Seat backs for vehicle seats

Abstract

To prevent heat generated by an inflator from reaching a connection member that connects end parts of a first webbing and a second webbing with each other in a storage part of a cushion member storing an airbag and the inflator.SOLUTION: A headrest comprises: side frames 54 disposed inside a cushion member 20 in which a storage part 40 is formed; a skin material 76 covering a surface of the cushion member; an airbag 74 stored in a folded state in the storage part; an inflator 64 disposed in the storage part; a first webbing 92 where one end part 92A is connected to a cleavage; a second webbing 96 where the one end part 96A is connected to the cleavage and the other end part 96B is connected to the other end part 92B of the first webbing; and a connection member 98 that connects the other end parts of the first webbing and the second webbing with each other in the storage part. As viewed along an axis line 64X of the inflator, front end parts 58 of the side frames are located in front of the inflator and the connection member is located in front of the front end parts of the side frames.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a seat back for a vehicle seat. [Background technology]

[0002] Patent Document 1 below discloses a vehicle seat. The seatback of this vehicle seat includes a cushion member having a storage section (recess) formed on one side, an airbag stored in the storage section in a folded state, and an inflator provided in the storage section. The seatback also includes a cover material that covers the surface of the cushion member and has a tear section formed therein. Furthermore, one end of a first webbing and a second webbing are connected to the tear section of the cover material.

[0003] When a collision occurs in a vehicle equipped with this vehicle seat and the inflator generates gas, the airbag supplied with the gas inflates to the outside of the skin material while tearing the tearing portion. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 3520357 Summary of the Invention [Problem to be solved by the invention]

[0005] Here, it is assumed that the other ends of the first and second webbing are positioned inside the storage compartment and sewn together with sewing thread, in which case the sewing thread may be significantly affected by the heat generated by the inflator when gas is generated.

[0006] In consideration of the above, the present invention aims to provide a seat back for a vehicle seat that is less susceptible to the effects of heat generated by an inflator on a joining member that joins the ends of a first webbing and a second webbing within a storage section of a cushion member that stores an airbag and an inflator. [Means for solving the problem]

[0007] The seat back of a vehicle seat according to the invention of claim 1 comprises a cushion member having a hollow storage portion formed on a side portion thereof, side frames that form sides of a seat back frame provided inside the cushion member, a skin covering a surface of the cushion member, an airbag stored in a folded state in the storage portion, and a cylindrical inflation device that is provided in the storage portion while being fixed to the side frames and that is capable of supplying gas to the airbag so that the airbag inflates outward from the skin member while tearing a tear portion formed in a part of the skin member. a first webbing having one end connected to the tear portion; a second webbing having one end connected to the tear portion and the other end connected to the other end of the first webbing, which forms a storage space between the first webbing and the second webbing to store the airbag and the inflator; and a joining member joining the other end portions of the first webbing and the second webbing together in the storage space, wherein, when viewed along the axis of the inflator, the front end of the side frame is located forward of the inflator, and the joining member is located forward of the front end of the side frame.

[0008] When the seat back of claim 1 is viewed along the axis of the inflator, the front end of the side frame is located forward of the inflator, and the joining member joining the other ends of the first webbing and the second webbing to each other is located forward of the front end of the side frame. That is, the distance between the inflator and the joining member in the front-to-rear direction is a certain length. Therefore, the joining member in the storage section of the cushion member is less susceptible to the heat generated by the inflator when gas is generated.

[0009] The seat back of the vehicle seat according to the invention described in claim 2 is the seat back of the vehicle seat described in claim 1, in which an inner end face, which is the inner end face of the storage section on the widthwise inner side of the seat back, faces the other end portions of the first webbing and the second webbing.

[0010] If the other ends of the first and second webbing were located at the widthwise outer edge of the seat back of the storage compartment, the other ends of the first and second webbing would press against the inner surface of the upholstery material, and a portion of the upholstery material pressed by the other ends would bulge outward. However, in the seat back of claim 2, the inner end face of the storage compartment and the other ends of the first and second webbing face each other. Therefore, there is no risk of a portion of the upholstery material bulging outward due to the other ends of the first and second webbing.

[0011] The seat back of a vehicle seat according to the invention of claim 3 is the seat back of the vehicle seat according to claim 2, wherein when viewed along the axis of the inflator, the front end face of the storage section is located forward of the front end face of the side frame, and the portion where the front end face and the inner end face of the storage section are connected faces the other end faces of the first webbing and the second webbing.

[0012] In the seat back of claim 3, the portion where the front end surface and the inner end surface of the storage portion are connected faces the other ends of the first webbing and the second webbing. Therefore, the distance between the inflator and the joining member in the front-to-rear direction is long. Therefore, the joining member in the storage portion of the cushion member is less likely to be affected by heat generated by the inflator.

[0013] The seat back of a vehicle seat according to the invention of claim 4 is the seat back of a vehicle seat according to claim 1 or claim 2, wherein the one end portions of the first webbing and the second webbing are sewn to the tear portion by a first sewing thread, and the other end portions of the first webbing and the second webbing are sewn to each other by a second sewing thread that is stronger than the first sewing thread.

[0014] In the seat back of claim 4, one end of the first webbing and the second webbing are sewn to the tear portion with a first sewing thread, and the other end of the first webbing and the second webbing are sewn to each other with a second sewing thread that is stronger than the first sewing thread. Therefore, the second sewing thread is less likely to be damaged by the heat generated by the inflator than when the strength of the second sewing thread is equal to or less than the strength of the first sewing thread. [Effects of the Invention]

[0015] As described above, according to the seat back of the vehicle seat of the present invention, the joining member that joins the ends of the first webbing and the second webbing within the storage section of the cushion member that stores the airbag and the inflator is less susceptible to the effects of heat generated by the inflator. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a perspective view of a vehicle seat including a seat back according to an embodiment of the present invention; [Figure 2] FIG. 2 is an exploded perspective view of the cover material, the cushion member, and the inflator as viewed from the rear. [Figure 3] FIG. 10 is a cross-sectional view of the front central constituent portion and front side constituent portion of the covering material, and the joining portion of the first webbing and the second webbing. [Figure 4] FIG. 4 is a rear view of the cushion member and the seat back frame. [Figure 5] FIG. 5 is a cross-sectional view taken along the arrow line 5-5 in FIG. 4. DETAILED DESCRIPTION OF THE INVENTION

[0017] A vehicle seat 10 (hereinafter referred to as seat 10) according to an embodiment of the present invention will be described below with reference to the accompanying drawings. Note that the arrow FR shown as appropriate in each drawing indicates the front direction of the vehicle, the arrow UP indicates the upward direction of the vehicle, and the arrow LH indicates the left side in the left-right direction of the vehicle (vehicle width direction). Hereinafter, when the terms front-rear, left-right, and up-down are used in the description, they refer to front-rear in the front-rear direction of the vehicle, left-right in the left-right direction of the vehicle (vehicle width direction), and up-down in the up-down direction of the vehicle.

[0018] 1 is provided on a floor surface 100 of the vehicle interior. The seat 10 includes a seat cushion 11, a seat back 15 whose lower end is rotatably connected to the rear end of the seat cushion 11, and a headrest 99. The seat cushion 11 is supported by slide rails (not shown) installed on the floor surface 100.

[0019] The seat back 15 includes a cushion member 20, a seat back frame 50, an inflator 64, an airbag 74, a cover material 76, a first webbing 92, and a second webbing 96.

[0020] The cushion member 20 shown in FIGS. 2, 4, and 5 is made of, for example, polyurethane foam. The cushion member 20 has a main body portion 22 and a back portion 24. The back portion 24 forms the rear of the cushion member 20, and the main body portion 22 forms the rest of the cushion member 20. The back portion 24 has an upper component portion 26 and a pair of left and right side component portions 28 extending downward from both left and right ends of the upper component portion 26. As shown in FIGS. 4 and 5, a frame accommodating space 30 that is generally U-shaped in rear view is formed between the rear surface of the main body portion 22 and the back portion 24. The frame accommodating space 30 includes an upper space 32 formed between the upper component portion 26 and the rear surface of the main body portion 22, a left side space 34 formed between the right half of the left side component portion 28 and the rear surface of the main body portion 22, and a right side space 36 formed between the left half of the right side component portion 28 and the rear surface of the main body portion 22. Furthermore, the lower ends of the left side space 34 and the right side space 36 are open at the lower end faces of the left and right side constituent parts 28 .

[0021] The cushion member 20 has a pair of left and right side portions 38. The left side portion 38 is formed by the left side portion of the main body portion 22, the left end portion of the upper constituent portion 26, and the left side constituent portion 28, while the right side portion 38 is formed by the right side portion of the main body portion 22, the right end portion of the upper constituent portion 26, and the right side constituent portion 28. Furthermore, the front portions of the left and right side portions 38 are formed by bulging portions 39 that protrude forward from the center portion of the front surface of the cushion member 20 (see FIG. 5). A hollow recess (storage portion) 40 extending in the vertical direction is formed in the side surface (surface) of the left side portion 38. The side shape of the recess 40 is approximately rectangular. Furthermore, as shown in FIG. 5, the cross-sectional shape of the recess 40 when cut along a horizontal plane is also approximately rectangular. A corner 46 is defined as a portion where an inner end surface 42, which is the inner end surface of the recess 40 in the vehicle width direction, and a front end surface 44 of the recess 40 intersect. The right side of the corner 46 is formed by the front end of the inner end surface 42. Furthermore, the rear part of the recess 40 communicates with part of the left side space 34.

[0022] 4, the metal seatback frame 50, which is a framework member of the seatback 15, includes an upper frame 52 extending in the left-right direction, and a pair of left and right side frames 54 extending downward from both left and right ends of the upper frame 52. The cushion member 20 is fixed to the seatback frame 50 with the upper frame 52 inserted into the upper space 32, the left side frame 54 inserted into the left side space 34, and the right side frame 54 inserted into the right side space 36. The lower ends of the left and right side frames 54 protrude downward from the lower ends of the left and right side constituent parts 28.

[0023] As shown in FIG. 5 , the left side frame 54 has a base 56 that contacts the left end face of the left side space 34, a front end 58 that contacts the front end face of the left side space 34, and a rear end 60 that contacts the rear end face of the left side space 34. Furthermore, although not shown, a pair of upper and lower through holes are formed in the base 56. The right side frame 54 is bilaterally symmetrical to the left side frame 54, except that it does not have through holes. That is, the right side frame 54 has a base 56 that contacts the right end face of the right side space 36, a front end 58 that contacts the front end face of the right side space 36, and a rear end 60 that contacts the rear end face of the right side space 36.

[0024] As shown in FIG. 2, the inflator 64 is a cylindrical member extending along an axis 64X. That is, the inflator 64 is a cylinder-type inflator. The overall length (vertical length) of the inflator 64 is shorter than the overall length (vertical length) of the recess 40. An ejection portion 66 is provided at the upper end of the inflator 64. Furthermore, one end of metal stud bolts 68 is fixed to two locations, one above and one below, on the outer circumferential surface (surface) of the inflator 64. Furthermore, a connecting portion (not shown) formed on the airbag 74 shown in FIG. 5 is airtightly connected to the ejection portion 66 of the inflator 64.

[0025] 1 and 2, the cover material 76 has an upper component 78, a front center component 80, a pair of left and right front side component parts 82, a pair of left and right side component parts 84, and a back component part 86. The cover material 76 is made of a flexible material. For example, the cover material 76 is made of genuine leather or synthetic leather. The front edge of the upper component part 78 and the upper edge of the front center component part 80 are sewn together with sewing thread (not shown), both left and right side edges of the upper component part 78 and the upper edges of the left and right side component parts 84 are sewn together with sewing thread (not shown), and the rear edge of the upper component part 78 and the upper edge of the back component part 86 are sewn together with sewing thread (not shown). Furthermore, the right front side component part 82 is sewn together with the right edge of the front center component part 80 and the front edge of the right side component part 84 with sewing thread (not shown). Furthermore, the left front side constituent part 82 is sewn with sewing thread (not shown) to the left edge of the front central constituent part 80. Furthermore, a first fastener 88 is provided at the rear edge of the left side surface constituent part 84 and the left edge of the back surface constituent part 86, and a second fastener 90 is provided at the rear edge of the right side surface constituent part 84 and the right edge of the back surface constituent part 86.

[0026] As shown in Figures 2, 3, and 5, the left edge of the left front side constituent part 82 and the front edge of the left side surface constituent part 84 are in contact with each other. Furthermore, one end (front end) 92A, 96A of a first webbing 92 and a second webbing 96, which are reinforcing fabrics, are joined (connected) to the left edge of the left front side constituent part 82 and the front edge of the left side surface constituent part 84 using a first sewing thread 94, which will be described later. The first webbing 92 and the second webbing 96 are both substantially rectangular when deployed. The vertical dimensions of the first webbing 92 and the second webbing 96 are substantially the same and are shorter than the vertical dimensions of the front side constituent part 82 and the side surface constituent part 84. The first webbing 92 and the second webbing 96 are made of a material that is less stretchy than the front side constituent part 82 and the side surface constituent part 84. For example, the first webbing 92 and the second webbing 96 are made of a resin sheet or polyester nonwoven fabric.

[0027] 3, the left side edge of the left front side constituent portion 82 and the front edge of the left side face constituent portion 84 are folded backward, and these left side edges and front edges are in contact with each other. Furthermore, one end portion 92A, 96A of the first webbing 92 and the second webbing 96 are sewn over their entire lengths to the left side edge of the left front side constituent portion 82 and the front edge of the left side face constituent portion 84 in the vertical center portion with a first sewing thread 94. Furthermore, the left side edge of the left front side constituent portion 82 and the front edge of the left side face constituent portion 84 are sewn together with the first sewing thread 94 except for the center portion.

[0028] As shown in FIG. 2, a pair of upper and lower through-holes 93 are formed in the first webbing 92. As shown in FIG. 5, the other end portions (rear end portions) 92B, 96B of the first webbing 92 and the second webbing 96 are sewn together along their entire lengths with a second sewing thread (jointing member) 98. That is, the first webbing 92 and the second webbing 96 form a tubular body that is open at both the top and bottom. A storage space SP is formed inside this tubular body (see FIG. 5). The first sewing thread 94 and the second sewing thread 98 are made of the same material, but the second sewing thread 98 is thicker than the first sewing thread 94. Therefore, the second sewing thread 98 has higher mechanical strength and heat resistance than the first sewing thread 94.

[0029] The covering material 76 (first webbing 92, second webbing 96), the inflator 64, and the airbag 74 are attached to the cushion member 20 in the following procedure.

[0030] 2, the first fastener 88 and the second fastener 90 of the covering material 76 separated from the cushion member 20 are opened. Next, the front central constituent portion 80 and the front side constituent portion 82 of the covering material 76, which are positioned immediately in front of the cushion member 20, are placed over the front surface of the cushion member 20, and the upper constituent portion 78 is placed over the top surface of the cushion member 20. Furthermore, the inflator 64 and airbag 74 integrated body is inserted into the storage space SP, which is the internal space of the first webbing 92 and the second webbing 96, so that the pair of stud bolts 68 fixed to the inflator 64 pass through the through holes 93 of the first webbing 92.

[0031] Next, the left side surface constituent part 84 is brought close to the left side part 38 of the cushion member 20 from the left side, and the one piece including the inflator 64, the airbag 74, the first webbing 92, and the second webbing 96 is inserted into the recess 40. Furthermore, the pair of stud bolts 68 fixed to the inflator 64 are inserted into the pair of through-holes in the side frame 54, and a portion of the first webbing 92 is sandwiched between the outer peripheral surface of the inflator 64 and the left side surface of the base 56, as shown in FIG. 5. Furthermore, the nuts 70 threaded onto each stud bolt 68 are pressed against the right side surface of the base 56. This fixes the inflator 64 to the base 56, and the base 56 and the inflator 64 are approximately parallel in a side view. Furthermore, as shown in FIG. 5, almost the entire recess 40 is filled with the inflator 64 and the airbag 74. As a result, a portion of the first webbing 92 contacts the inner end surface 42 and rear end surface 45 of the recess 40 and the left side surface of the base 56, and a portion of the second webbing 96 contacts the front end surface 44 of the recess 40. Furthermore, the other end 92B of the first webbing 92, the other end 96B of the second webbing 96, and the second sewing thread 98 are located at the corner 46. Furthermore, a flow path forming portion 96C, which is a portion of the second webbing 96 located forward of the recess 40, contacts the side surface of the left side constituent member 28, and the flow path forming portion 92C, which is the front portion of the first webbing 92, faces the flow path forming portion 96C.

[0032] 5, when the inside of the seat back 15 is viewed along the axis 64X, the front end portions 58 of the side frames 54 are located forward of the front ends of the inflator 64 at any position in the direction of the axis 64X. Furthermore, when the inside of the seat back 15 is viewed along the axis 64X, the distance LF1 from the front end of the inflator 64 to the front surface of the front end portion 58 is longer than the distance LR from the rear end of the inflator 64 to the rear end surface 45 of the recessed portion 40 at any position in the direction of the axis 64X. Furthermore, the distance LF2 from the front end of the inflator 64 to the front end surface 44 of the recessed portion 40 is longer than the distance LF1 at any position in the direction of the axis 64X.

[0033] Finally, the left and right side surface constituent parts 84 are placed over the side surfaces of the left and right side parts 38 of the cushion member 20, respectively (see FIG. 5 for the left side surface constituent part 84), and the back surface constituent part 86 is placed over the back surface of the cushion member 20. Then, the first fastener 88 and the second fastener 90 are closed. This completes the seat back 15 shown in FIG. 1. A headrest 99 is attached to the upper end of the completed seat back 15. Furthermore, the lower ends of the left and right side frames 54 are connected to a reclining device (not shown) provided at the rear end of the seat cushion 11. This completes the seat 10 shown in FIG. 1.

[0034] Next, the operation and effects of this embodiment will be described.

[0035] For example, when a vehicle equipped with the seat 10 collides with another object, the inflator 64 is activated and generates high-pressure gas. When this high-pressure gas is supplied from the ejection portion 66 to the interior of the airbag 74, the airbag 74 inflates while unfolding. As described above, the first webbing 92 and the second webbing 96 are less likely to stretch than the front side constituent portion 82 and the side surface constituent portion 84. Therefore, at this time, the first webbing 92 and the second webbing 96 limit the inflation direction of the airbag 74 to the forward direction. The airbag 74 inflates forward and passes between the flow path forming portions 92C and 96C. Furthermore, as the airbag 74 inflates forward, a large pressure is applied to one end 92A of the first webbing 92 and one end 96A of the second webbing 96. As a result, the first sewing thread 94 breaks, and the left edge of the front side constituent portion 82 and the right edge of the side surface constituent portion 84 are torn apart. The airbag 74 inflates toward the front of the seat back 15 through a rupture (opening) formed between the front side constituent portion 82 and the side surface constituent portion 84 .

[0036] When the inflator 64 generates gas, a large amount of heat generated by the inflator 64 is released into the recess 40 (storage space SP). For example, when the second sewing thread 98 (other ends 92B, 96B) is at position P1 indicated by the imaginary line in FIG. 5, the distance from the inflator 64 to the second sewing thread 98 is short, so a large amount of heat reaches the second sewing thread 98. In this case, there is a risk that the second sewing thread 98 will break due to the influence of heat before the airbag 74 inflates forward of the seatback 15 through the tear portion (opening). In this case, the function of the first webbing 92 and the second webbing 96 to limit the inflation direction of the airbag 74 is reduced, making it difficult for the airbag 74 to inflate forward of the seatback 15.

[0037] In contrast, in the seat back 15 of this embodiment, when the interior of the seat back 15 is viewed along the axis 64X of the inflator 64, the front end of the front end portion 58 of the side frame 54 is located forward of the front end of the inflator 64 at any position along the axis 64X, and the second sewing thread 98, which is a joining member joining the other ends 92B, 96B, is located forward of the front end of the front end portion 58. More specifically, the second sewing thread 98 is located at the corner portion 46. That is, the distance from the front end of the inflator 64 to the second sewing thread 98 is long. Therefore, the heat generated by the inflator 64 is less likely to affect the second sewing thread 98. Therefore, in this embodiment, when the inflator 64 generates heat, there is little risk that the function of the first webbing 92 and the second webbing 96 to limit the inflation direction of the airbag 74 will be reduced. Therefore, the airbag 74 is likely to inflate smoothly toward the front of the seat back 15.

[0038] Furthermore, if the other end portions 92B, 96B were located at the left end portion of the recessed portion 40 of the cushion member 20, the other end portions 92B, 96B would be pressed against the inner surface of the side surface forming portion 84 via the first webbing 92, and a portion of the side surface forming portion 84 pressed by the other end portions 92B, 96B might bulge outward. However, in this embodiment, the other end portions 92B, 96B are located at the corner portion 46 that is spaced to the right of the left end portion of the recessed portion 40. In other words, the other end portions 92B, 96B face the front end portion of the inner end surface 42 of the recessed portion 40. Therefore, there is no risk of a portion of the side surface forming portion 84 bulging outward due to the other end portions 92B, 96B.

[0039] Furthermore, the second sewing thread 98 has higher mechanical strength and heat resistance than the first sewing thread 94. Therefore, the second sewing thread 98 is less likely to be damaged by the heat generated by the inflator 64 than when the mechanical strength and heat resistance of the second sewing thread 98 are equal to or lower than those of the first sewing thread 94.

[0040] Although the embodiment of the present invention has been described above, the present invention is not limited to this embodiment.

[0041] For example, when looking at the inside of the seat back 15 along the axis 64X of the inflator 64, the other ends 92B, 96B and the second sewing thread 98 may be located rearward of the corner 46 at any position in the direction of the axis 64X, as long as they are located forward of the front end 58.

[0042] Furthermore, the positions of the other ends 92B, 96B and the second sewing thread 98 may be different from the right edge of the recess 40. For example, the positions of the other ends 92B, 96B and the second sewing thread 98 may be to the left of the inner end surface 42 and opposite the front end surface 44 of the recess 40.

[0043] The other end portions 92B and 96B may be joined by a joining member other than the second sewing thread 98. For example, the joining member may be an adhesive that bonds the other end portions 92B and 96B together. Alternatively, the other end portions 92B and 96B may be heat-welded together.

[0044] A recess 40 may be formed on the side surface (surface) of the right side portion 38, and the inflator 64 and the airbag 74 may be stored in this recess 40. In this case, when the inflator 64 generates gas, the inflated airbag 74 inflates forward of the seat back 15 while rupturing the joint between the right front side portion constituent portion 82 and the side surface constituent portion 84.

[0045] A hollow storage section with a closed left end may be formed inside the left side portion 38 in place of the recess 40, and the inflator 64 and the airbag 74 may be stored in this storage section. Also, a hollow storage section with a closed right end may be formed inside the right side portion 38 in place of the recess 40, and the inflator 64 and the airbag 74 may be stored in this storage section. [Explanation of symbols]

[0046] 10 Vehicle seats (seats) 15 Seat back 20 Cushion member 40 Recessed portion (storage area) 42 Inner end face 50 Seat back frame 54 Side frame 58 Front end 64 Inflator 64X axis 74 Airbag 76 Skin material 92 1st Lifu 92A One end 92B Other end 94 First Sewing Thread 96 2nd Lifu 96A One end 96B Other end 98 Second sewing thread (jointing material) SP storage space

Claims

1. a cushion member having a hollow storage portion formed on a side thereof; a side frame that forms a side portion of a seat back frame provided inside the cushion member; a skin material covering the surface of the cushion member; an airbag stored in a folded state in the storage section; a cylindrical inflator that is provided in the storage section while being fixed to the side frame and that is capable of supplying gas to the airbag so that the airbag inflates to the outside of the skin material while tearing a tearing portion formed in a part of the skin material; a first webbing having one end connected to the tear portion; a second webbing having one end connected to the tear portion and the other end connected to the other end of the first webbing, the second webbing forming an accommodation space between the first webbing and the second webbing for accommodating the airbag and the inflator; a joining member that joins the other end portions of the first webbing and the second webbing to each other in the storage section; Equipped with A seat back of a vehicle seat, wherein, when viewed along the axis of the inflator, the front end of the side frame is located forward of the inflator, and the joining member is located forward of the front end of the side frame.

2. 2. The seat back of a vehicle seat according to claim 1, wherein an inner end surface of the storage portion, which is an inner end surface of the seat back in the width direction, faces the other end portions of the first webbing and the second webbing.

3. When viewed along the axis of the inflator, a front end surface of the storage portion is located forward of the front end portion of the side frame, The seat back of a vehicle seat according to claim 2 , wherein a portion where the front end surface and the inner end surface of the storage portion are connected faces the other end portions of the first webbing and the second webbing.

4. the one end portions of the first webbing and the second webbing are sewn to the tear portion with a first sewing thread; 3. The seat back of a vehicle seat according to claim 1, wherein the other end portions of the first webbing and the second webbing are sewn together with a second sewing thread having a strength higher than that of the first sewing thread.

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