Seat cushion and seat

Abstract

To provide a seat cushion adapted to occupants of various physiques and capable of reducing the fatigue feeling of the occupant in long-time seating.SOLUTION: The seat cushion 2 includes an upper layer 4 and a lower layer 5 having elasticity relatively higher than that of the upper layer 4. The lower layer 5 includes a pair of ischial bone support portions 6, a middle support portion 7, and a pair of lateral support portions 8. The ischial bone support part 6 has a first plane part 6a for supporting the lower end part of the ischial bone. The intermediate support part 7 has a projecting part 9 projecting upward below the coccyx. The convex portion 9 has a second flat portion 9a and a pair of first inclined portion 9b. Each of the pair of outer support portions 8 has a second inclined portion 8a.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a seat cushion used in a seating portion of a seat such as an automobile seat. [Background technology]

[0002] Conventionally, reducing the feeling of fatigue caused by sitting for long periods of time has been an issue for automobile seats and other vehicles. Factors that contribute to the feeling of fatigue in seated persons include the concentration of pressure directly below the ischial bones while seated and the unconscious tension of the entire body in order to maintain a seated posture. Therefore, focusing on these factors, various seat cushions have been proposed with improved shapes and structures to reduce fatigue even when seated for long periods of time.

[0003] For example, the seat cushions described in Patent Documents 1 and 2 have a two-layer structure in which a soft cushion layer is laminated on top of a hard cushion layer, and the hard cushion layer has a recessed, approximately arc-shaped depression at the bottom that can accommodate the portion of the occupant's buttocks that corresponds to the ischial bones, which are particularly pointed downward. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 5038784 [Patent Document 2] Patent No. 5101184 Summary of the Invention [Problem to be solved by the invention]

[0005] The structure of the seat cushion described above has a recess that accommodates the ischial bones and is curved in an arc shape, so that the seat occupant whose buttocks fit into the recess is limited to those with an average body type of the people of the country of manufacture, etc., and is not suitable for occupants of various body types.

[0006] Therefore, if the occupant's body shape is significantly different from the average body shape, the position of the ischial bones will be significantly different from the specified position assumed by the recess, which will cause fatigue of the occupant. feeling cannot be reduced.

[0007] The present invention has been made in consideration of the above-mentioned circumstances, and aims to provide a seat cushion that is suitable for occupants of various physiques and can reduce the fatigue felt by occupants when sitting for long periods of time. [Means for solving the problem]

[0008] In order to solve the above problems, the seat cushion of the present invention is a seat cushion comprising an upper layer that comes into contact with the buttocks of a seated person, and a lower layer that is placed under the upper layer and has higher elasticity than the upper layer, the lower layer comprising a pair of ischial support parts that respectively support portions of the buttocks that correspond to the ischial bones on both sides, a middle support part that is placed between the pair of ischial support parts and supports portions of the buttocks that correspond to the coccyx, and a pair of outer support parts that are placed so as to sandwich the pair of ischial support parts from outside in the width direction of the seat cushion and support portions of the buttocks that correspond to a pair of femoral trochanters. the ischial support portion has a first flat portion that supports the lower end of the ischium in an area facing the lower end of the ischium, the intermediate support portion has a convex portion that protrudes upward below the coccyx, the convex portion has a second flat portion formed at the top of the convex portion, and a pair of first inclined portions that extend obliquely upward from the inner end of the first flat portion to the second flat portion on both sides in the width direction of the second flat portion, and each of the pair of outer support portions has a second inclined portion that extends obliquely upward from the outer end of the first flat portion to a position corresponding to the outer end of the femoral trochanter.

[0009] According to this configuration, the lower layer, which is more elastic than the upper layer, has the following configuration: The ischial support portion has a first flat portion that supports the lower end of the ischial bone in an area facing the lower end of the ischial bone. The intermediate support portion has a convex portion that protrudes upward below the coccyx. The convex portion has a second flat portion formed at the top of the convex portion and a pair of first inclined portions that extend obliquely upward along the buttocks from the inner end of the first flat portion to the second flat portion on both sides of the second flat portion in the width direction. Each of the pair of outer support portions has a second inclined portion that extends obliquely upward along the buttocks from the outer end of the first flat portion in the width direction to a position corresponding to the outer end of the femoral trochanter. This configuration ensures that the lower end of the ischial bone, which is subject to the highest pressure, is reliably supported by the first flat portion of the ischial support portion. Furthermore, the first flat portion, the second flat portion and first inclined surface of the convex portion, and the second inclined portions of the outer support portion support the entire buttocks while conforming to the shape of the buttocks. As a result, pressure is distributed well regardless of physique, making it possible to accommodate occupants of various physiques and reducing fatigue felt by occupants when seated for long periods of time.

[0010] In the seat cushion, the protrusion is preferably disposed in a range from the front end of the coccyx to the front end of the femoral trochanter in the front-rear direction.

[0011] With this configuration, the convex portion supports the area of ​​the seated person's buttocks from the front end of the coccyx to the front end of the femoral trochanter, thereby enabling pressure to be distributed in the front-to-back direction when seated.

[0012] In the above seat cushion, it is preferable that the width of the first planar portion is set so that the distance in the width direction from the center line of the seat cushion in the width direction is in the range of 40 to 80 mm.

[0013] By setting the width of the first flat portion within the above range, the lower end of the ischium can be reliably received by the first flat portion, and therefore it is possible to adequately accommodate a wide variety of physique differences.

[0014] In the above-mentioned seat cushion, it is preferable that the convex portion has a shape such that the width of the bottom of the convex portion gradually increases and the height of the convex portion gradually decreases as it moves forward from the anterior end of the femoral trochanter portion.

[0015] With this configuration, it is possible to reduce the discomfort caused by the protrusions hitting the thighs, and also to reduce the pressure difference in the front-to-back direction by gradually changing the pressure, thereby dispersing the pressure.

[0016] The seat of the present invention comprises the above-mentioned seat cushion and a frame supporting the seat cushion, wherein the frame has an elastic support portion extending in the width direction of the seat cushion and elastically supporting the seat cushion, and the lower layer is arranged within the range in which the elastic support portion is arranged.

[0017] With this configuration, the weight of the seated person is reliably received by the lower layer and the elastic support parts while the pressure received by the lower layer is reliably transmitted to the elastic support parts of the frame, providing a comfortable seating experience.

[0018] In the above-mentioned seat, it is preferable that the front end of the upper layer extends further forward than the front end of the lower layer, the frame is arranged forward of the elastic support portion and has a cushion pan that supports a portion including the front end of the upper layer, and the lower layer is arranged within a range up to the rear end of the cushion pan along with the arrangement range of the elastic support portion.

[0019] With this configuration, the cushion pan supports the portion of the upper layer that extends further forward than the front end of the lower layer in the frame, while the elastic support portion reliably supports the lower layer that bears the weight of the occupant, making the seating more comfortable. [Effects of the Invention]

[0020] As described above, the seat cushion of the present invention can accommodate occupants of various physiques and can reduce the fatigue felt by occupants who sit for long periods of time.

[0021] Furthermore, the seat of the present invention provides improved seating comfort. [Brief explanation of the drawings]

[0022] [Figure 1] 1 is an overall perspective view showing the overall configuration of a vehicle seat including a seat cushion according to an embodiment of the present invention; [Figure 2] 2 is a cross-sectional view of the vehicle seat of FIG. 1 cut vertically along a widthwise center line extending in the front-rear direction, illustrating the positional relationship between the vehicle seat and buttocks. FIG. [Figure 3] 2 is a cross-sectional view of the vehicle seat of FIG. 1 taken perpendicularly to the width direction at a position in the front-rear direction corresponding to the lower end of the ischial bones, and is an explanatory cross-sectional view showing the positional relationship between the vehicle seat and the buttocks. FIG. [Figure 4] FIG. 2 is an overall perspective view of the lower layer of FIG. [Figure 5] FIG. 2 is a plan view of the lower layer of FIG. [Figure 6] 6 is a cross-sectional explanatory view showing a cross section from the lower layer II cross section to the VI-VI cross section of FIG. 5 side by side. [Figure 7] 1 is a diagram showing the F / S characteristics and pressure distribution of a conventional single elastic cushion and the seat cushion of the present embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0023] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A seat cushion according to an embodiment of the present invention and a vehicle seat, which is an example of a seat including the seat cushion, will be described in detail below with reference to the drawings.

[0024] (Overall configuration of vehicle seat 1) As shown in FIG. 1, a vehicle seat 1 includes a seat cushion 2 having a two-layer structure with an upper layer 4 and a lower layer 5, and a frame 3 that supports the seat cushion 2.

[0025] Here, a brief description will be given of the frame 3. The frame 3 includes a frame main body 31, an elevating mechanism 32 that raises and lowers the frame main body 31, and a slide rail 33 that guides the frame main body 31 and the elevating mechanism 32 in the fore-and-aft direction X of the vehicle seat 1 and fixes them at any fore-and-aft position. The frame 3 also includes an elastic support portion 34 and a cushion pan 35 that are fixed to the frame main body 31.

[0026] The elastic support portion 34 extends in the width direction Y of the vehicle seat 1 and elastically supports the seat cushion 2 (particularly the lower layer 5 thereof) over the entire width direction Y. The elastic support portion 34 may be, for example, a so-called S-spring, more specifically, a linear spring that extends in the width direction Y and is continuously curved in a wave shape.

[0027] The cushion pan 35 is disposed on the front side of the elastic support portion 34 and supports the front portion of the upper layer 4 (the portion on the left side in FIG. 1).

[0028] (Seat cushion 2 explanation) Next, the seat cushion 2 of this embodiment will be described in detail.

[0029] The seat cushion 2 shown in FIGS. 2 to 6 includes an upper layer 4 that comes into contact with the buttocks PH of a seated person P, and a lower layer 5 that is placed under and overlaps the upper layer 4 and has higher elasticity than the upper layer 4.

[0030] The lower layer 5 may be made of a material having a higher elasticity, as indicated by Young's modulus, than the upper layer 4. The lower layer 5 may be formed of a material such as hard urethane or foam beads. On the other hand, the upper layer 4 may be made of a material that is softer than the lower layer 5, such as soft urethane. The lower layer 5 and the upper layer 4 may be stacked vertically, and are preferably integrated by adhesion, insert molding, or the like.

[0031] 2 and 3, the seat cushion 2 is shown in a state before the seated person P sits on it, and the position of the buttocks PH of the seated person P after sitting on it is indicated by a two-dot chain line.

[0032] 2, in the seat cushion 2 of this embodiment, the lower layer 5 is disposed in a range in which the elastic support portions 34 of the frame 3 are disposed. In addition, the front end 4a of the upper layer 4 extends forward of the front end 5a of the lower layer 5. The lower layer 5 is disposed within the range in which the elastic support portions 34 are disposed and up to the rear end 35a of the cushion pan 35. Moreover, the lower layer 5 becomes gradually thinner toward the front.

[0033] As shown in FIGS. 3 to 6, the lower layer 5 has, as its main components, a pair of ischial support portions 6, a middle support portion 7, and a pair of outer support portions 8.

[0034] The pair of ischial support portions 6 respectively support portions of the buttocks PH that correspond to the ischial bones PS on both sides. Each ischial support portion 6 has a first flat portion 6a that supports the lower end portion PS1 of the ischial bone PS in the area facing the lower end portion PS1. This ensures that the first flat portion 6a can reliably receive pressure from the lower end portion PS1 even if the seated occupant P has a different physique and the lower end portion PS1 of the ischial bone PS is in a different position.

[0035] As shown in FIG. 3, the width W of the first flat portion 6a is preferably set in a range of 40 to 80 mm in the width direction Y from the widthwise center line C of the seat cushion 2 so as to be able to adequately accommodate a variety of body sizes.

[0036] The intermediate support part 7 is disposed between the pair of ischial support parts 6 in the width direction Y. The intermediate support part 7 supports the part of the buttocks PH that corresponds to the coccyx PC. The intermediate support part 7 has a protrusion 9 that protrudes upward below the coccyx PC.

[0037] The convex portion 9 has a second flat portion 9a formed at the top of the convex portion 9, and a pair of first inclined portions 9b extending obliquely upward along the buttocks PH from the inner end of the first flat portion 6a to the second flat portion 9a on both sides of the width of the second flat portion 9a.

[0038] 2, the protrusion 9 extends within a range L from the anterior end PCa of the coccyx PC to the anterior end PFb of the femoral trochanter PF in the anterior-posterior direction X of the lower layer 5. Therefore, the protrusion 9 of this embodiment also supports the portion of the buttocks PH that corresponds to the coccyx PC and the pubic bone PP located between the pair of ischial bones PS.

[0039] As shown in Figures 4 to 6, the protrusion 9 has a shape such that the width WT of the base of the protrusion 9 gradually increases and the height HT of the protrusion 9 gradually decreases as it moves forward from the anterior end PFb of the femoral trochanter PF, i.e., from cross section II to cross section VI-VI in Figures 5 to 6.

[0040] In this embodiment, as shown in FIG. 3, the lower portion of the protrusion 9 is hollowed out to form a recess 10 extending in the front-rear direction X.

[0041] 3 to 6, the pair of outer support portions 8 are arranged in the width direction Y to sandwich the pair of ischial support portions 6 from the widthwise outer sides of the seat cushion. Each of the pair of outer support portions 8 supports a portion of the buttocks PH that corresponds to a pair of femoral trochanters PF. Each of the pair of outer support portions 8 has a second inclined portion 8a that extends obliquely upward along the buttocks PH from the widthwise outer end of the first flat portion 6a to a position that corresponds to the outer end PFa of the femoral trochanter PF.

[0042] The seat cushion 2 configured as described above has the lower layer 5 which has higher elasticity than the upper layer 4, and the lower layer 5 is capable of supporting the buttocks PH as a whole while dispersing pressure thereon.

[0043] (Performance comparison with conventional cushions) Next, as shown in FIG. 7, the F / S characteristics and pressure distribution are compared between the seat cushion 2 of this embodiment and a conventional single hardness cushion (that is, a cushion with a single layer structure).

[0044] Given that the cushion thickness and displacement amount when seated are the same, the characteristics of this structure allow the hardness of the upper layer to be set to a softer value. Comparing the F / S characteristics of the conventional structure and this structure, curve C1 for the conventional single-hardness cushion shows that the load F (i.e., the load applied when seated) and displacement S (i.e., the amount of cushion depression) are almost linear, whereas the cushion's rigidity in the seated state is maintained at the same level or higher, while the displacement amount at low to medium loads is increased. This allows the occupant to feel a softer sensation when seated. Furthermore, when an input greater than the occupant's weight (e.g., large-amplitude vibration) is applied, the displacement amount is smaller compared to the conventional structure, allowing the occupant to stabilize their posture with less force.

[0045] Furthermore, comparing the pressure distribution with reference to the pressure distribution diagram in FIG. 7 (a diagram in which pressure intensity is indicated by shading), with the conventional single-hardness cushion 22, the pressure is high at the portion M21 corresponding to the lower end PS1 of the ischium PS and the portion M23 corresponding to the anterior end PFb of the femoral trochanter PF, while there is almost no pressure at the portion M22 corresponding to the coccyx PC. Therefore, with the conventional single-hardness cushion 22, pressure is concentrated in the portions M21 and M23 and a narrow area near them, which is likely to cause fatigue. In contrast, with the seat cushion 2 of this embodiment, the pressure at the portion M1 corresponding to the lower end PS1 of the ischium PS and the portion M3 corresponding to the anterior end PFb of the femoral trochanter PF is alleviated and dispersed to the surrounding area, and the portion M2 corresponding to the coccyx PC is also subjected to pressure by the convex portion 9 of the intermediate support portion 7. Therefore, with the seat cushion 2 of this embodiment, pressure can be dispersed over a wide area including the portions M1 to M3, thereby improving the obstruction of blood flow around the ischium and reducing fatigue.

[0046] (Features of this embodiment) (1) 2 to 6, in the seat cushion 2 of this embodiment, the lower layer 5, which has higher elasticity than the upper layer 4, has the following configuration. Specifically, the ischial support portion 6 of the lower layer 5 has a first planar portion 6a that supports the lower end portion PS1 of the ischium PS in an area facing the lower end portion PS1. The intermediate support portion 7 of the lower layer 5 has a convex portion 9 that protrudes upward below the coccyx PC. The convex portion 9 has a second planar portion 9a formed at the top of the convex portion 9 and a pair of first inclined portions 9b that extend obliquely upward along the buttocks PH from the inner end of the first planar portion 6a to the second planar portion 9a on both sides of the second planar portion 9a in the width direction. Each of the pair of outer support portions 8 of the lower layer 5 has a second inclined portion 8a that extends obliquely upward along the buttocks PH from the outer end of the first planar portion 6a in the width direction to a position corresponding to the outer end PFa of the femoral trochanter portion PF.

[0047] With this configuration, the lower end portions PS1 of the ischial bones PS, which receive the highest pressure, can be reliably supported by the first flat portion 6a of the ischial support portion 6. In other words, even if the position of the lower end portions PS1 of the ischial bones PS of the seated occupant P varies depending on the occupant's body type, the lower end portions PS1 can be supported somewhere within the range of the first flat portion 6a. Furthermore, the second flat portion 9a and first inclined portion 9b of the convex portion 9 and the second inclined portion 8a of the outer support portion 8, together with the first flat portion 6a, support the entire buttocks PH while conforming to the shape of the buttocks PH. As a result, pressure is distributed well regardless of physique. This makes it suitable for occupants of various physiques and reduces fatigue felt by occupants when seated for long periods of time.

[0048] (2) In the seat cushion 2 of this embodiment, as shown in FIG. 2, the convex portion 9 is arranged in a range L in the front-rear direction X of the lower layer 5 from the anterior end PCa of the coccyx PC to the anterior end PFb of the femoral trochanter PF.

[0049] With this configuration, the convex portion 9 supports the area L from the anterior end PCa of the coccyx PC at the buttocks PH of the seated person P to the anterior end PFb of the femoral trochanter PF, thereby enabling pressure distribution in the front-to-back direction X when seated.

[0050] (3) In the seat cushion 2 of this embodiment, as shown in Figure 3, the width W of the first planar portion 6a is set to a range of 40 to 80 mm in distance from the widthwise center line C of the seat cushion 2 in the width direction Y.

[0051] By setting the width W of the first planar portion 6a within the above range, the lower end portions PS1 of the ischial bones PS can be reliably supported by the first planar portion 6a. In particular, for Japanese people, the lower end portions PS1 of the ischial bones PS can be more reliably supported by the first planar portion 6a. This makes it possible to adequately accommodate a wide variety of physiques.

[0052] (4) In the seat cushion 2 of this embodiment, as shown in Figures 4 to 6, the convex portion 9 has a shape such that the width WT of the bottom of the convex portion 9 gradually increases and the height HT of the convex portion 9 gradually decreases as it moves forward from the anterior end PFb of the femoral trochanter portion PF, i.e., from cross section II to cross section VI-VI in Figures 5 to 6.

[0053] This configuration reduces the discomfort caused by the convex portion 9 hitting the thigh (especially the area near the anterior end PFb of the femoral trochanter PF), and the gradual change reduces the pressure difference in the front-to-back direction, allowing for pressure dispersion.

[0054] (5) Furthermore, in the seat cushion 2 of this embodiment, portions below the protrusions 9 are hollowed out and have recesses 10 extending in the front-to-rear direction X. In this configuration, the protrusions 9 support the vicinity of the widthwise center of the buttocks PH while changing the pressure distribution according to the shape of the buttocks PH, while the recesses 10 below the protrusions 9 enable weight reduction. Also, by forming staggered slits in the lower surface of the lower layer 5 in the widthwise direction Y or the front-to-rear direction X, the properties (elasticity, hardness, etc.) of the lower layer 5 can be changed.

[0055] (6) Furthermore, in the seat cushion 2 of this embodiment, the lower layer 5 gradually becomes thinner toward the front. Specifically, the lower layer 5 has a shape in which the upper surface 51 and the lower surface 52 become closer to each other toward the front. This makes the front end of the lower layer 5, where the thighs (particularly the portion near the anterior end PF1 of the femoral trochanter PF) are located, a flexible layer, making it possible to suppress vibrations transmitted from the vehicle body to the thighs. Furthermore, because the front end of the lower layer 5 is soft, it does not interfere with pedal operation inside the vehicle cabin. Furthermore, gradual changes in the thickness of the front end of the lower layer 5 have the advantage of gradual changes in elasticity, preventing a foreign body sensation.

[0056] (7) The vehicle seat 1 of this embodiment includes the above-described seat cushion 2 and frame 3. The frame 3 has elastic support members 34 such as S-springs that extend in the width direction Y of the seat cushion 2 and elastically support the seat cushion 2. The lower layer 5 is disposed within the range in which the elastic support members 34 are disposed.

[0057] With this configuration, the pressure received by the lower layer 5 is reliably transmitted to the elastic support portions 34 of the frame 3, while the weight of the seated person P is reliably received by the lower layer 5 and the elastic support portions 34, providing a comfortable sitting experience.

[0058] (8) In the vehicle seat 1 of this embodiment, the front end 4a of the upper layer 4 of the seat cushion 2 extends further forward than the front end 5a of the lower layer 5. The frame 3 is disposed forward of the elastic support portions 34 and has a cushion pan 35 that supports a front portion of the upper layer 4, including the front end 4a. The lower layer 5 is disposed within the range of the elastic support portions 34 and up to the rear end 35a of the cushion pan 35.

[0059] According to this configuration, in the frame 3, the cushion pan 35 supports the portion of the upper layer 4 that extends forward of the front end 5a of the lower layer 5, while the elastic support portion 34 reliably supports the lower layer 5 that bears the weight of the seated person P, making it even more comfortable to sit on.

[0060] (Variation) In the above embodiment, a vehicle seat has been described as an example of the seat of the present invention, but the present invention is not limited to this. The seat of the present invention can be widely used in seats where there is a possibility of sitting for long periods of time, such as a vehicle seat, a boat seat, an airplane seat, or a theater seat.

[0061] In this embodiment, the first inclined portion 9b, the second inclined portion 8a, etc. are shown as linear planes in the drawings, but may have a curved shape. [Explanation of symbols]

[0062] 1. Vehicle seat 2 seat cushions 3 frames 4 Upper layer 5 Lower layer 6 Ischial support 6a 1st plane part 7 Intermediate support part 8 Outer support 8a 2nd slope part 9 Convex part 9a 2nd plane part 9b 1st slope 34 Elastic support part 35 Cushion Bread P seated person PC coccyx PF Femoral trochanteric region PFa outer edge PFb front end PH buttocks PS Sciatica PS1 bottom end

Claims

1. The upper layer that the seated person's buttocks come into contact with, a lower layer that is disposed under the upper layer and has higher elasticity than the upper layer; A seat cushion comprising: The lower layer is a pair of ischial support portions that respectively support portions of the buttocks corresponding to the ischial bones on both sides; an intermediate support portion disposed between the pair of ischial support portions and supporting a portion of the buttocks corresponding to the coccyx; a pair of outer support portions that are arranged to sandwich the pair of ischial support portions from the outer sides of the seat cushion in the width direction and support portions of the buttocks that correspond to the pair of femoral trochanters; and the ischial support portion has a first flat portion that supports a lower end of the ischial bone in an area facing the lower end of the ischial bone, the intermediate support portion has a convex portion that protrudes upward below the coccyx, The convex portion is a second flat portion formed on the top of the convex portion; a pair of first inclined portions extending obliquely upward from inner ends of the first flat portion to the second flat portion on both sides in the width direction of the second flat portion; and Each of the pair of outer support portions has a second inclined portion extending obliquely upward from an outer end portion in the width direction of the first flat portion to a position corresponding to an outer end of the femoral trochanter portion. A seat cushion characterized by:

2. The seat cushion according to claim 1, The convex portion is disposed in a range from the front end of the coccyx to the front end of the femoral trochanter in the anterior-posterior direction. A seat cushion characterized by:

3. The seat cushion according to claim 1 or 2, The width of the first planar portion is set to a range such that the distance in the width direction from the widthwise center line of the seat cushion is in the range of 40 to 80 mm. A seat cushion characterized by:

4. The seat cushion according to claim 1 or 2, The convex portion has a shape such that the width of the bottom of the convex portion gradually increases and the height of the convex portion gradually decreases as the convex portion moves forward from the anterior end of the femoral trochanter portion. A seat cushion characterized by:

5. The seat cushion according to claim 1; a frame supporting the seat cushion; Equipped with the frame has an elastic support portion that extends in a width direction of the seat cushion and elastically supports the seat cushion, The lower layer is disposed within a range in which the elastic support portion is disposed. A sheet characterized by:

6. The sheet according to claim 5, a front end of the upper layer extends forward of a front end of the lower layer; the frame has a cushion pan disposed on the front side of the elastic support portion and supporting a portion including a front end of the upper layer, The lower layer is disposed within a range up to the rear end of the cushion pan together with the range in which the elastic support portion is disposed. A sheet characterized by:

Images