Seat cushion spring

Abstract

The invention provides a seat cushion spring capable of appropriately improving roll rigidity of a side portion of a seat cushion. The seat cushion spring is provided with a molding line erected on the seat cushion frame in the front-back direction of the seat and a resin part combined with the molding line. The molding line is composed of a single line having a center line and a side line which are aligned with each other in the seat width direction and which extend in the seat front-rear direction such that one end of each of the center line and the side line is connected to each other. The center line and the side lines each have a plurality of crank sections bent so as to be alternately folded back in a crank shape in one side and the other side in the seat width direction. The resin member has a deflection restricting portion that connects the plurality of crank portions so as to restrict opening in the seat front-rear direction between three or more continuously arranged crank portions formed in the front-rear direction of the side line.

Description

Technical Field

[0001] The present invention relates to a seat cushion spring, and more particularly to a seat cushion spring which is mounted on a seat cushion frame in a seat front-rear direction and receives a load from a seated occupant on a surface thereof. Background Art

[0002] Patent document 1 discloses a seat cushion spring which is mounted on a seat cushion frame constituting a frame of a seat cushion and bears a load of a seated occupant on its surface. The seat cushion spring includes a pair of left and right forming lines which are mounted between a frame front portion and a frame rear portion of the seat cushion frame. Each forming line is folded back into a U-shaped shape when viewed from above. The folded back center line and side line of each forming line are mounted between a frame front portion and a frame rear portion of the seat cushion frame to extend in the front-rear direction.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Publication No. 2019-73115 Summary of the invention

[0006] Problems to be solved by the invention

[0007] In the structure described in Patent Document 1, the center line and the side line are mutually symmetrical. Therefore, in order to improve the roll rigidity of the side portion of the seat cushion, it is necessary to try to partially harden the side portion of the seat cushion cushion pad. However, in the structure in which the hardness of the seat cushion cushion pad is partially changed, fatigue, position deviation, and hardness deviation of the cushion pad are likely to occur, and the roll rigidity cannot be stably improved. Therefore, the present invention provides a seat cushion spring that can appropriately improve the roll rigidity of the side portion of the seat cushion.

[0008] Technical solutions to solve problems

[0009] As a means for solving the above-mentioned problems, the seat cushion spring of the present invention adopts the following means.

[0010] That is, the first invention of the present invention is a seat cushion spring, which is mounted on a seat cushion frame in the front-rear direction of the seat to bear the load of a seated occupant on its surface, wherein the seat cushion spring has: a molded line, which is mounted on the seat cushion frame in the front-rear direction of the seat; and a resin component, which is combined with the molded line, the molded line is composed of a single line, the single line having a center line and side lines extending in the seat front-rear direction in a manner that is arranged in a seat width direction and one end of each of which is connected to each other, the center line and the side lines are arranged in sequence from the center of the seat cushion frame in the seat width direction toward the outside, and have a plurality of crank portions bent in a manner that is alternately folded back in a crank shape toward one side and the other side in the seat width direction, respectively, the resin component having a deflection restricting portion, the deflection restricting portion connecting the plurality of crank portions to restrict opening in the seat front-rear direction between three or more continuously arranged crank portions formed in front of and behind the side lines.

[0011] According to the first invention, the bending limiting portion of the resin component effectively limits the bending of the crank portion formed on the side line. As a result, the side line is less likely to sink downward when the side line receives the load of the seated occupant on the surface. As a result, the roll rigidity of the side portion of the seat cushion can be appropriately improved.

[0012] A cushion spring according to a second aspect of the present invention is the first aspect, wherein the resin member has a cushion support surface that supports the seat cushion cushion in a planar manner from a cushion back side at a position higher than the plurality of crank portions.

[0013] According to the second technical solution, the cushion pad support surface formed on the resin member can function as a receiving surface when the load of the seated occupant is applied to the side portion of the seat cushion. The cushion pad support surface is integrally provided on the side line of the cushion spring where the deflection is restricted, so that the cushion spring can be stably supported and is difficult to sink downward.

[0014] A seat cushion spring according to a third aspect of the present invention is the seat cushion spring of the first or second aspect, wherein the deflection restricting portion extends so as to continuously connect all of the crank portions in the seat front-rear direction.

[0015] According to the third invention, it is possible to more effectively restrict the side line from sinking downward. As a result, it is possible to more appropriately increase the roll rigidity of the side portion of the seat cushion.

[0016] A fourth aspect of the present invention is a seat cushion spring according to the third aspect, wherein the deflection restricting portion has an expansion portion that continuously or intermittently expands a connection width in the seat width direction of a portion connecting the crank portions toward the rear of the seat and toward the inside in the seat width direction.

[0017] According to the fourth invention, the hardness of the side portion of the seat cushion can be adjusted so that the roll rigidity increases toward the rear of the seat where the seat pressure of the seated passenger increases, and decreases toward the front of the seat where the seat pressure of the seated passenger decreases. Thus, the improvement of the riding comfort when sitting and the improvement of the roll rigidity can be achieved at the same time.

[0018] A seat cushion spring according to a fifth aspect of the present invention is the seat cushion spring according to the fourth aspect, wherein the expansion portion extends inward in the seat width direction beyond the crank portion.

[0019] According to the fifth invention, in the region where the expansion portion protrudes inward in the seat width direction beyond the crank portion, the roll rigidity of the side portion of the seat cushion can be more appropriately increased.

[0020] A cushion spring according to a sixth aspect of the present invention is the first or second aspect, wherein the molding line is formed into a shape symmetrical in the seat width direction, and a pair of molding lines are provided symmetrically in the seat width direction with respect to the seat cushion frame.

[0021] According to the sixth invention, the shaping line can be easily shaped by making the shaping line symmetrical. In addition, the roll rigidity of both side portions of the seat cushion can be relatively easily increased symmetrically in the seat width direction. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a perspective view showing a schematic structure of a cushion spring according to the first embodiment.

[0023] Figure 2 It is a perspective view showing the inner frame of a seat cushion.

[0024] Figure 3 It is a three-dimensional diagram of a seat spring.

[0025] Figure 4 It is a three-dimensional diagram of the forming line.

[0026] Figure 5 It is a top view of the seat spring.

[0027] Figure 6 is along Figure 5 This is a cross-sectional view of the seat cushion cut along line VI-VI. DETAILED DESCRIPTION

[0028] Hereinafter, a mode for carrying out the present invention will be described using the drawings.

[0029] 《First Implementation Mode》

[0030] (Schematic Structure of Seat Cushion Spring 10)

[0031] First, use Figure 1 to Figure 6 The structure of the cushion spring 10 according to the first embodiment of the present invention will be described. In the following description, when directions such as front, back, up, down, left, and right are indicated, these directions are indicated in the drawings.

[0032] In addition, when "seat" is indicated in various directions such as "seat width direction", it means various directions based on the seat cushion 1. In the following description, when no specific reference drawing is shown or when there is no corresponding reference numeral in the reference drawing, reference will be made to the corresponding reference numeral as appropriate. Figure 1 to Figure 6 Any graph in .

[0033] like Figure 1 As shown, the cushion spring 10 of the present embodiment is applied to a seat cushion 1 of a vehicle seat. The vehicle seat includes a seat back (not shown) serving as a backrest for a seated passenger and a seat cushion 1 serving as a seat portion.

[0034] The seat cushion 1 is installed on a floor of a vehicle (not shown) and includes a seat cushion frame 2 constituting a frame thereof, a seat cushion cushion 3 covering the seat cushion frame 2 from above, and a seat cushion cover 4 covering the seat cushion cushion 3 from a cushion surface side.

[0035] The seat cushion 1 also includes a cushion spring 10 that is spanned on the seat cushion frame 2 in the seat front-rear direction. The cushion spring 10 functions as a cushion receiving portion that receives a load of a seated occupant on its surface via the seat cushion cushion pad 3 .

[0036] like Figure 2 As shown in FIG. 1 , the seat cushion frame 2 is composed of metal parts assembled into a frame shape in a plan view. Specifically, the seat cushion frame 2 includes lower arms 2A constituting left and right side frames of the seat cushion 1, and a front pipe 2B integrally mounted between the front portions of the lower arms 2A. In addition, the seat cushion frame 2 also includes a rear pipe 2C integrally mounted between the rear portions of the lower arms 2A, and a front panel 2D integrally mounted between the upper edges of the front end portions of the lower arms 2A.

[0037] Reference Figure 1 The seat cushion cushion pad 3 is made of a polyurethane foamed body. The seat cushion cushion pad 3 is provided in a manner to cover the entire upper area of ​​the seat cushion frame 2 from above the seat. Thus, the seat cushion cushion pad 3 is provided in a manner in which its peripheral portion is hard supported by the seat cushion frame 2 from below the seat and its central portion is softly supported by the seat cushion spring 10 from below the seat.

[0038] The seat cushion cover 4 is composed of a fabric surface member. The seat cushion cover 4 covers the seat cushion cushion pad 3 provided on the upper portion of the seat cushion frame 2 from the cushion surface side. And, each end of the front, rear, left, and right sides of the seat cushion cover 4 is pulled under the seat and fixed to the seat cushion frame 2. As a result, the seat cushion cover 4 is greatly stretched on the cushion surface of the seat cushion cushion pad 3, and the seat cushion cushion pad 3 is pressed against the upper portion of the seat cushion frame 2 to be kept in a fixed position.

[0039] like Figure 3 As shown in FIG. 1 , the seat cushion spring 10 includes a pair of left and right molded wires 11 formed of round rod-shaped processed springs bent into a U-shape in a plan view, and a resin member 12 connected to each molded wire 11. Figure 4 As shown, each shaping wire 11 is composed of a single wire bent into a U-shape in plan view.

[0040] Specifically, each shaping line 11 is formed of a line bent into a U-shaped shape in plan view, which has a center line 11A and a side line 11B arranged in the seat width direction and extending in the seat front-rear direction. The center line 11A and the side line 11B are formed into a U-shaped shape in plan view, with their rear ends connected to each other and their front ends open.

[0041] Each of the shaping lines 11 is symmetrical in shape in the seat width direction. In addition, each of the shaping lines 11 is arranged symmetrically in the seat width direction. Figure 3 As shown, the respective shaping lines 11 are provided such that a line arranged on the center side of the seat width direction of the seat cushion frame 2 is a center line 11A and a line arranged on the outside is a side line 11B.

[0042] A front hooking portion 11C is formed at each front end of the center line 11A and the side line 11B of each shaping line 11, and is bent into a shape that can be hooked on the front tube 2B from above. Also, a rear hooking portion 11D is formed at each rear end of the center line 11A and the side line 11B of each shaping line 11, and is bent into a shape that can be hooked on the rear tube 2C from above.

[0043] like Figure 4 As shown, a plurality of crank portions A1 and B1 are formed on the center line 11A and the side line 11B of each of the forming lines 11. The crank portions A1 formed on the center line 11A and the crank portions B1 formed on the side line 11B of each of the forming lines 11 are bent to be close to or away from each other in the seat width direction, and are symmetrical in the seat width direction.

[0044] Each of the shaping lines 11 is formed to extend in the seat width direction in addition to the seat front-rear direction by the crank portions A1 and B1. Thus, each of the shaping lines 11 is configured to support the seat cushion cushion pad 3 in a planar manner from the back side of the cushion pad (see Figure 1 ).

[0045] In each of the shaping lines 11, the center line 11A and the side line 11B are formed to be bent into a V-shape in a side view. By bending in the V-shape, each shaping line 11 can make the seat cushion cushion pad 3 (see Figure 1 )'s rear portion (the portion where the cushion pad is thicker toward the bottom) that supports the seated occupant's ischium is sunk deeply downward.

[0046] like Figure 3 As shown, the resin member 12 is combined with each molding line 11 in a symmetrical shape in the seat width direction. Specifically, the resin member 12 has a pair of deflection restricting portions 12A combined with each molding line 11 in a form extending in the seat front-rear direction along each side line 11B.

[0047] In addition, the resin member 12 has a cushion support surface 12B constituting the upper surface of each deflection restricting portion 12A. Each cushion support surface 12B is formed at a position higher than each side line 11B, and constitutes a cushion support surface 12B for supporting the seat cushion cushion 3 in a planar manner from the back side of the cushion (see Figure 1 ) support surface.

[0048] The resin member 12 also has a connection portion 12C extending in the seat width direction so as to connect the rear portions of the deflection restricting portions 12A. The resin member 12 is integrally formed with the molded wires 11 to be integrally connected with the molded wires 11 .

[0049] Next, the detailed structure of the resin member 12 will be described. Figure 5 As shown, the bending restricting portions 12A are formed to extend continuously in the seat front-rear direction along the straight longitudinal line portions B2 extending intermittently in the seat front-rear direction between the front hook portions 11C and the rear hook portions 11D relative to the side lines 11B. The longitudinal line portions B2 are arranged on the same straight line.

[0050] Thus, each deflection restricting portion 12A is formed to connect all the crank portions B1 adjacent to each other in front and rear of each side line 11B. Each deflection restricting portion 12A has an expansion portion A2 that extends in a manner such that the connection width of the portion connecting the crank portions B1 in the seat width direction continuously expands toward the rear of the seat and toward the inner side in the seat width direction.

[0051] Each expansion portion A2 is formed in a shape extending so as to describe an inner peripheral edge of a concave curved surface in a plan view along the outer edge of the seated person's buttocks. Due to these expansion portions A2, each deflection restricting portion 12A has a shape in which the connection width of the portion connecting the frontmost crank portion B1 of each side line 11B and the second crank portion B1 from the front is the narrowest.

[0052] Furthermore, each deflection restricting portion 12A is formed in a shape that is second to the width of the connection between the second crank portion B1 from the front and the third crank portion B1 from the front of each side line 11B. Furthermore, each deflection restricting portion 12A is formed in a shape that is second to the width of the connection between the third crank portion B1 from the front and the fourth crank portion B1 from the front of each side line 11B.

[0053] Specifically, each deflection restricting portion 12A is formed in such a shape that it extends inwardly in the seat width direction beyond the third crank portion B1 and the fourth crank portion B1 of each side wire 11B in the middle of the portion connecting the third crank portion B1 and the fourth crank portion B1 from the front, and is connected to the connecting portion 12C. In this sense, each expansion portion A2 extending inwardly in the seat width direction beyond the third crank portion B1 and the fourth crank portion B1 from the front becomes a part of the connecting portion 12C.

[0054] Each deflection restricting portion 12A is not formed in a portion (not shown) supporting the ischium of the seated occupant, but is formed at a position retreated from the portion supporting the ischium toward the outside in the seat width direction. In addition, the connecting portion 12C is also not formed in a portion (not shown) supporting the ischium of the seated occupant, but is formed at a position retreated from the portion supporting the ischium toward the rear of the seat.

[0055] The bending limiting portions 12A limit the opening of each shaping line 11 in the front-rear direction of the seat between the five crank portions B1 arranged in front and behind the side line 11B. More specifically, due to the shape of the connection width change of the bending limiting portions 12A, the opening between the frontmost crank portion B1 and the second crank portion B1 from the front of each side line 11B in the front-rear direction of the seat is most weakly limited.

[0056] Furthermore, the opening of each side wire 11B in the seat front-rear direction between the second crank portion B1 from the front and the third crank portion B1 from the front is restricted to the second degree. Furthermore, the opening of each side wire 11B in the seat front-rear direction between the third crank portion B1 from the front and the fourth crank portion B1 from the front is restricted to the second degree.

[0057] In addition, the fourth crank portion B1 and the fifth crank portion B1 from the front of each side line 11B are connected to each other over the entire area in the seat width direction by each deflection restricting portion 12A, thereby completely restricting the opening of the seat in the front-rear direction. The seat cushion spring 10 is configured by the resin member 12 so that even if the molding lines 11 are formed into shapes symmetrical to each other in the seat width direction, the center line 11A and the side line 11B are different in deflection ease when receiving a load from a seated occupant.

[0058] Specifically, if Figure 6 As shown, the seat cushion spring 10 receives a load from the seated occupant, and thus each center line 11A bends relatively softly to sink downward. On the other hand, each side line 11B is restrained from bending so as to be difficult to sink downward compared to each center line 11A.

[0059] Specifically, the bending restriction of each side line 11B is reduced toward the front side where the load applied by the seated occupant is reduced, and is increased toward the rear side where the load applied by the seated occupant is increased, by the shape of the connection width change of each bending restriction portion 12A. Thus, the roll rigidity of each side portion of the seat cushion 1 can be appropriately improved.

[0060] The cushion support surface 12B constituting the upper surface of each deflection restricting portion 12A functions as a receiving surface of the seat cushion cushion 3 when the load of the seated occupant is applied to each side portion of the seat cushion 1. Each cushion support surface 12B is integrally provided on each side line 11B of the seat cushion spring 10 where deflection is restricted, so that stable support can be achieved that is difficult to sink downward.

[0061] In more detail, the cushion support surfaces 12B are integrally connected to each other via the connection portion 12C, so when a load from a seated occupant is applied to one cushion support surface 12B, the load is also transmitted to the side line 11B on the opposite side via the other cushion support surface 12B. Thus, when a load from a seated occupant is applied to each side portion of the seat cushion 1, each cushion support surface 12B can stably receive the load without sinking downward.

[0062] like Figure 5 As shown, the grooves formed in the cushion pad support surfaces 12B along the shapes of the side lines 11B are grooves through which push pins for fixing the positions of the molding wires 11 in the molding die of the resin member 12 pass.

[0063] In summary, the cushion spring 10 of the present embodiment has the following structure. In addition, the reference numerals in parentheses below are reference numerals corresponding to the respective structures shown in the above-mentioned embodiment.

[0064] That is, the seat cushion spring (10) is a spring that is mounted on a seat cushion frame (2) in the front-rear direction of the seat and bears the load of a seated occupant on the surface. The seat cushion spring (10) includes a molding line (11) that is mounted on the seat cushion frame (2) in the front-rear direction of the seat and a resin component (12) that is connected to the molding line (11).

[0065] The shaping line (11) is composed of a line having a center line (11A) and a side line (11B) extending in the seat front-rear direction in a manner that the two lines are arranged in a seat width direction and connected to each other at one end. The center line (11A) and the side line (11B) are arranged in sequence from the center of the seat width direction of the seat cushion frame (2) toward the outside.

[0066] The center line (11A) and the side line (11B) each have a plurality of crank portions (A1, B1) bent in a manner that is alternately folded back in a crank shape toward one side and the other side in the seat width direction. The resin component (12) has a deflection limiting portion (12A) that connects the plurality of crank portions (B1) to limit the opening of three or more crank portions (B1) that are continuously arranged in the front and rear of the side line (11B) in the seat front-rear direction.

[0067] According to the above structure, the bending of the crank portion (B1) formed on the side line (11B) is effectively limited by the bending limiting portion (12A) of the resin component (12). As a result, the side line (11B) is less likely to sink downward when the surface receives the load of the seated occupant. As a result, the roll rigidity of the side portion of the seat cushion (1) can be appropriately improved.

[0068] In addition, the resin component (12) has a cushion support surface (12B) that supports the seat cushion cushion (3) in a planar manner from the back side of the cushion at a position higher than the plurality of crank portions (B1). According to the above structure, the cushion support surface (12B) formed on the resin component (12) can function as a bearing surface when a load of a seated occupant is applied to the side portion of the seat cushion (1). The cushion support surface (12B) is integrally provided on the side line (11B) of the seat cushion spring (10) that is restricted from bending, so that a stable bearing that is difficult to sink downward can be performed.

[0069] In addition, the deflection limiting portion (12A) extends in a manner that continuously connects all the crank portions (B1) in the front-rear direction of the seat. According to the above structure, the side line (11B) can be more effectively limited from sinking downward. As a result, the roll rigidity of the side portion of the seat cushion (1) can be more appropriately improved.

[0070] In addition, the deflection limiting portion (12A) has an expansion portion (A2) that continuously expands the connection width of the portion connecting the crank portions (B1) in the seat width direction toward the rear of the seat and toward the inside in the seat width direction. According to the above structure, the hardness of the side portion of the seat cushion (1) can be adjusted so that the roll rigidity increases toward the rear of the seat where the sitting pressure of the seated occupant increases, and the roll rigidity decreases toward the front of the seat where the sitting pressure of the seated occupant decreases. As a result, it is possible to simultaneously achieve an improvement in the riding comfort when sitting and an improvement in the roll rigidity.

[0071] In addition, the expansion portion (A2) extends inwardly in the seat width direction beyond the crank portion (B1). According to the above structure, in the area where the expansion portion (A2) extends inwardly in the seat width direction beyond the crank portion (B1), the roll rigidity of the side portion of the seat cushion (1) can be more appropriately improved.

[0072] In addition, the shaping line (11) is set to have a symmetrical shape in the seat width direction, and a pair of shaping lines (11) are provided in a manner symmetrical with respect to the seat cushion frame (2) in the seat width direction. According to the above configuration, the shaping line (11) can be easily shaped by making the shaping line (11) have a symmetrical shape. In addition, the roll rigidity of both side portions of the seat cushion (1) can be relatively easily increased in a symmetrical shape in the seat width direction.

[0073] 《Regarding other implementation methods》

[0074] As mentioned above, although the embodiment of the present invention was described using one embodiment, the present invention can be implemented in various forms other than the above-described embodiment.

[0075] 1. The seat cushion spring of the present invention can be applied to seat cushions of seats mounted on vehicles such as automobiles and railways, and can also be applied to seat cushions of seats mounted on vehicles other than vehicles such as airplanes and ships. In addition, the seat cushion spring can also be applied to seat cushions of seats other than vehicles.

[0076] 2. The seat cushion springs do not necessarily need to be arranged in a pair so that the forming lines are symmetrical with respect to the seat cushion frame in the seat width direction. That is, one forming line may be formed in a shape different from the other forming line. In addition, the forming lines do not necessarily need to be formed in a shape in which the center line and the side line are symmetrical with each other in the seat width direction.

[0077] 3. The cushion support surface of the resin component may form the upper surface of the region deviating from the deflection limiting portion in addition to the upper surface of the deflection limiting portion. The deflection limiting portion may be a structure that connects a plurality of crank portions to limit the opening of three or more crank portions arranged in a row in the front-rear direction of the seat. Therefore, the deflection limiting portion may be configured to directly connect only the frontmost crank portion and the last crank portion of the three or more crank portions arranged in a row, without connecting the crank portions between them.

[0078] The expansion portion of the deflection limiting portion may be discontinuously expanded in addition to continuously expanding the connection width of the portion connecting the crank portions in the seat width direction toward the rear of the seat and toward the inner side in the seat width direction. That is, it may also be provided with a region where the connection width is locally narrowed or constant. In addition, the deflection limiting portion may be a structure in which the connection width is constant in the entire region in the front-rear direction of the seat, or a shape in which the connection width is expanded toward the front of the seat.

[0079] Description of Reference Numerals

[0080] 1 Seat cushion

[0081] 2 Seat cushion frame

[0082] 2A Lower arm

[0083] 2B front pipe

[0084] 2C rear pipe

[0085] 2D front panel

[0086] 3 Seat cushion cushion

[0087] 4 Seat cushion cover

[0088] 10 Seat spring

[0089] 11 Forming line

[0090] 11A Central Line

[0091] A1 Crank

[0092] 11B Siding

[0093] B1 Crank

[0094] B2 vertical line

[0095] 11C Front hook

[0096] 11D rear hook

[0097] 12 Resin parts

[0098] 12A Deflection limiting section

[0099] A2 Expansion

[0100] 12B cushion support surface

[0101] 12C Connection

Claims

1. A seat spring, the surface of which bears the load of a seated occupant, wherein: The seat cushion spring has: A forming line is mounted on the seat cushion frame in the front-rear direction of the seat; and The resin part, combined with the molding wire, The shaping line is composed of one line having a center line and side lines extending in the seat front-rear direction in a manner that the two lines are arranged in the seat width direction and one end of each line is connected to each other. The center line and the side line are arranged in order from the center of the seat width direction of the seat cushion frame toward the outside, and have a plurality of crank portions bent in a crank-like manner alternately folded back in one direction and the other direction in the seat width direction, respectively. The resin member has a deflection restricting portion that connects the plurality of crank portions to restrict opening in the seat front-rear direction between three or more crank portions that are continuously arranged and formed in front of and behind the side line.

2. The seat spring according to claim 1, wherein: The resin member has a cushion pad support surface that supports the seat cushion cushion pad from a back side of the cushion pad at a position higher than the plurality of crank portions.

3. The seat spring according to claim 1 or 2, wherein: The deflection restricting portion extends so as to continuously connect all of the crank portions in the seat front-rear direction.

4. The seat spring according to claim 3, wherein: The deflection restricting portion includes an expansion portion that continuously or intermittently expands a connection width in the seat width direction of a portion connecting the crank portions to each other toward the rear of the seat toward the inner side in the seat width direction.

5. The seat spring according to claim 4, wherein: The expansion portion extends inward in the seat width direction beyond at least one of the crank portions.

6. The seat spring according to claim 1 or 2, wherein: The shaping lines are formed into shapes that are symmetrical in the seat width direction, and are provided in pair in a symmetrical manner with respect to the seat cushion frame in the seat width direction.

7. The seat spring according to claim 2, wherein: The cushion support surface has a groove concave along the shape of the side line.

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