LUMBAR SUPPORT DEVICE

Abstract

An object of the present invention is to provide a lumbar support device in which a driving unit is not to be large. The lumbar support device includes: a seat back frame (7) that has horizontal portions (7j, 7k) extending in a horizontal direction and is provided on the seat back for supporting a back of a seated person; a curved plate (23) that has hinge portions (23b) provided at one end portion so as to be rotatably engaged with the horizontal portions (7j, 7k); and a driving mechanism (9) which is provided on the seat back frame (7) and is connected to the other end portion of the curved plate (23) and which makes the other end portion approach and separate from the one end portion to change the degree of curvature of the curved plate (23).

Description

TECHNICAL FIELD

The present invention relates to a lumbar support device which presses a back of a seated person and supports a good posture of the seated person.

BACKGROUND ART

Some vehicle seats have lumbar support devices.

As an example of those lumbar support devices, there is the following structure.

On a seat back frame, a pair of big wires, which is formed by curving spring materials and extends in a vertical direction, is provided.

Further, on both sides of a curved plate for pressing a back of a seated person, guides are provided. The respective guides are engaged with the big wires, and the curved plate is able to move in the vertical direction along the big wires. The curved plate is able to rise and fail to a predetermined position of the big wires.

Furthermore, the interval between two positions of the curved plate in the vertical direction is changed by a driving unit, whereby the degree of curvature of the curved plate is changed and the amount of pressure to be applied to the back of the seated person is changed (see Patent Literature 1, for example).

CITATION LIST

Patent Literature

Patent Literature 1: Japanese Unexamined Patent Publication No. 2006-523105 (FIG. 2)

DISCLOSURE OF THE INVENTION

Technical Problem

However, in the lumbar support device disclosed in Patent Literature 1, if the curved plate is largely curved, twist between the guides of the curved plate and the big wires increases. That is, there is a problem that a large force is required to largely curve the curved plate and thus the size of the driving unit increases.

The present invention was made in view of the above described problem, and an object of the present invention is to provide a lumbar support device in which a driving unit is not to be large.

Solution to Problem

In order to achieve at least one of the above described objects, a lumbar support device reflecting an aspect of the present invention is characterized by including a seat back frame, which has a horizontal portion extending in a horizontal direction and is provided on a seat back for supporting a back of a seated person; a curved plate, which is provided with a hinge portion to be rotatably engaged with the horizontal portion at one end portion; and a driving mechanism, which is provided on the seat back frame and is connected to the other end portion of the curved plate and which makes the other end portion approach and separate from the one end portion to change the degree of curvature of the curved plate.

Other features of the present invention will become more apparent from the accompanying drawings and embodiments for carrying out the invention, described below.

Advantageous Effect of the Invention

According to the present invention, a lumbar support device in which a driving unit is not to be large is provided.

Other advantages of the present invention will become more apparent from the accompanying drawings and embodiments for carrying out the invention, described below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view of a lumbar support device of an embodiment.

FIG. 2 is a perspective view illustrating a seat back equipped with the lumbar support device of the embodiment.

FIG. 3 is a perspective view as seen from an arrow III direction of FIG. 2.

FIG. 4 is a perspective view in a state where a curved plate of the lumbar support device of the embodiment has been deformed in a direction to press a back of a seated person.

FIG. 5 is a perspective view as seen from an arrow V direction of FIG. 4.

FIG. 6 is a view illustrating a side surface of the curved plate of FIG. 1.

FIG. 7 is a view illustrating the operation of a driving mechanism of FIG. 1.

FIG. 8 is a view illustrating holding of the curved plate and reinforcing plates of FIG. 1.

FIG. 9 is a perspective view illustrating the mounting structure of a base plate, a fishmouth spring, and a big wire of FIG. 1.

FIG. 10 is a perspective view as seen from an arrow X direction of FIG. 9.

FIG. 11 is a perspective view illustrating the mounting structure of the curved plate and the big wire shown in FIG. 1.

EMBODIMENT FOR CARRYING OUT THE INVENTION

First, a seat back of a seat equipped with a lumbar support device of an embodiment will be described using FIGS. 1 to 3. FIG. 1 is an exploded perspective view of the lumbar support device of the embodiment, and FIG. 2 is a perspective view illustrating the seat back equipped with the lumbar support device of the embodiment, and FIG. 3 is a perspective view as seen from an arrow III direction of FIG. 2.

In FIGS. 1 to 3, an arrow F direction indicates a front side direction of the seat back (a direction facing a person sitting in the seat back), and an arrow B direction indicates a back side direction of the seat back.

In FIGS. 1 and 2, first, a seat back frame 1 for supporting a back of a seated person will be described. The seat back frame 1 of the present embodiment includes a main frame and a big wire.

As shown in FIG. 2, the main frame includes a right frame 1a and a left frame 1b. An upper frame 1c is provided so as to bridge between an upper portion of the right frame 1a and an upper portion of the left frame 1b. The upper frame 1c includes a base portion 1d which extends in a horizontal direction, a first vertical portion 1e which is bent from one end portion of the base portion 1d and is connected to the upper portion of the right frame 1a, and a second vertical portion 1f which is bent from the other end portion of the base portion 1d and is connected to the upper portion of the left frame 1b. A sub upper frame 1g is provided so as to form a bridge between a middle portion of the first vertical portion 1e and a middle portion of the second vertical portion 1f of the upper frame 1c. Further, a lower frame 1h is provided so as to form a bridge between the lower portion of the right frame 1a and the lower portion of the left frame 1b.

As shown in FIG. 1, on a front side of the sub upper frame 1g and the lower frame 1h of the seat back frame 1 of the seat back, a substantial U-shaped big wire (a portion of the seat back frame) 7, which is formed by curving a spring material having a circular cross-sectional shape and supports the back of a seated person, is disposed.

The big wire 7 of the present embodiment includes left and right upper vertical-extending portions 7a and 7b which are positioned on the upper side, left and right middle vertical-extending portions 7c and 7d which are positioned in the middle of the vertical direction, and left and right lower vertical-extending portions 7h and 7i which are positioned on the lower side. The left and right upper vertical-extending portions 7a and 7b, the left and right middle vertical-extending portions 7c and 7d, and the left and right lower vertical-extending portions 7h and 7i is respectively disposed so as to be line symmetry. A right-and-left interval between the middle vertical-extending portions 7c and 7d is narrower than a right-and-left interval between the upper vertical-extending portions 7a and 7b. A right-and-left interval between the lower vertical-extending portions 7h and 7i is narrower than a right-and-left interval between the middle vertical-extending portions 7c and 7d.

The lower end portions of the upper vertical-extending portions 7a and 7b and the upper end portions of the middle vertical-extending portions 7c and 7d are respectively connected by inclined portions 7e and 7f. The lower end portion of the vertically extending lower portion 7h and the lower end portion of the vertically extending lower portion 7i are connected by a bridge portion 7g.

Further, the lower end portions of the middle vertical-extending portions 7c and 7d and the upper end portions of the lower vertical-extending portions 7h and 7i are respectively connected by horizontal portions 7j and 7k extending in the horizontal direction.

As shown in FIG. 2, the vertically extending upper portion 7a of the big wire 7 is inserted through a cylindrical clip 3 attached to the front side the sub upper frame 1g of the seat back. Also, the vertically extending upper portion 7b of the big wire 7 is inserted through a cylindrical clip 5 attached to the sub upper frame 1g.

As shown in FIG. 1, on the back side of the lower portion of the big wire 7 of the seat back, a base plate 11 on which a driving mechanism 9 is mounted is attached. Also, the details of the driving mechanism 9 will be described below.

As shown in FIG. 2, the bridge portion 7g of the big wire 7 is connected to the lower frame 1h of the seat back frame 1 via a fishmouth spring 13.

As shown in FIG. 1, the fishmouth spring 13 includes base portions 13a and 13b. The base portions 13a and 13b are mounted on the lower frame 1h by two cut-and-raised clasps 15 and 17 formed at the lower frame 1h of the seat back frame 1. The interval between the cut-and-raised clasps 15 and 17 is set to be wider than the interval between the lower vertical-extending portions 7h and 7i of the big wire 7.

The fishmouth spring 13 includes rising portions 13c and 13d, base-portion facing portions 13e and 13f, torsion arm portions 13g and 13h, and a mounting portion 13i. The rising portions 13c and 13d extends upward from end portions of the base portions 13a and 13b on the right frame (1a) side and the left frame (1b) side of the seat back frame 1. The base-portion facing portions 13e and 13f bend from the leading end portions of the rising portions 13c and 13d and extend toward the lower vertical-extending portions 7h and 7i of the big wire 7. The torsion arm portions 13g and 13h bend from the leading end portions of the base-portion facing portions 13e and 13f and extend toward the bridge portion 7g of the big wire 7. The mounting portion 13i forms a bridge between the leading end portions of the torsion arm portions 13g and 13h and extends along the bridge portion 7g of the big wire 7.

Further, at the central portion of the mounting portion 13i, arm portions 13k and 13l are formed to intersect with the extension direction of the mounting portion 13i, and a step portion 13j is formed to form a bridge between the leading end portions of the arm portions 13k and 13l.

That is, in the fishmouth spring 13, the base portions 13a and 13b, the rising portions 13c and 13d, and the base-portion facing portions 13e and 13f serve as fixed base end portions of the torsion arm portions 13g and 13h, and the mounting portion 13i corresponds to the leading end portions of the torsion arm portions 13g and 13h.

Next, mounting of the base plate 11, the big wire 7, and the fishmouth spring 13 will be described using FIGS. 9 and 10. FIG. 9 is a perspective view illustrating mounting of the base plate, the fishmouth spring, and the big wire of FIG. 1, and FIG. 10 is a perspective view as seen from an arrow X direction of FIG. 9.

At each of the left and right side portions of the base plate 11, two side swage portions 11a (the total number of side swage portions is four) are formed to extend in the horizontal direction. The side swage portions 11a are swaged so as to be wrapped around the lower vertical-extending portions 7h and 7i of the big wire 7. As a result, the lower vertical-extending portions 7h and 7i of the big wire 7 are mounted on the base plate 11.

At the lower portion of the base plate 11, two lower swage portions 11b are formed to extend downward. The lower swage portions 11b are swaged so as to be wrapped around the bridge portion 7g of the big wire 7 and the mounting portion 13i of the fishmouth spring 13. As a result, the bridge portion 7g of the big wire 7 and the mounting portion 13i of the fishmouth spring 13 are mounted on the base plate 11.

On the front side of the lower vertical-extending portions 7h and 7i of the big wire 7 of the seat back, a curved plate 23 made of a resin substantially in a plate shape is disposed. The degree of curvature of the curved plate 23 can be changed by the driving mechanism 9.

Next, using FIG. 11, the mounting structure of the upper portion of the curved plate 23 and the big wire 7 will be described. FIG. 11 is a perspective view illustrating the mounting structure of the curved plate and the big wire shown in FIG. 1. At the upper portion of a main body 23a which is a curving portion of the curved plate 23, hinge portions 23b are integrally formed to be rotatably engaged with the horizontal portions 7j and 7k of the big wire 7.

The hinge portion 23b includes a main hinge body 23a which extends in the width direction of the seat back and a cantilever-like retaining portion 23f. The main hinge bodies 23e include grooves 23d having openings into which the horizontal portions 7j and 7k of the big wire (the seat back frame) 7 are inserted. The retaining portions 23f have elasticity. The retaining portions 23f protrude from the main hinge bodies 23e and face the openings of the grooves 23d with a space interposed therebetween.

In the present embodiment, the intervals between a surface of the retaining portions 23f, which faces the main hinge bodies 23e, and the openings of the grooves 23d of the main hinge bodies 23e are set to be equal to or greater than the diameter of the big wire 7 (the thickness in the vertical direction). Further, at the leading end portions of the retaining portions 23f, convex portions 23g are formed to protrude toward the main hinge bodies 23e such that the intervals between the leading end portions and the main hinge bodies 23e become less than the diameter of the big wire 7 (the thickness in the vertical direction).

If the horizontal portions 7j and 7k of the big wire 7 are pressed against the leading end portions of the retaining portions 23f of the hinge portions 23b and the leading end portions of the retaining portions 23f are curved upward, the intervals between the convex portions 23g and the main hinge bodies 23e become equal to or greater than the diameter of the big wire 7. Then, the horizontal portions 7j and 7k of the big wire 7 can be inserted into the grooves 23d, so that it is possible to mount the hinge portions 23b of the curved plate 23 on the horizontal portions 7j and 7k of the big wire 7.

Also, in a natural state where any force does not act on the leading ends of the retaining portions 23f, the intervals between the convex portions 23b of the retaining portions 23f and the main hinge bodies 23e are less than the diameter of the big wire 7 (the thickness in the vertical direction). Therefore, the horizontal portions 7j and 7k of the big wire 7 are prohibited from leaving from the grooves 23d to the outside.

Next, using FIGS. 1 to 5, 7, 9, and 10, the driving mechanism will be described. FIG. 4 is a perspective view in a state where the curved plate of the lumbar support device of the present embodiment has been deformed in a direction to press the back of a seated person, and FIG. 5 is a perspective view as seen from an arrow V direction of FIG. 4, and FIG. 7 is a view illustrating the operation of the driving mechanism of FIG. 1.

As shown in FIGS. 1 and 4, at the central portion of the front side of the base plate 11 of the seat back, there are formed a first upstanding wall portion 51 which extends in the vertical direction, a second upstanding wall portion 53 which is parallel to the first upstanding wall portion 51, and a bridge portion 56 which bridges between the first upstanding wall portion 51 and the second upstanding wall portion 52. In the first upstanding wall portion 51, a first guide hole 51a is formed to extend in the vertical direction, and even in the second upstanding wall portion 53, a second guide hole 53a (see FIG. 5) is formed to extend in the vertical direction and face the first guide hole 51a.

As shown in FIG. 9, the lower end surface of the first upstanding wall portion 51 and the lower end surface of the second upstanding wall portion 53 serve as abutting portions 51d and 53d which abut on the bridge portion 7g of the big wire 7.

Also, as shown in FIGS. 9 and 10, at the lower portions of the first upstanding wall portion 51 and the second upstanding wall portion 53, a first recess 51c and a second recess 53c are formed to be engaged with the step portion 13j of the fishmouth spring 13. Therefore, the fishmouth spring 13 is prohibited from rotating around the mounting portion 13i and the base-portion facing portions 13e and 13f (base end portions).

As shown in FIG. 1, the upper portion of the first upstanding wall portion 51 is bent toward the right frame 1a of the seat back frame 1, whereby a first gear box mounting portion 51b is formed. The upper portion of the second upstanding wall portion 53 is bent toward the left frame 1b of the seat back frame 1, whereby a second gear box mounting portion 53b is formed.

As shown in FIG. 1, on the first gear box mounting portion 51b and the second gear box mounting portion 53b, a gear box 59 is mounted using tightening screws 55 and 57 and nuts 55a and 57a. A motor 61 is integrally mounted on the gear box 59. Inside the gear box 59, a nut member having a hole having a female thread formed at the inner surface is provided to be rotatable. Further, the nut member can be rotated by the motor 61. Also, in mounting of the gear box 59, instead of the tightening screws 55 and 57 and the nuts 55a and 57a, tapping screws which do not need nuts may be used.

A threaded rod 63 having a male thread formed at the outer surface is disposed in a space between the first upstanding wall portion 51 and the second upstanding wall portion 53 and is screwed to the nut member provided in the gear box 59. A washer 52 is fit to a portion of the threaded rod 63 protruding outward from the gear box 59 and a stopper nut 54 is screwed.

Also, at the center of the lower portion of the base plate 11, a convex portion 58, which is able to support the pelvis of a seated person, is formed by the first upstanding wall portion 51, the second upstanding wall portion 53, and the bridge portion 56 and protrudes toward the front surface of the seat back.

At the central portion of the lower portion of the curved plate 23, a cutout 23h is formed to prevent interference with the convex portion 58 of the base plate 11. At the lower portion of the curved plate 23 except for the cutout 23h, a mounting portion 23i is formed over the entire area of the curved plate 23 in the width direction.

As shown in FIG. 6, at the mounting portion 23i, a hole 23j is formed to extend in the width direction of the curved plate 23. In the present embodiment, the cross-sectional shape of the hole 23j is a long hole shape. At the lower portion of the threaded rod 63, a hole 63a (see FIG. 1) is formed to be perpendicular to the axis of the threaded rod 63, and a rod (a pin: a mounting member) 65 (see FIG. 10) is fit into the hole 63a. In the present embodiment, the inner diameter of the hole 63a is set to be larger than the outer diameter of the rod 65, and an elastic bush 66 (see FIG. 9) is press-fitted between the hole 63a and the rod 65. The rod 65 is loosely fit into the hole 23j of the mounting portion 23i of the curved plate 23 through the first guide hole 51a of the first upstanding wall portion 51 and the second guide hole 53a of the second upstanding wall portion 53 of the convex portion 58. That is, the connection between the rod 65 and the lower portion of the curved plate 23 is a hinge connection.

Therefore, the threaded rod 63 is prohibited from rotating around the axis of the threaded rod 63 and can relatively move along the axis with respect to the motor 61. If the motor 61 is driven, the nut member in the gear box 59 rotates. The threaded rod 63 screwed to the nut member moves in the axial direction with respect to the motor 61, and the rod 65 fit in the threaded rod 63 moves along the first guide hole 51a and the second guide hole 53a. As a result, the lower portion of the curved plate 23 also moves along the first guide hole 51a and the second guide hole 53a.

In the present embodiment, the driving mechanism 9 includes the gear box 59 which has the nut member, the motor 61 which rotates the nut member provided inside the gear box 59, the threaded rod 63 which is screwed to the nut member provided inside the gear box 59, the rod 65 which connects the threaded rod 63 and the lower portion of the curved plate 23, and the second guide hole 53a of the second upstanding wall portion 53 and the first guide hole 51a of the first upstanding wall portion 51 through which the rod 65 is inserted.

Next, using FIGS. 1, 3, 5, 6, 8, and 11, reinforcing plates 101 will be described. FIG. 6 is a view illustrating a side surface of the curved plate 23 of FIG. 1, and FIG. 8 is a view illustrating holding of the curved plate 23 and the reinforcing plates 101 of FIG. 1.

On the back surface of the curved plate 23, two belt-like reinforcing plates 101 extending in the vertical direction are provided. At the lower portions of the reinforcing plates 101, rectangular holes 101a are formed. At the lower portion of the curved plate 23, convex portions 231 are formed to be fit into the holes 101a of the reinforcing plates 101. Further, at the lower portion of the curved plate 23, there are formed holding convex portions 23o which are composed of base portions 23m which face the lower end surfaces of the reinforcing plates 101 and bent portions 23n which are bent from the leading end portions of the base portions 23m and face the upper surfaces of the lower portions of the reinforcing plates 101.

The lower portions of the reinforcing plates 101 are held on the curved plate 23 by the convex portions 231, which are engaged with the holes 101a of the reinforcing plates 101, and the holding convex portions 23o.

Further, on the back surface of the curved plate 23, two guides 23p and one guide 23q, as non-interference portions, are formed to cover the peripheral surfaces of the reinforcing plates 101 with spaces interposed therebetween and allow the reinforcing plates 101 to move in the vertical direction with respect to the curved plate 23.

Next, using FIGS. 2 to 5, and 7, the operation of the above described configuration will be described.

A state shown in FIGS. 2 and 3 is a state where the threaded rod 63 is positioned on the lower side, and the degree of curvature of the curved plate 23 is small, and the threaded rod has been scarcely deformed in a direction to press the back of a seated person.

If the motor 61 is rotated in one direction from that state, the nut member in the gear box 59 rotates in one direction, and the threaded rod 63 rises as shown in FIG. 7. Further, since the upper portion of the curved plate 23 is prohibited from moving upward and downward by the hinge portions 23b, the lower portion of the curved plate 23 rises as shown in FIGS. 4 and 5. As a result, the curved plate 23 is largely curved and presses the back of the seated person.

Also, if the motor 61 is rotated in the other direction from the state shown in FIGS. 4 and 5, the nut member in the gear box 59 rotates in the other direction, and the threaded rod 63 moves downward, and the degree of curvature of the curved plate 23 decreases. As a result, the amount of deformation in the direction to press the back of the seated person decreases.

Also, when the curved plate 23 is curved, the mounting portion 23i of the curved plate 23 is sliding-contact with the base plate 11. In the present embodiment, as shown in FIG. 7, a sliding contact surface 23r of the mounting portion 23i of the curved plate 23 is an arc surface.

Also, the convex portion 58 of the base plate 11 of the present embodiment serves as a pelvis supporting portion which supports a pelvis of the seated person when the lower portion of the curved plate 23 rises.

According to this configuration, it is possible to obtain the following advantages.

(1) Unlike the above described embodiment, in a case where the upper portion of the curved plate 23 is fixed to the big wire 7, if a force is applied to the lower portion of the curved plate 23, the force is transmitted to the big wire 7 via the fixing portions of the big wire 7 fixing the upper portion of the curved plate 23. Therefore, twist occurs at the big wire 7. In order to resist a reaction force caused by the twist of the big wire 7, the driving mechanism 9 is required to apply a large force to the curved plate 23. For this reason, the size of the driving mechanism 9 increases.

However, according to the lumbar support device of the present embodiment described above, the upper portion of the curved plate 23 is rotatably supported on the big wire 7. Further, since the curved plate 23 can be curved between the upper portion and the lower portion, even if a force is applied to the lower portion of the curved plate 23, the force is difficult to be transmitted to the big wire 7 supporting the upper portion of the curved plate 23. Therefore, in order to curve the curved plate 23, the driving mechanism 9 is not required to apply a large force to the curved plate 23. Therefore, it is possible to suppress an increase in the size of the driving mechanism 9.

(2) Since the hinge portions 23b of the curved plate 23 are formed integrally with the curved plate 23, it is possible to implement the hinge portions by a simple configuration.

(3) Since the retaining portions 23f having elasticity are formed, it is possible to prevent the hinge portions 23b from leaving from the big wire 7, and it is easy to mount the big wire 7 to the hinge portions 23b.

(4) Since the connection between the rod 65 of the driving mechanism 9 and the curved plate 23 is a hinge connection, during curving of the curved plate 23, twist at the connection portion of the driving mechanism 9 and the curved plate 23 does not occur, and a smooth operation is achieved.

(5) Since the driving mechanism 9 which converts a rotational motion into a linear motion is configured by the threaded rod 63 and the nut member, the size of the driving unit is reduced.

Additionally, the present invention is not limited to the above described embodiment. The above described embodiment uses the curved plate 23 whose upper portion is rotatably supported on the seat back frame 1 and whose lower portion is able to move in the vertical direction such that the curved plate is deformed in a direction to press the back of a seated person. However, it also is possible to use a curved plate whose lower portion is rotatably supported on the seat back frame 1 and whose upper portion is able to move in the vertical direction such that the curved plate is deformed in a direction to press the back of a seated person.

Also, the above described embodiment uses the motor 61 as the driving mechanism 9. However, the driving mechanism may be manual.

Further, the sliding contact surface 23r of the curved plate 23 and the base plate 11 may be in line contact with each other.

This application claims priority from Japanese Patent Application (Application No. 2012-245718) filed with the Japan Patent Office on Nov. 7, 2012, the entire content of which is hereby incorporated by reference.

DESCRIPTION OF REFERENCE NUMERALS AND SYMBOLS

• • 7 BIG WIRE (SEAT BACK FRAME)
  • 7j, 7k HORIZONTAL PORTION
  • 9 DRIVING MECHANISM
  • 23 CURVED PLATE
  • 23b HINGE PORTION

Claims

1. A lumbar support device comprising:

a seat back frame, which has a horizontal portion extending in a horizontal direction and is provided on a seat back for supporting a back of a seated person;

a curved plate, which is provided with a hinge portion to be rotatably engaged with the horizontal portion at one end portion; and

a driving mechanism, which is provided on the seat back frame and is connected to the other end portion of the curved plate and which makes the other end portion approach and separate from the one end portion to change the degree of curvature of the curved plate.

2. The lumbar support device according to claim 1,

wherein the hinge portions is formed integrally with the curved plate, and

wherein the hinge portions is a groove into which the horizontal portions of the seat back frame is inserted from an opening.

3. The lumbar support device according to claim 2, further comprising:

a retaining portion, which has elasticity and face the opening of the grooves with spaces interposed therebetween and which are elastically deformed to allow the horizontal portions of the seat back frame to be inserted into the grooves, and which prohibit the horizontal portions of the seat back frame from leaving from the grooves in a normal state.

4. The lumbar support device according to claim 1,

wherein the connection of the driving mechanism with the other end portion of the curved plate is a hinge connection.

5. The lumbar support device according to claim 1,

wherein the driving mechanism has a threaded rod and a nut member,

wherein one of the threaded rod and the nut member is attached to the seat back frame,

wherein the other of the threaded rod and the nut member is attached to the curved plate,

wherein a rod extending in a direction intersecting with the threaded rod is provided, on the member attached to the curved plate, and

wherein the curved plate has a hole into which the rod is loosely fit.