Sensor Sheet

Abstract

To provide a sensor sheet improved in efficiency in the task of winding around a steering wheel.SOLUTION: A sensor sheet 21 is wound around a core material 19 of a steering wheel 10 having a central axis A of a projecting curve. The sensor sheet 21 includes: an insulating sheet 24 made of elastomer; and a first electrode layer 25a and a second electrode layer 25b stuck to front and rear surfaces of the insulating sheet 24. The sensor sheet 21 includes a sensor sheet winding portion 22 that is composed of the insulating sheet 24 and the first electrode layer 25a and the second electrode layer 25b and is wound around the core material 19. The sensor sheet winding portion 22 is formed so as to have a reference core line R of a shape corresponding to at least a part of the projecting curve of the central axis A of the core material 19, and a cross-sectional shape of a plane orthogonal to the reference core line R is formed in a C shape or a U shape.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a sensor sheet. [Background technology]

[0002] Patent Document 1 discloses a technique for wrapping a flexible sheet around a steering wheel having a three-dimensional curved surface. The sheet includes a flexible sheet-like substrate and a wiring pattern disposed on the substrate. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2016-16790 A Summary of the Invention [Problem to be solved by the invention]

[0004] When wrapping the sheet around the steering wheel, there is a concern that relatively large wrinkles may occur unevenly in the sheet, because a three-dimensional curved surface is not a curved surface that can be unfolded into a flat surface without stretching or contracting.

[0005] Specifically, the sheet is stretched as it is wrapped around the outer periphery of the steering wheel, while the edge of the sheet is wrapped around the inner periphery of the steering wheel while being folded inward. It is extremely cumbersome to wrap the sheet around the inner periphery of the steering wheel while preventing wrinkles from forming in the edge of the sheet that is wrapped around the inner periphery of the steering wheel and while accommodating the difference in circumferential length between the outer and inner peripheries of the steering wheel. Therefore, there is a need for a more efficient method of wrapping the sheet around the steering wheel.

[0006] The present invention has been made in view of the above background, and aims to provide a sensor sheet that can be wrapped around a steering wheel with improved efficiency. [Means for solving the problem]

[0007] One aspect of the present invention is A sensor sheet that is wound around a core material of a steering wheel whose central axis is a convex curve, The insulating sheet is made of an elastomer, and an electrode layer is laminated on at least one surface of the insulating sheet. the sensor sheet includes a sensor sheet winding portion that is configured by the insulating sheet and the electrode layer and that is wound around the core material; The sensor sheet winding portion is the core member is formed to have a reference core line having a shape corresponding to at least a part of the convex curve of the central axis line of the core material, and the cross-sectional shape of a plane perpendicular to the reference core line is formed to be C-shaped or U-shaped, The sensor sheet winding portion is a central region that is configured by the insulating sheet and the electrode layer, that is located at the center of the C-shape or U-shape, that corresponds to a position on the surface of the core material that faces away from the center of curvature of the convex curve, and that is located at the center in the winding direction around the core material; a pair of end regions formed by the insulating sheet, located at ends of the C-shape or U-shape, corresponding to positions on the surface of the core material that face the center of curvature of the convex curve, and located at ends in the winding direction; Equipped with The insulating sheet is a length of the central region of the sensor sheet winding portion in a direction along the reference core line is longer than a length of the pair of end regions in a direction along the reference core line, The sensor sheet is formed so that the thickness in the central region is thinner than the thickness in the pair of end regions. [Effects of the Invention]

[0008] According to one aspect of the present invention, the sensor sheet winding portion has a shape that corresponds to the convex curve of the steering wheel core. This reduces the amount of work required to wrap the insulating sheet around the inner periphery of the steering wheel to prevent wrinkles from forming at the two end regions of the insulating sheet, and to stretch the central region of the insulating sheet to accommodate differences in the circumferential length of the steering wheel, when assembling the sensor sheet winding portion to the surface of the steering wheel core. As a result, the efficiency of the sensor sheet assembly work can be improved.

[0009] As described above, according to one aspect of the present invention, the efficiency of the work of wrapping the sensor sheet around the steering wheel can be improved. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a front view showing a steering wheel according to a first embodiment. [Figure 2] FIG. 2 is an enlarged cross-sectional view taken along line II-II in FIG. [Figure 3] FIG. 1 is a plan view showing a sensor sheet according to a first embodiment. [Figure 4] 1 is a side view showing a sensor sheet according to Embodiment 1. FIG. [Figure 5] 2 is an enlarged cross-sectional view showing the sensor sheet according to the first embodiment, taken along line II-II in FIG. 1. FIG. [Figure 6] FIG. 1 is a plan view showing an unformed sensor sheet according to a first embodiment. [Figure 7] FIG. 7 is an enlarged cross-sectional view taken along line VII-VII in FIG. 6. [Figure 8] FIG. 6 is a cross-sectional view of the sensor sheet according to the first embodiment, and is an enlarged cross-sectional view of a sensor sheet having a different shape from that of FIG. 5. [Figure 9] FIG. 2 is a perspective view showing a state in which the unformed sensor sheet according to the first embodiment is attached to a mold. [Figure 10] FIG. 10 is a cross-sectional view showing an unformed sensor sheet according to a first modification of the first embodiment. [Figure 11]FIG. 10 is a front view showing a state in which the sensor sheet according to the second embodiment is attached to a steering wheel. [Figure 12] FIG. 10 is a side view showing a sensor sheet according to a second embodiment. [Figure 13] FIG. 10 is a plan view showing an unformed sensor sheet according to a second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] (Embodiment 1) 1. Overall configuration of the steering wheel 10 A first embodiment in which a sensor sheet 21 according to the present invention is applied to a steering wheel 10 will be described. First, the structure of the steering wheel 10 will be described with reference to Figures 1 and 2. As shown in Figure 1, the steering wheel 10 includes a core portion 11, a ring portion 12, and a plurality of (three in this embodiment) connection portions 13 that connect the core portion 11 and the ring portion 12. In the following description, the direction along the reference core line R of the sensor sheet 21 will be referred to as the reference core line direction X, the direction perpendicular to the surface of the sensor sheet 21 will be referred to as the thickness direction Z, and the direction in which the sensor sheet 21 is wrapped around the ring portion 12 of the steering wheel 10 will be referred to as the wrapping direction Y.

[0012] The ring portion 12 is formed in a shape such that the central axis A forms a convex curve. The ring portion 12 in this embodiment is formed in a circular ring shape. In this embodiment, the circular ring shape is an example of a convex curve. The surface of the ring portion 12 farther from the center of curvature C of the convex curve is the outer peripheral surface 14 of the ring portion 12, and the surface of the ring portion 12 closer to the center of curvature C of the convex curve is the inner peripheral surface 15 of the ring portion 12. However, the ring portion 12 is not limited to a circular shape and can be formed in any shape. The cross-sectional shape of the ring portion 12 perpendicular to the axis is formed, for example, in a circular shape, as shown in FIG. 2. Therefore, the surface of the ring portion 12 is formed as a three-dimensional curved surface rather than a single flat surface over the entire surface.

[0013] 2. Detailed configuration of the steering wheel 10 The detailed configuration of the steering wheel 10 will be described with reference to Figures 1 and 2. In particular, the detailed configuration of the ring portion 12 will be described.

[0014] The ring portion 12 includes a core material 19, a sensor sheet 21, and a skin material 18. The core material 19 includes a core body 16 and a resin inner layer material 17. The core body 16 forms the center of the ring portion 12 and is formed in a shape corresponding to the shape of the ring portion 12. That is, the core body 16 is formed in a circular ring shape and has a circular cross section perpendicular to its axis. Here, the cross section of the core body 16 perpendicular to its axis is not limited to a circular shape, and can be any shape such as an elliptical shape, an egg shape, a U-shape, a C-shape, or a polygonal shape. The core body 16 in this embodiment is formed from a metal such as aluminum or magnesium and is conductive. Materials other than metals can also be used as the material of the core body 16.

[0015] The resin inner layer material 17 covers the outer surface of the core body 16 along the entire circumference of the ring shape of the core body 16 and along the entire circumference of the circular cross section of the core body 16. In this embodiment, the cross section of the resin inner layer material 17 is circular. The resin inner layer material 17 is disposed slightly eccentrically on the radially outer periphery of the ring portion 12. If the core body 16 has a U-shaped cross section perpendicular to the axis, the resin inner layer material 17 is filled not only on the radially outer side of the cross section perpendicular to the axis of the core body 16 but also in the U-shaped recess of the core body 16. The resin inner layer material 17 is injection molded on the outer surface of the core body 16 and directly bonded to the outer surface of the core body 16. The cross section perpendicular to the axis of the resin inner layer material 17 is not limited to a circular shape but can be any shape, such as an oval, elliptical, or polygonal shape. The resin inner layer material 17 is molded, for example, from a foamed resin. For example, a foamed urethane resin is used for the resin inner layer material 17. Note that a non-foamed resin may also be used for the resin inner layer material 17.

[0016] A sensor sheet 21 is wrapped around the outer surface of the resin inner layer material 17 of the core material 19. The sensor sheet 21 forms a C-shape when wrapped around the core material 19. The sensor sheet 21 will be described in detail later.

[0017] The skin material 18 covers the outer surface of the sensor sheet 21 (the surface of the sensor sheet 21 opposite the core material 19) over the entire circumference of the ring shape of the sensor sheet 21 (the entire circumference in the X direction in FIG. 1 ) and over the entire circumference of the cross-sectional shape of the sensor sheet 21 perpendicular to the reference core line R (the entire circumference in the Y direction in FIG. 2 ). That is, as will be described later, when the first electrode layer 25 a is exposed on the first surface 27 of the insulating sheet 24, the skin material 18 also functions as a covering for the first electrode layer 25 a. The skin material 18 is formed by injection molding, and is wrapped around and joined to the outer surface of the sensor sheet 21. The skin material 18 is formed from, for example, urethane resin. The outer surface of the skin material 18 forms a design surface. Therefore, it is preferable to use a non-foamed urethane resin or a slightly foamed urethane resin for the skin material 18.

[0018] 3. Overall configuration of sensor sheet 21 The overall configuration of the sensor sheet 21 of the first embodiment will be described with reference to Figures 3 to 7. As shown in Figure 3, the sensor sheet 21 includes a plurality of (five in this embodiment) sensor sheet winding portions 22 and a plurality of (four in this embodiment) connecting portions 23 that connect adjacent sensor sheet winding portions 22. However, the number of sensor sheet winding portions 22 may be two to four, or six or more.

[0019] As shown in FIG. 4, the sensor sheet winding portion 22 is formed to have a reference core line R that has a shape that corresponds to at least a part of the convex curve of the central axis A of the core material 19. In this embodiment, the reference core line R is formed to form a part of a circular arc. When viewed from the side, the sensor sheet winding portion 22 is formed to form a part of a circular arc along the reference core line R. Furthermore, the sensor sheet winding portion 22 has a U-shaped planar shape (see FIG. 5) that is perpendicular to the reference core line R. As shown in FIG. 5, the sensor sheet winding portion 22 may include a pair of straight portions 37 that have a straight shape and a curved portion 38 that connects the pair of straight portions 37 in a curved shape, or may be configured to include only a curved portion that has a curved shape.

[0020] The sensor sheet 21 is formed into the predetermined shape by heating and softening an unformed sensor sheet 26 (see FIG. 6) formed in a long, flat shape, and then cooling it (see FIGS. 3 and 4). The longitudinal length of the unformed sensor sheet 26 is formed slightly shorter than the length of the surface of the core material 19 of the steering wheel 10 in the direction along the reference core line direction X at a position facing away from the center of curvature C of the convex curve.

[0021] 7 shows a cross-sectional view of the unformed sensor sheet 26. The unformed sensor sheet 26 includes an insulating sheet 24, a first electrode layer 25a, and a second electrode layer 25b. The first electrode layer 25a and the second electrode layer 25b are conductive and formed in a layered shape.

[0022] First electrode layer 25a is laminated on first surface 27 of insulating sheet 24. First electrode layer 25a is formed in a similar shape to but slightly smaller than insulating sheet 24. As a result, the edge portion of first surface 27 of insulating sheet 24 is exposed from the edge portion of first electrode layer 25a.

[0023] The second electrode layer 25b is laminated on the second surface 28 of the insulating sheet 24. The second electrode layer 25b is formed in a similar shape to but slightly smaller than the insulating sheet 24. As a result, the edge portion of the second surface 28 of the insulating sheet 24 is exposed from the edge portion of the second electrode layer 25b.

[0024] The first electrode layer 25a and the second electrode layer 25b may be the same shape and size, or may be similar in shape with one layer being slightly larger than the other. Note that even after the unformed sensor sheet 26 is formed into a predetermined shape, the laminated structure of the insulating sheet 24, the first electrode layer 25a, and the second electrode layer 25b remains unchanged.

[0025] The insulating sheet 24 is formed by including, for example, an elastomer as a main component. Therefore, the insulating sheet 24 is flexible. In other words, the insulating sheet 24 is flexible and is configured to be extensible in the planar direction. The insulating sheet 24 is formed by including, for example, a thermoplastic material, particularly a thermoplastic elastomer, as a main component. The insulating sheet 24 may be formed by using the thermoplastic elastomer itself, or may be formed by using the thermoplastic elastomer as a material and heating it to crosslink the elastomer as a main component.

[0026] Furthermore, the insulating sheet 24 may contain rubber, resin, or other materials other than thermoplastic elastomer. For example, if the insulating sheet 24 contains rubber such as ethylene-propylene rubber (EPM, EPDM), the flexibility of the insulating sheet 24 is improved. From the viewpoint of improving the flexibility of the insulating sheet 24, the insulating sheet 24 may contain a flexibility-imparting component such as a plasticizer. Furthermore, the insulating sheet 24 may be composed mainly of a reactive curing elastomer or a thermosetting elastomer.

[0027] Furthermore, a material with good thermal conductivity is suitable for the insulating sheet 24. Therefore, the insulating sheet 24 may be made of a thermoplastic elastomer with high thermal conductivity, or may contain a filler that can increase thermal conductivity.

[0028] The first electrode layers 25a are arranged on a first surface 27 of the insulating sheet 24, i.e., on the upper surface (upper surface in FIG. 7) of the insulating sheet 24, in the plane direction of the insulating sheet 24, and the second electrode layers 25b are arranged on a second surface 28 of the insulating sheet 24, i.e., on the lower surface (lower surface in FIG. 7) of the insulating sheet 24, in the plane direction of the insulating sheet 24. At least the first electrode layer 25a constitutes a detection electrode. The first electrode layer 25a and the second electrode layer 25b are conductive. Furthermore, the first electrode layer 25a and the second electrode layer 25b are flexible. That is, the first electrode layer 25a and the second electrode layer 25b are flexible and configured to be extensible in the plane direction.

[0029] 7, a detailed description will be given of a case where the first electrode layer 25a and the second electrode layer 25b are made of a conductive elastomer. In this case, the first electrode layer 25a and the second electrode layer 25b are formed by using an elastomer as a base material and incorporating a conductive filler. The elastomer that is the base material of the first electrode layer 25a and the second electrode layer 25b should preferably have the same main component as the insulating sheet 24. In particular, the first electrode layer 25a and the second electrode layer 25b should preferably be made of a thermoplastic elastomer.

[0030] However, first electrode layer 25a and second electrode layer 25b are formed of a material having a softening point higher than that of insulating sheet 24. This is because, when first electrode layer 25a and second electrode layer 25b are joined to insulating sheet 24 by fusion (thermal fusion) of insulating sheet 24 itself, insulating sheet 24 softens before first electrode layer 25a and second electrode layer 25b. As a result, insulating sheet 24 can be made to have a desired thickness.

[0031] Here, the first electrode layer 25a and the second electrode layer 25b are joined to the insulating sheet 24 by fusion (thermal fusion) of the insulating sheet 24 itself. Furthermore, when the first electrode layer 25a and the second electrode layer 25b are formed so that an elastomer is located on the surface layer, the first electrode layer 25a and the second electrode layer 25b are joined to the insulating sheet 24 by fusion (thermal fusion) of the first electrode layer 25a and the second electrode layer 25b themselves. In other words, the first electrode layer 25a and the second electrode layer 25b are joined to the insulating sheet 24 by mutual fusion. Note that the first electrode layer 25a and the second electrode layer 25b and the insulating sheet 24 may be joined by fusion of only one of them.

[0032] 4. Detailed shape of sensor sheet 21 The detailed shape of sensor sheet 21 will be described with reference to Figures 2 to 5 and 8. Sensor sheet 21 has protruding pieces 29 that protrude outward from the side edges. Terminals (not shown) for connecting first electrode layer 25a and second electrode layer 25b to an external circuit can be attached to protruding pieces 29.

[0033] As shown in FIG. 2, the sensor sheet winding portion 22 of the sensor sheet 21 is wound around the core material 19 of the steering wheel 10 in the winding direction Y. The sensor sheet winding portion 22 includes a central region 30 near the center of the winding direction Y, a pair of end regions 31 located at the ends of the winding direction Y, and a pair of intermediate regions 32 located between the central region 30 and the end regions 31. The central region 30 of the sensor sheet 21 is located on the outer peripheral surface 14 side of the ring portion 12, and the pair of end regions 31 are located on the inner peripheral surface 15 side of the ring portion 12. The straight portion 37 corresponds to the portion of the sensor sheet winding portion 22 from the intermediate region 32 to the end regions 31, and the curved portion 38 corresponds to the central region 30.

[0034] The first electrode layer 25a and the second electrode layer 25b are disposed continuously from both of the pair of end regions 31 to the central region 30. However, the first electrode layer 25a and the second electrode layer 25b may be disposed continuously from one of the pair of end regions 31 to the central region 30, or may be configured to be disposed continuously from the pair of intermediate regions 32 to the central region 30.

[0035] The central region 30 is stretched in the reference core line direction X over the entire area in the reference core line direction X by heating and softening the sensor sheet 21 and then pressing it.

[0036] The pair of intermediate regions 32 may or may not be stretched in the reference core line direction X over the entire area of ​​the reference core line direction X. When the pair of intermediate regions 32 are stretched, the sensor sheet 21 may be softened by heating and then press-formed.

[0037] As shown in FIG. 5, the sensor sheet winding portion 22 has a U-shaped cross section in a plane perpendicular to the reference core direction X. Note that, for ease of explanation, the thickness is exaggerated in FIG. 5 . Also, for ease of explanation, the insulating sheet 24, the first electrode layer 25a, and the second electrode layer 25b are depicted as an integrated component. The integrated element of the sensor sheet winding portion 22, including the insulating sheet 24, the first electrode layer 25a, and the second electrode layer 25b, is formed so that the thickness in the central region 30 is thinner than the thickness in the pair of intermediate regions 32. Furthermore, the thickness of the integrated element in the central region 30 is thinner than the thickness in the pair of end regions 31.

[0038] However, as shown in Figure 8, the sensor sheet winding portion 22 may have a C-shaped cross-sectional shape in a plane perpendicular to the reference core line direction X by curving a pair of intermediate regions 32 and a pair of end regions 31 along the outer shape of the core material 19.

[0039] 4, the insulating sheet 24 is formed so that the length L in the direction along the reference core wire R in the central region 30 of the sensor sheet winding portion 22 is longer than the length M in the direction along the reference core wire R in the pair of end regions 31. The length L of the insulating sheet 24 in the central region 30 of the sensor sheet winding portion 22 along the reference core wire direction X is 1.05 to 1.25 times the length M in the pair of end regions 31 along the reference core wire direction X.

[0040] By making the length L of the central region 30 in the direction along the reference core line R at least 1.05 times the length M of the pair of end regions 31 in the direction along the reference core line R, wrinkles are less likely to form in the pair of end regions 31 when the sensor sheet 21 is attached to the core material 19 of the steering wheel 10. By making the length L of the central region 30 in the direction along the reference core line R at most 1.25 times the length M of the pair of end regions 31 in the direction along the reference core line R, excessive stretching of the first electrode layer 25a and the second electrode layer 25b is suppressed.

[0041] As shown in FIG. 5, the insulating sheet 24 is formed so that the thickness of the central region 30 of the sensor sheet wound portion 22 is thinner than the thickness of the pair of end regions 31.

[0042] 3, the connecting portion 23 connects the positions of the plurality of sensor sheet winding portions 22 that correspond to the central region 30, and does not connect the positions of the plurality of sensor sheet winding portions 22 that correspond to a pair of end regions 31. The connecting portion 23 is continuous with the insulating sheet 24 of the sensor sheet winding portion 22, and is constituted by the sensor sheet winding portion 22.

[0043] In this embodiment, the connecting portion 23 also connects the positions of the plurality of sensor sheet winding portions 22 that correspond to a pair of intermediate regions 32. However, the connecting portion 23 may be configured to not connect the positions of the plurality of sensor sheet winding portions 22 that correspond to a pair of intermediate regions 32.

[0044] Although not shown in detail, the insulating sheet 24 is formed so that the thickness at the position that forms the connecting portion 23 is thicker than the thickness at the position that corresponds to the central region 30 of the sensor sheet winding portion 22. However, the insulating sheet 24 may be formed so that the thickness at the position that forms the connecting portion 23 is the same as the thickness at the position that corresponds to the central region 30 of the sensor sheet winding portion 22.

[0045] Furthermore, the thickness of the integrated element including the insulating sheet 24, the first electrode layer 25a, and the second electrode layer 25b at the position that forms the connecting portion 23 is formed to be thicker than the thickness corresponding to the central region 30 of the sensor sheet winding portion 22. However, the thickness of the integrated element including the insulating sheet 24, the first electrode layer 25a, and the second electrode layer 25b at the position that forms the connecting portion 23 may be formed to be the same as the thickness corresponding to the central region 30 of the sensor sheet winding portion 22.

[0046] The length of the sensor sheet 21 along the reference core line direction X in the central region 30 is formed to be the same as the length of the surface of the core material 19 along the reference core line direction X at a position facing away from the center of curvature C of the convex curve.

[0047] 5. Manufacturing method of steering wheel 10 Next, an example of a method for manufacturing the steering wheel 10 will be described with reference to Figures 1 to 6 and 9. Note that the method for manufacturing the steering wheel 10 is not limited to the following description.

[0048] The resin inner layer material 17 is injection molded onto the outer surface of the core body 16. That is, the core body 16 is placed in a mold (not shown), and a molding material is injected into the mold to form the resin inner layer material 17. In this way, the core body 16 and the resin inner layer material 17 are integrated.

[0049] The insulating sheet 24, the first electrode layer 25a, and the second electrode layer 25b are formed into a predetermined shape. The first electrode layer 25a and the second electrode layer 25b are bonded to the surface of the insulating sheet 24. This results in an unformed sensor sheet 26 before being formed into a predetermined shape (see FIG. 6).

[0050] As shown in Figure 9, the unformed sensor sheet 26 is attached to the outer surface of a mold 33 having the same shape as the steering wheel 10. A portion of the unformed sensor sheet 26 corresponding to the sensor sheet wrapping portion 22 is wrapped around the outer surface of the mold 33 in the wrapping direction. At this time, the unformed sensor sheet 26 is wrapped around the outer surface of the core material 19 while being stretched along the reference core line direction. Thereafter, the unformed sensor sheet 26 is heated, for example, with a heat gun (not shown), to a temperature equal to or higher than the softening points of the insulating sheet 24, first electrode layer 25a, and second electrode layer 25b.

[0051] Thereafter, the insulating sheet 24, the first electrode layer 25a, and the second electrode layer 25b are fixed in a predetermined shape by cooling, thereby completing the sensor sheet 21 (see FIGS. 3 to 5).

[0052] An adhesive is applied to the outer surface of the steering wheel 10 and the inner surface of the sensor sheet 21. The sensor sheet 21 is then attached to the outer surface of the core material 19 of the steering wheel 10. At this time, the sensor sheet 21 is wrapped around so that a pair of end regions 31 of the sensor sheet 21 are positioned on the inner circumferential side of the core material 19 and the central region 30 of the sensor sheet 21 is positioned on the outer circumferential side of the core material 19. The adhesive is then allowed to harden, thereby adhering the sensor sheet 21 to the outer surface of the core material 19 of the steering wheel 10.

[0053] Next, the skin material 18 is formed into a predetermined shape and wrapped around the outer surface of the sensor sheet 21. The sensor sheet 21 and the skin material 18 are then bonded or heat-sealed together. The skin material 18 may also be formed by placing the core body 16, the resin inner layer material 17, and the sensor sheet 21 in a mold (not shown) and injecting a molding material. This completes the steering wheel 10 (see FIGS. 1 and 2).

[0054] 6. Effects of Embodiment 1 Next, the effects of embodiment 1 will be described. According to this embodiment, the sensor sheet winding portion 22 has a shape that follows the convex curve of the core material 19 of the steering wheel 10. This reduces the amount of work required to wrap the insulating sheet 24 around the inner periphery of the steering wheel 10 so as to prevent wrinkles from forming in the pair of end regions 31 of the insulating sheet 24, and to stretch the central region 30 of the insulating sheet 24 to accommodate the difference in circumferential length of the steering wheel 10, when assembling the sensor sheet winding portion 22 to the surface of the core material 19 of the steering wheel 10. As a result, the efficiency of the sensor sheet 24 assembling work can be improved.

[0055] In this embodiment, the first electrode layer 25a and the second electrode layer 25b are made of a conductive elastomer and are disposed continuously from the pair of intermediate regions 32 to the central region 30, and the integrated element including the insulating sheet 24 and the first electrode layer 25a and the second electrode layer 25b is formed so that the thickness in the central region 30 is thinner than the thickness in the pair of intermediate regions 32. According to this embodiment, when the first electrode layer 25a and the second electrode layer 25b are disposed continuously from the pair of intermediate regions 32 to the central region 30, the sensor sheet winding portion 22 can be easily stretched in the winding direction Y, etc., in the central region 30. This allows the sensor sheet winding portion 22 to be easily deformed into a shape that follows the convex curve of the core material 19 of the steering wheel 10.

[0056] In addition, in this embodiment, the first electrode layer 25a and the second electrode layer 25b are made of a conductive elastomer and are arranged continuously from at least one of the pair of end regions 31 to the central region 30, and the integrated element including the insulating sheet 24 and the first electrode layer 25a and the second electrode layer 25b is formed so that its thickness in the central region 30 is thinner than its thickness in the pair of end regions 31.

[0057] According to this embodiment, when the first electrode layer 25a and the second electrode layer 25b are continuously disposed from at least one of the pair of end regions 31 to the central region 30, the sensor sheet winding portion 22 can be easily stretched in the winding direction Y or the like in the central region 30. This allows the sensor sheet winding portion 22 to be easily deformed into a shape that follows the convex curve of the core material 19 of the steering wheel 10.

[0058] Furthermore, in this embodiment, the first electrode layer 25 a and the second electrode layer 25 b can be disposed continuously from both of the pair of end regions 31 to the central region 30 .

[0059] According to this embodiment, the length of the central region 30 in the direction along the reference core line R is the same as the length of the surface of the core material 19 in the direction along the reference core line R at a position facing away from the center of curvature C of the convex curve.

[0060] According to this embodiment, when winding the sensor sheet winding portion 22 around the core material 19 of the steering wheel 10, it is not necessary to stretch the insulating sheet 24 in the direction along the reference core wire R. As a result, the efficiency of the sensor sheet assembly work can be improved.

[0061] According to this embodiment, the sensor sheet 21 comprises a plurality of sensor sheet winding portions 22 and a connecting portion 23 formed of at least an insulating sheet 24, which connects the positions of the plurality of sensor sheet winding portions 22 corresponding to the central region 30 and disconnects the positions of the plurality of sensor sheet winding portions 22 corresponding to a pair of end regions 31.

[0062] According to this embodiment, the sensor sheet 21 can be attached to the steering wheel 10 by sequentially winding a plurality of sensor sheet winding portions 22 around the core material 19 of the steering wheel 10. This allows for efficient installation work.

[0063] According to this embodiment, the insulating sheet 24 constituting the connecting portion 23 is continuous with the insulating sheet 24 constituting the sensor sheet winding portion 22 connected by the connecting portion 23, and the thickness of the insulating sheet 24 at the position constituting the connecting portion 23 is formed to be thicker than the thickness of the position corresponding to the central region 30 of the sensor sheet winding portion 22.

[0064] Because the connecting portion 23 disconnects a pair of end regions 31 of the multiple sensor sheet winding portions 22, the connecting portion 23 is narrower than the sensor sheet winding portions 22 by at least the width of the pair of end regions 31. This raises concerns that the strength of the connecting portion 23 may be reduced. According to this embodiment, the thickness of the insulating sheet 24 at the position that forms the connecting portion 23 is greater than the thickness of the insulating sheet 24 at the position that corresponds to the central region 30 of the sensor sheet winding portions 22, thereby preventing the strength of the connecting portion 23 from being reduced.

[0065] According to this embodiment, the first electrode layer 25a and the second electrode layer 25b are made of a conductive elastomer, the connecting portion 23 is made of an insulating sheet 24, the first electrode layer 25a and the second electrode layer 25b, and the integrated element including the insulating sheet 24 and the first electrode layer 25a and the second electrode layer 25b is formed so that the thickness at the position constituting the connecting portion 23 is thicker than the thickness at the position corresponding to the central region 30 of the sensor sheet winding portion 22.

[0066] According to this embodiment, the thickness of the integrated element of the insulating sheet 24, including the insulating sheet 24, the first electrode layer 25a, and the second electrode layer 25b at the position that constitutes the connecting portion 23 is formed to be thicker than the thickness of the position that corresponds to the central region 30 of the sensor sheet winding portion 22, thereby preventing a decrease in the strength of the connecting portion 23.

[0067] (Modification 1 of Embodiment 1) FIG. 10 illustrates a case where the first electrode layer 25a and the second electrode layer 25b are made of conductive cloth 34. A detailed description will be given of a case where the first electrode layer 25a and the second electrode layer 25b are made of conductive cloth 34. The conductive cloth 34 is a woven or nonwoven fabric made of conductive fibers. Here, the conductive fibers are formed by coating the surfaces of flexible fibers 35 with a conductive material 36. The conductive fibers are formed, for example, by plating the surfaces of resin fibers such as polyethylene with copper or nickel.

[0068] In this case, the first electrode layer 25a and the second electrode layer 25b are joined to the insulating sheet 24 by fusion (thermal fusion) of the insulating sheet 24 itself. Furthermore, the first electrode layer 25a and the second electrode layer 25b have a plurality of through-holes because they are made of cloth. Therefore, a portion of the insulating sheet 24 penetrates into the through-holes of the first electrode layer 25a and the second electrode layer 25b. In other words, at least a portion of the first electrode layer 25a and the second electrode layer 25b is embedded in the insulating sheet 24. The embedding depths of the first electrode layer 25a and the second electrode layer 25b in the insulating sheet 24 may be the same or different.

[0069] (Modification 2 of Embodiment 1) The following describes a case where the first electrode layer 25a and the second electrode layer 25b are formed from metal foil. Similar to the conductive cloth, the metal foil preferably has a plurality of through-holes. Therefore, the first electrode layer 25a and the second electrode layer 25b are flexible and can expand in the planar direction as the through-holes deform. The metal foil may be any conductive metal material, such as copper foil or aluminum foil. Furthermore, similar to the case of the conductive cloth, the first electrode layer 25a and the second electrode layer 25b are joined to the sensor sheet 21 by fusion (thermal fusion) of the insulating sheet 24 itself.

[0070] (Embodiment 2) Next, a second embodiment will be described with reference to Figures 11 to 13. As shown in Figure 11, in this embodiment, a plurality of sensor sheets 40 (four in this embodiment) are attached to the core material 19 of one steering wheel 10. As shown in Figure 12, one sensor sheet 40 in this embodiment has one sensor sheet winding portion 41. In other words, the sensor sheet 40 in this embodiment does not have a connecting portion 23. However, the number of sensor sheets 40 may be one to three, or five or more.

[0071] As shown in FIG. 13, the sensor sheet 40 is formed into a predetermined shape by heating an unformed sensor sheet 42 formed in a long, flat shape, softening it, deforming it into a predetermined shape, and then cooling it.

[0072] 12, the sensor sheet winding portion 41 is formed to have a reference core line R whose shape corresponds to at least a part of the convex curve of the central axis A of the core material 19. In this embodiment, the reference core line R is formed to form a part of a circular arc. When viewed from the side, the sensor sheet winding portion 41 is formed to form a part of a circular arc along the reference core line R. Although not shown in detail, the sensor sheet winding portion 41 has a C-shaped planar shape that is perpendicular to the reference core line R.

[0073] The sum of the lengths of the sensor sheet winding portions 41 of the four sensor sheets 40 along the reference core line direction X is the same as the length of the surface of the core material 19 in the direction along the reference core line direction X at a position facing away from the center of curvature C of the convex curve.

[0074] The configuration other than that described above is substantially the same as that of the first embodiment, so the same members are given the same reference numerals and redundant explanations will be omitted.

[0075] According to this embodiment, the sensor sheet winding portion 41 has a shape that follows the convex curve of the core material 19 of the steering wheel 10. This reduces the amount of work required to wrap the pair of end regions 31 of the insulating sheet 24 around the inner periphery of the steering wheel 10 so as not to form wrinkles when assembling the sensor sheet winding portion 41 on the surface of the core material 19 of the steering wheel 10, and to stretch the central region 30 of the insulating sheet 24 to accommodate the difference in circumferential length of the steering wheel 10. As a result, the efficiency of the sensor sheet 40 assembling work can be improved.

[0076] The technology disclosed in this specification is not limited to the embodiments described above and illustrated in the drawings, and also includes various aspects such as those described below.

[0077] The steering wheel 10 does not have to be circular, and any shape can be selected, such as an oval shape or a square shape with rounded corners.

[0078] In this embodiment, the first electrode layer 25a and the second electrode layer 25b are formed on both sides of the insulating sheet 24, but this is not limited to this, and the electrode layers may be formed on only one side of the insulating sheet 24.

[0079] The integrated element including the insulating sheet 24 and the first and second electrode layers 25a and 25b may have the same thickness in the central region 30 as in the pair of intermediate regions 32 or the pair of end regions 31.

[0080] (others) As one aspect of this embodiment, the following configurations and combinations are also included.

[0081] (1) A sensor sheet that is wrapped around a core material of a steering wheel whose central axis is a convex curve, The insulating sheet is made of an elastomer, and an electrode layer is laminated on at least one surface of the insulating sheet. the sensor sheet includes a sensor sheet winding portion that is configured by the insulating sheet and the electrode layer and that is wound around the core material; The sensor sheet winding portion is the core member is formed to have a reference core line having a shape corresponding to at least a part of the convex curve of the central axis line of the core material, and the cross-sectional shape of a plane perpendicular to the reference core line is formed to be C-shaped or U-shaped, The sensor sheet winding portion is a central region that is configured by the insulating sheet and the electrode layer, that is located at the center of the C-shape or U-shape, that corresponds to a position on the surface of the core material that faces away from the center of curvature of the convex curve, and that is located at the center in the winding direction around the core material; a pair of end regions formed by the insulating sheet, located at ends of the C-shape or U-shape, corresponding to positions on the surface of the core material that face the center of curvature of the convex curve, and located at ends in the winding direction; Equipped with The insulating sheet is a length of the central region of the sensor sheet winding portion in a direction along the reference core line is longer than a length of the pair of end regions in a direction along the reference core line, The sensor sheet is formed so that the thickness of the central region is thinner than the thickness of the pair of end regions.

[0082] (2) The sensor sheet winding portion further includes: a pair of intermediate regions that are formed by the insulating sheet and the electrode layer and connect the central region and the pair of end regions, respectively, in the C-shape or U-shape; the electrode layer is made of a conductive elastomer and is disposed continuously from the pair of intermediate regions to the central region; The integral element including the insulating sheet and the electrode layer is The sensor sheet according to (1) above, wherein the thickness of the central region is smaller than the thickness of the pair of intermediate regions.

[0083] (3) The electrode layer is made of a conductive elastomer and is disposed continuously from at least one of the pair of end regions to the central region; The integral element including the insulating sheet and the electrode layer is The sensor sheet according to (1) or (2) above, wherein the thickness of the central region is smaller than the thickness of the pair of end regions.

[0084] (4) The sensor sheet according to (3) above, wherein the electrode layer is disposed continuously from both of the pair of end regions to the central region.

[0085] (5) The sensor sheet according to any one of (1) to (4) above, wherein the length of the central region in the direction along the reference core wire is 1.05 to 1.25 times the length of the pair of end regions in the direction along the reference core wire.

[0086] (6) A sensor sheet according to any one of (1) to (5) above, wherein the length in the direction along the reference core line in the central region is the same as the length in the direction along the reference core line at a position on the surface of the core material that faces away from the center of curvature of the convex curve.

[0087] (7) The sensor sheet A plurality of the sensor sheet winding portions; a connecting portion formed at least by the insulating sheet, which connects the sensor sheet winding portions at positions corresponding to the central region and disconnects the sensor sheet winding portions at positions corresponding to the pair of end regions; The sensor sheet according to any one of (1) to (6) above, comprising:

[0088] (8) The insulating sheet constituting the connecting portion is continuous with the insulating sheet constituting the sensor sheet wrapping portion connected by the connecting portion, The insulating sheet is The sensor sheet described in (7) above, wherein the thickness at the position that forms the connecting portion is formed to be thicker than the thickness at the position of the sensor sheet winding portion that corresponds to the central region.

[0089] (9) The electrode layer is made of a conductive elastomer, the connecting portion is constituted by the insulating sheet and the electrode layer, The integral element including the insulating sheet and the electrode layer is The sensor sheet according to (8) above, wherein the thickness at the position that constitutes the connecting portion 23 is formed to be thicker than the thickness at the position of the sensor sheet winding portion that corresponds to the central region. [Explanation of symbols]

[0090] 10: steering wheel, 19: core material, 21, 40: sensor sheet, 22, 41: sensor sheet winding portion, 23: connecting portion, 24: insulating sheet, 25a: first electrode layer, 25b: second electrode layer, 30: central region, 31: end region, 32: intermediate region, A: central axis, C: center of curvature, R: reference core wire, Y: winding direction

Claims

1. A sensor sheet that is wound around a core material of a steering wheel whose central axis is a convex curve, The insulating sheet is made of an elastomer, and an electrode layer is laminated on at least one surface of the insulating sheet. the sensor sheet includes a sensor sheet winding portion that is configured by the insulating sheet and the electrode layer and that is wound around the core material; The sensor sheet winding portion is the core member is formed to have a reference core line having a shape corresponding to at least a part of the convex curve of the central axis line of the core material, and the cross-sectional shape of a plane perpendicular to the reference core line is formed to be C-shaped or U-shaped, The sensor sheet winding portion is a central region that is configured by the insulating sheet and the electrode layer, that is located at the center of the C-shape or U-shape, that corresponds to a position on the surface of the core material that faces away from the center of curvature of the convex curve, and that is located at the center in the winding direction around the core material; a pair of end regions formed by the insulating sheet, located at ends of the C-shape or U-shape, corresponding to positions on the surface of the core material that face the center of curvature of the convex curve, and located at ends in the winding direction; Equipped with The insulating sheet is a length of the central region of the sensor sheet winding portion in a direction along the reference core line is longer than a length of the pair of end regions in a direction along the reference core line, The sensor sheet is formed so that the thickness of the central region is thinner than the thickness of the pair of end regions.

2. The sensor sheet winding portion further includes: a pair of intermediate regions that are formed by the insulating sheet and the electrode layer and connect the central region and the pair of end regions, respectively, in the C-shape or U-shape; the electrode layer is made of a conductive elastomer and is disposed continuously from the pair of intermediate regions to the central region; The integral element including the insulating sheet and the electrode layer is The sensor sheet according to claim 1 , wherein the thickness of the central region is smaller than the thickness of the pair of intermediate regions.

3. the electrode layer is made of a conductive elastomer and is disposed continuously from at least one of the pair of end regions to the central region; The integral element including the insulating sheet and the electrode layer is The sensor sheet according to claim 1 , wherein the thickness of the central region is smaller than the thickness of the pair of end regions.

4. The sensor sheet according to claim 3 , wherein the electrode layer is disposed continuously from both of the pair of end regions to the central region.

5. 2. The sensor sheet according to claim 1, wherein the length of the central region in the direction along the reference core line is 1.05 to 1.25 times the length of the pair of end regions in the direction along the reference core line.

6. 2. The sensor sheet according to claim 1, wherein the length of the central region in the direction along the reference core line is the same as the length of the surface of the core material in the direction along the reference core line at a position facing away from the center of curvature of the convex curve.

7. The sensor sheet comprises: A plurality of the sensor sheet winding portions; a connecting portion formed at least by the insulating sheet, which connects the sensor sheet winding portions at positions corresponding to the central region and disconnects the sensor sheet winding portions at positions corresponding to the pair of end regions; The sensor sheet according to any one of claims 1 to 6, comprising:

8. the insulating sheet constituting the connecting portion is continuous with the insulating sheet constituting the sensor sheet wrapping portion connected by the connecting portion, The insulating sheet is The sensor sheet according to claim 7 , wherein the thickness of the portion that forms the connecting portion is greater than the thickness of the portion of the sensor sheet wound portion that corresponds to the central region.

9. the electrode layer is made of a conductive elastomer, the connecting portion is constituted by the insulating sheet and the electrode layer, The integral element including the insulating sheet and the electrode layer is The sensor sheet according to claim 8 , wherein the thickness of the portion that forms the connecting portion is greater than the thickness of the portion of the sensor sheet wound portion that corresponds to the central region.

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