Back pad and seat pad

Abstract

This product provides back pads and seat pads that improve comfort when the body is leaning against the back pad. [Solution] The back pad 3 is a back pad 3 of the seat pad 1 formed from a foam material. The back pad 3 includes an upper part 3a that is located above the seat pad when installed in the vehicle, and a lower part that is located below the upper part 3a when installed in the vehicle. The upper part 3a is harder than the lower part, and the hardness of the upper part 3a is 140N or more. The seat pad 1 includes the back pad 3.

Description

Technical Field

[0001] The present invention relates to a back pad and a seat pad.

Background Art

[0002] In a conventional seat pad, in order to improve the comfort of a seated person who relaxes by placing the whole body on the seat rather than in a tense state during driving, in the back pad included in the seat pad, the hardness of the upper part of the back pad is set to be smaller than the hardness of the lower part (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the seat pad described in Patent Document 1, when a seated person leans on the back pad, the seated person may feel discomfort due to vibrations transmitted through the shoulders. Therefore, there is room for improvement in the comfort when leaning on the back pad in the conventional seat pad.

[0005] An object of the present invention is to provide a back pad and a seat pad in which the comfort when leaning on the back pad is improved.

Means for Solving the Problems

[0006] The back pad according to the present invention is a back pad for a seat pad formed of a foamed material, and the back pad includes an upper portion that is located above the upper portion when installed in a vehicle, and a lower portion that is located below the upper portion when installed in a vehicle, the upper portion being harder than the lower portion, and the hardness of the upper portion being 140 (N) or more. The back pad according to the present invention improves comfort when leaning the body against the back pad.

[0007] In the back pad according to the present invention, it is preferable that the upper portion can be folded forward relative to the lower portion when mounted on a vehicle. In this case, it is effective in improving comfort when leaning the body against the back pad.

[0008] In the back pad according to the present invention, the hardness of the upper part is preferably 150 (N) or more. In this case, the comfort when leaning the body against the back pad is further improved.

[0009] In the back pad according to the present invention, the hardness of the lower portion is preferably 100 to 120 (N). In this case, the lower portion can be made of a general-purpose back pad.

[0010] The seat pad according to the present invention includes a back pad as described in any of the above. According to the seat pad according to the present invention, comfort is improved when leaning the body against the back pad. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide a back pad and a seat pad that improve comfort when leaning the body against the back pad. [Brief explanation of the drawing]

[0012] [Figure 1] This is a schematic perspective view showing a back pad according to one embodiment of the present invention, and a seat pad according to one embodiment of the present invention, including the back pad. [Figure 2]Figure 1 is a schematic skeleton diagram showing the reclining position of the seat pad. [Figure 3A] This is the result of random vibration analysis performed on the upper part 3a of multiple high-damping back pads with different upper stiffnesses, while varying the backrest angle α. [Figure 3B] This is the result of random vibration analysis performed on the central part 3c of multiple high-damping back pads with different upper stiffnesses, while varying the backrest angle α. [Figure 3C] This is the result of random vibration analysis performed on the lower part 3b of multiple high-damping back pads with different upper stiffnesses, while varying the backrest angle α. [Figure 4A] This is the result of random vibration analysis performed on the upper part 3a of multiple high-elasticity back pads with different upper stiffnesses, while varying the backrest angle α. [Figure 4B] This is the result of random vibration analysis performed on the central part 3c of multiple high-elasticity back pads with different upper stiffness, while varying the backrest angle α. [Figure 4C] This is the result of random vibration analysis performed on the lower part 3b of multiple high-elasticity back pads with different upper stiffnesses, while varying the backrest angle α. [Figure 5A] This is the result of random vibration analysis of the vibrations transmitted to the upper part of the back pad when the back pad is in a reclined position relative to the cushion pad. [Figure 5B] This is the result of random vibration analysis of the vibrations transmitted to the center of the back pad when the back pad is in a reclined position relative to the cushion pad. [Figure 5C] This is the result of random vibration analysis of the vibrations transmitted to the lower part of the back pad when the back pad is in a reclined position relative to the cushion pad.

Mode for Carrying Out the Invention

[0013] Hereinafter, referring to the drawings, a back pad according to an embodiment of the present invention and a seat pad according to an embodiment of the present invention including the back pad will be described. In the following description, front and rear, left and right, and up and down are based on the state when the seat pad is mounted on a vehicle.

[0014] Referring to FIG. 1, reference numeral 1 denotes a seat pad according to an embodiment of the present invention. The seat pad 1 includes a back pad (also referred to as a “seat back”) 3 according to an embodiment of the present invention. The back pad 3 is a back pad for supporting the back of a seated person and is formed of a foamed material. The back pad 3 includes an upper portion 3a located on the upper side when mounted on a vehicle and a lower portion located below the upper portion 3a when mounted on a vehicle. The upper portion 3a of the back pad 3 is harder than the lower portion of the back pad 3. The hardness of the upper portion 3a is 140 (N) or more. Here, the unit of hardness (N: Newton) conforms to JIS (Japanese Industrial Standards) K6400-B / JASО B 408.

[0015] The seat pad 1 according to the present embodiment is a cushion material constituting a part of a seat for an automobile. The seat pad 1 according to the present embodiment includes, in addition to the back pad 3, a cushion pad (also referred to as a “seat cushion”) 2 for supporting the buttocks and thighs of a seated person and a headrest 4 for supporting the head of the seated person.

[0016] The backrest 3 according to this embodiment includes an upper part 3a, a lower part 3b, and a central part 3c interposed between the upper part 3a and the lower part 3b. The upper part 3a of the backrest 3 is configured to support at least the shoulder on the back side of the seated person (for example, the scapula). Also, the lower part 3b of the backrest 3 is configured to support at least the lumbar region on the back side of the seated person. The central part 3c of the backrest 3 is configured to support the area between the shoulder and the lumbar region of the seated person.

[0017] Moreover, the backrest 3 according to this embodiment has a center pad portion 31 and two side pad portions 32 disposed on both the left and right sides of the center pad portion 31. The center pad portion 31 is configured to support the back and the lumbar region of the seated person from the rear side. The two side pad portions 32 are configured to support the back and the lumbar region of the seated person from both the left and right sides.

[0018] Furthermore, in this embodiment, the center pad portion 31 is divided into three regions: an upper center pad portion 31a, a lower center pad portion 31b, and a central center pad portion 31c. The upper center pad portion 31a is located on the upper side when mounted on the vehicle and is configured to support, for example, the shoulder on the back side of the seated person from the rear side of the seated person. The lower center pad portion 31b is located on the lower side when mounted on the vehicle and is configured to support, for example, the lumbar region on the back side of the seated person from the rear side of the seated person. The central center pad portion 31c is located between the upper and lower sides when mounted on the vehicle and is configured to support, for example, the portion between the shoulder and the lumbar region on the back side of the seated person from the rear side of the seated person.

[0019] Furthermore, in this embodiment, the two side pad portions 32 are each divided into three areas: the upper side pad portion 32a, the lower side pad portion 32b, and the central side pad portion 32c. The upper side pad portion 32a is located to the left and right of the upper center pad portion 31a and is configured to support, for example, the shoulder portion on the back of the seated person from the left or right side of the seated person. The lower side pad portion 32b is located to the left and right of the lower center pad portion 31b and is configured to support, for example, the waist portion on the back of the seated person from the left or right side of the seated person. The central side pad portion 32c is located to the left and right of the central center pad portion 31c and is configured to support, for example, the portion between the shoulder portion and the waist portion on the back of the seated person from the left or right side of the seated person.

[0020] Referring to Figure 1, in the back pad 3 according to this embodiment, the boundary line L1 between the upper center pad portion 31a and the central center pad portion 31c is the boundary line between the upper part 3a of the back pad 3 and the portion of the back pad 3 excluding the upper part 3a. That is, in the back pad 3 according to this embodiment, the upper part 3a of the back pad 3 is composed of the upper center pad portion 31a and the upper side pad portion 32a, which are above the boundary line L1. Also, in the back pad 3 according to this embodiment, the boundary line L2 between the lower center pad portion 31b and the central center pad portion 31c is the boundary line between the lower part 3b of the back pad 3 and the portion of the back pad 3 excluding the lower part 3b. That is, in the back pad 3 according to this embodiment, the lower part 3b of the back pad 3 is composed of the lower center pad portion 31b and the lower side pad portion 32b, which are below the boundary line L2. Furthermore, in the back pad 3 according to this embodiment, the portion between the upper boundary line L1 and the lower boundary line L2 constitutes the central portion 3c of the back pad 3. In other words, in this embodiment, the central portion 3c of the back pad 3 is composed of a central center pad portion 31c and a central side pad portion 32c, located between the upper boundary line L1 and the lower boundary line L2.

[0021] As described above, in the back pad 3 according to this embodiment, the upper part 3a of the back pad 3 is the upper center pad portion 31a and the upper side pad portion 32a. Also, in the back pad 3 according to this embodiment, the lower part 3b of the back pad 3 is the lower center pad portion 31b and the lower side pad portion 32b. Also, in the back pad 3 according to this embodiment, the central part 3c of the back pad 3 is the central center pad portion 31c and the central side pad portion 32c. Therefore, in the back pad 3 according to this embodiment, the lower portion of the back pad 3 is the central center pad portion 31c and the central side pad portion 32c, and the lower center pad portion 31b and the lower side pad portion 32b. That is, in this embodiment, the upper center pad portion 31a and the upper side pad portion 32a are harder than the central center pad portion 31c and the central side pad portion 32c, and the lower center pad portion 31b and the lower side pad portion 32b, and their hardness is 140 (N) or more.

[0022] When a person sits in the seat, they lean their body against the back pad 3. However, when vibrations are transmitted to the shoulders while leaning against the back pad 3, the person tends to feel discomfort from these vibrations. This discomfort tends to be felt, for example, when the backrest (back pad 3) of the seat is tilted backward, and especially when the head is tilted forward, through the shoulders on the back. This is thought to be because when the person leans against the back pad 3 and raises their head, a large amount of pressure is applied from the upper part 3a of the back pad 3 to the shoulders on the back. The vibration frequencies that cause this discomfort are mainly in the range of 10 to 30 Hz, and the vibration frequencies that cause more discomfort are in the range of 20 to 30 Hz.

[0023] In particular, in autonomous vehicles, drivers are freed from the need to operate the vehicle, allowing them to engage in activities such as reading or using a computer. Furthermore, similar to airplanes and trains, it is expected that drivers will recline their seats to enhance comfort. However, unlike airplanes and trains, even in autonomous vehicles, occupants will still try to obtain information from the front (direction of travel). Therefore, reclining the seat will cause them to raise their heads, which can increase strain on the neck and shoulders and may not necessarily lead to improved comfort.

[0024] To address this issue, possible solutions include extending the headrest forward or incorporating a folding mechanism into the back pad to improve forward visibility when reclining.

[0025] While the headrest and neck rest enhance comfort under static, vibration-free conditions when reclining, during actual driving, vibrations are transmitted to the head not only from the backrest but also directly from the head or the neck rest itself. This makes activities such as reading or using a computer significantly more difficult and does not contribute to improved comfort.

[0026] On the other hand, a back pad with a folding mechanism is more effective than a headrest / neckrest that directly supports the head, because the upper part of the folding mechanism supports the area around the shoulders. However, a back pad with a folding mechanism does not take into account the vibrations that come in from the backrest when reclining, and therefore does not optimize workability and comfort while driving.

[0027] Furthermore, conventional seat comfort during driving has often focused on the cushioning characteristics under the buttocks, and has not given much consideration to vibrations entering from the backrest. In particular, it has not focused on optimizing input vibrations by dividing the backrest into upper, middle, and lower sections.

[0028] Figures 5A-5C show the results of random vibration analysis of the vibrations transmitted to the upper (upper back: shoulder area), lower (lower back: lumbar area), and central (central back: between the shoulder and lumbar areas) parts of the back pad when the back pad is reclined relative to the cushion pad. The analysis results represent the input vibrations measured in the upper back, central back, and lower back when the backrest angle (recline angle) of the back pad relative to the cushion pad is tilted in 10° increments from 28° to 58° (28°, 38°, 48°, 58°). In Figures 5A-5C, the vertical axis shows the power spectral density, and the horizontal axis shows the vibration frequency.

[0029] In the above analysis, a high-damping type (ball rebound value: 63%) urethane was used for the back pad, and the 25% hardness was set to a standard hardness of 92.2N. From these analysis results, it can be seen that changing the angle of the back pad (backrest) changes the incoming vibration. Furthermore, from these analysis results, it can be seen that the magnitude of the vibration also changes depending on the location on the upper, middle, and lower part of the back.

[0030] Furthermore, based on the analysis results above, from the perspective of workability and comfort, the following two points must be considered when reclining the seat while driving.

[0031] (a) In order to ensure forward visibility and improve various aspects of work efficiency, the seated person needs to raise their head even when reclined, and therefore the head, neck, and shoulders must be supported. (i) Reduction of vibrations coming in from the backrest In particular, reducing vibrations from areas close to the head, which have a significant impact on work efficiency and comfort, is crucial.

[0032] In contrast, in this embodiment, the upper part 3a of the back pad 3 (the part above the boundary line L1) is harder than the lower part below the upper part 3a of the back pad 3 (the part below the boundary line L1: the central part 3c and lower part 3b of the back pad 3), and the hardness of the upper part 3a is 140 (N) or more. In this case, when a sitter leans their body against the back pad 3, vibrations transmitted from the upper part 3a of the back pad 3 through the shoulders that may cause discomfort to the sitter are reduced, specifically vibrations with frequencies (10-30 Hz) that can cause discomfort to the sitter. That is, according to the back pad 3 of this embodiment, vibrations transmitted through the shoulders on the back are reduced. Therefore, according to the back pad 3 of this embodiment, the comfort of the sitter when they lean their body against the back pad 3 can be improved.

[0033] Furthermore, it is preferable that the hardness of the upper part 3a of the back pad 3 be 150 (N) or more. In this case, since the hardness of the upper part 3a of the back pad 3 is increased, vibrations transmitted through the shoulder area on the back side are further reduced. Therefore, according to the back pad 3 of this embodiment, the comfort of the seated person when they lean their body against the back pad 3 can be further improved.

[0034] Furthermore, in this embodiment, the upper part 3a of the back pad 3 can be folded forward when mounted on a vehicle relative to the lower portion below the upper part 3a of the back pad 3. In other words, in this embodiment, the back pad 3 is a back pad having a so-called folding structure. In the back pad 3 according to this embodiment, the upper part 3a of the back pad 3 can be folded in the front-rear direction relative to the central part 3c of the back pad, with the boundary line L1 as the starting point.

[0035] The back pad 3 of this embodiment can be tilted backward relative to the cushion pad 2. In addition, in the back pad 3 according to this embodiment, the upper part 3a of the back pad 3 can be folded forward relative to the central part 3c of the back pad, with the boundary line L1 as the pivot point. That is, with the back pad 3, the entire back pad 3 can be tilted backward while only the upper part 3a of the back pad 3 is raised forward. In this case, the occupant is supported by the back pad 3 in a state where their back is tilted significantly backward while their shoulders are raised. As a result, even when the occupant lies on their back by tilting the back pad 3 backward so that they can lean their body against the back pad 3, for example, when sitting in the passenger seat or when driving without operation required due to autonomous driving, the upper part 3a of the back pad 3 raised forward will support their head. This allows the occupant to maintain a forward-facing position comfortably without straining their neck. With the development of autonomous driving technology, it is conceivable that a back pad 3 with such a folding structure could be applied not only to passenger seats but also to the driver's seat.

[0036] Furthermore, even when reclining on their backs, occupants may try to lift their heads to obtain information about what's in front of the vehicle. In this case, the strain on the occupant's neck or shoulders increases. In contrast, a folding seat structure allows the occupant to lift the area above their shoulders (towards the head) without having to lift their head, making it an effective measure to alleviate this strain. Another measure to alleviate this strain is to move the headrest 4 forward relative to the back pad 3. This measure is effective when no vibration is input to the seat pad 1 (for example, when the vehicle is stationary).

[0037] However, conventional folding back pads cannot reduce vibrations transmitted through the shoulders when vibrations are being input (for example, when idling or driving). While folding back pads are indeed more effective than measures taken at the headrest 4, which is closer to the head, because the upper part 3a of the back pad 3 supports the area around the shoulders, there is still room for improvement as a measure to suppress vibrations transmitted through the shoulders when driving.

[0038] On the other hand, according to the back pad 3 of this embodiment, the vibration itself transmitted from the upper part 3a of the back pad 3 through the shoulder area is suppressed. Therefore, with the back pad 3 of this embodiment, even if the seated person lifts their head further forward in the vehicle while the back pad 3 is folded in the middle with the boundary line L1 as the base point, the vibration transmitted through the shoulder area is reduced. Accordingly, the back pad 3 of this embodiment is effective in improving comfort when leaning the body against the back pad 3.

[0039] Figure 2 schematically shows the reclined state of the seat pad 1. In this reclined state, the back pad 3 is tilted backward relative to the cushion pad 2, and the upper part 3a of the back pad 3 is raised forward with respect to the boundary line L1. As shown in Figure 2, if the acute angle of inclination that the upper part 3a of the back pad 3 makes with respect to the vertical direction is defined as the backrest angle α, the vibration transmitted from the upper part 3a of the back pad 3 through the shoulder area increases as the backrest angle α increases. In particular, when the backrest angle α is 48 degrees or more, the vibration becomes significantly larger. For this reason, using the back pad 3 as a back pad configured so that the backrest angle α is 48 degrees or more, preferably 50 degrees or more, and more preferably 58 degrees or more, is even more effective in improving comfort when leaning against the back pad.

[0040] Incidentally, the hardness of the upper part 3a of the back pad 3 is harder than the lower part below the upper part 3a of the back pad 3 (i.e., the central part 3c and the lower part 3b), so the hardness of the lower part 3b of the back pad 3 is less than 140 (N). In this embodiment, the hardness of the central part 3c and the lower part 3b of the back pad 3 is 100 to 120 (N). In this case, the lower part of the back pad 3 can be made of a general-purpose back pad.

[0041] The foam material forming the seat pad 1 is a foamed resin. The back pad 3 is also formed from a foamed material. Examples of the foamed resin include polyurethane. Flexible polyurethane is preferred as the polyurethane. Examples of the flexible polyurethane include flexible foamed polyurethane produced by mixing a foaming agent with a flexible polyurethane resin. However, according to the present invention, various foamed resins can be used as the foaming material.

[0042] The hardness of the upper part 3a of the back pad 3 can be increased, for example, by changing the density of the back pad 3. Generally, increasing the density of the upper part 3a of the back pad 3 will make the upper part 3a of the back pad 3 harder as the density increases. One way to change the density is to modify the internal structure of the back pad 3 using a 3D printer (additive manufacturing). Specifically, this could involve using a 3D printer to (a) make the internal cell skeleton of the upper part 3a of the back pad 3 thicker than the lower part 3b of the back pad 3, or (b) make the shape of the internal cell skeleton of the upper part 3a of the back pad 3 more rigid than the lower part 3b of the back pad 3. The hardness of the upper part 3a of the back pad 3 can also be increased by changing the material of the foam material. Specifically, this could involve using a material that is harder than the lower part 3b of the back pad 3 as the material of the foam material that makes up the upper part 3a of the back pad 3.

[0043] Furthermore, in the back pad 3 according to this embodiment, it is preferable that both the upper part 3a and the lower part 3b of the back pad 3 are formed of a high-rebound material with a ball rebound rate of 60 or higher, more preferably 75 or higher. Here, the ball rebound value (rebound elasticity) is a value measured in accordance with JIS K 6400.

[0044] In this embodiment, the upper part 3a of the back pad 3 is defined as the portion above the boundary line L1 of the back pad 3, including the side pad portion 32. However, according to the present invention, the upper part 3a of the back pad 3 with a hardness of 140 (N) can consist only of the upper center pad portion 31a. Also, in this embodiment, the portion below the upper part 3a of the back pad 3 is defined as the portion below the boundary line L1 of the back pad 3, including the side pad portion 32. However, according to the present invention, the portion below the upper part 3a of the back pad 3 can consist only of the central center pad portion 31c and the lower center pad portion 31b. Furthermore, as long as the upper part 3a of the back pad 3 is harder than the portion below the upper part 3a of the back pad 3, the hardness of the central portion 3c and the lower portion 3b of the back pad 3 may be the same or different. Moreover, the central portion 3c and the lower portion 3b of the back pad 3 can be constructed integrally.

[0045] Furthermore, in this embodiment, the cushion pad 2, back pad 3, and headrest 4 are each constructed as separate components. However, according to the present invention, the cushion pad 2 and back pad 3, the back pad 3 and headrest 4, or the cushion pad 2, back pad 3 and headrest 4 can be formed as a single unit. Also, according to the present invention, the seat pad 1 can be formed by omitting at least one of the cushion pad 2 and the headrest 4. In other words, according to the present invention, the seat pad 1 only needs to include at least the back pad 3, assuming that at least one of the cushion pad 2 and the headrest 4 is assembled as a separate component.

[0046] As described above, the seat pad 1 according to this embodiment includes a back pad 3 according to this embodiment. Therefore, according to the seat pad 1 of this embodiment, comfort is improved when leaning the body against the back pad 3.

[0047] Therefore, according to the present invention, it is possible to provide a back pad 3 and a seat pad 1 that improve comfort when leaning the body against the back pad 3. [Examples]

[0048] Figures 3A to 3C show the results of random vibration analysis performed on the upper 3a, middle 3c, and lower 3b of each back pad 3, using multiple back pads 3 with different stiffness levels in the upper part 3a as samples, while varying the backrest angle α of each sample. In Figures 3A to 3C, the vertical axis represents the sum of power spectral densities, and the horizontal axis represents the backrest angle α of the upper part 3a relative to the middle part 3c of the back pad 3.

[0049] In Figures 3A to 3C, ○ represents the analysis results of the first sample as Example 1 of the present invention. In Example 1, the hardness of the upper part 3a of the back pad 3 is 217.5 (N). □ represents the analysis results of the second sample as Example 2 of the present invention. In Example 2, the hardness of the upper part 3a of the back pad 3 is 157.9 (N). △ represents the analysis results of the third sample as a comparative example. In Comparative Example 1, the hardness of the upper part 3a of the back pad 3 is 92.2 (N).

[0050] Figures 3A to 3C show the results of each analysis, illustrating the magnitude of vibrations entering from the upper 3a, middle 3c, and lower 3b of the back (= sum of input vibrations from 1 to 30 Hz) when the backrest angle α is changed, using highly damped urethane foam with different hardness levels.

[0051] (1) Referring to Figures 3A to 3C, as the back pad 3 is tilted (=angle increases), the vibrations coming from the central part 3c and lower part 3b of the back increase only slightly, but in the upper part 3a, they increase sharply when the angle exceeds 48°.

[0052] (2) Furthermore, in the central section 3c and the lower section 3b, the magnitude of vibration hardly changes even when the hardness of the urethane foam is changed, but in the upper section 3a, when using urethane foam with a 25% hardness of about 100N, which is commonly used in backrests, the vibration increases rapidly.

[0053] In contrast, increasing the 25% hardness to 140N, or more preferably 150N or higher, suppresses the increase in vibration.

[0054] Furthermore, from the results of (1) and (2) above, a folding mechanism for the seat is effective in supporting the head while maintaining comfort when the seat is reclined, and in reducing vibrations coming in from the backrest (especially from the upper part 3a). In this case, when the upper part 3a of the back pad 3 is less than 50°, more preferably less than 48°, the increase in input vibration can be suppressed. That is, in the case of a seat with a folding mechanism, it is preferable that the seat with the folding mechanism be able to maintain only the upper part 3a at 50°, more preferably less than 48°, even when the backrest is reclined.

[0055] Furthermore, as mentioned above, increasing the hardness of the urethane foam in the upper part 3a of the back pad 3 to 150N or more by 25% can suppress the increase in vibration caused by reclining.

[0056] The stiffness of the back pad 3 is difficult to change significantly overall in order to obtain static tactile feel, comfort, and appropriate flex characteristics. In particular, there are constraints in the central part 3c and the lower part 3b, where the load distribution is large. To balance these constraints with comfort when reclining, it is desirable to change the stiffness of the back pad 3 at the boundary between the upper part 3a and the central part 3c and lower part 3b.

[0057] Specifically, as in this embodiment, if the 25% hardness of the upper part 3a of the back pad 3 is set to 140N, more preferably 150N or higher, input vibration can be reduced. In addition, if a folding mechanism is provided in the back pad 3 as in this embodiment, and the backrest angle α of the upper part 3a of the back pad 3 can be maintained at 48° or less, the input vibration can be reduced to less than half of what it is when the backrest angle α is 58°. Furthermore, if the 25% hardness is increased to 140N, more preferably 150N or higher, the input vibration can be reduced by another halving.

[0058] Figures 4A to 4C show the results of a random vibration analysis using a highly elastic polyurethane foam with greater rebound (ball rebound value: 75%). As shown in Figures 4A to 4C, a similar trend is observed even with the highly elastic polyurethane foam with greater rebound.

[0059] The above describes exemplary embodiments of the present invention, and various modifications can be made without departing from the scope of the claims. [Explanation of Symbols]

[0060] 1: Seat pad, 2: Cushion pad, 3: Back pad, 3a: Upper part of back pad, 3b: Lower part of back pad, 3c: Center part of back pad, 31: Center pad section, 31a: Upper center pad section, 31b: Lower center pad section 31c: Center pad section, 32: Side pad section, 4: Headrest, L1: (Upper) boundary line, L2: (Lower) boundary line

Claims

1. A back pad for a seat pad made of foam material, The aforementioned back pad includes an upper portion that is positioned above the vehicle when installed, and a lower portion that is positioned below the upper portion when installed on the vehicle. The upper part is harder than the lower part. The aforementioned upper hardness is 140 (N) or more, a back pad.

2. The back pad according to claim 1, wherein the upper part is foldable toward the front when mounted on a vehicle relative to the lower part.

3. The back pad according to claim 1 or 2, wherein the hardness of the upper part is 150 (N) or more.

4. The back pad according to any one of claims 1 to 3, wherein the hardness of the lower portion is 100 to 120 (N).

5. A seat pad comprising a back pad as described in any one of claims 1 to 4.

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