part 13a has such a rigidity that deformation is not easily caused by the body pressure of the sitting person (however, slight deformation may occur).

[0088] The rear boss part 13b is fitted into the rear-side second recess 25 provided in the vertically elongated member 4a of the back frame 4. A third bolt 26 is inserted into the rear-side second recess 25 from below. A nut (not shown) into which the third bolt 26 is inserted is incorporated in the rear boss part 13b of the second support device 13. A flange 13d overlapping with the opening edge of the rear-side second recess 25 is provided in the rear boss part 13b.

[0089] As clearly shown in FIGS. 6A and 6B, a front-side second recess 27 into which a front boss 13c of the second support device 13 is fitted is formed in the side member 9a of the backrest 3. The front-side second recess 27 has a substantially box-shaped external appearance and then a bolt hole 28 through which a bolt (not shown) is inserted is opened in the inner wall 27a. On the other hand, a nut attaching groove 29 is provided in the front boss part 13c of the second support device 13. Then, a bolt is inserted into the nut arranged in the nut attaching groove 29.

[0090] In this case, a step part 30 for increasing the thickness of the portion of the bolt hole 28 so as to enhancing the strength is formed in an inner plate 25a of the front-side second recess 27. On the other hand, a cut-off part 31 overlapping with the step part 30 of the front-side second recess 27 is formed in the front boss part 13c of the second support device 13. Further, a flange 13e overlapping with the opening edge of the front-side second recess 27 is provided in the front boss part 13c of the second support device 13.

[0091] (3). Lumbar Support Member

[0092] Next, the lumbar support member 11 is described below mainly with reference to FIGS. 7A to 7C. The lumbar support member 11 is composed of a molded article fabricated from a raw material of resin and formed from a raw material such as polypropylene having certain elasticity. Then, the lumbar support member 11 has a shape horizontally elongated in the right and left directions and crossing the backrest 3. In plan view, the lumbar support member 11 is gradually curved concave frontward. Further, in vertical sectional side view, the lumbar support member 11 is slightly curved convex frontward.

[0093] Slide boss members 34 having a prism shape and protruding rearward are formed integrally at both right and left ends of the lumbar support member 11. The slide boss member 34 is fitted, in a freely slidable manner, into a guide frame part 35 elongated in the up and down directions provided in the side member 9a of the backrest 3. As shown in FIGS. 6A and 6B, the inner periphery of the guide frame part 35 is constructed from a plate part and then the front-side second recess 27 described above is connected integrally to the upper end of the guide frame part 35.

[0094] As shown in FIGS. 7A to 7C, a frontward protruding part 36a having a block shape and provided in a knob 36 is fitted into the rear end of the slide boss member 34. The frontward protruding part 36a of the knob 36 is fixed to the slide boss member 34 with a bolt (not shown). A nut insertion groove 37 is provided in the slide boss member 34. The lumbar support member 11 can be held in a manner that the height is adjusted stepwise. Then, as shown in FIG. 6A, as height adjusting means, a large number of stopper holes 38 are provided at a large number of vertical stages in the inner plate of the guide frame part 35.

[0095] Then, a configuration is widely employed that a lumbar support member is provided in the backrest. However, in general, in many cases, the lumbar support member is arranged on the back side of a cushion or on the back side of a mesh material. Nevertheless, in a case that the cushion or the mesh material intervenes between the lumbar support member and the body, in some cases, a person who desires a strong “feeling of abutting” feels unsatisfaction. Further, in some cases like a case that the backrests is not provided with a cushion or a mesh, a lumbar support member need be arranged on the near side of the back plate.

[0096] As an example of this, JP-A-2008-237333 discloses an approach that in a configuration that a backrest is constructed from a frame part and a back plate located in the inner side thereof and then a large number of slits are provided in the back plate, a lumbar support member is arranged on the near side of the back plate. Further, this document discloses a configuration that handles of clip type fitted onto a frame part from the outer side are provided integrally in both right and left end parts of the lumbar support member and then the frame part is elastically held by the handles from below.

[0097] Nevertheless, in the configuration that the handles are fitted onto the frame part from outside like in the above-mentioned prior-art patent document, the handles run off to the right and left outer sides of the frame part and hence a trouble is expected that a person's clothes are caught in the handle or, alternatively, an object abuts against the handle so that the handle is damaged. Further, the handles maintain the height merely by friction and hence a possibility arises that the lumbar support member is slid such as to be raised or lowered by the body pressure of the seat occupant.

[0098] In contrast, in the present embodiment, the slide bosses 34 provided in both right and left end parts of the lumbar support member 11 penetrate the guide frame parts 35 of the framework 9. Thus, the knobs 36 can be arranged such as not to run off the right and left outer sides of the framework 9. By virtue of this, a situation that the clothes are caught in the knob 36 or, alternatively, an object abuts against it can be avoided or, alternatively, suppressed remarkably. Further, it is also easy to provide height holding means constructed from the stopper holes 38 for height adjustment of the guide frame part 35. Thus, the lumbar support member 11 can be held at a desired height in a manner not permitting deviation movement.

[0099] Here, the height adjusting means may employ various configurations. In a case that the stopper holes 38 are provided in the guide frame part 35 like in the embodiment, it is sufficient that an elastic member fitted into and detached from the guide frame part 35 is provided in the block-shaped frontward protruding part of the knob 36. The guide frame part 35 has a certain amount of frontward and rearward width and hence strength degradation is not caused by the penetration of the slide boss member 34. The knob 36 may be fabricated in a simple plate shape and then may be screwed to the slide boss member 34.

[0100] (4). Structure of Backrest

[0101] Next, within the backrest 3, details of the structure of the body support part 10 are described below mainly with reference to FIGS. 8 to 10. As shown in FIG. 8, in the present embodiment, the body support part 10 includes: groups of horizontally elongated side stays 40 connected to the right and left side members 9a; and a group of horizontally elongated center stays 41 located between the groups of side stays 40. Both groups of stays 40 and 41 are arranged in a state of being deviated up and down. The center area is constructed from the group of center stays 41 and the side areas are constructed from the groups of side stays 40.

[0102] Then, both right and left ends of the center stays 41 and the tips of the side stays 40 adjacent in the right and left directions are connected integrally with linkage pieces (joint stays) 42. In this case, there are slight gaps in the right and left directions between the tips of the side stays 40 and the ends of the center stays 41. Thus, the linkage pieces (the joint stays) 42 are in an inclined attitude in front view. Further, the center stays 41 and the side stays 40 are arranged in a manner of being deviated up and down and hence linkage pieces (joint stays) 42 adjacent in the up and down directions are in attitudes of opposite orientation. Further, the bases of linkage pieces (the joint stays) 42 and stays 40 and 41 adjacent in the up and down directions are connected integrally. Thus, the groups of linkage pieces (joint stays) 42 have a zigzag shape in front view.

[0103] The backrest 3 is constricted such that the portion close to the lower side becomes narrow in front view. Thus, together with the side members 9a of the backrest 3, a shape curved concave outward is formed. Further, the linkage pieces (the joint stays) 42 also are curved concave outward in front view such as to follow the shape of the side members 9a. Further, the side member 9a and the center stay 41 have substantially the same length in the right and left directions.

[0104] The side stay 40 and the center stay 41 have a plate-shaped structure whose front and rear faces are wide. However, as shown in FIG. 10, a rib 43 is provided integrally in the rear faces of the side stay 40 and the center stay 41. Thus, the cross sections of the side stay 40 and the center stay 41 have a sideways T-shape. The rear face of the rib 43 is in plane with the rear face of the linkage piece (the joint stay) 42. The linkage piece (the joint stay) 42 has an external appearance of a thin band plate and hence can easily be deformed such that the angle of the sideways V becomes wide or narrow. That is, in the lumbar support member 111, the density of stays 140 and 141 is high. By virtue of this, the lumbar support part has a higher rigidity than the other parts.

[0105] The groups of side stays 40 and center stays 41 are arranged at a large number of vertical stages. Thus, a space 44 horizontally elongated in the right and left directions is opened individually between side stays 40 and between center stays 41 adjacent in the up and down directions. Then, in the present embodiment, except for the lumbar support part, the vertical width dimension of the space 44 is twice or the like of the vertical width of the stay 40 or 41. In the lumbar support part, the vertical width dimension of the space 44 is set substantially at the same level as the vertical width of the stay 40 or 41. Thus, the lumbar support part has a higher rigidity.

[0106] From the first, the vertical width and the pitch (the density) of the side stay 40 and the center stay 41 may be set up arbitrarily. For example, the vertical width dimension of the stay 40 or 41 and the space 44 may be set substantially at the same level over the entirety in the up and down directions. Alternatively, the vertical width dimension of the stay 40 or 41 may be set smaller than the vertical width dimension of the space 44 over the entirety.

[0107] Further, in the present embodiment, the body support part 10 has been constructed from two rows of the side stays 40 and one row of the center stays 41. However, employable configurations need not be limited to this. That is, the center stays 41 may be not provided and then the body support part 10 may be constructed from right and left side stays 40 and from one linkage piece (one joint stay) 42 for connecting these. Alternatively, the body support part 10 may be constructed from two rows of the side stays 40 and two rows of intermediate stays located between them. In a case that two rows of the intermediate stays are provided, three linkage pieces (three joint stays) 42 are necessary. Further, the body support part 10 may be constructed from five rows of stay groups consisting of two rows of the side stays 40, one row of the center stays 41, and two rows of the intermediate stays. Further, the backrest 3 may employ other configurations.

[0108] (5). Summary

[0109] Next, the operation is described below with reference to FIG. 11. First, a rocking state is described below.

[0110] For example, the body pressure of a seat occupant in a rocking state acts on the backrest 3 from the front as indicated by an arrow F. Then, the load acting on the backrest 3 is supported by the first support device 12 and the second support device 13. Then, as indicated by an arrow Y, the first support device 12 can perform bending deformation such that the upper end is moved rearward by the load from the front in side view. On the other hand, as indicated by an arrow X, the second support device 13 can perform bending deformation such that the tip is moved rearward in plan view. However, since the second support device 13 has a high rigidity, the back frame 4 of the backrest 3 is firmly held by the second support device 13 and hence the lumbar of the seat occupant is held with satisfactory stability.

[0111] On the other hand, the moment by rocking acts largely on the upper end part in the backrest 3. However, the first support device 12 has a lower rigidity than the second support device 13 and hence easily performs warp deformation in accordance with the body pressure. Thus, at the time of rocking, the backrest 3 can perform warp deformation such that the upper end part thereof approaches the upper end part of the back frame 4. This warp deformation of the backrest 3 can improve the cushioning property at the time of rocking.

[0112] Further, in a rocking state, when the person twists the upper half body in the right or left direction or, alternatively, shifts the shoulder in the right or left direction, the two right and left spring parts 12a constituting the first support device 12 perform bending deformation unevenly so that the backrest 3 can be deformed and twisted such as to follow the twist or the shift of the body. Thus, the backrest 3 can follow the change of the attitude of the body. As a result, comfort can be improved.

[0113] As clearly seen from FIG. 11, the backrest 3 is gradually curved concave frontward in plan view. The degree of the curve is largest in the vicinity of the lumbar support member 11 and then the upper end part is in an almost flat state. Thus, in a state that the lumbar is held such as not to be deviated right or left, the shoulder (or the portion close to the shoulder) can easily be shifted right and left. Also from this point, high comfort can be obtained.

[0114] As shown in FIG. 2B, in a neutral state that the seat occupant does not lean on the backrest 3, the backrest 3 is slightly in a rearward inclined attitude and the lumbar support member 11 is located on the most front side. Then, when the user performs desk work such as PC operation, the user takes an attitude that the lumbar abuts against the lumbar support member 11 of the backrest 3. However, since the second support device 13 has a high rigidity, the backrest 3 does not perform warp deformation in association with the body pressure of the seat occupant in a neutral state and hence the lumbar of the person is supported by the backrest 3 with satisfactory stability. Thus, the upper half body of the user does not become unsteady and is held in a preferable attitude that the back is straightened. Thus, the present configuration excels also in the attitude maintaining function in a neutral state (a non-rocking state).

[0115] Since the side stays 40 and the center stays 41 are deviated up and down and the linkage pieces (the joint stays) 42 are in a zigzag configuration, the backrest 3 of the present embodiment can perform warp deformation such that the body support part 10 swells rearward in accordance with the body pressure of the seat occupant. Thus, the present configuration excels in the fit property to the body of the user and excels also in the follow-up property for the movement of the body.

[0116] Further, when the linkage pieces (the joint stays) 42 adjacent in the up and down directions are deformed such that the mutual opening angle (the angle of V) becomes small, a tendency arises that the center stays 41 are deviated rearward. As a result, the body support part 10 is deformed such as to swell rearward. This improves the cushioning and the fit property to the body of the user.

[0117] The present application is based on U.S. Provisional Application for Patent (61/831,763) filed on Jun. 6, 2013, the contents of which are incorporated herein by reference.

[0118] The present invention can provide a chair in which comfort in a leaning-on state is improved. Further, a chair can be provided in which the strength can be ensured, the time and effort in manufacturing can be saved, and variation in the quality can be prevented.

• [0119] 1 Leg device
• [0120] 2 Seat
• [0121] 3 Backrest
• [0122] 4 Back frame
• [0123] 5 Leg pillar
• [0124] 6 Center tube
• [0125] 7 Base
• [0126] 8 Joint member
• [0127] 9 Framework
• [0128] 9a Side member
• [0129] 9b Upper member
• [0130] 9c Lower member
• [0131] 10 Body support part
• [0132] 11 Lumbar support member
• [0133] 12 First support device
• [0134] 12a Spring part
• [0135] 12b Upper attaching part
• [0136] 12c Lower attaching part
• [0137] 13 Second support device
• [0138] 13a Arm part
• [0139] 13b Rear boss part
• [0140] 13c Front boss part
• [0141] 13e Flange
• [0142] 15 Rear-side first recess
• [0143] 16 First bolt
• [0144] 18 Inner wall
• [0145] 19 Intermediate wall
• [0146] 22 Second bolt
• [0147] 23 Nut holding part
• [0148] 24 Stopper piece
• [0149] 25 Rear-side second recess
• [0150] 25a Inner plate
• [0151] 26 Third bolt
• [0152] 27 Front-side second recess
• [0153] 28 Bolt hole
• [0154] 29 Nut attaching groove
• [0155] 30 Step part
• [0156] 31 Cut-off part
• [0157] 34 Slide boss member
• [0158] 35 Guide frame part
• [0159] 36 Knob
• [0160] 36a Frontward protruding part
• [0161] 37 Nut insertion groove
• [0162] 38 Stopper hole
• [0163] 40 Side stay
• [0164] 41 Center stay
• [0165] 42 Linkage piece
• [0166] 43 Rib
• [0167] 44 Space