TECHNICAL FIELD
[0001] The present invention relates to a chair having a backrest which can be tilted back
as a back support post for supporting the backrest tilts back.
BACKGROUND TECHNIQUE
[0002] Conventionally, as a chair having a backrest which can be tilted back as a back support
post for supporting the backrest tilts back, there is a known chair in which a lower
end portion of the back support post is pivoted on a support base portion and a resilient
body such as a coil spring for generating a reaction force as the back support post
tilts back is provided between the back support post and the support base portion
(see Patent Document 1 described below, for example).
[0003] The Patent document 1 discloses a structure in which the support base portion is
formed in a substantially box shape open upward and having a bottom wall portion and
rising side wall portions rising from opposite side edges of the bottom wall portion,
the back support post has a pair of left and right back support post main bodies disposed
on an inner side of opposite side faces (the rising side wall portions) of the support
base portion and a connecting shaft housed in the support base portion to connect
lower end portions of the pair of back support post main bodies, and the connecting
shaft moves in the support base portion to bias the coil spring in such a direction
as to accumulate resilience when the back support post is tilted back.
Patent Document 1: Japanese Patent Application Laid-Open No. 2006-181101 (see FIG. 3)
DISCLOSURE OF THE INVENTION
PROBLEMS TO BE SOLVED BY THE INVENTION
[0004] However, the pair of left and right back support post main bodies is disposed on
the inner side of the opposite side faces of the support base portion in the prior-art
chair described above and therefore a depth of an inside of the support base portion,
i.e., a height of the support base portion needs to be increased in order to secure
a space for rotating movements of the lower end portions of the back support post
main bodies and the connecting shaft in the support base portion and it is difficult
to make the support base portion thin. Moreover, because the pair of left and right
back support post main bodies is disposed on the inner side of the opposite side faces
of the support base portion, portions of the back support post main bodies protruding
from the support base portion need to be formed in such shapes as to escape from the
support base portion in order to avoid interference of the portions of the back support
post main bodies protruding from the support base portion with the support base portion
in the backward tilting operation of the back support post, which reduces a degree
of freedom in design and confines the portions to simple shapes. Furthermore, because
the pair of back support post main bodies are merely connected by the connecting shaft
and the back support post itself is not really a structure with high rigidity, the
back support post does not contribute much to increase in mounting strength in a state
in which the back support post is mounted to the support base portion.
[0005] The present invention has been made while focusing on such problems and it is a main
obj ect to provide a chair having a backrest which can be tilted back as a back support
post for supporting the backrest tilts back, in which a support base portion can be
made thin without impairing a function of generating a reaction force at all in tilting
back the back support post, strength of mounting of the back support post and the
support base portion to each other can be increased, and a structure of the back support
post can be simplified.
APPROACH FOR SOLVING THE PROBLEMS
[0006] In other words, a chair according to the present invention includes: a back support
post for supporting a backrest and capable of tilting back; a support base portion
on which a lower end portion or a portion near the lower end portion of the back support
post is pivoted; and a resilient body disposed between the back support post and the
support base portion to generate a reaction force as the back support post tilts back,
wherein the back support post includes a pair of left and right back support post
main bodies disposed on outer sides of opposite side faces of the support base portion
and a rigid connection shaft rigidly connecting lower end portions of the pair of
back support post main bodies to bias the resilient body in such a direction as to
accumulate resilience in tilting back of the back support post and the rigid connection
shaft is disposed below a lower face of the support base portion.
[0007] With this structure, the lower end portions of the pair of back support post main
bodies are rigidly connected by the rigid connection shaft and therefore at least
the portions near the lower end portions of the back support post become structures
having high rigidity and the back support post greatly contributes to increase of
the mounting strength in the state in which the back support post is mounted to the
support base portion. Moreover, because the pair of left and right back support post
main bodies are disposed on the outer sides of the opposite side faces of the support
base portion and the rigid connection shaft is disposed below the lower face of the
support base portion, it is unnecessary to sufficiently increase a depth of an inside
of the support base portion, i.e., a height of the support base portion to secure
a space for rotating movements of the lower end portions of the back support post
main bodies and the rigid connection shaft in the support base portion as in the prior
art and the support base portion can be made thin. Furthermore, because the pair of
left and right back support post main bodies are disposed on the outer sides of the
opposite side faces of the support base portion, portions of the back support post
main bodies protruding from the support base portion do not need to be formed in such
shapes as to avoid interference with the support base portion in the backward tilting
operation of the back support post as in the prior art, no unnecessary limitation
is imposed on a degree of freedom in design of the back support post main bodies,
and the back support post main bodies can be formed in simple shapes. Moreover, because
the rigid connection shaft of the back support post biases the resilient body in such
a direction as to accumulate the resilience, it is unnecessary to employ a separate
special biasing member and it is possible to simplify the structure of the back support
post.
[0008] Especially, if the support base portion is formed in the substantially box shape
open downward and the back support post can be fitted with the support base portion
from behind and, as a result, the back support post can be mounted to the support
base portion while sandwiching the support base portion between the pair of left and
right back support post main bodies from opposite sides, it is possible to smoothly
mount the back support post to the support base portion. Moreover, because the box-shaped
support base portion having high rigidity is sandwiched between the pair of back support
post main bodies from opposite sides, the mounting strength is increased and deformation
of the back support post main bodies due to an external force can be prevented by
existence of the support base portion between the back support post main bodies even
if the external force acts in such a direction as to narrow an interval between the
back support post main bodies.
[0009] As a preferable example, the support base portion may include the upper wall portion
and the pair of hanging side wall portions hanging from the opposite side edge portions
of the upper wall portion and house at least one end portion of the resilient body
disposed so that the direction of accumulating the resilience is inclined a predetermined
angle with respect to a vertical direction in the housing space surrounded with the
respective wall portions and open downward and the other end portion of the resilient
body may be supported on the rigid connection shaft disposed below the lower face
of the support base portion. If the support base portion has the housing space open
downward in this manner, a portion of the resilient body disposed in a diagonal attitude
may protrude downward from the housing space and the shape and dimensions of the resilient
body can be changed appropriately according to specifications and the like.
EFFECTS OF THE INVENTION
[0010] As described above, according to the invention, it is possible to provide the chair
having the backrest which can be tilted back as the back support post for supporting
the backrest tilts back, in which the support base portion can be made thin without
impairing the function of generating the reaction force at all in tilting back the
back support post, strength of mounting of the back support post and the support base
portion to each other can be increased, and the structure of the back support post
can be simplified.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011]
[FIG. 1] A general view from a diagonally front side of a chair according to an embodiment
of the present invention.
[FIG. 2] A general view from a diagonally back side of the chair according to the
embodiment.
[FIG. 3] A side view of the chair in a normal state in the embodiment.
[FIG. 4] A back view of the chair in the normal state in the embodiment.
[FIG. 5] An operation explanatory view showing FIG. 3 while omitting part of it.
[FIG. 6] A view from a direction of an arrow X in FIG. 5.
[FIG. 7] A vertical sectional view schematically showing part of FIG. 5, i.e., only
a back shell and taken at a center in a lateral width direction.
[FIG. 8] A drawing schematically showing a manner in which the back shell and a back
support post are mounted to each other in an area Y in FIG. 5.
[FIG. 9] A drawing showing the chair in a synchronous rocking state in the embodiment
and corresponding to FIG. 3.
[FIG. 10] A drawing showing the chair in the synchronous rocking state in the embodiment
and corresponding to FIG. 5.
[FIG. 11] A drawing showing the chair in a back tilt state in the embodiment and corresponding
to FIG. 3.
[FIG. 12] A drawing showing the chair in the back tilt state in the embodiment and
corresponding to FIG. 5.
[FIG. 13] Drawings schematically showing a variation of a slide engagement mechanism
in the embodiment and corresponding to FIGS. 5 and 12.
[0012]
1 ... chair
3 ... support base portion
31 ... upper wall portion
32 ... hanging side wall portion
6 ... back support post
62 ... lower back frame
621 ... back support post main body (lower back frame main body)
622...rigid connection shaft
7...backrest
911...resilient body (coil spring)
BEST MODE FOR CARRYING OUT THE INVENTION
[0013] An embodiment of the present invention will be described below with reference to
the drawings.
[0014] As shown in FIGS. 1 to 5, a chair 1 according to the present embodiment is what is
called a rotary chair including a leg 2, a support base portion 3 mounted on an upper
end side of the leg 2 to be able to turn horizontally, a seat receiver 4 supported
at its front portion on the support base portion 3, a seat 5 mounted on the seat receiver
4, a back support post 6 pivoted at its lower end portion on the support base portion
3 and supporting a back portion of the seat receiver 4, and a backrest 7 mounted to
the back support post 6.
[0015] The leg 2 is made up of a plurality of (five in the example in the drawings) leg
blades 21 each having a caster at a tip end thereof and a leg stay 22 rising from
a portion where base end portions of the respective leg blades 21 gather.
[0016] As shown in FIG. 6, which shows a state viewed from a direction of an arrow X in
FIG. 5, the support base portion 3 is a member made of metal, for example, and including
an upper wall portion 31, a pair of hanging side wall portions 32 respectively hanging
integrally from opposite side edges of the upper wall portion 31 by bending, and a
pair of partition walls 33 and 34 provided between front end portions of the pair
of hanging side wall portions 32 and serving as reinforcing ribs and the support base
portion 3 is supported on the leg stay 22 by mounting an upper end portion of the
leg stay 22 to a rear end portion of the upper wall portion 31. The partition wall
33 on a relatively back side out of the pair of partition walls 33 and 34 is provided
with a retainer guide portion 33a formed in a wall thickness direction to guide a
retainer 912b inserted through the retainer guide portion 33a for moving forward and
backward in a compressive forward/backward moving direction of a coil spring 911 described
later. A first support shaft X1 for axially supporting the back support post 6 for
turning is laterally supported like a bridge between portions of the support base
portion 3 slightly displaced backward from substantially central portions of the left
and right hanging side wall portions 32. Furthermore, elongated holes 32a for supporting
a front frame (not shown) of the seat receiver 4 (described later) are respectively
formed in a wall thickness direction at front end portions of the left and right hanging
side wall portions 32. The support base portion 3 is covered with a support base portion
cover body 3c from below so that it cannot be seen directly from outside (see FIG.
3).
[0017] The seat receiver 4 is located above the support base portion 3 and supported on
the support base portion 3 with the rod-shaped front frame (not shown) provide at
a front end portion of the seat receiver 4 inserted through the elongated holes 32a
of the support base portion 3. The chair 1 in the embodiment has armrests 8 respectively
extending upward from portions near left and right opposite side edge portions of
the seat receiver 4. Although the armrests 8 shown in FIG. 1 and the like are not
height-adjustable, it is possible to employ height-adjustable armrests in place of
the armrests 8. Alternatively, the chair may not have armrests.
[0018] The seat 5 includes a seat shell 51 performing a function as a structural member
for uniformly supporting a load applied on the seat 5, a seat cushion (not shown)
provided above the seat shell 51, and a seat cushion cover 52 covering the seat cushion.
[0019] The backrest 7 includes a back shell 71 serving as a structural member for uniformly
supporting a load applied on the backrest 7 and supported on the back support post
6, a back cushion (not shown) provided in front of the back shell 71, and a back cushion
cover 72 covering the back cushion.
[0020] The back shell 71 is mainly made up of an elastic plate-shaped body made of resin
and has a three-dimensional shape with an upper portion and a lower portion protruding
further backward than its central portion in a height direction and left and right
opposite side edge portions protruding further forward than its central portion in
the lateral width direction. An area of the back shell 71 above a lumbar support portion
71L capable of supporting a lumbar part of a seated person and more specifically an
area of the back shell 71 above its central portion in the height direction is provided
with a large number of apertures 711 so that an aperture ratio which is a ratio of
the apertures 711 to a predetermined area of the back shell 71 gradually increases
toward an upper edge portion and the opposite side edge portions of the back shell
71. In the following description, the whole area provided with the apertures 711 out
of the back shell 71 will be referred to as "a back shell upper portion 71T". In other
words, as shown in FIG. 4 and the like, the back shell 71 integrally includes the
back shell upper portion 71T, a back shell central portion 71S which is the central
portion of the back shell 71 in the height direction, the lumbar support portion 71L
positioned slightly below the back shell central portion 71S, and a back shell lower
portion 71U which is an area below the lumbar support portion 71L. The back shell
central portion 71S, the lumbar support portion 71L, and the back shell lower portion
71U have the same curvature of curved faces in a plan view and the curvature is set
to a magnitude greater than a curvature of a curved face of the back shell upper portion
71T in the plan view. As shown in FIG. 7 (which is a vertical sectional view corresponding
to FIG. 5, schematically showing only the back shell 71, and taken at the center in
the lateral width direction), the back shell central portion 715, the lumbar support
portion 71L, and the back shell lower portion 71U having the relatively greater curvature
are curved and arched to be continuous with each other while the back shell upper
portion 71T having the relatively smaller curvature is in a substantially straight
shape along the height direction. The back shell central portion 71S and the back
shell upper portion 71T are continuous with each other at a discontinuous line 712
as a border therebetween.
[0021] The lumbar support portion 71L of the back shell 71 is provided with a deformation
trigger means 713 which is more likely to be deformed than portions of the lumbar
support portion 71L around it. In the embodiment, slits 713a extending in the lateral
width direction are employed as the deformation trigger means 713. A single slit 713a
or a plurality of slits 713a may be provided and the pair of upper and lower slits
713a with a predetermined interval therebetween in the height direction is provided
in the embodiment.
[0022] As shown in FIG. 8 (which is a drawing schematically showing a state before mounting
of the back shell upper portion 71T to the back support post 6 in order to show a
manner of mounting of the back shell 71 and the back support post 6 to each other
in an area Y in FIG. 5), the back shell upper portion 71T is integrally or substantially
integrally provided with an engagement portion 714 protruding backward and capable
of being engaged in a slide engagement hole 611 formed in an upper end portion of
an upper back frame 61 (described later). In FIG. 8, the apertures 711 in the back
shell upper portion 71T are not shown. The engagement portion 714 is substantially
in a block shape and integrally has a flange portion 714a at a tip end portion (an
end portion on a side away from a back face of the back shell 71).
[0023] As shown in FIG. 5 and the like, the back shell lower portion 71.U is integrally
or substantially integrally provided with supported portions 715 protruding backward
and supported on an upper end portion of a lower frame (described later). In the embodiment,
the pair of left and right thin plate-shaped supported portions 715 is provided at
a lower end portion of the back shell lower portion 71U, i.e., a lower end portion
of the back shell 71.
[0024] As shown in FIG. 5 and the like, the back support post 6 for supporting the back
shell 71 includes the upper back frame 61 for supporting a portion of the back shell
71 above the lumbar support portion 71L supporting the lumbar part of the seated person
and specifically the back shell upper portion 71T and a lower back frame 62 for supporting
the back shell lower portion 71U. A pivot point (a third support shaft X3 that will
be described later) between the upper back frame 61 and the lower back frame 62 is
set behind a lower end portion of the back shell 71 so that the upper back frame 61
can tilt about the pivot point with respect to the lower back frame 62 (tilting operation).
As shown in FIG. 2, the upper back frame 61 and the lower back frame 62 are covered
with an upper back frame cover body 61c and a lower back frame cover body 62c from
behind and below, respectively, and cannot be directly seen from outside.
[0025] As shown in FIGS. 5, 6, and the like, the lower back frame 62 includes a pair of
left and right lower back frame main bodies 621 (corresponding to "the back support
post main bodies" in the invention) disposed on outer sides of opposite side faces
of the support base portion 3 and a rigid connection shaft 622 for rigidly connecting
lower end portions of the pair of lower back frame main bodies 621 and disposed below
a lower face of the support base portion 3.
[0026] The respective lower back frame main bodies 621 are substantially in plate shapes
and are in shapes, in a side view, gradually extending diagonally backward from their
lower end portions toward their portions near their upper end portions and bent diagonally
forward at their portions near their upper end portions.
[0027] The rigid connection shaft 622 is in a rod shape and is laid and fixed like a bridge
between the lower end portions of the lower back frame main bodies 621 by appropriate
means such as welding so that it cannot be detached.
[0028] To mount the lower back frame 62 to the support base portion 3, the pair of left
and right lower back frame main bodies 621 is brought from behind close to the support
base portion 3 in such a manner as to sandwich the support base portion 3 between
the portions near the lower end portions of the respective lower back frame main bodies
621 after rigidly connecting the lower back frame main bodies 621 by the rigid connection
shaft 622 and the first support shaft X1 is inserted through insertion holes 621a
formed at the portions near the lower end portions of the respective lower back frame
main bodies 621 and through holes (not shown) formed at the opposite hanging side
wall portions 32 of the support base portion 3 after making the insertion holes communicating
with each other. In this way, the lower back frame 62 and eventually the back support
post 6 becomes able to turn about the first support shaft X1 with respect to the support
base portion 3. In the embodiment, extending portions 621b extending further forward
than other portions are integrally provided to the portions near the lower end portions
of the respective lower back frame main bodies 621 and the insertion holes 621a are
formed in the respective extending portions 621b. The first support shaft X1 is disposed
on an upper back side with respect to the rigid connection shaft 622.
[0029] In a state in which the lower back frame 62 is mounted to the support base portion
3 in the chair 1 according to the embodiment, the rigid connection shaft 622 of the
lower back frame 62 is located below the lower face of the support base portion 3
(specifically, lower faces of the hanging side wall portions 32) and the coil spring
911 which is a resilient body of the invention for generating a reaction force as
the back support post 6 tilts back is disposed between the rigid connection shaft
622 and the support base portion 3. When the lower back frame 62 tilts back about
the first support shaft X1, the rigid connection shaft 622 biases the coil spring
911 in such a direction as to accumulate resilience.
[0030] To put it concretely, as shown in FIG. 6, the rigid connection shaft 622 supports
a coil spring receiving portion 911x provided on one end side of the coil spring 911
(described later) at its central portion in a longitudinal direction. The coil spring
911 and the coil spring receiving portion 911x form a tilting reaction force adjusting
device 9 for adjusting the reaction force in tilting back the back support post 6.
[0031] As shown in FIGS. 5 and 6, at least part of the tilting reaction force adjusting
device 9 is housed in the support base portion 3 and the tilting reaction force adjusting
device 9 includes a reaction force generating portion 91 for generating the reaction
force in tilting back the back support post 6 independently of the seat receiver 4
and a reaction force adjusting operation portion 92 provided on a front end side of
a side edge of the seat 5 for adjusting operation of strength of the reaction force
of the reaction force generating portion 91.
[0032] To put it more concretely, the reaction force generating portion 91 includes the
coil spring 911 and a compressing and expanding portion 912 provided on one end side
of the coil spring 911 to compress or expand the coil spring 911 in synchronization
with the adjusting operation applied to the reaction force adjusting operation portion
92. The compressing and expanding portion 912 is made up of a slider 912a in a trapezoidal
shape in a plan view and for moving forward and backward in a direction orthogonal
to a direction of compression and expansion of the coil spring 911 in synchronization
with the adjusting operation applied to the reaction force adjusting operation portion
92, a retainer 912b in a trapezoidal shape in a plan view and for moving forward and
backward in the direction of the compression and expansion while sliding against the
slider 912a and supporting the coil spring 911, and the retainer guide portion 33a
for guiding the forward and backward movements of the retainer 912b in the direction
of the compression and expansion. As described above, the retainer guide portion 33a
is formed on the partition wall 33 of the support base portion 3 for supporting the
seat receiver 4.
[0033] The reaction force adjusting operation portion 92 includes a rod 921 extending in
the lateral width direction while passing through one of the hanging side wall portions
32 of the support base portion 3 and an operation grip 922 provided to a tip end portion
of the rod 921 to rotate the rod 921 about an axis.
[0034] Getting back to description of the lower back frame 62, the respective lower back
frame main bodies 621 of the lower back frame 62 are integrally provided with second
extending portions 621c extending further forward than portions around them at portions
slightly below central portions in the height direction and a second support shaft
X2 laid and fixed like a bridge between the second extending portions 621c supports
a rear end side of the seat receiver 4. Furthermore, the supported portions 715 of
the back shell 71 are fixed to portions near the upper end portions of the respective
lower back frame main bodies 621 by appropriate means such as screws so that relative
angles cannot be changed.
[0035] As shown in FIG. 5, the upper back frame 61 pivoted on the upper end portion of the
lower back frame 62 having the above-described structure has such width as to be sandwiched
between the pair of left and right lower back frame main bodies 621 and is substantially
in a shape of < in a side view with its upper end portion and lower end portion protruding
further backward than its central portion in the height direction. As shown in FIG.
8, the slide engagement hole 611 in which the engagement portion 714 provided to the
back shell upper portion 71T can be engaged by sliding is formed in the upper end
portion of the upper back frame 61. The slide engagement hole 611 is made up of a
large hole portion 611a in and from which the flange portion 714a of the engagement
portion 714 can be inserted and withdrawn and a small hole portion 611b formed continuously
with an upper side of the large hole portion 611a and allowing a relative sliding
movement of the engagement portion 714 while prohibiting withdrawal of the flange
portion 714a that has been inserted from the large hole portion 611a. The small hole
portion 611b is greater than the large hole portion 611a in height so as to secure
a margin for relative sliding movements of the slide engagement hole 611 and the engagement
portion 714.
[0036] An insertion hole (not shown) is formed to pass through a lower end portion of the
upper back frame 61 in the lateral width direction and the third support shaft X3
is inserted through the insertion hole and insertion holes 621d formed in the upper
end portions of the respective lower back frame main bodies 621 after making the insertion
holes communicating with each other to thereby enable the upper back frame 61 to tilt
back about the third support shaft X3. In the embodiment, the third support shaft
X3 is located behind the lower end portion of the back shell 71. The' upper back frame
61 includes an overhanging portion 612 extending downward from the pivot point (third
support shaft X3) and a second coil spring 63 for generating a reaction force as the
upper back frame 61 tilts back is disposed between the overhanging portion 612 and
the lower back frame 62. In the embodiment, a fourth support shaft X4 is laid and
fixed like a bridge between portions of the pair of left and right lower back frame
main bodies 621 of the lower back frame 62 slightly below the bent portions near the
upper end portions, one end portion of the second coil spring 63 is supported on the
fourth support shaft X4, and the other end portion of the second coil spring 63 is
supported on the overhanging portion 612 of the upper back frame 61.
[0037] In a state in which the back shell upper portion 71T and the back shell lower portion
71U are supported on the upper end portion of the upper back frame 61 and the upper
end portion of the lower back frame 62, respectively, a space is formed between the
back shell 71 and the back support post 6 (specifically, the upper back frame 61).
[0038] Next, usage and operation of the chair 1 according to the embodiment and made up
of the above-described respective members will be described.
[0039] The chair 1 according to the embodiment can be brought into at least a normal state
(S) in which the backrest 7 is in a standing attitude as shown in FIGS. 1 to 5, a
synchronous rocking (synchronous tilt) state (R) in which the seat 5 slides in such
a direction as to sink backward in synchronization with the backward tilting operation
of the backrest 7 as shown in FIGS. 9 and 10, and a back tilt state (T) in which the
upper back frame 61 tilts back about the third support shaft X3 when the seated person
purposely puts his/her weight on an upper portion of the backrest 7 in the normal
state (S) and, as a result, the whole back shell 71 is curved and arched in the side
view as shown in FIGS. 11 and 12.
[0040] In the normal state (S), the back shell 71 that is mainly made up of the elastic
plate-shaped body is in an arched and curved shape in the side view against its elasticity.
[0041] If the seated person leans at his/her entire back against the backrest 7 of the chair
1 in this normal state (S), the back support post 6 tilts back about the first support
shaft X1 while keeping the relative angle between the upper back frame 61 and the
lower back frame 62 and the back shell 71 tilts back as well as shown in FIG. 10.
At this time, because the weight of the seated person is applied substantially uniformly
on the whole backrest 7 and therefore the back shell 71 tilts back while maintained
in substantially the same shape as in the normal state (S) without tilting back of
the upper back frame 61 with respect to the lower back frame 62, i.e., without changing
the relative angle between the upper back frame 61 and the lower back frame 62. Then,
the seat receiver 4 with its rear end side supported by the second support shaft X2
of the lower back frame 62 slides in such a direction as to sink backward while moving
the front frame (not shown) provided on its front end portion in the elongated holes
32a as a result of the backward tilting operation of the back support post 6. As a
result, the whole seat 5 supported on the seat receiver 4 slides in the same direction
as the seat receiver 4, i.e., in such a direction as to sink backward (see FIG. 9)
to thereby bring the chair 1 into the synchronous rocking state (R).
[0042] In the synchronous rocking state (R), the rigid connection shaft 622 of the lower
back frame 62 presses the coil spring 911 in such a direction as to accumulate the
resilience. Therefore, if the seated person moves his/her back away from the backrest
7, i.e., sits up, the whole back support post 6 naturally returns into a normal attitude
before titling back due to the resilience of the coil spring 911. In the embodiment,
it is possible to adjust the reaction force in tilting back the backrest 7 by using
the tilting reaction force adjusting device 9. To put it concretely, if the operation
grip 922 is rotated in one of clockwise and counterclockwise directions (e.g., in
the clockwise direction), the slider 912a moves in such a direction as to approach
the operation grip 922 in synchronization with the rotation and the slider 912a presses
the retainer 912b. Then, the retainer 912b pressed by the slider 912a moves in such
a direction as to compress the coil spring 911 to thereby increase the reaction force
in tilting back the backrest 7. On the other hand, if the operation grip 922 is rotated
in the reverse direction (e.g., in the counterclockwise direction), it is possible
to reduce the reaction force in tilting back the backrest 7.
[0043] On the other hand, if the seated person purposely puts his/her weight on the back
shell upper portion 71T in the normal state (S), the upper back frame 61 of the back
support post 6 tilts back about the third support shaft X3 with respect to the lower
back frame 62 as shown in FIG. 12. As the upper back frame 61 tilts back, a force
for leaning back is applied to the back shell upper portion 71T of the back shell
71 supported on the upper back frame 61 while the lower end portion of the back shell
71 supported on the lower back frame 62 tries to stay in its position in the normal
state (S) due to the lower back frame 62 which does not tilt back. Therefore, the
back shell 71 is arched and curved to protrude its portion between the back shell
upper portion 71T and the back shell lower portion 71U further forward. In the embodiment,
because the lumbar support portion 71L of the back shell 71 is provided with the deformation
trigger means 713 which is specifically the slits 713a, the lumbar support portion
71L is deformed in such a direction as to reduce height of the openings of the slits
713a when the whole back shell 71 is arched and curved and, as a result, the lumbar
support portion 71L protrudes further forward than in the normal state (S). In the
embodiment, the back shell upper portion 71T is engaged and supported in the upper
back frame 61 so that it can relatively slide in the height direction. By relatively
sliding the engagement portion 714 provided to the back shell upper portion 71T in
the height direction in the slide engagement hole 611 formed in the upper end portion
of the upper back frame 61 in such a range as not to be disengaged from the slide
engagement hole 611 in the tilting back of the upper back frame 61, the whole back
shell 71 can be curved to follow the backward tilting operation of the upper back
frame 61. In the chair 1 in the embodiment, because the curvature of the curved face
of the back shell 71 in the plan view is smaller than that of the other portion and
the upper end portion of the upper back frame 61 relatively slides against the back
shell upper portion 71T in a substantially straight line shape along the height direction,
it is possible to achieve the smooth sliding movement in the stable state.
[0044] As the chair 1 shifts from the normal state (S) into the back tilt state (T), the
overhanging portion 612 of the upper back frame 61 presses the second coil spring
63 disposed between the overhanging portion 612 and the lower back frame 62 in such
a direction as to accumulate the resilience. Therefore, if the seated person moves
his/her back away from the backrest 7, i.e., sits up, the upper back frame 61 naturally
returns into its normal attitude before the tilting back of the upper back frame 61
due to the resilience of the second coil spring 63 and the chair 1 returns from the
back tilt state (T) to the normal state (S). Moreover, when the chair 1 shifts from
the normal state (S) to the back tilt state (T), an elastic recovering force of the
back shell 71 which has been further arched and curved than in the normal state (S)
acts as a force for biasing the upper back frame 61 in such a direction as to pull
the upper back frame 61 back forward. Therefore, if the seated person purposely puts
his/her weight on the lumbar support portion 71L when the chair 1 is in the back tilt
state (T), the biasing force further increases, the biasing force and the resilience
of the second coil spring 63 combine with each other, and, when the seated person
moves his/her back away from the backrest 7, i.e., sits up, the upper back frame 61
follows the operation and quickly and automatically returns to its normal attitude
before the tilting back.
[0045] If the seated person puts his/her weight on the whole backrest 7 after the chair
1 is shifted from the normal state (S) into the back tilt state (T), the lower back
frame 62 tilts back about the first support shaft X1 while maintaining the upper back
frame 61 in the backward tilted attitude with respect to the lower back frame 62.
As a result, the chair 1 is brought into a most reclined state (not shown) which is
a combination of the back tilt state (T) and the synchronous rocking state (R). Substantially
similarly, if the seated person purposely puts his/her weight on the upper back frame
61 after the chair 1 is shifted from the normal state (S) into the synchronous rocking
state (R), the upper back frame 61 tilts back about the third support shaft X3 with
respect to the lower back frame 62 and the chair 1 is brought into the most reclined
state (not shown) which is the combination of the synchronous rocking state (R) and
the back tilt state (T).
[0046] In other words, the chair 1 according to the embodiment is brought into the normal
state (S), the synchronous rocking state (R), the back tilt state (T), the most reclined
state, or an intermediate state between two different states of them (e.g., an intermediate
state between the normal state (S) and the synchronous rocking state (R) and an intermediate
state between the normal state (S) and the back tilt state (T) (not shown)) depending
on how the seated person sits and more specifically how the seated person puts his/her
weight on the chair 1.
[0047] The chair 1 in the embodiment includes a tilting braking device A provided between
the back support post 6 and the support base portion 3 to selectively enable the tilting
operation of the backrest 7. A lower end portion of the tilting braking device A is
supported for swinging on a rear end side of the support base portion 3 and an upper
end portion of the tilting braking device A is supported for swinging on the fourth
support shaft X4 of the lower back frame 62. As shown in FIG. 6, employed as the tilting
braking device A in the embodiment is a known gas spring which has a substantially
cylindrical gas spring main body A1 and a piston rod portion (not shown) for moving
forward and backward so that substantially the whole piston rod portion is housed
in the gas spring main body A1 and which functions as a tilting braking portion and
the tilting braking device A will not be described in detail.
[0048] As described above, in the chair 1 according to the embodiment, the lower end portions
of the pair of lower back frame main bodies 621 of the lower back frame 62 of the
back support post 6 and rotatably mounted to the support base portion 3 are rigidly
connected by the rigid connection shaft 622. Therefore, at least the portions near
the lower end portions of the back support post 6 become structures having high rigidity
and the lower back frame 62 greatly contributes to increase of the mounting strength
in the state in which the lower back frame 62 is mounted to the support base portion
3. Moreover, because the pair of left and right lower back frame main bodies 621 are
disposed on the outer sides of the opposite side faces (and specifically outward faces
of the hanging side wall portions 32) of the support base portion 3 and the rigid
connection shaft 622 is disposed below the lower face of the support base portion
3, it is unnecessary to secure a space for rotating movements of the lower end portions
of the lower back frame main bodies 621 and the rigid connection shaft 622 in the
support base portion 3 and the support base portion 3 can be made thin. Furthermore,
because the pair of left and right lower back frame main bodies 621 are disposed on
the outer sides of the opposite side faces of the support base portion 3, the lower
back frame main bodies 621 do not need to be formed in such shapes as to escape from
the support base portion 3 in the backward tilting operation of the back support post
6 and the lower back frame main bodies 621 may be formed in simple shapes without
being affected by a height and a shape of the support base portion 3. Moreover, because
the rigid connection shaft 622 biases the coil spring 911 in such a direction as to
accumulate the resilience, it is unnecessary to employ a separate special biasing
member and it is possible to effectively simplify the structure of the lower back
frame 62 and eventually the structure of the back support post 6.
[0049] Especially, the support base portion 3 is formed in the substantially box shape open
downward and the lower back frame 62 can be fitted with the support base portion 3
from behind and, as a result, the lower back frame 62 and eventually the back support
post 6 can be mounted to the support base portion 3 while sandwiching the support
base portion 3 between the pair of left and right lower back frame main bodies 621
from opposite sides. Therefore, it is possible to smoothly mount the back support
post 6 to the support base portion 3. Moreover, because the box-shaped support base
portion 3 having high rigidity is sandwiched between the pair of lower back frame
main bodies 621 from opposite sides, the mounting strength is increased and deformation
of the lower back frame main bodies 621 due to an external force can be prevented
by existence of the support base portion 3 between the lower back frame main bodies
621 even if the external force acts in such a direction as to narrow an interval between
the lower back frame main bodies 621.
[0050] In addition, if the support base portion is in a box shape having a housing space
open upward as in prior art, the coil spring has to be housed in the housing space,
which confines a shape and dimensions of the coil spring to those which can be housed
in the housing space and reduces a degree of freedom in design. In the embodiment,
on the other hand, the support base portion 3 includes the upper wall portion 31 and
the pair of hanging side wall portions 32 hanging from the opposite side edge portions
of the upper wall portion 31 and houses at least one end portion of the coil spring
911 disposed so that the direction of accumulating the resilience is inclined a predetermined
angle with respect to a vertical direction in the housing space surrounded with the
respective wall portions (the upper wall portion 31 and the hanging side wall portions
32) and open downward and the other end portion of the coil spring 911 is supported
on the rigid connection shaft 622 disposed below the lower face of the support base
portion 3. Therefore, a portion of the coil spring 911 disposed in a diagonal attitude
may protrude downward from the housing space in the support base portion 3 and the
shape and dimensions of the coil spring 911 can be changed appropriately according
to specifications.
[0051] The invention is not limited to the embodiment described above in detail.
[0052] For example, though the back support post in the embodiment includes the lower back
frame and the upper back frame capable of tilting back with respect to the lower back
frame, the back support post is not limited to this. A relative angle between the
upper portion and the lower portion of the back support post may not be variable.
As an example of the back support post in this case, the back support post may be
formed in a substantially L shape in the side view with its lower end portion or its
portion near the lower end portion pivoted on the support base portion disposed below
the seat.
[0053] As the resilient body for generating the reaction force as the back support post
tilts back, it is possible to use rubber, a leaf spring, or what is called a coil
spring with its axial direction substantially aligned with the lateral width direction
of the chair and its opposite end portions extending away from each other from an
axial center. Furthermore, the rigid connection shaft may be a shaft for pulling the
resilient body in such a direction as to accumulate the resilience as the back support
post tilts back.
[0054] The upper back frame 61 supports the back shell upper portion 71T while engaged with
the back shell upper portion 71T for sliding movements in the height direction in
the example shown in the embodiment. Instead, the lower back frame may support the
lower portion of the back shell while engaged with the lower portion for sliding movements
in the height direction or both the upper back frame and the lower back frame may
support the back shell while engaged with the back shell for sliding movements in
the height direction. In other words, the slide engagement mechanism for allowing
relative sliding movements of the back shell and the back support post may be provided
only between the upper back frame and the back shell, only between the lower back
frame and the back shell, or between each of the back frames and the back shell. Furthermore,
a distance of sliding may be changed appropriately according to specifications and
the like. Although the engagement portion is engaged in the engagement hole in the
example shown in the embodiment, an engagement groove may be employed in place of
the engagement hole. Moreover, as the slide engagement mechanism, an engagement recessed
portion such as an engagement hole and an engagement groove may be integrally provided
to the back shell and an engagement protruding portion that can be engaged in the
engagement recessed portion by sliding may be provided to the back frame. For example,
as shown in FIG. 13, a pocket-shaped engagement recessed portion 714' open downward
is integrally provided to a back face of the back shell 71 (back shell upper portion)
and an upward engagement protruding portion 611' which is in an L shape in the side
view and which can be inserted into the engagement recessed portion 714' from below
is provided to the back support post (upper back frame 61). As the upper back frame
61 tilts back, an amount of covering of the engagement protruding portion 611' with
the engagement recessed portion 714' is reduced in such a range as not to disengage
the engagement protruding portion 611' and the engagement recessed portion 714' from
each other. In this way, the back shell 71 can slide in the height direction with
respect to the back support post (upper back frame 61). In this case, it is possible
to engage the engagement recessed portion and the engagement protruding portion with
each other by slipping the back shell over the back support post from above, which
facilitates an assembly operation.
[0055] . The specific structures of the respective portions are not limited to those in
the above-descried embodiment but can be changed in various ways without departing
from the gist of the invention.
INDUSTRIAL APPLICABILITY
[0056] As described above, according to the invention, it is possible to provide the chair
having the backrest which can be tilted back as a back support post for supporting
the backrest tilts back, in which the support base portion can be made thin without
impairing the function of generating the reaction force at all in tilting back the
back support post, the strength of mounting of the back support post and the support
base portion to each other can be increased, and the structure of the back support
post can be simplified.